CN106410599B - Brillouin single longitudinal mode frequency shift optical fiber laser - Google Patents
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- 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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
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Abstract
The invention provides a Brillouin single longitudinal mode frequency shift fiber laser which comprises a light source module, an optical fiber circulator, an optical amplifier, an optical fiber isolator, a first optical fiber coupler, a first frequency shift optical fiber, a second frequency shift optical fiber and a second optical fiber coupler. The unidirectional active ring resonant cavity is constructed, based on the technical scheme of the optical fiber composite cavity, the cavity longitudinal mode interval is larger than the Brillouin gain spectrum width by utilizing the mode selection characteristic of the composite cavity, so that only one cavity longitudinal mode can start vibrating in the Brillouin gain spectrum range and form laser emission, and the output of the Brillouin single longitudinal mode operation transfer frequency optical fiber laser is realized with high efficiency and low cost. The Brillouin single-frequency laser frequency always follows the pumping seed light, the broadband frequency shift effect is stable, single longitudinal mode operation is realized based on the composite cavity, the structure is simple, the complex control requirement is avoided, and the harsh application requirement of the self-Brillouin scattering-based distributed optical fiber temperature strain sensing system on the broadband frequency shift technology can be fully met.
Description
Technical Field
The invention relates to a broadband frequency shift technology required by a distributed optical fiber sensing system based on self-Brillouin scattering, in particular to a Brillouin single longitudinal mode frequency shift optical fiber laser.
Background
In a distributed optical fiber sensing (BOTDR) system based on self-Brillouin scattering, the frequency shift of the spontaneous Brillouin scattered light relative to incident light is affected by temperature and strain, the frequency shift of the spontaneous Brillouin scattered light relative to the incident light is about 11GHz for a single mode optical fiber in a communication band, wherein the linear coefficient of the change in the frequency shift of the spontaneous Brillouin scattered light caused by temperature is 1.09+/-0.08 MHz/DEGC, the linear coefficient of the change in the frequency shift of the spontaneous Brillouin scattered light caused by strain is 0.052+/-0.004 MHz/. Mu.epsilon, and the extraction of 10 is realized on an ultra-high frequency substrate of 11GHz -4 The relative frequency variation is a key technology for the BOTDR system to realize temperature and strain sensing. By using a broadband frequency shift scheme, proper local beat frequency light is selected, so that the difference frequency signal of the brillouin spontaneous scattering light and the local beat frequency light is reduced to the magnitude of 100MHz from 11GHz, and the extraction of the signal and the reduction of the cost of a system device are facilitated.
Therefore, various wideband frequency shift schemes have been developed, such as scheme one, which adopts a laser with a frequency difference close to brillouin frequency shift with seed light as a local laser (see Toshio Kurashima, et al, IEICE trans, communication, E76-B (4) (1993)), and in this scheme, two lasers are required for the BOTDR system, which makes the cost and structure complex, and meanwhile, this scheme has extremely high requirements for the stability of the frequency and frequency difference of the two lasers; scheme two adopts the acousto-optic to shift the frequency ring and carries out broadband frequency shifting (see Kaoru Shimizu, et al, J.Lightwave technology, 12, 730-736 (1994)), but the acousto-optic frequency shifter can only shift frequency by more than one hundred MHz at a time, and can realize the frequency change of 11GHz only through the cyclic frequency shifting of hundreds of times, which all put forward high requirements on the performance of the acousto-optic frequency shifter. And the complexity of an optical part in the system is increased by adopting the acousto-optic frequency shift loop, and the stability and the measurement accuracy of the system are affected. The third scheme adopts the electro-optic modulator to carry out broadband electro-optic modulation frequency shift (see Song Mouping, optical report, 24, 1110-1114 (2004)), the electro-optic modulator can realize the frequency shift of 11GHz at one time, the optical path is relatively simplified, but the electro-optic modulator has high requirements on the polarization control characteristic of the optical path. Meanwhile, the electro-optical modulator is utilized to realize that the energy loss of broadband frequency shift is overlarge, and the acquired frequency shift optical power is smaller.
Compared with the schemes, the implementation of broadband frequency shift by using the Brillouin laser is a novel efficient and low-cost technical scheme (see Jihong Geng, et al, appl. Opt. 46, 5928-5932 (2007)), and many researchers are attracted to research and application of the related aspects. Because the brillouin gain spectrum width is about 30MHz, and the cavity length of an active annular cavity brillouin laser is generally in the order of tens of meters (the corresponding cavity longitudinal mode interval is 2-10 MHz), a multi-longitudinal mode operation mode is easy to appear, so that the frequency shift quantity has larger fluctuation, and the measurement accuracy in a BOTDR system is directly reduced. In order to avoid multi-longitudinal mode operation, researchers have a scheme of laser frequency stabilization, namely, the frequency of injected pump seed light and the brillouin laser operation frequency are simultaneously locked on two longitudinal modes of a certain cavity of a resonant cavity, so that brillouin laser output of single-longitudinal mode operation is realized (see Jihong Geng, et al, IEEE photon, technical l. Lett. 18, 1813-1815 (2006)), but the scheme relates to a complex feedback control system, stability is not easy to be good, frequency stabilization loss lock is easy to occur under external disturbance, stability of the whole BOTDR system is reduced, and cost is greatly increased.
Disclosure of Invention
In order to overcome the defects of the prior art and better meet the actual requirements of a BOTDR system on a broadband frequency-shifting Brillouin laser, the invention provides the Brillouin laser which is high in efficiency and low in cost and realizes single longitudinal mode operation.
The basic principle of the invention is as follows: an active annular cavity Brillouin laser is constructed, and the laser mainly comprises a pumping light source and an active annular cavity. The pumping light source needs to select a single-frequency laser with the line width smaller than 1MHz and the communication C band. The annular cavity comprises an optical fiber composite cavity unit and an optical fiber coupler, wherein the optical fiber composite cavity unit consists of a three-port circulator, an optical amplifier and a frequency-shifting optical fiber. The unidirectional characteristic of the circulator is used for constructing an annular cavity which can only transmit in one direction, the optical amplifier is used for providing amplification in the cavity, the frequency-shifting optical fiber is used as a nonlinear medium for providing gain for amplifying Brillouin scattered light, and the coupler is used for outputting laser in the cavity.
The Brillouin type single longitudinal mode frequency shift optical fiber laser comprises a light source module, an optical fiber circulator, an optical amplifier, an optical fiber isolator, a first optical fiber coupler, a first frequency shift optical fiber, a second frequency shift optical fiber and a second optical fiber coupler; the tail fiber output of the light source module is connected with a first port of the optical fiber circulator, a second port of the optical fiber circulator is connected with an input port of the optical amplifier, and an output port of the optical amplifier is connected with a first port of the first optical fiber coupler; the second port and the fourth port of the first optical fiber coupler are connected into a loop through optical fibers, and devices connected in the loop comprise an optical fiber isolator and a first frequency shifting optical fiber, wherein the forward conduction input port of the optical fiber isolator is connected with the second port of the first optical fiber coupler, the forward conduction output port of the optical fiber isolator is connected with the first frequency shifting optical fiber, and the other end of the first frequency shifting optical fiber is connected with the fourth port of the first optical fiber coupler; one end of the second frequency shift optical fiber is connected with the third port of the first optical fiber coupler, and the other end of the second frequency shift optical fiber is connected with the first port of the second optical fiber coupler; the third port of the second optical fiber coupler is connected with the third port of the optical fiber circulator and is closed into a large optical fiber loop, and the second port of the second optical fiber coupler is used as an output port of the single longitudinal mode Brillouin laser; based on the technical scheme of the optical fiber composite cavity, the cavity longitudinal mode interval is larger than the Brillouin gain spectrum width by utilizing the mode selection characteristic of the composite cavity, only one cavity longitudinal mode can start vibrating in the gain spectrum range and form laser emission, and finally the Brillouin single longitudinal mode frequency-shift optical fiber laser output is realized with high efficiency and low cost.
Further, the light source module is a narrow linewidth laser, the linewidth is smaller than 1MHz, and the output power can reach 20mW.
Further, the optical fiber circulator is a three-port optical fiber circulator, is in one-way conduction, and can be replaced by a mode of accessing an optical fiber coupler and an isolator to play a role of the optical fiber circulator.
Furthermore, the optical amplifier is mainly used for amplifying the pump light signal and the weak Brillouin scattering signal, and an optical amplifier with a shorter optical action length is needed, and the optical amplifier can be built by taking the erbium-doped fiber with a high gain coefficient as a gain medium, or a 1550nm wave band Semiconductor Optical Amplifier (SOA) is selected.
Furthermore, the optical amplifier can be constructed by selecting an erbium-doped fiber with a high gain coefficient and a length of 1 m.
Further, the optical fiber isolator is used for unidirectional conduction to prevent reverse resonance, and can be used for commercial 1550 nm-band optical fiber isolator.
Further, the first optical fiber coupler adopts a coupler with 1550nm wave band, 2 x 2 ports and 50:50 spectral ratio of a common single-mode optical fiber.
Further, the first frequency-shift optical fiber and the second frequency-shift optical fiber adopt common communication single-mode optical fibers and can adopt commercial G652 model communication single-mode optical fibers; the lengths of the first frequency-shift optical fiber and the second frequency-shift optical fiber are selected in two ways: firstly, the two cavities forming the composite cavity are equal or approximate in length; and secondly, one cavity length forming the composite cavity is multiple times of the other cavity length.
Further, the second optical fiber coupler is a 1×2 common single-mode optical fiber coupler, the center wavelength is 1550nm, the splitting ratio is 10:90, and 10% of ports are used as output ends of the brillouin laser.
When no pump light is injected at the input, the laser corresponds to an erbium-doped fiber laser, and the output wavelength depends on the net gain profile in the cavity and the final lasing mode established by free oscillation. When pump light is injected into the input end of the laser, and the pump light intensity reaches the threshold value of the stimulated Brillouin scattering light resonance in the cavity, the laser works in a Brillouin optical fiber laser mode. When the pump light is injected into the annular cavity from the input end of the circulator, amplified by the optical amplifier and enters the frequency shift optical fiber, the backward scattered light is excited in the frequency shift optical fiber, and the pump light is continuously transmitted to the circulator to be cut off. The scattered light can be circularly transmitted in the cavity, the scattered light can be amplified when passing through the optical amplifier, when passing through the frequency-shifting optical fiber, the brillouin signal light in the scattered light and the incident pumping light generate nonlinear brillouin action in the opposite transmission process, nonlinear brillouin gain amplification can be obtained, and the Rayleigh scattered light which is transmitted backwards in the same way cannot be amplified at the position. If the comprehensive gain of the Brillouin scattering optical signal in the cavity is larger than the Rayleigh scattering light and the spontaneous emission noise light, the Brillouin scattering optical signal is subjected to repeated cyclic transmission amplification in the cavity to establish oscillation, and finally stable Brillouin laser output can be formed.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) Compared with the traditional broadband frequency shift technical scheme, the single longitudinal mode laser based on the fiber Brillouin nonlinear effect has the advantages that the laser frequency of the single longitudinal mode laser always follows the seed light, so that the broadband frequency shift effect is stable, the structure is simple, and the complex control requirement is avoided.
(2) Compared with a frequency-stabilized brillouin laser, the mode selection is performed by using the optical fiber composite cavity, so that the cavity longitudinal mode is Yu Buli and the brillouin gain spectrum is wide, and only one cavity longitudinal mode can start vibrating within the brillouin gain spectrum range to form laser emission. And the frequency-stabilized brillouin laser needs to build a complex optical structure for extracting error signals and feeding back and adjusting seed light to realize stable single longitudinal mode brillouin laser output. The single longitudinal mode Brillouin laser technical scheme has the advantages of simple principle, no need of complex feedback control, stable optical structure and cost reduction by more than 90 percent, and can be well applied to a BOTDR sensing system as a broadband frequency shift local light source.
Drawings
A schematic diagram of a composite cavity longitudinal mode frequency selection in the example of fig. 1;
another schematic diagram of a composite cavity longitudinal mode frequency selection in the example of fig. 2;
the structure of the single longitudinal mode brillouin laser based on the optical fiber composite cavity in the example of fig. 3 is schematically shown.
Detailed Description
The practice of the invention will be further described with reference to examples and drawings, but the practice and protection of the invention are not limited thereto, and it should be noted that the following processes or parameters, if any, which are not specifically described, are all within the skill of the art with reference to the prior art.
In order to obtain the output of brillouin laser, the invention needs to solve two problems: 1. the self-radiation noise of the optical amplifier is prevented from generating oscillation to form laser; 2. avoiding the Rayleigh scattering light resonance to form laser. First, it is necessary to set the amplification performance of the optical amplifier at a low position so that the ratio of the gain provided by the optical amplifier is as small as possible among the overall gains obtained by the brillouin scattering signal. The problem can be well solved by setting the gain coefficient of the optical amplifier; the second problem is that the brillouin nonlinear gain needs to be increased as much as possible, so that the gain provided by the optical amplifier only by the rayleigh scattering light cannot compete for more than the brillouin scattering light in the cavity, and finally the rayleigh scattering cannot resonate to form laser emission.
In order to suppress the formation of laser output by the rayleigh scattered light, the second problem is to increase the brillouin nonlinear gain as much as possible, and the power of the pumping light source is increased or the length of the frequency-shifted optical fiber for providing the brillouin nonlinear gain is increased. Simply relying on the power of the pump light source to increase the power will result in reduced energy transfer and utilization, and the cost of the narrow linewidth laser will also increase sharply with the increase of power, so the simplest and economical way is to increase the length of the intra-cavity optical fiber as much as possible. In this case, a new problem is introduced: in a communication band single mode fiber (the fiber with the lowest frequency shift cost is realized), the brillouin gain spectrum width is about 30MHz, and the cavity length of an active annular cavity brillouin laser is generally in the order of tens of meters (the corresponding cavity longitudinal mode interval is 2-10 MHz), so that a multi-longitudinal mode operation mode is easy to appear. Therefore, by utilizing the scheme of the composite cavity, the Brillouin laser output of single longitudinal mode operation can be realized efficiently and at low cost.
The basic principle of the composite cavity for realizing longitudinal mode selection is as shown in fig. 1 and 2, and the cavity lengths of the composite cavities are respectivelyL 1 、L 2 The longitudinal mode sequence interval of the two cavities respectively corresponding to the two cavities is△f 1 =c/nL 1 ，△f 2 =c/nL 2 The resonant frequencies of the two cavity-forming compound cavity lasers must be aligned at the same time with a certain order of frequencies of the two sets of longitudinal mode intervals to form effective resonance and finally form laser output. Therefore, according to the vernier caliper principle, the cavity longitudinal mode sequence interval of the composite cavity is as follows:
△f= m
1
c/(nL
1
)= m
2
c/(n L
2
); L
2
/ L
1
=m
2
/m
1
wherein,,m 1 、m 2 is a positive integer without common divisor.
In this case, there are two cases, one is as shown in FIG. 1, in which the cavity length can be better selectedL 1 And cavity lengthL 2 Substantially equivalent, when the longitudinal mode spacing of the composite cavity is substantially inversely proportional to the difference in cavity lengths of the two cavities, i.e△f≈c/ (nL 1 -nL 2 )At this time, the cavity lengthL 1 And cavity lengthL 2 Can select longer optical fiber, fully meet the requirement of the laser on Brillouin nonlinear gain, and simultaneously select the cavity lengthL 1 And cavity lengthL 2 The length is close, at this time, the cavity longitudinal mode interval of the composite cavity can be fully ensured to be far larger than the Brillouin gain spectrum width, and then only one cavity longitudinal mode can start vibrating in the gain spectrum range to form laser emission.
Another case is a cavity length as shown in FIG. 2L 2 Longer than another cavityL 1 Many times longer, when the longitudinal mode spacing of the composite cavity is substantially equal to that of the short cavityL 1 Longitudinal cavity mode of (i.e.)△f≈c/(n L 1 )Length of cavityL 1 The selection is shorter, and the selectable cavity length is smaller than4mThereby (a)△f 1 >50MHz，Is larger than Brillouin gain spectrum width and cavity lengthL 2 Can be selected to be longer than the cavityL 1 And the laser is ten times longer, the requirement of the laser on the Brillouin nonlinear gain is fully met, and the condition can also meet the condition that only one cavity longitudinal mode can start oscillation in the gain spectrum range and form laser emission.
According to the basic principle, the structural design of the single longitudinal mode Brillouin laser based on the optical fiber composite cavity in the embodiment is shown in fig. 3, and the single longitudinal mode Brillouin laser comprises a light source module (1), an optical fiber circulator (2), an optical amplifier (3), an optical fiber isolator (4), a first optical fiber coupler (5), a first frequency shift optical fiber (6), a second frequency shift optical fiber (7) and a second optical fiber coupler (8); the tail fiber output of the light source module 1 is connected with a first port 201 of the optical fiber circulator 2, a second port 202 of the optical fiber circulator 2 is connected with an input port 301 of the optical amplifier 3, an output port 302 of the optical amplifier 3 is connected with a first port 501 of the optical fiber coupler 5, a plurality of optical devices are connected between a second port 502 and a fourth port 504 of the optical fiber coupler 5, the devices connected in the loop are connected into a loop through optical fibers, the devices connected in the loop comprise an optical fiber isolator 4 and a frequency shifting optical fiber 6, wherein a forward conduction input port 401 of the optical fiber isolator 4 is connected with a second port 502 of the optical fiber coupler 5, a forward conduction output port 402 of the optical fiber isolator 4 is connected with the frequency shifting optical fiber 6, and the other end of the frequency shifting optical fiber 6 is connected with a fourth port 504 of the optical fiber coupler 5. One end of the other section of frequency shift optical fiber 7 is connected with the third port 503 of the optical fiber coupler 5, the other end is connected with the first port 801 of the optical fiber coupler 8, the third port 803 of the optical fiber coupler 8 is connected with the third port 203 of the optical fiber circulator, a large optical fiber loop is closed, and the second port 802 of the optical fiber coupler 8 serves as an output port of the single longitudinal mode Brillouin laser.
Specific embodiments of the device modules are illustrated below.
The light source module 1 is a pumping light source of a single longitudinal mode Brillouin laser based on an optical fiber composite cavity. Because the brillouin gain spectrum is only on the order of tens of MHz, the linewidth of the pump seed light source is required to be narrow. The light source adopted by the embodiment is a 1550 nm-band narrow-linewidth single-frequency optical fiber laser, the linewidth is 2kHz, and the laser power can reach 100mW; other types of narrow linewidth lasers may be used, but linewidths cannot exceed 10MHz.
The optical fiber circulator 2 is a three-port optical fiber circulator and is conducted in a unidirectional manner, and can also be connected with an optical fiber coupler and an isolator to play a role of the optical fiber circulator.
The optical amplifier 3 is mainly used for amplifying a pump optical signal and a weak brillouin scattering signal in a loop, and in order not to affect the output performance of brillouin laser, an optical amplifier with a shorter optical action length needs to be adopted, for example, an erbium-ytterbium co-doped phosphate glass optical fiber with a high gain coefficient with a length of 2cm can be selected as a gain medium to construct the optical fiber amplifier, or a commercial 1550 nm-band Semiconductor Optical Amplifier (SOA) is directly adopted.
The optical fiber isolator 4 is mainly used for a unidirectional conduction function, and the forward conduction input port 401 to the forward conduction output port 402 are conducted, and the forward conduction input port and the forward conduction output port 402 are not conducted in turn, so that pump light cannot be circularly transmitted in a loop formed by the optical fiber coupler 5, and backward Brillouin scattering can be realized.
The optical fiber coupler 5 is a coupler with a 1550nm band, a port 2 multiplied by 2 and a 50:50 spectral ratio of a common single-mode optical fiber.
The first frequency-shift optical fiber 6 and the second frequency-shift optical fiber 7, where the frequency-shift optical fibers function to provide self-brillouin scattered light and brillouin nonlinear amplification gain, may be a commercial G652 model communication single-mode optical fiber, and according to the discussion of the principles, there are two specific embodiments regarding the lengths of the first frequency-shift optical fiber 6 and the second frequency-shift optical fiber 7: the two cavities forming the composite cavity are close in length, the length of the first frequency-shift optical fiber can be set to be about 1m, the length of the two cavities can be 1m, and the two cavities can have one cavity longitudinal mode in the Brillouin gain spectrum range; and secondly, the length of one cavity forming the composite cavity is multiple times of the length of the other cavity, wherein the length of the first frequency-shift optical fiber 6 can be set to be 30m, and the length of the second frequency-shift optical fiber 7 is about 3m, so that the length of the long cavity is 10 times that of the short cavity, the longitudinal mode interval of the composite cavity is basically consistent with that of the short cavity, and the condition that the composite cavity has one cavity longitudinal mode in the Brillouin gain spectrum range can be completely satisfied.
The optical fiber coupler 8 has a 1550nm band of a common single-mode optical fiber, a port 1 multiplied by 2, a central wavelength 1550nm and a beam splitting ratio of 10:90, wherein 10% of ports are used as output ends of the Brillouin laser.
An annular cavity is constructed through an optical fiber circulator 2, and an optical amplifier 3, an optical fiber isolator 4 for isolating reverse light, an optical fiber coupler 5 for constructing a composite cavity, an optical fiber coupler 8 for coupling out and frequency shift optical fibers 6 and 7 for providing Brillouin nonlinear gain are cascaded in the circulator. The seed laser is input through the first port of the circulator, and can only be transmitted in the cavity in the clockwise direction, the backward Brillouin scattering light can be circularly transmitted in the composite cavity, and finally the brillouin laser is emitted by only one cavity longitudinal mode in the brillouin gain spectrum range.
The unidirectional active ring resonant cavity is constructed, based on the technical scheme of the optical fiber composite cavity, the cavity longitudinal mode interval is larger than the Brillouin gain spectrum width by utilizing the mode selection characteristic of the composite cavity, so that only one cavity longitudinal mode can start vibrating in the Brillouin gain spectrum range and form laser emission, and the output of the Brillouin single longitudinal mode operation transfer frequency optical fiber laser is realized with high efficiency and low cost. The Brillouin single-frequency laser frequency always follows the pumping seed light, the broadband frequency shift effect is stable, single longitudinal mode operation is realized based on the composite cavity, the structure is simple, the complex control requirement is avoided, and the harsh application requirement of the self-Brillouin scattering-based distributed optical fiber temperature strain sensing system on the broadband frequency shift technology can be fully met.
Claims (5)
1. The Brillouin type single longitudinal mode frequency shift fiber laser is characterized by comprising: the optical fiber coupler comprises a light source module (1), an optical fiber circulator (2), an optical amplifier (3), an optical fiber isolator (4), a first optical fiber coupler (5), a first frequency shift optical fiber (6), a second frequency shift optical fiber (7) and a second optical fiber coupler (8); the tail fiber output of the light source module (1) is connected with a first port (201) of the optical fiber circulator (2), a second port (202) of the optical fiber circulator (2) is connected with an input port (301) of the optical amplifier (3), and an output port (302) of the optical amplifier (3) is connected with a first port (501) of the first optical fiber coupler (5); the second port (502) and the fourth port (504) of the first optical fiber coupler (5) are connected into a loop through optical fibers, and devices connected in the loop comprise an optical fiber isolator (4) and a first frequency shift optical fiber (6), wherein a forward conduction input port (401) of the optical fiber isolator (4) is connected with the second port (502) of the first optical fiber coupler (5), a forward conduction output port (402) of the optical fiber isolator (4) is connected with the first frequency shift optical fiber (6), and the other end of the first frequency shift optical fiber (6) is connected with the fourth port (504) of the first optical fiber coupler (5); one end of the second frequency shift optical fiber (7) is connected with the third port (503) of the first optical fiber coupler (5), and the other end is connected with the first port (801) of the second optical fiber coupler (8); the third port (803) of the second optical fiber coupler (8) is connected with the third port (203) of the optical fiber circulator, and is closed into a large optical fiber loop, and the second port (802) of the second optical fiber coupler (8) is used as an output port of the single longitudinal mode Brillouin laser; the first frequency shift optical fiber (6) and the second frequency shift optical fiber (7) adopt common communication single mode optical fibers, and the lengths of the first frequency shift optical fiber (6) and the second frequency shift optical fiber (7) are selected in two ways: firstly, the two cavities forming the composite cavity are equal or approximate in length; secondly, one cavity length forming the composite cavity is multiple times of the other cavity length; the optical fiber isolator (4) is used for preventing reverse resonance by unidirectional conduction; the first optical fiber coupler (5) adopts a coupler with 1550nm wave band, 2 multiplied by 2 ports and 50:50 spectral ratio of a common single-mode optical fiber.
2. Brillouin type single longitudinal mode frequency shifted fiber laser according to claim 1, characterized in that the light source module (1) is a narrow linewidth laser with linewidth less than 1MHz.
3. The brillouin type single longitudinal mode frequency shifted fiber laser according to claim 1, wherein said optical fiber circulator (2) is a three port optical fiber circulator, which is turned on unidirectionally, and the optical fiber circulator (2) can be replaced by an access optical fiber coupler and an isolator to function as an optical fiber circulator.
4. A brillouin type single longitudinal mode frequency shifted optical fiber laser according to claim 1, wherein said optical amplifier (3) is constructed by selecting a high gain factor erbium doped optical fiber as a gain medium, or by selecting a 1550nm band Semiconductor Optical Amplifier (SOA).
5. The brillouin type single longitudinal mode frequency shifted fiber laser according to claim 1, wherein said second fiber coupler (8) is a 1 x 2 common single mode fiber coupler having a center wavelength of 1550nm and a split ratio of 10:90, wherein 10% of the ports are used as the output end of the brillouin type laser.
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| CN107785771B (en) * | 2017-10-27 | 2023-07-04 | 西安深瞳智控技术有限公司 | Single-longitudinal-mode multi-wavelength tunable laser system and method for improving wavelength output efficiency |
| CN108923240B (en) * | 2018-07-24 | 2020-07-03 | 太原理工大学 | Wavelength frequency stabilization system based on cascade stimulated Brillouin scattering effect |
| CN110970785B (en) * | 2019-11-07 | 2021-12-28 | 中山大学 | Coherent swept-frequency light source with enhanced Fourier domain injection locking |
| CN113324652B (en) * | 2021-05-28 | 2022-07-01 | 中电科思仪科技股份有限公司 | Fine frequency sweeping signal generation device and method of Brillouin spectrometer |
| CN115102023B (en) * | 2022-08-26 | 2022-12-30 | 苏州大学 | Frequency shift injection locking ultra-narrow linewidth Brillouin laser and system |
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