CN104577675B - Linear cavity multi-wavelength thulium-doped fiber laser based on M Z interferometers - Google Patents

Abstract

The linear cavity multi-wavelength thulium-doped fiber laser based on M-Z interferometer belongs to the field of optical information technology. The a end of the division multiplexer is connected, the b end and c end of the wavelength division multiplexer are respectively connected with the single-mode thulium-doped fiber and the first polarization controller, and the other end of the first polarization controller is connected with the first coupler d1 end connection, the d3 end of the first coupler is connected to the second polarization controller, the other end of the second polarization controller is connected to the polarization-maintaining thulium-doped fiber, the other end of the polarization-maintaining thulium-doped fiber is connected to the e1 end of the second coupler, the second The e2 end of the second coupler is connected to the d4 end of the first coupler, the e3 end of the second coupler is connected to the e4 end, the d2 end of the first coupler is used as the output end, the other end of the thulium-doped fiber is connected to the f1 end of the circulator connection, the f2 end of the circulator is connected with the f3 end to form an all-fiber laser linear cavity laser.

Description

Linear cavity multi-wavelength Thulium-doped fiber laser based on M-Z interferometer

technical field

The invention relates to a linear cavity multi-wavelength thulium-doped fiber laser based on a Mach-Zehnder (M-Z) interferometer, belonging to the technical field of optical information.

Background technique

Thulium-doped fiber lasers work in the eye-safe band, and have good application prospects in the fields of lidar, remote sensing, medical treatment, free space optical communication, etc., and have become one of the most promising laser technologies today.

Multi-wavelength thulium-doped fiber laser can replace the complex structure composed of multiple traditional lasers in wavelength division multiplexing, and meet the requirements of multiple channels at the same time, which can greatly simplify the system structure and reduce costs.

At present, the invention and research on multi-wavelength thulium-doped fiber lasers are still in their infancy. The existing multi-wavelength thulium-doped fiber lasers mainly have the following schemes: 1. Using nonlinear polarization rotation and four-wave mixing effect; 2. Using Non-linear fiber loop mirror; 3. High birefringence fiber Bragg grating is used. Both scheme 1 and scheme 2 are based on the nonlinear effect, which can effectively suppress the mode competition, but it needs to introduce a highly nonlinear optical fiber of more than 100 meters into the laser cavity, which has a high threshold, poor stability, and complex structure, which is not conducive to device integration and integration. miniaturization. The number of wavelengths of the multi-wavelength laser obtained in Scheme 3 is limited, and the number of wavelengths cannot be tuned, so it is difficult to generate more than 3 wavelengths of output. Therefore, simplifying the structure of multi-wavelength fiber lasers and effectively suppressing the mode competition caused by the uniform broadening of thulium atoms is the most effective way to improve the performance of multi-wavelength fiber lasers and reduce costs.

Contents of the invention

In order to solve the technical problems of the existing multi-wavelength thulium-doped fiber laser with high threshold, poor stability and complex structure, the present invention proposes a linear cavity multi-wavelength thulium-doped fiber laser based on an M-Z interferometer.

A linear cavity multi-wavelength thulium-doped fiber laser based on an M-Z interferometer, including a laser pump source, a wavelength division multiplexer, a single-mode thulium-doped fiber, a first polarization controller, a second polarization controller, a first coupler, and a second polarization controller Two couplers, polarization maintaining thulium-doped fiber and circulator;

It is characterized in that the laser pumping source is connected to the a-end of the wavelength division multiplexer, the b-end and c-end of the wavelength division multiplexer are respectively connected to the single-mode thulium-doped optical fiber and the first polarization controller, and the first polarization controller The other end of the first coupler is connected to the d1 end of the first coupler, the d3 end of the first coupler is connected to the second polarization controller, the other end of the second polarization controller is connected to the polarization-maintaining thulium-doped fiber, and the other end of the polarization-maintaining thulium-doped fiber is connected to The e1 end of the second coupler is connected, the e2 end of the second coupler is connected to the d4 end of the first coupler, the e3 end of the second coupler is connected to the e4 end, and the d2 end of the first coupler is used as the output end. The other end of the thulium fiber is connected to the f1 end of the circulator, and the f2 end of the circulator is connected to the f3 end to form an all-fiber laser linear cavity laser structure.

The pump source adopts a 1573nm laser diode, and the a, b, and c terminals of the wavelength division multiplexer are respectively the 1570nm terminal, the common terminal and the 2000nm terminal.

The length of the single-mode thulium-doped fiber is preferably 4m, and the length of the polarization-maintaining thulium-doped fiber is preferably 4m.

Beneficial effects of the present invention: the present invention adopts a M-Z all-fiber interferometer with a novel structure, which greatly improves the stability of the output laser, reduces the threshold power, simplifies the structure, and adjusts the second polarization controller (4-2) Changing the light intensity ratio of the two interference arms can change the peak intensity of the M-Z interferometer filter, so that the number of wavelengths can be adjusted from 1 to 4, the wavelength interval is 2.3nm, and the single wavelength linewidth is 0.045nm. The wavelength interval can be kept by changing The length of the polarizing fiber 6 is changed, and the polarization-maintaining thulium-doped fiber 6 acts as a phase retarder and a saturable absorber at the same time, which can absorb the self-excited oscillation mode in the linear cavity, weaken the mode competition between the self-excited oscillation mode and the multi-wavelength laser, and optimize the output Spectrum, improve the stability of the output laser, the wavelength stability of output multi-wavelength laser within one hour is better than 0.02nm, and the power stability is better than 0.5dB. The single-wavelength tunable range is close to 20nm.

The invention has the advantages of simple structure, low cost, low threshold value, high stability and easy integration, and has good application prospects in the fields of wavelength division multiplexing, optical fiber sensing, optical communication and the like.

Description of drawings

FIG. 1 is a schematic structural diagram of a linear cavity multi-wavelength thulium-doped fiber laser based on an M-Z interferometer according to the present invention.

In Fig. 2, (a) is the single-wavelength laser output spectrum within one hour; (b) is the dual-wavelength laser output spectrum within one hour; (c) is the three-wavelength laser output spectrum within one hour; (d) is the four-wavelength laser output spectrum within one hour. wavelength laser output spectrum.

Figure 3 is the 1.91μm band single-wavelength laser spectrum.

Figure 4 shows the single-wavelength tunable range.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the linear cavity multi-wavelength thulium-doped fiber laser based on the M-Z interferometer includes a laser pump source 1, a wavelength division multiplexer 2, a single-mode thulium-doped fiber 3, a first polarization controller 4-1, A second polarization controller 4-2, a first coupler 5-1, a second coupler 5-2, a polarization-maintaining thulium-doped fiber 6, and a circulator 7.

All parts of the laser are connected by optical fiber fusion. The 1573nm laser pump source 1 is connected to the a-end of the wavelength division multiplexer 2, and the b-end of the wavelength division multiplexer 2 is connected to the end of the single-mode thulium-doped fiber 3. The c end of the multiplexer 2 is connected to one end of the first polarization controller 4-1, the other end of the first polarization controller 4-1 is connected to the d1 end of the first coupler 5-1, and the single-mode thulium-doped fiber 3 The other end is connected to the f1 end of the circulator 7, and the f2 end of the circulator 7 is connected to the f3 end to form a feedback loop structure.

Among them, the maximum output of the 1573nm laser diode pump source 1 is 250mW, and the terminals a, b and c of the wavelength division multiplexer 2 are respectively the 1570nm terminal, the common terminal and the 2000nm terminal. The length of the single-mode thulium-doped fiber 3 is optimized to 4m, which corresponds to the highest conversion efficiency under the pumping condition of 250mW.

In the present invention, the M-Z interferometer includes a 3dB first coupler 5-1, a 3db second coupler 5-2, a second polarization controller 4-2, a polarization-maintaining thulium-doped fiber 6, and d3 of the first coupler 5-1 One end is connected with the second polarization controller 4-2, and the other end of the second polarization controller 4-2 is connected with the polarization-maintaining thulium-doped fiber 6, and the length of the polarization-maintaining thulium-doped fiber 6 is optimized to 4m, and the second polarization controller 4- 2 forms a variable phase delay with the polarization-maintaining thulium-doped fiber 6, and the other end of the polarization-maintaining thulium-doped fiber 6 is connected to the e1 end of the second coupler 5-2 to form an interference arm of the Mach-Zendr interferometer, and the second coupling The e3 and e4 ends of the coupler 5-2 are connected to form a reflective optical path, and the e2 end of the second coupler 5-2 is connected to the d4 end of the first coupler to form another interference arm of the M-Z interferometer. The first coupler The d2 terminal is used as the output terminal.

Turn on the laser pump source 1, and adjust the power of the laser pump source 1 within the range of 175mW-250mW to change the laser output power. The pumping light is injected into the 4m single-mode thulium-doped fiber 3 through the wavelength division multiplexer 2, and the generated 2 μm band back-amplified spontaneous emission light passes through the first polarization controller 4-1, and then passes through the d1 of the first coupler 5-1 The end is injected into the M-Z interference filter, and the amplified spontaneous emission light is divided into two parts with the same intensity by the first coupler 5-1, and propagates through two interference arms respectively, wherein the light propagating along the interference arm from the d3 end to the e1 end passes through the second An additional phase delay is generated after the polarization controller 4-2 and the polarization-maintaining thulium-doped fiber 6, resulting in a fixed optical path difference for the amplified spontaneous emission light passing through the two arms, forming interference at the second coupler 5-2, and passing through the second After reflection by the coupler 5-2, interference is formed again at the output of the first coupler 5-1, thereby realizing comb filtering, and part of the broadband light after filtering is returned to the cavity by the d1 end of the first coupler and then fed back by the circulator 7. Therefore, the continuous oscillation in the linear cavity forms multi-wavelength laser output.

Figure 2 (a), (b), (c), and (d) are the output spectra of single wavelength, double wavelength, three wavelengths, and four wavelengths in one hour, respectively, and the recording interval is 10 minutes. By adjusting the second polarization controller (4-2) By changing the light intensity ratio of the two interference arms, the M-Z interferometer filter peak intensity can be changed, thereby realizing wavelength tuning. The wavelength interval can be tuned by changing the length of the polarization-maintaining thulium-doped fiber 6, and the tuning rule is: a long optical fiber corresponds to a short wavelength interval, which shows a linear variation law.

Figure 3 shows the output spectrum of the single-wavelength laser at 1.91 μm, the side mode suppression ratio is 45dB, and the 3dB linewidth is 0.045nm.

The reference of the second polarization controller 4-2 and the polarization-maintaining thulium-doped fiber 6 effectively optimizes the filtering characteristics of the M-Z interferometer. The comb filter period of the traditional reflective M-Z interferometer needs to be changed by changing the length difference between the two interference arms. , The operation is cumbersome, and the filter interval of more than 1nm is usually achieved, and the arm length difference needs to be accurate to within 0.1mm, which requires high technology. In this structure, only by changing the length of the polarization-maintaining thulium-doped optical fiber 6, the filter period can be changed, and the operation is simple and effective. Among them, another function of the polarization-maintaining thulium-doped fiber 6 is as a saturable absorber, which can absorb the self-excited oscillation mode in the linear cavity, weaken the mode competition between the self-excited oscillation mode and multi-wavelength laser, optimize the output spectrum, and improve the stability of the output laser. Sex, its wavelength stability is less than 0.02nm, power stability is less than 0.5dB.

Adjust the second polarization controller 4-2 to keep the number of output wavelengths at one, and then adjust the first polarization controller 4-1 to achieve a single-wavelength tuning range (1895nm-1915nm) close to 20nm. As shown in Figure 4.

Claims (3)

1. the linear cavity multi-wavelength thulium-doped fiber laser based on M-Z interferometers, including laser pumping source (1), wavelength division multiplexer (2), single mode thulium doped fiber (3), the first Polarization Controller (4-1), the second Polarization Controller (4-2), the first coupler (5-1), Second coupler (5-2), polarization-maintaining thulium doped fiber (6) and circulator (7)；

It is characterized in that, laser pumping source (1) is connected with a ends of wavelength division multiplexer (2), the b ends and c ends point of wavelength division multiplexer (2) It is not connected with single mode thulium doped fiber (3) and the first Polarization Controller (4-1), the other end of the first Polarization Controller (4-1) and One coupler (5-1) d1 ends are connected, the d3 ends of the first coupler (5-1) and the second Polarization Controller (4-2) connection, the second polarization Controller (4-2) other end and polarization-maintaining thulium doped fiber (6) connection, polarization-maintaining thulium doped fiber (6) other end and the second coupler (5-2) The connection of e1 ends, the d4 ends connection of the e2 ends of the second coupler (5-2) and the first coupler (5-1), the second coupler (5-2) E3 ends and the connection of e4 ends, the d2 ends of the first coupler (5-1) as output end, thulium doped fiber (3) other end and circulator (7) F1 ends are connected, the f2 ends of circulator (7) and the connection of f3 ends, form full optical fiber laser linear laser cavity structure.

2. the linear cavity multi-wavelength thulium-doped fiber laser according to claim 1 based on M-Z interferometers, pumping source (1) Using 1573nm laser diode, a, b, c end of wavelength division multiplexer (2) are respectively 1570nm ends, common port and 2000nm ends.

3. the linear cavity multi-wavelength thulium-doped fiber laser according to claim 1 based on M-Z interferometers, single mode mixes thulium light Fine (3) length preferred 4m, polarization-maintaining thulium doped fiber (6) preferred 4m of length.