Super-continuum spectrum fiber laser with high coherence degree

Abstract

The invention provides a high-coherence super-continuum spectrum fiber laser, and belongs to the technical field of fiber lasers. The system specifically comprises a femtosecond oscillator module which is used for generating mode-locked pulse laser output and providing a seed source for the whole laser system; the inverted chirp menu module is connected with an output end light path of the femtosecond oscillator module and is used for carrying out pulse number selection and dispersion regulation and control on the input high-frequency pulse laser and outputting modulated laser; and the amplification output module is in light path connection with the output end of the inverted chirp menu module and is used for performing reverse amplification and spectrum broadening on the input modulated laser and outputting super-continuum spectrum laser. According to the scheme, by optimizing the cavity structure and cooperating with the acousto-optic or electro-optic menu, the selectable output laser frequency of 10-50 MHz is achieved, the chirp grating is used for conducting pre-dispersion compensation on the initial laser, the laser of the hundred femtosecond magnitude is injected into the gain optical fiber to be amplified, self-phase modulation and cross-phase modulation broadening are conducted in the amplification process, and the light path structure is simple.

Description

Technical Field

[0001] The 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 lasers refer to lasers with a pulse width of 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. The conventional solution usually uses 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 larger 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;

[0008] The amplifying output module is connected to the output optical path of the inverted chirp menu 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 scheme, 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 the port d of the 2×2 beam splitter; the third end of the wavelength division multiplexer is optically connected to the port c of the 2×2 beam splitter, the port b of the 2×2 beam splitter is optically connected to the output device, and the 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 optical 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 optical 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 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 chirp 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] More 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 whose corresponding signal is greater than or equal to the reference level passes through, and the mode-locked pulse laser whose corresponding signal is less than the reference level is isolated, thereby realizing the pulse quantity 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 beam 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 beam combiner, the second end of the beam combiner is optically connected to the output end of the multimode pump, and the third end of the beam 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 beam 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 central 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: Wherein 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, 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 beneficial effects compared with the prior art:

[0019] (1) This scheme 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 of the mode-locked output is combined with an acousto-optic or electro-optic switch to further achieve an output frequency in the range of 10-50MHz, which can match a variety of different application scenarios.

[0020] (2) The second chirped grating performs pre-dispersion compensation on the seed light source, and then injects hundreds of femtosecond laser light into the ytterbium-doped gain fiber for amplification through a circulator. 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

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

[0023] Figure 2 A schematic diagram of an output spectrum of a 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 optical 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 described embodiments 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 creative work 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, a reverse chirp menu module 2 and an amplification output module 3 arranged in sequence, wherein:

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

[0029] 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;

[0030] The amplification 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; 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 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 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 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 one of a phase shifter, an optical isolator or an optical directional amplifier. The phase difference between the input light of the port a of the 2×2 beam splitter 15 and the reflected light of the port b determines whether the laser interferes destructively or constructively at this location, thereby realizing the control of 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, is absorbed by the first ytterbium-doped fiber 13 and radiates fluorescent photons; the fluorescent photons pass through the non-reciprocal device 14 and reach the 2×2 beam splitter 15; a part of the fluorescent photons pass through the port b of the 2×2 beam splitter 15 and the output device 16 to output outside the cavity structure to reduce the accumulation of nonlinearity; the other part of the fluorescent photons pass through the port a of the 2×2 beam splitter 15 and enter the first chirped grating 17, and the first chirped grating 17 reflects the fluorescent photons back into the cavity structure. The reflected laser propagates in the cavity structure along two opposite paths, passes through the first ytterbium-doped fiber 13 and the non-reciprocal device 14 for optical amplification and phase shift, 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 inverse chirp menu module 2 through the first chirped grating 17.

[0033] 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 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 reflected by the first chirped grating 17 to the 2×2 beam splitter 15, the phase difference 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 brought 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. 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 should be calculated twice.

[0035] The specific optical path of the femtosecond oscillator module 1 works as follows: the single-mode pump 11 outputs a 976nm pump laser, which is sent to the first ytterbium-doped optical fiber 13 through a wavelength division multiplexer. The 976nm pump laser is absorbed by Yb, and the gain output is a fluorescence containing a 1030nm band. After being reflected by the non-reciprocal device 14, the 2×2 beam splitter 15 and the first chirped grating 17, the reflected laser is formed into two different reflected light paths by the 2×2 beam splitter 15. After the two beams pass through the non-reciprocal device, the phase difference increases by π / 2. After completing the reflected light path, they return to the 2×2 beam splitter 15 again and form interference. The above steps are repeated. After the gain and loss in the resonant cavity are balanced, the oscillation outputs a mode-locked pulse laser. The repetition rate of the mode locking can be achieved by controlling the cavity length L of the cavity structure, and the maximum repetition rate can be 50MHz, and the 3dB spectrum can be 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 chirp menu module 2 includes a menu device 21, a circulator 22 and a second chirped grating 23. The input end of the menu device 21 is optically connected to the output end of the first chirped grating 17. The menu device 21 performs pulse quantity selection processing on the mode-locked pulse laser. The output end of the menu 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 pulse laser after the pulse quantity selection processing. The pulse width of the laser is reduced by dispersion compensation of the laser, so that the pulse width of the current laser is 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 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 dispersion range of the first chirped grating 17 is between 0.5ps / nm-0.7ps / 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, and the mode-locked pulse laser corresponding to the signal greater than or equal to the reference level passes, and the mode-locked pulse laser corresponding to the signal less than the reference level is isolated, thereby realizing the pulse quantity selection processing of the mode-locked pulse laser. Each port of the circulator 22 has a unidirectional conduction function, which can prevent the laser from propagating in the opposite direction.

[0038] like Figure 1 As shown, the amplification output module 3 includes a mode field adapter 31, a second ytterbium-doped fiber 32, a beam combiner 33, a multimode pump 34 and a collimation output component 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 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 beam combiner 33, the second end of the beam combiner 33 is optically connected to the output end of the multimode pump 34, and the third end of the beam combiner 33 is optically connected to the input end of the collimation output component 35; the pump laser output by the multimode pump 34 is injected into the second ytterbium-doped 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.

[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 optical fiber propagation length 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 multiple frequency adjustments. Only a first-stage power amplification structure is used, and the overall structure is simple and clear. It can achieve a smooth and flat spectrum output from 1000 to 1150 nm, and is very suitable for biological imaging 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 protection scope of the present invention.

Claims

1. A high coherence supercontinuum fiber laser, characterized in that: include: A femtosecond oscillator module (1), 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; The amplification output module (3) is connected to the output optical path of the inverted chirp selection module (2) and is used to reversely amplify and spectrum broaden the input modulated laser light to output supercontinuum laser light.

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 (14) is optically connected to the first end of the non-reciprocal device (14). 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) form 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 pass through the port b of the 2×2 beam splitter (15) and the output device (16) to be output outside the cavity structure, and another portion of the fluorescent photons pass through the port a of the 2×2 beam splitter (15) to be 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 in the cavity structure along two opposite paths, passes through the first ytterbium-doped optical fiber (13) and the non-reciprocal device (14) for optical amplification and phase shift, 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 inverse 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 light propagates along two opposite paths in the cavity structure, one of which is: the reflected laser light 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 light 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 two opposite propagation paths in the cavity structure.

5. A 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. A 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 non-reciprocal device (14); L represents the cavity length of the cavity structure, which is the sum of the optical path length between the wavelength division multiplexer (12), the first ytterbium-doped optical fiber (13), the non-reciprocal 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. A high coherence supercontinuum fiber laser according to claim 3, characterized in that: The inverse chirp menu module (2) comprises a menu device (21), a circulator (22) and a second chirped grating (23); the input end of the menu device (21) is optically connected to the output end of the first chirped grating (17); the menu device (21) performs pulse quantity selection processing on the mode-locked pulse laser; the output end of the menu 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 pulse laser 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.

8. A high coherence supercontinuum fiber laser according to claim 7, 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.

9. A high coherence supercontinuum fiber laser according to claim 7, characterized in that: 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 component (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 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 light intensity, and the spectrum of the laser is broadened in both directions along the central wavelength.

10. A high coherence supercontinuum fiber laser according to claim 9, 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), 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