CN115603162A - Method and system for improving stimulated Brillouin scattering threshold of optical fiber laser - Google Patents

Method and system for improving stimulated Brillouin scattering threshold of optical fiber laser Download PDF

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CN115603162A
CN115603162A CN202211283497.3A CN202211283497A CN115603162A CN 115603162 A CN115603162 A CN 115603162A CN 202211283497 A CN202211283497 A CN 202211283497A CN 115603162 A CN115603162 A CN 115603162A
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laser
polarized light
fiber laser
brillouin scattering
stimulated brillouin
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CN115603162B (en
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彭珏
雷敏
姜永亮
张晶
梁慧生
刘厚康
胡金萌
李强
武春风
李龙
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China Space Sanjiang Group Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
    • H01S3/06712—Polarising fibre; Polariser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H01S3/06758—Tandem amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10053—Phase control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10061—Polarization control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
    • H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

The invention provides a method and a system for improving a stimulated Brillouin scattering threshold of a fiber laser. According to the method, laser emitted by a laser is regulated and controlled into first polarized light and second polarized light which are orthogonal to each other according to a preset time interval through a polarization control system, so that the first polarized light and the second polarized light are transmitted alternately, the polarization states of the polarized light and backward Stokes light are ensured to be orthogonal to each other so as to reduce stimulated Brillouin scattering gain, and therefore the threshold value of stimulated Brillouin scattering of the optical fiber laser is improved. According to the invention, the first polarized light and the second polarized light which are orthogonal to each other are transmitted alternately, the first backward Stokes light and the second polarized light generated by the first polarized light cannot generate SBS gain, and the second backward Stokes light and the first polarized light generated by the second polarized light cannot generate SBS gain, so that the energy of the backward Stokes light is increased discontinuously and discontinuously, and the SBS threshold of the optical fiber laser is increased.

Description

Method and system for improving stimulated Brillouin scattering threshold of optical fiber laser
Technical Field
The invention relates to the technical field of fiber laser, in particular to a method and a system for improving a stimulated Brillouin scattering threshold of a fiber laser.
Background
The high-power narrow-linewidth linearly polarized optical fiber laser technology is continuously broken through under the promotion of the fields of light beam synthesis, coherent radar, nonlinear frequency conversion and the like. The high-power narrow-linewidth linearly polarized fiber laser is long in fiber length and small in fiber core sectional area, and various nonlinear effects can be easily generated after the transmission power of the laser reaches a certain level. Among various nonlinear effects, the lowest threshold value of Stimulated Brillouin Scattering (SBS) is a main factor for limiting the further improvement of the power of the high-power narrow-linewidth linearly polarized optical fiber laser at present.
There are three main ways to raise the SBS threshold: increasing the effective mode field area of the fiber, reducing the effective length of the fiber and reducing the SBS gain coefficient. The increase of the effective mode field area of the optical fiber and the reduction of the effective length of the optical fiber can enhance The Mode Instability (TMI) effect of the optical fiber laser while inhibiting the SBS effect, and are not beneficial to the improvement of the laser power; reducing the SBS gain factor becomes the primary method of raising the SBS threshold. Researchers have made a lot of studies on changing the stimulated brillouin gain spectrum to suppress the SBS effect, and proposed a number of methods such as broadening the seed laser linewidth, applying temperature, stress gradient, and sound field clipping through phase modulation operation, but the SBS effect is still the largest technical bottleneck in increasing the power of a narrow linewidth fiber laser.
The SBS effect is generated by exciting a backward Stokes light (backward Stokes light) after the high-intensity signal light is transmitted, interference occurs between the backward Stokes light propagating in the backward direction and the forward direction signal light, and an acoustic wave is generated, and the acoustic wave further excites the backward Stokes light to grow exponentially. It is well known that the SBS effect is closely related to the polarization direction of the laser light: when the polarization states of the signal light (namely the laser emitted by the laser) and the backward Stokes light (generated by the SBS effect of the laser) are the same, the SBS gain is maximum, and the SBS threshold is minimum; when the polarization states of the signal light and the backward Stokes light are orthogonal, the SBS gain is zero, so that the SBS threshold is improved, and thus the SBS effect of the polarization maintaining system is strongest (the polarization states of the signal light and the backward Stokes light of the polarization maintaining system are the same), which makes it particularly difficult to output high-power linear polarization laser with narrow line width.
Researchers have proposed that linearly polarized signal light be incident into polarization maintaining fiber at 45 ° to reduce SBS gain, however, the results show that the SBS threshold is not significantly increased by using 45 ° fusion splicing to make linearly polarized signal light be incident into polarization maintaining fiber amplifier at 45 °. The reason for this is that after the signal light is incident on the polarization maintaining fiber at 45 °, the polarization states of the generated backward Stokes light tend to meet the signal light in the backward transmission process, so that the polarization states of the backward Stokes light and the signal light tend to be the same, which increases the SBS gain, and thus the SBS threshold is not significantly increased.
The patent of application No. CA2342538C provides an optical fiber transmission system for reducing the SBS effect, which splits the incident light into p-light and s-light with time delay (destroying the coherence between the p-light and the s-light), although the SBS threshold of the laser can theoretically be increased by 2 times, the output light of the system is unpolarized light, and cannot meet the application requirements of some linearly polarized high-power lasers. On the basis of this patent, the patent with application number US8995049B2 provides a method and apparatus for suppressing the SBS effect using polarization control with birefringent delay elements, by adding coherence compensation means at the output to restore the output light to linearly polarized light, but the optical delay line used must be placed in the main optical path at the output of the amplifier, which undoubtedly increases the effective fiber length of the amplifier, and the SBS threshold boosting effect is significantly compromised when the system linewidth is narrow.
In view of the above, there is a need to design an improved method and system for raising the stimulated brillouin scattering threshold of a fiber laser to solve the above problems.
Disclosure of Invention
The invention aims to provide a method and a system for improving the stimulated Brillouin scattering threshold of an optical fiber laser, wherein laser emitted by the laser is regulated and controlled into a first polarized light and a second polarized light which are orthogonal to each other according to a preset time interval through a polarization control system, the first polarized light and the second polarized light are alternately transmitted, and in the process of alternately transmitting the first polarized light and the second polarized light forwards, a first backward Stokes light and a second polarized light generated by the first polarized light are in a mutually orthogonal state and cannot generate SBS gain (namely the SBS gain is zero); similarly, the second backward Stokes light generated by the second polarized light and the first polarized light are in a mutually orthogonal state, and the two lights do not generate SBS gain, so that the energy of the backward Stokes light is discontinuously increased but not continuously increased, and the SBS gain of the laser emitted by the laser can be effectively reduced by the mode, so that the SBS threshold of the optical fiber laser is improved.
In order to achieve the above object, the present invention provides a method for increasing the stimulated brillouin scattering threshold of an optical fiber laser, which adjusts and controls laser emitted by the laser into a first polarized light and a second polarized light orthogonal to each other according to a preset time interval through a polarization control system, so that the first polarized light and the second polarized light are alternately transmitted, and it is ensured that the polarization states of the polarized light and the backward stokes light are orthogonal to each other to reduce the stimulated brillouin scattering gain, thereby increasing the stimulated brillouin scattering threshold of the optical fiber laser.
In order to achieve the above object, the present invention further provides a system for increasing the stimulated brillouin scattering threshold of an optical fiber laser, which is used for achieving the above method for increasing the stimulated brillouin scattering threshold of the optical fiber laser, and the system comprises a laser, a first polarization control system, an optical fiber collimation end cap and a second polarization control system, which are connected in sequence, wherein laser emitted by the laser is regulated and controlled by the first polarization control system, and first polarized light and second polarized light which are orthogonal to each other are generated according to a preset time interval, so that the first polarized light and the second polarized light are alternately transmitted to the optical fiber collimation end cap, and the first polarized light or the second polarized light is output through the optical fiber collimation end cap and is output after being reduced into linearly polarized light by the second polarization control system.
As a further improvement of the invention, an optical fiber laser pre-amplification stage and an optical fiber laser main amplification stage are arranged between the first polarization control system and the optical fiber collimation end cap, polarized light regulated and controlled by the first polarization control system is subjected to power amplification primarily by the optical fiber laser pre-amplification stage and is subjected to power amplification again by the optical fiber laser main amplification stage to obtain the high-power optical fiber.
As a further improvement of the present invention, a phase adjustment assembly is disposed between the laser and the first polarization control system, and is configured to broaden a spectrum of laser light emitted by the laser, so as to reduce stimulated brillouin scattering gain and improve a threshold of stimulated brillouin scattering of the optical fiber laser.
As a further improvement of the present invention, a high-power polarization-preserving annular isolator is arranged between the fiber laser pre-amplification stage and the fiber laser main amplification stage, and is configured to transmit forward-propagating polarized light and transmit backward stokes light that propagates backward to a third port where the annular isolator is not connected to the main optical path.
As a further improvement of the present invention, a stimulated brillouin scattering power detector is connected to a third port of the annular isolator, and is configured to detect a power change of backward stokes light, so as to determine whether laser of the optical fiber laser main amplification stage reaches a stimulated brillouin scattering threshold.
As a further improvement of the present invention, the optical signal output end of the second polarization control system is provided with a main power meter for detecting the power of the polarized light output from the second polarization control system.
As a further improvement of the present invention, the first polarization control system and the second polarization control system are both composed of a piezoelectric polarization controller and a signal generator; the piezoelectric polarization controller is one of an azimuth type polarization controller or a retardation type polarization controller.
As a further improvement of the present invention, the laser is a linearly polarized single frequency fiber laser, and the linearly polarized single frequency fiber laser is one of a distributed feedback laser or a single frequency ring laser.
As a further improvement of the invention, the laser emitted by the laser is one of continuous laser or pulse laser.
The beneficial effects of the invention are:
(1) According to the method for improving the stimulated Brillouin scattering threshold of the optical fiber laser, laser emitted by the laser is regulated and controlled into first polarized light and second polarized light which are orthogonal to each other according to a preset time interval through a polarization control system, the first polarized light and the second polarized light are alternately transmitted, in the process that the first polarized light and the second polarized light are alternately transmitted forwards, a first backward Stokes light and a second polarized light generated by the first polarized light are in a mutually orthogonal state, and an SBS gain cannot be generated by the first backward Stokes light and the second polarized light (namely the SBS gain is zero); similarly, the second backward Stokes light generated by the second polarized light and the first polarized light are in a mutually orthogonal state, and the two lights can not generate SBS gain; the energy of the backward Stokes light can be enhanced only when the backward Stokes light meets the polarized light with the same polarization state, but the energy of the backward Stokes light does not increase when the backward Stokes light meets the polarized light orthogonal to the polarization state, and the energy of the backward Stokes light is continuously enhanced until the backward Stokes light meets the next section of polarized light with the same polarization state, so that the energy of the backward Stokes light is intermittently increased but not continuously increased, and the SBS gain of the laser emitted by the laser can be effectively reduced by the mode, and the SBS threshold of the optical fiber laser is improved.
(2) According to the system for improving the stimulated Brillouin scattering threshold of the optical fiber laser, the phase of the laser emitted by the laser is adjusted by arranging the phase adjusting component, so that the spectrum of the laser is broadened, and the SBS gain is initially reduced. By arranging the first polarization control system, the laser generates mutually orthogonal first polarized light and second polarized light according to a preset time interval, and the first polarized light and the second polarized light are alternately transmitted forwards, so that the possibility of backward Stokes light energy enhancement caused by interference between the forward transmitted polarized light and the backward Stokes light transmitted reversely is fundamentally reduced, and the SBS gain is reduced. The power of the polarized light is amplified in multiple stages by arranging the optical fiber laser pre-amplification stage and the optical fiber laser main amplification stage, so that the power of the output laser is further improved. And the high-power laser is restored to be linearly polarized and output by arranging the first polarization control system. Therefore, through the synergistic effect of all the components in the system, the SBS gain is reduced, the SBS threshold is improved, and the output of high-power narrow-linewidth linearly polarized laser is realized. The system provides a simple and effective solution for breaking through the bottleneck encountered in the process of increasing the output power of the laser.
Drawings
Fig. 1 is a schematic structural diagram of a system for increasing the stimulated brillouin scattering threshold of an optical fiber laser according to the present invention.
Fig. 2 is a schematic diagram of a stimulated brillouin scattering effect generated by polarized light in an optical transmission process by using the method for improving the stimulated brillouin scattering threshold of the optical fiber laser provided by the present invention.
Reference numerals
1-a laser; 2-a first polarization control system; 3-a fiber alignment end cap; 4-a second polarization control system; 5-fiber laser pre-amplification stage; 6-optical fiber laser main amplification stage; 7-a phase adjustment assembly; 8-a ring isolator; 9-stimulated Brillouin scattering power detector; 10-output power detector.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the aspects of the present invention are shown in the drawings, and other details not closely related to the present invention are omitted.
In addition, it is also to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention provides a method for improving stimulated Brillouin scattering threshold of an optical fiber laser, which comprises the steps of regulating and controlling laser emitted by the laser into first polarized light and second polarized light which are orthogonal to each other according to a preset time interval through a polarization control system, enabling the first polarized light and the second polarized light to be transmitted alternately, enabling the first polarized light transmitted forwards to generate first backward Stokes light which is transmitted reversely (namely transmitted backwards), and enabling the second polarized light transmitted forwards to generate second backward Stokes light which is transmitted reversely. In this way, during the process that the first polarized light and the second polarized light are transmitted forwards alternately, the first backward Stokes light and the second polarized light generated by the first polarized light are in a mutually orthogonal state, and the first backward Stokes light and the second polarized light do not generate Stimulated Brillouin Scattering (SBS) gain (namely, the SBS gain is zero); similarly, the second backward Stokes light generated by the second polarized light and the first polarized light are in a mutually orthogonal state, and the two lights do not generate the SBS gain. Therefore, in the forward transmission process of the polarized light (the first polarized light and the second polarized light), the energy of the backward Stokes light can be enhanced only when encountering the polarized light with the same polarization state, but the energy of the backward Stokes light does not increase when encountering the polarized light orthogonal to the polarization state, the energy is continuously enhanced until encountering the next polarized light with the same polarization state, and the energy of the backward Stokes light increases discontinuously but not continuously, so that the SBS gain of the laser emitted by the laser can be effectively reduced, and the SBS threshold of the optical fiber laser is improved.
Referring to fig. 1, the present invention further provides a system for increasing the stimulated brillouin scattering threshold of an optical fiber laser, which is used to implement the method for increasing the stimulated brillouin scattering threshold of the optical fiber laser. The system for improving the stimulated Brillouin scattering threshold of the optical fiber laser is a fully polarization maintaining optical fiber laser system and comprises a laser 1, a first polarization control system 2, an optical fiber collimation end cap 3 and a second polarization control system 4 which are sequentially connected. According to the arrangement, after the laser emitted by the laser 1 is periodically regulated and controlled by the first polarization control system 2, the first polarized light and the second polarized light which are orthogonal to each other are generated according to the preset time interval (the first polarized light and the second polarized light can keep the original polarization state of the polarization maintaining optical fiber in the subsequent polarization maintaining optical fiber), so that the first polarized light and the second polarized light are alternately transmitted to the optical fiber collimation end cap 3, and the first polarized light or the second polarized light is output through the optical fiber collimation end cap 3 and is output after being reduced into linearly polarized light by the second polarization control system 4.
Specifically, the laser 1 is a linearly polarized single frequency fiber laser, which is one of a distributed feedback laser or a single frequency ring laser. The wavelength of the laser light emitted by the laser 1 varies depending on the type of the laser 1 to be selected, and the wavelength of the laser light emitted by the laser 1 is 1 to 2 μm. The laser light emitted from the laser 1 is either continuous laser light or pulsed laser light.
The first polarization control system 2 and the second polarization control system 4 are both composed of a piezoelectric type polarization controller and a signal generator; the piezoelectric polarization controller is one of an azimuth polarization controller or a retardation polarization controller. As shown in fig. 1, the piezoelectric polarization controller is disposed in the main optical path, and the signal generator adjusts the working state of the piezoelectric polarization controller through a preset coding program therein, specifically, the signal generator codes a required program and transmits the program to the piezoelectric polarization controller connected thereto, and then the piezoelectric polarization controller controls the polarization state of the laser.
In this embodiment, the first polarized light and the second polarized light alternately output by the first polarization control system 2 are p light and s light, and the output time interval of the p light and the s light is ensured to be less than the time for transmitting a photon in the whole optical fiber system. Preferably, the output time of each of the p light and the s light is set to 1. As shown in fig. 2, the energy of the backward Stokes light increases discontinuously, not continuously.
As shown in fig. 1, a phase adjusting assembly 7 is disposed between the laser 1 and the first polarization control system 2, and is configured to broaden a spectrum of laser light emitted from the laser 1 from a source, so as to increase a spectral width of SBS gain, reduce SBS gain, and increase an SBS threshold of the fiber laser.
An optical fiber laser pre-amplification stage 5 and an optical fiber laser main amplification stage 6 are arranged between the first polarization control system 2 and the optical fiber collimation end cap 3, polarized light regulated and controlled by the first polarization control system 2 is subjected to power amplification primarily through the optical fiber laser pre-amplification stage 5, and is subjected to power amplification again through the optical fiber laser main amplification stage 6, so that an optical fiber with high power is obtained.
The pump laser of the fiber laser pre-amplification stage 5 and the fiber laser main amplification stage 6 has a wavelength of 900-1100 nm, preferably 915nm or 976nm, and 1018nm
A high-power polarization-maintaining annular isolator 8 is arranged between the optical fiber laser pre-amplification stage 5 and the optical fiber laser main amplification stage 6 and is used for transmitting forward-propagating polarized light and transmitting backward Stokes light which is reversely propagated to a third port, which is not connected into a main light path, of the annular isolator 8 (three ports are arranged on the annular isolator 8, a first port and a second port are connected into the main light path, and a third port is not connected into the main light path; specifically, an output end of the optical fiber laser pre-amplification stage 5 is connected into the first port of the annular isolator 8, a second port of the annular isolator 8 is connected into an input end of the optical fiber laser main amplification stage 6, and an optical signal is input from the first port of the annular isolator 8 and output from the second port). Meanwhile, a stimulated brillouin scattering power detector 9 is connected to a third port of the annular isolator 8, and is used for detecting power change of backward Stokes light so as to judge whether laser emitted by the optical fiber laser main amplification stage 6 reaches an SBS threshold value. Specifically, the polarized light continuously generates backward Stokes light in the forward transmission process, the backward Stokes light in the backward transmission process is coupled out through the third port of the ring isolator 8, and the signal is transmitted to the stimulated brillouin scattering power detector 9 connected with the ring isolator 8; when the stimulated brillouin scattering power detector 9 detects that the power of the backward Stokes light is exponentially increased, it indicates that the laser of the optical fiber laser main amplification stage 6 reaches the SBS threshold.
In some embodiments, the optical signal output of the second polarization control system 4 is provided with an output power detector 10 for detecting the power of the polarized light output from the second polarization control system 4.
The working principle of the system for improving the stimulated Brillouin scattering threshold of the optical fiber laser is as follows: the laser that laser 1 sent passes through phase place adjusting part 7, adjusts the phase place of laser, makes its spectrum widen, realizes the reduction of SBS gain preliminarily. And then, the laser after spectrum broadening enters a first polarization control system 2, at the moment, a preset coding program in a signal generator is transmitted to a piezoelectric polarization controller, the polarization state of the laser is controlled by the piezoelectric polarization controller, the laser generates a first polarized light and a second polarized light which are mutually orthogonal according to a preset time interval, and the first polarized light and the second polarized light are alternately transmitted forwards. The forward transmitted polarized light firstly passes through the fiber laser pre-amplification stage 5 to primarily realize power amplification, and then enters the fiber laser main amplification stage 6 through the annular isolator 8 to realize power re-amplification, so as to obtain a high-power fiber. Polarized light output from the optical fiber laser main amplification stage 6 passes through the optical fiber collimation end cap 3, and the optical fiber collimation end cap 3 expands the beam of output light, so that the power density of the output end is reduced, and the end face of an optical fiber is prevented from being burnt. Polarized light output from the optical fiber collimation end cap 3 passes through the second polarization control system 4, and high-power laser alternately output by the first polarized light and the second polarized light is reduced into linearly polarized laser by the second polarization control system 4, so that the output of the high-power narrow-linewidth linearly polarized laser is realized; finally, the power of the output laser is detected by the output power detector 10. In the process of continuously transmitting the polarized light to the front, backward Stokes light is continuously generated, the backward Stokes light transmitted in the backward direction is coupled and output through a third port of the annular isolator 8, the signal is transmitted to a stimulated brillouin scattering power detector 9 connected with the annular isolator 8, and when the stimulated brillouin scattering power detector 9 detects that the power of the backward Stokes light is exponentially increased, it is indicated that the laser of the optical fiber laser main amplification stage 6 reaches the SBS threshold. The system for improving the stimulated Brillouin scattering threshold of the optical fiber laser can realize the multi-stage power amplification of incident laser, and the amplification stages are not limited.
In summary, according to the method and system for increasing the stimulated brillouin scattering threshold of the fiber laser provided by the present invention, the laser emitted by the laser is controlled by the polarization control system according to the preset time interval to be the first polarized light and the second polarized light which are orthogonal to each other, and at the same time, the first polarized light and the second polarized light are transmitted alternately, and in the process of transmitting the first polarized light and the second polarized light alternately forward, the first backward Stokes light and the second polarized light generated by the first polarized light are in the state of being orthogonal to each other, and the two do not generate SBS gain (that is, SBS gain is zero); similarly, the second backward Stokes light generated by the second polarized light and the first polarized light are in a mutually orthogonal state, and the two lights do not generate SBS gain, so that the energy of the backward Stokes light is discontinuously increased but not continuously increased, and the SBS gain of the laser emitted by the laser can be effectively reduced by the mode, so that the SBS threshold of the fiber laser is improved; the system provides a simple and effective solution for breaking through the bottleneck encountered in the process of increasing the output power of the laser.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.

Claims (10)

1. A method for improving the stimulated Brillouin scattering threshold of an optical fiber laser is characterized in that laser emitted by the laser is regulated and controlled into first polarized light and second polarized light which are orthogonal to each other according to a preset time interval through a polarization control system, the first polarized light and the second polarized light are transmitted alternately, the polarization states of the polarized light and backward Stokes light are ensured to be orthogonal to each other so as to reduce stimulated Brillouin scattering gain, and therefore the stimulated Brillouin scattering threshold of the optical fiber laser is improved.
2. A system for improving the stimulated Brillouin scattering threshold of an optical fiber laser is used for realizing the method for improving the stimulated Brillouin scattering threshold of the optical fiber laser, and is characterized by comprising the laser, a first polarization control system, an optical fiber collimation end cap and a second polarization control system which are connected in sequence, wherein laser emitted by the laser generates first polarized light and second polarized light which are orthogonal to each other according to a preset time interval after being regulated and controlled by the first polarization control system, the first polarized light and the second polarized light are alternately transmitted to the optical fiber collimation end cap, and the first polarized light or the second polarized light is output by the optical fiber collimation end cap and is output after being reduced into linearly polarized light by the second polarization control system.
3. The system for increasing the stimulated Brillouin scattering threshold of the fiber laser according to claim 2, wherein a fiber laser pre-amplification stage and a fiber laser main amplification stage are disposed between the first polarization control system and the fiber collimating end cap, and the polarized light controlled by the first polarization control system is primarily power-amplified by the fiber laser pre-amplification stage, and is then power-amplified again by the fiber laser main amplification stage to obtain a high-power fiber.
4. The system for improving the stimulated Brillouin scattering threshold of the fiber laser according to claim 2, wherein a phase adjusting component is disposed between the laser and the first polarization control system, and is configured to broaden a spectrum of the laser emitted by the laser, so as to reduce a stimulated Brillouin scattering gain and improve the stimulated Brillouin scattering threshold of the fiber laser.
5. The system for improving the stimulated Brillouin scattering threshold of the fiber laser according to claim 3, wherein a high-power polarization-preserving ring isolator is arranged between the fiber laser pre-amplification stage and the fiber laser main amplification stage, and is used for transmitting forward-propagating polarized light and transmitting backward-propagating Stokes light to a third port, where the ring isolator is not connected to a main light path.
6. The system for increasing the stimulated brillouin scattering threshold of the optical fiber laser according to claim 5, wherein a stimulated brillouin scattering power detector is connected to the third port of the annular isolator, and is configured to detect a power change of backward stokes light, so as to determine whether the laser of the optical fiber laser main amplification stage reaches the stimulated brillouin scattering threshold.
7. The system for increasing the stimulated brillouin scattering threshold of the fiber laser according to claim 2, wherein the optical signal output end of the second polarization control system is provided with an output power detector for detecting the power of the polarized light output from the second polarization control system.
8. The system for improving the stimulated Brillouin scattering threshold of the fiber laser according to claim 2, wherein the first polarization control system and the second polarization control system are both composed of a piezoelectric polarization controller and a signal generator; the piezoelectric polarization controller is one of an azimuth type polarization controller or a retardation type polarization controller.
9. The system for increasing the stimulated brillouin scattering threshold of a fiber laser according to claim 2, wherein the laser is a linearly polarized single frequency fiber laser, and the linearly polarized single frequency fiber laser is one of a distributed feedback laser or a single frequency ring laser.
10. The system for increasing the stimulated brillouin scattering threshold of the fiber laser according to claim 9, wherein the laser emitted by the laser is one of continuous laser or pulse laser.
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CN103840883A (en) * 2013-08-16 2014-06-04 北京邮电大学 Method for restraining stimulated Raman scattering crosstalk in two-way optical fiber transmission
CN114336251A (en) * 2021-12-06 2022-04-12 上海大学 Orthogonal polarization add-drop multiplexing multi-wavelength Brillouin optical fiber random laser

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