A phase-modulation-based dual-comb spectral measurement system and method

Abstract

The application discloses a phase modulation based dual-comb spectrum measurement system and method. In the measurement system: a dual-comb generating unit generates two sets of optical frequency combs with slightly different repetition frequencies, there is a set of optical comb teeth with equal absolute values of optical frequency difference between the two sets of optical frequency combs, a signal generator generates a modulation signal to modulate the optical phase difference between the optical frequency comb 1 and the optical frequency comb 2, at least one of the two optical frequency combs is input into a unit to be measured and output, and the two optical frequency combs are jointly input into an optical detector to generate a measurement signal through beat frequency, in the beat frequency process, the set of optical comb teeth with equal absolute values of optical frequency difference will beat the same frequency component and superimpose to form the measurement signal; and a data acquisition and processing unit samples and processes the measurement signal to obtain the spectrum information of the unit to be measured. The application can eliminate the same frequency beat frequency aliasing generated by the beat frequency of the set of optical comb teeth with the same optical frequency difference by using the changing optical phase difference between the two sets of optical frequency combs, and the technology can be used for simple, low-cost and easily integrated dual-comb spectrum measurement.

Description

Technical Field

[0001] This invention relates to the field of optical frequency combs and spectral measurement. Specifically, it relates to a dual-optical-comb spectral measurement system and method based on phase modulation. Background Technology

[0002] An optical frequency comb, or simply optical frequency comb, is a rapidly developing optical technology in recent years. It refers to an optical signal with equally spaced, discrete frequency components in its spectrum, corresponding to an equally spaced repeating sequence in the time domain. Like a set of teeth on the spectrum, the optical frequency comb plays an important role in various metrology fields.

[0003] In 2002, Schiller proposed the dual-comb spectroscopy technique. Its advantages in wide spectral coverage, high sensitivity, rapid measurement and high resolution have enabled the dual-comb method, which uses two optical frequency combs with small repetition frequencies to achieve measurement, to be applied in fields such as precision laser spectroscopy.

[0004] In dual-comb technology, the center wavelength and spectral resolution of spectral measurement methods based on electro-optic modulation are easily adjustable. In 2014, NIST proposed a method using two dual-drive Mach-Zehnder modulators to generate dual optical combs and using an acousto-optic modulator to measure gas spectra (Opt. Lett., 39, 2688-2690 (2014)). DC light is split into two paths by a beamsplitter, each passing through a single-frequency sinusoidal signal-driven dual-drive Mach-Zehnder modulator to generate two optical combs with slightly different repetition frequencies. One of these combs is then split by another beamsplitter to form a reference path and a measurement path. The measurement path first passes through the gas sample and then undergoes frequency shifting via the acousto-optic modulator. The reference path only undergoes frequency shifting via the acousto-optic modulator. The measurement and reference paths are combined and beat on the other optical comb to obtain the radio frequency spectrum, which reflects the gas's absorption spectrum. This method requires two dual-drive Mach-Zehnder modulators for separate modulation to facilitate frequency shifting of one optical comb, thus preventing aliasing of positive and negative frequencies after beats. In 2015, Pedro Martin-Mateos et al. used two phase modulators and one acousto-optic modulator to perform gas absorption spectroscopy measurements (IEEE Photonics Technology Letters, 27, 1309-1312 (2015)). DC light is split into two paths by a beam splitter. Two phase modulators driven by single-frequency sinusoidal signals generate two optical combs with slightly different repetition frequencies. An acousto-optic modulator is added to one of these paths to generate a frequency shift. The two optical combs are then combined and split again, one passing through the gas sample and the other serving as a reference. The gas absorption spectrum is obtained by comparing the spectra of the two paths. Both of these methods split the light into two paths, each modulated by an electro-optic modulator. One path is then fitted with an acousto-optic frequency shifter. The reason for using a two-electro-optic modulator structure is that a frequency shift must be performed on one optical comb to avoid aliasing of positive and negative frequencies after beat frequency. In 2020, Miguel Soriano-Amat et al. proposed an electro-optic modulation dual-comb structure using a single electro-optic modulator (Lightwave Technol. 38, 5107-5115 (2020)). A single Mach-Zehnder modulator is driven by a multi-frequency signal generated by an arbitrary waveform generator. This multi-frequency signal contains two sets of frequency combs with slightly different repetition frequencies, modulating the input DC optical signal into a dual-comb with comb teeth of two different repetition frequencies. The signal is then passed through an optically tunable bandpass filter to obtain a single-sided modulated optical signal. This structure simplifies the system structure by using only one Mach-Zehnder modulator, but it employs an expensive arbitrary waveform generator to produce a complex multi-frequency signal driving the single Mach-Zehnder modulator, and also uses an optical bandpass filter to avoid aliasing during down-conversion. While this reduces the complexity of the system structure, it significantly increases the system cost.In 2023, DALong et al. proposed a single-comb spectral measurement structure that achieves electro-optic frequency shifting by adding a ramp signal to the bias port of a single electro-optic modulator (Optica Letters. 48, 892-895 (2023)). This system adds a linear phase to the optical signal by adding a ramp electrical signal to the bias port of a single modulated signal, and uses the electro-optic effect to replace the acousto-optic frequency shifter for frequency shifting, thereby achieving aliasing frequency resolution. However, this system uses a large-bandwidth detector for single-comb spectral measurement, which increases the system cost. This invention aims to reduce the system complexity and cost of dual-comb spectral measurement systems. It uses a changing signal to drive a phase modulation device to generate a changing phase difference between the two combs, and combines it with a post-processing algorithm to conduct experimental dual-comb spectral measurements without the need for optical frequency shifters or optical filters.

[0005] This invention proposes a phase-modulated dual-comb spectral measurement system and method. By using a changing signal to generate a changing phase difference between the two combs, it is possible to distinguish the aliased beat frequency signals of the dual-comb without optical frequency shifters or filters, providing a new technical path for the application of dual-comb technology. Summary of the Invention

[0006] This invention provides a phase-modulated dual-comb spectral measurement system, comprising:

[0007] The system comprises a dual optical comb generation unit, a signal generator, a unit under test (DUT), a photodetector, and a data acquisition and processing unit. The dual optical comb generation unit generates an optical comb 1 with a frequency interval f1 and another optical comb 2 with a frequency interval f2. The frequency intervals f1 and f2 have a repetition frequency difference Δf. Different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference exist between the teeth of optical comb 1 and optical comb 2. The dual optical comb generation unit modulates the optical phase difference between optical comb 1 and optical comb 2. The signal generator generates a modulation signal, which is input to the dual optical comb generation unit. The dual optical comb generation unit modulates the optical phase difference between optical comb 1 and optical comb 2 according to the modulation signal. Optical comb 1 is input to the DUT. Optical comb 2 is directly connected to the unit under test (DUT). The optical frequency comb 1 of the measurement unit is input to the photodetector together to generate a beat frequency signal, or the optical frequency comb 2 is also input to the photodetector together with the optical frequency comb 1 of the measurement unit to generate a beat frequency signal. Different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference in optical frequency comb 1 and optical frequency comb 2 generate beat frequency components with the same frequency in the beat frequency signal, the frequency of which is equal to the absolute value of the optical frequency difference. The phase difference between the beat frequency components is affected by the optical phase difference between optical frequency comb 1 and optical frequency comb 2. The superposition of each beat frequency component forms the measurement signal. The data acquisition and processing unit samples the measurement signal and, based on the differences in the measurement signal under different optical phase differences, analyzes the amplitude or phase of each beat frequency component in the measurement signal to obtain the spectral information of the measurement unit.

[0008] In one example, the dual optical comb generating unit is characterized by generating an optical frequency comb using the electro-optic effect, the saturable absorption effect, or the Kerr effect.

[0009] In one example, the dual optical comb generation unit is characterized by having an optical phase modulation module, which modulates the optical phase difference between optical frequency comb 1 and optical frequency comb 2 using electro-optic effect, magneto-optic effect, thermo-optic effect, photoelastic effect, or spatial delay variation.

[0010] In one example, the signal generator is characterized in that it generates a jump signal having multiple discrete values, each discrete value having a duration greater than or equal to 1 / Δf, or a continuous ramp signal or triangular wave signal that can cause a linear and continuous change in the optical phase difference between two optical frequency combs.

[0011] In one example, the photodetector is characterized by achieving photodetection through photoelectric, photoacoustic, photothermal, and photomagnetic effects.

[0012] In one example, the system is characterized by the absence of an optical filter that filters out one of the components of an optical comb combination with the same absolute value of optical frequency difference.

[0013] In one example, the dual optical comb generation unit is characterized by generating optical comb 1 and optical comb 2 using two separate sets of devices or a set of devices having at least some shared components.

[0014] In one example, the dual optical comb generation unit is characterized by using discrete phase modulators, integrated phase modulation modules, or the inherent characteristics of the optical frequency comb source for modulation.

[0015] This invention provides a phase-modulated dual-comb spectral measurement method, characterized by comprising the following steps:

[0016] Step 1: The dual optical comb generation unit generates an optical frequency comb 1 with a frequency interval f1 and another optical frequency comb 2 with another frequency interval f2. The frequency interval f1 and the other frequency interval f2 have a repetition frequency difference Δf. There are different combinations of optical comb teeth with the same absolute value of optical frequency difference between the optical comb teeth of optical frequency comb 1 and optical frequency comb 2.

[0017] Step 2: Input the signal generated by the signal generator into the dual optical comb generation unit to modulate the optical phase of at least one of the optical frequency combs 1 and 2, so that the dual optical comb generation unit generates a corresponding time-varying optical phase difference between the optical frequency combs 1 and 2.

[0018] Step 3: Input optical frequency comb 1 or optical frequency comb 1 and optical frequency comb 2 together into the unit under test;

[0019] Step 4: Input the optical frequency comb 1 that has passed through the unit under test and the optical frequency comb 2 that has passed through or has not passed through the unit under test to the photodetector to generate a beat frequency signal. Different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference in optical frequency comb 1 and optical frequency comb 2 generate beat frequency components with the same frequency in the beat frequency signal, which are equal to the absolute value of the optical frequency difference. The phase difference between the beat frequency components is affected by the optical phase difference between optical frequency comb 1 and optical frequency comb 2. The superposition of each beat frequency component forms the measurement signal.

[0020] Step 5: The data acquisition and processing unit samples the measurement signal and, based on the changes in the measurement signal caused by the change in optical phase difference, analyzes the amplitude or phase of different beat frequency components of the same frequency from the measurement signal, thereby obtaining the spectral information of the unit under test.

[0021] In one example, the optical phase difference varies among multiple discrete values ​​in step 2, and in step 5, time-frequency transformation is performed on the measurement signals under different optical phase differences to obtain the amplitude or phase of each measurement signal component under different optical phase differences. Based on the relationship between the optical phase difference and the amplitude or phase of each measurement signal component, the amplitude or phase of different co-frequency beat frequency components generated by different optical comb combinations with equal absolute values ​​of optical frequency difference are calculated.

[0022] In one example, the characteristic is that the amplitudes of the different beat frequency components generated by the different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference are A1 and A2, the phases of the two beat frequency components are θ1 and θ2, and the optical phase difference generated by the modulation between optical comb 1 and optical comb 2 is... At this point, the amplitude of the measurement signal component formed by the superposition of the two beat frequency components at the same frequency is Phase is Based on the variation of the amplitude or phase of the measured signal component with the phase difference of light, the amplitude or phase of different beat frequency components at the same frequency are fitted or calculated.

[0023] In one example, the optical phase difference in step 2 changes continuously in the form of a ramp or a triangular wave, with a phase change rate of v rad / s. In step 5, the measurement signal with multiple beat frequency cycles of time length greater than or equal to 2π / v is subjected to time-frequency transformation to obtain a multi-cycle spectrum. On the multi-cycle spectrum, different beat frequency components of the same frequency generated by different combinations of optical combs with equal absolute values ​​of optical frequency difference are separated. The amplitude or phase of the separated components can be directly calculated by the spectrum to distinguish the amplitude and phase of the different beat frequency components of the same frequency. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0025] Figure 1This is a structural diagram of a phase-modulated dual-comb spectral measurement system;

[0026] Figure 2 This is the system architecture diagram for Example 1;

[0027] Figure 3 This is a schematic diagram of beat frequency superposition in Example 1;

[0028] Figure 4 This is a graph showing the amplitude variation of the beat frequency component under different bias voltages in Example 1.

[0029] Figure 5 This is the transmittance spectrum of the device under test measured by the system in Example 1;

[0030] Figure 6 This is the system architecture diagram for Example 2. Detailed Implementation

[0031] The technical solutions of the present invention will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] Example 1

[0033] Figure 2 A schematic diagram of a phase-modulated dual-comb spectral measurement system is presented. The system includes an adjustable single-frequency laser 1, a dual-arm electro-optic intensity modulator 2, sinusoidal signal generators 3 and 4, comb signal generators 5 and 6, a signal generator 7, an acetylene-filled gas chamber 8, a photodetector 9, and a data acquisition and processing unit 10.

[0034] In this example, the dual-comb generation unit consists of a continuous-wave light source, a dual-arm photoelectric intensity modulator, a sine wave generator, and a comb-shaped signal generator. The continuous-wave light source is a tunable single-frequency laser with an output wavelength of 1530.34 nm and a linewidth of 10 kHz. The output single-frequency coherent light enters the dual-arm optical modulator and is divided into upper and lower arms. Each arm has an electro-optic intensity modulation module, which modulates the amplitude of the light passing through it using the electro-optic effect. The modulation bandwidth is 22 GHz, and the half-wave voltage is 3.5 V. The upper arm also has a phase modulation module, which can change the optical phase difference between the two arms by applying a changing electrical signal to the bias port. The sine wave generated by the sine wave generator is converted into an electrical pulse signal with a corresponding repetition frequency by the comb-shaped signal generator. The two different sine wave generators and comb-shaped signal generators can generate two sets of electrical pulse signals with different repetition frequencies, which serve as the modulation signals for the electro-optic intensity modulation modules of the upper and lower arms, respectively. The sinusoidal electrical signals generated by the two sets of sinusoidal signal generators have frequencies of 100MHz and 99.86MHz, respectively. Therefore, the repetition frequency difference Δf between the electrical pulse signals output by the two sets of comb signal generators is 0.16MHz. By using these two sets of electrical pulse signals to modulate the upper and lower arms of the dual-arm electro-optic intensity modulation module, two optical frequency combs 1 and 2 with different repetition frequencies can be obtained. Since the two optical frequency combs are generated by the same continuous wave source, the two optical frequency combs have the same center wavelength, which corresponds to the frequency fc. The +n order comb teeth (n is a positive integer) in the modulated optical frequency comb 1 and the +n order comb teeth in the optical frequency comb 2 have an optical frequency difference of nΔf. There is also an optical frequency difference of nΔf between the -n order comb teeth of optical frequency comb 1 and optical frequency comb 2. That is, there is a combination of optical frequency comb teeth with equal absolute values ​​of optical frequency difference between optical frequency comb 1 and optical frequency comb 2.

[0035] In this example, signal generator 7 generates a periodic stepped signal with a repetition frequency of 5Hz and a voltage variation range of -5V to +5V. Each period contains 128 voltage steps of equal duration. This periodic stepped signal is used as a bias voltage input to the bias port of the dual-arm electro-optic intensity modulator 2. This voltage is applied to the phase modulation module in the dual-arm electro-optic intensity modulator 2, thereby changing the optical phase difference between the two optical frequency combs. The duration of each voltage step in the stepped signal is 1.5625ms, which is longer than the period of the dual-comb beat frequency signal, i.e., 1 / Δf = 6.25μs. The optical signals from the upper and lower arms of the dual-arm electro-optic intensity modulator are combined into a single dual-comb optical signal at the output of the dual-arm electro-optic intensity modulator.

[0036] The combined optical signal containing optical frequency comb 1 and optical frequency comb 2 is input into the acetylene gas chamber 8 to be tested. The acetylene gas chamber has a pressure of 20 torr, a length of 10 cm, and an absorption peak near 1530 nm. The optical signal output of the gas chamber is optical frequency comb 1 and optical frequency comb 2 containing the spectral information of the gas to be tested.

[0037] The dual-comb optical signal output from the acetylene gas chamber 8 is input into the photodetector 9. Optical frequency combs 1 and 2 generate beat frequency signals from their respective comb tooth combinations via beat frequency generation. Since there are multiple comb tooth combinations with equal absolute values ​​of optical frequency difference between optical frequency combs 1 and 2, multiple pairs of combinations with the same beat frequency are generated. The superposition of a pair of signals with the same beat frequency constitutes a frequency component of the measurement signal with that beat frequency. The phase difference between beat frequency components of the same frequency is affected by the optical phase difference between optical frequency combs 1 and 2. Multiple such frequency components together constitute the measurement signal. The photodetector used has a bandwidth of 150MHz. Furthermore, the same parameters and settings are used for measurement when removing acetylene gas from the gas chamber, and a reference signal is generated by the photodetector via beat frequency generation.

[0038] In this example, the data acquisition and processing unit includes a data acquisition card with a sampling rate of 20 MSa / s and a computer. The data acquisition and processing unit samples the measurement signal, which also exhibits periodicity, with the same repetition frequency as the periodic step signal generated by signal generator 7. The data acquisition and processing unit performs a Fast Fourier Transform on the sampled measurement signal under each bias voltage step, i.e., each optical phase difference. This yields the amplitude of the frequency components of each measurement signal under different optical phase differences. Based on the relationship between the optical phase difference and the amplitude of the frequency components of each measurement signal, the amplitudes of different beat frequency components generated by different combinations of optical combs with equal absolute optical frequency differences are calculated. Furthermore, the relationship between the optical phase difference and the phase of the frequency components of each measurement signal can also be used to calculate the phase information of different beat frequency components generated by different combinations of optical combs with equal absolute optical frequency differences.

[0039] The data acquisition and processing unit performs similar processing on the reference signal. Finally, by comparing the amplitude and phase of each beat frequency component obtained from the measured signal and the reference signal, the spectral information of the acetylene gas chamber under test can be obtained.

[0040] According to the downconversion principle, optical frequency components with the same repetition frequency difference Δf that are integer multiples of each other will superimpose during downconversion. The amplitude of the superimposed frequency during downconversion is related to the amplitude of different optical comb combinations with equal absolute values ​​of the optical frequency difference and the optical phase difference between the upper and lower arms of the dual-arm electro-optic intensity modulator. A schematic diagram of the aliasing principle is shown below. Figure 3As shown in the figure, two optical frequency combs have comb teeth with the same frequency located at frequency fc. The optical frequency difference between the two sets of optical frequency comb tooth combinations that are symmetrical about this frequency fc is equal. The optical frequency difference between the two sets of optical frequency comb teeth is an integer multiple of the repetition frequency difference Δf. They will be downconverted to the same frequency and superimposed. Let the amplitudes of the different beat frequency components generated by the beat frequencies of different optical frequency comb tooth combinations with equal absolute values ​​of optical frequency difference be A1 and A2, and the phases of the two beat frequency components be θ1 and θ2. The optical phase difference generated by the modulation between optical frequency comb 1 and optical frequency comb 2 is... At this point, the amplitude of the measurement signal component formed by the superposition of the two beat frequency components at the same frequency is Phase is

[0041] The optical phase difference between the two optical frequency combs can be changed by altering the bias voltage between the upper and lower arms of the dual-arm electro-optic intensity modulator. This allows us to obtain different amplitudes and phases of the measured and reference signal components. The bias voltage between the two arms can be varied among multiple values, and the amplitude variation curve can be fitted using the above formula. This yields the amplitude variation and fitted curve of the superimposed measured signal components, as shown in the figure. Figure 4 As shown. The amplitudes A1 and A2 of the two overlapping beat frequency components can be obtained through fitting; the amplitudes θ1 and θ2 of the two overlapping beat frequency components can be obtained by fitting the phase change curve of the beat frequency components using the above formula.

[0042] The beat frequency components of the measured signal and the reference signal are calculated separately. The acetylene gas under test causes a change in the amplitude of the dual-comb optical signal, which in turn causes a change in the amplitude of the beat frequency components. The transmittance as a function of optical frequency can be obtained by dividing the amplitudes of the same beat frequency components in the measured signal and the reference signal. Figure 5 As shown, this is the spectral information of the gas to be measured.

[0043] In Example 1, the continuous wave source can also be a single-frequency ultraviolet, visible, infrared source or terahertz wave source.

[0044] In Example 1, the dual-arm optical modulation device can also be a dual-arm electro-optic phase modulator, a dual-arm electro-optic polarization modulator, a dual-arm magneto-optic modulator, a dual-arm acousto-optic modulator, a dual-arm thermo-optic modulator, etc.

[0045] In Example 1, the two optical frequency combs in the dual optical comb generation unit can also be generated by fiber lasers, laser-pumped nonlinear optical microcavities, nonlinear micro-ring devices, discrete electro-optic modulators, etc.

[0046] In Example 1, the sine wave generator and the comb generator can also be arbitrary waveform generators.

[0047] In Example 1, the optical signal output by the dual-arm electro-optic intensity modulator can be passed through devices such as optical amplifiers and nonlinear systems before entering the system under test.

[0048] In Example 1, the photodetector can also be a photoacoustic detector, a photoconductive antenna, a photothermal converter, etc.

[0049] Example 2

[0050] Figure 6 A schematic diagram of another phase-modulated dual-comb spectral measurement system is presented. This system includes a microcavity optical frequency comb source 1, a microcavity optical frequency comb source 2, a function signal generator 3, a phase modulator 4, a filter for the light under test 5, an optical coupler 6, a photodetector 7, and a data acquisition and processing unit 8.

[0051] In this example, the dual optical comb generation unit consists of two microcavity optical comb sources and a phase modulator. Microcavity optical comb source 1 and microcavity optical comb source 2 generate optical comb 1 and optical comb 2 respectively, with repetition frequencies of 1GHz and 1GHz+10MHz respectively, a repetition frequency difference of 10MHz, and a center wavelength of 1553nm for both output optical combs. Through a frequency locking device, optical comb 1 and optical comb 2 have one comb tooth with the same optical frequency, denoted as fc. The optical frequency difference between the positive and negative n-order comb teeth of optical comb 1 and optical comb 2 symmetrical about fc is nΔf, that is, the two sets of optical combs contain optical comb tooth combinations with equal absolute values ​​of optical frequency difference.

[0052] A function signal generator produces a continuously changing ramp signal, which drives a phase modulator. The half-wave voltage of the phase modulator is 4V, and the bandwidth is 20GHz. This ramp signal causes a change in the optical phase difference between the two optical frequency combs through the phase modulator. The voltage of the ramp signal changes by 8V in the time interval T, causing a change of 2π in the phase difference between the two optical frequency combs. Therefore, the rate of change of the phase difference is 2π / T, and in this real-time example, T = 1μs.

[0053] The modulated optical frequency comb 1 passes through the optical filter under test, and then the output of the optical filter under test is combined with optical frequency comb 2 through an optical coupler. The combined optical signal is then input into a photodetector to generate a measurement signal through beat frequency. The bandwidth of the photodetector used is 500MHz. During the beat frequency process, the absolute value of the optical frequency difference between optical frequency comb 1 and optical frequency comb 2 is equal to f at every moment. b Different combinations of optical comb teeth will produce frequencies equal to the absolute value f of the optical frequency difference. b The beat frequency components of the same frequency, the superposition of each pair of beat frequency components of the same frequency forms a frequency f in the measurement signal. b The signal.

[0054] In this example, the data acquisition and processing unit includes a data acquisition card with a sampling rate of 1GSa / s and a computer. The data acquisition and processing unit samples the measurement signal, and the time length of the processed signal must be greater than or equal to 2π / (2π / T), i.e., T. In this example, a fast Fourier transform is performed on a measurement signal segment of length T.

[0055] The amplitudes of the same-frequency beat frequency components generated by different combinations of optical combs with equal absolute values ​​of optical frequency difference undergo continuous phase modulation under the action of a continuous external modulation signal. According to the rate of change of the phase difference, 2π / T, this continuous phase modulation causes the originally same-frequency beat frequency components to separate, and the two beat frequency components return to their original same-frequency point f. b Moving 1 / T in different directions around the center creates two separate beat frequency components. The frequency f is then calculated in the frequency spectrum. b -1 / T and f b By combining the amplitude and phase of the two frequency points +1 / T, the amplitude and phase of the original beat frequency component can be obtained, thus yielding the spectral information of the optical filter under test.

[0056] In Example 2, microcavity optical frequency comb source 1 and microcavity optical frequency comb source 2 can also be fiber lasers, microring lasers, single electro-optic modulators generating dual optical frequency combs, discrete electro-optic modulated optical comb sources, or combinations thereof.

[0057] In Example 2, the electro-optic phase modulator can also be a magneto-optic phase modulator, a thermo-optic phase modulator, or an optical delay line, etc.

[0058] In Example 2, the unit under test can also be other devices or samples that have a frequency response to a specific spectrum, such as optical modulators, gases, etc.

[0059] In Example 2, the modulated optical frequency comb 1 can pass through devices such as an optical amplifier and a nonlinear system before entering the system under test.

[0060] In Example 2, the photodetector can also be a photoacoustic detector, a light guide antenna, a photothermal converter, etc.

[0061] In Example 2, the signal generated by the signal generator can also be a multi-level transition signal or a continuous triangular wave signal, etc.

Claims

1. A phase-modulated dual-comb spectral measurement system, characterized in that, include: Dual optical comb generation unit, signal generator, unit under test, photodetector, data acquisition and processing unit; The dual-comb generation unit generates an optical frequency comb 1 with a frequency interval f1 and another optical frequency comb 2 with a different frequency interval f2. The frequency interval f1 and the other frequency interval f2 have a repetition frequency difference. f, There are different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference between the optical comb teeth of optical comb 1 and optical comb 2. The dual optical comb generation unit modulates the optical phase difference between optical comb 1 and optical comb 2. The signal generator generates a modulation signal and inputs it to the dual optical comb generation unit. The dual optical comb generation unit modulates the optical phase difference between optical comb 1 and optical comb 2 according to the modulation signal. Optical frequency comb 1 is input to the unit under test; optical frequency comb 2 is directly input to the photodetector together with optical frequency comb 1 that has passed through the unit under test to generate a beat frequency signal, or optical frequency comb 2 is also input to the photodetector together with optical frequency comb 1 that has passed through the unit under test to generate a beat frequency signal. Different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference in optical frequency comb 1 and optical frequency comb 2 generate beat frequency components with the same frequency as the absolute value of optical frequency difference in the beat frequency signal. The phase difference between the beat frequency components with the same frequency is affected by the optical phase difference between optical frequency comb 1 and optical frequency comb 2. The superposition of each beat frequency component forms the measurement signal. The data acquisition and processing unit samples the measurement signal and, based on the differences in the measurement signal under different optical phase differences, analyzes the amplitude or phase of the beat frequency component at the same frequency from the measurement signal to obtain the spectral information of the unit under test.

2. The phase-modulated dual-comb spectral measurement system according to claim 1, characterized in that, The dual optical comb generating unit generates an optical frequency comb using the electro-optic effect, saturable absorption effect, or Kerr effect.

3. The phase-modulated dual-comb spectral measurement system according to claim 1, characterized in that, The dual optical comb generation unit includes an optical phase modulation module, which modulates the optical phase difference between optical frequency comb 1 and optical frequency comb 2 using electro-optic effect, magneto-optic effect, thermo-optic effect, photoelastic effect, or spatial delay variation.

4. The phase-modulated dual-comb spectral measurement system according to claim 1, characterized in that, The signal generator produces signals with multiple discrete values, each discrete value having a duration greater than or equal to 1 / f is a jump signal or a continuous ramp signal or triangular wave signal that can cause a linear and continuous change in the optical phase difference between two optical frequency combs.

5. The phase-modulated dual-comb spectral measurement system according to claim 1, characterized in that, The photodetector achieves optical detection through photoelectric, photoacoustic, photothermal, and photomagnetic effects.

6. The phase-modulated dual-comb spectral measurement system according to claim 1, characterized in that, The system does not contain an optical filter that filters out one of the components of an optical comb combination with the same absolute value of optical frequency difference.

7. A dual-comb spectral measurement method based on phase modulation, characterized in that, Includes the following steps: Step 1: The dual-comb generation unit generates an optical frequency comb 1 with a frequency interval f1 and another optical frequency comb 2 with a different frequency interval f2. The frequency interval f1 and the other frequency interval f2 have a repetition frequency difference. f, There is a common optical frequency comb tooth between the optical frequency comb 1 and the optical frequency comb 2. Different combinations of optical comb teeth with varying absolute values ​​of optical frequency difference; Step 2: Input the signal generated by the signal generator into the dual optical comb generation unit to modulate the optical phase of at least one of the optical frequency combs 1 and 2, so that the dual optical comb generation unit generates a corresponding time-varying optical phase difference between the optical frequency combs 1 and 2. Step 3: Input optical frequency comb 1 or optical frequency comb 1 and optical frequency comb 2 together into the unit under test; Step 4: Input the optical frequency comb 1 that has passed through the unit under test and the optical frequency comb 2 that has passed through or has not passed through the unit under test to the photodetector to generate a beat frequency signal. Different combinations of optical comb teeth with equal absolute values ​​of optical frequency difference in optical frequency comb 1 and optical frequency comb 2 generate beat frequency components with the same frequency in the beat frequency signal, which are equal to the absolute value of the optical frequency difference. The phase difference between the beat frequency components is affected by the optical phase difference between optical frequency comb 1 and optical frequency comb 2. The superposition of each beat frequency component forms the measurement signal. Step 5: The data acquisition and processing unit samples the measurement signal and, based on the changes in the measurement signal caused by the change in optical phase difference, analyzes the amplitude or phase of different beat frequency components of the same frequency from the measurement signal, thereby obtaining the spectral information of the unit under test.

8. The dual-comb spectral measurement method based on phase modulation according to claim 7, characterized in that, In step 2, the optical phase difference varies among multiple discrete values. In step 5, time-frequency transformation is performed on the measurement signals under different optical phase differences to obtain the amplitude or phase of each measurement signal component under different optical phase differences. Based on the relationship between the optical phase difference and the amplitude or phase of each measurement signal component, the amplitude or phase of different co-frequency beat frequency components generated by different combinations of optical combs with equal absolute values ​​of optical frequency difference are calculated.

9. The dual-comb spectral measurement method based on phase modulation according to claim 7, characterized in that, The amplitudes of the different beat frequency components generated by different combinations of optical combs with equal absolute values ​​of optical frequency difference are A1 and A2, and the phases of the two beat frequency components are... and The optical phase difference generated by the modulation between optical frequency comb 1 and optical frequency comb 2 is At this time, the amplitude of the measurement signal component formed by the superposition of the two beat frequency components with the same frequency is Phase is Based on the variation of the amplitude or phase of the measured signal component with the phase difference of light, the amplitude or phase of different beat frequency components at the same frequency is fitted or calculated.

10. The dual-comb spectral measurement method based on phase modulation according to claim 7, characterized in that, In step 2, the optical phase difference changes continuously in the form of a ramp or a triangular wave, with a phase change rate of v rad / s. In step 5, for a time length greater than or equal to 2... The measurement signal of multiple beat frequency cycles of / v is transformed by time-frequency conversion to obtain a multi-cycle spectrum. On the multi-cycle spectrum, different beat frequency components of the same frequency generated by different combinations of optical combs with equal absolute values ​​of optical frequency difference are separated. The amplitude and phase of different beat frequency components of the same frequency can be distinguished directly by calculating the amplitude or phase of each separated component of the spectrum.

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