CN113834574A - Ultrashort optical pulse measurement system and method - Google Patents

Abstract

The present invention provides an ultra-short optical pulse measurement system and method. The system includes: a first optical filter for performing spectrum sampling on the ultra-short optical pulse to be measured to obtain discrete frequency components, wherein the first optical filter is: a periodic optical filter; a time lens for down-converting the discrete frequency components obtained by spectral sampling of the periodic optical filter to obtain multiple groups of compressed spectral components; a second optical filter for converting from The frequency components of predetermined frequency values are filtered out from the multiple groups of compressed spectral components; the continuous light laser is used to generate laser signals of continuous wavelengths; the balanced photodetector is used to compare the optical pulses and continuous wavelengths output by the second optical filter. The optical pulse output by the optical laser is coherently detected, and the detected signal is down-converted to the radio frequency domain, thereby realizing the compression of the optical pulse signal bandwidth. The present invention can solve the problem that the traditional dispersion-based time stretching scheme has large transmission delay and cannot directly measure the phase.

Description

Ultrashort optical pulse measurement system and method

technical field

The invention relates to the technical field of photoelectric detection, in particular to an ultra-short optical pulse measurement system and method.

Background technique

Observing ultrashort, non-repetitive light pulses at large time scales is a great challenge for digital signal processing. For optical pulses whose duration is on the order of femtoseconds to picoseconds, the analog-to-digital converter is limited by the sampling accuracy and storage depth, and cannot complete the measurement of optical pulses. The use of optical time stretching can break through the electronic bottleneck, so that continuous observation of ultrashort pulses can be realized by commercial analog-to-digital converters. In the time-stretching system, the envelope is uniformly broadened after the ultrashort pulse is transmitted in the dispersive medium. The pulses can be collected and observed in real time using commercial analog-to-digital converters. Optical time stretching has played a huge role in the observation of many transient phenomena. The first observations of optical giant waves were achieved by means of time stretching. Subsequent observations of soliton dynamics and supercontinuum using time stretching have also been widely reported. Time stretching has achieved great success in the observation of transient physical phenomena. In 2012, the time-stretching technique was proposed as the standard means of observation in ultrafast nonlinear optics.

Existing time stretching is achieved by transport in dispersive media. For broadband optical signals, the only suitable dispersive medium is optical fiber. However, the introduction of optical fibers will bring about problems of large delay and large volume. Taking dispersion compensation fiber as an example, the dispersion realized by one kilometer dispersion compensation fiber is about 100ps/nm, and the delay time is about 5 microseconds. In dispersion-based time-stretching techniques, the time delay brought by dispersion-compensating fibers is usually on the order of hundreds of microseconds. The dispersion of tens of kilometers is difficult to integrate, so the volume of the time-stretching system is relatively large. In addition, the dispersion-based time-stretching scheme can only complete the amplification of the signal envelope, and the measurement of the input signal phase requires additional digital signal processing. Currently, the Gerchberg-Saxton algorithm can recover phase information through time-domain and spectrograms, but the data processing delay will greatly reduce the observation rate of the system.

How to overcome the large delay of the existing ultra-short optical pulse measurement system and how to realize the direct measurement of the phase is an urgent problem to be solved.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the prior art, the purpose of the present invention is to provide an ultra-short optical pulse measurement system and method to solve the problem that the traditional dispersion-based time stretching scheme has large transmission delay and cannot directly measure the phase.

One aspect of the present invention provides an ultrashort optical pulse measurement system, the system comprising:

a first optical filter, used to perform spectrum sampling on the ultra-short optical pulse to be measured to obtain discrete frequency components, and the first optical filter is a periodic optical filter;

a time lens for down-converting the discrete frequency components obtained by spectral sampling of the periodic optical filter to obtain multiple groups of compressed spectral components;

a second optical filter, used for filtering out frequency components of predetermined frequency values from multiple groups of compressed spectral components;

Continuous light lasers for generating continuous wavelength laser signals;

The balanced photodetector is used for coherent detection of the optical pulse output by the second optical filter and the optical pulse output by the continuous light laser, and down-converting the detected signal to the radio frequency domain, thereby realizing the compression of the optical pulse signal bandwidth .

In some embodiments of the present invention, a dispersive element, at least one phase modulator, and at least one intensity modulator; wherein,

The dispersive element is used to eliminate the nonlinear phase response characteristic of the time lens, wherein the dispersion value of the dispersive element is opposite to the dispersion value of the time lens;

the phase modulator for generating a periodic frequency response to the signal from the dispersive element;

The intensity modulator is used to flatten the resulting periodic frequency response.

In some embodiments of the present invention, the driving frequency of the intensity modulator is the same as the driving frequency of the phase modulator, or is half of the driving frequency of the phase modulator.

In some embodiments of the present invention, the phase modulator further receives a first radio frequency signal, and the intensity modulator further receives a second radio frequency signal; the driving frequencies and powers of the first radio frequency signal and the second radio frequency signal For tuning the free spectral range and nonlinear phase response characteristics of the temporal lens.

In some embodiments of the present invention, the at least one phase modulator is a plurality of phase modulators connected in series; the intensity modulator is a single intensity modulator.

In some embodiments of the present invention, the frequency response characteristic of the periodic optical filter conforms to: ∑ _k H(ω-k·2πFSR _VCF );

where k is a positive integer, representing the serial number of the transmission peak of the periodic optical filter, ω is the angular frequency, FSR _VCF represents the free spectral range of the periodic optical filter, and H is the shape of each transmission peak;

The frequency transfer function of the time lens is:

∑ _m δ(ω-m·2πFSR _OFC );

Among them, δ is the impulse function, FSR _OFC is the free spectral range of the frequency response characteristic of the time lens, m is a positive integer, and m is the series corresponding to the frequency response characteristic of the time lens;

The time-domain stretching factor of the system is:

Another aspect of the present invention provides a method for measuring ultrashort optical pulses, the method comprising the following steps:

The first optical filter is used to sample the spectrum of the ultra-short optical pulse to be measured to obtain discrete frequency components. Wherein the first optical filter is a periodic optical filter;

Down-converting the discrete frequency components obtained by the spectral sampling through a time lens to obtain multiple groups of compressed spectral components;

Use the second optical filter to filter out frequency components of predetermined frequency values from the multiple groups of compressed spectral components;

Using a continuous light laser to generate a single-wavelength laser signal for mixing with the light pulse output by the second optical filter;

A photodetector is used to coherently detect the optical pulse output by the second optical filter and the optical pulse output by the continuous light laser, and the detected signal is down-converted to the radio frequency domain.

The ultrashort optical pulse measurement system and method provided by the embodiments of the present invention can realize the stretching of the duration of the signal by compressing the bandwidth of the signal, thereby realizing the measurement of the ultrashort optical pulse. The system and method of the present invention get rid of the dependence on large dispersion and greatly reduce the transmission delay of the system, and can directly measure the phase of the input signal without additional digital signal processing, which greatly improves the real-time measurement of ultra-short pulses. sex.

Additional advantages, objects, and features of the present invention will be set forth in part in the description that follows, and in part will become apparent to those of ordinary skill in the art upon study of the following, or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Those skilled in the art will appreciate that the objects and advantages that can be achieved with the present invention are not limited to those specifically described above, and that the above and other objects that can be achieved by the present invention will be more clearly understood from the following detailed description.

Description of drawings

The accompanying drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present application, and do not constitute a limitation to the present invention. In the attached image:

FIG. 1 is a schematic block diagram of an ultrashort optical pulse measurement system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a frequency spectrum and a time-domain waveform of an input pulse in an embodiment of the present invention.

FIG. 3 is a schematic diagram of the frequency spectrum and time domain waveform of the output pulse when the frequency spectrum compression factor is 73 in another embodiment of the present invention.

FIG. 4 is a schematic diagram of the frequency spectrum and time domain waveform of the output pulse when the frequency spectrum compression factor is 85 according to another embodiment of the present invention.

FIG. 5 is a schematic flowchart of a method for measuring an ultrashort optical pulse according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and the related structures and/or processing steps are omitted. Other details not relevant to the invention.

It should be emphasized that the term "comprising/comprising" when used herein refers to the presence of a feature, element, step or component, but does not exclude the presence or addition of one or more other features, elements, steps or components.

In order to solve the problem that the traditional dispersion-based time stretching scheme has large propagation delay and cannot directly measure the phase, the embodiments of the present invention provide a measurement system and a corresponding measurement method for ultra-short optical pulses. In the measurement system of the ultra-short optical pulse according to the embodiment of the present invention, the stretching of the pulse duration is realized by bandwidth compression, which gets rid of the dependence on the large dispersion. The bandwidth compression in the ultrashort optical pulse measurement scheme of the present invention is divided into two steps: (1) spectral sampling of the light pulse to be measured by a periodic optical filter; (2) subsequently, the discrete frequency components are converged by a time lens Together, the interval between the frequency components is narrowed, thereby equivalently realizing the bandwidth compression of the pulse. After bandwidth compression, the measurement of ultra-short optical pulses is achieved by optical filtering and coherent detection. The embodiments of the present invention will be described in detail below with reference to the structural block diagram of the ultrashort optical pulse measurement system.

FIG. 1 is a schematic block diagram of an ultrashort optical pulse measurement system according to an embodiment of the present invention. As shown in FIG. 1 , the ultra-short optical pulse measurement system includes: a periodic optical filter (a first optical filter), a time lens, a second optical filter, a continuous light laser and a photodetector.

Wherein, the periodic optical filter (the first optical filter) is used for spectrum sampling of the pulse to be measured. In the embodiment of the present invention, the light pulse to be measured is a light pulse with an ultra-short duration (a light pulse with a pulse width of picoseconds or shorter). As an example, the frequency response characteristic of the periodic optical filter can conform to: ∑ _k H(ω-k·2πFSR _VCF ), where k is a positive integer, representing the serial number of the transmission peak of the periodic optical filter, and ω is the angular frequency , FSR _VCF represents the free spectral range of the periodic optical filter, and H is the shape of each transmission peak. Here, the periodic optical filter is also called a Vernier comb filter, and the periodic optical filter can be a fiber ring, an integrated microring, or a Fabry-Perot interferometer (Fabry-Perot interferometer). –Pérot interferometer). Periodic optical filters output a series of discrete spectral components, a process that can be thought of as "spectral" sampling. The propagation delay of the periodic optical filter can be estimated by the delay-bandwidth product, that is, the product of bandwidth and delay is about 1. In the parameter setting of the present invention, the delay of the periodic optical filter is in the order of ten nanoseconds, which is much smaller than the transmission delay in the dispersive fiber.

The time lens is used to down-convert and modulate the discrete frequency components in the signal frequency sampled by the periodic optical filter, so that the frequency interval is narrowed, and multiple groups of compressed spectral components are obtained. That is, the time lens is used to bring together discrete frequency components, so that the original broadband optical signal is compressed into a narrowband optical signal, and the time domain is broadened after the bandwidth compression, so the bandwidth compression and time domain stretching have equivalent effects. . In the embodiment of the present invention, the time lens is implemented based on an electro-optical modulator.

The time lens modulates the frequency-sampled signal, and the frequency transfer function of the time lens can be expressed as Σ _m δ(ω-m·2πFSR _OFC ). The frequency response characteristics of the time lens are consistent with the spectral shape of an optical frequency comb. Among them, δ is the impulse function, FSR _OFC represents the free spectral range of the frequency response characteristic of the time lens, m is a positive integer, and m represents the series corresponding to the frequency response characteristic of the time lens. As an example, as shown in FIG. 1, a time lens may include a dispersive element, a phase modulator, and an intensity modulator. Among them, the dispersive element is used to eliminate the nonlinear phase response characteristic of the time lens, that is, a dispersive element whose dispersion value is exactly opposite to the dispersion value of the time lens is introduced before the time lens to eliminate the nonlinear phase response characteristic of the time lens. Phase modulators are used to generate periodic frequency responses, and intensity modulators are used to flatten these frequency responses. The FSR _OFC is determined by the drive frequency of the phase modulator. The expression of the time lens can be determined by combining the transmission characteristics of the phase modulator and the intensity modulator. From the frequency point of view, the transfer function of the time lens can be regarded as the superposition of a series of impulse functions, and the convolution with the impulse function in the frequency domain corresponds to the down-conversion operation in the system. Therefore, the function of the time lens is to perform multiple different down-conversion operations for the input frequency components, and the frequency interval of the frequency-converted spectral components is FSR _OFC .

The discrete frequency components output by the periodic optical filter are down-converted by the time lens, the frequency interval is greatly reduced, and multiple groups of compressed spectral components are obtained.

In the embodiment of the present invention, the delay of the electro-optic modulator for realizing the time lens can be designed to be in the order of ten nanoseconds, which is much smaller than the propagation delay in the dispersive fiber.

The second optical filter is used for filtering out frequency components of predetermined frequency values from a plurality of groups of compressed spectral components. After time lensing, multiple groups of compressed frequency components are output, which do not overlap each other in spectrum, and the spectral information contained in each group is the same. The second optical filter is used to extract a group from a plurality of components with the same frequency information, and filter out other frequency components,

Continuous light lasers are used to generate continuous wavelength laser signals.

The photodetector is used for coherently detecting the optical pulse signal output by the second optical filter and the optical signal output by the continuous light laser, and down-converting the detected signal to the radio frequency domain, thereby realizing bandwidth compression of the optical pulse signal. In an embodiment of the present invention, a coherent detection method is adopted in the process of signal receiving, that is, the local oscillator light and the signal light are mixed and then received by the photodetector. Since the coherent detection method is adopted here, the photodetector used in the embodiment of the present invention is a balanced photodetector.

After the bandwidth is compressed, the time domain is widened, which makes it possible to use commercial analog-to-digital converters to perform frequency acquisition of high-speed, transient optical signals.

In the embodiment of the present invention, both the frequency sampling of the periodic optical filter and the bandwidth compression of the time lens can maintain the initial phase, so the bandwidth compression process is coherent and does not introduce additional phase information.

In addition, in the embodiments of the present invention, no additional nonlinear phase is introduced in the process of frequency domain sampling, temporal lens modulation, optical filtering, and coherent detection. Therefore, in the output result, not only can the time-domain envelope of the input signal be stretched, but also the phase information of the input pulse is preserved. Therefore, both the time-domain envelope shape and phase information of the light pulse to be measured can be directly measured by the system without relying on complex algorithms and additional digital signal processing. This enables rapid and sequential observations of transient physical phenomena.

In the embodiment of the present invention, the frequency interval of the initial input signal of the light pulse to be measured is the spectral component of the FSR _VCF , which is compressed to (FSR _VCF - FSR _OFC ) after passing through the measurement system, and the multiple of the bandwidth compression can be expressed as FSR _VCF /( FSR _VCF - FSR _oFC ), for the pulse of the Fourier transform limit, that is, the pulse whose frequency-phase response is linear, the multiple of bandwidth compression is equal to the multiple of time domain stretching. Therefore, the multiple of the time domain stretching can be expressed as:

Based on the above formula, the time domain stretching factor can be controlled by FSR _VCF or ((FSR _VCF - FSR _OFC ) in the test system of the present invention.

In the embodiment of the present invention, the time lens is generated by cascading an intensity modulator and a phase modulator. In Figure 1, the dispersive element is used to cancel the nonlinear phase response characteristic of the time lens. Phase modulators are used to generate periodic frequency responses, and intensity modulators are used to flatten these frequency responses. From the frequency domain point of view, the time lens has a quadratic phase response characteristic, which is consistent with the expression form of dispersion. The size of the dispersion is determined by the driving frequency and driving power of the phase modulator and the intensity modulator, which can be expressed as V _π /(πV _m FSR _OFC ² ) in the formula, where V _π is the half-wave voltage of the phase modulator, and V _m is The peak-to-peak value of the drive signal on the intensity modulator. The nonlinear phase response characteristic of the time lens is eliminated by introducing a dispersive element whose dispersion value is exactly opposite to that of the time lens before the time lens. RF signal 1 and RF signal 2 are generated by an external microwave source. The driving frequency and power of RF signal 1 and RF signal 2 determine the free spectral range and nonlinear phase response characteristics of the time lens. In other words, the first RF signal and the second RF signal The driving frequency and power of the RF signal are used to tune the free spectral range and nonlinear phase response characteristics of the time lens. By increasing the number of phase modulators connected in series or increasing the driving power of the phase modulators, the bandwidth range of the frequency response can be increased. Therefore, in this embodiment of the present invention, one phase modulator may be set in the time lens, or multiple phase modulators may be set. a series phase modulator. When the intensity modulator works in the RZ-50 modulation format, the time lens can be generated only when the driving frequency of the intensity modulator and the driving frequency of the phase modulator are consistent. When the intensity modulator works in the RZ-33 modulation format, the time lens can be generated only when the driving frequency of the intensity modulator is half the driving frequency of the phase modulator. In the embodiment of the present invention, there is only one intensity modulator, but multiple phase modulators in series can be set to improve the observation bandwidth of the system.

Since both the periodic optical filter and the electro-optical modulator for realizing the time lens have mature integration schemes, the system proposed in the embodiments of the present invention has good integration potential. It can overcome the defect that the volume of the ultrashort optical pulse is too large in the prior art by utilizing the envelope stretching effect of dispersion on the ultrashort pulse to realize the measurement of the ultrashort optical pulse.

2-4 show the comparison results of input pulses and output pulses in some embodiments of the present invention. Wherein, (a) and (b) in FIG. 2 are respectively the frequency spectrum and time domain waveform of the input pulse in an embodiment of the present invention, wherein the input pulse is obtained by simulation. (a) and (b) in FIG. 3 are respectively the frequency spectrum and time domain waveform of the output pulse in an embodiment of the present invention, the frequency spectrum compression factor is 73, and the time domain envelope stretching factor is 73. (a) and (b) in FIG. 4 are respectively the frequency spectrum and time domain waveform of the output pulse in an embodiment of the present invention, the frequency spectrum compression factor is 85, and the time domain envelope stretching factor is 85. Figures 3 and 4 are both experimental results. In order to facilitate the comparison of phase and envelope, the output signals are digitally up-converted to the fundamental frequency.

From the comparison of Figure 2-4, it can be seen that the system can well complete the time-domain envelope stretching of ultra-short pulses, and the phase information of the input signal can also be preserved during the stretching process. The output results are consistent with the theoretical results. The analysis showed good agreement.

In the traditional scheme, the measurement of ultrashort optical pulses is realized by utilizing the envelope stretching effect of dispersion on ultrashort pulses. This scheme relies on a large dispersion medium, which makes the system bulky and the transmission delay large. Moreover, the dispersion-based scheme cannot directly measure the phase information of the input optical pulse. However, the present invention completely gets rid of the dependence on large dispersion and greatly reduces the transmission delay of the system. The present invention can directly measure the phase of the input signal without additional digital signal processing, which greatly improves the real-time performance of ultra-short pulse measurement.

Corresponding to the aforementioned system, the present invention also provides a method for measuring ultrashort optical pulses, as shown in FIG. 5 , the method includes the following steps:

Step S110, using the first optical filter to perform spectrum sampling on the ultrashort optical pulse to be measured to obtain discrete frequency components. The first optical filter is a periodic optical filter.

In step S120, the discrete frequency components obtained by spectral sampling in step S110 are down-converted through a time lens to obtain multiple groups of compressed spectral components.

Step S130, using the second optical filter to filter out frequency components of predetermined frequency values from the multiple groups of compressed spectral components.

In step S140, a continuous light laser is used to generate a continuous wavelength laser signal to mix with the light pulse output by the second optical filter.

Step S150, use a photodetector (eg, a balanced photodetector) to perform coherent detection on the optical pulse output by the second optical filter and the optical pulse output by the CW laser, and down-convert the detected signal to the radio frequency domain.

Thus, the compression of the bandwidth of the optical pulse signal is achieved.

As described above, the ultrashort optical pulse measurement system and method of the present invention realizes the stretching of the duration of the signal by compressing the bandwidth of the signal, thereby realizing the measurement of the ultrashort optical pulse. In addition, the frequency of the input optical pulse is sampled by a periodic optical filter, and then the discrete frequency components are converged by a time lens based on an electro-optical modulator, thereby equivalently realizing bandwidth compression. Among them, the frequency phase response of the time lens is linear, and the nonlinear phase response is eliminated by the dispersive medium. Further, the output after the optical filter can be mixed with the continuous light laser for coherent detection to realize the measurement of the intensity and phase of the input pulse. The present invention can also directly detect by a photodetector when it is not necessary to measure the phase information, and can also realize the stretching of the pulse time domain envelope.

It should be noted that the exemplary embodiments mentioned in the present invention describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above steps, that is, the steps may be performed in the order mentioned in the embodiments, or may be different from the order in the embodiments, or several steps may be performed simultaneously.

In the present invention, features described and/or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, and/or in combination with or in place of features of other embodiments Features of the implementation.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, various modifications and changes may be made to the embodiments of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. the measurement system of an ultrashort light pulse, is characterized in that, this system comprises: a first optical filter, used to perform spectrum sampling on the ultra-short optical pulse to be measured to obtain discrete frequency components, and the first optical filter is a periodic optical filter; a time lens for down-converting the discrete frequency components obtained by spectral sampling of the periodic optical filter to obtain multiple groups of compressed spectral components; a second optical filter, used for filtering out frequency components of predetermined frequency values from multiple groups of compressed spectral components; Continuous light lasers for generating continuous wavelength laser signals; The balanced photodetector is used for coherent detection of the optical pulse output by the second optical filter and the optical pulse output by the continuous light laser, and down-converting the detected signal to the radio frequency domain, thereby realizing the compression of the optical pulse signal bandwidth . 2. The system of claim 1, wherein the time lens comprises: a dispersive element, at least one phase modulator, and at least one intensity modulator; wherein, The dispersive element is used to eliminate the nonlinear phase response characteristic of the time lens, wherein the dispersion value of the dispersive element is opposite to the dispersion value of the time lens; the phase modulator for generating a periodic frequency response to the signal from the dispersive element; The intensity modulator is used to flatten the resulting periodic frequency response. 3. The system of claim 2, wherein: The driving frequency of the intensity modulator is the same as the driving frequency of the phase modulator, or is half of the driving frequency of the phase modulator. 4. The system of claim 2, wherein: The phase modulator further receives the first radio frequency signal, and the intensity modulator further receives the second radio frequency signal; The driving frequency and power of the first radio frequency signal and the second radio frequency signal are used to adjust the free spectral range and nonlinear phase response characteristics of the time lens. 5. The system of claim 2, wherein: The at least one phase modulator is a plurality of phase modulators connected in series; The one intensity modulator is a single intensity modulator. 6. The system of claim 1, wherein: The frequency response characteristic of the periodic optical filter conforms to: ∑ _k H(ω-k·2πFSR _VCF ); where k is a positive integer, representing the serial number of the transmission peak of the periodic optical filter, ω is the angular frequency, FSR _VCF represents the free spectral range of the periodic optical filter, and H is the shape of each transmission peak; The frequency transfer function of the time lens is: ∑ _m δ(ω-m·2πFSR _OFC ); Among them, δ is the impulse function, FSR _OFC is the free spectral range of the frequency response characteristic of the time lens, m is a positive integer, and m is the series corresponding to the frequency response characteristic of the time lens; The time-domain stretching factor of the system is:

7. The measuring method of an ultrashort optical pulse, it is characterised in that the method comprises the following steps: The first optical filter is used to sample the spectrum of the ultra-short optical pulse to be measured to obtain discrete frequency components. Wherein the first optical filter is a periodic optical filter; Down-converting the discrete frequency components obtained by the spectral sampling through a time lens to obtain multiple groups of compressed spectral components; Use the second optical filter to filter out frequency components of predetermined frequency values from the multiple groups of compressed spectral components; Using a continuous light laser to generate a single-wavelength laser signal for mixing with the light pulse output by the second optical filter; A photodetector is used to coherently detect the optical pulse output by the second optical filter and the optical pulse output by the continuous light laser, and the detected signal is down-converted to the radio frequency domain. 8. The method of claim 7, wherein the time lens comprises: a dispersive element, at least one phase modulator and at least one intensity modulator; wherein, The dispersive element is used to eliminate the nonlinear phase response characteristic of the time lens, wherein the dispersion value of the dispersive element is opposite to the dispersion value of the time lens; the phase modulator for generating a periodic frequency response to the signal from the dispersive element; The intensity modulator is used to flatten the resulting periodic frequency response. 9. The method of claim 7, wherein The driving frequency of the intensity modulator is the same as the driving frequency of the phase modulator, or is half of the driving frequency of the phase modulator. 10. The method of claim 7, wherein: The phase modulator further receives the first radio frequency signal, and the intensity modulator further receives the second radio frequency signal; The driving frequency and power of the first radio frequency signal and the second radio frequency signal are used to adjust the free spectral range and nonlinear phase response characteristics of the time lens.

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