Multi-wavelength Random Fiber Laser Based on Inclined Parallel Inscribed Fiber Bragg Grating Arrays

Abstract

The present invention discloses a multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array, belonging to the technical field of fiber lasers. It includes a pump light source, a fiber grating array, a grating axial stretching device, a wavelength division multiplexer, and a gain amplification unit. The pump light is coupled into the gain amplification unit through the wavelength division multiplexer to excite it, and the gain amplification unit amplifies the pump light source in the optical path. After the fiber grating array adjusts the strain through the grating axial stretching device to change its central wavelength, it provides the feedback of the gain light and wavelength selection. The gain light reflected by the fiber grating array is amplified in the gain amplification unit, and gradually forms a multi-wavelength random laser output as the power of the pump light source increases. The present invention uses an inclined parallel inscribed fiber grating array as both a multi-wavelength selection device and a high-reflection mirror at one end of the laser cavity, and uses a Raman fiber at the other end to provide Rayleigh scattering feedback, reducing the number of components constituting the laser and making the structure simpler.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber lasers, and more specifically, relates to a multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array. Background Art

[0002] Multi-wavelength fiber lasers are widely used in fields such as optical communication, fiber sensing, laser ranging, and spectral analysis. Currently, there are mainly two ways to achieve multi-wavelength lasing in multi-wavelength fiber lasers:

[0003] (1) Adding multi-wavelength selection devices into the cavity, such as Fabry-Perot filters, fiber Bragg gratings, Sagnac loops, and Lyot filters, etc. This method can adjust the multi-wavelength lasing parameters by adjusting the multi-wavelength selection device, but it will damage the original cavity structure and introduce additional losses;

[0004] (2) Utilizing nonlinear effects such as stimulated Brillouin scattering, stimulated Raman scattering, and four-wave mixing. This method can control the lasing wavelength by adjusting the pump light wavelength, but multi-wavelength parameters such as wavelength interval are determined by the optical fiber, and the tunability is poor;

[0005] In recent years, random fiber lasers have gradually become an important way to generate multi-wavelength lasers. Compared with traditional multi-wavelength fiber lasers using rare-earth doped fibers to provide gain, random fiber lasers have the advantages of simple structure, no mode, and low coherence. At the same time, they can conveniently combine stimulated Raman scattering to improve the pump utilization efficiency and achieve lasing in more bands. With the development of femtosecond laser direct writing technology, various parameters of fiber gratings can be flexibly prepared using femtosecond lasers. Based on this technology and combined with random fiber laser technology, it is expected to realize a multi-wavelength random fiber laser with flexible tunability of multiple parameters, which is beneficial to practical applications. Summary of the Invention

[0006] Aiming at the above-mentioned defects or improvement requirements of the prior art, the present invention provides a multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array, aiming to provide feedback and wavelength selection of the gain light by fixing the fiber grating array on a grating axial stretching device to adjust the central wavelength through strain, thereby solving the technical problem of poor tunability of multi-wavelength random fiber lasers in the prior art.

[0007] To achieve the above object, according to one aspect of the present invention, there is provided a multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array. The laser is a semi-open cavity structure, and includes a pump light source, a fiber grating array, a grating axial stretching device, a wavelength division multiplexer, and a gain amplification unit;

[0008] The pump light source is connected to the input end of the wavelength division multiplexer; the output end of the wavelength division multiplexer is connected to the gain amplification unit; the fiber grating array is fixedly arranged on the grating axial stretching device.

[0009] The pump light source is used to generate pump light, and the pump light is coupled into the gain amplification unit through the wavelength division multiplexer to excite it. The gain amplification unit is used to generate erbium ion gain, Raman gain and Rayleigh scattering feedback by stimulated emission and amplify the pump light source in the optical path. After the center wavelength of the fiber grating array is changed by strain adjustment through the grating axial stretching device, it provides feedback of the gain light and wavelength selection. The gain light reflected by the fiber grating array is amplified in the gain amplification unit, and multi-wavelength random laser output is gradually formed as the power of the pump light source increases.

[0010] Preferably, the fiber grating array includes a fiber core and a plurality of high-reflectivity fiber gratings, and the plurality of high-reflectivity fiber gratings are distributed in parallel along the axial direction of the fiber core.

[0011] Preferably, the plurality of high-reflectivity fiber gratings have the same reflectivity but different center wavelengths.

[0012] Preferably, the plurality of high-reflectivity fiber gratings are all written by femtosecond laser using the point-by-point method.

[0013] Preferably, the manufacturing method of the fiber grating array is specifically as follows: Place the optical fiber on the displacement platform, use the femtosecond laser to write the first fiber grating by the point-by-point method, then move the optical fiber axially by a certain distance, and write another fiber grating with a longer center wavelength; during the writing process, monitor the transmission spectrum and reflection spectrum of the fiber grating in real time until an inclined parallel written fiber grating array with the target transmission spectrum and reflection spectrum is obtained.

[0014] Preferably, the gain amplification unit includes a gain fiber and a Raman fiber; one end of the gain fiber is connected to the output end of the wavelength division multiplexer, and the other end is connected to the Raman fiber.

[0015] Preferably, the gain fiber is an erbium-doped fiber.

[0016] Preferably, an isolator is further included, and the isolator is connected to one end of the Raman fiber as the laser output end.

[0017] Preferably, the center wavelength of the pump light source is 1455 nm.

[0018] Preferably, one end of the fiber grating array is cut obliquely to eliminate parasitic feedback at the port.

[0019] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0020] 1. Compared with the traditional multi-wavelength fiber laser that requires additional multi-wavelength selection devices, the multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array proposed by the present invention uses the inclined parallel inscribed fiber grating array as both a multi-wavelength selection device and a high-reflection mirror at one end of the laser cavity, and uses Raman fiber at the other end to provide Rayleigh scattering feedback, reducing the number of devices constituting the laser, and thus having a simpler structure.

[0021] 2. The multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array proposed by the present invention is easy to fabricate in various bands, enabling the multi-wavelength random fiber laser of the invention to flexibly select the types of gain fiber, Raman fiber, and pump light source wavelength.

[0022] 3. The multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array proposed by the present invention, in which the inclined parallel inscribed fiber grating array is fabricated by femtosecond laser using the inclined parallel inscription method, has the advantages of simple and rapid fabrication, flexible control of wavelength interval and wavelength number, and small device size.

[0023] 4. Compared with the random fiber laser based on a single gain mechanism, the multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array proposed by the present invention simultaneously utilizes the gain of the gain fiber and the stimulated Raman scattering gain of the single-mode fiber, and thus can effectively reduce the lasing threshold and increase the output power. Description of the Drawings

[0024] Figure 1 is a schematic diagram of the inclined parallel inscribed fiber grating array of the present invention;

[0025] Figure 2 (a) is the reflection spectrum of the inclined parallel inscribed fiber grating array fabricated by the present invention;

[0026] Figure 2 (b) is the transmission spectrum of the inclined parallel inscribed fiber grating array fabricated by the present invention;

[0027] Figure 3 is a schematic diagram of the multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array of the present invention;

[0028] Figure 4 is the output power curve diagram of the multi-wavelength random fiber laser based on the inclined parallel inscribed fiber grating array of the present invention;

[0029] Figure 5It is the output spectrum diagram of the multi-wavelength random fiber laser based on the tilted parallel inscribed fiber grating array of the present invention when using tilted parallel inscribed fiber grating arrays with different numbers of wavelengths.

[0030] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 11 - the first high-reflectivity fiber grating; 12 - the second high-reflectivity fiber grating; 13 - the third high-reflectivity fiber grating; 14 - the last high-reflectivity fiber grating; 15 - the axial spacing between adjacent high-reflectivity fiber gratings; 16 - the fiber core; 17 - the fiber cladding; 31 - the pump light source; 32 - the tilted cutting; 33 - the grating axial stretching device; 34 - the fiber grating array; 35 - the wavelength division multiplexer; 36 - the gain fiber; 37 - the Raman fiber; 38 - the isolator. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] As Figures 1-5 shown, the present invention provides a multi-wavelength random fiber laser based on a tilted parallel inscribed fiber grating array, including a pump light source 31, a grating axial stretching device 33, a tilted parallel inscribed fiber grating array 34, a wavelength division multiplexer 35, a gain fiber 36, a Raman fiber 37 and an isolator 38; the fiber grating array 34 is composed of a plurality of high-reflectivity fiber gratings with different central wavelengths but the same reflectivity; the central wavelengths of the fiber grating array 34 should basically correspond to the gain spectral lines of the gain fiber 36 and the Raman fiber 37; the fiber grating array 34 is prepared by femtosecond laser using the tilted parallel inscription technique; the fiber grating array 34 is fixed on the grating axial stretching device 33 by glue or a fiber clamp; one end of the fiber grating array 34 is tilted and cut 32.

[0033] Furthermore, the pump light source 31 is coupled into the gain fiber 36 and the Raman fiber 37 through the wavelength division multiplexer 35 to amplify the multi-wavelength laser; the Raman fiber 37 simultaneously provides stimulated Raman scattering gain and Rayleigh scattering feedback; the isolator 38 isolates the reflected light and serves as the laser output end.

[0034] As a preferred embodiment of the present invention, the gain fiber 36 is an erbium-doped fiber.

[0035] As a preferred embodiment of the present invention, the Raman optical fiber 37 is an ordinary single-mode optical fiber with a length of 10 km.

[0036] The working principle of the present invention:

[0037] The pump light source with a central wavelength of 1455 nm pumps both the erbium-doped optical fiber and the Raman optical fiber simultaneously. The initially generated broadband spontaneous emission light is selected and reflected by the high-reflectivity fiber grating array at one end to return the light of the corresponding wavelength to the cavity for amplification, and then combined with the Rayleigh scattering feedback provided by the Raman optical fiber at the other end to finally form multi-wavelength lasing.

[0038] The technical solution of the present invention will be further described below through specific embodiments.

[0039] Embodiment 1

[0040] A multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array. The schematic diagram of the inclined parallel inscribed fiber grating array is as Figure 1 shown, and it is composed of a first high-reflectivity fiber grating 11, a second high-reflectivity fiber grating 12, a third high-reflectivity fiber grating 13, and a last high-reflectivity fiber grating 14 with different central wavelengths but the same reflectivity and parallelly distributed along the axial direction of the fiber core 16. Each of the high-reflectivity fiber gratings is inscribed by femtosecond laser using the point-by-point method.

[0041] Furthermore, the central wavelength, reflectivity, and axial spacing 15 of the fiber grating are determined according to actual needs and preparation effects; the reflectivity should be as high as possible while ensuring a small insertion loss of the fiber grating to reduce the laser threshold; the axial spacing should be as small as possible while ensuring that adjacent fiber gratings do not interfere with each other to shorten the total length of the inclined parallel inscribed fiber grating array.

[0042] Embodiment 2

[0043] A preparation method for an inclined parallel inscribed fiber grating array for a multi-wavelength random fiber laser, which is used to prepare the inclined parallel inscribed fiber grating array, and its operation method is as follows:

[0044] Step 1: Fix a section of optical fiber on the displacement platform so that the femtosecond laser beam is vertically incident and focused in the fiber core

[0045] Step 2: Control the optical fiber to move along a straight line at an angle inclined to the optical fiber axis relative to the femtosecond laser focused spot, and use the point-by-point method to inscribe the first target fiber grating, and monitor the transmission spectrum and reflection spectrum;

[0046] Step 3: Control the optical fiber to move a certain axial distance along the fiber axis, and then write another fiber grating with a longer central wavelength but the same other parameters, and monitor the transmission spectrum and reflection spectrum;

[0047] Step 4: Repeat Step 3 until an inclined parallel inscribed fiber grating array with a target transmission spectrum and reflection spectrum is obtained.

[0048] In this embodiment, the optical fiber is a common single-mode optical fiber; the axial length of the fiber grating is 4000 μm, and the axial spacing is 1000 μm; the reflection spectrum and transmission spectrum of a three-wavelength inclined parallel inscribed fiber grating array are as Figure 2 (a) and Figure 2 (b) shown. The reflectivity of the fiber grating is 65%, the central wavelength spacing is 4 nm, and the loss of the long wavelength is 15%.

[0049] Embodiment 3

[0050] The experimental setup of this experiment is as Figure 3 shown, including a pump light source 31. The pump light source 31 enters the gain fiber 36 and Raman fiber 37 through a wavelength division multiplexer 35 for excitation; the gain fiber is an erbium-doped fiber that provides gain using erbium ions; the Raman fiber is a common single-mode fiber with a length of 10 km, which provides both Raman gain and Rayleigh scattering feedback; the inclined parallel inscribed fiber grating array 34 is used to provide feedback and wavelength selection, and is fixed on the grating axial stretching device 33 to adjust the central wavelength through strain; the light reflected by the fiber grating array 34 is amplified in the gain fiber 36 and Raman fiber 37, and gradually forms random laser output as the pump power increases; one end is inclined and cut 32 to avoid parasitic feedback; the polarization-independent isolator 38 isolates the reflected light and serves as the laser output end; the entire laser is a semi-open cavity structure.

[0051] The laser output power curve based on the inclined parallel inscribed fiber grating array in Embodiment 2 is as Figure 4 shown. The threshold power is about 0.7 W. Linear fitting shows that the slope efficiency of the laser is about 49.6%. An output power of 0.883 W can be obtained at a maximum pump power of 2.49 W, corresponding to an optical-optical conversion efficiency of about 35.5%, and both the laser output power and the lasing multi-wavelength spectrum remain stable. By replacing the inclined parallel inscribed fiber grating array, laser outputs with different numbers of wavelengths as shown in Figure 5 can be obtained, and each wavelength corresponds well to the used inclined parallel inscribed fiber grating array. In addition, the central wavelength of the output laser can be easily changed by using the grating axial stretching device to provide strain.

[0052] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array, characterized in that, The laser is a semi-open cavity structure, including a pump light source (31), an optical fiber grating array (34), a grating axial stretching device (33), a wavelength division multiplexer (35), and a gain amplification unit; The pump light source (31) is connected to the input end of the wavelength division multiplexer (35); the output end of the wavelength division multiplexer (35) is connected to the gain amplification unit; the optical fiber grating array (34) is fixedly arranged on the grating axial stretching device (33); The pump light source (31) is used to generate pump light, and the pump light is coupled into the gain amplification unit through the wavelength division multiplexer (35) to excite it. The gain amplification unit is used to generate erbium ion gain, Raman gain, and Rayleigh scattering feedback by stimulated emission and amplify the pump light source in the optical path; after the center wavelength of the optical fiber grating array (34) is changed by strain adjustment through the grating axial stretching device (33), it provides feedback of the gain light and wavelength selection; the gain light reflected by the optical fiber grating array (34) is amplified in the gain amplification unit, and as the power of the pump light source (31) increases, multi-wavelength random laser output is gradually formed; The optical fiber grating array (34) includes an optical fiber core (16) and a plurality of high-reflectivity optical fiber gratings, and the plurality of high-reflectivity optical fiber gratings are distributed in parallel along the axial direction of the optical fiber core (16); The reflectivities of the plurality of high-reflectivity optical fiber gratings are the same, but the center wavelengths are all different; The plurality of high-reflectivity optical fiber gratings are all written by the point-by-point method using femtosecond laser; The manufacturing method of the optical fiber grating array (34) is specifically as follows: place the optical fiber on the displacement platform, use the point-by-point method with femtosecond laser to write the first optical fiber grating, then move the optical fiber axially by a certain distance, and write another optical fiber grating with a longer center wavelength; during the writing process, monitor the transmission spectrum and reflection spectrum of the optical fiber grating in real time until an inclined parallel written optical fiber grating array with the target transmission spectrum and reflection spectrum is obtained.

2. The multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array according to claim 1, characterized in that, The gain amplification unit includes a gain optical fiber (36) and a Raman optical fiber (37); one end of the gain optical fiber (36) is connected to the output end of the wavelength division multiplexer (35), and the other end is connected to the Raman optical fiber (37).

3. The multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array according to claim 2, characterized in that, The gain optical fiber (36) is an erbium-doped optical fiber.

4. The multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array according to claim 2, characterized in that, An isolator (38) is further included, and the isolator (38) is connected to one end of the Raman optical fiber (37) as the laser output end.

5. The multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array according to claim 1, characterized in that, The center wavelength of the pump light source (31) is 1455 nm.

6. The multi-wavelength random fiber laser based on an inclined parallel inscribed fiber grating array according to claim 1, characterized in that, One end of the optical fiber grating array (34) is inclinedly cut to eliminate the parasitic feedback at the port.

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