A dual-pump cascade type Brillouin random laser with ultra-narrow linewidth

Abstract

The application discloses a double-pump cascade type super-narrow linewidth Brillouin random laser, which comprises a pump laser, a fiber amplifier, an optical isolator, a fiber coupler, a first fiber circulator, a second fiber circulator, a third fiber circulator, an adjustable fiber attenuator, a first Brillouin gain fiber, a second Brillouin gain fiber and a tunable filter; the application adopts two optical fibers which are subjected to stimulated Brillouin scattering frequency shift superposition, stimulated Brillouin scattering occurs in the first Brillouin gain fiber, Stokes light generated by the first Brillouin gain fiber is further provided with a Stokes light signal source for the second Brillouin gain fiber after passing through the adjustable fiber attenuator, meanwhile, Rayleigh scattering occurs in the second Brillouin gain fiber and provides random feedback for the first Brillouin gain fiber after passing through the third fiber circulator; in the system, higher Brillouin gain is realized, laser linewidth can be further compressed, and finally super-narrow linewidth random laser is output.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of fiber lasers, in particular to a double-pump cascade type super-narrow linewidth Brillouin random laser. BACKGROUND

[0002] A super-narrow linewidth laser with a magnitude of 100 Hz can provide a longer coherence length, realize higher sensitivity sensing and longer distance detection, and has great application value in the fields of sensing and detection, and is widely applied to the fields of high-precision fiber sensing, long-distance coherent optical communication, high-resolution radar imaging and the like, and the performance directly influences the precision of sensing and imaging and the distance of optical communication, at present, the narrow linewidth laser has an increasingly obvious application prospect and value.

[0003] As early as 1972, the stimulated Brillouin scattering technology has been concerned, the stimulated Brillouin scattering is the highest transmission efficiency nonlinear effect in an optical fiber, has a narrow linewidth gain, a low power threshold and a very high conversion efficiency, on the other hand, the Brillouin random laser structure is relatively simple, and has a lower requirement for pumping, optical fibers and other devices, with the lapse of time and the accumulation of technology, the way of generating a narrow linewidth laser by using the Brillouin random laser is more and more favored by scientists.

[0004] At present, one way of generating a narrow linewidth laser by using the Brillouin random laser is to use a Brillouin gain fiber as a gain medium and a Rayleigh scattering fiber as a random feedback, after the Stokes light obtains a gain in the Brillouin gain fiber, the backward Rayleigh scattering is generated in the Rayleigh scattering fiber and the seed light is re-injected into the Brillouin gain fiber in the form of the seed light, so as to circulate and finally output the narrow linewidth laser. Although the structure can output stable and low-to-500 Hz level linewidth, the structure still has certain deficiencies, on the one hand, the output light power is low, when the high-power Stokes light is injected into the Rayleigh scattering fiber, the Brillouin threshold is reached, the stimulated Brillouin scattering is generated, the output laser power is lost, the output laser spectrum is widened, and the output is unstable, on the other hand, the above reasons also lead to that a higher pump light power cannot be injected into the Brillouin gain fiber, the Brillouin gain cannot be further improved, so that the output laser linewidth cannot be further compressed.

[0005] Therefore, it is necessary to develop a double-pump cascade type super-narrow linewidth Brillouin random laser to solve the above problems. SUMMARY

[0006] The purpose of the application is to design a double-pump cascade type super-narrow linewidth Brillouin random laser to solve the above problems.

[0007] The application achieves the above purpose by the following technical scheme:

[0008] The application discloses a double-pump cascade type super-narrow line width Brillouin random laser, which comprises a pump laser, a fiber amplifier, an optical isolator, a fiber coupler, a first fiber circulator, a second fiber circulator, a third fiber circulator, an adjustable fiber attenuator, a first Brillouin gain fiber, a second Brillouin gain fiber and a tunable fiber filter, wherein the pump laser, the fiber amplifier, the optical isolator and the fiber coupler are sequentially connected; a port one of the first fiber circulator and a port one of the second fiber circulator are connected with two ports of the fiber coupler respectively; two ends of the first Brillouin gain fiber are connected with a port two of the second fiber circulator and a port three of the third fiber circulator respectively; the second Brillouin gain fiber is connected with a port two of the first fiber circulator and a first end of the tunable fiber filter respectively; two ends of the adjustable fiber attenuator are connected with a port three of the second fiber circulator and a port one of the third fiber circulator respectively; a second end of the tunable fiber filter is connected with a port two of the third fiber circulator; the total gain of the system is generated by the cascade of the first Brillouin gain fiber and the second Brillouin gain fiber; wherein the second Brillouin gain fiber is used for power amplification and line width compression of the Stokes light output from the first Brillouin gain fiber and provides random feedback for the first Brillouin gain fiber; the first Brillouin gain fiber is used for amplifying the Stokes light randomly fed back by the second Brillouin gain fiber and further providing a Stokes light signal source for the second Brillouin gain fiber amplification output.

[0009] Preferably, all the devices in the laser are connected through fiber flanges or directly fused into one body.

[0010] Preferably, the adjustable fiber attenuator is used for adjusting the power of the Stokes light output from the second Brillouin gain fiber, avoiding gain saturation of the Stokes light output from the second Brillouin gain fiber and ensuring that the output laser reaches the narrowest line width.

[0011] Preferably, the Brillouin gain spectra of the first Brillouin gain fiber and the second Brillouin gain fiber are coincident or overlapping.

[0012] Preferably, the tunable fiber filter is used for filtering out the pump light and allowing the Stokes light to pass, so as to prevent the pump light output from the second Brillouin gain fiber from entering the first stimulated Brillouin gain fiber.

[0013] Preferably, the pump laser is a narrow line width laser, and the output power of the fiber amplifier is adjustable.

[0014] The application has the following beneficial effects:

[0015] The application promotes the system's Brillouin gain, further compresses the output laser line width and realizes the laser output of super-narrow line width under the premise of ensuring the stability of the output laser through the structure of two same Brillouin scattering frequency shift Brillouin gain optical fibers and double side pumping; on the other hand, the system structure of the application adopts the adjustable optical fiber attenuator to control the Stokes light power size injected into the second Brillouin gain optical fiber, so that the laser output can reach the best effect; finally, the application reasonably uses the adjustable optical fiber harmonic filter to block the pump light output from the second Brillouin gain optical fiber from being injected into the first Brillouin gain optical fiber, thereby improving the stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structure schematic diagram of a double-pump cascade type super-narrow line width Brillouin random laser of the application;

[0017] Figure 2 is a structure schematic diagram of a delay self-heterodyne method measuring device;

[0018] Marked in the figure: 101-pump laser; 102-optical fiber amplifier; 103-optical isolator; 104-first optical fiber coupler; 105-first optical fiber ring; 106-second optical fiber ring; 107-third optical fiber ring; 108-adjustable optical fiber attenuator; 109-first Brillouin gain optical fiber; 110-second Brillouin gain optical fiber; 111-tunable optical fiber filter; 201-second optical fiber coupler; 202-delay optical fiber; 203-acousto-optic frequency shifter; 204-third optical fiber coupler; 205-balance photoelectric detector; 206-spectrum analyzer. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in conjunction with the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. The components of the embodiments of the application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the application without creative labor are within the scope of protection of the application.

[0021] It should be noted that: similar labels and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0022] In the description of the present application, it should be understood that the terms "upper", "lower", "inner", "outer", "left", "right", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly understood by those skilled in the art, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0023] In addition, the terms "first", "second", and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "provided", "connected" and the like should be understood broadly, for example, "connected" can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium, or can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0026] As Figure 1As shown, a double-pump cascade type ultra-narrow linewidth Brillouin random laser includes a pump laser 101, a fiber amplifier 102, an optical isolator 103, a fiber coupler 104, a first fiber circulator 105, a second fiber circulator 106, a third fiber circulator 107, an adjustable fiber attenuator 108, a first Brillouin gain fiber 109, a second Brillouin gain fiber 110, and a tunable fiber filter 111. The pump laser 101, the fiber amplifier 102, the optical isolator 103, and the fiber coupler 104 are connected in sequence. The port one of the first fiber circulator 105 and the port one of the second fiber circulator 106 are connected to two ports of the fiber coupler 104 respectively. The two ends of the first Brillouin gain fiber 109 are connected to the port two of the second fiber circulator 106 and the port three of the third fiber circulator 107 respectively. The second Brillouin gain fiber 110 is connected to the port two of the first fiber circulator 105 and the first end of the tunable fiber filter 111 respectively. The two ends of the adjustable fiber attenuator 108 are connected to the port three of the second fiber circulator 106 and the port one of the third fiber circulator 107 respectively. The second end of the tunable fiber filter 111 is connected to the port two of the third fiber circulator 107. The total gain of the system is generated by the cascade of the first Brillouin gain fiber 109 and the second Brillouin gain fiber 110. The second Brillouin gain fiber 110 is used to amplify the power and compress the linewidth of the Stokes light output from the first Brillouin gain fiber 109, and provides random feedback to the first Brillouin gain fiber 109. The first Brillouin gain fiber 109 is used to amplify the Stokes light feedback from the second Brillouin gain fiber 110, and further provides a Stokes light signal source for the second Brillouin gain fiber 110.

[0027] All devices in the laser are connected by fiber flanges or directly fused into one body.

[0028] The adjustable fiber attenuator 108 is used to adjust the power of the Stokes light output from the second Brillouin gain fiber 110, avoid the gain saturation of the Stokes light output from the second Brillouin gain fiber 110, and ensure that the output laser reaches the narrowest linewidth.

[0029] The Brillouin gain spectra of the first Brillouin gain fiber 109 and the second Brillouin gain fiber 110 are coincident or overlapping.

[0030] The tunable fiber filter 111 is used to filter out the pump light and allow the Stokes light to pass through, so as to prevent the pump light output from the second Brillouin gain fiber 110 from entering the first stimulated Brillouin gain fiber 109.

[0031] The pump laser 101 is a narrow linewidth laser, and the output power of the fiber amplifier 102 is adjustable.

[0032] The working principle of the present application is as follows: the pump laser is sequentially passed through the optical fiber amplifier and the optical isolator, and the pump laser is injected into the first and second Brillouin gain optical fibers by the optical fiber coupler. When the pump light is injected into the first Brillouin gain optical fiber through the second optical fiber circulator, stimulated Brillouin scattering occurs, and the generated backward Stokes light is injected into the second Brillouin gain optical fiber through the second optical fiber circulator, the adjustable optical fiber attenuator, the third optical fiber circulator and the tunable optical fiber filter. Since the Brillouin scattering frequency shift of the first and second Brillouin gain optical fibers is the same, the backward Stokes light of the first Brillouin gain optical fiber can be used as the seed light of the second Brillouin gain optical fiber, so that the line width of the Stokes light is further compressed. On the other hand, in the second Brillouin gain optical fiber, the Stokes light will undergo backward Rayleigh scattering, and the tunable optical fiber filter only allows the Stokes light to pass through but not the pump light, so the backward Rayleigh scattering light will pass through the tunable filter and the third optical fiber circulator and be injected into the first Brillouin gain optical fiber to serve as the seed light of the first Brillouin gain optical fiber. This process is repeated and finally the super-narrow line width laser is output.

[0033] In the system structure of the present application, the adjustable optical fiber attenuator is used to control the power of the Stokes light injected into the second Brillouin gain optical fiber. If the power of the Stokes light injected into the second Brillouin gain optical fiber is too large, the stimulated Brillouin scattering central wavelength gain will be saturated, resulting in spectral line broadening. If the power of the Stokes light injected into the second Brillouin gain optical fiber is too small, the injected seed light will not be dominant in the stimulated Brillouin scattering, also resulting in spectral line broadening. Therefore, the adjustable optical fiber attenuator is needed to obtain the best laser output.

[0034] In some embodiments, the first Brillouin gain optical fiber 109 and the second Brillouin gain optical fiber 110 are both single-mode optical fibers, and the lengths are 10 km and 15 km, respectively.

[0035] The stimulated Brillouin scattering frequency shift of the first Brillouin gain optical fiber 109 and the second Brillouin gain optical fiber 110 is the same.

[0036] The coupling ratio of the first optical fiber coupler 104 is 20:80. The port one of the first optical fiber circulator 105 is connected to the 80% optical power port of the first optical fiber coupler 104. The port one of the second optical fiber circulator 106 is connected to the 20% optical power port of the first optical fiber coupler 104.

[0037] The pump laser 101 is a semiconductor laser with a central wavelength of 1550 nm, a line width of 20 kHz and an output power of 10 mW.

[0038] The adjustable range of the adjustable optical fiber attenuator 108 is 0.8 dB~64 dB.

[0039] The tunable fiber filter 111 has a center wavelength adjustable range of 1525 nm~1610 nm and a 3 dB adjustable bandwidth of 0.03 nm~3 nm.

[0040] All the devices in the Brillouin random fiber laser are connected through FC / APC fiber heads and flanges.

[0041] The working process of the present application is as follows: at the beginning, the pump light generated by the pump laser 101 passes through the fiber amplifier 102, the optical isolator 103 and the first fiber coupler 104, and in the first fiber coupler, 20% of the power of the laser is injected into the first Brillouin gain fiber 109 and 80% of the power of the laser is injected into the second Brillouin gain fiber 110. In the two fibers, the first Brillouin scattering will be generated due to the thermal motion of the molecules in the fiber, and when the first Brillouin scattering reaches a certain intensity, the stimulated Brillouin scattering will be generated by interference with the pump light. The Stokes light generated by the stimulated Brillouin scattering in the first Brillouin gain fiber 109 is injected into the second Brillouin gain fiber after passing through the adjustable fiber attenuator 108 and the tunable fiber filter 111, and the Stokes light has the same Brillouin scattering frequency shift as the first Brillouin gain fiber 109 and the second Brillouin gain fiber 110, so the Stokes light can be used as the seed light of the Brillouin gain and further gain in the second Brillouin gain fiber 110. In addition, in the second Brillouin gain fiber, the Stokes light will also generate Rayleigh backscattering, and the Rayleigh backscattering light passes through the tunable fiber filter 111, filters out the pump light and is injected into the first Brillouin gain fiber 109 as the seed light. When the gain of the Stokes light is equal to the total loss, the system can output stable ultra-narrow linewidth laser.

[0042] In the system structure of the present application, the adjustable fiber attenuator 108 controls the power of the Stokes light injected into the second Brillouin gain fiber 110. If the power of the Stokes light injected into the second Brillouin gain fiber 110 is too large, the stimulated Brillouin scattering center wavelength gain will be saturated, resulting in spectral line broadening. If the power of the Stokes light injected into the second Brillouin gain fiber 110 is too small, the injected seed light will not dominate the stimulated Brillouin scattering, also resulting in spectral line broadening. Therefore, the adjustable fiber attenuator 108 should be adjusted in the experiment to obtain the laser output with the narrowest linewidth.

[0043] The structure of the delay self-heterodyne method measuring device is as shown in Figure 2As shown, first, the laser to be measured is divided into two parts by a second optical fiber coupler 201, 99% of the optical power is injected into a 100 km delay optical fiber 202, and 1% of the optical power is injected into an acousto-optic frequency shifter 203. The modulation of the acousto-optic frequency shifter produces a frequency shift of 70 MHz, so that the two lights are completely incoherent. Then, the two lights pass through a third optical fiber coupler 204, generating two beat frequency difference signals with a center frequency of 70 MHz. Then, a photoelectric balance detector 205 is used to obtain the time domain signal of the beat frequency light, and a spectrum analyzer 206 is used to observe the spectrum of the beat frequency signal, so that the spectrum information of the output laser can be observed. The measured laser output has a line width of 100 Hz.

[0044] The above is only the preferred embodiment of the present application, and it should be pointed out that for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A dual-pump cascade ultra-narrow linewidth Brillouin random laser, characterized in that: The invention comprises a pump laser (101), an optical fiber amplifier (102), an optical isolator (103), an optical fiber coupler (104), a first optical fiber circulator (105), a second optical fiber circulator (106), a third optical fiber circulator (107), an adjustable optical fiber attenuator (108), a first Brillouin gain optical fiber (109), a second Brillouin gain optical fiber (110) and a tunable optical fiber filter (111); a pump laser (101), an optical fiber amplifier (102), an optical isolator (1 03) and the optical fiber coupler (104) are connected in sequence; port one of the first optical fiber circulator (105) and port one of the second optical fiber circulator (106) are respectively connected to the two ports of the optical fiber coupler (104); the two ends of the first Brillouin gain optical fiber (109) are respectively connected to port two of the second optical fiber circulator (106) and port three of the third optical fiber circulator (107); the second Brillouin gain optical fiber (110) is respectively connected to port two of the first optical fiber circulator (105) and the tunable optical fiber filter ( The first end of the adjustable optical fiber attenuator (108) is connected to the first end of the second optical fiber circulator (106) and the first end of the third optical fiber circulator (107); the two ends of the adjustable optical fiber attenuator (108) are respectively connected to the third port of the second optical fiber circulator (106) and the first port of the third optical fiber circulator (107); the second end of the tunable optical fiber filter (111) is connected to the second port of the third optical fiber circulator (107); the first Brillouin gain fiber (109) and the second Brillouin gain fiber (110) have the same Brillouin dispersion frequency shift, and the total gain of the system is generated by cascading the first Brillouin gain fiber (109) and the second Brillouin gain fiber (110); wherein the second Brillouin gain fiber (110) is used to power amplify and linewidth compress the Stokes light output from the first Brillouin gain fiber (109), and provide random feedback to the first Brillouin gain fiber (109); the first Brillouin gain fiber (109) is used to amplify the Stokes light randomly fed back by the second Brillouin gain fiber (110), and further provide a Stokes light signal source for the amplified output of the second Brillouin gain fiber (110).

2. A dual-pump cascade ultra-narrow linewidth Brillouin random laser according to claim 1, characterized in that: All components in the laser are connected via optical fiber flanges or directly fused into one.

3. A dual-pump cascade ultra-narrow linewidth Brillouin random laser according to claim 1 or 2, characterized in that: The adjustable optical fiber attenuator (108) is used to adjust the Stokes light power output by the second Brillouin gain optical fiber (110) to avoid gain saturation of the Stokes light output by the second Brillouin gain optical fiber (110) and ensure that the output laser reaches the narrowest linewidth.

4. A dual-pump cascade ultra-narrow linewidth Brillouin random laser according to claim 1 or 2, characterized in that: The Brillouin gain spectra of the first Brillouin gain fiber (109) and the second Brillouin gain fiber (110) coincide with or overlap.

5. A dual-pump cascade ultra-narrow linewidth Brillouin random laser according to claim 1 or 2, characterized in that: The tunable optical fiber filter (111) is used to filter out the pump light and allow the Stokes light to pass through, so as to prevent the pump light output from the second Brillouin gain optical fiber (110) from entering the first Brillouin gain optical fiber (109).

6. A dual-pump cascade ultra-narrow linewidth Brillouin random laser according to claim 1 or 2, characterized in that: The pump laser (101) is a narrow linewidth laser, and the output power of the optical fiber amplifier (102) is adjustable.

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