DESC:
TECHNICAL FIELD

The present subject matter is generally related to stabilization of optical nonlinear scattering processes and more particularly, but not exclusively, to method and system for suppressing Stimulated Brillouin Scattering (SBS) effect during transmission and/or amplification of a narrow linewidth optical signal.

BACKGROUND

Fiber laser sources are utilized across multiple sectors of advanced manufacturing such as automotive industries, electronics industries, jewelry, and accessories industries for material processing such as marking, drilling, engraving, ablation, cutting, and welding of materials. For applications such as deep laser welding, directed energy and the like, high level of output power, in order of hundreds of kilowatts, is desirable. Generally, to achieve such high level of output power, power scaling of fiber laser sources is accomplished by combining outputs of a plurality of single fiber laser sources. As power combining of laser beams are interferometric in nature, to avoid destructive interference during power combining process of multiple laser beams, it is necessary to utilize narrow linewidth fiber lasers. However, the power scaling in the narrow linewidth fiber lasers is limited by an optical nonlinear phenomenon, known as Stimulated Brillouin Scattering (SBS). Particularly, the SBS occurs when narrow-band optical signals from the laser sources such as single-frequency lasers are amplified in fiber amplifiers or propagated through passive fibers. Here, the narrow-band optical signals generate acoustic waves that produce variations in the refractive index causing light waves to scatter in a backward direction towards the laser sources. These backscattered light waves experience gain from the forward propagating light waves, thereby leading to depletion of the signal power. Thus, the nonlinear phenomenon, caused due to SBS, adversely affects the power scaling of narrow linewidth high power lasers.

Conventional systems mitigate SBS impairment through linewidth broadening of laser signal by performing a phase modulation of a narrow linewidth optical signal with a white noise signal. In such conventional systems, peak spectral density associated with the laser line is reduced by spreading it around a band using the phase modulation of the narrow linewidth optical signal with the white noise signal. As a result, SBS gain is reduced, which in turn increases SBS threshold power. However, the conventional systems are limited by SBS seeding from fiber end facet reflections due to presence of residual power at Stokes wavelength (10-20GHz lower than laser frequency in optical fibers depending on the frequency of operation) in line broadened spectrum. Further, performing the linewidth broadening, using the phase modulation of the narrow linewidth optical signal with the white noise signal, creates a broad tail in the laser line spectrum. Although white noise sources, owing to their simplicity, have been extensively used for the linewidth broadening, resulting laser line-shape has a slow roll-off in the tail and poor flatness at a center frequency of the laser line spectrum. The slow roll-off seeds the SBS process from reflections, causing poor flatness of the line-shape. In other words, performing the linewidth broadening using the phase modulation of the narrow linewidth optical signal with the white noise signal increases the maximum peak spectral power within the SBS bandwidth. As a result, overall SBS threshold is reduced and the power scaling of the narrow linewidth optical signal becomes limited. Other alternative conventional systems mitigate the SBS impairment through phase modulation of the narrow linewidth optical signal with one of sinusoid signal, signal associated with Pseudo-Random Binary Sequence (PRBS), and signals from Arbitrary Waveform Generators (AWG). Although, the SBS threshold is increased, cost and complexity associated with system set up involving the use of PRBS and AWG for line-broadening is higher when compared to performing phase modulation with white noise.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY

Disclosed herein is a method for suppressing SBS effect during transmission and/or amplification of a narrow linewidth optical signal. The method comprises receiving a narrow linewidth optical signal from an optical signal source. Thereafter, the method comprises modulating the narrow linewidth optical signal with one or more tailored noise signals and one or more periodic signals to obtain an optimized optical signal. By such modulation, the SBS effect is suppressed during transmission of the optimized optical signal.

Further, the present disclosure discloses a SBS suppression system for suppressing SBS effect during transmission of a narrow linewidth optical signal. The system comprises one or more tailored noise sources, one or more periodic waveform sources, and a modulation system. The one or more tailored noise sources generate one or more tailored noise signals, and the one or more periodic waveform sources generate one or more periodic signals. The modulation system receives a narrow linewidth optical signal from an optical signal source. Further, modulation system modulates the narrow linewidth optical signal with the one or more tailored noise signals and the one or more periodic signals. The modulation system modulates the narrow linewidth optical signal to obtain an optimized optical signal. Here, the SBS effect is suppressed during transmission and/or amplification of the optimized optical signal.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and regarding the accompanying figures, in which:

Fig. 1 illustrates exemplary architecture for suppressing SBS effect during transmission of a narrow linewidth optical signal in accordance with some embodiments of the present disclosure;

Fig. 2 illustrates a block diagram of an SBS suppression system in accordance with some embodiments of the present disclosure;

Fig. 3A illustrates a tailored white noise source used in an SBS suppression system in accordance with some embodiments of the present disclosure;

Fig. 3B illustrates single modulator implementation of modulation system in an SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 3C illustrates dual modulator implementation of modulation system in an SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 3D illustrates an exemplary embodiment of a multi-stage fiber amplifier system utilized in an SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 4A illustrates a setup for homodyne linewidth measurement of an optimized optical signal obtained from a SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 4B illustrates a comparative analysis of measured homodyne line spectra of an exemplary optimized optical signal obtained from a SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 4C illustrates comparative analysis of line-shape of an exemplary optimized optical signal obtained from a SBS suppression system, in accordance with some embodiments of the present disclosure;

Fig. 4D illustrates comparative analysis of output power of an exemplary optimized optical signal obtained from a SBS suppression system, in accordance with some embodiments of the present disclosure; and

Fig. 5 illustrates a flowchart illustrating method for suppressing SBS effect during transmission of a narrow linewidth optical signal in accordance with some embodiments of the present disclosure.

It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether such computer or processor is explicitly shown.

DETAILED DESCRIPTION

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the specific forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

The terms “comprises”, “comprising”, “includes”, “including” 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.

Various industrial processes may require high output power level, which may be achieved by scaling power of narrow linewidth fiber lasers. Particularly, multiple narrow linewidth lasers may be combined through coherent beam combining or spectral beam combining to achieve very high-power sources. However, SBS may predominantly affect power scaling of the narrow linewidth fiber lasers. This limits achievable output power. The present disclosure provides an SBS suppression system and a method for suppressing SBS effect during transmission of a narrow linewidth optical signal. Here, the SBS suppression system may receive the narrow linewidth optical signal from an optical signal source. To suppress the SBS effect, the SBS suppression system may perform line width broadening of the narrow linewidth optical signal by utilizing both noise signals and periodic signals. Particularly, the SBS suppression system may modulate the narrow linewidth optical signal with one or more tailored noise signals and one or more periodic signals to obtain the optimized optical signal. Further, the SBS suppression system may sequentially amplify the optimized optical signal using one or more fiber amplifying units for scaling power of the optimized optical signal to a predefined factor.

In one implementation, the SBS suppression system may utilize a common modulating unit for modulating the narrow linewidth optical signal with one or more tailored noise signals and one or more periodic signals. More specifically, the SBS suppression system may perform combining of each tailored noise signal with respective periodic signal utilizing a power combiner unit. Further, the SBS suppression system may amplify the combined signal utilizing an amplifying unit. Thereafter, the SBS suppression system may modulate the narrow linewidth optical signal with the amplified combined signal utilizing a modulating unit to obtain the optimized optical signal.

Alternatively, the SBS suppression system may utilize at least two separate modulating units for modulating the narrow linewidth optical signal with one or more tailored noise signals and one or more periodic signals. More specifically, the SBS suppression system may amplify each tailored noise signal utilizing respective amplifying unit. Further, the SBS suppression system may modulate the narrow linewidth optical signal with each amplified tailored noise signal utilizing a first modulating unit to obtain a first modulated signal. Further, the SBS suppression system may modulate the narrow linewidth optical signal with each periodic signal using a second modulating unit to obtain a second modulated signal. Thereafter, the SBS suppression system may combine the first modulated signal and the second modulated signal in a sequential manner to obtain the optimized optical signal.

The disclosed SBS suppression system may modulate the narrow linewidth optical signal with one or more tailored noise signals and one or more periodic signals such that a line shape may be synthesized, in which the line shape attains a fast roll-off near tail, and an improved flatness near a center frequency of a line spectrum corresponding to the optimized optical signal. The improved flatness of the synthesized line shape may result in reduced peak spectral power at the center frequency of the line spectrum which consequently may reduce SBS seeding from fiber end-facet reflections. Due to the aforesaid features of the synthesized laser line shape, an enhancement of SBS threshold may be achieved, which may further enable higher power scaling at narrow linewidths of the optical sources. The disclosed SBS suppression system may provide at least twofold increase in output power level of the line broadened laser signal as compared to existing techniques of linewidth broadening through white noise modulation. Further, the set up required for linewidth broadening through modulation by combined tailored noise signal and periodic signal may be simple and cost efficient as compared to the set up involving the use of PRBS and AWG for line-broadening.

Fig. 1 illustrates exemplary architecture for suppressing SBS effect during transmission of a narrow linewidth optical signal in accordance with some embodiments of the present disclosure.

As shown in Fig.1, the architecture 100 may include an optical signal source 103, and a SBS suppression system 101. The optical signal source 103 may be, but is not limited to, a Continuous Wave (CW) fiber laser, a pulsed fiber laser, and an ultrafast fiber laser. Further, the fiber laser may be one of a polarization maintaining fiber laser and a non-polarization maintaining fiber laser. In an embodiment, the optical signal source 103 may be a narrow linewidth seed laser source, which may include, but is not limited to, a semiconductor laser, an External Cavity Diode Laser (ECDL), a Distributed Bragg Reflector (DBR) laser, a Distributed Feedback (DFB) laser. As illustrated in Fig.1, the optical signal source 103 may generate a narrow linewidth optical signal 105. In some embodiments, linewidth associated with the narrow linewidth optical signal 105 may be less than 1 GHz. The generated narrow linewidth optical signal 105 may be provided to the SBS suppression system 101, where the narrow linewidth optical signal 105 may be modulated with one or more tailored noise signals and one or more periodic signals. The one or more periodic signals may include, but are not limited to, one of sinusoidal signal, triangle signal, square signal, rectangular signal, and saw tooth signal. The SBS suppression system 101 may line broaden the narrow linewidth optical signal 105 through modulation by tailored noise signal and periodic signal in a combined manner to obtain an optimized optical signal 107. The SBS suppression system 101 is configured to obtain the optimized optical signal 107 in a frequency domain s(f). In the frequency domain, the narrow linewidth optical signal 105 and the optimized optical signal 107 frequencies differ from each other as shown in the Fig.1. In time domain I (t), a narrow linewidth optical signal 105a and an optimized optical signal 107a intensities remain same as shown in Fig.1. Thereby, the SBS suppression system 101 obtains the optimized optical signal 107 in the frequency domain s(f) while corresponding time domain intensity remains unchanged.

In an embodiment, the modulation of the narrow linewidth optical signal 105 may include a phase modulation. In an alternative embodiment, the modulation of the narrow linewidth optical signal 105 may include an additional component of amplitude modulation and a frequency modulation. In an embodiment, the SBS suppression system 101 may modulate the narrow linewidth optical signal 105 with a modified Radio-Frequency (RF) source, whose output may be well approximated as a summation of the one or more periodic signals and the one or more tailored noise signals. In an embodiment, the linewidth broadening of the narrow linewidth optical signal 105 may be direct current modulation by the combined one or more tailored noise signals and the one or more periodic signals. Performing the linewidth broadening through combined periodic signal and tailored noise signal modulation, may improve SBS threshold-limited power scaling of the optical signal source 103 and SBS limited power transmission limit of optical fiber links for a given operational linewidth of the optical signal source 103.

As an example, a polarization-maintaining, 1064 nm DBR source of ~30 mW power with <1MHz linewidth may be phase modulated with a tailored white noise signal and a sinusoid signal by the SBS suppression system 101 to generate an optimized line broadened signal of ~7.2GHz linewidth. Consider the sinusoid signal may be generated utilizing a Radio-Frequency (RF) sine wave generator. Further, the phase modulated signal may be amplified by a multistage fiber amplifier to achieve 721W output power. Conventionally, when the laser is line-broadened only by white noise modulation to have an RMS linewidth of 7.3 GHz, the power scaling is limited to 306W output power. Thus, a significant improvement in the power scaling by a factor of 2.36 times may be achieved due to phase modulation of the 7.2 GHz linewidth laser with the combined white noise and sinusoid signals.

Fig. 2 illustrates a block diagram of an SBS suppression system in accordance with some embodiments of the present disclosure.

As shown in Fig. 2, the SBS suppression system 101 may include one or more tailored noise sources 201, one or more periodic waveform sources 203, modulation system 205 and a plurality of fiber amplifying units 207. The modulation system 205 may receive a narrow linewidth optical signal 105 from an optical signal source 103. The narrow linewidth optical signal 105 may be one of continuous-wave optical signal and pulsed optical signal. The continuous-wave optical signal may be an uninterrupted beam, in which output power remains constant throughout duration of the beam. Further, the pulsed optical signal may be discrete optical beam occurring at a particular pulse repetition frequency. Further, the narrow linewidth optical signal 105 may have a linewidth less than 1 GHz. In an embodiment, the one or more tailored noise sources 201 may generate one or more tailored noise signals, and the one or more tailored noise sources 201 may generate one or more periodic signals, after the narrow linewidth optical signal 105 is received at the modulation system 205. In an alternative embodiment, while receiving the narrow linewidth optical signal 105, the one or more tailored noise sources 201, and the one or more tailored noise sources 201 may simultaneously generate the one or more tailored noise signals, and the one or more periodic signals, respectively. Here, the one or more periodic signals may have either identical frequencies or different frequencies. Further, the one or more periodic signals may be at least one of sinusoidal signal, triangle signal, square signal, rectangular signal, and saw tooth signal.

Further, the modulation system 205 may modulate the received narrow linewidth optical signal 105 with the one or more tailored noise signals and the one or more periodic signals utilizing either single modulator design implementation or dual modulator design implementation. The modulation system 205 may perform linewidth broadening of the narrow linewidth optical signal 105 through the modulation with combined tailored noise signal and periodic signal to obtain an optimized optical signal 107. Line shape of the optimized optical signal 107 may have faster roll-off rate at tail, and improved flatness at central frequency of the line spectrum with reduced residual power near Stokes wavelength.

In the SBS suppression system 101, the one or more tailored noise sources 201 may be implemented utilizing a white noise source 301 and a Low Pass Filter (LPF) bank 303 in the SBS suppression system 101, as illustrated in Fig. 3A. As an example, the white noise source 301 utilized for constructing the one or more tailored noise sources 201 may have a 3-dB bandwidth of 3 GHz. Further, the output white noise signal 302 generated from the white noise source 301 may be input to the LPF bank 303. In the LPF bank 303, an array of a plurality of LPFs 3031, 3032, 3033, 303N may be utilized to provide one or more discrete passbands. As an example, the plurality of LPFs 3031, 3032, 3033, 303N may provide the discrete passbands of 400 MHz, 700 MHz, 1 GHz, 2 GHz, and 3 GHz for generating the one or more tailored noise signals 304. In the tailored noise source of the SBS suppression system 101, the LPF bank 303 coupled to the white noise source 301 may control bandwidth of the white noise source 301 for generating the one or more tailored noise signals 304. Each of the one or more tailored noise signals 304 may be a random signal with a constant power spectral density including Gaussian white noise.

In an embodiment, the modulation system 2051 may be realized as single modulator implementation in the SBS suppression system 101, as illustrated in Fig. 3B. Such modulation system 2051 may comprise a power combiner unit 305, an amplifying unit 307, and a modulating unit 309. The power combiner unit 305 may receive the one or more tailored noise signals 304 from the one or more tailored noise sources 201. Further, the power combiner unit 305 may also receive the one or more periodic signals from the one or more tailored noise sources 201. The power combiner unit 305 may combine each of the one or more tailored noise signals 304 with each of the one or more periodic signals to obtain a combined signal. As an example, an RF power combiner may be utilized for combining powers and bandwidths of a tailored white noise signal 302 and a sinusoid signal. In the modulation system 2051, the power combiner unit 305 may combine the one or more tailored noise signals 304 and the one or more periodic signals in a pre-determined ratio. Particularly, the power combiner unit 305 may combine output power of the one or more tailored noise signals 304 and the one or more periodic signals to provide a common output, maintaining characteristic impedance of inputs. The power combining may be optimized for SBS threshold enhancement. Further, the amplifying unit 307 may receive the combined signal from the power combiner unit 305. The amplifying unit 307 may amplify the combined signal to meet voltage and power requirements for driving the modulating unit 309. As an example, a RF amplifier may convert the input low power combined signal into a higher power amplified signal, which may have sufficient power to drive a Lithium Niobate (LiNbO3) electro-optic phase modulator. Further, the modulating unit 309 may modulate the narrow linewidth optical signal 105 with the combined signal to obtain the optimized optical signal 107. In a preferred embodiment, the modulating unit 309 may perform phase modulation of the narrow linewidth optical signal 105 with the combined signal of the one or more tailored noise signals 304 and the one or more periodic signals for linewidth broadening of the optical signal source 103. In an embodiment, the modulating unit 309 may be an integrated or on-chip phase modulator. Further, the modulating unit 309 may provide the line broadened optical signal to the plurality of fiber amplifying units 207 for further processing. In the single modulator architecture, resulting line-shape and linewidth of the optimized optical signal 107 may be determined based on a bandwidth of the tailored noise signal 304 and a signal strength of the periodic signal.

In an alternative embodiment, the modulation system 2052 may be realized as dual modulator implementation in the SBS suppression system 101, as illustrated in Fig. 3C. The dual modulator architecture may reduce complexity of utilizing a power combiner unit 305 at cost of another modulating unit. The dual modulator architecture may be utilized as an alternative to the single modulator architecture based on resource availability. As shown in Fig. 3C, in the dual modulator architecture, the modulation system 2052 may comprise a plurality of amplifying units 311, one or more first modulating units 313, and one or more second modulating units 315. In the modulation system 2052, each of the one or more first modulating units 313 and each of the one or more second modulating units 315 may be arranged in series for modulating the narrow linewidth optical signal 105 with the one or more tailored noise signals 304 and the one or more periodic signals.

As illustrated in Fig. 3C, the plurality of amplifying units 311 of the modulation system 2052 may receive the one or more tailored noise signals 304 from the one or more tailored noise sources 201 of the SBS suppression system 101. Each of the plurality of amplifying units 311 may amplify the tailored noise signal 304 based on the voltage and power requirements of the one or more first modulating units 313. Particularly, each of the plurality of amplifying units 311 may convert input low power tailored noise signal 304 into a high-power amplified signal for driving the one or more first modulating units 313. In an alternative embodiment, the one or more tailored noise signals 304 may be directly inputted to the one or more first modulating units 313 without performing amplification if powers of the one or more tailored noise signals 304 are sufficient to drive the one or more first modulating units 313.

As illustrated in Fig. 3C, the one or more first modulating units 313 may receive the narrow linewidth optical signal 105 from the optical signal source 103. In an embodiment, the one or more first modulating units 313 may either receive the amplified tailored noise signals 304 from the plurality of amplifying units 311 or directly receive the one or more tailored noise signals 304 from the one or more tailored noise sources 201 based on the driving power and voltage requirements. Thereafter, each of the one or more first modulating units 313 may modulate the narrow linewidth optical signal 105 with each of the one or more tailored noise signals 304 to obtain a first modulated signal. As an example, five first modulating units 313 may be utilized to perform phase modulation of the narrow linewidth optical signal 105 with five tailored noise signals 304 to obtain five first modulated signals. In an embodiment, the one or more first modulating units 313 may be integrated or on-chip phase modulators.

As illustrated in Fig. 3C, the one or more second modulating units 315 may receive the narrow linewidth optical signal 105 from the optical signal source 103. In an embodiment, the one or more second modulating units 315 may either directly receive the one or more periodic signals from the one or more tailored noise sources 201 or receive the amplified periodic signals from the plurality of amplifying units 311. Thus, the amplification of the one or more periodic signals may be performed based on the driving power and voltage requirements for the one or more second modulating units 315 and output power and voltage of the one or more periodic signals. Further, each of the one or more second modulating units 315 may modulate the narrow linewidth optical signal 105 with each of the one or more periodic signals to obtain a second modulated signal. As an example, five second modulating units 315 may be utilized to perform phase modulation of the narrow linewidth optical signal 105 with five periodic signals to obtain five second modulated signals. In an embodiment, the one or more second modulating units 315 may be integrated or on-chip phase modulators. Upon generating the first modulated signal and the second modulated signal, the one or more first modulating units 313 and the one or more second modulating units 315 may combine the first modulated signal and the second modulated signal in a sequential manner to obtain the optimized optical signal 107. As an example, an output obtained from a first modulating unit 313 may be input to a second modulating unit 315 to be phase modulated with a periodic signal. Further, an output obtained from the second modulating unit 315 may be input to another first modulating unit 313 to be phase modulated with a tailored noise signal 304. Thereafter, an output obtained from the another first modulating unit 313 may be input to another second modulating unit 315 to be phase modulated with another periodic signal.

In the SBS suppression system 101, the plurality of fiber amplifying units 207 may receive the optimized optical signal 107 from the modulation system 2051, 2052, as illustrated in Figs. 3B and 3C. In an embodiment, the plurality of fiber amplifying units 207 of the SBS suppression system 101 may sequentially amplify the optimized optical signal 107 for scaling power of the optimized optical signal 107 to a predefined factor. Fig. 3D illustrates an exemplary multi-stage fiber amplifier system 316 utilized in the SBS suppression system 101. The multi-stage fiber amplifier system 316 may power scale the optimized optical signal 107 from a few milli-watts to nearly a kilowatt. The multi-stage fiber amplifier system 316 may comprise the plurality of fiber amplifying units 207, a plurality of optical isolators 3171, 3172, and a plurality of optical fiber couplers 3191, 3192. In an embodiment, each of the plurality of fiber amplifying units 207 may consist of a glass fiber doped with rare earth ions. The fiber amplifying unit 207 may include, but not limited to Erbium-Doped Fiber Amplifier (EDFA), Neodymium-Doped Fiber Amplifier (NDFA), Ytterbium-Doped Fiber Amplifier (YDFA), Praseodymium-Doped Fiber Amplifier (PDFA), and Thulium Doped Fiber Amplifier (TDFA). Each of plurality of fiber amplifying units 207 may be pumped by a low-brightness pump diode. In the multi-stage fiber amplifier system 316, each of the plurality of optical isolators 3171, 3172 may transmit the amplified optical signal in a forward direction, and simultaneously block propagation of the optical signal in a backward direction. Thus, the plurality of optical isolators 3171, 3172 of suitable power handling capacity may protect a preceding stage of fiber amplifying unit 207 from backward propagating power of a succeeding stage of fiber amplifying unit 207. Further, the plurality of optical fiber couplers 3191, 3192 may be utilized for continuous SBS monitoring in the backward direction of the multi-stage fiber amplifier system 316.

Fig. 4A illustrates a setup for homodyne linewidth measurement of an optimized optical signal 107 obtained from a SBS suppression system 101, in accordance with some embodiments of the present disclosure. Here, the optical signal source 103 may provide the narrow linewidth optical signal 105 to a phase modulator 405 for performing line shaping of the narrow linewidth optical signal 105 through modulation with a modulating signal 404. Thereafter, linewidth of the line broadened optical signal may be measured by utilizing the homodyne measurement setup as shown in Fig. 4A. A polarizer 407 may be utilized to maximize signal-to-noise ratio in the measurement. Further, a fiber coupler 4012 may be utilized to connect fiber ends from the polarizer 407, a photodiode 409, and a Personal Computer (PC) 4032. The photodiode 409 may be utilized to detect a beat signal. Further, an RF spectrum analyzer 411 may be utilized to measure RMS linewidth corresponding to the detected beat signal.

For comparing a line spectrum of the optimized signal (obtained from the SBS suppression system 101) with a line spectrum of a conventional line broadened optical signal (obtained from pure white noise modulation), a first homodyne line spectrum 413 and a second homodyne line spectrum 415 may be measured by providing different modulating signals 404 to the phase modulator 405 of the homodyne setup. As an example, the first homodyne line spectrum 413 may be measured for the optimized optical signal 107, by phase modulating the narrow linewidth optical signal 105 with the modulating signal 404. For, the first homodyne line spectrum 413, the modulating signal 404 may be a combined tailored noise signal 304 and the periodic signal. Further, the second homodyne line spectrum 415 may be measured, by phase modulating the narrow linewidth optical signal 105 with the modulating signal 404, which is a white noise signal 302. Fig. 4B illustrates comparison between the first homodyne line spectrum 413 and the second homodyne line spectrum 415 to analyze performance of the disclosed SBS suppression system 101 over the conventional linewidth broadening technique through white noise modulation. From Fig. 4B, it may be clearly observed that a peak normalized power of the first homodyne line spectrum 413 is less in comparison with a peak normalized power of the first homodyne line spectrum 413 at 0 GHz frequency. Also, the first homodyne line spectrum 413 may exhibit improved flatness near the central frequency. Further, the normalized power of the first homodyne line spectrum 413 may decline at a faster rate in comparison to the second homodyne line spectrum 415, within a frequency range from 6 GHz to 14 GHz. This may indicate that the synthesized line shape obtained from the SBS suppression system 101 has a fast roll-off near tail such that normalized power at Stokes frequency (16 GHz) may become negligible (almost 0 dB). The improved flatness and faster roll-off rate at tail in the first homodyne line spectrum 413 may indicate that the SBS effect may be significantly suppressed by the SBS suppression system 101.

Fig. 4C illustrates comparative analysis of line-shape of an exemplary optimized optical signal 107 obtained from the SBS suppression system 101, in accordance with some embodiments of the present disclosure. Here, a first line-shape 417 may be achieved through phase modulation of the narrow linewidth optical signal 105 with combined tailored noise signal 304 and periodic signal. Further, a second line-shape 419 may be achieved through phase modulation of the narrow linewidth optical signal 105 with only white noise signal 302. The first line-shape 417 and the second line-shape 419 may have same RMS linewidth. From comparison of the first line-shape 417 and the second line-shape 419 as illustrated in Fig. 4C, it can be observed that for the second line-shape 419, a significant amount of power may be present at the Stokes frequency. This may result in SBS seeding through fiber end facet reflections. Consequently, the power scaling of the narrow linewidth optical signal 105 may be reduced. Further, linewidth broadening through modulation with only periodic signal may generate discrete harmonics 421 spaced by a predefined repetition, as shown in Fig. 4C. With periodic phase modulation, the discrete harmonics 421 may not be uniform in intensity, which may result in underutilization of total spectral width. Further, in case of discrete spectra, threshold reduction may be related to number of lines rather than total bandwidth. In contrast, the first line-shape 417 may have negligible power at Stokes frequency along with improved flatness near the center frequency. Thus, for a given linewidth, the aforesaid features may be achieved by the SBS suppression system 101, and power scaling for the narrow linewidth may be improved.

Fig. 4D illustrates comparative analysis of output power of an exemplary optimized optical signal 107 obtained from a SBS suppression system 101, in accordance with some embodiments of the present disclosure. A first curve 423 may be obtained by plotting backward power as a function of output power for line-shaping with combined periodic signal and tailored noise signal modulation. A second curve 425 may be obtained by plotting backward power as a function of output power for line-shaping with only white noise modulation. Both the first curve 423 and the second curve 425 may exhibit a rise in average backward power with increase in output power. However, when the narrow line width optical signal is line-broadened only by white noise modulation to have an RMS linewidth of 7.3 GHz, the achievable output power may be limited to 306W, as shown in the second curve 425 in Fig. 4D. However, when the narrow line width optical signal is line-broadened by combined periodic signal and tailored noise signal modulation to have an RMS linewidth of 7.2 GHz, the output power may be power scaled up to 721 W, as shown in the first curve 423 in Fig. 4D. This may correspond to a significant improvement in power scaling by a factor of 2.36 times by the SBS suppression system 101. Thus, at least twofold increase in output power associated with the line broadened laser signal as compared to those of existing techniques of modulating solely with white noise signal 302 may be achieved by modulating the narrow linewidth optical signal 105 with combined tailored noise signal 304 and periodic signal.

Fig. 5 illustrates a flowchart illustrating method for suppressing SBS effect during transmission of a narrow linewidth optical signal in accordance with some embodiments of the present disclosure.

As illustrated in Fig. 5, the method 500 includes one or more blocks illustrating a method for suppressing SBS effect during transmission of a narrow linewidth optical signal 105. The order in which the method 500 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the spirit and scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or combination thereof.

At block 501, the method may include receiving, by the SBS suppression system 101, a narrow linewidth optical signal 105 from an optical signal source 103. Here, the narrow linewidth optical signal 105 may be one of continuous-wave optical signal and pulsed optical signal. Further, the linewidth associated with the narrow linewidth optical signal 105 may be less than 1 GHz.

At block 503, the method may include modulating, by the SBS suppression system 101, the narrow linewidth optical signal 105 with one or more tailored noise signals 304 and one or more periodic signals to obtain an optimized optical signal 107. Here, SBS effect is suppressed during transmission of the optimized optical signal 107. The modulation of the narrow linewidth optical signal 105 using the one or more tailored noise signals 304 and the one or more periodic signals may be phase modulation. Each of the one or more tailored noise signals 304 may be generated by controlling bandwidth of a white noise source 301 with a low pass filter bank 303. Further, the one or more periodic signals utilized for the modulation of the narrow linewidth optical signal 105 may comprise at least one of sinusoidal signal, triangle signal, square signal, rectangular signal, and saw tooth signal. Frequency associated with each of the one or more periodic signals may be one of identical and different with respect to each other.

In an embodiment, for modulating the narrow linewidth optical signal 105, each of the one or more tailored noise signals 304 may be combined with each of the one or more periodic signals using a power combiner unit 305 in the SBS suppression system 101, to obtain a combined signal. In such embodiment, the one or more tailored noise signals 304 and the one or more periodic signals may be combined in a pre-determined ratio. Further, the combined signal may be amplified using an amplifying unit 307 in the SBS suppression system 101, for modulating with the narrow linewidth optical signal 105. Thereafter, the narrow linewidth optical signal 105 may be modulated with the amplified combined signal, using a modulating unit 309 in the SBS suppression system 101, to obtain the optimized optical signal 107. Further, the optimized optical signal 107 may be sequentially amplified using one or more fiber amplifying units 207 for scaling power of the optimized optical signal 107 to a predefined factor.

In an alternative embodiment, the narrow linewidth optical signal 105 may be modulated with each of the one or more tailored noise signals 304 using a first modulating unit 313 from a plurality of modulating units in the SBS suppression system 101 to obtain a first modulated signal. Prior to modulating using the first modulating unit 313, each of the one or more tailored noise signals 304 may be amplified using respective amplifying unit 311 from a plurality of amplifying units 311 in the SBS suppression system 101. Further, the narrow linewidth optical signal 105 may be modulated with each of the one or more periodic signals using a second modulating unit 315 from the plurality of modulating units in the SBS suppression system 101, to obtain a second modulated signal. Thereafter, the first modulated signal and the second modulated signal may be combined in a sequential manner to obtain the optimized optical signal 107. Further, the optimized optical signal 107 may be sequentially amplified using one or more fiber amplifying units 207 for scaling power of the optimized optical signal 107 to a predefined factor.

Advantages of the embodiment of the present disclosure are illustrated herein.
In an embodiment, the present disclosure provides a method and a system for suppressing SBS effect during transmission of a narrow linewidth optical signal.

In an embodiment, the present disclosure provides a method and a system for synthesizing a line shape to attain a fast roll-off near tail of the line spectrum and an improved flatness near carrier reducing the peak spectral power, which consequently reduces SBS seeding from end-facet reflections.

In an embodiment, the present disclosure provides a method and a system for improving power scaling of narrow linewidth high power optical signals by suppressing SBS effect.

In an embodiment, the present disclosure provides a method and a system for performing a combined periodic and tailored noise modulation of the narrow linewidth optical signal for increasing a SBS threshold by a predefined factor in comparison to the SBS threshold achieved by linewidth broadening through pure noise modulation scheme for a given linewidth in polarization-maintaining and non-polarization-maintaining lasers and amplifiers.

In an embodiment, the present disclosure provides a simple and cost efficient set up for linewidth broadening through modulation by combined tailored noise signal and periodic signal as compared to conventional set up involving the use of PRBS and AWG for line-broadening.

The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise.

The terms "including", "comprising", “having” and variations thereof mean "including but not limited to", unless expressly specified otherwise. The enumerated listing of items does not imply that any or all the items are mutually exclusive, unless expressly specified otherwise.

The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise.
A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.

When a single device or article is described herein, it will be clear that more than one device/article (whether they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether they cooperate), it will be clear that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the embodiments of the present invention are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals:
Reference Number Description
100 Architecture
101 SBS suppression system
103 Optical signal source
105 Narrow linewidth optical signal
107 Optimized optical signal
201 Tailored noise sources
203 Periodic waveform sources
205, 2051, 2052 Modulation system
207 Fiber amplifying units
301 White noise source
302 White noise signal
303 Low pass filter bank
3031, 3032, 3033, 303N LPF
304 Tailored noise signal
305 Power combiner unit
307 Amplifying unit
309 Modulating unit
311 Amplifying units
313 First modulating units
315 Second modulating units
316 Multi-stage fiber amplifier system
3171, 3172 Isolator
3191, 3192 Coupler
4011, 4012 Fiber coupler
4031, 4032 Personal computer
404 Modulating signal
405 Phase modulator
407 Polarizer
409 Photodiode
411 RF spectrum analyzer
413 First homodyne line spectrum
415 Second homodyne line spectrum
417 First line-shape
419 Second line-shape
421 Discrete harmonics
423 First curve
425 Second curve

,CLAIMS:
We claim:
1. A method for suppressing Stimulated Brillouin Scattering (SBS) effect during transmission of a narrow linewidth optical signal 105, the method comprising:
receiving, by an SBS suppression system 101, a narrow linewidth optical signal 105 from an optical signal source 103; and
modulating, by the SBS suppression system 101, the narrow linewidth optical signal 105 with one or more tailored noise signals 304 and one or more periodic signals, to obtain an optimized optical signal 107, wherein SBS effect is suppressed during transmission of the optimized optical signal 107.

2. The method as claimed in claim 1, wherein modulating the narrow linewidth optical signal 105 with the one or more tailored noise signals 304 and the one or more periodic signals comprises:
combining each of the one or more tailored noise signals 304 with each of the one or more periodic signals using a power combiner unit 305 in the SBS suppression system 101, to obtain a combined signal; and
modulating the narrow linewidth optical signal 105 with the combined signal, using a modulating unit 309 in the SBS suppression system 101, to obtain the optimized optical signal 107.

3. The method as claimed in claim 2, further comprises, amplifying the combined signal, using an amplifying unit 307 in the SBS suppression system 101, for modulating with the narrow linewidth optical signal 105.

4. The method as claimed in claim 2, wherein the one or more tailored noise signals 304 and the one or more periodic signals are combined in a pre-determined ratio.

5. The method as claimed in claim 1, wherein modulating the narrow linewidth optical signal 105 with the one or more tailored noise signals 304 and the one or more periodic signals comprises:
modulating the narrow linewidth optical signal 105 with each of the one or more tailored noise signals 304 using a first modulating unit 313 from a plurality of modulating units in the SBS suppression system 101 to obtain a first modulated signal;
modulating the narrow linewidth optical signal 105 with each of the one or more periodic signals using a second modulating unit 315 from the plurality of modulating units in the SBS suppression system 101, to obtain a second modulated signal; and
combining the first modulated signal and the second modulated signal in a sequential manner to obtain the optimized optical signal 107.

6. The method as claimed in claim 5, further comprises, prior to modulating using the first modulating unit 313, amplifying each of the one or more tailored noise signals 304 using respective amplifying unit 311 from a plurality of amplifying units 311 in the SBS suppression system 101.

7. The method as claimed in claim 1, wherein the narrow linewidth optical signal 105 is one of continuous-wave optical signal and pulsed optical signal.

8. The method as claimed in claim 1, wherein linewidth associated with the narrow linewidth optical signal 105 is less than 1 GHz.

9. The method as claimed in claim 1, further comprises generating each of the one or more tailored noise signals 304 by controlling bandwidth of a white noise source 301 with a low pass filter bank 303.

10. The method as claimed in claim 1, wherein frequency associated with each of the one or more periodic signals is one of identical and different with respect to each other.

11. The method as claimed in claim 1, wherein the modulation of the narrow linewidth optical signal 105 using the one or more tailored noise signals 304 and the one or more periodic signals is phase modulation.

12. The method as claimed in claim 1, wherein the one or more periodic signals comprises at least one of sinusoidal signal, triangle signal, square signal, rectangular signal, and saw tooth signal.

13. The method as claimed in claim 1, further comprises, sequentially amplifying the optimized optical signal 107 using one or more fiber amplifying units 207 for scaling power of the optimized optical signal 107 to a predefined factor.

14. A Stimulated Brillouin Scattering (SBS) suppression system 101 for suppressing SBS effect during transmission of a narrow linewidth optical signal 105, the system comprising:
one or more tailored noise sources 201 for generating one or more tailored noise signals 304;
one or more periodic waveform sources 203 for generating one or more periodic signals; and
a modulation system 205 configured to:
receive a narrow linewidth optical signal 105 from an optical signal source 103; and
modulate the narrow linewidth optical signal 105 with the one or more tailored noise signals 304 and the one or more periodic signals, to obtain an optimized optical signal 107, wherein SBS effect is suppressed during transmission of the optimized optical signal 107.

15. The SBS suppression system 101 as claimed in claim 14, wherein the modulation system 2051 comprises:
a power combiner unit 305 for combining each of the one or more tailored noise signals 304 with each of the one or more periodic signals to obtain a combined signal; and
a modulating unit 309 for modulating the narrow linewidth optical signal 105 with the combined signal to obtain the optimized optical signal 107.

16. The SBS suppression system 101 as claimed in claim 15, wherein the modulation system 2051 further comprises an amplifying unit 307 for amplifying the combined signal for modulating with the narrow linewidth optical signal 105.

17. The SBS suppression system 101 as claimed in claim 15, wherein the one or more tailored noise signals 304 and the one or more periodic signals are combined in a pre-determined ratio.

18. The SBS suppression system 101 as claimed in claim 14, wherein the modulation system 2052 comprises:
a plurality of modulating units comprising one or more first modulating units 313 and one or more second modulating units 315;
wherein each of the one or more first modulating units 313 modulates the narrow linewidth optical signal 105 with each of the one or more tailored noise signals 304 to obtain a first modulated signal, and each of the one or more second modulating units 315 modulates the narrow linewidth optical signal 105 with each of the one or more periodic signals to obtain a second modulated signal,
wherein each of the one or more first modulating units 313 and each of the one or more second modulating units 315 are arranged in series for combining the first modulated signal and the second modulated signal in a sequential manner to obtain the optimized optical signal 107.

19. The SBS suppression system 101 as claimed in claim 18, further comprises:
a plurality of amplifying units 311 for amplifying each of the one or more tailored noise signals 304 prior to modulating using each of the one or more first modulating units 313.

20. The SBS suppression system 101 as claimed in claim 14, wherein the narrow linewidth optical signal 105 is one of continuous-wave optical signal and pulsed optical signal.

21. The SBS suppression system 101 as claimed in claim 14, wherein linewidth associated with the narrow linewidth optical signal 105 is less than 1 GHz.

22. The SBS suppression system 101 as claimed in claim 14, wherein each of the one or more tailored noise sources 201 comprises a white noise source 301 and a low pass filter bank 303 coupled to the white noise source 301 for controlling bandwidth of the white noise source 301.

23. The SBS suppression system 101 as claimed in claim 14, wherein frequency associated with each of the one or more periodic signals is one of identical and different with respect to each other.

24. The SBS suppression system 101 as claimed in claim 14, wherein the modulation of the narrow linewidth optical signal 105 using the one or more tailored noise signals 304 and the one or more periodic signals is phase modulation.

25. The SBS suppression system 101 as claimed in claim 14, wherein the one or more periodic signals comprises at least one of sinusoidal signal, triangle signal, square signal, rectangular signal, and saw tooth signal.

26. The SBS suppression system 101 as claimed in claim 14, further comprises a plurality of fiber amplifying units 207 for sequentially amplifying the optimized optical signal 107 for scaling power of the optimized optical signal 107 to a predefined factor.