FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
QCL DEVICE, EXTERNAL RESONANCE-TYPE QCL MODULE DEVICE, ANALYZER,
AND LIGHT IRRADIATION METHOD;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
- 2 –
Description
Title
QCL DEVICE, EXTERNAL RESONANCE-TYPE QCL MODULE DEVICE, ANALYZER,
AND LIGHT IRRADIATION METHOD5
Field
[0001]
The present disclosure relates to a QCL device, an external resonance-type QCL module
device, an analyzer, and a light irradiation method.
Background10
[0002]
An external resonance-type laser module device using a QCL (Quantum Cascade Laser)
device is known as a laser light source. For example, PTL 1 discloses an external resonance-
type laser module device including a QCL device and a diffraction reflecting section. The
module device includes the QCL device and a MEMS (Micro Electro Mechanical Systems)15
diffraction grating. The MEMS diffraction grating returns a portion of light emitted from the
QCL device back to the QCL device.
Citation List
Patent Literature
[0003]20
[PTL 1] JP 2019-036577 A
Non Patent Literature
[0004]
- 3 –
[NPL 1] J. Kim, M. Lerttamrab, S. L. Chuang, C. Gmachl, D. L. Sivco, F. Capasso, and A. Y.
Cho, "Theoretical and experimental study of optical gain and linewidth enhancement factor of
type-I quantum-cascade lasers," IEEE J. Quantum Electron., Vol. 40, No. 12, pp. 1663-1674,
2004
Summary5
Technical Problem
[0005]
However, with the module device described above, a wavelength band that can be
returned by the MEMS diffraction grating is wider than a wavelength band of a gain of the QCL
device that is generated by current injection. Therefore, there is a problem in that a wavelength10
band that can be swept as a module device is limited by the wavelength band of the gain of the
QCL device generated by current injection.
[0006]
In order to solve the problem described above, a first object of the present disclosure is to
provide a QCL device that enables a wavelength sweep over a wider wavelength band to be15
performed by providing two different gain bands.
[0007]
In addition, a second object of the present disclosure is to provide an external resonance-
type QCL module device that enables a wavelength sweep over a wider wavelength band to be
performed by providing two different gain bands.20
[0008]
Furthermore, a third object of the present disclosure is to provide an analyzer that enables
a wavelength sweep over a wider wavelength band to be performed by providing two different
gain bands.
- 4 –
[0009]
Moreover, a fourth object of the present disclosure is to provide a light irradiation method
that enables a wavelength sweep over a wider wavelength band to be performed by providing two
different gain bands.
Solution to Problem5
[0010]
The first aspect of the present disclosure is preferably a QCL device, comprising a first
electrode, a second electrode, and a core region which is formed between the first electrode and
the second electrode and which has a plurality of stages, wherein each stage includes: an active
region in which a plurality of alternating barrier layers and well layers are formed and which10
emits light; and an injector region in which a plurality of alternating barrier layers and well layers
are formed and which injects electrons into the active region, when an electric field is applied
from the second electrode to the first electrode, a first subband group is formed in the stage, the
first subband group includes a first subband, a second subband, a third subband, and a fourth
subband, each subband is configured so that the first subband and the second subband have15
electrons predominantly in the active region, the second subband has a higher energy level and a
higher electron density than the first subband, the third subband has a lower energy level than the
first subband, the fourth subband has a higher energy level than the second subband, when an
electric field is applied from the first electrode to the second electrode, a second subband group is
formed in the stage, the second subband group includes a fifth subband, a sixth subband, a20
seventh subband, and an eighth subband, each subband is configured so that the fifth subband and
the sixth subband have electrons predominantly in the active region, the sixth subband has a
higher energy level and a higher electron density than the fifth subband, the seventh subband has
- 5 –
a lower energy level than the fifth subband, and the eighth subband has a higher energy level than
the sixth subband.
[0011]
The second aspect of the present disclosure is preferably an external resonance-type QCL
module device, comprising the QCL device according to the first aspect and a MEMS diffraction5
grating, wherein the MEMS diffraction grating includes a diffraction reflecting section which
diffracts and reflects light emitted from the QCL device, and returns a part of the light back to the
QCL device by swinging the diffraction reflecting section.
[0012]
The third aspect of the present disclosure is preferably an analyzer, comprising: the10
external resonance-type QCL module device according to the second aspect; a photodetector
which detects light emitted from the external resonance-type QCL module device and transmitted
through an analyte; and a computing unit which calculates an absorption spectrum based on a
detection result of the photodetector.
[0013]15
The fourth aspect of the present disclosure is preferably a light irradiation method using
the QCL device according to the first aspect, the light irradiation method comprising: emitting
light of a first frequency band by applying an electric field from the second electrode toward the
first electrode; and emitting light of a second frequency band by applying an electric field from
the first electrode toward the second electrode.20
Advantageous Effects of Invention
[0014]
According to the first to fourth aspects of the present disclosure, a wavelength sweep over
a wider wavelength band can be performed by providing two different gain bands.
- 6 –
Brief Description of Drawings
[0015]
Fig. 1 is a perspective view showing a QCL device according to a first embodiment of the
present disclosure.
Fig. 2 is a diagram showing a band structure when an electric field is applied from the5
second electrode toward the first electrode of the QCL device according to the first embodiment
of the present disclosure.
Fig. 3 is a diagram showing an existence probability of electrons when an electric field is
applied from the second electrode toward the first electrode of the QCL device according to the
first embodiment of the present disclosure.10
Fig. 4 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the QCL device according to the
first embodiment of the present disclosure.
Fig. 5 is a diagram showing an existence probability of electrons when an electric field is
applied from the first electrode toward the second electrode of the QCL device according to the15
first embodiment of the present disclosure.
Fig. 6 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the QCL device according to the
first embodiment of the present disclosure.
Fig. 7 is a first graph showing wavelength dependence of the gain of the QCL device20
according to the first embodiment of the present disclosure.
Fig. 8 is a second graph showing wavelength dependence of the gain of the QCL device
according to the first embodiment of the present disclosure.
- 7 –
Fig. 9 is a diagram showing a band structure when an electric field is applied from the
second electrode toward the first electrode of a first modification of the QCL device according to
the first embodiment of the present disclosure.
Fig. 10 is a diagram showing an existence probability of electrons when an electric field is
applied from the second electrode toward the first electrode of the first modification of the QCL5
device according to the first embodiment of the present disclosure.
Fig. 11 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure.
Fig. 12 is a diagram showing an existence probability of electrons when an electric field is10
applied from the first electrode toward the second electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure.
Fig. 13 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure.15
Fig. 14 is a graph showing wavelength dependence of the gain of the first modification of
the QCL device according to the first embodiment of the present disclosure.
Fig. 15 is a diagram showing a band structure when an electric field is applied from the
second electrode toward the first electrode of a second modification of the QCL device according
to the first embodiment of the present disclosure.20
Fig. 16 is a diagram showing an existence probability of electrons when an electric field is
applied from the second electrode toward the first electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure.
- 8 –
Fig. 17 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure.
Fig. 18 is a diagram showing an existence probability of electrons when an electric field is
applied from the first electrode toward the second electrode of the second modification of the5
QCL device according to the first embodiment of the present disclosure.
Fig. 19 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure.
Fig. 20 is a graph showing wavelength dependence of the gain of the second10
modification of the QCL device according to the first embodiment of the present disclosure.
Fig. 21 is a top view showing an external resonance-type QCL module device according
to a second embodiment of the present disclosure.
Fig. 22 is a sectional view showing the external resonance-type QCL module device
according to the second embodiment of the present disclosure.15
Fig. 23 is a diagram showing a drive method of the MEMS diffraction grating and the
QCL device according to the second embodiment of the present disclosure.
Fig. 24 is a diagram showing a modification of a drive method of the external resonance-
type QCL module device according to the second embodiment of the present disclosure.
Fig. 25 is a diagram showing an analyzer according to a third embodiment of the present20
disclosure.
Description of Embodiments
[0016]
First Embodiment
- 9 –
[Configuration of QCL Device According to First Embodiment]
Fig. 1 is a perspective view showing a QCL device according to a first embodiment of the
present disclosure. A QCL device 200 is an embedded ridge-type QCL device with a resonator
length L and a ridge width W.
[0017]5
The QCL device 200 includes a first electrode 1. A substrate 2 is bonded on top of the
first electrode 1. For example, the substrate 2 is an n-type InP substrate. A buffer layer 3 is
bonded on top of the substrate 2. For example, the buffer layer 3 is an n-type InP layer with a
layer thickness of 1.0 μm.
[0018]10
A light confinement layer 4 is bonded on top of the buffer layer 3. For example, the
light confinement layer 4 is an n-type Ga0.47In0.53As (hereinafter, referred to as GaInAs) layer
with a layer thickness of 230 nm. A core region 5 is bonded on top of the light confinement
layer 4. For example, the core region 5 is a core region constituted of 35 stages. Details of the
core region 5 will be provided later.15
[0019]
A light confinement layer 6 is bonded on top of the core region 5. For example, the light
confinement layer 6 is an n-type GaInAs layer with a layer thickness of 230 nm. A cladding
layer 7 is bonded on top of the light confinement layer 6. For example, the cladding layer 7 is
an n-type InP layer with a layer thickness of 3.5 μm. A contact layer 8 is bonded on top of the20
cladding layer 7. For example, the contact layer 8 is an n-type GaInAs layer with a layer
thickness of 500 nm.
[0020]
- 10 –
A second electrode 9 is bonded on top of the contact layer 8. A current blocking layer
10 is present in a region that is between the second electrode 9 and the buffer layer 3 and that
surrounds the light confinement layer 4, the core region 5, the light confinement layer 6, the
cladding layer 7, and the contact layer 8. For example, the current blocking layer 10 is a Fe-
doped InP layer.5
[0021]
Conventional QCL devices have only been used to perform current injection in one
direction, from the first electrode 1 to the second electrode 9. However, the QCL device
according to the present embodiment performs current injection from the second electrode 9 to
the first electrode 1 in addition to performing current injection from the first electrode 1 to the10
second electrode 9. In other words, two different gain bands are provided by injecting current
from two directions.
[0022]
[Analysis of Laser Characteristics in QCL Device According to First Embodiment]
Fig. 2 is a diagram showing a band structure when an electric field is applied from the15
second electrode toward the first electrode of the QCL device according to the first embodiment
of the present disclosure. In this case, a band structure of a conduction band is shown in which
an injector region of a stage 41 that is one of the stages included in the core region 5 has been
added to a stage 42 that is a stage adjacent to the stage 41. In addition, a strength of the applied
electric field is 5.0  106 V/m.20
[0023]
In the QCL device according to the present embodiment, the core region 5 is made up of
35 stages. In other words, a same stage is provided consecutively 35 times. One stage is made
- 11 –
up of one active region and one injector region. A description of the active region and the
injector region will be provided later.
[0024]
The stage 42 includes an active region 39. The active region 39 is a region that emits
light when electrons transition between subbands formed within the active region. In addition,5
the active region 39 is constructed by bonding barrier layers and well layers to each other in an
alternating manner. Here, an aspect in which the number of wells is three is shown as an
example.
[0025]
The active region 39 includes a barrier layer 21. For example, the barrier layer 21 is an10
undoped Al0.48In0.52As (hereafter referred to as AlInAs) layer with a layer thickness of 2.4 nm.
A well layer 22 is adjacent to the barrier layer 21. For example, the well layer 22 is an undoped
GaInAs layer with a film thickness of 6.5 nm. A barrier layer 23 is adjacent to the well layer 22.
For example, the barrier layer 23 is an undoped AlInAs layer with a layer thickness of 0.9 nm.
A well layer 24 is adjacent to the barrier layer 23. For example, the well layer 24 is an undoped15
GaInAs layer with a film thickness of 6.4 nm. A barrier layer 25 is adjacent to the well layer 24.
For example, the barrier layer 25 is an undoped AlInAs layer with a layer thickness of 1.5 nm.
A well layer 26 is adjacent to the barrier layer 25. For example, the well layer 26 is an undoped
GaInAs layer with a film thickness of 3.4 nm. A barrier layer 27 is adjacent to the well layer 26.
For example, the barrier layer 27 is an undoped AlInAs layer with a layer thickness of 4.0 nm.20
[0026]
In addition, the stage 42 includes an injector region 40. The injector region 40 is a
region that injects electrons into an active region and is adjacent to the active region 39. In
addition, the injector region 40 is constructed by bonding barrier layers and well layers to each
- 12 –
other in an alternating manner. In this case, an aspect in which the number of wells is five is
shown as an example.
[0027]
The injector region 40 includes the barrier layer 27 described above. A well layer 28 is
adjacent to the barrier layer 27. For example, the well layer 28 is an undoped GaInAs layer with5
a film thickness of 4.1 nm. A barrier layer 29 is adjacent to the well layer 28. For example,
the barrier layer 29 is an undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer
30 is adjacent to the barrier layer 29. For example, the well layer 30 is an undoped GaInAs
layer with a film thickness of 3.7 nm. A barrier layer 31 is adjacent to the well layer 30. For
example, the barrier layer 31 is an undoped AlInAs layer with a layer thickness of 1.2 nm.10
[0028]
A well layer 32 is adjacent to the barrier layer 31. For example, the well layer 32 is a
GaInAs layer doped to an n-type (hereinafter, referred to as an n-type GaInAs layer) with a film
thickness of 3.4 nm. A barrier layer 33 is adjacent to the well layer 32. For example, the
barrier layer 33 is an n-type AlInAs layer with a layer thickness of 1.1 nm. A well layer 34 is15
adjacent to the barrier layer 33. For example, the well layer 34 is an n-type GaInAs layer with a
film thickness of 3.4 nm.
[0029]
A barrier layer 35 is adjacent to the well layer 34. For example, the barrier layer 35 is an
undoped AlInAs layer with a layer thickness of 1.1 nm. A well layer 36 is adjacent to the20
barrier layer 35. For example, the well layer 36 is an undoped GaInAs layer with a film
thickness of 2.9 nm. A barrier layer 37 is adjacent to the well layer 36. For example, the
barrier layer 37 is an undoped AlInAs layer with a layer thickness of 2.4 nm.
[0030]
- 13 –
Furthermore, the stage 42 is adjacent to an injector region 38 of the stage 41. The
injector region 38 is constructed by bonding barrier layers and well layers to each other in an
alternating manner. In this case, an aspect in which the number of wells is five is shown as an
example.
[0031]5
The injector region 38 includes a barrier layer 11. For example, the barrier layer 11 is an
undoped AlInAs layer with a layer thickness of 4.0 nm. A well layer 12 is adjacent to the
barrier layer 11. For example, the well layer 12 is an undoped GaInAs layer with a film
thickness of 4.1 nm. A barrier layer 13 is adjacent to the well layer 12. For example, the
barrier layer 13 is an undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer 14 is10
adjacent to the barrier layer 13. For example, the well layer 14 is an undoped GaInAs layer with
a film thickness of 3.7 nm. A barrier layer 15 is adjacent to the well layer 14. For example,
the barrier layer 15 is an undoped AlInAs layer with a layer thickness of 1.2 nm.
[0032]
A well layer 16 is adjacent to the barrier layer 15. For example, the well layer 16 is an15
n-type GaInAs layer with a film thickness of 3.4 nm. A barrier layer 17 is adjacent to the well
layer 16. For example, the barrier layer 17 is an n-type AlInAs layer with a layer thickness of
1.1 nm. A well layer 18 is adjacent to the barrier layer 17. For example, the well layer 18 is an
n-type GaInAs layer with a film thickness of 3.4 nm.
[0033]20
A barrier layer 19 is adjacent to the well layer 18. For example, the barrier layer 19 is an
undoped AlInAs layer with a layer thickness of 1.1 nm. A well layer 20 is adjacent to the
barrier layer 19. For example, the well layer 20 is an undoped GaInAs layer with a film
thickness of 2.9 nm. The barrier layer 21 described earlier is adjacent to the well layer 20.
- 14 –
[0034]
A doping amount of n-type AlInAs layers in the injector regions 38 and 40 is, for
example, 2.5  1017 cm-3.
[0035]
Fig. 3 is a diagram showing an existence probability of electrons when an electric field is5
applied from the second electrode toward the first electrode of the QCL device according to the
first embodiment of the present disclosure. Fig. 3 shows a square of a wave function at each
energy level in the stage 42. In other words, Fig. 3 shows a degree of the existence probability
of electrons at each energy level.
[0036]10
As described earlier, in the QCL device according to the present embodiment, the core
region 5 is made up of 35 stages. In other words, a same stage is provided consecutively 35
times. Therefore, when analyzing laser characteristics, analyzing laser characteristics with
respect to one stage will suffice. Subsequent analyses were performed based on NPL 1.
[0037]15
In this case, there are 10 different energy levels allowed in the stage 42. The 10 energy
levels are numbered from #1 to #10, starting with a lowest energy level. In addition, each
energy level is shown by a solid line if the electrons are mainly present in the active region 39
and by a dashed line if the electrons are mainly present in the injector region 40. The levels
where electrons are mainly present in the active region 39 are #1, #2, #4, #7, and #10. The20
levels where electrons are mainly present in the injector region 40 are #3, #5, #6, #8, and #9.
[0038]
- 15 –
Fig. 4 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the QCL device according to the
first embodiment of the present disclosure.
[0039]
There are three conditions necessary for laser oscillation to occur in a QCL device. The5
first is that a population inversion has occurred in the active region 39. In other words, in
energy levels where electrons are mainly present in the active region, there need only be an upper
energy level with a higher electron density than an electron density of a lower energy level.
Accordingly, since electronic transitions from the upper energy level to the lower energy level are
facilitated, laser oscillation is also facilitated.10
[0040]
The second is that there is a lower energy level than the lower energy level described
above. Accordingly, electrons can be pulled from the lower energy level.
[0041]
The third is that there is a higher energy level than the higher energy level described15
above. Accordingly, electrons can be injected into the higher energy level.
[0042]
Laser oscillation can occur when the above three conditions are satisfied by the energy
levels allowed in the stage and the electron densities of the energy levels. In consideration
thereof, the three conditions will be confirmed with respect to the energy levels and the electron20
densities shown in Fig. 4.
[0043]
In energy levels where electrons are mainly present in the active region 39, there is an
upper energy level #4 with a higher electron density than an electron density of a lower energy
- 16 –
level #2. In addition, there is an energy level #1 that is a lower energy level than the lower
energy level #2. Furthermore, there are energy levels #5, #6, #7, #8, #9, and #10 that are higher
energy levels than the higher energy level #4.
[0044]
As described above, the energy levels and the electron densities shown in Fig. 4 satisfy5
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the second electrode toward the first electrode of the QCL device
according to the present embodiment.
[0045]
Fig. 5 is a diagram showing an existence probability of electrons when an electric field is10
applied from the first electrode toward the second electrode of the QCL device according to the
first embodiment of the present disclosure. Fig. 5 shows a square of a wave function at each
energy level in the stage made of the active region 39 and the injector region 38. For
convenience of calculation, an orientation of each layer has been reversed so that potential energy
increases toward the right. In addition, the strength of the applied electric field is 5.0  106 V/m15
which is the same as in Figs. 2 and 3.
[0046]
In this case, there are nine different energy levels allowed in the stage the active region
39 and the injector region 38.. The nine energy levels are numbered from #1 to #9, starting
with a lowest energy level. In addition, each energy level is shown by a solid line if the20
electrons are mainly present in the active region 39 and by a dashed line if the electrons are
mainly present in the injector region 40. The levels where electrons are mainly present in the
active region 39 are #1, #2, #3, and #8. The levels where electrons are mainly present in the
injector region 40 are #4, #5, #6, #7, and #9.
- 17 –
[0047]
Fig. 6 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the QCL device according to the
first embodiment of the present disclosure.
[0048]5
The three conditions will be confirmed with respect to the energy levels and the electron
densities shown in Fig. 6. In energy levels where electrons are mainly present in the active
region 39, there is an upper energy level #8 with a higher electron density than an electron density
of a lower energy level #3. In addition, there are energy levels #1 and #2 that are lower energy
levels than the lower energy level #3. Furthermore, there is an energy level #9 that is a higher10
energy level than the higher energy level #8.
[0049]
As described above, the energy levels and the electron densities shown in Fig. 6 satisfy
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the first electrode toward the second electrode of the QCL device15
according to the present embodiment.
[0050]
As described above, in the QCL device according to the present embodiment, laser
oscillation can occur whether current is injected from the first electrode 1 toward the second
electrode 9 or from the second electrode 9 toward the first electrode 1. In other words, two20
different gain bands can be provided by injecting current into the QCL device from two
directions.
[0051]
- 18 –
Fig. 7 is a first graph showing wavelength dependence of the gain of the QCL device
according to the first embodiment of the present disclosure. In this case, gains when using an
embedded ridge-type QCL device with a resonator length L of 1.36 mm and a ridge width of 14
m are shown. A gain 45 when an electric field is applied from the second electrode 9 toward
the first electrode 1 and a current of 137 mA is injected is shown by a solid line. A gain 465
when an electric field is applied from the first electrode 1 toward the second electrode 9 and a
current of 326 mA is injected is shown by a dashed line. The line width  is 5.5 meV.
[0052]
A peak wavelength of the gain 45 is 10.45 m and a bandwidth at half-maximum is 1.13
m. On the other hand, a peak wavelength of the gain 46 is 6.82 m and a bandwidth at half-10
maximum is 0.48 m.
[0053]
As described above, two different gain bands can be provided by injecting current into the
QCL device from two directions.
[0054]15
Fig. 8 is a second graph showing wavelength dependence of the gain of the QCL device
according to the first embodiment of the present disclosure. In the gain shown in Fig. 7, a line
width  is set to 5.5 meV by setting a doping concentration in the injector region to 2.5  1017 cm-
3. However, an impurity scattering time in subbands can be reduced by further increasing the
doping concentration. Accordingly, since the line width  can be increased, a gain band can be20
broadened while hardly changing the peak gain wavelength.
[0055]
Here, a case where the line width  is set to 15 meV is shown as an example showing a
result of broadening the gain band. A gain 47 when an electric field is applied from the second
- 19 –
electrode 9 toward the first electrode 1 and a current of 372 mA is injected is shown by a solid
line. A gain 48 when an electric field is applied from the first electrode 1 toward the second
electrode 9 and a current of 887 mA is injected is shown by a dashed line. The line width  is
5.5 meV.
[0056]5
A peak wavelength of the gain 47 is 10.31 m and a bandwidth at half-maximum is 3.06
m. On the other hand, a peak wavelength of the gain 48 is 6.78 m and a bandwidth at half-
maximum is 1.31 m.
[0057]
As described above, by further increasing the doping concentration and increasing the line10
width , the gain band can be broadened while hardly changing the peak gain wavelength.
When this method is applied to an external resonance-type QCL module device to be described
later, if the loss of an external resonator is less than 2.1 cm-1, a wavelength sweep can be
performed over a wide wavelength range from 5.8 m to 14.0 m.
[0058]15
[Analysis of Laser Characteristics in First Modification of QCL Device According to First
Embodiment]
Fig. 9 is a diagram showing a band structure when an electric field is applied from the
second electrode toward the first electrode of a first modification of the QCL device according to
the first embodiment of the present disclosure. In this case, a band structure of a conduction20
band is shown in which an injector region of a stage 83 that is one of the stages included in the
core region 5 has been added to a stage 84 that is a stage adjacent to the stage 83. In addition, a
strength of the applied electric field is 5.0  106 V/m. An active region 81 included in the first
- 20 –
modification of the QCL device differs from the active region 39 in that the number of wells is
four.
[0059]
The stage 84 includes the active region 81. The active region 81 includes a barrier layer
61. For example, the barrier layer 61 is an undoped AlInAs layer with a layer thickness of 3.55
nm. A well layer 62 is adjacent to the barrier layer 61. For example, the well layer 62 is an
undoped GaInAs layer with a film thickness of 3.0 nm. A barrier layer 63 is adjacent to the well
layer 62. For example, the barrier layer 63 is an undoped AlInAs layer with a layer thickness of
1.5 nm. A well layer 64 is adjacent to the barrier layer 63. For example, the well layer 64 is an
undoped GaInAs layer with a film thickness of 6.5 nm. A barrier layer 65 is adjacent to the well10
layer 64. For example, the barrier layer 65 is an undoped AlInAs layer with a layer thickness of
0.9 nm. A well layer 66 is adjacent to the barrier layer 65. For example, the well layer 66 is an
undoped GaInAs layer with a film thickness of 6.5 nm. A barrier layer 67 is adjacent to the well
layer 66. For example, the barrier layer 67 is an undoped AlInAs layer with a layer thickness of
0.9 nm. A well layer 68 is adjacent to the barrier layer 67. For example, the well layer 68 is an15
undoped GaInAs layer with a film thickness of 5.4 nm. A barrier layer 69 is adjacent to the well
layer 68. For example, the barrier layer 69 is an undoped AlInAs layer with a layer thickness of
2.4 nm.
[0060]
In addition, the stage 84 includes an injector region 82. The injector region 82 includes20
the barrier layer 69 described above. A well layer 70 is adjacent to the barrier layer 69. For
example, the well layer 70 is an undoped GaInAs layer with a film thickness of 2.9 nm. A
barrier layer 71 is adjacent to the well layer 70. For example, the barrier layer 71 is an undoped
AlInAs layer with a layer thickness of 1.1 nm.
- 21 –
[0061]
A well layer 72 is adjacent to the barrier layer 71. For example, the well layer 72 is an
n-type GaInAs layer with a film thickness of 3.4 nm. A barrier layer 73 is adjacent to the well
layer 72. For example, the barrier layer 73 is an n-type AlInAs layer with a layer thickness of
1.1 nm. A well layer 74 is adjacent to the barrier layer 73. For example, the well layer 74 is an5
n-type GaInAs layer with a film thickness of 3.4 nm.
[0062]
A barrier layer 75 is adjacent to the well layer 74. For example, the barrier layer 75 is an
undoped AlInAs layer with a layer thickness of 1.2 nm. A well layer 76 is adjacent to the
barrier layer 75. For example, the well layer 76 is an undoped GaInAs layer with a film10
thickness of 3.7 nm. A barrier layer 77 is adjacent to the well layer 76. For example, the
barrier layer 77 is an undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer 78 is
adjacent to the barrier layer 77. For example, the well layer 78 is an undoped GaInAs layer with
a film thickness of 4.1 nm. A barrier layer 79 is adjacent to the well layer 78. For example,
the barrier layer 79 is an undoped AlInAs layer with a layer thickness of 3.5 nm.15
[0063]
In addition, the stage 84 is adjacent to an injector region 80 of the stage 83. The injector
region 80 includes a barrier layer 51. For example, the barrier layer 51 is an undoped AlInAs
layer with a layer thickness of 2.4 nm. A well layer 52 is adjacent to the barrier layer 51. For
example, the well layer 52 is an undoped GaInAs layer with a film thickness of 2.9 nm. A20
barrier layer 53 is adjacent to the well layer 52. For example, the barrier layer 53 is an undoped
AlInAs layer with a layer thickness of 1.1 nm.
[0064]
- 22 –
A well layer 54 is adjacent to the barrier layer 53. For example, the well layer 54 is an
n-type GaInAs layer with a film thickness of 3.4 nm. A barrier layer 55 is adjacent to the well
layer 54. For example, the barrier layer 55 is an n-type AlInAs layer with a layer thickness of
1.1 nm. A well layer 56 is adjacent to the barrier layer 55. For example, the well layer 56 is an
n-type GaInAs layer with a film thickness of 3.4 nm.5
[0065]
A barrier layer 57 is adjacent to the well layer 56. For example, the barrier layer 57 is an
undoped AlInAs layer with a layer thickness of 1.2 nm. A well layer 58 is adjacent to the
barrier layer 57. For example, the well layer 58 is an undoped GaInAs layer with a film
thickness of 3.7 nm. A barrier layer 59 is adjacent to the well layer 58. For example, the10
barrier layer 59 is an undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer 60 is
adjacent to the barrier layer 59. For example, the well layer 60 is an undoped GaInAs layer with
a film thickness of 4.1 nm. The barrier layer 61 described earlier is adjacent to the well layer 60.
[0066]
A doping amount of n-type AlInAs layers in the injector regions 80 and 82 is, for15
example, 2.5  1017 cm-3.
[0067]
Fig. 10 is a diagram showing an existence probability of electrons when an electric field is
applied from the second electrode toward the first electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure. Fig. 10 shows a square of a20
wave function at each energy level in the stage 84. In other words, Fig. 10 shows a degree of
the existence probability of electrons at each energy level.
[0068]
- 23 –
In this case, there are 10 different energy levels allowed in the stage 84. The 10 energy
levels are numbered from #1 to #10, starting with a lowest energy level. In addition, each
energy level is shown by a solid line if the electrons are mainly present in the active region 81
and by a dashed line if the electrons are mainly present in the injector region 82. The levels
where electrons are mainly present in the active region 81 are #1, #2, #3, #4, and #8. The levels5
where electrons are mainly present in the injector region 82 are #5, #6, #7, #9, and #10.
[0069]
Fig. 11 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure. Laser oscillation can occur10
when the three conditions described earlier are satisfied by the energy levels allowed in the stage
and the electron densities of the energy levels. In consideration thereof, the three conditions will
be confirmed with respect to the energy levels and the electron densities shown in Fig. 11.
[0070]
In energy levels where electrons are mainly present in the active region 81, there is an15
upper energy level #8 with a higher electron density than an electron density of a lower energy
level #3. In addition, there are energy levels #1 and #2 that are lower energy levels than the
lower energy level #3. Furthermore, there are energy levels #9 and #10 that are higher energy
levels than the higher energy level #8.
[0071]20
As described above, the energy levels and the electron densities shown in Fig. 11 satisfy
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the second electrode toward the first electrode of the first
modification of the QCL device according to the present embodiment.
- 24 –
[0072]
Fig. 12 is a diagram showing an existence probability of electrons when an electric field is
applied from the first electrode toward the second electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure. Fig. 12 shows a square of a
wave function at each energy level in the stage made of the active region 81 and the injector5
region 80.. For convenience of calculation, an orientation of each layer has been reversed so
that potential energy increases toward the right. In addition, the strength of the applied electric
field is 5.0  106 V/m which is the same as in Figs. 10 and 11.
[0073]
In this case, there are 10 different energy levels allowed in the stage made of the active10
region 81 and the injector region 80.. The 10 energy levels are numbered from #1 to #10,
starting with a lowest energy level. In addition, each energy level is shown by a solid line if the
electrons are mainly present in the active region 81 and by a dashed line if the electrons are
mainly present in the injector region 82. The levels where electrons are mainly present in the
active region 81 are #1, #2, #3, #6, #8, and #10. The levels where electrons are mainly present15
in the injector region 82 are #4, #5, #7, and #9.
[0074]
Fig. 13 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the first modification of the QCL
device according to the first embodiment of the present disclosure.20
[0075]
The three conditions will be confirmed with respect to the energy levels and the electron
densities shown in Fig. 13. In energy levels where electrons are mainly present in the active
region 81, there is an upper energy level #6 with a higher electron density than an electron density
- 25 –
of a lower energy level #3. In addition, there are energy levels #1 and #2 that are lower energy
levels than the lower energy level #3. Furthermore, there are energy levels #7, #8, #9, and #10
that are higher energy levels than the higher energy level #6.
[0076]
As described above, the energy levels and the electron densities shown in Fig. 13 satisfy5
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the first electrode toward the second electrode of the first
modification of the QCL device according to the present embodiment.
[0077]
As described above, in the first modification of the QCL device according to the present10
embodiment, laser oscillation can occur whether current is injected from the first electrode 1
toward the second electrode 9 or from the second electrode 9 toward the first electrode 1. In
other words, two different gain bands can be provided by injecting current into the QCL device
from two directions.
[0078]15
Fig. 14 is a graph showing wavelength dependence of the gain of the first modification of
the QCL device according to the first embodiment of the present disclosure. In this case, gains
when using an embedded ridge-type QCL device with a resonator length L of 1.36 mm and a
ridge width of 14 m are shown. A gain 85 when an electric field is applied from the second
electrode 9 toward the first electrode 1 and a current of 1652 mA is injected is shown by a solid20
line. A gain 86 when an electric field is applied from the first electrode 1 toward the second
electrode 9 and a current of 407 mA is injected is shown by a dashed line.
[0079]
- 26 –
A peak wavelength of the gain 85 is 7.22 m and a bandwidth at half-maximum is 0.54
m. On the other hand, a peak wavelength of the gain 86 is 9.09 m and a bandwidth at half-
maximum is 0.85 m.
[0080]
As described above, two different gain bands can be provided by injecting current into the5
QCL device from two directions.
[0081]
[Analysis of Laser Characteristics in Second Modification of QCL Device According to First
Embodiment]
Fig. 15 is a diagram showing a band structure when an electric field is applied from the10
second electrode toward the first electrode of a second modification of the QCL device according
to the first embodiment of the present disclosure. In this case, a band structure of a conduction
band is shown in which an injector region of a stage 125 that is one of the stages included in the
core region 5 has been added to a stage 126 that is a stage adjacent to the stage 125. In addition,
a strength of the applied electric field is 5.0  106 V/m. An active region 123 included in the15
second modification of the QCL device differs from the active region 39 in that the number of
wells is five.
[0082]
The stage 126 includes the active region 123. The active region 123 includes a barrier
layer 101. For example, the barrier layer 101 is an undoped AlInAs layer with a layer thickness20
of 2.4 nm. A well layer 102 is adjacent to the barrier layer 101. For example, the well layer
102 is an undoped GaInAs layer with a film thickness of 5.0 nm. A barrier layer 103 is adjacent
to the well layer 102. For example, the barrier layer 103 is an undoped AlInAs layer with a
layer thickness of 0.9 nm. A well layer 104 is adjacent to the barrier layer 103. For example,
- 27 –
the well layer 104 is an undoped GaInAs layer with a film thickness of 6.0 nm. A barrier layer
105 is adjacent to the well layer 104. For example, the barrier layer 105 is an undoped AlInAs
layer with a layer thickness of 0.9 nm. A well layer 106 is adjacent to the barrier layer 105.
For example, the well layer 106 is an undoped GaInAs layer with a film thickness of 6.0 nm. A
barrier layer 107 is adjacent to the well layer 106. For example, the barrier layer 107 is an5
undoped AlInAs layer with a layer thickness of 0.8 nm. A well layer 108 is adjacent to the
barrier layer 107. For example, the well layer 108 is an undoped GaInAs layer with a film
thickness of 4.5 nm. A barrier layer 109 is adjacent to the well layer 108. For example, the
barrier layer 109 is an undoped AlInAs layer with a layer thickness of 0.8 nm. A well layer 110
is adjacent to the barrier layer 109. For example, the well layer 110 is an undoped GaInAs layer10
with a film thickness of 3.0 nm. A barrier layer 111 is adjacent to the well layer 110. For
example, the barrier layer 111 is an undoped AlInAs layer with a layer thickness of 3.5 nm.
[0083]
In addition, the stage 126 includes an injector region 124. The injector region 124
includes the barrier layer 111 described above. A well layer 112 is adjacent to the barrier layer15
111. For example, the well layer 112 is an undoped GaInAs layer with a film thickness of 4.1
nm. A barrier layer 113 is adjacent to the well layer 112. For example, the barrier layer 113 is
an undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer 114 is adjacent to the
barrier layer 113. For example, the well layer 114 is an undoped GaInAs layer with a film
thickness of 3.7 nm. A barrier layer 115 is adjacent to the well layer 114. For example, the20
barrier layer 115 is an undoped AlInAs layer with a layer thickness of 1.2 nm.
[0084]
A well layer 116 is adjacent to the barrier layer 115. For example, the well layer 116 is
an n-type GaInAs layer with a film thickness of 3.4 nm. A barrier layer 117 is adjacent to the
- 28 –
well layer 116. For example, the barrier layer 117 is an n-type AlInAs layer with a layer
thickness of 1.1 nm. A well layer 118 is adjacent to the barrier layer 117. For example, the
well layer 118 is an n-type GaInAs layer with a film thickness of 3.4 nm.
[0085]
A barrier layer 119 is adjacent to the well layer 118. For example, the barrier layer 1195
is an undoped AlInAs layer with a layer thickness of 1.1 nm. A well layer 120 is adjacent to the
barrier layer 119. For example, the well layer 120 is an undoped GaInAs layer with a film
thickness of 2.9 nm. A barrier layer 121 is adjacent to the well layer 120. For example, the
barrier layer 121 is an undoped AlInAs layer with a layer thickness of 2.4 nm.
[0086]10
In addition, the stage 126 is adjacent to an injector region 122 of the stage 125. The
injector region 122 includes a barrier layer 91. For example, the barrier layer 91 is an undoped
AlInAs layer with a layer thickness of 3.5 nm. A well layer 92 is adjacent to the barrier layer
91. For example, the well layer 92 is an undoped GaInAs layer with a film thickness of 4.1 nm.
A barrier layer 93 is adjacent to the well layer 92. For example, the barrier layer 93 is an15
undoped AlInAs layer with a layer thickness of 1.7 nm. A well layer 94 is adjacent to the
barrier layer 93. For example, the well layer 94 is an undoped GaInAs layer with a film
thickness of 3.7 nm. A barrier layer 95 is adjacent to the well layer 94. For example, the
barrier layer 95 is an undoped AlInAs layer with a layer thickness of 1.2 nm.
[0087]20
A well layer 96 is adjacent to the barrier layer 95. For example, the well layer 96 is an
n-type GaInAs layer with a film thickness of 3.4 nm. A barrier layer 97 is adjacent to the well
layer 96. For example, the barrier layer 97 is an n-type AlInAs layer with a layer thickness of
- 29 –
1.1 nm. A well layer 98 is adjacent to the barrier layer 97. For example, the well layer 98 is an
n-type GaInAs layer with a film thickness of 3.7 nm.
[0088]
A barrier layer 99 is adjacent to the well layer 98. For example, the barrier layer 99 is an
undoped AlInAs layer with a layer thickness of 1.1 nm. A well layer 100 is adjacent to the5
barrier layer 99. For example, the well layer 100 is an undoped GaInAs layer with a film
thickness of 2.9 nm. The barrier layer 101 described earlier is adjacent to the well layer 100.
[0089]
A doping amount of n-type AlInAs layers in the injector regions 122 and 124 is, for
example, 2.5  1017 cm-3.10
[0090]
Fig. 16 is a diagram showing an existence probability of electrons when an electric field is
applied from the second electrode toward the first electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure. Fig. 16 shows a square
of a wave function at each energy level in the stage 126. In other words, Fig. 16 shows a degree15
of the existence probability of electrons at each energy level.
[0091]
In this case, there are 10 different energy levels allowed in the stage 126. The 10 energy
levels are numbered from #1 to #10, starting with a lowest energy level. In addition, each
energy level is shown by a solid line if the electrons are mainly present in the active region 12320
and by a dashed line if the electrons are mainly present in the injector region 124. The levels
where electrons are mainly present in the active region 123 are #1, #2, #3, #4, #7, and #9. The
levels where electrons are mainly present in the injector region 124 are #5, #6, #8, and #10.
[0092]
- 30 –
Fig. 17 is a table showing energy levels and electron densities when an electric field is
applied from the second electrode toward the first electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure. Laser oscillation can
occur when the three conditions described earlier are satisfied by the energy levels allowed in the
stage and the electron densities of the energy levels. In consideration thereof, the three5
conditions will be confirmed with respect to the energy levels and the electron densities shown in
Fig. 17.
[0093]
In energy levels where electrons are mainly present in the active region 123, there is an
upper energy level #7 with a higher electron density than electron densities of lower energy levels10
#3 and #4. In addition, there is an upper energy level #9 with a higher electron density than the
electron densities of the lower energy levels #3 and #4. An actual calculation revealed that the
highest gain when a current with a same magnitude is injected is obtained when the upper energy
level is #7 and the lower energy level is #4. Therefore, a gain when transitioning between these
energy levels will be considered.15
[0094]
There are energy levels #1, #2, and #3 that are lower energy levels than the lower energy
level #4. Furthermore, there are energy levels #8, #9, and #10 that are higher energy levels than
the higher energy level #7.
[0095]20
As described above, the energy levels and the electron densities shown in Fig. 17 satisfy
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the second electrode toward the first electrode of the second
modification of the QCL device according to the present embodiment.
- 31 –
[0096]
Fig. 18 is a diagram showing an existence probability of electrons when an electric field is
applied from the first electrode toward the second electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure. Fig. 18 shows a square
of a wave function at each energy level in the stage made of the active region 123 and the5
injector region 122. For convenience of calculation, an orientation of each layer has been
reversed so that potential energy increases toward the right. In addition, the strength of the
applied electric field is 5.0  106 V/m which is the same as in Figs. 16 and 17.
[0097]
In this case, there are 11 different energy levels allowed in the stage made of the active10
region 123 and the injector region 122 . The 11 energy levels are numbered from #1 to #11,
starting with a lowest energy level. In addition, each energy level is shown by a solid line if the
electrons are mainly present in the active region 123 and by a dashed line if the electrons are
mainly present in the injector region 124. The levels where electrons are mainly present in the
active region 123 are #1, #2, #3, #4, #5, and #10. The levels where electrons are mainly present15
in the injector region 124 are #6, #7, #8, and #9.
[0098]
Fig. 19 is a table showing energy levels and electron densities when an electric field is
applied from the first electrode toward the second electrode of the second modification of the
QCL device according to the first embodiment of the present disclosure.20
[0099]
The three conditions will be confirmed with respect to the energy levels and the electron
densities shown in Fig. 19. In energy levels where electrons are mainly present in the active
region 123, there is an upper energy level #10 with a higher electron density than an electron
- 32 –
density of a lower energy level #4. In addition, there are energy levels #1, #2, and #3 that are
lower energy levels than the lower energy level #4. Furthermore, there is an energy level #11
that is a higher energy level than the higher energy level #10.
[0100]
As described above, the energy levels and the electron densities shown in Fig. 19 satisfy5
the three conditions necessary for laser oscillation. Therefore, laser oscillation can occur when
an electric field is applied from the first electrode toward the second electrode of the second
modification of the QCL device according to the present embodiment.
[0101]
As described above, in the second modification of the QCL device according to the10
present embodiment, laser oscillation can occur whether current is injected from the first
electrode 1 toward the second electrode 9 or from the second electrode 9 toward the first
electrode 1. In other words, two different gain bands can be provided by injecting current into
the QCL device from two directions.
[0102]15
Fig. 20 is a graph showing wavelength dependence of the gain of the second modification
of the QCL device according to the first embodiment of the present disclosure. In this case,
gains when using an embedded ridge-type QCL device with a resonator length L of 1.36 mm and
a ridge width of 14 m are shown. A gain 127 when an electric field is applied from the second
electrode 9 toward the first electrode 1 and a current of 226 mA is injected is shown by a solid20
line. A gain 128 when an electric field is applied from the first electrode 1 toward the second
electrode 9 and a current of 600 mA is injected is shown by a dashed line.
[0103]
- 33 –
A peak wavelength of the gain 127 is 10.09 m and a bandwidth at half-maximum is 1.06
m. On the other hand, a peak wavelength of the gain 128 is 6.21 m and a bandwidth at half-
maximum is 0.40 m.
[0104]
As described above, two different gain bands can be provided by injecting current into the5
QCL device from two directions.
[0105]
While examples in which the numbers of wells constituting active regions are three, four,
and five have been shown in the present embodiment, the number of wells is not limited thereto
and other numbers of layers may also be adopted. The same is true for the number of wells in10
injector regions.
In addition, the value of the injection current is changed in the wavelength dependence of
gain in order to unify the values of gain peaks to 20 cm-1. Since laser oscillation occurs when a
gain and a loss as a resonator become equal, the injection current may be varied according to a
magnitude of the loss.15
[0106]
Second Embodiment
[Configuration of External Resonance-Type QCL Module Device According to Second
Embodiment]
Fig. 21 is a top view showing an external resonance-type QCL module device according20
to a second embodiment of the present disclosure. An external resonance-type QCL module
device 300 according to the present embodiment includes a QCL device 136 according to the first
embodiment. In addition, Fig. 22 is a sectional view showing the external resonance-type QCL
module device according to the second embodiment of the present disclosure. Fig. 22 is a
- 34 –
sectional view showing an aspect of the external resonance-type QCL module device 300 of Fig.
21 cut along I-II.
[0107]
The external resonance-type QCL module device 300 includes an enclosure 131. The
enclosure 131 includes a window 131a for taking out output light to the outside and a drawer5
131b for drawing out wiring and the like to the outside.
[0108]
In addition, the external resonance-type QCL module device 300 includes a base member
132. For example, the base member 132 is made of aluminum (Al) or copper (Cu). The base
member 132 includes a side wall section 132b and an inclined surface 132c. A MEMS10
diffraction grating 138 is fixed on the inclined surface 132c via a mounting member 149.
Details of the MEMS diffraction grating 138 will be provided later.
[0109]
In addition, the base member 132 has a flat bottom section 132a. The bottom section
132a is fixed to a bottom section of the enclosure 131 via a cooler 133. For example, the cooler15
133 is a cooling device including a Peltier element. Furthermore, a heat sink 134 is bonded to
an upper part of the bottom section 132a. For example, the heat sink 134 is made of a heat-
dissipating member such as copper (Cu).
[0110]
The QCL device 136 is fixed on top of the heat sink 134 via a submount 141. For20
example, the submount 141 is made of aluminum nitride (AlN) or silicon carbide (SiC).
[0111]
The QCL device 136 includes a first electrode 136a and a second electrode 136b. In
addition, the QCL device 136 includes a first end surface 137a. A reflection reducing section
- 35 –
139 is provided on the first end surface 137a. For example, the reflection reducing section 139
is constituted of an AR (Anti-Reflection) layer with a reflectance of less than 1%.
[0112]
In addition, the QCL device 136 includes a second end surface 137b. The second end
surface 137b opposes the first end surface 137a. A reflection reducing section 140 is provided5
on the second end surface 137b. For example, the reflection reducing section 140 is constituted
of a low reflectance layer with a reflectance of around 10%. The second end surface 137b
constitutes an external resonator with the MEMS diffraction grating 138 to be described later.
[0113]
In addition, lenses 135a and 135b are installed on top of the heat sink 134 via an10
ultraviolet-curing resin 142. The lenses 135a and 135b are aspherical lenses. The lenses 135a
and 135b are made of a material with low absorption of mid-infrared light such as zinc selenide
(ZnSe) or germanium (Ge).
[0114]
The lens 135b is arranged on a side of the second end surface 137b with respect to the15
QCL device 136. In addition, the lens 135b collimates light emitted from the second end surface
137b. The light collimated by the lens 135b is outputted to the outside through the window
131a.
[0115]
The lens 135a is arranged on a side of the first end surface 137a with respect to the QCL20
device 136. In addition, the lens 135a collimates light emitted from the first end surface 137a.
[0116]
The light collimated by the lens 135a is incident to the MEMS diffraction grating 138.
By diffracting and reflecting the incident light, the MEMS diffraction grating 138 causes light of
- 36 –
a specific wavelength in the incident light to return to the first end surface 137a. Since the first
end surface 137a is provided with the reflection reducing section 139 that is constituted of AR
with a reflectance of 1% or less, more than 99% of the light is coupled to the QCL device 136 and
directed toward the second end surface 137b. The second end surface 137b is provided with the
reflection reducing section 140 that is constituted of a low reflectance layer with a reflectance of5
around 10%. Therefore, around 90% of the incident light is emitted outside the QCL device 136
and the remaining 10% is reflected and directed toward the first end surface 137a. Accordingly,
an external resonator is constructed between the second end surface 137b and the MEMS
diffraction grating 138.
[0117]10
A support section 143 included in the MEMS diffraction grating 138 supports a movable
section 145 and the like via a pair of coupling sections 144. Each coupling section 144 extends
along an axis x. In addition, each coupling section 144 couples the movable section 145 to the
support section 143 on the axis x so that the movable section 145 is freely swingable around the
axis x.15
[0118]
The movable section 145 is a flat plate-shaped member that is circular in plan view and is
positioned inside the support section 143. The movable section 145 is coupled by the support
section 143 so as to be freely swingable. The support section 143, the coupling sections 144,
and the movable section 145 are integrally formed by, for example, being fabricated on a single20
SOI (Silicon on Insulator) substrate.
[0119]
A diffraction reflecting section 150 is provided on a surface of the movable section 145
on a side of the QCL device 136. The diffraction reflecting section 150 includes a diffraction
- 37 –
reflecting surface that diffracts and reflects light emitted from the QCL device 136. For
example, the diffraction reflecting section 150 is provided over the surface of the movable section
145. In addition, the diffraction reflecting section 150 is constituted of a resin layer on which a
diffraction grating pattern is formed and a metal layer. The metal layer is provided over the
surface of the resin layer so as to follow the diffraction grating pattern. Alternatively, the5
diffraction reflecting section 150 may be provided on the movable section 145 and solely
constituted of a metal layer on which a diffraction grating pattern is formed. For example, the
diffraction grating pattern is a grating with a saw blade-shaped cross-section, a grating with a
rectangular cross-section, or a grating with a sinusoidal cross-section.
[0120]10
A coil 146 is embedded in a groove formed on the surface of the movable section 145.
The coil 146 is spirally wound a plurality of times in plan view. Wiring for connection to the
outside is electrically connected to an outer end and an inner end of the coil 146. For example,
the wiring is provided over the support section 143, the coupling sections 144, and the movable
section 145 and is electrically connected to electrodes provided on the support section 143.15
[0121]
A magnetic field acting on the coil 146 is generated by a pair of magnets 147. Each of
the pair of magnets 147 is formed in a rectangular parallelepiped shape and the pair of magnets
147 is arranged so as to oppose a pair of edges of the support section 143 that is parallel to the
axis x. An array of magnetic poles in each magnet 147 is, for example, a Halbach array. A20
yoke 148 is arranged at a position surrounding the pair of magnets 147 and the support section
143. The yoke 148 has a rectangular frame shape in plan view and amplifies a magnetic force of
the magnets 147.
[0122]
- 38 –
When a current flows through the coil 146, a magnetic field generated by the pair of
magnets 147 in the MEMS diffraction grating 138 creates a Coulomb force. The Coulomb force
is created in a predetermined direction with respect to electrons flowing in the coil 146.
Accordingly, the coil 146 is subjected to a force in the predetermined direction. Therefore, the
movable section 145 can be caused to swing by controlling an orientation, a magnitude, or the5
like of the current flowing in the coil 146. In other words, the diffraction reflecting section 150
can be caused to swing around the axis x. In addition, the movable section 145 can be caused to
swing at high speed at a resonant frequency level by passing a current with a frequency
corresponding to the resonant frequency of the movable section 145 through the coil 146. In
this manner, the coil 146 and the pair of magnets 147 function as an actuator section that causes10
the movable section 145 to swing.
[0123]
[Operation of QCL Device According to Second Embodiment]
Fig. 23 is a diagram showing a drive method of the MEMS diffraction grating and the
QCL device according to the second embodiment of the present disclosure. Here, a method of15
driving the MEMS diffraction grating and the QCL device for performing a wavelength sweep in
two wavelength bands by applying an electric field in two directions will be described.
[0124]
As described in the first embodiment, a gain band of the QCL device 136 differs between
when the electric field is applied from the second electrode 136b toward the first electrode 136a20
and when the electric field is applied from the first electrode 136a toward the second electrode
136b. In other words, wavelength sweeps in two wavelength bands can be performed by
applying an electric field in two directions. Therefore, a drive method when the QCL device
- 39 –
136 shares a same configuration as the QCL device 200 according to the first embodiment will
now be described.
[0125]
In Fig. 23, a top graph shows a current flowing through the MEMS diffraction grating 138
and a bottom graph shows a current flowing through the QCL device 136. An orientation of the5
diffraction reflecting section 150 or, in other words, an orientation of the movable section 145
that operates the diffraction reflecting section 150 is shown above the graph showing a current
flowing through the MEMS diffraction grating 138.
[0126]
First, a drive current c1 is applied to the MEMS diffraction grating 138 or, in other words,10
the coil 146. The drive current c1 is a pulsed current of a first frequency f1. Accordingly, the
diffraction reflecting section 150 or, in other words, the movable section 145 swings repeatedly at
the first frequency. Therefore, a period T1 of the swing of the diffraction reflecting section 150
is 1/f1. In this case, the period T1 is the time required for the diffraction reflecting section 150
to make one round trip. In addition, a wavelength of output light from the external resonance-15
type QCL module device 300 varies with an angle of rotation of the diffraction reflecting section
150.
[0127]
At this point, a drive current c2 is first passed from the first electrode 136a to the second
electrode 136b in the QCL device 136. In other words, an electric field is applied from the first20
electrode 136a toward the second electrode 136b. In this case, the drive current c2 is a pulsed
current of a second frequency f2 that is a higher frequency than the first frequency.
Accordingly, pulsed light of the second frequency f2 is emitted from the QCL device 136. In
other words, a waveform of the pulsed light emitted from the QCL device 136 is similar to that of
- 40 –
the drive current c2. Therefore, a period T2 of the pulsed light is 1/f2. If a pulse width of the
pulsed light is denoted by T3, a duty ratio is T3/T2 which is a value greater than 0% and smaller
than around 10%.
[0128]
Fig. 23 shows the drive current c2 at an initial phase before a phase of the pulsed light is5
changed as will be described later. In this example, a rising point of the pulse light in the initial
phase coincides with a folding point of the diffraction reflecting section 150.
[0129]
When the QCL device 136 is driven in this manner, pulsed light is emitted from the QCL
device 136 n-number of times during an outward period in the swing of the diffraction reflecting10
section 150 or, in other words, during T1/2. In this case, n is equal to (T1/2)/T2. Since a
rotation angle of the diffraction reflecting section 150 differs depending on a timing of each light
emission, the wavelength of the emitted light assumes mutually different values 1', 2', 3', ,
n'. For example, when the output light is swept in order from a short wavelength side, 1' < 2'
< 3' <  < n' is satisfied.15
[0130]
On the other hand, pulsed light is also emitted from the QCL device 136 n-number of
times during a return period in the swing of the diffraction reflecting section 150. As described
above, when the output light is swept in order from the short wavelength side during the outward
period, the output light is swept in order from a long wavelength side in the return period which is20
contrary to the outward period. In other words, at wavelengths n+1', n+2', n+3', , 2n of light
sequentially emitted from the QCL device 136, n+1' > n+2' > n+3' >  > 2n is satisfied.
[0131]
- 41 –
In this case, the wavelengths n+1', n+2', n+3', , 2n of the output light during the return
period are approximately equal to wavelengths obtained by inverting the wavelengths 1', 2', 3',
, n during the outward period with respect to time based on a time point where the outward
period and the return period are switched. Therefore, either the outward period or the return
period is used in an analyzer to be described later. Due to the above, for example, the QCL5
device 200 according to the first embodiment is capable of performing a wavelength sweep by a
short wavelength-side gain shown in Figs. 7 and 8.
[0132]
Next, a drive current c3 is passed from the second electrode 136b toward the first
electrode 136a in the QCL device 136. In other words, an electric field is applied from the10
second electrode 136b toward the first electrode 136a. In this case, the drive current c3 is a
pulsed current of a second frequency f2 that is a higher frequency than the first frequency. In
addition, the drive current c1 is applied to the MEMS diffraction grating 138 or, in other words,
the coil 146. The drive current c1 is a pulsed current of the first frequency f1 which is the same
as when a pulsed current is passed from the first electrode 136a to the second electrode 136b.15
Accordingly, the diffraction reflecting section 150 performs a same operation as the swing
described earlier. Therefore, a wavelength of output light varies with an angle of rotation of the
diffraction reflecting section 150. In other words, the output light is similar to the case
described above with the exception of an orientation and a current value of the current being
different.20
[0133]
When the QCL device 136 is driven, pulsed light is emitted from the QCL device 136 n-
number of times during an outward period in the swing of the diffraction reflecting section 150
or, in other words, during T1/2. In this case, n is equal to (T1/2)/T2. At this point, the
- 42 –
wavelength of the emitted light assumes mutually different values 1', 2', 3', , n'. For
example, when the output light is swept in order from a short wavelength side, 1' < 2' < 3' < 
< n' is satisfied.
[0134]
In a similar manner, pulsed light is also emitted from the QCL device 136 n-number of5
times during a return period in the swing of the diffraction reflecting section 150. As described
above, when the output light is swept in order from the short wavelength side during the outward
period, the output light is swept in order from a long wavelength side in the return period which is
contrary to the outward period. In other words, at wavelengths n+1', n+2', n+3', , 2n of light
sequentially emitted from the QCL device 136, n+1' > n+2' > n+3' >  > 2n is satisfied.10
[0135]
In this case, the wavelengths n+1', n+2', n+3', , 2n of the output light during the return
period are approximately equal to wavelengths obtained by inverting the wavelengths 1', 2', 3',
, n during the outward period with respect to time based on a time point where the outward
period and the return period are switched. Therefore, either the outward period or the return15
period is used in an analyzer to be described later. Due to the above, for example, the QCL
device 200 according to the first embodiment is capable of performing a wavelength sweep by a
long wavelength-side gain shown in Figs. 7 and 8.
[0136]
A wavelength range that can be swept by the angle of rotation of the diffraction reflecting20
section 150 is wider than a gain range obtained by adding a gain range when a current is passed
from the second electrode 136b to the first electrode 136a in the QCL device 136 to a gain range
when a current is passed from the first electrode 136a to the second electrode 136b in the QCL
device 136.
- 43 –
[0137]
[Modification of External Resonance-Type QCL Module Device According to Second
Embodiment]
Fig. 24 is a diagram showing a modification of a drive method of the external resonance-
type QCL module device according to the second embodiment of the present disclosure. The5
drive method according to the present modification differs from the second embodiment in that a
phase of a drive current is changed for each round trip of the diffraction reflecting section 150.
[0138]
While a case where a current is passed from the second electrode 136b toward the first
electrode 136a or, in other words, an electric field is applied from the second electrode 136b10
toward the first electrode 136a will be shown here as an example, the same applies when a current
is passed from the first electrode 136a toward the second electrode 136b.
[0139]
In the present modification, by changing a phase of a current that drives the QCL device
136 by T3 every time the diffraction reflecting section 150 makes a round trip, a phase of emitted15
pulsed light is changed by a pulse width of T3. For example, let us suppose that the phase of a
first drive current c3a is 1. A phase 2 of a drive current c3b after one round trip of the
diffraction reflecting section 150 is  + T3. A phase 3 of a drive current c3c after another
round trip of the diffraction reflecting section 150 is 2 + T3.
[0140]20
Accordingly, the phase of the drive current is shifted by a pulse width of T3 each time the
diffraction reflecting section 150 makes one round trip. In doing so, the phase of the pulsed
light emitted from the QCL device 136 also changes by a pulse width of T3 as the phase of the
drive current changes. This phase change is repeated p-1-number of times, where p = T2/T3.
- 44 –
Accordingly, since a wavelength spectrum of output light on a time axis is filled without gaps, an
apparently continuous wavelength sweep is achieved.
[0141]
Third embodiment
Fig. 25 is a diagram showing an analyzer according to a third embodiment of the present5
disclosure. The analyzer according to the present embodiment is a device that includes an
external resonance-type QCL module device 161 according to the second embodiment and that
performs spectroscopic analysis by measuring an absorption spectrum of an analyte 162.
[0142]
The external resonance-type QCL module device 161 irradiates the analyte 162 with10
output light emitted from the window 131a. The analyte 162 may be any of a gas, a liquid, or a
solid.
[0143]
The absorption spectrum of the analyte 162 is detected by a photodetector 163. The
photodetector 163 is, for example, a mercury cadmium telluride (MCT) detector, an indium15
arsenic antimony (InAsSb) photodiode, or a thermopile.
[0144]
A detection result of the photodetector 163 is transmitted to a controller 164. The
controller 164 calculates an absorption spectrum based on the detection result. In addition, the
controller 164 is electrically connected to, and controls, the external resonance-type QCL module20
device 161 and the photodetector 163.
[0145]
The controller 164 includes a diffraction grating control unit 164a. The diffraction
grating control unit 164a controls drive of the MEMS diffraction grating 138. In addition, the
- 45 –
controller 164 includes a QCL device control unit 164b. The QCL device control unit 164b
controls drive of the QCL device 136. Furthermore, the controller 164 includes a computing
unit 164c. The computing unit 164c calculates an absorption spectrum based on the detection
result of the photodetector 163.
[0146]5
In addition, the controller 164 may be constituted of a computer including an arithmetic
circuit such as a CPU (Central Processing Unit) in which arithmetic processing is performed, a
recording medium constituted of a memory such as a RAM (Random Access Memory) and a
ROM (Read Only Memory), and an input/output device. Furthermore, the controller 164
operates by loading a computer program or the like.10
[0147]
While an aspect in which Ga0.47In0.53As as a well layer and Al0.48In0.52As as a barrier layer
are latticed-matched with InP has been shown in the embodiments of the present disclosure, the
present disclosure is not limited to this aspect. For example, a compressive or tensile strain may
be multiplied on the well layer or the barrier layer.15
[0148]
While an aspect of an InP-based QCL device using an InP substrate has been shown in the
embodiments of the present disclosure, the present disclosure is not limited to this aspect. For
example, the QCL device may be a GaAs-based QCL device with a GaAs well layer and an
AlGaAs barrier layer using a GaAs substrate. Alternatively, the QCL device may be a GaN-20
based QCL device with a GaN well layer and an AlGaN barrier layer using a GaN substrate.
[0149]
In addition, while an aspect in which a doping concentration of an injector region is set to
2.5  1017 cm-3 has been shown in the embodiments of the present disclosure, the present
- 46 –
disclosure is not limited to this aspect. A higher doping concentration enables a gain band to be
broadened. A lower doping concentration narrows the gain band but increases a value of a gain
peak, thereby lowering a threshold current. Layers to be doped can also be set arbitrarily.
[0150]
Furthermore, while an aspect in which the QCL device has a resonator length of 1.36 mm5
and a ridge width of 14m has been shown in the embodiments of the present disclosure, other
resonator lengths and ridge widths may be adopted. In addition, a structure of the QCL device is
also not limited to an embedded ridge-type. For example, the structure may be a current
constriction structure due to ion implantation of protons or the like or a current constriction
structure due to an insulating film.10
Reference Signs List
[0151]
1 first electrode, 5 core region, 9 second electrode, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33,
35, 37 barrier layer, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 well layer, 38 injector region,
39 active region, 40 injector region, 41, 42 stage, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75,15
77, 79 barrier layer, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78 well layer, 80 injector
region, 81 active region, 82 injector region, 83, 84 stage, 91, 93, 95, 97, 99, 101, 103, 105, 107,
109, 111, 113, 115, 117, 119, 121 barrier layer, 92 94, 96, 98, 100, 102, 104, 106, 108, 110, 112,
114, 116, 118, 120 well layer, 122 injector region, 123 active region, 124 injector region, 125,
126 stage, 136a first electrode, 136b second electrode, 150 diffraction reflecting section, 16320
photodetector, 164c computing unit.
- 47 –
We claim:
1. A QCL device (136), comprising a first electrode (1), a second electrode(9), and a core
region(5) which is formed between the first electrode(1) and the second electrode(9) and which
has a plurality of stages, wherein
each stage includes:5
an active region(39) in which a plurality of alternating barrier layers and well layers are
formed and which emits light; and
an injector region in which a plurality of alternating barrier layers and well layers are
formed and which injects electrons into the active region,
when an electric field is applied from the second electrode (9) to the first electrode (1), a10
first subband group is formed in the stage,
the first subband group includes a first subband, a second subband, a third subband, and a
fourth subband, each subband is configured so that
the first subband and the second subband have electrons predominantly in the active
region(39),15
the second subband has a higher energy level and a higher electron density than the first
subband,
light emits when electrons transition from the second subband to the first subband,
the third subband has a lower energy level than the first subband,
the fourth subband has a higher energy level than the second subband,20
when an electric field is applied from the first electrode(1) to the second electrode(9), a
second subband group is formed in the stage,
the second subband group includes a fifth subband, a sixth subband, a seventh subband,
and an eighth subband, each subband is configured so that
- 48 –
the fifth subband and the sixth subband have electrons predominantly in the active
region(39),
the sixth subband has a higher energy level and a higher electron density than the fifth
subband,
light emits when electrons transition from the sixth subband to the fifth subband,5
the seventh subband has a lower energy level than the fifth subband, and
the eighth subband has a higher energy level than the sixth subband.
2. An external resonance-type QCL module device (161), comprising
the QCL device(136) as claimed in claim 1 and a MEMS diffraction grating(138),
wherein10
the MEMS diffraction grating (138)
includes a diffraction reflecting section(150) which diffracts and reflects light emitted
from the QCL device(136), and
returns a part of the light back to the QCL device (136) by swinging the diffraction
reflecting section(150).15
3. An analyzer, comprising:
the external resonance-type QCL module device(161) as claimed in claim 2;
a photodetector(163) which detects light emitted from the external resonance-type QCL
module device(161) and transmitted through an analyte(162); and
a computing unit(164c) which calculates an absorption spectrum based on a detection20
result of the photodetector(163).
4. A light irradiation method using the QCL device(136) as claimed in claim 1, the light
irradiation method comprising:
- 49 –
emitting light of a first frequency band by applying an electric field from the second
electrode (9) toward the first electrode (1); and
emitting light of a second frequency band by applying an electric field from the first
electrode (1) toward the second electrode (9).