Narrow-linewidth mid-infrared frequency-modulated continuous wave generation measurement device and generation and measurement method

Abstract

The application relates to the field of optical technology, in particular to a narrow-line-width mid-infrared frequency-modulated continuous wave generation and measurement device and a generation and measurement method, wherein the generation device comprises an arbitrary function generator, an ultra-low-noise driving source and a band intercascade laser, the arbitrary function generator is connected with the ultra-low-noise driving source, and the ultra-low-noise driving source is connected with the band intercascade laser; two simple and economical mid-infrared frequency-modulated continuous wave signal generation schemes are provided, including a current modulation scheme and a temperature modulation scheme; a test device for analyzing the mid-infrared frequency-modulated continuous wave signal is provided; the device can analyze the time-frequency signal, linearity and spectral information of the mid-infrared frequency-modulated continuous wave; and the defects in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a narrow linewidth mid-infrared frequency-modulated continuous wave generating, measuring device and method. BACKGROUND

[0002] The mid-infrared waveband (2.5-25 μm) contains many absorption lines of gas molecules, and has low loss and weak scattering in the atmosphere, strong anti-interference ability, so it has attracted the attention of many researchers.

[0003] Interband cascade lasers are high-quality mid-infrared laser sources that generate 3-6 μm wavebands, and have the advantages of narrow linewidth, high modulation efficiency, high quantum efficiency, low power consumption, and stable room temperature operation. Currently, this laser has been widely used in military and civilian fields such as gas detection, free space optical communication, and infrared laser weapons.

[0004] Mid-infrared frequency-modulated continuous wave sources have the unique advantages of the mid-infrared waveband, which can ensure that the radar source can resist stray light interference while avoiding the interference of scattered coherent light to accurately identify necessary targets. Secondly, due to the unique advantages of interband cascade lasers, i.e. narrow linewidth and high modulation efficiency, the frequency-modulated continuous wave signals generated based on this laser can have longer coherence distance and larger sweep bandwidth compared to other laser sources. In addition, the lack of mid-infrared waveband (3-6 μm) optical fibers and measuring instruments makes it difficult to analyze and optimize the generated signals. Therefore, developing a device that can measure mid-infrared frequency-modulated continuous wave signals in real time is also a research focus.

[0005] Currently, researchers have conducted related research on mid-infrared frequency-modulated continuous wave signal generating devices. In patent CN214124313U, a mid-infrared parallel frequency-modulated continuous wave signal generating device is proposed, which mainly uses a chalcogenide photonic chip to generate an optical comb and generates multiple parallel frequency-modulated continuous wave signals through modulation of the photonic chip.

[0006] However, this scheme is not mature and is mainly affected by source power, external interference, environmental vibration, etc. Based on this, the present application proposes a narrow linewidth mid-infrared frequency-modulated continuous wave generating and measuring device. SUMMARY

[0007] The purpose of the present application is to provide a narrow linewidth mid-infrared frequency-modulated continuous wave generating, measuring device and method, which solves the problem that the existing mid-infrared parallel frequency-modulated continuous wave signal generating device is affected by source power, external interference, environmental vibration, etc.

[0008] In order to achieve the above object, the present application provides a narrow linewidth mid-infrared frequency-modulated continuous wave generating device, comprising an arbitrary function generator, an ultra-low noise driving source and an interband cascade laser, the arbitrary function generator is connected with the ultra-low noise driving source, and the ultra-low noise driving source is connected with the interband cascade laser.

[0009] The arbitrary function generator is used to generate a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal, and the signal is used to modulate the current input or temperature input of the ultra-low noise driving source.

[0010] The ultra-low noise driving source is used to control the current and temperature parameters of the interband cascade laser, and also cooperates with the external arbitrary function signal to modulate the current and temperature parameters.

[0011] The interband cascade laser is used to output a narrow linewidth mid-infrared frequency-modulated continuous wave optical signal.

[0012] The ultra-low noise driving source comprises a current module, and the current module is connected with the arbitrary function generator and the interband cascade laser respectively.

[0013] The ultra-low noise driving source comprises a temperature module, and the temperature module is connected with the arbitrary function generator and the interband cascade laser respectively.

[0014] A narrow linewidth mid-infrared frequency-modulated continuous wave measuring device comprises an optical isolator, a Michelson interferometer, an optical beam splitter, a Fourier infrared spectrometer and a photodetector, the optical isolator is connected with the interband cascade laser and connected in series with the Michelson interferometer, the Michelson interferometer and the optical beam splitter are directly connected, and the Fourier infrared spectrometer and the photodetector are connected at two ends of the optical beam splitter respectively.

[0015] The optical isolator is used to isolate the feedback light from the testing device to the generating device.

[0016] The Michelson interferometer is used to convert the frequency-modulated continuous wave optical signal into a time optical beat signal.

[0017] The optical beam splitter is used to split the frequency-modulated continuous wave optical signal input by the interband cascade laser, and combine the optical signals reflected from two mirrors, the optical signals are further split by the optical beam splitter, a part of the optical signals is transmitted to the Fourier infrared spectrometer, and another part of the optical signals is transmitted to the photodetector.

[0018] The Fourier infrared spectrometer is used to analyze the scanning spectrum of the frequency-modulated continuous wave optical signal and read the scanning width.

[0019] The photoelectric detector is used for receiving the time optical beat signal from the Michelson interferometer and generating a beat frequency electric signal, which is subsequently transmitted to the digital storage oscilloscope and the computer terminal.

[0020] The measurement device of the narrow linewidth mid-infrared frequency-modulated continuous wave further comprises a digital storage oscilloscope and a computer terminal, the digital storage oscilloscope is connected with the photoelectric detector, and the computer terminal is connected with the digital storage oscilloscope.

[0021] The digital storage oscilloscope is used for recording and observing the real-time beat frequency electric signal.

[0022] The computer terminal is used for offline processing of the beat frequency electric signal.

[0023] The method for generating the narrow linewidth mid-infrared frequency-modulated continuous wave comprises the following steps:

[0024] An arbitrary function generator is used to generate a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal;

[0025] The generated signal is used to modulate the current input or temperature input of an ultra-low noise driving source, so as to control the current and temperature parameters of the interband cascade laser.

[0026] Through the modulation, the interband cascade laser outputs a narrow linewidth mid-infrared frequency-modulated continuous wave light signal.

[0027] The method for measuring the narrow linewidth mid-infrared frequency-modulated continuous wave comprises the following steps:

[0028] The frequency-modulated continuous wave light signal is input into the Michelson interferometer through an optical isolator to generate an optical beat signal.

[0029] Part of the light signal is transmitted to a Fourier infrared spectrometer, which is used for analyzing the scanning spectrum of the frequency-modulated continuous wave light signal and reading the sweep width, and the other part of the light signal is transmitted to a photoelectric detector, which is used for receiving the time optical beat signal and generating a beat frequency electric signal, which is then transmitted to a digital storage oscilloscope and a computer terminal.

[0030] The computer terminal is used for processing the collected beat frequency signal, including beat frequency signal declination, cutting, Hilbert transform, instantaneous frequency calculation and output.

[0031] The application discloses a narrow-line-width mid-infrared frequency-modulated continuous wave generating and measuring device and method. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced.

[0033] Figure 1 is a structure schematic view of the narrow-line-width mid-infrared frequency-modulated continuous wave generating device and the narrow-line-width mid-infrared frequency-modulated continuous wave measuring device of the application.

[0034] Figure 2 is a theoretical verification diagram of the generating device of the embodiment of the application, wherein (a1) is the change of the photon number with time, (a2) is the change of the carrier number with time, and (a3) is the change of the instantaneous frequency with time when no modulation is applied; (b1) is the change of the photon number with time, (b2) is the change of the carrier number with time, and (b3) is the change of the instantaneous frequency with time when the modulation is applied.

[0035] Figure 3 is a theoretical verification diagram of the test device of the embodiment of the application, wherein (a1) is the change of the instantaneous frequency of the output of the short arm of the Michelson interferometer with time, (a2) is the change of the instantaneous frequency of the output of the long arm of the Michelson interferometer with time, and (a3) is the change of the beat frequency with time.

[0036] Figure 4 is a spectrum diagram of the interband cascade laser of the embodiment of the application when no modulation is applied, and a broken line statistics of the change of the lasing frequency with time, wherein,Figure 4 (a) represents the change of light intensity at the same wavelength and different current; Figure 4 (b) represents the change of current to frequency.

[0037] Figure 5 is the spectrum diagram of the inter-band cascade laser of the embodiment of the present application under different modulation frequencies, wherein, Figure 5 (a) represents the change of light intensity at the same wavelength and different temperature; Figure 5 (b) represents the change of temperature to frequency.

[0038] Figure 6 is the spectrum diagram of the frequency-modulated continuous wave output by the present application under different modulation amplitudes and the spectrum diagram of the light without modulation amplitude. Figure 6 (a) represents the change of different wavelengths at different wavelengths and different adjustment amplitudes; Figure 6 (b) represents the different bandwidths corresponding to different adjustment amplitudes.

[0039] Figure 7 is the spectrum diagram of the frequency-modulated continuous wave output by the present application under different modulation frequencies and the spectrum diagram of the light without modulation.

[0040] Figure 8 is the step flow chart of the method for generating the narrow linewidth mid-infrared frequency-modulated continuous wave of the present application.

[0041] Figure 9 is the step flow chart of the method for measuring the narrow linewidth mid-infrared frequency-modulated continuous wave of the present application.

[0042] In the figure: 1- arbitrary function generator, 2- ultra-low noise driving source, 3- inter-band cascade laser, 4- optical isolator, 5- Michelson interferometer, 6- optical beam splitter, 7- photodetector, 8- Fourier infrared spectrometer, 9- digital storage oscilloscope, 10- computer terminal. DETAILED DESCRIPTION

[0043] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, the embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0044] The first embodiment of the present application is:

[0045] Please refer to Figure 1 , wherein, Figure 1 is the structure diagram of the generating device of the narrow linewidth mid-infrared frequency-modulated continuous wave and the measuring device of the narrow linewidth mid-infrared frequency-modulated continuous wave of the present application.

[0046] The application provides a narrow linewidth mid-infrared frequency-modulated continuous wave generating device, which comprises an arbitrary function generator 1, an ultra-low noise driving source 2 and an interband cascade laser 3.

[0047] For the specific embodiment, the arbitrary function generator 1 is connected with the ultra-low noise driving source 2, and the ultra-low noise driving source 2 is connected with the interband cascade laser 3.

[0048] The arbitrary function generator 1 is used for generating a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal, and the signal is loaded to an AC modulation port of a current source and used for modulating a current output or a temperature output of the ultra-low noise driving source 2, at this time, the current for controlling the laser can be expressed as: The temperature for controlling the laser can be expressed as: Wherein Ib and T0 represent an initial control current and an initial control temperature, A represents a modulation amplitude, and F is a triangular wave modulation function.

[0049] The ultra-low noise driving source 2 controls the current and temperature parameters of the interband cascade laser 3 through an electric control line and a temperature control line, and also cooperates with an external arbitrary function signal to modulate the current and temperature parameters, and the modulation method is consistent with the above.

[0050] The interband cascade laser 3 is used for outputting a narrow linewidth mid-infrared frequency-modulated continuous wave light signal.

[0051] The ultra-low noise driving source 2 comprises a current module, and the current module is connected with the arbitrary function generator 1 and the interband cascade laser 3 respectively.

[0052] Secondly, the ultra-low noise driving source 2 comprises a temperature module, and the temperature module is connected with the arbitrary function generator 1 and the interband cascade laser 3 respectively.

[0053] The application further provides a narrow linewidth mid-infrared frequency-modulated continuous wave generating device,

[0054] The application relates to a kind of narrow line width mid-infrared frequency-modulated continuous wave signal generation device and measurement device, which comprises two kinds of devices for generating mid-infrared frequency-modulated continuous wave signal, and the first and second devices for generating mid-infrared frequency-modulated continuous wave signal each comprise the arbitrary function generator 1 (AFG, Arbitrary Function Generator), the ultra-low noise driving source 2 (ULN-LDC, Ultra-Low Noise Laser Diode Controller) with current and temperature module, and the interband cascade laser 3 (ICL, Interband Cascade Laser). The arbitrary function generator 1 is used to generate a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal, which is used to modulate the current input or temperature input of the ultra-low noise driving source 2. The ultra-low noise driving source 2 with current and temperature module is mainly used to control the current and temperature parameters of the interband cascade laser 3 (the current control range of the interband cascade laser is 0-200 mA, and the temperature control range is 18-25 DEG C), and the ultra-low noise driving source 2 can also modulate the current and temperature parameters in cooperation with an external arbitrary function signal. The interband cascade laser 3 is used to output a narrow line width mid-infrared frequency-modulated continuous wave light signal.

[0055] In the first generation device, the arbitrary function generator 1 and the current module of the ultra-low noise driving source 2 are directly connected, and the output of the driving source is directly connected with the interband cascade laser 3.

[0056] In the second generation device, the arbitrary function generator 1 and the temperature module of the ultra-low noise driving source 2 are directly connected, and the output of the driving source is directly connected with the interband cascade laser 3.

[0057] The first generation device is a current-modulated interband cascade laser 3, which mainly utilizes carrier effect and thermal effect to change the laser emission frequency. The second generation device is a temperature-modulated interband cascade laser 3, which mainly utilizes thermal effect to change the laser emission frequency.

[0058] In some embodiments, the modulation waveform generated by the arbitrary function generator 1 is a triangular wave, the modulation period is 1-100 kHz, and the modulation amplitude is 4 Vpp. Two simple and economical mid-infrared frequency-modulated continuous wave signal generation schemes are provided, including a current modulation scheme and a temperature modulation scheme. The deficiencies in the prior art are solved.

[0059] The second embodiment of the application is:

[0060] Based on the first embodiment, refer to Figure 1 , wherein, Figure 1 is a structure diagram of the narrow line width mid-infrared frequency-modulated continuous wave signal generation device and measurement device.

[0061] The measuring device of the narrow linewidth mid-infrared frequency-modulated continuous wave of the embodiment comprises an optical isolator 4, a Michelson interferometer 5, an optical beam splitter 6, a Fourier infrared spectrometer 8, a photodetector 7, a digital storage oscilloscope 9 and a computer terminal 10.

[0062] For the specific embodiment, the optical isolator 4 is connected with the interband cascade laser 3 and connected in series with the Michelson interferometer; the Michelson interferometer is directly connected with the optical beam splitter 6; the Fourier infrared spectrometer 8 and the photodetector 7 are respectively connected at two ends of the optical beam splitter 6.

[0063] The optical isolator 4 is used to isolate the feedback light from the testing device to the generating device.

[0064] The Michelson interferometer 5 is used to obtain a heterodyne differential signal. The signal is a low-frequency interference signal generated by different lengths of two arms of the Michelson interferometer.

[0065] The optical beam splitter 6 is used to split the frequency-modulated continuous wave optical signal input by the interband cascade laser 3 and combine the light signals reflected from two mirrors. The light signal is further split by the optical beam splitter 6, and a part of the light signal is transmitted to the Fourier infrared spectrometer 8, and another part of the light signal is transmitted to the photodetector 7.

[0066] The Fourier infrared spectrometer 8 is used to collect a scanning spectrum of the frequency-modulated continuous wave optical signal and read a scanning width.

[0067] The photodetector 7 is used to receive a time optical beat signal from the Michelson interferometer, generate a beat frequency electrical signal, and then transmit the beat frequency electrical signal to the digital storage oscilloscope 9 and the computer terminal 10.

[0068] The digital storage oscilloscope 9 is connected with the photodetector 7, and the computer terminal 10 is connected with the digital storage oscilloscope 9.

[0069] The digital storage oscilloscope 9 is used to record and observe a real-time beat frequency electrical signal.

[0070] The computer terminal 10 is used to process the beat frequency electrical signal offline.

[0071] The measurement device of the narrow linewidth mid-infrared frequency-modulated continuous wave in the embodiment comprises the optical isolator 4 (ISO, Isolator), the Michelson interferometer 5 (MCI, Michelson Interferometer), the beam splitter 6 (BS, Beam Splitter), the gold mirror (GM, Gold Mirror), the Fourier transform infrared spectrometer 8 (Fourier transform Infrared Spectroscopy), the photo detector 7 (PD, Photo detector), the digital storage oscilloscope 9 (DSO, Digital storage Oscilloscope), and the computer 10 (PC, Personal Computer). The optical isolator 4 is used to isolate the feedback light from the test module to the generation module; the Michelson interferometer 5 is used to down-convert the frequency-modulated continuous wave light signal (high-frequency signal) into a time optical beat signal (low-frequency signal); the beam splitter 6 is an important component of the Michelson interferometer, which is used to split the frequency-modulated continuous wave light signal input by the inter-band cascade laser 3 and combine the light signals reflected from the two mirrors. Subsequently, the light signal is further split by the beam splitter, and part of the light signal is transmitted to the Fourier transform infrared spectrometer 8, and the other part of the light signal is transmitted to the photo detector 7; the Fourier transform infrared spectrometer 8 is used to analyze the scanning spectrum of the frequency-modulated continuous wave light signal and read the sweep width; the photo detector 7 is used to receive the time optical beat signal (low-frequency signal) from the Michelson interferometer and generate a beat frequency electric signal, which is then transmitted to the digital storage oscilloscope 9 and the computer 10. The digital storage oscilloscope 9 is used to record and observe the real-time beat frequency electric signal; and the computer 10 is used to process the beat frequency electric signal offline. The optical isolator 4 and the Michelson interferometer are connected in series, the Michelson interferometer and the beam splitter 6 are directly connected, and the Fourier transform infrared spectrometer 8 and the photo detector 7 are connected at both ends of the beam splitter 6. In some embodiments of the measurement device, the Michelson interferometer 5 is used to obtain the beat frequency signal, and the structure thereof comprises a beam splitter and two gold mirrors. The beam splitter has a splitting ratio of 5:5 or 3:7; and the reflectivity of the gold mirror is greater than 99%. In some embodiments of the measurement device, the arm length difference of the Michelson interferometer 5 is 60 cm (2L1-2L2). L1 is the long arm, and L2 is the short arm. In some embodiments of the measurement device, the frequency-modulated signal is measured by the Fourier transform infrared spectrometer 8; and the beat frequency signal is measured and recorded by the photo detector 7 and the digital storage oscilloscope 9. When measuring the frequency-modulated signal, one arm of the Michelson interferometer 5 needs to be removed.The resolution of the Fourier infrared spectrometer 8 is 0.5 cm-1; the bandwidth of the digital oscilloscope is 2.5 GHz, and the sampling rate is 20 Gsa / s; and the bandwidth of the photoelectric detector 7 is 500 MHz. In the measurement device of some embodiments, the two light signals of the measured spectrum and time sequence are shared through a beam splitter, and the splitting ratio of the beam splitter is 5:5. In the measurement device of some embodiments, the optical isolator 4 is used to isolate the return light of the Michelson interferometer 5 from the laser, so as to prevent the laser from jumping mode during frequency modulation. In the measurement device of some embodiments, the computer 10 is used to process the collected beat frequency signal, and the processing content includes beat frequency signal de-skewing, cutting, Hilbert transform, instantaneous frequency calculation and output. De-skewing refers to removing the slowly changing envelope signal in the beat frequency signal due to modulation, and the main method is polynomial fitting; cutting refers to cutting the upper and lower chirps of the beat frequency signal, and extracting the beat frequency corresponding to each chirp; Hilbert transform refers to extracting the quadrature signal of the beat frequency signal using the algorithm, and obtaining the change of the phase of the laser with time using the quadrature signal; and the calculation of the instantaneous frequency refers to that the instantaneous frequency signal can be obtained by differentiating the instantaneous phase using the relationship between the phase and the frequency.

[0072] The third embodiment of the present application is:

[0073] Based on the first embodiment, refer to Figure 8 , wherein, Figure 8 is a step flow chart of the narrow linewidth mid-infrared frequency-modulated continuous wave generation method of the present application. The narrow linewidth mid-infrared frequency-modulated continuous wave generation method of the present application comprises the following steps:

[0074] S101: using an arbitrary function generator 1 to generate a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal;

[0075] S102: using the generated signal to modulate the current input or temperature input of the ultra-low noise driving source 2, so as to control the current and temperature parameters of the interband cascade laser 3;

[0076] S103: through modulation, the interband cascade laser 3 outputs a narrow linewidth mid-infrared frequency-modulated continuous wave light signal.

[0077] Specifically, an arbitrary function generator 1 is used to generate a frequency-adjustable and amplitude-adjustable triangular wave or sawtooth wave voltage signal. The generated signal is used to modulate the current input or temperature input of the ultra-low noise driving source 2 to control the current and temperature parameters of the interband cascade laser 3. Through modulation, the interband cascade laser 3 outputs a narrow linewidth mid-infrared frequency-modulated continuous wave light signal. In the first generating device, the arbitrary function generator 1 and the current module of the ultra-low noise driving source 2 are directly connected, and the driving source output is directly connected with the interband cascade laser 3 to realize current modulation. In the second generating device, the arbitrary function generator 1 and the temperature module of the ultra-low noise driving source 2 are directly connected, and the driving source output is directly connected with the interband cascade laser 3 to realize laser temperature control. The modulation waveform is set to a triangular wave, the modulation period is 1-100 kHz, and the modulation amplitude is 4Vpp. Two simple and economical mid-infrared frequency-modulated continuous wave signal generation schemes are provided, including current modulation and temperature modulation schemes. The deficiencies in the prior art are solved.

[0078] The fourth embodiment of the present application is:

[0079] On the basis of the second embodiment, refer to Figure 9 , wherein, Figure 9 is the step flow chart of the narrow linewidth mid-infrared frequency-modulated continuous wave measurement method of the present application. The narrow linewidth mid-infrared frequency-modulated continuous wave measurement method of the present application includes the following steps:

[0080] S201: The frequency-modulated continuous wave light signal is input into the Michelson interferometer 5 through the optical isolator 4 to generate an optical beat signal;

[0081] S202: A part of the light signal is transmitted to the Fourier infrared spectrometer 8 for analyzing the scanning spectrum of the frequency-modulated continuous wave light signal and reading the scanning width, and another part of the light signal is transmitted to the photodetector 7 for receiving the time beat signal and generating a beat frequency electric signal, and then transmitted to the digital storage oscilloscope 9 and the computer end 10;

[0082] S203: The beat frequency signal collected at the computer end 10 is processed, including beat frequency signal de-skewing, cutting, Hilbert transform, instantaneous frequency calculation, and output.

[0083] Specifically, the frequency-modulated continuous wave light signal is input into the Michelson interferometer 5 through the optical isolator 4 to generate an optical beat signal. Part of the light signal is transmitted to the Fourier infrared spectrometer 8 for analyzing the scanning spectrum of the frequency-modulated continuous wave light signal and reading the sweep width. Another part of the light signal is transmitted to the photodetector 7 for receiving a time optical beat signal and generating a beat frequency electrical signal, which is then transmitted to the digital storage oscilloscope 9 and the computer terminal 10. The collected beat frequency signal is processed at the computer terminal 10, including beat frequency signal de-skewing, cutting, Hilbert transform, instantaneous frequency calculation, and output. De-skewing refers to removing the slowly changing envelope signal in the beat frequency signal due to modulation, and the main method adopted is polynomial fitting. Cutting refers to cutting the upper and lower chirps of the beat frequency signal to extract the beat frequency corresponding to each chirp. Hilbert transform refers to extracting the quadrature signal of the beat frequency signal using the algorithm, and obtaining the change of the laser phase with time using the quadrature signal. The calculation of the instantaneous frequency refers to obtaining the instantaneous frequency signal by differentiating the instantaneous phase using the relationship between the phase and the frequency.

[0084] Case-1: Theoretical simulation of mid-infrared frequency-modulated continuous wave generation

[0085] The theoretical generation scheme of the mid-infrared frequency-modulated continuous wave signal relies on the L-K mean field model, which includes a set of equations for the number of photons, the number of carriers, and the instantaneous phase rate. This model can describe the complex dynamics of the laser, including relaxation oscillation, carrier clamping, phase fluctuation, and photon oscillation. The differential equations are as follows:

[0086]

[0087] where N is the number of carriers, η is the injection current efficiency, I is the bias current, q is the electron charge constant, Γ p is the mode field confinement factor, v g is the optical field group velocity, g is the single-stage differential gain coefficient, S is the number of photons, τ sp is the carrier lifetime, m is the cascade order, τ p is the photon lifetime, β is the spontaneous emission coefficient, and α h is the linewidth enhancement factor. The analysis of the frequency-modulated continuous wave instantaneous frequency can observe the sweep width and sweep rate of the generated frequency-modulated continuous wave. The instantaneous frequency analysis relies on the instantaneous phase of equation (3), which can be represented as:

[0088]

[0089] Figure 2is the theoretical verification diagram of the generating device of the application, including the change of the photon number with time (a1), the change of the carrier number with time (a2), the change of the instantaneous frequency with time (a3) when no current modulation is applied; the change of the photon number with time (b1), the change of the carrier number with time (b2), the change of the instantaneous frequency with time (b3) when current modulation is applied. As can be seen from the diagram, when there is no modulation, the photons and carriers remain stable after transient relaxation oscillation, the instantaneous frequency does not change with time, at this time the laser output is continuous light and the center frequency does not change with time. When a certain size of modulation is applied, the carriers and photons will appear the same fluctuations as the modulation signal after relaxation oscillation. At the same time, the instantaneous frequency also changes with time, proving that a frequency-modulated continuous wave signal is generated at this time. In addition, it can be seen that the fluctuation of the photon number with time is large, that is, the output power fluctuation is large, and due to the carrier clamping effect, the carrier number fluctuation is very small.

[0090] After the above generation process, the output light field of the mid-infrared frequency-modulated continuous wave signal source can be represented as:

[0091]

[0092] wherein E is the output light field of the frequency-modulated continuous wave source, is the amplitude of the frequency-modulated continuous wave source output light field, f is the center frequency of the laser at t=0, μ is the sweep speed, is the sweep nonlinear term, and φ is the phase noise term of the frequency-modulated continuous wave source. In the theoretical modeling, the sweep nonlinear term is set to 0, that is, ; the phase noise is set to a Gaussian white noise with a very small amplitude. The output light fields of the two arms in the Michelson interferometer, the 7 photodetector beat frequency signal photocurrent can be represented as equations (6) and (7):

[0093]

[0094] wherein τn represents the Michelson interferometer arm length of different delay line lengths (n=1, 2), I represents the beat frequency signal photocurrent, η is the imbalance of the two arms of the Michelson interferometer 5, R is the sensitivity of the photodetector 7, and μ(τ2-τ1) is the beat frequency, which can be adjusted by the delay length of the two arms. After measuring the beat frequency signal, the instantaneous frequency can be obtained from the signal:

[0095]

[0096] wherein arg represents the complex signal phase extraction operation, and H represents the Hilbert transform.

[0097] Figure 3is a test device theoretical verification diagram of the present application. It includes the first arm instantaneous frequency of the Michelson interferometer 5 changing with time (a1); the second arm instantaneous frequency of the Michelson interferometer 5 changing with time (a2), and the beat frequency changing with time (a3). As can be seen from the diagram, the different arm lengths of the two arms of the Michelson interferometer in the measuring device will bring different delay times to the output frequency-modulated continuous wave light field, and the delay time is positively correlated with the difference in the arm lengths of the two arms.

[0098] Case-2 experimental verification of the generation of the mid-infrared frequency-modulated continuous wave:

[0099] We built an experimental device as shown in Figure 1 , and generated a narrow linewidth mid-infrared frequency-modulated continuous wave signal by current modulation of the interband cascade laser 3.

[0100] Figure 4 is the output spectrum diagram and the broken line diagram of the frequency changing with the current of the interband cascade laser 3 under different current biases when no modulation is added. As can be seen from the diagram, the laser output has high suppression ratio and narrow spectral linewidth.

[0101] Figure 5 is the output spectrum diagram and the broken line diagram of the frequency changing with the current of the interband cascade laser 3 under different temperatures when no modulation is added.

[0102] Figure 6 is the frequency-modulated continuous wave spectrum output under different modulation amplitudes compared with the spectrum when no modulation is added. As can be seen from the diagram, different modulation amplitudes will broaden the spectrum, i.e. generate frequency-continuous-scan frequency-modulated continuous wave signals. The sweep half-width increases with the increase of the modulation amplitude, and when the modulation amplitude is 4.5V, the sweep half-width is about 49GHz.

[0103] Figure 7 is the frequency-modulated continuous wave spectrum output under different modulation frequencies compared with the spectrum when no modulation is added. As can be seen from the diagram, different modulation frequencies will broaden the spectrum, i.e. generate frequency-continuous-scan frequency-modulated continuous wave signals. Under the modulation frequency of 1-200kHz, the sweep half-width is about 57GHz.

[0104] The above only discloses one or more preferred embodiments of the present application, and cannot limit the scope of the rights of the present application. Those skilled in the art can understand that the implementation of all or part of the above-mentioned embodiments, and the equivalent changes made according to the claims of the present application, still belong to the scope covered by the present application.

Claims

1. A device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves, characterized in that, Includes generating devices and measuring devices; The generating device includes an arbitrary function generator, an ultra-low noise driving source, and an interband cascaded laser. The arbitrary function generator is connected to the ultra-low noise driving source, and the ultra-low noise driving source is connected to the interband cascaded laser. The arbitrary function generator is used to generate a triangular wave or sawtooth wave voltage signal with adjustable frequency and amplitude. The signal is applied to the AC modulation port of the current source to modulate the current output or temperature output of the ultra-low noise drive source. The ultra-low noise drive source is used to control the current and temperature parameters of the interband cascaded laser, and also modulates the current and temperature parameters in conjunction with an external arbitrary function signal. The interband cascaded laser is used to output a narrow-linewidth, mid-infrared frequency-modulated continuous wave optical signal; The measuring device includes an optical isolator, a Michelson interferometer, an optical beam splitter, a Fourier transform infrared spectrometer, and a photodetector. The optical isolator is connected to the interband cascaded laser and is connected in series with the optical path of the Michelson interferometer. The optical paths of the Michelson interferometer and the optical beam splitter are connected. The Fourier transform infrared spectrometer and the photodetector are respectively connected to both ends of the optical beam splitter. The optical isolator is used to isolate feedback light from the testing device to the generating device; The Michelson interferometer is used to obtain a heterodyne differential signal, and the signal is a low-frequency interference signal generated by different lengths of two arms of the Michelson interferometer; wherein the output light field of the two arms in the Michelson interferometer, the photoelectric current of the beat frequency signal after passing through the photoelectric detector can be expressed as formulas (6) and (7): wherein, represent the Michelson interference arm length of different delay line lengths n=1, 2, I represents the beat frequency signal photoelectric current, η is the imbalance of the two arms of the Michelson interferometer, and R is the sensitivity of the photoelectric detector, is the beat frequency, which can be adjusted by the delay length of the two arms; is the amplitude of the output light field of the frequency-modulated continuous wave source; and φ is a phase noise term of the frequency-modulated continuous wave source. The instantaneous frequency can be obtained from the beat signal after measurement: where arg denotes the complex signal phase extraction operation and H denotes the Hilbert transform. The optical beam splitter is used to split the frequency-modulated continuous wave optical signal input from the interband cascaded laser. After further splitting by the optical beam splitter, part of the optical signal is transmitted to the Fourier transform infrared spectrometer, and the other part of the optical signal is transmitted to the photodetector. The Fourier transform infrared spectrometer is used to collect the scanning spectrum of the frequency-separated continuous wave light signal and read the sweep width. The photodetector is used to receive the time-frequency beat signal from the Michelson interferometer and generate a beat frequency electrical signal, which is then transmitted to the digital storage oscilloscope and the computer.

2. The device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves as described in claim 1, characterized in that, The ultra-low noise driving source includes a current module, which is connected to the arbitrary function generator and the interband cascaded laser, respectively.

3. The device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves as described in claim 1, characterized in that, The ultra-low noise driving source includes a temperature module, which is connected to the arbitrary function generator and the interband cascaded laser, respectively.

4. The device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves as described in claim 1, characterized in that, The measurement device for the narrow linewidth mid-infrared frequency-modulated continuous wave also includes a digital storage oscilloscope and a computer terminal. The digital storage oscilloscope is connected to the photodetector, and the computer terminal is connected to the digital storage oscilloscope. The digital storage oscilloscope is used to record and observe real-time beat frequency electrical signals; The computer terminal is used for offline processing of beat frequency electrical signals.

5. The device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves as described in claim 4, characterized in that, The beat frequency electrical signal includes: beat frequency signal deskewing, segmentation, Hilbert transform, instantaneous frequency determination, and output.

6. The device for generating and measuring narrow-linewidth mid-infrared frequency-modulated continuous waves as described in claim 1, characterized in that, Set the modulation waveform to a triangular wave, the modulation period to 1-100kHz, and the modulation amplitude to 4Vpp.

7. A method for generating narrow-linewidth mid-infrared frequency-modulated continuous waves, applicable to the narrow-linewidth mid-infrared frequency-modulated continuous wave generation and measurement device as described in claim 1, characterized in that, Includes the following steps: Use an arbitrary function generator to generate triangular or sawtooth wave voltage signals with adjustable frequency and amplitude. The generated signal is used to modulate the current or temperature input of the ultra-low noise drive source to control the current and temperature parameters of the interband cascaded laser. Through modulation, interband cascaded lasers output narrow-linewidth, mid-infrared frequency-modulated continuous wave optical signals.

8. A method for measuring narrow-linewidth mid-infrared frequency-modulated continuous waves, applicable to the narrow-linewidth mid-infrared frequency-modulated continuous wave generation and measurement device as described in claim 1, characterized in that, Includes the following steps: The frequency-modulated continuous wave optical signal is input into the Michelson interferometer through an optical isolator to generate an optical beat signal; Part of the optical signal is transmitted to a Fourier transform infrared spectrometer to analyze the scanning spectrum of the frequency-modulated continuous wave optical signal and read the sweep width. The other part of the optical signal is transmitted to a photodetector to receive the time-frequency beat signal and generate a beat frequency electrical signal, which is then transmitted to a digital storage oscilloscope and a computer. The acquired beat frequency electrical signals are processed on the computer, including beat frequency signal deskewing, segmentation, Hilbert transform, instantaneous frequency determination, and output.

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