A low-pumping-threshold narrow-linewidth pulsed fiber laser

Abstract

The application discloses a low-pumping threshold narrow-line-width pulse fiber laser, and belongs to the technical field of lasers, which comprises a pumping laser, a wavelength division multiplexer, an erbium-doped optical fiber, an optical isolator, a low-pumping threshold pulse generation unit, an optical polarization controller, an optical coupler, a photodetector and a data processing unit; the wavelength division multiplexer, the erbium-doped optical fiber, the optical isolator, the low-pumping threshold pulse generation unit, the optical polarization controller and the optical coupler are sequentially connected to form a ring resonant cavity; the pumping laser is connected to the wavelength division multiplexer; and the optical coupler is sequentially connected to the photodetector and the data processing unit. The low-pumping threshold pulse generation unit is used to make the light intensity in the ring resonant cavity rapidly reach the threshold condition required by pulse output with lower pumping power, so that stable narrow-line-width pulse laser output is realized, the operation energy consumption and equipment cost are reduced, and the stability of output spectrum is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber lasers, and particularly relates to a narrow-linewidth pulse fiber laser with a low pump threshold. BACKGROUND

[0002] At present, some narrow-linewidth pulse fiber lasers can simultaneously obtain picosecond or femtosecond order ultra-short pulse width and picometer order spectral linewidth, and have important application value in the fields of differential absorption laser radar, Doppler laser radar, precise optical coherent detection and high-resolution sensing.

[0003] There are two methods commonly used to realize narrow-linewidth pulse laser: one is to inject a narrow-linewidth seed laser into a pulse fiber laser; and the other is to directly generate pulse laser in a narrow-linewidth fiber laser resonant cavity. However, the narrow-linewidth pulse fiber lasers developed according to the two methods mostly have a high pump threshold, and the output power of the pump laser is also high, generally in the order of hundreds of milliwatts. This will lead to increased energy consumption and cost of the narrow-linewidth pulse fiber laser, limit the application scenarios, and also exist potential stability and reliability problems. Therefore, it is of great significance to develop a narrow-linewidth pulse laser with low power consumption, high stability and low pump threshold. SUMMARY

[0004] The present application aims to overcome the problems of high pump threshold, high energy consumption and low stability of the prior art narrow-linewidth pulse fiber laser, and provides a narrow-linewidth pulse fiber laser with a low pump threshold.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a narrow-linewidth pulse fiber laser with a low pump threshold is provided, characterized in that it comprises a pump laser, a wavelength division multiplexer, an erbium-doped fiber, an optical isolator, a low-pump-threshold pulse generation unit, an optical polarization controller, an optical coupler, a photodetector and a data processing unit, the wavelength division multiplexer, the erbium-doped fiber, the optical isolator, the low-pump-threshold pulse generation unit, the optical polarization controller and the optical coupler are sequentially connected to form a ring resonant cavity, the pump laser is connected to the wavelength division multiplexer, and the optical coupler is sequentially connected to the photodetector and the data processing unit.

[0006] The low-pump-threshold pulse generation unit comprises a circulator, an erbium-doped short fiber, a fiber grating and a saturable absorber, the input port of the circulator is connected to the output port of the optical isolator, the first output port of the circulator is connected to the input port of the erbium-doped short fiber, the second output port of the circulator is connected to the saturable absorber, the output port of the erbium-doped short fiber is connected to the fiber grating, and the saturable absorber is connected to the input port of the optical polarization controller.

[0007] In one embodiment, the length of the erbium-doped short optical fiber is 5–20 cm.

[0008] In one embodiment, the saturable absorber is a thin film made of a mixture of single-walled carbon nanotubes and polyvinyl alcohol, and the saturable absorber is integrated into the annular resonant cavity via an optical fiber socket.

[0009] In one embodiment, the fiber grating has a center wavelength of 1547 nm, a reflectivity of 92%, and a 3 dB bandwidth of 0.25 nm.

[0010] In one embodiment, the pump laser source is a 980nm continuous light laser.

[0011] In one embodiment, the wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer.

[0012] In one embodiment, the erbium-doped fiber is 1.5m long.

[0013] In one embodiment, 90% of the output port of the optical coupler is connected to the 1550nm output port of the wavelength division multiplexer, and 10% of the output port of the optical coupler is connected to the photodetector.

[0014] In summary, this invention discloses a low-pump-threshold, narrow-linewidth pulsed fiber laser. Through the low-pump-threshold pulse generation unit, the light intensity within the ring resonant cavity quickly reaches the threshold condition required for pulse output with relatively low pump power, effectively achieving stable narrow-linewidth pulsed laser output. The laser of this invention is simple to fabricate, can effectively achieve precise output with both narrow spectral width and narrow pulse width, and also possesses a low pump-threshold characteristic, greatly reducing operating energy consumption and equipment costs while ensuring the stability of the output spectrum.

[0015] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a narrow-linewidth pulsed fiber laser with a low pump threshold provided by the present invention.

[0017] Figure 2 for Figure 1 A schematic diagram of the structure of the low-to-medium pump threshold pulse generation unit.

[0018] Figure 3 This is the spectrum of the narrow-linewidth pulsed laser output of the laser of the present invention with a 3dB linewidth of 22.4pm when the pump power is 40mW.

[0019] Figure 4The pulse repetition sequence of the laser of the present application at a pump power of 40 mW and a pulse interval of 102 ns.

[0020] Figure 5 The RF spectrum diagram of the laser output of the laser of the present application at a pump power of 40 mW and a repetition frequency of 5.322 MHz.

[0021] Figure 6 The stability test diagram of the laser output spectrum of the laser of the present application recorded every 5 minutes at a pump power of 40 mW. DETAILED DESCRIPTION

[0022] In order to make the purpose and technical solutions of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the scope of protection of the present application.

[0023] Figure 1 The structural schematic diagram of a low-pump-threshold narrow-linewidth pulsed fiber laser in the present application. As shown in Figure 1 the low-pump-threshold narrow-linewidth pulsed fiber laser comprises a pump laser 1, a wavelength division multiplexer 2, an erbium-doped fiber 3, an optical isolator 4, a low-pump-threshold pulse generation unit 5, an optical polarization controller 6, an optical coupler 7, an optical-electricity detector 8 and a data processing unit 9, the wavelength division multiplexer 2, the erbium-doped fiber 3, the optical isolator 4, the low-pump-threshold pulse generation unit 5, the optical polarization controller 6 and the optical coupler 7 are connected in sequence to form a ring resonant cavity, the pump laser 1 is connected to the wavelength division multiplexer 2, the optical coupler 7 is connected to the optical-electricity detector 8 and the data processing unit 9 in sequence.

[0024] The pump laser source can be a 980nm continuous light laser, and the wavelength division multiplexer 2 can be a 980 / 1550nm wavelength division multiplexer. The pump light output by the pump laser 1 is input into the erbium-doped fiber 3 through the 980nm output port of the wavelength division multiplexer 2. The erbium-doped fiber 3 has a length of 1.5m, and is a gain fiber. Under the action of the pump light, the erbium-doped fiber 3 will generate stimulated radiation to produce laser. The laser is transmitted in a clockwise direction in the ring resonator under the action of the optical isolator 4, and is injected into the low-pump-threshold pulse generation unit 5 through the optical isolator 4. The low-pump-threshold pulse generation unit 5 converts the laser generated by the erbium-doped fiber 3 into narrow linewidth pulsed laser at a low pump threshold. The optical polarization controller 6 further modulates the polarization state of the narrow linewidth pulsed laser output by the low-pump-threshold pulse generation unit 5, so that the narrow linewidth pulsed laser stably oscillates in the ring cavity. The 90% output port of the optical coupler 7 is connected with the 1550nm output port of the wavelength division multiplexer 2 to form a ring resonator and provide intra-cavity positive feedback; and the 10% output port of the optical coupler 7 is used as a laser output port to output narrow linewidth pulsed laser. In addition, the 10% output port of the optical coupler 7 is connected with the photodetector 8 and the data processing unit 9 in sequence to detect the output optical signal.

[0025] Figure 2 For Figure 1 the structure of the low-pump-threshold pulse generation unit in the low-pump-threshold pulse generation unit 5. As shown in Figure 2 , the low-pump-threshold pulse generation unit 5 includes a circulator 51, an erbium-doped short fiber 52, a fiber grating 53, and a saturable absorber 54. The input port a of the circulator 51 is connected with the output port of the optical isolator 4, the first output port b of the circulator 51 is connected with the input port of the erbium-doped short fiber 52, the second output port c of the circulator 51 is connected with the saturable absorber 54, the output port of the erbium-doped short fiber 52 is connected with the fiber grating 53, and the saturable absorber 54 is connected with the input port of the optical polarization controller 6.

[0026] The laser outputted from the WDM 2, the Er-doped fiber 3 and the optical isolator 4 in turn is injected into the circulator 51 from the input port a, and the circulator 51 outputs the control laser from the first output port b. The laser outputted from the first output port b is reflected by the mirror at the end of the Er-doped short fiber 52, and then passes through the Er-doped short fiber 52 again and enters the circulator 51 from the first output port b, and finally is outputted from the second output port c. Since the second output port c is connected to the saturable absorber 54, the laser outputted from the second output port c passes through the saturable absorber 54 and enters the optical polarization controller 6.

[0027] The length of the Er-doped short fiber 52 can be 5-20 cm.

[0028] The center wavelength of the fiber grating 53 can be 1547 nm, the reflectivity can be 92%, and the 3dB bandwidth can be 0.25 nm.

[0029] The frequency and polarization state of the laser before and after being reflected by the mirror at the end of the fiber grating 53 are the same, and the two form a standing wave in the fiber. At this time, the Er-doped short fiber 52 absorbs weakly at the standing wave peak and strongly at the standing wave antinode, that is, the frequency loss of the interference light is smaller at the peak and larger at the antinode, so the longitudinal mode corresponding to the peak is selected, that is, the laser generated by the Er-doped fiber 3 is converted into narrow linewidth laser.

[0030] The saturable absorber 54 can be a film made of single-walled carbon nanotubes mixed with polyvinyl alcohol, and the saturable absorber 54 is integrated in the ring resonant cavity through a fiber ferrule. The saturable absorber 54 has nonlinear optical characteristics, can effectively suppress the noise and broadband components in the ring resonant cavity, and makes the narrow linewidth laser gradually strengthen; and the saturable absorber 54 can compress the laser spectrum to realize the output of narrow linewidth pulsed laser.

[0031] In summary, the low pump threshold pulse generation unit 5 adjusts the light field distribution and mode structure in the ring resonant cavity, not only optimizes the light field to make the laser more easily form a stable narrow linewidth laser state, but also reduces the energy loss required for generating pulsed laser, and accelerates the accumulation of light field in the ring resonant cavity, so that the light intensity in the ring resonant cavity can quickly reach the threshold condition required for pulse output under the condition of lower pump power.

[0032] The detection by the photodetector 8 and the data processing unit 9 shows that when the pump power of the laser is increased to 30 mW, there is continuous laser output; when the pump power is continuously increased to 40 mW, the laser produces stable narrow linewidth pulsed laser output by adjusting the polarization controller 6; due to the hysteresis effect, when the pump power is gradually reduced to 35 mW, the narrow linewidth pulsed laser output becomes continuous laser output. Therefore, the pump threshold of the laser is 35 mW, and stable narrow linewidth pulsed laser output can be obtained when the pump power is 40 mW.

[0033] As shown in Figures 3 to 6 When the pump power is 40 mW, the laser has stable narrow linewidth pulsed output, at this time the center wavelength of the pulsed spectrum is 1547.02 nm, the 3dB bandwidth is 22.4 pm, the pulse repetition rate is 5.322 MHz, and the pulse sequence interval is 187.9 ns. When the pump power is set to 40 mW, the output spectrum of the laser is recorded by the spectrum analyzer every 5 minutes, and the output spectrum of the spectrum analyzer is recorded for 70 minutes. It can be seen that the low pump threshold narrow linewidth pulsed fiber laser provided by the application has low pulse output pump threshold, narrow spectral linewidth and high output spectrum stability.

[0034] In summary, the application discloses a low pump threshold narrow linewidth pulsed fiber laser, which realizes stable narrow linewidth pulsed laser output by rapidly reaching the threshold condition required for pulse output of the light intensity in the ring resonant cavity by the low pump threshold pulse generation unit 5 with low pump power. The laser of the application is simple to prepare, can effectively realize precise output of narrow spectral width and narrow pulse width, has low pump threshold characteristics, greatly reduces operating energy consumption and equipment cost, and ensures the stability of the output spectrum.

[0035] Although the application has been disclosed as above, it is not intended to limit the application, and anyone with ordinary knowledge in the art can make some changes and modifications without departing from the spirit and scope of the application, so the protection scope of the application shall be defined by the appended patent claim scope.

Claims

1. A narrow-linewidth pulsed fiber laser with a low pump threshold, characterized in that, The device includes a pump laser, a wavelength division multiplexer, an erbium-doped fiber, an optical isolator, a low pump threshold pulse generation unit, an optical polarization controller, an optical coupler, a photodetector, and a data processing unit. The wavelength division multiplexer, the erbium-doped fiber, the optical isolator, the low pump threshold pulse generation unit, the optical polarization controller, and the optical coupler are sequentially connected to form a ring resonant cavity. The pump laser is connected to the wavelength division multiplexer, and the optical coupler is sequentially connected to the photodetector and the data processing unit. The low pump threshold pulse generation unit includes a circulator, an erbium-doped short fiber, a fiber grating, and a saturable absorber. The input port of the circulator is connected to the output port of the optical isolator. The first output port of the circulator is connected to the input port of the erbium-doped short fiber. The second output port of the circulator is connected to the saturable absorber. The output port of the erbium-doped short fiber is connected to the fiber grating. The saturable absorber is connected to the input port of the optical polarization controller.

2. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 1, characterized in that, The length of the erbium-doped short optical fiber is 5–20 cm.

3. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 2, characterized in that, The saturable absorber is a thin film made of a mixture of single-walled carbon nanotubes and polyvinyl alcohol, and the saturable absorber is integrated into the annular resonant cavity through an optical fiber socket.

4. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 3, characterized in that, The fiber grating has a center wavelength of 1547nm, a reflectivity of 92%, and a 3dB bandwidth of 0.25nm.

5. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 1, characterized in that, The pump laser source is a 980nm continuous light laser.

6. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 5, characterized in that, The wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer.

7. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 6, characterized in that, The erbium-doped optical fiber is 1.5m long.

8. A narrow-linewidth pulsed fiber laser with low pump threshold as described in claim 1, characterized in that, The 90% output port of the optical coupler is connected to the 1550nm output port of the wavelength division multiplexer, and the 10% output port of the optical coupler is connected to the photodetector.

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