A high-coherence supercontinuum fiber laser

Abstract

The present invention proposes a high-coherence supercontinuum fiber laser, belonging to the field of fiber laser technology. It specifically includes: a femtosecond oscillator module for generating a mode-locked pulsed laser output, providing a seed source for the entire laser system; an inverted chirp menu module, connected to the output optical path of the femtosecond oscillator module, for selecting the number of pulses and performing dispersion control on the input high-frequency pulsed laser, outputting a modulated laser; and an amplification output module, connected to the output optical path of the inverted chirp menu module, for reversely amplifying and spectrally broadening the input modulated laser, outputting a supercontinuum laser. This solution achieves a selectable output laser frequency of 10-50 MHz by optimizing the cavity structure and combining it with an acousto-optic or electro-optical menu. A chirped grating is used to pre-dispersion compensate the initial laser, and hundreds of femtosecond lasers are injected into the gain fiber for amplification. Self-phase modulation and cross-phase modulation broadening are performed during the amplification process, resulting in a simple optical path structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber lasers, and in particular to a high-coherence supercontinuum optical fiber laser. Background Art

[0002] In industry, lasers can be divided into four categories according to the duration of light output: continuous, quasi-continuous, nanosecond pulse and ultrafast pulse. Ultrafast laser refers to the laser output pulse width in picoseconds (10 -12 s) level, or pulsed lasers less than picoseconds. Ultrafast lasers have great application prospects in the fields of medicine, industry, and national defense due to their narrow pulse width and high peak power. Among them, bioimaging applications require femtosecond light sources with high coherence, high stability, and a wide spectrum. The conventional solution is gain-managed nonlinear amplification technology (GMNA), which uses nonlinear effects and SRS to generate a supercontinuum spectrum during the power amplification process, and then compresses it to obtain a pulsed laser of tens of femtoseconds. Conventional solutions usually use two to three stages of amplification, and the main amplification link usually uses large mode field fiber amplification or photonic crystal fiber (PCF) amplification, which has a complex structure, poor output spectrum smoothness, and poor power stability.

[0003] Therefore, it is very necessary to provide a high-coherence supercontinuum fiber laser, which can output high-coherence laser by controlling dispersion through chirped grating and self-phase modulation spectrum broadening, so as to improve the current situation of complex structure and spectral imbalance of conventional supercontinuum laser. Summary of the Invention

[0004] In view of this, the present invention proposes a supercontinuum fiber laser with an optimized cavity structure, capable of mode locking in a large frequency range, and an optimized spectrum broadening structure and high coherence.

[0005] The present invention provides a high-coherence supercontinuum fiber laser, comprising:

[0006] Femtosecond oscillator module, used to generate high-frequency and high-stability mode-locked pulse laser output, providing a seed source for the entire laser system;

[0007] The inverted chirp selection module is connected to the output optical path of the femtosecond oscillator module, and is used to select the number of pulses and control the dispersion of the input high-frequency pulse laser, and output modulated laser light;

[0008] The amplifying output module is connected to the output optical path of the inverted chirp selection module, and is used to reversely amplify and spectrum broaden the input modulated laser to output supercontinuum laser.

[0009] On the basis of the above technical solution, preferably, the femtosecond oscillator module includes a single-mode pump, a wavelength division multiplexer, a first ytterbium-doped fiber, a non-reciprocal device, a 2×2 beam splitter, an output device and a first chirped grating; the first end of the wavelength division multiplexer is optically connected to the output end of the single-mode pump, the second end of the wavelength division multiplexer is optically connected to one end of the first ytterbium-doped fiber, the other end of the first ytterbium-doped fiber is optically connected to the first end of the non-reciprocal device, and the second end of the non-reciprocal device is optically connected to port d of the 2×2 beam splitter; the third end of the wavelength division multiplexer is optically connected to port c of the 2×2 beam splitter, port b of the 2×2 beam splitter is optically connected to the output device, and port a of the 2×2 beam splitter is optically connected to the first chirped grating; the wavelength division multiplexer, the first ytterbium-doped fiber, the non-reciprocal device, the 2×2 beam splitter and the first chirped grating constitute a complete cavity structure.

[0010] Preferably, the pump laser output by the single-mode pump passes through the wavelength division multiplexer and the first ytterbium-doped optical fiber in sequence, is absorbed by the first ytterbium-doped optical fiber and radiates fluorescent photons; the fluorescent photons pass through the non-reciprocal device and reach the 2×2 beam splitter; a part of the fluorescent photons pass through the port b of the 2×2 beam splitter and the output device to the outside of the cavity structure, and the other part of the fluorescent photons pass through the port a of the 2×2 beam splitter and are sent to the first chirped grating; the first chirped grating reflects the fluorescent photons back into the cavity structure, and the reflected laser propagates in the cavity structure along two opposite paths, passes through the first ytterbium-doped optical fiber and the non-reciprocal device for optical amplification and phase shifting, and then returns to the 2×2 beam splitter for interference, and the above process is repeated. When the gain and loss in the resonant cavity are balanced, a stable mode-locked pulse laser is output to the inverted chirp menu module through the first chirped grating.

[0011] Further preferably, the reflected laser propagates in the cavity structure along two opposite paths, one of which is: the reflected laser passes through the non-reciprocal device, the first ytterbium-doped fiber, the wavelength division multiplexer and the port c of the 2×2 beam splitter in sequence; the other path is: the reflected laser passes through the wavelength division multiplexer, the first ytterbium-doped fiber, the non-reciprocal device and the port d of the 2×2 beam splitter in sequence; each time the two components of the laser light reflected by the first chirped grating to the 2×2 beam splitter, the phase difference after passing through the non-reciprocal device on two opposite propagation paths in the cavity structure always remains π / 2.

[0012] Further preferably, the non-reciprocal device is one of a phase shifter, an optical isolator or an optical directional amplifier.

[0013] Further preferably, the calculation formula of the reflectivity R of the 2×2 beam splitter is as follows: k is the splitting ratio of the 2×2 beam splitter; n1 is the nonlinear coefficient of the optical fiber in the cavity structure; λ is the wavelength; A is the light intensity; A eff represents the effective mode field area; represents the nonlinear phase shift caused by the nonreciprocal device; L represents the cavity length of the cavity structure, which is the sum of the optical path lengths of the wavelength division multiplexer, the first ytterbium-doped fiber, the nonreciprocal device and two adjacent devices of the 2×2 beam splitter, and twice the optical path between port a of the 2×2 beam splitter and the first chirped grating.

[0014] Further preferably, the inverted chirped menu module includes a menu device, a circulator and a second chirped grating, the input end of the menu device is optically connected to the output end of the first chirped grating, the menu device performs pulse number selection processing on the mode-locked pulse laser, the output end of the menu device is optically connected to the first end of the circulator, the second end of the circulator is optically connected to the second chirped grating, the second chirped grating performs dispersion control on the mode-locked pulse laser after the pulse number selection processing, and reflects the dispersion-controlled mode-locked pulse laser back to the second end of the circulator; the third end of the circulator is optically connected to the amplification output module; the first end of the circulator is unidirectionally connected to the second end, and the second end of the circulator is unidirectionally connected to the third end.

[0015] Further preferably, the selection device is an acousto-optic selection device or an electro-optic selection device; the selection device sets a reference level, and the mode-locked pulse laser corresponding to the signal greater than or equal to the reference level passes through, and the mode-locked pulse laser corresponding to the signal less than the reference level is isolated, thereby realizing the pulse number selection processing of the mode-locked pulse laser.

[0016] More preferably, the amplification output module includes a mode field adapter, a second ytterbium-doped fiber, a combiner, a multimode pump and a collimation output component; the third end of the circulator is optically connected to one end of the mode field adapter, the other end of the mode field adapter is connected to one end of the second ytterbium-doped fiber, the other end of the second ytterbium-doped fiber is optically connected to the first end of the combiner, the second end of the combiner is optically connected to the output end of the multimode pump, and the third end of the combiner is optically connected to the input end of the collimation output component; the pump laser output by the multimode pump is injected into the second ytterbium-doped fiber through the combiner, and the laser output by the inverted chirp menu module is reversely amplified, the amplified laser is subjected to self-phase modulation and cross-phase modulation related to the light intensity, and the spectrum of the laser is broadened in both directions along the center wavelength.

[0017] Still further preferably, the amplified laser light is subjected to self-phase modulation and cross-phase modulation related to light intensity, wherein the modulation amount Φ generated by the self-phase modulation and cross-phase modulation related to light intensity is expressed as follows: Where n represents the linear refractive index of the optical fiber at the amplifying output module, n2 represents the nonlinear refractive index of the optical fiber at the amplifying output module, l represents the propagation length of the optical fiber at the amplifying output module, and λ represents the wavelength. In the amplifying output module, as the power of the laser in the combiner increases rapidly, the light intensity A increases, and the modulation amount Φ generated by the self-phase modulation and cross-phase modulation related to the light intensity also increases. The phase of the laser in the combiner is a function that changes with time. When the pulse phase changes with time, the spectrum of the laser is broadened.

[0018] The high-coherence supercontinuum fiber laser provided by the present invention has the following advantages over the prior art:

[0019] (1) This solution provides an improved seed light source based on the NALM principle. By optimizing the cavity design, high-frequency and high-stability mode-locked laser output is achieved. The seed light output of the mode-locked laser is combined with an acousto-optic or electro-optic switch to further achieve an output frequency range of 10-50 MHz, which can match a variety of application scenarios.

[0020] (2) The second chirped grating performs pre-dispersion compensation on the seed light source, and then a circulator is used to inject hundreds of femtosecond laser light into the ytterbium-doped gain fiber for amplification. During the amplification process, the laser light is broadened by self-phase modulation and cross-phase modulation. Compared with the traditional method of first performing chirped pulse amplification and then performing spectrum broadening, the optical path structure of the present application is simpler, and the smoothness and power stability of the output spectrum are better. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a schematic structural diagram of a high-coherence supercontinuum fiber laser according to the present invention;

[0023] Figure 2 This is a schematic diagram of the output spectrum of the first chirped grating of a high-coherence supercontinuum fiber laser of the present invention;

[0024] Figure 3 The invention discloses a broadened output spectrum of an amplified output module of a high-coherence supercontinuum fiber laser.

[0025] Figure numerals: 1. Femtosecond oscillator module; 2. Inverted chirp menu module; 3. Amplification output module; 11. Single-mode pump; 12. Wavelength division multiplexer; 13. First ytterbium-doped fiber; 14. Non-reciprocal device; 15. 2×2 beam splitter; 16. Output device; 17. First chirped grating; 21. Menu device; 22. Circulator; 23. Second chirped grating; 31. Mode field adapter; 32. Second ytterbium-doped fiber; 33. Combiner; 34. Multimode pump; 35. Collimation output component. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, the present invention provides a high coherence supercontinuum fiber laser, comprising a femtosecond oscillator module 1, an inverted chirp menu module 2 and an amplification output module 3 arranged in sequence, wherein:

[0028] Femtosecond oscillator module 1 is used to generate mode-locked pulse laser output and provide a seed source for the entire laser system;

[0029] The inverted chirp selection module 2 is optically connected to the output end of the femtosecond oscillator module 1, and is used to select the number of pulses and control the dispersion of the input high-frequency pulse laser, and output modulated laser light;

[0030] The amplifying output module 3 is optically connected to the output end of the inverse chirp selection module 2 and is used to reversely amplify and spectrum broaden the input modulated laser to output supercontinuum laser.

[0031] The femtosecond oscillator module 1 is an improved mode-locked oscillator based on NALM. Specifically, the femtosecond oscillator module 1 includes a single-mode pump 11, a wavelength division multiplexer 12, a first ytterbium-doped fiber 13, a non-reciprocal device 14, a 2×2 beam splitter 15, an output device 16 and a first chirped grating 17. The first end of the wavelength division multiplexer 12 is optically connected to the output end of the single-mode pump 11, the second end of the wavelength division multiplexer 12 is optically connected to one end of the first ytterbium-doped fiber 13, and the other end of the first ytterbium-doped fiber 13 is optically connected to the output end of the non-reciprocal device 14. The first end is optically connected, the second end of the non-reciprocal device 14 is optically connected to port d of the 2×2 beam splitter 15; the third end of the wavelength division multiplexer 12 is optically connected to port c of the 2×2 beam splitter 15, port b of the 2×2 beam splitter 15 is optically connected to the output device 16, and port a of the 2×2 beam splitter 15 is optically connected to the first chirped grating 17; the wavelength division multiplexer 12, the first ytterbium-doped fiber 13, the non-reciprocal device 14, the 2×2 beam splitter 15, and the first chirped grating 17 form a complete cavity structure. In this embodiment, the non-reciprocal device 14 is a phase shifter, an optical isolator, or an optical directional amplifier. The phase difference between the input light at port a and the reflected light at port b of the 2×2 beam splitter 15 determines whether the laser light interferes destructively or constructively at that location, thereby controlling the output pulse light.

[0032] The pump laser output by the single-mode pump 11 passes through the wavelength division multiplexer 12 and the first ytterbium-doped fiber 13 in sequence, where it is absorbed by the first ytterbium-doped fiber 13 and emits fluorescent photons. The fluorescent photons pass through the non-reciprocal device 14 and reach the 2×2 beam splitter 15. A portion of the fluorescent photons is output outside the cavity structure through port b of the 2×2 beam splitter 15 and the output device 16 to reduce nonlinear accumulation. The other portion of the fluorescent photons passes through port a of the 2×2 beam splitter 15 and enters the first chirped grating 17. The first chirped grating 17 reflects the fluorescent photons back into the cavity structure. The reflected laser light propagates along two opposite paths within the cavity structure, undergoes optical amplification and phase shifting in the first ytterbium-doped fiber 13 and the non-reciprocal device 14, and then returns to the 2×2 beam splitter 15 for interference. The above process is repeated. When the gain and loss in the resonant cavity are balanced, stable mode-locked pulsed laser light is output to the inverse chirp menu module 2 through the first chirped grating 17.

[0033] The reflected laser propagates along two opposite paths in the cavity structure. One path is: the reflected laser passes through the non-reciprocal device 14, the first ytterbium-doped fiber 13, the wavelength division multiplexer 12 and the port c of the 2×2 beam splitter 15 in sequence; the other path is: the reflected laser passes through the wavelength division multiplexer 12, the first ytterbium-doped fiber 13, the non-reciprocal device 14 and the port d of the 2×2 beam splitter 15 in sequence; each time the two components of the laser light reflected by the first chirped grating 17 to the 2×2 beam splitter 15, the phase difference between the two components on the two opposite propagation paths in the cavity structure always remains π / 2 after passing through the non-reciprocal device.

[0034] The greater the reflectivity of the 2×2 beam splitter 15, the easier it is for the femtosecond oscillator module 1 to mode-lock and output pulse light. The calculation formula for the reflectivity R of the 2×2 beam splitter 15 is as follows: k is the splitting ratio of the 2×2 beam splitter 15. In this embodiment, the splitting ratio is 4:6; n1 represents the nonlinear coefficient of the optical fiber in the cavity structure; λ represents the wavelength; A represents the light intensity; A eff represents the effective mode field area; represents the nonlinear phase shift caused by the nonreciprocal device 14; L represents the cavity length of the cavity structure, which is the sum of the optical path lengths of the wavelength division multiplexer 12, the first ytterbium-doped fiber 13, the nonreciprocal device 14 and the two adjacent devices of the 2×2 beam splitter 15, and twice the optical path between port a of the 2×2 beam splitter 15 and the first chirped grating 17. Because there is an incident and reflection relationship between the first chirped grating 17 and port a of the 2×2 beam splitter 15, the optical path length of this part needs to be calculated twice.

[0035] The specific optical path of the femtosecond oscillator module 1 operates as follows: a single-mode pump 11 outputs a 976nm pump laser, which is fed through a wavelength division multiplexer into the first ytterbium-doped fiber 13. The 976nm pump laser is absorbed by the Yb, resulting in a gain-generated fluorescence output encompassing the 1030nm wavelength band. After reflection by the nonreciprocal device 14, the 2×2 beam splitter 15, and the first chirped grating 17, the reflected laser is then formed into two distinct reflected light paths by the 2×2 beam splitter 15. After passing through the nonreciprocal device, the two beams experience a phase difference of π / 2. After completing the reflected light paths, they return to the 2×2 beam splitter 15 and interfere with each other. This process repeats until the gain and loss within the resonant cavity are balanced, resulting in the output of mode-locked pulsed laser light. The repetition rate of mode locking can be adjusted by controlling the cavity length L, achieving a maximum repetition rate of 50MHz and a 3dB spectrum greater than 10nm. The dispersion range of the first chirped grating 17 is between 0.18 ps / nm and 0.25 ps / nm. The output spectrum of the first chirped grating 17 is shown in FIG. Figure 2 The first chirped grating 17 is used for mode locking. When the mode is locked and pulse light is output, the corresponding reflectivity R is set to a value not less than 60%.

[0036] like Figure 1As shown, the inverted chirped selection module 2 includes a selection device 21, a circulator 22, and a second chirped grating 23. The input end of the selection device 21 is optically connected to the output end of the first chirped grating 17. The selection device 21 performs pulse number selection processing on the mode-locked pulsed laser. The output end of the selection device 21 is optically connected to the first end of the circulator 22. The second end of the circulator 22 is optically connected to the second chirped grating 23. The second chirped grating 23 performs dispersion control on the mode-locked pulsed laser after the pulse number selection processing. By compensating for the laser dispersion, the laser pulse width is shortened to a value close to the limit pulse width, and the modulated laser is reflected back to the second end of the circulator 22. The third end of the circulator 22 is optically connected to the amplifier output module 3. The first and second ends of the circulator 22 are in unidirectional communication, and the second and third ends of the circulator 22 are in unidirectional communication. The dispersion range of the first chirped grating 17 is between 0.5 ps / nm and 0.7 ps / nm.

[0037] In this embodiment, the selection device 21 is an acousto-optic selection device 21 or an electro-optic selection device 21. The selection device 21 sets a reference level. Mode-locked laser pulses with signals greater than or equal to the reference level pass through, while signals less than the reference level are isolated. This allows for pulse quantity selection of the mode-locked laser pulses. Each port of the circulator 22 has a unidirectional conduction function, preventing reverse propagation of the laser beam.

[0038] like Figure 1 As shown, the amplification output module 3 includes a mode field adapter 31, a second ytterbium-doped fiber 32, a combiner 33, a multimode pump 34 and a collimation output assembly 35; the third end of the circulator 22 is optically connected to one end of the mode field adapter 31, the other end of the mode field adapter 31 is optically connected to one end of the second ytterbium-doped fiber 32, the other end of the second ytterbium-doped fiber 32 is optically connected to the first end of the combiner 33, the second end of the combiner 33 is optically connected to the output end of the multimode pump 34, and the third end of the combiner 33 is optically connected to the input end of the collimation output assembly 35; the pump laser output by the multimode pump 34 is injected into the second ytterbium-doped fiber 32 through the combiner 33, and the laser output by the inverted chirp menu module 2 is reversely amplified. The amplified laser undergoes self-phase modulation and cross-phase modulation related to the light intensity, and the spectrum of the laser is broadened in both directions along the central wavelength.

[0039] The amplified laser is subjected to self-phase modulation and cross-phase modulation related to the light intensity, wherein the modulation amount Φ generated by the self-phase modulation and cross-phase modulation related to the light intensity is expressed as follows: Where n represents the linear refractive index of the optical fiber at the amplifying output module 3, n2 represents the nonlinear refractive index of the optical fiber at the amplifying output module 3, l represents the propagation length of the optical fiber at the amplifying output module 3, and λ represents the wavelength. In the amplifying output module 3, the power of the laser in the combiner 33 increases rapidly, the light intensity A increases, and the modulation amount Φ generated by the self-phase modulation and cross-phase modulation related to the light intensity also increases. The phase of the laser in the combiner 33 is a function that changes with time. When the pulse phase changes with time, the spectrum of the laser is broadened, and the broadened spectrum has very good coherence. The output spectrum of the spectrally broadened laser output is as follows: Figure 3 shown. Figure 2 and Figure 3 The horizontal axis is the wavelength of the laser, and the vertical axis is the relative light intensity corresponding to the wavelength.

[0040] The present invention oscillates and outputs a mode-locked pulse laser through a specific cavity structure, and then utilizes an acousto-optic menu to achieve multi-frequency adjustment. Only a first-stage power amplification structure is used, and the overall structure is simple and clear. It can output a smooth and flat spectrum from 1000 to 1150 nm, making it very suitable for bioimaging and biomedicine.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high coherence supercontinuum fiber laser, characterized in that: include: A femtosecond oscillator module (1) is used to generate a mode-locked pulse laser output and provide a seed source for the entire laser system; The inverted chirp selection module (2) is connected to the output optical path of the femtosecond oscillator module (1) and is used to select the number of pulses and control the dispersion of the input high-frequency pulse laser and output modulated laser light; an amplifying output module (3) connected to the output optical path of the inverted chirp selection module (2) and used for reversely amplifying and spectrum broadening the input modulated laser light to output supercontinuum laser light; The inverted chirp selection module (2) comprises a selection device (21), a circulator (22) and a second chirped grating (23); the input end of the selection device (21) receives the seed source output by the femtosecond oscillator module (1); the selection device (21) performs pulse quantity selection processing on the seed source; the output end of the selection device (21) is optically connected to the first end of the circulator (22); the second end of the circulator (22) is optically connected to the second chirped grating (23); the second chirped grating (23) performs dispersion control on the seed source after the pulse quantity selection processing, and reflects the dispersion-controlled mode-locked pulse laser back to the second end of the circulator (22); the third end of the circulator (22) is optically connected to the amplification output module (3); the first end of the circulator (22) is unidirectionally connected to the second end, and the second end of the circulator (22) is unidirectionally connected to the third end; The amplification output module (3) comprises a mode field adapter (31), a second ytterbium-doped optical fiber (32), a beam combiner (33), a multimode pump (34) and a collimation output assembly (35); the third end of the circulator (22) is optically connected to one end of the mode field adapter (31), the other end of the mode field adapter (31) is optically connected to one end of the second ytterbium-doped optical fiber (32), the other end of the second ytterbium-doped optical fiber (32) is optically connected to the first end of the beam combiner (33), and the beam combiner (33) is optically connected to the first end of the mode field adapter (31). The second end is connected to the output optical path of the multimode pump (34), and the third end of the beam combiner (33) is connected to the input optical path of the collimated output component (35); the pump laser output by the multimode pump (34) is injected into the second ytterbium-doped optical fiber (32) through the beam combiner (33), and the laser output by the inverted chirp menu module (2) is reversely amplified. The amplified laser is subjected to self-phase modulation and cross-phase modulation related to the light intensity, and the spectrum of the laser is broadened in both directions along the central wavelength.

2. A high coherence supercontinuum fiber laser according to claim 1, characterized in that: The femtosecond oscillator module (1) comprises a single-mode pump (11), a wavelength division multiplexer (12), a first ytterbium-doped optical fiber (13), a non-reciprocal device (14), a 2×2 beam splitter (15), an output device (16) and a first chirped grating (17); a first end of the wavelength division multiplexer (12) is optically connected to the output end of the single-mode pump (11), a second end of the wavelength division multiplexer (12) is optically connected to one end of the first ytterbium-doped optical fiber (13), the other end of the first ytterbium-doped optical fiber (13) is optically connected to the first end of the non-reciprocal device (14), and the non-reciprocal device ( The second end of the wavelength division multiplexer (14) is optically connected to the port d of the 2×2 beam splitter (15); the third end of the wavelength division multiplexer (12) is optically connected to the port c of the 2×2 beam splitter (15); the port b of the 2×2 beam splitter (15) is optically connected to the output device (16); and the port a of the 2×2 beam splitter (15) is optically connected to the first chirped grating (17); the wavelength division multiplexer (12), the first ytterbium-doped optical fiber (13), the non-reciprocal device (14), the 2×2 beam splitter (15) and the first chirped grating (17) constitute a complete cavity structure.

3. A high coherence supercontinuum fiber laser according to claim 2, characterized in that: The pump laser output by the single-mode pump (11) passes through the wavelength division multiplexer (12) and the first ytterbium-doped optical fiber (13) in sequence, is absorbed by the first ytterbium-doped optical fiber (13) and radiates fluorescent photons; Fluorescent photons pass through the non-reciprocal device (14) and arrive at the 2×2 beam splitter (15); a portion of the fluorescent photons passes through the port b of the 2×2 beam splitter (15) and the output device (16) and is output outside the cavity structure, and another portion of the fluorescent photons passes through the port a of the 2×2 beam splitter (15) and is sent to the first chirped grating (17); the first chirped grating (17) reflects the fluorescent photons back into the cavity structure, and the reflected laser propagates along two opposite paths in the cavity structure, passes through the first ytterbium-doped optical fiber (13) and the non-reciprocal device (14) for optical amplification and phase shifting, and then returns to the 2×2 beam splitter (15) for interference, and the above process is repeated. When the gain and loss in the resonant cavity are balanced, a stable mode-locked pulse laser is output to the inverted chirp menu module (2) through the first chirped grating (17).

4. A high coherence supercontinuum fiber laser according to claim 3, characterized in that: The reflected laser propagates along two opposite paths in the cavity structure. One of the paths is: the reflected laser passes through the non-reciprocal device (14), the first ytterbium-doped optical fiber (13), the wavelength division multiplexer (12) and the port c of the 2×2 beam splitter (15) in sequence; the other path is: the reflected laser passes through the wavelength division multiplexer (12), the first ytterbium-doped optical fiber (13), the non-reciprocal device (14) and the port d of the 2×2 beam splitter (15) in sequence; each time, the two components of the laser light reflected by the first chirped grating (17) to the 2×2 beam splitter (15) always maintain a phase difference of π / 2 after passing through the non-reciprocal device on the two opposite propagation paths in the cavity structure.

5. The high coherence supercontinuum fiber laser according to claim 3, characterized in that: The non-reciprocal device (14) is one of a phase shifter, an optical isolator or an optical directional amplifier.

6. The high coherence supercontinuum fiber laser according to claim 3, characterized in that: The calculation formula of the reflectivity R of the 2×2 beam splitter (15) is as follows: k is the splitting ratio of the 2×2 beam splitter (15); n1 represents the nonlinear coefficient of the optical fiber in the cavity structure; λ represents the wavelength; A represents the light intensity; A eff represents the effective mode field area; represents the nonlinear phase shift caused by the nonreciprocal device (14); L represents the cavity length of the cavity structure, which is the sum of the optical path lengths between the wavelength division multiplexer (12), the first ytterbium-doped optical fiber (13), the nonreciprocal device (14) and two adjacent devices of the 2×2 beam splitter (15), and twice the optical path between port a of the 2×2 beam splitter (15) and the first chirped grating (17).

7. The high coherence supercontinuum fiber laser according to claim 1, characterized in that: The selection device (21) is an acousto-optic selection device (21) or an electro-optic selection device (21); the selection device (21) sets a reference level, and the mode-locked pulse laser corresponding to a signal greater than or equal to the reference level passes through, and the mode-locked pulse laser corresponding to a signal less than the reference level is isolated, thereby realizing pulse quantity selection processing of the mode-locked pulse laser.

8. The high coherence supercontinuum fiber laser according to claim 1, characterized in that: The amplified laser is subjected to self-phase modulation and cross-phase modulation related to the light intensity, wherein the modulation amount φ generated by the self-phase modulation and cross-phase modulation related to the light intensity is expressed as follows: Wherein n represents the linear refractive index of the optical fiber at the amplifying output module (3), n2 represents the nonlinear refractive index of the optical fiber of the amplifying output module (3), l represents the propagation length of the optical fiber at the amplifying output module (3), and λ represents the wavelength; in the amplifying output module (3), when the power of the laser in the beam combiner (33) increases rapidly, the light intensity A increases, and the modulation amount Φ generated by the self-phase modulation and cross-phase modulation related to the light intensity also increases. The phase of the laser in the beam combiner (33) is a function that changes with time. When the pulse phase changes with time, the spectrum of the laser is broadened.

Images