System and method for generating optical frequency comb from visible light to middle infrared band

Abstract

The invention belongs to the field of laser measurement, and particularly relates to a system and a method for generating an optical frequency comb from visible light to middle-infrared band. The system for generating the optical frequency comb from the visible light to the middle infrared band comprises a full polarization maintaining optical fiber frequency comb module and an optical comb spectrum expansion module, the full polarization-maintaining fiber frequency comb module is used for generating coherent wide-spectrum laser with uniform frequency and spectral line intervals; the optical comb spectrum expansion module is used for carrying out spectrum expansion on the frequency-locked wide-spectrum coherent light source to realize output from visible light to an intermediate infrared section optical frequency comb; the optical comb spectrum expansion module comprises an amplifier B, a 90: 10 beam splitter, an all-polarization-maintaining compressed optical fiber B, an all-polarization-maintaining compressed optical fiber C, a 1100-2350 nm super-continuum spectrum unit and a 500-1100 nm super-continuum spectrum unit; and by opening and closing a circuit of the semiconductor laser diode unit C, the output and closing of laser from near-infrared to middle-infrared band of 1100-2350 nm are realized.

Description

Technical Field

[0001] The invention belongs to the field of laser measurement, and in particular relates to a system and method for generating an optical frequency comb in the visible to mid-infrared band, which is used for calibrating lasers of different wavelengths and measuring different gases. Background Art

[0002] The optical frequency comb (OFC) has the ability to define optical frequencies completely based on microwave frequencies. It can accurately transmit the phase and frequency information from a high-stability reference to hundreds or thousands of frequency beats in the optical domain. It also has nearly continuous spectral coverage from microwave frequencies to extreme ultraviolet rays, making it an irreplaceable role in basic scientific research, frequency standard metrology, laser ranging, optical communications and other research fields.

[0003] Specific application: The most direct application of optical frequency comb is precision optical frequency measurement. The reason why optical frequency comb can be used for precision optical frequency measurement is that the optical frequency comb is a discrete comb structure in the frequency domain. When the frequency is traced back to a stable reference source, each comb tooth has ultra-high frequency stability and accuracy. Therefore, it can be regarded as an optical frequency ruler with extremely high accuracy in the frequency domain [Kim S W. Metrology: Combs rule [J]. Nature Photonics, 2009, 3 (6): 313-314.].

[0004] The application of optical frequency comb in the field of precision spectral measurement. Generally speaking, when molecules interact with light sources, absorption will occur in specific bands, and each molecule will have multiple absorption bands, and the specific absorption band depends on the energy level structure of the molecule. Different types of molecules correspond to different absorption bands, which is equivalent to each molecule having a specific identifier. Since the frequency comb teeth of the optical frequency comb are very rich, its output spectrum generally contains millions of optical frequency comb teeth. When the frequency of the optical frequency comb is traced back to an atomic clock or optical reference, each optical comb tooth can be regarded as a continuous laser with stable frequency and narrow linewidth. Therefore, when the optical frequency comb interacts with molecules as a light source, a characteristic absorption spectrum will be generated. Then, by analyzing the obtained spectrum, the type and content of the molecule to be measured can be known.

[0005] Currently, a near-infrared optical frequency comb combined with nonlinear frequency transfer technology can transfer the comb tooth frequency to the mid-infrared band [SCHLIESSER A, PICQUE N, HANSCH T W. Mid-infrared frequency combs [J]. Nature Photonics, 2012, 6 (7): 440-449.], and is widely used in the generation of mid-infrared optical frequency combs, such as optical parametric oscillators [JIN YW, CRISTESCU SM, HARREN FJM, et al. Two-crystal mid-infrared optical parametric oscillator for absorption and dispersion dual-comb spectroscopy [J]. Optics Letters, 2014, 39 (11): 3270-3273.] (Opticalparametric oscillators, OPOs).

[0006] In 2018, Ycas et al. from the National Institute of Standards and Technology of the United States used a near-infrared mode-locked femtosecond fiber frequency comb to pump a PPLN crystal to generate a mid-infrared idler frequency comb (such as Figure 1 ), the spectrum of idler light accumulates from 3000nm to 5000nm [YCAS G, GIORGETTA FR, BAUMANN E, et al. High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2μm [J]. Nature Photonics, 2018, 12(4): 202-208.].

[0007] At present, although there have been reports on the use of nonlinear frequency conversion technology to convert the working wavelength of the near-infrared band pump light comb source to the mid-infrared band, it is only the conversion of the working wavelength to a spectral window of a specific wavelength. The bandwidth of the optical frequency comb is not widened. Only local spectrum expansion is obtained in the band far from the pump frequency, and there is noise accumulation, resulting in serious degradation of the comb tooth structure. Currently, there are no reports in the industry on optical frequency combs with wavelengths covering the visible light to mid-infrared optical (500-2350nm) band.

[0008] The reason why it is necessary to obtain an optical frequency comb in the visible light to mid-infrared optical (500-2350nm) band is that the visible light to mid-infrared optical (500-2350nm) range covers the spectral range of multiple typical commercial lasers, such as 543nm, 633nm, 1030nm, 1064nm, 1550nm, 2000nm lasers, etc. The development of an optical frequency comb device in the visible light to mid-infrared light band of 500-2350nm can realize the wavelength metrology calibration of the above-mentioned typical commercial lasers. At the same time, in the range of 500-2350nm, there are absorption peaks of gas molecules and toxic gases such as water vapor (H2O), hydrogen peroxide (H2O2), ammonia (NH3), carbon dioxide (CO2), carbon monoxide (CO), hydrogen sulfide (H2S), hydrogen chloride (HCl), hydrogen fluoride (HF), methane (CH4), ethane (C2H4), acetylene (C2H2), and many molecules have characteristic absorption lines in this spectrum range. Therefore, the development of optical frequency comb devices from visible light to mid-infrared light band (500-2350nm) has important application value in spectral analysis and molecular detection.

[0009] In addition, the optical comb is usually locked to an external reference light source (the frequency of the external light source) to improve the accuracy and stability of the optical comb. In this case, the external reference light source often uses a rubidium atomic clock to provide a highly stable and accurate frequency. This ensures that the frequency of the optical comb is synchronized with the frequency of the reference light source, thereby improving the accuracy and stability of the optical comb. However, the repetition frequency stability after the rubidium atomic clock is locked is usually around 10 -11 Magnitude or close to 10 -12 How to improve the measurement accuracy by increasing the order of magnitude of repetition frequency stability is a technical problem that needs to be solved urgently. Summary of the invention

[0010] In view of this, the present invention provides a system and method for generating an optical frequency comb in the visible to mid-infrared band. Through this system, the comb tooth frequency of the optical frequency comb can be broadened to the visible to mid-infrared band, providing important application value for spectral analysis and molecular detection.

[0011] The optical frequency comb generation system in the visible to mid-infrared band includes: a full polarization-maintaining fiber frequency comb module and an optical comb spectrum expansion module;

[0012] The fully polarization-maintaining fiber frequency comb module is used to generate a wide-spectrum laser with uniform and coherent frequency and spectral line spacing;

[0013] The optical comb spectrum expansion module is used to expand the spectrum of the frequency-locked wide-spectrum coherent light source to achieve the output of the optical frequency comb from visible light to mid-infrared;

[0014] The optical comb spectrum expansion module includes an amplifier B, a 90:10 beam splitter, a full polarization-maintaining compression fiber B, a full polarization-maintaining compression fiber C, a 1100-2350nm supercontinuum unit and a 500-1100nm supercontinuum unit;

[0015] The locked laser generated from the full polarization-maintaining fiber frequency comb module enters the amplifier B for pulse amplification and then is split by a 90:10 beam splitter;

[0016] The laser passing through the 10% energy port of the 90:10 beam splitter enters the 1100-2350nm supercontinuum unit through the fully polarization-maintaining compression fiber C;

[0017] The laser passing through the 90% energy port of the 90:10 beam splitter enters the 500-1100nm supercontinuum unit through the fully polarization-maintaining compression fiber B;

[0018] The 1100-2350nm supercontinuum unit includes an amplifier C, a passive optical fiber and a highly nonlinear optical fiber B; the laser light passing through the fully polarization-maintaining compression optical fiber C enters the amplifier C and then passes through the passive optical fiber and the highly nonlinear optical fiber B in sequence;

[0019] The amplifier C is connected to the semiconductor laser diode unit C through an optical fiber, and the output and shutoff of the 1100-2350nm near-infrared to mid-infrared band laser are achieved by opening and closing the circuit of the semiconductor laser diode unit C.

[0020] Preferably,

[0021] The full polarization-maintaining fiber frequency comb module includes a laser, an amplifier A, a full polarization-maintaining compression fiber A, a highly nonlinear fiber A, a colinear self-referenced f-2f beat frequency detection device and a frequency locking system;

[0022] The laser output by the laser sequentially enters the amplifier A, the full polarization-maintaining compression fiber A, the high nonlinear fiber A, the colinear self-reference f-2f beat frequency detection device and the frequency locking system;

[0023] The repetition frequency is locked to the atomic clock of the frequency locking system by stretching the optical fiber in the laser through a piezoelectric ceramic brake;

[0024] The colinear self-reference f-2f beat frequency detection device locks the beat radio frequency signal fceo signal on the atomic clock of the frequency locking system;

[0025] The atomic clock is a hydrogen atomic clock.

[0026] Preferably,

[0027] The laser comprises a SESAM device, a polarization-maintaining erbium-doped optical fiber, a first semiconductor laser diode and an output mirror;

[0028] The SESAM device is located on one side of the linear laser cavity of the laser;

[0029] The first semiconductor laser diode is a pump source, which is reflected by an output mirror located at the other side of the linear laser cavity and enters the polarization-maintaining erbium-doped optical fiber to provide pump excitation;

[0030] One end of the polarization-maintaining erbium-doped optical fiber is connected to the SESAM device, and the other end is connected to the output mirror;

[0031] The output ratio of the output mirror is 90:10, and the output mirror uses 10% of the signal light in the linear laser cavity as the output of the femtosecond laser.

[0032] Preferably,

[0033] The 500-1100nm supercontinuum unit includes a collimation system and a half-wave plate A, a PPLN crystal B, a collimation system and a half-wave plate B and a photonic crystal fiber.

[0034] The laser passes through the collimation system and the half-wave plate A and then enters the PPLN crystal B for frequency doubling, and then enters the collimation system, the half-wave plate B and the photonic crystal fiber in sequence;

[0035] The shape of the supercontinuum spectrum and the spectral power density distribution are controlled by adjusting the pulse pump laser power incident into the PPLN crystal B and the photonic crystal fiber by the collimation system and the half wave plate A and the collimation system and the half wave plate B.

[0036] Preferably,

[0037] The optical fibers contained in the linear laser cavity include polarization-maintaining erbium-doped optical fibers and standard polarization-maintaining single-mode optical fibers, both of which are negative dispersion optical fibers;

[0038] The pump power of the amplifier B comes from the semiconductor laser diode unit B.

[0039] When the pump power of the semiconductor laser diode unit B is increased to 2000 mW, the average output power of the amplifier B reaches 600 mW.

[0040] Beneficial effects:

[0041] (i) The optical frequency comb generation system of the visible to mid-infrared band of the present invention can realize the opening and closing of the laser output in the near-infrared to mid-infrared band of 1100-2350nm by sequentially opening or closing the circuit of the two semiconductor laser diode units C of the amplifier C, and more specifically and efficiently measuring the laser to be measured.

[0042] (ii) The optical frequency comb generation system for the visible to mid-infrared band of the present invention adopts a fully polarization-maintaining fiber frequency comb module and an optical comb spectrum expansion module structure to achieve supercontinuum output of an optical frequency comb covering the visible to mid-infrared band of 500-2350nm, and can provide detection means for lasers of more wavelengths. In addition, it can realize simultaneous measurement of multiple gases.

[0043] (III) The optical frequency comb generation system of the present invention in the visible to mid-infrared band uses a hydrogen atomic clock as the optical comb locking reference module, and the repetition frequency stability can reach 10 -13 The locking accuracy is one order of magnitude higher than that of the current rubidium atomic clock, which improves the measurement accuracy of the laser wavelength to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the principle of the device for generating a mid-infrared band idler light comb based on a PPLN crystal mentioned in the background technology of the present invention;

[0045] Figure 2 This is a composition diagram of the optical frequency comb generation system from visible light to mid-infrared band of the present invention;

[0046] Among them, 1-full polarization-maintaining fiber frequency comb module, 2-optical comb spectrum expansion module, 3-laser, 31-polarization-maintaining erbium-doped fiber, 32-first semiconductor laser diode, 33-output mirror, 34-SESAM device, 35-piezoelectric ceramic brake, 5-amplifier A, 51-second semiconductor laser diode, 52-third semiconductor laser diode, 53-fourth semiconductor laser diode, 6-full polarization-maintaining compression fiber A, 7-high nonlinear fiber A, 8-collinear self-reference f-2f beat frequency detection device, 81-first lens, 82-second lens, 83-third lens, 84-fourth lens, 85-PPLN crystal A, 9-frequency locking system, 10-atomic clock, 11-amplifier B, 11-1-semiconductor laser diode unit B, 11-1 -1-the fifth semiconductor laser diode, 11-1-2-the sixth semiconductor laser diode, 11-1-3-the seventh semiconductor laser diode, 12-90:10 beam splitter, 13-full polarization-maintaining compression fiber B, 14-full polarization-maintaining compression fiber C, 15-1100-2350nm supercontinuum unit, 15-2-amplifier C, 15-2-1-the eighth semiconductor laser diode, 15-2-2-the ninth semiconductor laser diode, 15-3-high nonlinear fiber B, 15-4-semiconductor laser diode unit C, 16-500-1100nm supercontinuum unit, 16-1-PPLN crystal B, 16-2-photonic crystal fiber, 16-3-collimation system and half wave plate A, 16-4-collimation system and half wave plate B. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 making creative work are within the scope of protection of the present invention.

[0048] like Figure 2 As shown, the visible to mid-infrared optical frequency comb generation system includes a full polarization-maintaining fiber frequency comb module 1 and an optical comb spectrum expansion module 2; the full polarization-maintaining fiber frequency comb module 1 is used to generate a wide-spectrum laser with uniform and coherent frequency and spectral line spacing; the optical comb spectrum expansion module 2 is used to expand the spectrum of the laser from visible light to near-infrared band laser and from near-infrared band to mid-infrared band laser band.

[0049] The fully polarization-maintaining fiber frequency comb module 1 includes a laser 3, an amplifier A5, a fully polarization-maintaining compression fiber A6, a highly nonlinear fiber A7, a colinear self-referenced f-2f beat frequency detection device 8 and a frequency locking system 9;

[0050] The optical comb spectrum expansion module 2 includes an amplifier B11, a 90:10 beam splitter 12, a fully polarization-maintaining compression fiber B13, a fully polarization-maintaining compression fiber C14, a 1100-2350nm supercontinuum unit 15 and a 500-1100nm supercontinuum unit 16; the amplifier B11 is used to amplify the pulse power output by the amplifier A5 and simultaneously widen the spectrum width by utilizing the nonlinear self-phase modulation effect; the pump power of the amplifier B11 comes from the semiconductor laser diode unit B11-1.

[0051] The 1100-2350nm supercontinuum unit 15 includes an amplifier C15-2, a passive optical fiber and a highly nonlinear optical fiber B15-3; the amplifier C15-2 is connected to a semiconductor laser diode unit C15-4 via an optical fiber, and the output and shutoff of the 1100-2350nm near-infrared to mid-infrared band laser are achieved by opening and closing the circuit of the semiconductor laser diode unit C15-4.

[0052] As an example, the laser 3 is a fully polarization-maintaining linear cavity-mode-locked erbium-doped fiber laser based on SESAM;

[0053] As an example, the amplifier A5 is a fully polarization-maintaining fiber femtosecond pulse amplifier;

[0054] As an example, the amplifier C15-2 is a fully polarization-maintaining fiber femtosecond pulse amplifier;

[0055] The laser 3 is a linear cavity structure, which includes a SESAM device 34, a polarization-maintaining erbium-doped fiber 31, a first semiconductor laser diode 32 and an output mirror 33. The laser 3 uses a fiber-coupled SESAM device 34 to finally achieve self-starting mode locking. The SESAM device 34 is located on one side of the linear laser cavity, and its pigtail length is about 15 cm, and the modulation depth and absorption coefficient are 15% and 25% respectively. The pump source uses a first semiconductor laser diode 32 with a central wavelength of 976 nm, and is reflected by the output mirror 33 located on the other side of the linear laser cavity into the polarization-maintaining erbium-doped fiber 31 to provide pump excitation, that is, one end of the polarization-maintaining erbium-doped fiber 31 is connected to the SESAM device 34, and the other end is connected to the output mirror 33. The output ratio of the output mirror 33 is 90:10. The output mirror 33 uses 10% of the signal light in the linear laser cavity as the output of the femtosecond laser. The output laser enters the amplifier A5, the fully polarization-maintaining compression fiber A6, the highly nonlinear fiber A7, the colinear self-reference f-2f beat frequency detection device 8 and the frequency locking system 9 in sequence.

[0056] As an example, the optical fibers contained in the linear laser cavity include polarization-maintaining erbium-doped optical fibers and standard polarization-maintaining single-mode optical fibers, both of which are negative dispersion optical fibers. (The dispersion coefficients of polarization-maintaining erbium-doped optical fibers and standard polarization-maintaining single-mode optical fibers at 1550nm are similar, both of which are 17ps / nm / km. Considering that in a linear laser cavity, the light pulse is transmitted back and forth twice in the cavity within one cycle, it can be calculated that the net dispersion in the cavity is about -0.02ps2).

[0057] Amplifier A5 and amplifier B11 both include an all-in-one device formed by three sets of wavelength division multiplexers (WDM) and optical isolators (ISO), and three semiconductor laser diodes connected by optical fibers, all of which are used to widen the width and pre-amplify the power of the laser pulse output from the output mirror 33, and to maintain the spectrum shape. Each set of all-in-one devices is connected to a semiconductor laser diode through an optical fiber, and the second semiconductor laser diode 51, the third semiconductor laser diode 52, and the fourth semiconductor laser diode 53 are respectively connected to the amplifier A5 through three optical fibers.

[0058] Amplifier A5 is a two-stage femtosecond pulse amplification system based on fully polarization-maintaining single-mode optical fiber and optical fiber devices. The pulse amplification system includes a low-gain and high-dispersion erbium-doped fiber pre-amplifier, a high-gain and low-dispersion erbium-doped fiber main amplifier, and a compressor consisting of a section of negative-dispersion optical fiber.

[0059] As an example, the central wavelength of the second semiconductor laser diode 51 , the third semiconductor laser diode 52 , and the fourth semiconductor laser diode 53 is 976 nm, and the maximum power is 1600 mW.

[0060] Amplifier B11 uses high-gain, low-dispersion erbium-doped fiber, which is a high-doping concentration polarization-maintaining erbium-doped fiber main amplifier. Amplifier B11 is used to amplify the pulse power output by amplifier A5 and simultaneously use the nonlinear self-phase modulation effect to broaden the spectrum width. A fifth semiconductor laser diode 11-1-1, a sixth semiconductor laser diode 11-1-2, and a seventh semiconductor laser diode 11-1-3 are connected to amplifier B11 through three optical fibers.

[0061] Working principle of full polarization-maintaining fiber frequency comb module 1:

[0062] 1. The pump current of the first semiconductor laser diode 32 is increased. When the pump power is 39.6 mW, the 3 dB bandwidth of the output spectrum is 13.3 nm, and the average pulse output power reaches 12.66 mW.

[0063] 2. The driving current of the second semiconductor laser diode 51 and the third semiconductor laser diode 52 is increased. When the pump power reaches 1542 mW, the pulse spectrum width output by the amplifier A5 is 25.15 nm, and the corresponding average output power reaches 332 mW.

[0064] The full polarization-maintaining compression fiber A6 (equivalent to an optical fiber) is connected to the output end of the amplifier A5 in order to generate a broadband supercontinuum that can cover an octave and increase the peak power of the pulse. The full polarization-maintaining compression fiber A6 contains a section of negative dispersion fiber, that is, the dispersion coefficient of the fiber at 1550nm is 18ps / nm / km, and the mode field diameter is 10.5μm. As an example, when the output pulse power of the amplifier A5 is the maximum, the pulse width can be compressed to less than 100 femtoseconds by optimizing the length of the full polarization-maintaining compression fiber A6.

[0065] The laser enters the high nonlinear fiber A7 through the full polarization-maintaining compression fiber A6, and the supercontinuum spectrum shape and spectral power density distribution generated are controlled by adjusting the pulsed pump laser power incident on the high nonlinear fiber A7 (length 57 cm). The supercontinuum spectrum generated by the high nonlinear fiber A7 is further coupled into the colinear self-referenced f-2f beat frequency detection device 8 to detect the fceo signal.

[0066] In the colinear self-referenced f-2f beat frequency detection device 8, the laser sequentially passes through the first lens 81, the second lens 82, the PPLN crystal A85, the third lens 83 and the fourth lens 84. It uses two self-focusing lenses with pigtails (the first lens 81 and the second lens 82) to collimate and focus the supercontinuum spectrum into the PPLN crystal A85, and the 1015nm light pulse generated by frequency doubling and the original 1015nm spectral component in the supercontinuum spectrum are sequentially coupled into the third lens 83 and the fourth lens 84, and interference beat frequency occurs. The RF signal obtained by the beat frequency is the fceo signal. The detected optical frequency signal fceo is locked to the hydrogen atomic clock 10 of the frequency locking system 9 through the servo feedback circuit in the frequency locking system 9, and the locking accuracy is one order of magnitude higher than that of the current rubidium atomic clock.

[0067] When the full polarization-maintaining fiber frequency comb module 1 completes the locking of the repetition frequency and the offset frequency (specifically: the piezoelectric ceramic brake 35 stretches the optical fiber in the laser 3 to lock the repetition frequency on the atomic clock 10 of the frequency locking system 9; the colinear self-referenced f-2f beat frequency detection device 8 locks the beat radio frequency signal fceo signal (offset frequency) on the atomic clock 10 of the frequency locking system 9), the laser output from the laser 3 is a series of wide-spectrum lasers with uniform and coherent frequency and spectral line intervals, namely, a femtosecond optical frequency comb. In order to achieve the spectrum expansion output of the femtosecond optical frequency comb, the pulse after passing through the amplifier A5 in the full polarization-maintaining fiber frequency comb module 1 is again amplified by the amplifier B11, and then the pulse is split by the 90:10 beam splitter 12. The laser passing through the 10% energy port of the 90:10 beam splitter is used to generate a spectrum in the mid-infrared band, and the laser passing through the 90% energy port of the 90:10 beam splitter is used to generate a spectrum in the visible light band.

[0068] Working principle of optical comb spectrum extension module 2:

[0069] First, the femtosecond laser output by the full polarization-maintaining fiber frequency comb module 1 passes through the amplifier B11 (including a first-stage low-gain and high-dispersion erbium-doped fiber preamplifier and a first-stage high-gain and low-dispersion erbium-doped fiber main amplifier). The fifth semiconductor laser diode 11-1-1 (playing the role of preamplification), the sixth semiconductor laser diode 11-1-2 (playing the role of hybrid main amplifier) ​​and the seventh semiconductor laser diode 11-1-3 are connected to the amplifier B11. (The fifth semiconductor laser diode 11-1-1, the sixth semiconductor laser diode 11-1-2 and the seventh semiconductor laser diode 11-1-3 constitute the semiconductor laser diode unit B11-1).

[0070] Operation of amplifier B11:

[0071] When the pump current of the fifth semiconductor laser diode 11-1-1 is increased to 460mW, the average pulse output power reaches 46mW. Then, the drive current of the sixth semiconductor laser diode 11-1-2 and the seventh semiconductor laser diode 11-1-3 is increased. When the pump power reaches 2000mW, the average output power of the amplifier B11 reaches 600mW. When the output pulse power of the amplifier B11 is the maximum, the pulse width is compressed to less than 100 femtoseconds by optimizing the length of the full polarization-maintaining compression fiber B13 and the full polarization-maintaining compression fiber C14.

[0072] 1100-2350nm near infrared to mid infrared band supercontinuum unit 15 working principle:

[0073] The laser passing through the 10% energy port of the 90:10 beam splitter 12 is used to generate a spectrum in the mid-infrared band. Since the power after beam splitting is relatively low, in order to achieve the peak power required for nonlinear transformation, the amplifier C15-2 (connecting the eighth semiconductor laser diode 15-2-1 and the ninth semiconductor laser diode 15-2-2) is first used to amplify the power of the 1560nm laser passing through the full polarization-maintaining compression fiber C14, and the laser power is amplified to 200mW, and then the pulse is compressed through a section of passive optical fiber, and the compressed 1560nm laser is expanded through a section of high nonlinear optical fiber B15-3 to achieve 1100-2350nm near-infrared to mid-infrared band laser output.

[0074] In this embodiment, the fiber length of the high nonlinear fiber B15-3 is determined to be 40 cm. The pulse pump laser power incident into the fully polarization-maintaining high nonlinear fiber B15-3 can be adjusted by adjusting the current power of the eighth semiconductor laser diode 15-2-1 and the ninth semiconductor laser diode 15-2-2, so as to control the shape of the supercontinuum spectrum and the spectral power density distribution generated. By turning on or off the circuits of the eighth semiconductor laser diode 15-2-1 and the ninth semiconductor laser diode 15-2-2, the laser output and shutdown in the near-infrared to mid-infrared band of 1100-2350nm can be realized, and the laser to be measured can be measured more efficiently in a more targeted manner.

[0075] 500-1100nm visible light to near infrared band supercontinuum unit 16 working principle:

[0076] The laser passing through the 90% energy port of the 90:10 beam splitter 12 is used to generate a spectrum in the visible light band. In order to achieve the peak power required for nonlinear conversion, the pulse width is first compressed through a section of passive optical fiber; the 1560nm fundamental frequency light pulse compressed by the full polarization-maintaining compression fiber B13 enters the periodically polarized lithium niobate crystal (PPLN crystal B16-1) for frequency doubling, generating 780nm frequency-doubled light, with an average power of 160mW and a frequency doubling efficiency of 28.6%. Subsequently, the frequency-doubled 780nm signal light is injected into a section of photonic crystal fiber 16-2 for spectrum expansion, realizing the output of an optical frequency comb of 500-1100nm visible light near-infrared band laser.

[0077] Specifically, a collimation system and a half wave plate A16-3 are provided in front of the PPLN crystal B16-1; a collimation system and a half wave plate B16-4 are provided in front of the photonic crystal fiber 16-2; the power of the pulsed pump laser incident on the periodically poled lithium niobate crystal (PPLN crystal B16-1) and the photonic crystal fiber 16-2 is adjusted by adjusting the collimation system and the half wave plate A16-3 and the collimation system and the half wave plate B, so as to control the shape of the supercontinuum spectrum and the spectral power density distribution.

[0078] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. An optical frequency comb generation system from visible light to mid-infrared band, characterized by: It comprises a full polarization-maintaining optical fiber frequency comb module (1) and an optical comb spectrum expansion module (2); The fully polarization-maintaining fiber frequency comb module (1) is used to generate a wide-spectrum laser with uniform frequency and spectral line spacing and coherence; The optical comb spectrum expansion module (2) is used to expand the spectrum of the broadband laser to achieve the output of an optical frequency comb from visible light to mid-infrared range; The optical comb spectrum expansion module (2) comprises an amplifier B (11), a beam splitter (12), a 1100-2350 nm supercontinuum unit (15) and a 500-1100 nm supercontinuum unit (16); The wide spectrum laser enters the amplifier B (11) for pulse amplification and then is split by a beam splitter (12); one part enters the 1100-2350nm supercontinuum unit (15), and the other part enters the 500-1100nm supercontinuum unit (16); The 1100-2350nm supercontinuum unit (15) comprises an amplifier C (15-2), a passive optical fiber and a highly nonlinear optical fiber B (15-3); the laser light entering the 1100-2350nm supercontinuum unit (15) enters the amplifier C (15-2) and then passes through the passive optical fiber and the highly nonlinear optical fiber B (15-3) in sequence; The amplifier C (15-2) is connected to the semiconductor laser diode unit C (15-4), and the output and shutoff of the 1100-2350nm band laser are achieved by opening and closing the circuit of the semiconductor laser diode unit C (15-4).

2. The visible to mid-infrared optical frequency comb generation system according to claim 1, characterized in that: The beam splitter (12) is a 90:10 beam splitter; The optical comb spectrum expansion module (2) further comprises a full polarization-maintaining compression optical fiber B (13) and a full polarization-maintaining compression optical fiber C (14); The broadband laser enters the 1100-2350 nm supercontinuum unit (15) through the 10% energy port of the 90:10 beam splitter via the full polarization-maintaining compression optical fiber C (14); The broadband laser enters the 500-1100 nm supercontinuum unit (16) through the 90% energy port of the 90:10 beam splitter via the full polarization-maintaining compression optical fiber B (13).

3. The visible to mid-infrared optical frequency comb generation system according to claim 2, characterized in that: The fully polarization-maintaining fiber frequency comb module (1) comprises a laser (3), an amplifier A (5), a fully polarization-maintaining compression fiber A (6), a highly nonlinear fiber A (7), a colinear self-reference f-2f beat frequency detection device (8) and a frequency locking system (9); The laser light output by the laser (3) sequentially enters the amplifier A (5), the fully polarization-maintaining compression optical fiber A (6), the highly nonlinear optical fiber A (7), the colinear self-reference f-2f beat frequency detection device (8) and the frequency locking system (9); The optical fiber in the laser (3) is stretched by a piezoelectric ceramic brake (35) to lock the repetition frequency to the atomic clock (10) of the frequency locking system (9); The colinear self-reference f-2f beat frequency detection device (8) locks the beat radio frequency signal fceo signal onto the atomic clock (10) of the frequency locking system (9); The atomic clock (10) is a hydrogen atomic clock.

4. The visible to mid-infrared optical frequency comb generation system according to claim 3, characterized in that: The laser (3) comprises a SESAM device (34), a polarization-maintaining erbium-doped optical fiber (31), a first semiconductor laser diode (32) and an output mirror (33); The SESAM device (34) is located on one side of the linear cavity structure of the laser (3); The first semiconductor laser diode (32) is a pump source, which is reflected by an output mirror (33) located on the other side of the linear cavity structure and enters the polarization-maintaining erbium-doped optical fiber (31) to provide pump excitation; One end of the polarization-maintaining erbium-doped optical fiber (31) is connected to the SESAM device (34), and the other end is connected to the output mirror (33); The output ratio of the output mirror (33) is 90:10, and the output mirror (33) uses 10% of the signal light in the linear cavity structure as the output of the femtosecond laser.

5. The visible to mid-infrared optical frequency comb generation system according to claim 4, characterized in that: The optical fibers contained in the linear cavity structure include polarization-maintaining erbium-doped optical fibers and standard polarization-maintaining single-mode optical fibers, both of which are negative dispersion optical fibers; The pump power of the amplifier B (11) comes from a semiconductor laser diode unit B (11-1), When the pump power of the semiconductor laser diode unit B (11-1) is increased to 2000mW, the average output power of the amplifier B (11) reaches 600mW.

6. The visible to mid-infrared optical frequency comb generation system according to any one of claims 1 to 5, characterized in that: The 500-1100 nm supercontinuum unit (16) comprises a collimation system and a half wave plate A (16-3), a PPLN crystal B (16-1), a collimation system and a half wave plate B (16-4) and a photonic crystal optical fiber (16-2). The laser passes through the collimation system and the half-wave plate A (16-3) and enters the PPLN crystal B (16-1) for frequency doubling, and then enters the collimation system, the half-wave plate B (16-4) and the photonic crystal fiber (16-2) in sequence; By adjusting the collimation system and the half wave plate A (16-3) and the collimation system and the half wave plate B (16-4) to be incident on the PPLN crystal B (16-1) and the pulse in the photonic crystal fiber (16-2), The pump laser power is used to control the shape of the supercontinuum spectrum and the spectral power density distribution.

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