CN115541518A - Long-wave infrared standard wavelength generation device and method based on optical comb locking - Google Patents
Long-wave infrared standard wavelength generation device and method based on optical comb locking Download PDFInfo
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Abstract
The invention discloses a device and a method for generating long-wave infrared standard wavelength based on optical comb locking, and belongs to the technical field of long-wave infrared waves. The method comprises the following steps: generating an optical comb signal of a long-wave infrared band based on a near-infrared light difference frequency mechanism; according to the wavelength point to be calibrated, realizing a stable standard wavelength signal of a long-wave infrared band; when standard light sources on other wavelength points of the long-wave infrared band need to be generated, the wavelength of the long-wave infrared tunable laser is tuned to be locked to the optical comb again; and leading the standard optical wavelength signal into the calibrated spectral measuring instrument, and calibrating the calibrated spectral measuring instrument according to the error value between the measured value and the standard value. The long-wave infrared standard light wavelength uncertainty level is high; the uncertainty of the optical wavelength measurement in the long-wave infrared band is better than 10 ‑10 (ii) a The wavelength of the standard light can be continuously tuned, so that the calibration of the long-wave infrared spectrum measuring instrument on a series of wavelength points is realized.
Description
Technical Field
The invention belongs to the technical field of long-wave infrared waves, and particularly relates to a long-wave infrared standard wavelength generation device and method based on optical comb locking.
Background
The long-wave infrared band generally refers to an electromagnetic band with the wavelength of 8-14 mu m, and the band is an important atmospheric window and has important application value in the fields of night investigation, product drying, medical treatment and the like. The calibration of long-wave infrared band spectrum measuring instruments such as Fourier transform infrared spectrometers and Fabry-Perot interferometers is of great significance to the application of the bands, but effective calibration sources are lacked for a long time.
Most of the existing calibration schemes are realized based on standard substances, the calibration precision is poor, the calibration wavelength points are few, and the requirements of current substance component analysis, standard spectrum database establishment and the like on high-precision spectrum measurement cannot be met. For example, in calibration of a fourier transform spectrometer, polystyrene is generally used as a standard substance, the fourier transform spectrometer is used to measure a characteristic absorption frequency of the substance in the vicinity of 11 μm, and calibration of the spectrometer is then performed based on an error between the standard value and the measured value.
The prior art scheme has the following disadvantages:
(1) The calibration accuracy is poor. The standard spectral data of the standard substance is measured under a specific environment, and the accuracy of the calibration scheme is affected due to the inevitable inconsistency between the environmental conditions of the actual calibration process and the standard spectral measurement environment.
(2) The calibration wavelength points are few. The standard substance has few characteristic peaks in the long-wave infrared, and therefore, few calibration wavelength points are available.
The invention provides a calibration method and a calibration device for a long-wave infrared spectrum measuring instrument based on optical comb locking, which can lock a long-wave infrared tunable narrow linewidth light source onto a long-wave infrared optical comb, realize high-precision calibration of the spectrum measuring instrument in a wide waveband range, and achieve the measurement uncertainty of 10 -10 The problems of few wavelength point calibration and insufficient precision of the conventional calibration method are well solved.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides the long-wave infrared standard wavelength generation device and method based on optical comb locking, which are reasonable in design, overcome the defects in the prior art and have good effects.
In order to achieve the purpose, the invention adopts the following technical scheme:
a long-wave infrared standard wavelength generating device based on optical comb locking comprises a femtosecond oscillator, a filter, an isolator, a first erbium-doped optical fiber, a first wavelength division multiplexer, a first photodiode, an optical fiber beam splitter, a second erbium-doped optical fiber, a second wavelength division multiplexer, a second photodiode, a high nonlinear optical fiber, a first optical fiber collimator, a first half-wave plate, a third wavelength division multiplexer, a third photodiode, a third erbium-doped optical fiber, a fourth wavelength division multiplexer, a fourth photodiode, a second optical fiber collimator, an optical delayer, a second half-wave plate, a dichroic mirror, a first convergent lens, a difference frequency crystal, a long-wave infrared tunable laser, a semi-transparent semi-reflective mirror, a beam combining mirror, a second convergent lens collimation, a low-pass filter, a grating, a second photodetector and a second phase-locked loop;
the femtosecond oscillator, the filter, the isolator, the first erbium-doped fiber, the first wavelength division multiplexer and the first photodiode are sequentially connected through a circuit;
the first erbium-doped fiber, the first wavelength division multiplexer and the first photodiode form an amplifying unit;
the first wavelength division multiplexer, the optical fiber beam splitter, the second erbium-doped optical fiber, the second wavelength division multiplexer, the high nonlinear optical fiber, the first optical fiber collimator and the first half-wave plate are sequentially connected through a line;
the second wavelength division multiplexer and the second photodiode are connected through a line;
the second erbium-doped fiber, the second wavelength division multiplexer and the second photodiode form an amplifying unit;
the optical fiber beam splitter, the third wavelength division multiplexer, the third erbium-doped optical fiber, the fourth wavelength division multiplexer, the second optical fiber collimator, the optical retarder and the second half-wave plate are sequentially connected through a line;
the third wavelength division multiplexer and the third photodiode are connected through a line; the fourth wavelength division multiplexer and the fourth photodiode are connected through a line;
the first half-wave plate and the second half-wave plate are respectively connected to the dichroic mirror through lines;
the dichroic mirror, the first converging lens, the difference frequency crystal, the second converging lens for collimation, the low-pass filter and the beam combining mirror are sequentially connected through a circuit;
the long-wave infrared tunable laser, the semi-transmitting semi-reflecting mirror, the beam combining mirror, the grating, the second photoelectric detector and the second phase-locked loop are sequentially connected through a circuit to form a closed loop;
an optical delayer configured to control a time delay amount of the path of light;
a second half-wave plate configured to adjust the polarization state of the optical signal after the delay control to be vertical polarization;
a first half-wave plate configured to adjust a collimated beam output from the first fiber collimator to a horizontal polarization;
a dichroic mirror configured to combine the beams of the two different polarization states;
a femtosecond oscillator configured to provide a femtosecond pulse signal required for generating a long-wave infrared optical comb signal;
femtosecond light pulses output by the femtosecond oscillator are amplified by an amplifying unit consisting of a first erbium-doped fiber, a first wavelength division multiplexer and a first photodiode after passing through a filter and an isolator, and then are divided into two paths by a fiber beam splitter;
the first path is amplified and time domain compressed through an amplifying unit consisting of a second erbium-doped optical fiber, a second wavelength division multiplexer and a second photodiode, the compressed pulse generates a supercontinuum through a high nonlinear optical fiber, and is output after being collimated by a first optical fiber collimator and modulated by a first half wave plate, and a long-wave frequency shift soliton is extracted from the supercontinuum as a fundamental frequency signal pulse;
the second path is amplified and time domain compressed by an amplifying unit consisting of a third wavelength division multiplexer, a third photodiode, a third erbium-doped fiber, a fourth wavelength division multiplexer and a fourth photodiode, the compressed pulse is directly used as a fundamental frequency pumping pulse, and a pumping pulse signal of the second path is output after being modulated by a second fiber collimator, an optical delayer and a second half-wave plate;
the second path of pulse signal and the first path of pulse signal are jointly incident into a dichroic mirror, then the two paths of high peak power fundamental frequency pulses are input into a difference frequency crystal through a first converging lens, the time synchronization, the space coincidence and the light spot size of the dichroic fundamental frequency pulses are adjusted, a long-wave infrared tunable laser passes through a semi-transparent semi-reflecting mirror, light of a reflecting part is incident into a beam combining mirror, the light is combined with a long-wave infrared comb signal which is collimated through a second converging lens and filtered by a low-pass filter and then incident onto a grating, the grating extracts spectral components which are close to the output of the tunable laser in the long-wave infrared comb and then reflects two beams of light onto a second photoelectric detector for beat frequency, and an error electric signal generated after beat frequency enters a second phase-locked loop to control a wavelength stabilization control unit of the long-wave infrared tunable laser.
Preferably, the apparatus further comprises a first photodetector, a first phase-locked loop, and a PZT drive; the femtosecond oscillator, the first photoelectric detector, the first phase-locked loop and the PZT drive are connected in sequence through a circuit to form a closed loop.
Preferably, the femtosecond oscillator is a full-fiber laser, the center wavelength of which is located in a 1.55 μm band, and the output linear polarization pulse sequence repetition frequency is 100MHz, and is configured to provide the femtosecond pulse signal required for generating the long-wave infrared optical comb signal.
Preferably, the femtosecond oscillator has 5 optical output ports, the light output by the Mon output port of the 5 optical output ports is tested for the repetition frequency by using the first photoelectric detector, then the output electrical signal of the first photoelectric detector is sent to the first phase-locked loop to obtain an error locking signal, and the locking signal is input into the piezoelectric displacement control interface of the femtosecond oscillator to realize the locking of the repetition frequency of the femtosecond oscillator.
Preferably, the optical fiber beam splitter adopts a 30; the two operating wavelengths of the dichroic mirror are 1.55 μm and 1.9 μm, respectively.
Preferably, the difference frequency crystal adopts GaSe material; the second convergent lens is made of germanium material; the grating is a blazed grating with the model of LG-120-50, the spectral range of 7-16 mu m, the size of 68mm multiplied by 68mm and the resolution of 0.6nm.
Preferably, the long-wave infrared tunable laser is a quantum cascade laser, the spectrum tuning range is 9.2-10.4 μm, the line width is 100MHz, and the tuning and locking control of the output wavelength is realized by controlling the angle of a plane mirror in a cavity of the long-wave infrared tunable laser through an error electric signal generated by a second phase-locked loop.
In addition, the invention also provides a long-wave infrared standard wavelength generation method based on optical comb locking, which adopts the long-wave infrared standard wavelength generation device based on optical comb locking and specifically comprises the following steps:
step 1: generating an optical comb signal of a long-wave infrared band based on a near-infrared light difference frequency mechanism;
and 2, step: selecting comb teeth of an optical comb close to the wavelength point to be calibrated according to the wavelength point to be calibrated, and locking a long-wave infrared tunable laser on the selected comb teeth to realize a stable standard wavelength signal of a long-wave infrared band;
and step 3: when standard light sources on other wavelength points of the long-wave infrared band need to be generated, the wavelength of the long-wave infrared tunable laser is tuned to be locked to the optical comb again;
and 4, step 4: and leading the standard optical wavelength signal into the calibrated spectral measuring instrument, and calibrating the calibrated spectral measuring instrument according to an error value between a measured value and a standard value.
Preferably, step 1 specifically includes the following steps:
step 1.1: femtosecond light pulses output by the femtosecond oscillator are amplified by an amplifying unit consisting of a first erbium-doped fiber, a first wavelength division multiplexer and a first photodiode after passing through a filter and an isolator, and then are divided into two paths by a fiber beam splitter;
wherein 70% of the ends are subjected to self-similar amplification and optical fiber compression through an amplification unit consisting of a second erbium-doped optical fiber, a second wavelength division multiplexer and a second photodiode, the average power and pulse width of the amplified and compressed pulses are respectively 338mW and 38fs, the compressed pulses are incident into a polarization-maintaining nonlinear optical fiber to generate a supercontinuum, are output after being collimated by a first optical fiber collimator and modulated by a first half wave plate, and long-wave frequency-shift solitons are extracted from the supercontinuum to serve as fundamental frequency signal pulses;
the 30% end realizes self-similar amplification and pulse width compression through an amplification unit consisting of a third wavelength division multiplexer, a third photodiode, a third erbium-doped optical fiber, a fourth wavelength division multiplexer and a fourth photodiode, the average power and the pulse width of the amplified and compressed pulse are 485mW and 45fs respectively, the compressed pulse is directly used as a fundamental frequency pumping pulse, and the pumping pulse signal of the path is output after being modulated by a second optical fiber collimator, an optical delayer and a second half-wave plate;
step 1.2: two paths of pulse signals are jointly incident into the dichroic mirror, two beams with different polarization states are combined by the dichroic mirror and then enter the first converging lens;
step 1.3: the first converging lens focuses the combined beam and inputs the focused beam to the difference frequency crystal;
step 1.4: and generating a long-wave infrared optical comb signal based on a nonlinear difference frequency process of the difference frequency crystal, collimating by a second convergent lens, and filtering out fundamental frequency light by a low-pass filter to obtain the long-wave infrared optical comb signal.
Preferably, the step 2 specifically includes the following steps:
step 2.1: adjusting the azimuth angle of the difference frequency crystal according to the output wavelength of the long-wave infrared tunable laser, so that the center wavelength of a long-wave infrared optical comb signal generated by the difference frequency crystal is close to the output wavelength of the long-wave infrared tunable laser;
step 2.2: the output light beam of the long-wave infrared tunable laser is split by a semi-transparent semi-reflecting mirror, and the split reflected light beam is incident on a grating after being combined with a long-wave infrared comb signal;
step 2.3: the grating reflects the light beam of the long-wave infrared tunable laser and the comb teeth of the optical comb close to the output wavelength of the light beam to the second photoelectric detector together to generate a beat frequency signal, the beat frequency signal is sent to the second phase-locked loop to be locked and generate an error electric signal, and the electric signal is used for controlling the electric control displacement mechanism of the long-wave infrared tunable laser so as to control the angle of the plane mirror in the laser cavity of the long-wave infrared tunable laser, thus completing the locking of the wavelength of the long-wave infrared light and generating a standard light source.
The invention has the following beneficial technical effects:
(1) The uncertainty level of the long-wave infrared standard light wavelength is high. The uncertainty of the optical wavelength measurement in the long-wave infrared band is better than 10 -10 Compared with the prior art, the method is improved by more than 4 orders of magnitude;
(2) The wavelength of the standard light can be continuously tuned, so that the calibration of the long-wave infrared spectrum measuring instrument on a series of wavelength points is realized.
Drawings
FIG. 1 is a diagram of a long-wave infrared standard wavelength source implementation.
Detailed Description
The invention is described in further detail below with reference to the following figures and detailed description:
the invention provides a method and a device for calibrating a long-wave infrared spectrum measuring instrument based on optical comb locking. Firstly, generating an optical comb signal of a long-wave infrared band based on a near-infrared light difference frequency mechanism; then, according to the wavelength point to be calibrated, the long-wave infrared narrow-linewidth tunable laser is locked on the comb teeth of the optical comb, which are close to the output wavelength of the long-wave infrared narrow-linewidth tunable laser, in the optical comb signal, so that the stable standard wavelength signal of the long-wave infrared waveband is realized; when standard light sources on other wavelength points of the long-wave infrared band need to be generated, the method is realized by tuning the wavelength of the long-wave infrared narrow-linewidth laser and locking the wavelength to the optical comb again; and then, the standard optical wavelength signal is led into the calibrated spectral measurement instrument, and the calibrated spectral measurement instrument is calibrated according to the error value between the measured value and the standard value.
The implementation process of the scheme is as follows, as shown in fig. 1, the femtosecond oscillator with locked repetition frequency is amplified by an amplifying unit (composed of a first erbium-doped fiber, a first wavelength division multiplexer and a first photodiode) after passing through a filter and an isolator, and then is divided into two paths by an optical fiber beam splitter, wherein the first path is amplified and time domain compressed by a second erbium-doped fiber, a second wavelength division multiplexer and a second photodiode, then pumps a high nonlinear fiber to obtain a supercontinuum, is collimated by a first fiber collimator and modulated by a first half-wave plate and then is output, and a long-wave frequency shift soliton is extracted from the first path to be used as a fundamental frequency signal pulse; the second path of the laser is directly used as fundamental frequency pumping pulse after being amplified by a third wavelength division multiplexer, a third photodiode and a third erbium-doped optical fiber and time domain compressed, the pumping pulse signal is subjected to time delay by an optical delayer and modulation by a second half-wave plate and then enters a dichroic mirror together with the first path of pulse signal, then the two paths of high-peak power fundamental frequency pulses are input into a GaSe difference frequency crystal by a first convergent lens, time synchronization, space coincidence and light spot size adjustment of the dichroic fundamental frequency pulses are carried out, and the crystal position, phase matching angle and other parameters are precisely regulated and controlled by a multi-dimensional precise regulating platform based on a first class of phase matching conditions to realize the tuning of the long-wave infrared optical comb signal with the central wavelength. After the long-wave infrared tunable laser passes through the semi-transparent semi-reflective mirror, reflected light enters the beam combining mirror, is combined with a long-wave infrared comb signal which is collimated by the second converging lens and filtered by the low-pass filter and then enters the grating, the grating extracts spectral components which are close to the output of the tunable laser in the long-wave infrared comb and then reflects two beams of light to the second photoelectric detector for beat frequency, and an error electric signal generated after beat frequency enters the second phase-locked loop to control a wavelength stabilizing control unit (in the invention, the angle of a plane mirror in a cavity of the quantum cascade laser) of the long-wave infrared tunable laser so as to lock the output wavelength of the laser. Moreover, by jointly adjusting the wavelength of the tunable laser and the central wavelength of the optical comb signal, a series of output wavelengths of the laser can be locked, namely standard light is realizedGeneration and continuous tuning of the wavelength. The locked output wavelength is locked to the comb teeth of the optical comb, and the relative wavelength precision can reach 10 -10 The magnitude is more than four orders of magnitude higher than the existing level, so that a novel high-precision long-wavelength infrared light wavelength standard is formed.
The femtosecond oscillator is an M-comb type all-fiber laser of Menlosystems company, has the advantages of stable work and small volume, has the central wavelength positioned in a 1.55 mu M wave band, outputs a linear polarization pulse sequence with the repetition frequency of 100MHz and the pulse width of about 63fs, and has the function of providing a femtosecond pulse signal required for generating a long-wave infrared optical comb signal. The femtosecond oscillator is provided with 5 optical output ports, the light output by the Mon output port is tested for the repetition frequency by the photoelectric detector 1, then the output electric signal of the photoelectric detector 1 is sent to the phase-locked loop 1 to obtain an error locking signal, and the repetition frequency of the femtosecond oscillator is locked by inputting the locking signal into a piezoelectric displacement control interface of the femtosecond oscillator.
The femtosecond light pulse output by the femtosecond oscillator with the locked repetition frequency is filtered by a filter to realize the filtering of the pulse spectrum, and only the frequency component in the spectrum range of 1543 nm-1557 nm is reserved to meet the requirement of the following self-similar amplification on the spectrum range. Then, in order to meet the requirement of self-similar amplification on femtosecond optical power, after the isolator is used for realizing isolation on reflected light, femtosecond optical pulses are required to be subjected to optical amplification, and an optical amplification unit consists of a first erbium-doped optical fiber, a first wavelength division multiplexer and a first photodiode.
The femtosecond light pulses are amplified and then divided into two paths by an optical fiber beam splitter of 30; the 30% end realizes self-similar amplification and pulse width compression through an amplification unit consisting of a third wavelength division multiplexer, a third photodiode, a third erbium-doped optical fiber, a fourth wavelength division multiplexer and a fourth photodiode, the average power and the pulse width of the amplified and compressed pulse are 485mW and 45fs respectively, and collimation output is realized through a second optical fiber collimator.
Because the difference frequency process requires that the bicolor fundamental frequency pulse meets the accurate time synchronization, an optical delayer needs to be introduced behind a second optical fiber collimator to control the time delay amount of the path of light, and then a second half-wave plate is used for adjusting the polarization state of the optical signal after delay control to be vertical polarization; meanwhile, the collimated beam output from the optical fiber collimator 1 is adjusted to be horizontally polarized by a first half-wave plate, and then two beams in different polarization states are combined by a dichroic mirror, wherein two working wavelengths of the dichroic mirror are respectively 1.55 mu m and 1.9 mu m. The spatial light path is finely adjusted, two beams of light which are combined by the dichroic mirror are strictly overlapped in space, and then are focused by an achromatic lens with a focal length of 40mm and then are incident to a difference frequency crystal, the difference frequency crystal is made of GaSe materials, the crystal is cut into a circle along a (001) plane, the diameter of the crystal is 7mm, the thickness of the crystal is 1mm, the crystal is glued in an aluminum ring, and the aluminum ring is installed on a multidimensional displacement adjusting mechanism so as to adjust a phase matching angle and an azimuth angle of the crystal. After the phase matching is realized by adjusting the position of the crystal, the generation of a high-power long-wave infrared optical comb signal is realized based on the nonlinear difference frequency process of the GaSe crystal, and then after the signal is collimated by a second converging lens made of a germanium material, the fundamental frequency light is filtered by a low-pass filter, so that the output of the long-wave infrared optical comb signal is obtained. The tuning of the center wavelength of the optical comb spectrum can be realized by adjusting the multidimensional displacement adjusting mechanism to change the phase matching angle of the GaSe crystal, the measured wavelength tuning range is 7.5-10.5 mu m, the average output power in the range is more than 250 mu W, and the power stability is less than 1%.
After the long-wave infrared optical comb signal is obtained, the long-wave infrared optical comb signal can be used for carrying out frequency stabilization locking on a narrow-linewidth laser of a long-wave infrared waveband, so that the long-wave infrared optical comb signal becomes a long-wave infrared optical wavelength standard. Firstly, adjusting the azimuth angle of a difference frequency crystal according to the output wavelength of a narrow linewidth laser, so that the center wavelength of a generated long-wave infrared optical comb signal is close to the output wavelength of the narrow linewidth laser; then the output light beam of the long wave infrared tunable laser is split by a semi-transparent semi-reflecting mirror, and the split reflected light beam and the long wave infrared optical comb signalAfter the combination, the light is incident on the grating. Thus, the grating can reflect the light beam of the long-wave infrared tunable laser and the comb teeth of the optical comb close to the output wavelength of the long-wave infrared tunable laser to the second photoelectric detector together to generate a beat frequency signal, the beat frequency signal is sent to the second phase-locked loop to be locked and generate an error electric signal, the electric signal is used for controlling the electric control displacement mechanism of the long-wave infrared tunable laser and controlling the angle of the plane mirror in the laser cavity, the locking of the wavelength of the long-wave infrared light can be completed, and the generated precision is better than 10 -10 The standard light source of (1). The grating used in the process is a blazed grating with the model of LG-120-50, the spectral range of 7-16 mu m, the size of 68mm multiplied by 68mm and the resolution of 0.6nm; the long-wave infrared narrow-linewidth laser is a quantum cascade laser, the spectral tuning range is 9.2-10.4 mu m, the linewidth is 100MHz, and the tuning and locking control of the output wavelength is realized by controlling the angle of a plane mirror in the cavity.
The long-wave infrared comb can output a series of stable comb teeth in a wave band of 7.5-10.5 mu m, and a series of optical wavelength standards of the middle infrared wave band can be established by locking a quantum cascade laser or other types of long-wave infrared narrow-line width lasers in the long-wave infrared wave band. The standard precision of the long-wave infrared light wavelength established by the scheme is better than 10 -10 Compared with the prior art, the method is improved by more than 4 orders of magnitude.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make various changes, modifications, additions and substitutions within the spirit and scope of the present invention.
Claims (10)
1. A long-wave infrared standard wavelength generating device based on optical comb locking is characterized in that: the fiber laser comprises a femtosecond oscillator, a filter, an isolator, a first erbium-doped fiber, a first wavelength division multiplexer, a first photodiode, a fiber beam splitter, a second erbium-doped fiber, a second wavelength division multiplexer, a second photodiode, a high nonlinear fiber, a first fiber collimator, a first half-wave plate, a third wavelength division multiplexer, a third photodiode, a third erbium-doped fiber, a fourth wavelength division multiplexer, a fourth photodiode, a second fiber collimator, an optical retarder, a second half-wave plate, a dichroscope, a first convergent lens, a difference frequency crystal, a long-wave infrared tunable laser, a semi-transmitting and semi-reflecting mirror, a beam combining mirror, a second convergent lens collimation, a low-pass filter, a grating, a second photodetector and a second phase-locked loop;
the femtosecond oscillator, the filter, the isolator, the first erbium-doped fiber, the first wavelength division multiplexer and the first photodiode are sequentially connected through a circuit;
the first erbium-doped fiber, the first wavelength division multiplexer and the first photodiode form an amplifying unit;
the first wavelength division multiplexer, the optical fiber beam splitter, the second erbium-doped optical fiber, the second wavelength division multiplexer, the high nonlinear optical fiber, the first optical fiber collimator and the first half-wave plate are sequentially connected through a line;
the second wavelength division multiplexer and the second photodiode are connected through a line;
the second erbium-doped fiber, the second wavelength division multiplexer and the second photodiode form an amplifying unit;
the optical fiber beam splitter, the third wavelength division multiplexer, the third erbium-doped optical fiber, the fourth wavelength division multiplexer, the second optical fiber collimator, the optical retarder and the second half-wave plate are sequentially connected through a line;
the third wavelength division multiplexer and the third photodiode are connected through a line; the fourth wavelength division multiplexer and the fourth photodiode are connected through a line;
the first half-wave plate and the second half-wave plate are respectively connected to the dichroic mirror through lines;
the dichroic mirror, the first converging lens, the difference frequency crystal, the second converging lens for collimation, the low-pass filter and the beam combining mirror are sequentially connected through a circuit;
the long-wave infrared tunable laser, the semi-transmitting semi-reflecting mirror, the beam combining mirror, the grating, the second photoelectric detector and the second phase-locked loop are sequentially connected through a circuit to form a closed loop;
an optical delayer configured to control a time delay amount of the path light;
a second half-wave plate configured to adjust a polarization state of the optical signal after the delay control to a vertical polarization;
a first half-wave plate configured to adjust a collimated beam output from the first fiber collimator to a horizontal polarization;
a dichroic mirror configured to combine beams of two different polarization states;
a femtosecond oscillator configured to provide a femtosecond pulse signal required for generating a long-wave infrared optical comb signal;
femtosecond light pulses output by the femtosecond oscillator are amplified by an amplifying unit consisting of a first erbium-doped fiber, a first wavelength division multiplexer and a first photodiode after passing through a filter and an isolator, and then are divided into two paths by a fiber beam splitter;
the first path is amplified and time domain compressed by an amplifying unit consisting of a second erbium-doped optical fiber, a second wavelength division multiplexer and a second photodiode, the compressed pulse generates a supercontinuum by a high nonlinear optical fiber, and is output after being collimated by a first optical fiber collimator and modulated by a first half-wave plate, and a long-wave frequency shift soliton is extracted from the supercontinuum as a fundamental frequency signal pulse;
the second path is amplified and time domain compressed by an amplifying unit consisting of a third wavelength division multiplexer, a third photodiode, a third erbium-doped fiber, a fourth wavelength division multiplexer and a fourth photodiode, the compressed pulse is directly used as a fundamental frequency pumping pulse, and a pumping pulse signal of the second path is output after being modulated by a second fiber collimator, an optical delayer and a second half-wave plate;
the second path of pulse signal and the first path of pulse signal are jointly incident into a dichroic mirror, then the two paths of high-peak-power fundamental-frequency pulses are input into a difference frequency crystal through a first convergent lens, the time synchronization, the space coincidence and the light spot size of the dichroic fundamental-frequency pulses are adjusted, a long-wave infrared tunable laser passes through a semi-transparent semi-reflecting mirror, light of a reflecting part is incident into a beam combining mirror, the light is combined with a long-wave infrared comb signal which is collimated through a second convergent lens and filtered by a low-pass filter and then incident onto a grating, the grating extracts spectral components which are close to the output of the tunable laser in the long-wave infrared comb and then reflects two beams of light onto a second photoelectric detector for beat frequency, and an error electric signal generated after beat frequency enters a second phase-locked loop to control a wavelength stability control unit of the long-wave infrared tunable laser.
2. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 1, wherein: the device also comprises a first photoelectric detector, a first phase-locked loop and a PZT drive; the femtosecond oscillator, the first photoelectric detector, the first phase-locked loop and the PZT drive are connected in sequence through a circuit to form a closed loop.
3. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 2, wherein: the femtosecond oscillator is an all-fiber laser, the central wavelength of the all-fiber laser is positioned in a 1.55 mu m wave band, the repetition frequency of an output linear polarization pulse sequence is 100MHz, and the all-fiber laser is configured to be used for providing a femtosecond pulse signal required for generating a long-wave infrared optical comb signal.
4. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 3, wherein: the femtosecond oscillator is provided with 5 optical output ports, the light output by a Mon output port of the 5 optical output ports is tested for the repetition frequency by a first photoelectric detector, then an output electric signal of the first photoelectric detector is sent to a first phase-locked loop to obtain an error locking signal, and the repetition frequency of the femtosecond oscillator is locked by inputting the locking signal into a piezoelectric displacement control interface of the femtosecond oscillator.
5. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 1, wherein: the optical fiber beam splitter adopts a 30; the two operating wavelengths of the dichroic mirror are 1.55 μm and 1.9 μm, respectively.
6. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 1, wherein: the difference frequency crystal adopts GaSe material; the second convergent lens is made of germanium material; the grating is a blazed grating with the model of LG-120-50, the spectral range of 7-16 mu m, the size of 68mm multiplied by 68mm and the resolution of 0.6nm.
7. The optical comb locking-based long-wave infrared standard wavelength generating device as claimed in claim 1, wherein: the long-wave infrared tunable laser is a quantum cascade laser, the spectrum tuning range is 9.2-10.4 mu m, the line width is 100MHz, and the tuning and locking control of the output wavelength are realized by controlling the angle of a plane mirror in a cavity through an error electric signal generated by a second phase-locked loop.
8. A long-wave infrared standard wavelength generation method based on optical comb locking is characterized by comprising the following steps: the optical comb locking-based long-wave infrared standard wavelength generation device adopted by the method as claimed in claim 5 comprises the following steps:
step 1: generating an optical comb signal of a long-wave infrared band based on a near-infrared light difference frequency mechanism;
step 2: selecting comb teeth of an optical comb close to the wavelength point to be calibrated according to the wavelength point to be calibrated, and locking a long-wave infrared tunable laser on the selected comb teeth to realize a stable standard wavelength signal of a long-wave infrared band;
and 3, step 3: when standard light sources on other wavelength points of the long-wave infrared band need to be generated, the wavelength of the long-wave infrared tunable laser is tuned to be locked to the optical comb again;
and 4, step 4: and leading the standard optical wavelength signal into the calibrated spectral measuring instrument, and calibrating the calibrated spectral measuring instrument according to an error value between a measured value and a standard value.
9. The optical comb locking based long-wave infrared standard wavelength generation method as claimed in claim 8, wherein: in the step 1, the method specifically comprises the following steps:
step 1.1: femtosecond light pulses output by the femtosecond oscillator are amplified by an amplifying unit consisting of a first erbium-doped fiber, a first wavelength division multiplexer and a first photodiode after passing through a filter and an isolator, and then are divided into two paths by a fiber beam splitter;
wherein 70% of the ends are amplified in a self-similar way and compressed by optical fibers through an amplifying unit consisting of a second erbium-doped optical fiber, a second wavelength division multiplexer and a second photodiode, the average power and the pulse width of the amplified and compressed pulses are respectively 338mW and 38fs, the compressed pulses are incident into the polarization-preserving nonlinear optical fiber to generate a supercontinuum, are collimated by a first optical fiber collimator and modulated by a first half-wave plate and then are output, and long-wave frequency-shift solitons are extracted from the supercontinuum to serve as fundamental frequency signal pulses;
the 30% end realizes self-similar amplification and pulse width compression through an amplification unit consisting of a third wavelength division multiplexer, a third photodiode, a third erbium-doped optical fiber, a fourth wavelength division multiplexer and a fourth photodiode, the average power and the pulse width of the amplified and compressed pulse are 485mW and 45fs respectively, the compressed pulse is directly used as a fundamental frequency pumping pulse, and the pumping pulse signal of the path is output after being modulated by a second optical fiber collimator, an optical delayer and a second half-wave plate;
step 1.2: two paths of pulse signals are jointly incident into the dichroic mirror, two beams with different polarization states are combined by the dichroic mirror and then enter the first converging lens;
step 1.3: the first converging lens focuses the combined beam and inputs the focused beam to the difference frequency crystal;
step 1.4: and generating a long-wave infrared optical comb signal based on a nonlinear difference frequency process of the difference frequency crystal, collimating by a second convergent lens, and filtering out fundamental frequency light by a low-pass filter to obtain the long-wave infrared optical comb signal.
10. The optical comb locking based long-wave infrared standard wavelength generation method as claimed in claim 8, wherein: in the step 2, the method specifically comprises the following steps:
step 2.1: adjusting the azimuth angle of the difference frequency crystal according to the output wavelength of the long-wave infrared tunable laser, so that the center wavelength of a long-wave infrared optical comb signal generated by the difference frequency crystal is close to the output wavelength of the long-wave infrared tunable laser;
step 2.2: the output light beam of the long-wave infrared tunable laser is split by a semi-transparent semi-reflecting mirror, and the split reflected light beam is incident on a grating after being combined with a long-wave infrared comb signal;
step 2.3: the grating reflects the light beam of the long-wave infrared tunable laser and the comb teeth of the optical comb close to the output wavelength of the long-wave infrared tunable laser to the second photoelectric detector together to generate beat frequency signals, the beat frequency signals are sent to the second phase-locked loop to be locked and generate error electric signals, and the electric signals are used for controlling the electric control displacement mechanism of the long-wave infrared tunable laser so as to control the angle of the plane mirror in the laser cavity of the long-wave infrared tunable laser, thus completing the locking of the wavelength of the long-wave infrared light and generating a standard light source.
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