Optical frequency comb generation system and method for visible light to mid-infrared band

Abstract

The present invention belongs to the field of laser measurement, and specifically relates to a system and method for generating an optical frequency comb in the visible to mid-infrared band. The system comprises a fully polarization-maintaining fiber frequency comb module and a comb spectrum expansion module. The fully polarization-maintaining fiber frequency comb module is used to generate a broadband laser with uniform and coherent frequency and spectral line spacing. The comb spectrum expansion module is used to expand the spectrum of the frequency-locked broadband coherent light source to achieve the output of an optical frequency comb in the visible to mid-infrared band. The comb spectrum expansion module comprises an amplifier B, a 90:10 beam splitter, a fully polarization-maintaining compression fiber B, a fully polarization-maintaining compression fiber C, an 1100-2350nm supercontinuum unit, and a 500-1100nm supercontinuum unit. The output and shutoff of the 1100-2350nm near-infrared to mid-infrared laser are achieved by switching the circuit of the semiconductor laser diode unit C.

Description

Technical Field

[0001] The present 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 (abbreviated as "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, and has nearly continuous spectral coverage from microwave frequencies to extreme ultraviolet rays, making it play an irreplaceable role in basic scientific research, frequency standard metrology, laser ranging, optical communications and other research fields.

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

[0004] The application of optical frequency combs in the field of precision spectral measurement. Generally speaking, when molecules interact with light sources, absorption occurs at specific wavelengths, and each molecule has multiple absorption bands, depending on the energy level structure of the molecule. Different molecular types correspond to different absorption bands, which is equivalent to each molecule having a specific identifier. Because the frequency 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. By analyzing the obtained spectrum, the type and content of the molecule to be measured can be determined.

[0005] Currently, a near-infrared frequency comb combined with nonlinear frequency transfer technology can transfer the comb teeth 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 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.] (Optical parametric 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 an idler frequency comb in the mid-infrared band (such as Figure 1 ), the spectrum of the 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 of using nonlinear frequency conversion technology to convert the operating wavelength of a near-infrared pump light comb source to the mid-infrared band, this only converts the operating 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 a band far from the pump frequency, and noise accumulation causes 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 band (500-2350nm).

[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, and 2000nm lasers. The development of an optical frequency comb device in the visible light to mid-infrared light band of 500-2350nm can realize the wavelength metrological 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), and acetylene (C2H2). Many molecules have characteristic absorption lines in this spectral range. Therefore, the development of optical frequency comb devices in the 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 of the rubidium atomic clock after locking is usually around 10 -11 Magnitude or close to 10 -12 How to improve the measurement accuracy by increasing the magnitude of the 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 in spectral analysis and molecular detection.

[0011] The optical frequency comb generation system for 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 frequency and spectral line spacing and coherence;

[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 range;

[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 by 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 light 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 light passing through the 90% energy port of the 90:10 beam splitter enters the 500-1100 nm 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 via an optical fiber, and the output and shutoff of the 1100-2350nm near-infrared to mid-infrared 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 collinear 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 highly nonlinear fiber A, the collinear self-reference f-2f beat frequency detection device and the frequency locking system;

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

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

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

[0026] Preferably,

[0027] The laser includes 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 on 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 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] (1) The optical frequency comb generation system for the visible to mid-infrared band of the present invention can turn on and off the laser output in the 1100-2350nm near-infrared to mid-infrared band by sequentially turning on or off the circuits of the two semiconductor laser diode units C of the amplifier C, thereby more specifically and efficiently measuring the laser to be measured.

[0042] (2) The optical frequency comb generation system for visible light to mid-infrared bands of the present invention adopts a fully polarization-maintaining fiber frequency comb module and an optical comb spectrum expansion module structure to achieve supercontinuum spectrum output of an optical frequency comb covering the visible light to mid-infrared light band of 500-2350nm. It can provide detection means for lasers of more wavelengths and can also realize the simultaneous measurement of multiple gases.

[0043] (3) 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 Schematic diagram of the device principle for generating a mid-infrared idler comb based on a PPLN crystal as mentioned in the background of the present invention;

[0045] Figure 2 This is a diagram showing the composition of the optical frequency comb generation system for the visible to mid-infrared range 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-referenced 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-fifth semiconductor laser diode, 11-1-2-sixth semiconductor laser diode, 11-1-3-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-eighth semiconductor laser diode, 15-2-2-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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. The described embodiments are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort 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 a light 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 light comb spectrum expansion module 2 is used to expand the spectrum of the laser from visible light to near-infrared band and from near-infrared band to mid-infrared band.

[0049] The full polarization-maintaining fiber frequency comb module 1 includes a laser 3, an amplifier A5, a full polarization-maintaining compression fiber A6, a highly nonlinear fiber A7, a collinear 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, an 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 the 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] Laser 3 has a linear cavity structure, comprising a SESAM device 34, a polarization-maintaining erbium-doped fiber 31, a first semiconductor laser diode 32, and an output mirror 33. Laser 3 utilizes a fiber-coupled SESAM device 34 to achieve self-starting mode locking. The SESAM device 34 is located on one side of the linear laser cavity, with a pigtail length of approximately 15 cm, a modulation depth of 15%, and an absorption coefficient of 25%. The pump source, a first semiconductor laser diode 32 with a central wavelength of 976 nm, is reflected by an 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. Specifically, 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 collinear self-referenced f-2f beat frequency detection device 8 and the frequency locking system 9 in sequence.

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

[0057] Amplifier A5 and amplifier B11 both contain an all-in-one device consisting of three sets of wavelength division multiplexers (WDMs) and optical isolators (ISOs), as well as three semiconductor laser diodes connected via optical fibers. These devices are used to stretch and pre-amplify the laser pulses output from output mirror 33, while also maintaining the spectral shape. Each set of all-in-one devices is connected to a semiconductor laser diode via optical fibers. Amplifier A5 is connected to a second semiconductor laser diode 51, a third semiconductor laser diode 52, and a fourth semiconductor laser diode 53 via three optical fibers, respectively.

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

[0059] As an example, the center 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 utilizes high-gain, low-dispersion erbium-doped fiber. It serves as a highly doped, polarization-maintaining erbium-doped fiber main amplifier. Amplifier B11 amplifies the pulse power output from amplifier A5 and simultaneously broadens the spectral width using nonlinear self-phase modulation. Amplifier B11 is connected to the fifth, sixth, and seventh semiconductor laser diodes 11-1-1, 11-1-2, and 11-1-3 via three optical fibers.

[0061] Working principle of the fully 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] Connecting a fully polarization-maintaining compression fiber A6 (equivalent to a single optical fiber) to the output of amplifier A5 generates a broadband supercontinuum covering an entire octave, thereby increasing the peak power of the pulses. This fiber comprises a section of negative-dispersion fiber with a dispersion coefficient of 18 ps / nm / km at 1550 nm and a mode field diameter of 10.5 μm. As an example, when amplifier A5 outputs maximum pulse power, the pulse width can be compressed to less than a hundred femtoseconds by optimizing the length of the fully polarization-maintaining compression fiber A6.

[0065] Laser light enters the highly nonlinear fiber A7 through fully polarization-maintaining compression fiber A6. The shape and spectral power density of the resulting supercontinuum spectrum are controlled by adjusting the power of the pulsed pump laser incident on the highly nonlinear fiber A7 (57 cm in length). The supercontinuum generated by the highly nonlinear fiber A7 is further coupled into a collinear self-referenced f-2f beat frequency detector 8 to detect the fceo signal.

[0066] In the collinear 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. Two self-focusing lenses with pigtails (the first lens 81 and the second lens 82) collimate and focus the supercontinuum spectrum into the PPLN crystal A85. The 1015nm optical pulse generated by frequency doubling and the original 1015nm spectral component of the supercontinuum spectrum are then sequentially coupled into the third lens 83 and the fourth lens 84, where they interfere with each other and beat. The resulting radio frequency signal is the fceo signal. The servo feedback circuit in the frequency locking system 9 locks the detected optical frequency signal fceo to the hydrogen atomic clock 10 of the frequency locking system 9, with the locking accuracy improved by an order of magnitude compared to the current rubidium atomic clock.

[0067] After the full-polarization-maintaining fiber frequency comb module 1 completes repetition frequency and offset frequency locking (specifically: the piezoelectric ceramic brake 35 stretches the optical fiber in the laser 3 to lock the repetition frequency to the atomic clock 10 of the frequency locking system 9; the collinear self-referenced f-2f beat frequency detection device 8 locks the beat radio frequency signal fceo (offset frequency) to 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 frequencies and spectral lines, namely, a femtosecond optical frequency comb. To achieve spectrum expansion output of the femtosecond optical frequency comb, the pulses after passing through amplifier A5 in the full-polarization-maintaining fiber frequency comb module 1 are further amplified by amplifier B11 and then split by a 90:10 beam splitter 12. The laser light 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 light 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 expansion module 2:

[0069] First, the femtosecond laser output by the full-polarization-maintaining fiber frequency comb module 1 passes through amplifier B11 (which includes a low-gain, high-dispersion erbium-doped fiber preamplifier and a high-gain, low-dispersion erbium-doped fiber main amplifier). Amplifier B11 is connected to a fifth semiconductor laser diode 11-1-1 (which serves as a preamplifier), a sixth semiconductor laser diode 11-1-2 (which serves as a hybrid main amplifier), and a seventh semiconductor laser diode 11-1-3. (The fifth, sixth, and seventh semiconductor laser diodes 11-1-1, 11-1-2, and 11-1-3 form 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 was increased to 460mW, the average pulse output power reached 46mW. Subsequently, by increasing the drive current of the sixth and seventh semiconductor laser diodes 11-1-2 and 11-1-3, when the pump power reached 2000mW, the average output power of amplifier B11 reached 600mW. With amplifier B11 outputting maximum pulse power, the pulse width was compressed to below 100 femtoseconds by optimizing the lengths of fully polarization-maintaining compression fibers B13 and C14.

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

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

[0074] In this embodiment, the fiber length of the highly nonlinear fiber B15-3 is set to 40 cm. By adjusting the current power of the eighth semiconductor laser diode 15-2-1 and the ninth semiconductor laser diode 15-2-2, the pulsed pump laser power incident on the fully polarization-maintaining highly nonlinear fiber B15-3 can be adjusted, thereby controlling the shape of the generated supercontinuum spectrum and the spectral power density distribution. By turning the circuits of the eighth semiconductor laser diode 15-2-1 and the ninth semiconductor laser diode 15-2-2 on and off, laser output in the near-infrared to mid-infrared wavelength range of 1100-2350 nm can be achieved, enabling more targeted and efficient measurement of the laser being measured.

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

[0076] The laser light passing through the 90% energy port of the 90:10 beam splitter 12 is used to generate a spectrum in the visible light band. To achieve the peak power required for nonlinear transformation, the pulse width is first compressed through a passive optical fiber. After compression by the fully polarization-maintaining compression fiber B13, the 1560nm fundamental frequency light pulse enters a periodically poled 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%. The frequency-doubled 780nm signal light is then injected into a photonic crystal fiber 16-2 for spectrum expansion, achieving the output of an optical frequency comb in the 500-1100nm visible and near-infrared laser band.

[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; by adjusting the collimation system and the half-wave plate A16-3 and the collimation system and the half-wave plate B, 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 to control the shape of the supercontinuum spectrum and the spectral power density distribution.

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

Claims

1. An optical frequency comb generation system from visible light to mid-infrared, characterized by: It 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 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 broadband laser enters the amplifier B (11) for pulse amplification and then is split by a beam splitter (12); a portion enters the 1100-2350 nm supercontinuum unit (15), and the other portion enters the 500-1100 nm 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 realizes the output and shutoff of the 1100-2350nm band laser by opening and closing the circuit of the semiconductor laser diode unit C (15-4); 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 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; The shape of the supercontinuum spectrum and the spectral power density distribution are controlled by adjusting the pulse pump laser power incident on the PPLN crystal B (16-1) and the photonic crystal fiber (16-2) by the collimation system and half-wave plate A (16-3) and the collimation system and half-wave plate B (16-4).

2. The optical frequency comb generation system for visible to mid-infrared wavelengths 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 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 full polarization-maintaining fiber frequency comb module (1) comprises a laser (3), an amplifier A (5), a full polarization-maintaining compression fiber A (6), a highly nonlinear fiber A (7), a collinear self-referenced 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 collinear 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 collinear self-reference f-2f beat frequency detection device (8) locks the beat radio frequency signal fceo signal to 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 the 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.

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