Narrow linewidth pulse fiber laser with low pumping threshold

Abstract

The invention discloses a narrow linewidth pulse fiber laser with a low pumping threshold, which belongs to the technical field of lasers and comprises a pumping laser, a wavelength division multiplexer, an erbium-doped fiber, an optical isolator, a low pumping threshold pulse generation unit, an optical polarization controller, an optical coupler, a photoelectric detector and a data processing unit. The wavelength division multiplexer, the erbium-doped fiber, the optical isolator, the low pumping threshold pulse generation unit, the optical polarization controller and the optical coupler are sequentially connected to form an annular resonant cavity, and the pumping laser is connected with the wavelength division multiplexer. And the optical coupler is sequentially connected with the photoelectric detector and the data processing unit. Through the low pumping threshold pulse generation unit, the light intensity in the annular resonant cavity rapidly reaches the threshold condition required by pulse output with low pumping power, stable narrow linewidth pulse laser output is realized, the operation energy consumption and the equipment cost are reduced, and the stability of an output spectrum is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber lasers, and in particular to a narrow-linewidth pulse fiber laser with a low pumping threshold. Background Art

[0002] At present, some narrow-linewidth pulse fiber lasers can simultaneously obtain ultrashort pulse widths of the order of picoseconds or femtoseconds and spectral linewidths of the order of picometers, and they have important application value in the fields of differential absorption lidar, Doppler lidar, precision optical coherence detection, and high-resolution sensing.

[0003] There are two commonly used methods to achieve narrow linewidth pulsed lasers: one is to inject a narrow linewidth seed laser into a pulsed fiber laser; the other is to directly generate a pulsed laser in the resonant cavity of a narrow linewidth fiber laser. However, most of the narrow linewidth pulsed fiber lasers developed according to these two methods have a high pumping threshold, and the output power of the pump laser is also high, and the general pumping power is in the order of hundreds of milliwatts. This will lead to increased energy consumption and cost of narrow linewidth pulsed fiber lasers, limited application scenarios, and potential stability and reliability issues. Therefore, it is of great significance to develop a narrow linewidth pulsed laser with low power consumption, high stability and low pumping threshold. Summary of the invention

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

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is: to provide a low pump threshold narrow linewidth pulse fiber laser, characterized in that it includes a pump laser, a wavelength division multiplexer, an erbium-doped fiber, an optical isolator, a low pump threshold pulse generating unit, an optical polarization controller, an optical coupler, a photodetector and a data processing unit, wherein the wavelength division multiplexer, the erbium-doped fiber, the optical isolator, the low pump threshold pulse generating unit, the optical polarization controller and the optical coupler are sequentially connected to form a ring resonator, 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 generating unit comprises a circulator, an erbium-doped short fiber, a fiber Bragg 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 Bragg 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 to 20 cm.

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

[0009] In one embodiment, the central wavelength of the fiber grating is 1547 nm, the reflectivity is 92%, and the 3dB bandwidth is 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 length of the erbium-doped optical fiber is 1.5 m.

[0013] In one embodiment, 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.

[0014] In summary, the present invention discloses a low pump threshold narrow line width pulse fiber laser, through the low pump threshold pulse generating unit, the light intensity in the ring resonator quickly reaches the threshold condition required for pulse output with a relatively low pump power, and effectively realizes stable narrow line width pulse laser output. The laser of the present invention is simple to prepare, can effectively realize the precise output of narrow spectral width and narrow pulse width, and has the characteristics of low pump threshold, greatly reduces the operating energy consumption and equipment cost, and ensures the stability of the output spectrum.

[0015] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of a narrow-linewidth pulse fiber laser with a low pumping threshold provided by the present invention.

[0017] Figure 2 for Figure 1 Schematic diagram of the structure of the medium and low pump threshold pulse generation unit.

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

[0019] Figure 4It is a pulse repetition sequence of laser output of the laser of the present invention with a pulse interval of 102ns when the pump power is 40mW.

[0020] Figure 5 This is a radio frequency spectrum diagram of the laser output of the laser of the present invention when the pump power is 40 mW and the repetition frequency is 5.322 MHz.

[0021] Figure 6 This is a stability test chart of the laser output spectrum of the laser of the present invention recorded every 5 minutes when the pump power is 40 mW. DETAILED DESCRIPTION

[0022] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Figure 1 FIG. 1 is a schematic diagram of the structure of a narrow linewidth pulse fiber laser with a low pump threshold in the present invention. Figure 1 As shown, the low pumping threshold narrow linewidth pulse fiber laser comprises a pump laser 1, a wavelength division multiplexer 2, an erbium-doped fiber 3, an optical isolator 4, a low pumping threshold pulse generating unit 5, an optical polarization controller 6, an optical coupler 7, a photodetector 8 and a data processing unit 9. The wavelength division multiplexer 2, the erbium-doped fiber 3, the optical isolator 4, the low pumping threshold pulse generating unit 5, the optical polarization controller 6 and the optical coupler 7 are sequentially connected to form a ring resonator. The pump laser 1 is connected to the wavelength division multiplexer 2, and the optical coupler 7 is sequentially connected to the photodetector 8 and the data processing unit 9.

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

[0025] Figure 2 for Figure 1 Schematic diagram of the structure of the low pump threshold pulse generating unit in FIG. Figure 2 As shown, the low pump threshold pulse generating 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 to the output port of the optical isolator 4, the first output port b of the circulator 51 is connected to the input port of the erbium-doped short fiber 52, the second output port c of the circulator 51 is connected to the saturable absorber 54, the output port of the erbium-doped short fiber 52 is connected to the fiber grating 53, and the saturable absorber 54 is connected to the input port of the optical polarization controller 6.

[0026] The laser light outputted from the wavelength division multiplexer 2, the erbium-doped fiber 3 and the optical isolator 4 in sequence is injected into the circulator 51 from the input port a, and the circulator 51 controls the laser light to be outputted from the first output port b. The laser light outputted from the first output port b will be reflected by the reflector at the end of the fiber grating 53 after passing through the erbium-doped short fiber 52, and the reflected laser light will pass through the erbium-doped short fiber 52 again, and enter the circulator 51 from the first output port b, and finally be outputted from the second output port c. Since the second output port c is connected to the saturable absorber 54, the laser light outputted from the second output port c will be input into the optical polarization controller 6 after passing through the saturable absorber 54.

[0027] The length of the erbium-doped short optical fiber 52 may be 5 to 20 cm.

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

[0029] The frequency and polarization state of the laser light before and after being reflected by the reflector at the end of the fiber grating 53 are the same, and the two form a standing wave in this section of the fiber. At this time, the erbium-doped short fiber 52 absorbs weakly at the crest of the standing wave, and absorbs strongly at the antinode of the standing wave, that is, the frequency loss of the interference light at the crest is small, and the frequency loss at the antinode is large, therefore, the longitudinal mode corresponding to the crest is selected, that is, the laser light generated by the erbium-doped fiber 3 is converted into a narrow line width laser light.

[0030] The saturable absorber 54 can be a film made of a mixture of single-walled carbon nanotubes and polyvinyl alcohol, and the saturable absorber 54 is integrated in the ring resonator through an optical fiber sleeve. The saturable absorber 54 has nonlinear optical properties, which can effectively suppress the noise and broadband components in the ring resonator, so that the narrow line width laser is gradually enhanced; and the saturable absorber 54 can compress the laser spectrum to achieve the output of narrow line width pulse laser.

[0031] In summary, the low pump threshold pulse generating unit 5 not only optimizes the light field by adjusting the light field distribution and mode structure in the ring resonator, making it easier for the laser to form a stable narrow linewidth laser state; it also reduces the energy loss required to generate pulsed lasers and accelerates the light field accumulation in the ring resonator. Therefore, under lower pump power conditions, the light intensity in the ring resonator can also quickly reach the threshold condition required for pulse output.

[0032] It can be seen from the detection using the photodetector 8 and the data processing unit 9 that when the pump power of the laser increases to 30mW, there is continuous laser output; when the pump power continues to increase to 40mW, the polarization controller 6 is adjusted, and the laser produces stable narrow line width pulse laser output; due to the hysteresis effect, when the pump power is gradually reduced to 35mW, the narrow line width pulse laser output becomes continuous laser output. Therefore, the pump threshold of the laser is 35mW, and when the pump power is 40mW, a stable narrow line width pulse laser output can be obtained.

[0033] like Figures 3 to 6 As shown in the figure, when the pump power is 40mW, the laser has a stable narrow linewidth pulse output, at which the central wavelength of the pulse spectrum is 1547.02nm, the 3dB bandwidth is 22.4pm, the pulse repetition rate is 5.322MHz, and the pulse sequence is 187.9ns. The pump power is set to 40mW, and the laser output wavelength is recorded every 5 minutes by the spectrum analyzer, and the output spectrum of the spectrum analyzer is recorded for 70 minutes. It can be seen that the pulse output pump threshold of the narrow linewidth pulse fiber laser with a low pump threshold provided by the present invention is low, the spectral linewidth is narrow, and the output spectrum stability is high.

[0034] In summary, the present invention discloses a low pump threshold narrow line width pulse fiber laser, through the low pump threshold pulse generating unit 5, the light intensity in the ring resonator quickly reaches the threshold condition required for pulse output with a relatively low pump power, and effectively realizes stable narrow line width pulse laser output. The laser of the present invention is simple to prepare, can effectively realize the precise output of narrow spectrum width and narrow pulse width, and has the characteristics of low pump threshold, greatly reduces the operating energy consumption and equipment cost, and ensures the stability of the output spectrum.

[0035] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A narrow linewidth pulse fiber laser with low pump threshold, characterized in that: The invention comprises a pump laser, a wavelength division multiplexer, an erbium-doped optical fiber, an optical isolator, a low pump threshold pulse generating 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 pump threshold pulse generating unit, the optical polarization controller and the optical coupler are sequentially connected to form a ring resonator. 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 generating unit comprises a circulator, an erbium-doped short fiber, a fiber Bragg 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 Bragg grating, and the saturable absorber is connected to the input port of the optical polarization controller.

2. A low pump threshold narrow linewidth pulse fiber laser as claimed in claim 1, characterized in that: The length of the erbium-doped short optical fiber is 5 to 20 cm.

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

4. A low pump threshold narrow linewidth pulse fiber laser as claimed in claim 3, characterized in that: The central wavelength of the fiber Bragg grating is 1547nm, the reflectivity is 92%, and the 3dB bandwidth is 0.25nm.

5. A low pump threshold narrow linewidth pulse fiber laser as claimed in claim 1, characterized in that: The pump laser source is a 980nm continuous light laser.

6. A low pump threshold narrow linewidth pulse fiber laser as claimed in claim 5, characterized in that: The wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer.

7. A low pump threshold narrow linewidth pulse fiber laser as claimed in claim 6, characterized in that: The length of the erbium-doped optical fiber is 1.5 m.

8. A low pump threshold narrow linewidth pulse fiber laser as claimed 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.

Images