A random fiber laser with continuously tunable wavelength

Abstract

The present invention discloses a randomly fiber laser with continuously tunable wavelength, which comprises a first pump combiner, the signal end of which is connected to a first 1:1 coupler, and the pump end of which is connected to a first laser diode pump source; the common end of the first pump combiner is sequentially connected to a first ytterbium-doped fiber, a Raman fiber and an optical fiber bevel end face; the first input end of the first 1:1 coupler is connected to a broadband fiber loop mirror, and the second input end of the first 1:1 coupler is connected to a laser seed source; the laser seed source is used for outputting randomly ytterbium-doped laser with continuously tunable wavelength; by connecting a wavelength-tunable laser seed source and a broadband fiber loop mirror to the signal end of the pump combiner, the present invention solves the problems of complex structure and high cost caused by using special wavelength fiber gratings and wavelength division multiplexers, and solves the problem of limited output wavelength.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber laser, and specifically relates to a randomly fiber laser with continuously tunable wavelength. Background Art

[0002] Different from the fixed resonant cavity and cavity mirror feedback mechanism in traditional lasers, a randomly fiber laser realizes laser oscillation by using the random backward Rayleigh scattering feedback in the optical fiber. It has unique advantages such as simple structure, narrow spectral line width, and low threshold power. Compared with rare-earth doped fiber lasers, a random Raman fiber laser obtains gain by using stimulated Raman scattering in the optical fiber. It is a high-power fiber laser technology with flexible wavelength, scalability, and the ability to span wavelength spectra, and is also an important means to obtain special wavelength output.

[0003] The semi-open cavity structure composed of a short single-mode optical fiber and a point mirror at the pump end can greatly reduce the laser output threshold of the random Raman fiber laser. Currently, a fiber grating corresponding to the output random laser wavelength is usually placed at one end of the single-mode optical fiber, or a broadband mirror is connected through a wavelength division multiplexer to provide point feedback for each level of Raman random laser, forming a semi-open cavity structure. However, the preparation process of special wavelength fiber gratings is complex and costly, and the wavelength tunability of the randomly fiber laser based on fiber grating feedback is poor. For the randomly fiber laser using a wavelength division multiplexer to connect a broadband mirror, the working wavelength tuning range is limited by the wavelength conduction range of the wavelength division multiplexer, and the output laser power is limited by the power that the wavelength division multiplexer can withstand. Summary of the Invention

[0004] The present invention provides a randomly fiber laser with continuously tunable wavelength for the problems existing in the prior art.

[0005] A randomly fiber laser with continuously tunable wavelength includes a first pump combining coupler, whose signal end is connected to a first 1:1 coupler, and the pump end is connected to a first laser diode pump source; the common end of the first pump combining coupler is sequentially connected to a first ytterbium-doped fiber, a Raman fiber, and an optical fiber bevel end face; the first input end of the first 1:1 coupler is connected to a broadband fiber loop mirror, and the second input end is connected to a laser seed source;

[0006] The laser seed source is used to output ytterbium-doped random laser with continuously tunable wavelength.

[0007] Further, the laser seed source includes a second pump combining coupler, whose pump end is connected to a second laser diode pump source, and the signal end is connected to a wavelength-selectable point mirror; the common end of the second pump combining coupler is sequentially connected to a second ytterbium-doped fiber and a single-mode fiber.

[0008] Further, an isolator is arranged between the laser seed source and the first 1:1 coupler.

[0009] Furthermore, the broadband fiber loop mirror is composed of a second 1:1 coupler, and the two output ends of the second 1:1 coupler are directly connected.

[0010] Furthermore, the wavelength-selectable point mirror includes a wavelength tunable filter and a third 1:1 coupler.

[0011] Furthermore, the tuning range of the laser seed source is 1040 nm to 1090 nm, the output power is greater than 500 mW, and the output laser frequency has no longitudinal mode.

[0012] Furthermore, the Raman fiber is one of dispersion-shifted fiber and single-mode fiber.

[0013] Furthermore, both the first laser diode pump source and the second laser diode pump source are 976 nm diode pump sources.

[0014] Furthermore, the length of the second ytterbium-doped fiber is 6 m, and the length of the single-mode fiber is 5 km.

[0015] Furthermore, the length of the first ytterbium-doped fiber is 7 m, and the length of the Raman fiber is 4 km.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) The structure of the present invention is simple and compact, without the need for special wavelength fiber gratings corresponding to each order of Stokes light at high cost, nor the need for wavelength division multiplexers with low power tolerance.

[0018] (2) The present invention avoids the problem of wavelength limitation caused by using a wavelength division multiplexer to couple the Raman pump source between the amplified ytterbium-doped random fiber laser and the Raman fiber.

[0019] (3) The present invention adopts a wavelength tunable laser seed source and a broadband fiber loop mirror connected to the signal end of the pump combiner, which can reflect each order of Stokes light and output a laser with continuously tunable wavelength, avoiding the use of multiple specially wavelength-customized fiber gratings. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the random fiber laser with continuously tunable wavelength of the present invention.

[0021] Figure 2 It is a spectrogram of the first four orders of Stokes light in the embodiment of the present invention.

[0022] In the figure: 1 - Second laser diode pump source, 2 - Wavelength tunable filter, 3 - Third 1:1 coupler, 4 - Second pump beam combiner, 5 - Second ytterbium-doped fiber, 6 - Single-mode fiber, 7 - Isolator, 8 - Second 1:1 coupler, 9 - First 1:1 coupler, 10 - First pump beam combiner, 11 - First laser diode pump source, 12 - First ytterbium-doped fiber, 13 - Raman fiber, 14 - Fiber beveled end face. Specific embodiments

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] As Figure 1 shown, a wavelength continuously tunable random fiber laser includes a first pump beam combiner 10, whose signal end is connected to a first 1:1 coupler and whose pump end is connected to a first laser diode pump source 11; the common end of the first pump beam combiner 10 is sequentially connected to a first ytterbium-doped fiber 12, a Raman fiber 13, and a fiber beveled end face 14; the first input end of the first 1:1 coupler is connected to a broadband fiber loop mirror, and the second input end is connected to a laser seed source; the broadband fiber loop mirror is composed of a second 1:1 coupler 8, and the two output ends of the second 1:1 coupler are directly connected. The Raman fiber 13 is one of a dispersion-shifted fiber and a single-mode fiber, and other fibers with Raman gain can also be used.

[0025] The laser seed source is used to output wavelength continuously tunable ytterbium-doped random laser. The laser seed source includes a second pump beam combiner 4, whose pump end is connected to a second laser diode pump source 1 and whose signal end is connected to a wavelength selectable point mirror; the common end of the second pump beam combiner 4 is sequentially connected to a second ytterbium-doped fiber 5 and a single-mode fiber 6. An isolator 7 is provided between the laser seed source and the first 1:1 coupler 9. The tuning range of the laser seed source is 1040 nm to 1090 nm.

[0026] The second laser diode pumping source 1 is connected to the pumping end of the second pumping beam combiner 4, and the signal end of the second pumping beam combiner 4 is connected to a wavelength-selective point mirror composed of a wavelength tunable filter 2 and a third 1:1 coupler 3. Through the ytterbium-doped gain effect of the second ytterbium-doped fiber 5 and the random Rayleigh scattering feedback effect of the single-mode fiber 6, a continuously tunable ytterbium-doped random laser of 1040 nm - 1090 nm is output. The second 1:1 coupler 8, the first 1:1 coupler 9, the first pumping beam combiner 10, the first laser diode pumping source 11, the first ytterbium-doped fiber 12, the Raman fiber 13, and the fiber bevel end face 14 together form a high-order Raman random fiber laser. The input ytterbium-doped random laser is amplified in the first ytterbium-doped fiber 12 and then serves as the pumping source of the cascaded Raman random fiber laser in the Raman fiber 13. The signal end of the first pumping beam combiner 10 is connected to the first 1:1 coupler 9. The first input end of the first 1:1 coupler 9 is connected to a broadband fiber loop mirror formed by directly connecting the two output ends of the second 1:1 coupler 8 to provide point feedback for each order of Stokes light. The second input end of the first 1:1 coupler 9 is connected to a laser seed source. A cascaded Raman random laser output is formed by combining with the random Rayleigh scattering effect in the Raman fiber 13. The wavelength tuning of the cascaded Raman random fiber laser is achieved by tuning the wavelength of the ytterbium-doped random fiber laser seed source. The end of the Raman fiber 13 is a fiber bevel end face 14, which is the laser output port, and the reflectivity of this end face is less than 10 -5 .

[0027] The following takes the first to fourth-order Stokes spectra as examples for illustration, and the spectrogram is as shown in Figure 2 . The first laser diode pumping source 11 and the second laser diode pumping source 1 are both 976 nm diode pumping sources. The wavelength range of the output ytterbium-doped random laser by adjusting the mechanical knob of the wavelength tunable filter 2 is 1040 nm - 1090 nm. The length of the first ytterbium-doped fiber 12 is 7 m; the length of the Raman fiber 13 is 4 km; the length of the second ytterbium-doped fiber 5 is 6 m; the length of the single-mode fiber 6 is 5 km. The two output ends of the second 1:1 coupler 8 are directly connected to form a broadband fiber loop mirror to provide point feedback for each order of Stokes light. The first-order Stokes light with a continuously tunable wavelength range of 1100 nm - 1150 nm can be achieved. The second-order Stokes light of 1150 nm - 1200 nm, the third-order Stokes light of 1200 nm - 1280 nm, and the fourth-order Stokes light of 1280 nm - 1350 nm. It can be seen that by increasing the pumping power, higher-order Stokes light can be lasered, and ultimately a continuously tunable cascaded Raman random laser of 1 μm - 2 μm can be achieved.

[0028] The tunable wavelength ytterbium-doped random fiber laser seed source of the present invention is amplified by a ytterbium-doped fiber amplifier and then excites cascaded Raman fiber random laser in a Raman fiber. A broadband fiber loop mirror connected to the signal end of a pump combiner is used to provide feedback for the cascaded Raman fiber random laser, realizing a random fiber laser with continuously tunable wavelength.

[0029] The structure of the present invention is simple and compact, without the need for special wavelength fiber gratings corresponding to each order of Stokes light at high cost; nor the need for a wavelength division multiplexer with low power tolerance. After the tunable wavelength ytterbium-doped random laser seed source is injected into the first ytterbium-doped fiber through a first 1:1 coupler for power amplification, it acts as a pump source for the cascaded Raman random fiber laser in the Raman fiber. A broadband fiber loop mirror formed by directly connecting the two output ends of a second 1:1 coupler, which is connected to the signal end of the first pump combiner through the first 1:1 coupler, provides point feedback for each order of Stokes light, and combines with the random Rayleigh scattering effect in the Raman fiber to form cascaded Raman random laser output. The wavelength of the cascaded Raman random fiber laser is tuned by tuning the wavelength of the ytterbium-doped random fiber laser seed source. It avoids the problem of wavelength limitation caused by using a wavelength division multiplexer to couple the Raman pump source between the amplified ytterbium-doped random fiber laser and the Raman fiber. In addition, due to the use of a broadband fiber loop mirror, it can reflect each order of Stokes light and output a continuously tunable wavelength, also avoiding the use of multiple specially wavelength-customized fiber gratings. This solution not only solves the technical problems of complex structure and high cost brought by using special wavelength fiber gratings and wavelength division multiplexers in the prior art, but also solves the technical problem of limited output wavelength, and has the advantages of simple structure and low cost. Connect the signal end of the second pump combiner in the tunable wavelength ytterbium-doped fiber laser seed source to a wavelength-selectable point mirror based on a third 1:1 coupler and a wavelength tunable filter. By rotating the mechanical knob of the wavelength tunable filter, the output wavelength of the cascaded Raman random laser can be flexibly adjusted.

Claims

1. A randomly fiber laser with continuously tunable wavelength, characterized in that, Comprising a first pump combiner (10), whose signal end is connected to a first 1:1 coupler (9), and whose pump end is connected to a first laser diode pump source (11); the common end of the first pump combiner (10) is sequentially connected to a first ytterbium-doped fiber (12), a Raman fiber (13), and an optical fiber bevel end face (14); the first input end of the first 1:1 coupler (9) is connected to a broadband fiber loop mirror, and the second input end is connected to a laser seed source; the broadband fiber loop mirror is constituted by a second 1:1 coupler (8), and the two output ends of the second 1:1 coupler (8) are directly connected; The laser seed source is used to output a ytterbium-doped random laser with continuously tunable wavelength; the laser seed source includes a second pump combiner (4), whose pump end is connected to a second laser diode pump source (1), and whose signal end is connected to a wavelength-selectable point mirror; The wavelength-selectable point mirror includes a wavelength tunable filter (2) and a third 1:1 coupler (3); the common end of the second pump combiner (4) is sequentially connected to a second ytterbium-doped fiber (5) and a single-mode fiber (6); An isolator (7) is provided between the laser seed source and the first 1:1 coupler (9).

2. The wavelength continuously tunable random fiber laser according to claim 1, wherein The tuning range of the laser seed source is 1040 nm to 1090 nm, the output power is greater than 500 mW, and the output laser frequency has no longitudinal mode.

3. A randomly fiber laser with continuously tunable wavelength according to claim 1, characterized in that The Raman fiber (13) is one of a dispersion-shifted fiber and a single-mode fiber.

4. A randomly fiber laser with continuously tunable wavelength according to claim 1, characterized in that, Both the first laser diode pump source (11) and the second laser diode pump source (1) are 976 nm diode pump sources.

5. A randomly tunable fiber laser with continuously tunable wavelength according to claim 1, characterized in that The length of the second ytterbium-doped fiber (5) is 6 m, and the length of the single-mode fiber (6) is 5 km.

6. The wavelength continuously tunable random fiber laser according to claim 1, characterized in that, The length of the first ytterbium-doped fiber (12) is 7 m, and the length of the Raman fiber (13) is 4 km.

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