DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

Title: METHOD AND SYSTEM FOR REALIZATION OF COMPACT MONOLITHIC TUNABLE PEAK POWER NARROW PULSE-WIDTH FIBER LASER

APPLICANT DETAILS:
(a) NAME: BHARAT ELECTRONICS LIMITED
(b) NATIONALITY: Indian
(c) ADDRESS: Outer Ring Road, Nagavara, Bangalore - 560045

PREAMBLE TO THE DESCRIPTION:
The following specification (particularly) describes the nature of the invention (and the manner in which it is to be performed):
METHOD AND SYSTEM FOR REALIZATION OF COMPACT MONOLITHIC TUNABLE PEAK POWER NARROW PULSE-WIDTH FIBER LASER

FIELD OF INVENTION:
The present disclosure relates to a design architecture for the realization of compact and economical monolithic tunable MW peak power narrow pulse width fiber laser. Specifically, the present disclosure relates to a method and system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser.

BACKGROUND OF THE INVENTION:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication expressly or implicitly referenced is prior art.
The available prior arts disclose pulse source generation with an oscillator design which controls pulse width and repetition rate as disclosed in US20130271824A1 titled “Optical pulse source”. This design induces picker electronics between 1st and 2nd amplification stage to alter pulse repetition frequency.
Further, the US patent no. 8340141 titled “Method of operating all-fiber-based ultra-pulse laser system” describe the method of realization of ultra-pulse laser using saturable absorber with pump and signal source incorporating mode locking architecture with reduced pulse dispersion via dispersed fiber.
Also, the US20220181839A1 patent application titled “High - peak - power single - frequency narrow - linewidth nanosecond fiber laser based on a triangular pulse” discloses the design of three stage narrow line width high peak power laser system. Triangular pulse shaping is used which is achieved by modulating pulsed laser seed through Electro-optic modulator and Acousto-optic modulator. Linewidth broadening through self-pulse modulation is also suppressed by utilizing multi-stage amplification architecture.
However, there is a need for a design architecture for the realization of compact and economical monolithic Tunable kW peak power Narrow pulse width fiber laser.

OBJECTIVES OF THE INVENTION:
The primary object of the present invention is to overcome the problem stated in the prior art.
Another object of the present invention is to provide a compact and economical monolithic tunable kW peak power narrow pulse width fiber laser. Specifically, the present disclosure relates to a method and system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser.

SUMMARY OF THE INVENTION:
In an aspect, present invention provides a system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser comprising:
a) an optical seed source comprises an optical laser source (1) of NIR wavelength with narrow line width and driver electronics (2);
b) a pre-amplifier unit comprises the following components:
i. a filter is a band pass filter (3) which allows only the desired signal wavelength with bandwidth ±2.5 nm;
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength pulse and protect the source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 optical pump combiner (4) that can be of dimension 9/125 µm or 5/125 for signal is spliced with wavelength stabilized pump diode (8) having range of 915 nm – 980 nm;
iv. an optical fiber is Yb doped or Er doped where active fiber (6) of dimension 9/130 µm or 5/130 µm is spliced with the pump;
v. a power stripper of bare fiber dimension 6/130 or 9/125 µm is spliced at the end to prevent heating and higher modes generation.
c) a main amplifier unit comprises the following components:
i. a dimension matching element (11);
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength and protects the preamplifier stage and source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 pump combiner (5) for dimension 25/300 µm or 20/400 µm is splice to provide high pump power from 915 nm -980 nm wavelength stabilized pump diode (9);
iv. an Optical fiber Yb doped or Er-doped active fiber of dimension 25/250 µm or 20/400 (10) is spliced to achieve desired amplification;
v. a power stripper (7) comprises a clad power stripper or a copper plate (7) is spliced with active fiber with high power handling capacity;
wherein tunable signal source (1) is modulated by the pulsing electronics (2) and has the line width of < 0.1 nm to achieve a tunable pulse width with a tunable repetition rate.

DETAILED DESCRIPTION OF DRAWINGS:
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of their scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings in which:

Fig. 1: illustrates a layout of the two staged Narrow pulse width laser architecture wherein the 1st stage is pre-amplifier stage and 2nd stage is the Power amplifier stage.
Fig. 2: illustrates a detailed block architecture of the Tunable high peak power Linearly Polarized narrow pulse width system.
Fig. 3: illustrates block diagram of pulsing electronics driving the signal source to achieve Tunable pulse width and repetition rate.
Fig. 3(a): illustrates a optical spectrum of the signal source.
Fig. 3(b): illustrates the pulsing of signal source through pulsing electronics module.
Fig. 3(c): illustrates the pulsed laser modulated by the pulsing electronics.
Fig. 4: illustrates the average output power of the preamplifier stage operated at different repetition rate.
Fig. 5: illustrates an increase of Average output power with respect to the input pump power.

DETAILED DESCRIPTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
In an aspect, present invention provides a system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser comprising:
a) an optical seed source comprises an optical laser source (1) of NIR wavelength with narrow line width and driver electronics (2);
b) a pre-amplifier unit comprises the following components:
i. a filter is a band pass filter (3) which allows only the desired signal wavelength with bandwidth ±2.5 nm;
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength pulse and protect the source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 optical pump combiner (4) that can be of dimension 9/125 µm or 5/125 for signal is spliced with wavelength stabilized pump diode (8) having range of 915 nm – 980 nm;
iv. an optical fiber is Yb doped or Er doped where active fiber (6) of dimension 9/130 µm or 5/130 µm is spliced with the pump;
v. a power stripper of bare fiber dimension 6/130 or 9/125 µm is spliced at the end to prevent heating and higher modes generation.
c) a main amplifier unit comprises the following components:
i. a dimension matching element (11);
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength and protects the preamplifier stage and source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 pump combiner (5) for dimension 25/300 µm or 20/400 µm is splice to provide high pump power from 915 nm -980 nm wavelength stabilized pump diode (9);
iv. an Optical fiber rare earth-doped active fiber of dimension 25/250 µm or 20/400 (10) is spliced to achieve desired amplification;
v. a power stripper (7) comprises a clad power stripper or a copper plate (7) is spliced with active fiber with high power handling capacity;
wherein tunable signal source (1) is modulated by the pulsing electronics (2) and has the line width of < 0.1 nm to achieve a tunable pulse width with a tunable repetition rate.
Referring to figure 1, figure 1 illustrates a layout of the two staged Narrow pulse width laser architecture. 1st stage is pre-amplifier stage and 2nd stage is the Power amplifier stage in according to an exemplary implementation of the present disclosure. IR signal source is modulated through pulsing electronics. Dual stage amplification design architecture as shown in fig-1 is incorporated to achieve desired target specification. Further, polarization maintaining optical fiber and components are used for the designing of Linearly Polarized fiber laser detailed design architecture is shown in fig 2. Figure 2 illustrates the detailed block architecture of the Tunable high peak power linearly polarized narrow pulse width system. Components used in this architecture are as follows:
Optical seed source: It comprises of optical laser source [1] of NIR wavelength with narrow line width and the driver electronics [2]
Pre-amplifier stage: It consist of the following components:
Filter: This component is the band pass filter [3] which allows only the desired signal wavelength with bandwidth ±2.5 nm.
Isolation: This element [4] provides isolation from back reflected high power signal wavelength pulse and protect the source from damage.
Combiner & Pump: 2 x 1 or 4 x 1 or 6 x 1 optical pump combiner [4] that can be of dimension 9/125 or 5/125 µm for signal is spliced with wavelength stabilized pump diode [8] which can be in the range of 915 nm – 980 nm.
Optical fiber: Rare eath doped active fiber [6] of dimension 9/130 µm or 5/130 µm is spliced with the pump.
Power stripper: Clad mode power stripper or copper plate [7] of bare fiber dimension 6/130 or 9/125 µm is spliced at the end to prevent heating and higher modes generation.
Main amplifier stage: This Power amplification stage consist of the following components:
Dimension matching element [11].
Isolation: This element [4] provides isolation from back reflected high power signal wavelength and protects the preamplifier stage and source from damage.
Combiner & Pump: 2 x 1 or 4 x 1 or 6 x 1 pump combiner [5] for dimension 25/300 µm or 20/400 µm is splice to provide high pump power from 915 nm -980 nm wavelength stabilized pump diode [9].
Optical fiber: Rare earh -doped active fiber of dimension 25/250 µm or 20/400 [10] is spliced to achieve desired amplification.
Power stripper: Clad power stripper or copper plate [7] is spliced with active fiber with high power handling capacity.
Tunable signal source [1] modulated by pulsing electronics [2] as shown in fig-3 and has the line width of < 0.1 nm as shown in fig-3(a) to achieve tunable pulse width with tunable repetition rate which can be seen in fig 3(b)&(c) emits average power in mW range, Detailed schematic of Pre-amplifier stage as shown in fig-2 incorporating filter to pass only signal wavelength with bandwidth(@ -0.5dBm) of ± 2.5 nm [3] with isolation of > 45 dBm [4] from the backward signal light and wavelength stabilized pump (915 nm -980 nm) with pump power in the range of Watts [8] is supplied to rare earth doped active fiber of lower dimension 5/130 µm or 9/125 µm [5] with the absorption of 1.65 dB/m or 1.8 dB/m depending on the doping concentration and pump wavelength which reduces the length of the fiber . Average power in range of few Watts and Peak power in the range of few kilowatts is achieved from pre-amplifier stage, for designed configuration > 29 dB gain is achieved with conversion efficiency of >75%.
The stability of the pre-amplifier stage is tested by operating it with different repetition rate and pulse width. For varying repetition rate and pulse width for a wide range almost constant maximum average power is achieved as shown in fig 4.
To boost the power amplification, the main amplifier stage is designed as shown in fig 2. Preamplifier stage is operated at optimum average output power to minimize the heat generation through (915 nm – 980 nm) pump diode [8]. Pre-amplifier is spliced with main amplifier with dimension matching element [11]. High level power handling equipment with isolation of > 45 dB [4] is employed for Power amplifier stage to prevent the source from damage through back reflected signal wavelength. Pump input power of higher power [9] is applied to the rare earth doped active fiber of higher dimension (25/300 or 20/400) than pre-amplifier stage [10] with 1.5 dB/m or 5 dB/m absorption depending on the pumping wavelength and doping concentration. Peak power in the range of few Megawatts is achieved with designed laser architecture as shown in fig 5. Output Power without maximum heat generation and without inducing multiple modes easily dissipated through copper plate or by incorporating clad mode stripper [7] with maximum power handling capability of >100 W, we stripped the fiber for few cm to eliminate heat generation. The system design can be thermally stabilized through Air cooling/water cooling mechanism depending on the application requirement.
In accordance with one embodiment of the present discourse, the method and design architecture is to realize highly efficient and high gain linearly polarized narrow pulse width laser comprises of IR signal source with pulsing electronics and dual amplification stage with high thermal stability. Pre amplification stage and power amplification stage are integrated with signal source modulated by pulsing mechanism with filter of desired wavelength and isolation from backward reflection.
Further, 1st amplification stage incorporates wavelength stabilized pump, higher absorptive pump wavelength is accumulated in the design architecture to reduce the rare earth doped active optical fiber length making system more compact and economical.
The design system is operated with variable Pulse repetition rate (few kHz) and pulse width (1 ns – 500 ns) and constant average output power with gain (28 dB – max 30 dB) is achieved. The 2nd stage of power amplification with active fiber of higher dimension than pre amplification stage integrated with the means of dimension matching element which achieves higher absorption with high absorptive wavelength stabilized pump.
The integrated system is tested for variable pulse width and repetition rate and achieved constant average output power of max up to 20 dB gain and tunable peak power in range of Megawatts - kilowatts with higher thermal stability. Also, the integrated test setup can be operated to obtain tunable average energy (millijoules- microjoules) and peak power with respect to the desired power density as constant average power is observed at each iteration.
The advantageous aspect of the present invention includes:
1. The designed Laser can be operated with tunable pulse width (1 ns – 500 ns) and repetition rate (1 kHz – 500 kHz) with constant average power.
2. Optimized pre-amplifier architecture with reduced active fiber length to achieve conversion efficiency > 70% with elimination of heat generation in wavelength stabilized pumping diode.
3. Dual stage architecture with high thermal stability is achieved to realize the system in small form factor.
4. Constant average power is observed in the realized system with the change in repetition frequency and pulse width of the designed architecture.
5. Tunable (MW-kW) peak power can be extracted by operating designed system with required pulse width and repetition rate.
6. Average energy can be tuned in the range of milli Joules – µ Joules with the respect to the desired power density.
7. Gain > 29 dB is achieved in pre amplifier stage and > 18 dB is achieved in Power amplification stage while maintaining narrow line width.
The foregoing description has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:We Claim:

1. A system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser comprising:
a) an optical seed source comprises an optical laser source (1) of NIR wavelength with narrow line width and driver electronics (2);
b) a pre-amplifier unit comprises the following components:
i. a filter is a band pass filter (3) which allows only the desired signal wavelength with bandwidth ±2.5 nm;
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength pulse and protect the source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 optical pump combiner (4) that can be of dimension 9/125 µm or 5/125 for signal is spliced with wavelength stabilized pump diode (8) having range of 915 nm – 980 nm;
iv. Rare earth doped optical fiber (6) of dimension 9/130 µm or 5/130 µm is spliced with the pump;
v. a power stripper of bare fiber dimension 6/130 or 9/125 µm is spliced at the end to prevent heating and higher modes generation.
c) a main amplifier unit comprises the following components:
i. a dimension matching element (11);
ii. an isolation element (4) provides isolation from back reflected high power signal wavelength and protects the preamplifier stage and source from damage;
iii. a combiner & pump: 2 x 1 or 4 x 1 or 6 x 1 pump combiner (5) for dimension 25/300 µm or 20/400 µm is splice to provide high pump power from 915 nm -980 nm wavelength stabilized pump diode (9);
iv. Rare earth doped Optical fiber (Yb doped or Er-doped active fiber) of dimension 25/250 µm or 20/400 (10) is spliced to achieve desired amplification;
v. a power stripper (7) comprises a clad power stripper or a copper plate (7) is spliced with active fiber with high power handling capacity;
wherein tunable signal source (1) is modulated by the pulsing electronics (2) and has the line width of < 0.1 nm to achieve a tunable pulse width with a tunable repetition rate.
2. The system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser as claimed in claim 1, wherein the filter (3) pass only signal wavelength with bandwidth(@ -0.5dBm) of ± 2.5 nm [3] with isolation of > 45 dBm (4) from the backward signal light and wavelength stabilized pump (915 nm -980 nm) with pump power in the range of Watts (8) is supplied to rare earth doped active fiber of lower dimension 5/130 µm or 9/125 µm (5) with the absorption of 1.65 dB/m or 1.8 dB/m depending on the doping concentration and pump wavelength which reduces the length of the fiber.
3. The system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser as claimed in claim 1, wherein the system is operated with variable Pulse repetition rate (few kHz) and pulse width (1 ns – 500 ns) and constant average output power with gain (28 dB – max 30 dB) is achieved.
4. The system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser as claimed in claim 1, wherein the pre-amplifier unit reduced active fiber length to achieve conversion efficiency > 70% with elimination of heat generation in wavelength stabilized pumping diode.
5. The system for realization of compact monolithic tunable peak power narrow pulse-width fiber laser as claimed in claim 1, wherein the gain > 29 dB is achieved in preamplifier unit and > 18 dB is achieved in power amplification unit.