MULTI-WAVELENGTH AND SINGLE-FREQUENCY Q-SWITCHING OPTICAL FIBER LASER DEVICE

Abstract

The invention discloses a multi-wavelength and single-frequency Q-switching optical fiber laser device. The laser device comprises a saturable absorber, a high gain optical fiber, a polarization-maintaining multi-wavelength narrow-band fiber Bragg grating, a resonant cavity temperature control module, a polarization-maintaining wavelength division multiplexer, a pump source and a polarization-maintaining light isolator. By taking a highly doped phosphate optical fiber as a laser gain medium, two ends of the optical fiber device are connected with the saturable absorber and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating respectively to form a short linear laser cavity. A short cavity length of the short linear laser cavity can realize single longitudinal mode operation of laser in the resonant cavity, and meanwhile, a stable multi-wavelength and single-frequency pulse laser output is realized in the resonant cavity by combining multi-wavelength resonance caused by the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating with passive Q-switching performance of the saturable absorber in the cavity. The multi-wavelength single-frequency Q-switching optical fiber laser device of the invention realizes output of a plurality of wavelength pulse laser with adjusted repeated frequency simultaneously, and the laser in each wavelength is maintained in single-frequency operation, such that the multi-wavelength single-frequency Q-switching optical fiber laser device can be widely applied to aspects of laser radar, laser sensing, gas detection and the like.

Claims

1. A multi-wavelength and single-frequency Q-switching optical fiber laser device, characterized in that, comprising: a Bragg laser resonant cavity, a cavity temperature control module (2), a high gain optical fiber (3), a polarization-maintaining wavelength division multiplexer (5), a pump source (6) and a polarization-maintaining light isolator (7), the Bragg laser resonant cavity comprises the high gain optical fiber (3), a saturable absorber (1) and a polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4), two ends of the high gain optical fiber (3) are connected with the saturable absorber (1) and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4) respectively, and the Bragg laser resonant cavity is placed in the cavity temperature control module (2) to carry out temperature control; a pump end of the polarization-maintaining wavelength division multiplexer (5) is connected with the pump source (6), a common end of the polarization-maintaining wavelength division multiplexer (5) is connected with the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4), and a signal end of the polarization-maintaining wavelength division multiplexer (5) is connected with an input end of the polarization-maintaining light isolator (7).

2. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that a relaxation time of the saturable absorber (1) is shorter than 20 ps, a reflectivity of the saturable absorber to a laser signal light with each wavelength is greater than 80%, and a saturable absorber thereof to a pump light is smaller than 20%.

3. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that the high gain optical fiber (3) is a rare earth doped single mode glass optical fiber, and a fiber core component of the high gain optical fiber (3) comprises more than one of phosphate glass, germanate glass, silicate glass and fluoride glass; the fiber core of the high gain optical fiber (3) is doped with luminous ions in high concentration, and the luminous ions are a complex of one or more of lanthanide ions and transition metal ions; and a doping concentration of the luminous ions is greater than 1*1019 ions/cm3 and the luminous ions are uniformly doped in the fiber core of the high gain optical fiber (3).

4. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4) is structured such that two or more Bragg gratings with different center wavelengths are written onto a polarization-maintaining optical fiber, such that the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating has selective comb reflection on a laser signal wavelength.

5. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that a 3 dB reflective bandwidth of each of reflective sections of the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4) is not greater than 0.08 nm, and a reflectivity of the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating to the laser signal light wavelength is greater than 50%.

6. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating (4) and the high gain optical fiber (3) are directly butt-coupled by grinding and polishing optical fiber end surfaces thereof respectively or are weld-coupled by means of an optical fiber fusion splicer.

7. The multi-wavelength and single-frequency Q-switching optical fiber laser device according to claim 1, characterized in that the cavity temperature control module (2) comprises a semiconductor refrigerator (TEC) and a control precision of the cavity temperature control module (2) is +/−0.01° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a structural schematic diagram of the multi-wavelength and single-frequency Q-switching optical fiber laser device provided by the present invention.

[0016] In the drawings, 1—saturable absorber, 2—resonant cavity temperature control module, 3—high gain optical fiber, 4—polarization-maintaining multi-wavelength narrow-band fiber Bragg grating, 5—polarization-maintaining wavelength division multiplexer, 6—pump source, 7—polarization-maintaining light isolator.

DETAILED DESCRIPTION

[0017] Further detailed description will be made on the present invention below by specific embodiments, and it should be noted that the claimed scope of protection of the present invention is not limited to the scope represented by the embodiments.

[0018] As shown in the FIG. 1, the multi-wavelength and single-frequency Q-switching optical fiber laser device includes the saturable absorber 1, the high gain optical fiber 3, the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating 4, the resonant cavity temperature control module, the pump source 6, the polarization-maintaining wavelength division multiplexer 5, and the polarization-maintaining light isolator 7. A structural relationship among the parts is as follows: one end of the high gain optical fiber 3 is connected with the saturable absorber 1 and the other end of the high gain optical fiber 3 is connected with one end of the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating 4, the saturable absorber, the high gain optical fiber and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating are connected to form the distributed Bragg single-frequency laser resonant short cavity, i.e., the Bragg laser resonant cavity, and the Bragg laser resonant cavity is placed in the resonant cavity temperature control module 2 for precise temperature control. The pump end of the polarization-maintaining wavelength division multiplexer 5 is connected with a tail fiber of the pump source 6, the common end of the polarization-maintaining wavelength division multiplexer 5 is connected with the other end of the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating 4, and the signal end of the polarization-maintaining wavelength division multiplexer 5 is connected with the input end of the polarization-maintaining light isolator 7. The multi-wavelength and single-frequency Q-switching optical fiber laser generated by the Bragg laser resonant cavity finally is output via the output end of the polarization-maintaining light isolator 7.

[0019] The laser working medium high gain optical fiber 3 used in the embodiment is a thulium-doped phosphate glass optical fiber. The doping concentration of thulium ions of the phosphate optical fiber in the fiber core is 4.5*10.sup.20 ions/cm.sup.3 and a using length thereof is 2 cm. The saturable absorber 1 is a semiconductor saturable adsorbing mirror based on group III-V semiconductors, the reflective bandwidth is 1880-2040 nm, the reflectivity near 1950 nm is 90% and the relaxation time is 10 ps. The polarization-maintaining multi-wavelength narrow-band fiber Bragg grating 4 in the embodiment is structured such that two Bragg optical gratings are written into a same position of the polarization-maintaining optical fiber, such that a reflectance spectrum of the narrow-band optical Bragg grating has four reflecting peaks at a wavelength interval of 0.4 nm, wherein slow axis center wavelengths are respectively 1950.4 nm and 1951.2 nm and fast axis enter wavelengths are respectively 1950 nm and 1950.8 nm, the 3 dB reflective bandwidth of the reflective peak at each wavelength is 0.08 nm, and the reflectivity of the laser signal wavelength thereof is 65%. The saturable absorber 1 is abutted and coupled with the thulium-doped phosphate glass optical fiber on end surface, and the thulium-doped phosphate glass optical fiber and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating 4 are abutted and coupled via its end surface respectively, and the saturable absorber, the thulium-doped phosphate glass optical fiber and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating are combined to form the Bragg laser resonant cavity. The Bragg laser resonant cavity is placed in a metal copper tank, and the metal copper tank has a good wrapping property on the resonant cavity and can fix and protect the resonant cavity, and the resonant cavity control temperature module 2 formed by the TEC cooler controls the temperature of the whole Bragg laser resonant cavity precisely, and the control precision is +/−0.01° C. The pump source 6 with the working wavelength of 1610 nm is selected as well, and the pump output power thereof is 200 mW. The pump source 6 plays a role of pumping and transporting the Bragg laser resonant cavity via the 1610/1950 nm polarization-maintaining wavelength division multiplexer 5, and finally, the multi-wavelength and single-frequency Q-switching pulse laser output by the Bragg laser resonant cavity is output by the polarization-maintaining isolator 7 with a working center wavelength of 1950 nm. Based on the above mode, output of the Q-switching pulse optical fiber laser with multi-wavelengths (the working center wavelengths are respectively 1950, 1950.4, 1950.8 and 1951.2 nm) operating in the single longitudinal mode in each wavelength can be realized finally.