CN113834574A - Ultra-short optical pulse measurement system and method - Google Patents
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Abstract
The invention provides an ultrashort optical pulse measuring system and method, wherein the system comprises: the first optical filter is used for carrying out frequency spectrum sampling on the ultrashort optical pulse to be detected to obtain discrete frequency components, and the first optical filter is a periodic optical filter; the time lens is used for carrying out down-conversion on discrete frequency components obtained by the frequency spectrum sampling of the periodic optical filter to obtain a plurality of groups of compressed frequency spectrum components; a second optical filter for filtering frequency components of a predetermined frequency value from the plurality of sets of compressed spectral components; the continuous light laser is used for generating a laser signal with continuous wavelength; and the balanced photoelectric detector is used for performing coherent detection on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser, and down-converting a signal obtained by detection to a radio frequency domain, so that the compression of the bandwidth of the optical pulse signal is realized. The invention can solve the problems that the traditional time stretching scheme based on chromatic dispersion has large transmission delay and can not directly measure the phase.
Description
Technical Field
The invention relates to the technical field of photoelectric detection, in particular to an ultrashort optical pulse measuring system and method.
Background
Observing ultra-short, non-repetitive optical pulses over a large time scale presents a significant challenge for digital signal processing. For optical pulses with durations on the order of femtoseconds to picoseconds, the analog-to-digital converter is limited by sampling accuracy and storage depth, and cannot complete measurement of the optical pulses. The electronic bottleneck can be broken through by means of optical time stretching, so that continuous observation of ultrashort pulses can be realized through a commercial analog-to-digital converter. In a time stretch system, the envelope of an ultrashort pulse is uniformly broadened after the ultrashort pulse is transmitted in a dispersive medium. The pulses can be acquired and observed in real time using commercially available analog-to-digital converters. Optical time stretching plays a great role in the observation of many transient phenomena. The first observation of the optical billows is realized by a time stretching means. Subsequent observation of the dynamic processes of solitons and supercontinuum with time stretching is also widely reported. Time stretching has enjoyed great success in the observation of transient physical phenomena. In 2012, time-stretch techniques were proposed as standard observation means for ultrafast nonlinear optics.
Existing time stretching is achieved by transmission in a dispersive medium. For broadband optical signals, a suitable dispersive medium is only an optical fiber. However, the introduction of the optical fiber causes problems of large delay and large volume. Taking the dispersion compensation fiber as an example, the dispersion achieved by a kilometer of dispersion compensation fiber is about 100ps/nm, and the delay is about 5 microseconds. In dispersion-based time-stretch techniques, the delay introduced by a dispersion compensating fiber is typically on the order of hundreds of microseconds. Dispersion over tens of kilometers is difficult to integrate, so the volume of the time stretch system is large. Furthermore, the dispersion-based time stretching scheme can only accomplish amplification of the signal envelope, and measurement of the input signal phase requires additional digital signal processing. Currently, the Gerchberg-Saxton algorithm can recover phase information through a time domain graph and a frequency spectrum graph, but the observation rate of the system is greatly reduced due to data processing delay.
How to overcome the large delay of the existing ultrashort optical pulse measurement system and how to realize the direct measurement of the phase is an urgent problem to be solved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide an ultrashort optical pulse measuring system and method to solve the problems that the traditional time stretching scheme based on dispersion has large transmission delay and cannot directly measure the phase.
In one aspect of the present invention, there is provided an ultrashort optical pulse measuring system, including:
the first optical filter is used for carrying out frequency spectrum sampling on the ultrashort optical pulse to be detected to obtain discrete frequency components, and the first optical filter is a periodic optical filter;
the time lens is used for carrying out down-conversion on discrete frequency components obtained by the frequency spectrum sampling of the periodic optical filter to obtain a plurality of groups of compressed frequency spectrum components;
a second optical filter for filtering frequency components of a predetermined frequency value from the plurality of sets of compressed spectral components;
the continuous light laser is used for generating a laser signal with continuous wavelength;
and the balanced photoelectric detector is used for performing coherent detection on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser, and down-converting a signal obtained by detection to a radio frequency domain, so that the compression of the bandwidth of the optical pulse signal is realized.
In some embodiments of the invention, the dispersive element, the at least one phase modulator and the at least one intensity modulator; wherein,
the dispersive element is used for eliminating 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 is used for generating a periodic frequency response for the signal from the dispersive element;
the intensity modulator is used to flatten the generated periodic frequency response.
In some embodiments of the invention, the drive frequency of the intensity modulator coincides with the drive frequency of the phase modulator, or is half the drive 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 frequency and power of the first radio frequency signal and the second radio frequency signal are used for adjusting the free spectral range and the nonlinear phase response characteristic of the time lens.
In some embodiments of the 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 characteristics of the periodic optical filter are in accordance with: sigmakH(ω-k·2πFSRVCF)；
Wherein k is a positive integer, denotes the number of transmission peaks of the periodic optical filter, ω is the angular frequency, FSRVCFRepresents the free spectral range of the periodic optical filter, H being the shape of each transmission peak;
the frequency transfer function of the time lens is:
∑mδ(ω-m·2πFSROFC)；
where δ is the impulse function, FSROFCRepresenting a free spectral range of the frequency response characteristic of the time lens, wherein m is a positive integer and represents the corresponding series of the frequency response characteristic of the time lens;
the time domain stretching multiple of the system is as follows:
in another aspect of the present invention, there is provided an ultrashort optical pulse measuring method, including the steps of:
and performing spectrum sampling on the ultrashort optical pulse to be detected by using the first optical filter to obtain discrete frequency components. Wherein the first optical filter is a periodic optical filter;
carrying out down-conversion on discrete frequency components obtained by the frequency spectrum sampling through a time lens to obtain a plurality of groups of compressed frequency spectrum components;
filtering out frequency components of predetermined frequency values from the plurality of groups of compressed spectral components using a second optical filter;
generating a laser signal with a single wavelength by using a continuous light laser to be mixed with the optical pulse output by the second optical filter;
and coherent detection is carried out on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser by using the photoelectric detector, and the detected signal is down-converted to a radio frequency domain.
The ultrashort optical pulse measuring system and method provided by the embodiment of the invention can realize the stretching of the duration of the signal by performing bandwidth compression on the signal, thereby realizing the measurement of the ultrashort optical pulse. The system and the method of the invention get rid of dependence on large dispersion, greatly reduce transmission delay of the system, and can directly measure the phase of the input signal without additional digital signal processing, thereby greatly improving the real-time property of ultrashort pulse measurement.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It will be appreciated by those skilled in the art that the objects and advantages that can be achieved with the present invention are not limited to the specific details set forth above, and that these and other objects that can be achieved with the present invention will be more clearly understood from the detailed description that follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a schematic block diagram of an ultra-short optical pulse measurement system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a frequency spectrum and a time domain waveform of an input pulse according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating the frequency spectrum and time domain waveform of an output pulse with a spectrum compression factor of 73 according to another embodiment of the present invention.
FIG. 4 is a diagram of the spectrum and time domain waveforms of the output pulse with a spectrum compression factor of 85 according to another embodiment of the present invention.
Fig. 5 is a flowchart illustrating an ultra-short optical pulse measurement method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, elements, steps or components, but does not preclude the presence or addition of one or more other features, elements, steps or components.
In order to solve the problems that the traditional time stretching scheme based on dispersion has large transmission delay and cannot directly measure the phase, the embodiment of the invention provides a measuring system and a corresponding measuring method of ultrashort optical pulses. In the measuring system of the ultrashort optical pulse of the embodiment of the invention, the stretching of the pulse duration is realized by bandwidth compression, and the dependence on large dispersion is eliminated. The bandwidth compression in the measuring scheme of the ultrashort optical pulse is divided into two steps: (1) carrying out spectrum sampling on the optical pulse to be detected through a periodic optical filter; (2) then, the discrete frequency components are converged together through a time lens, so that the intervals between the frequency components are reduced, thereby equivalently realizing the bandwidth compression of the pulse. And after bandwidth compression, the ultra-short light pulse is further measured through light filtering and coherent detection. The following describes an embodiment of the present invention in detail with reference to a block diagram of an ultra-short optical pulse measurement system.
Fig. 1 is a schematic block diagram of an ultra-short optical pulse measurement system according to an embodiment of the present invention. As illustrated in fig. 1, the ultra-short light pulse measuring system includes: a periodic optical filter (first optical filter), a time lens, a second optical filter, a continuous light laser, and a photodetector.
The periodic optical filter (first optical filter) is used for sampling the frequency spectrum of the optical pulse to be measured. In the embodiment of the invention, the optical pulse to be measured is an ultra-short-duration optical pulse (an optical pulse with a pulse width of picoseconds or shorter). As an example, the frequency response characteristics of the periodic optical filter may conform to: sigmakH(ω-k·2πFSRVCF) Where k is a positive integer representing the number of transmission peaks of the periodic optical filter, ω is the angular frequency, FSRVCFRepresenting the free spectral range of the periodic optical filter, H is the shape of each transmission peak. The periodic optical filter is also referred to as a Vernier comb filter (Vernier comb filter), and the periodic optical filter may be a fiber ring, an integrated micro-ring, or a Fabry-perot interferometer (Fabry-perot interferometer) structurally. The periodic optical filter outputs a series of discrete spectral components, which can be viewed as "spectral" sampling. The transmission delay of the periodic optical filter can be estimated by a delay-bandwidth product, i.e., the product of bandwidth and delay is about 1. In the parameter setting of the 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 optical fiber.
The time lens is used for carrying out down-conversion modulation on discrete frequency components in the signal after frequency sampling of the periodic optical filter, so that the frequency interval is reduced, and a plurality of groups of compressed frequency spectrum components are obtained. That is, the time lens is used to converge discrete frequency components together, so that the original broadband optical signal is compressed into a narrowband optical signal, and the time domain is broadened after the bandwidth is compressed, so that the bandwidth compression and the time domain stretching have equivalent effects. In the embodiment of the invention, the time lens is realized based on an electro-optical modulator.
The time lens modulates the signal after frequency sampling, and the frequency transfer function of the time lens can be expressed as sigmamδ(ω-m·2πFSROFC). Frequency response characteristic and optical frequency comb (optical frequency) of time lenscy comb) the spectral shape is uniform. Where δ is the impulse function, FSROFCAnd the free spectral range of the time lens frequency response characteristic is shown, m is a positive integer, and m represents the corresponding stage number of the time lens frequency response characteristic. As an example, as shown in fig. 1, the time lens may include a dispersive element, a phase modulator, and an intensity modulator. The dispersion element is used for eliminating the time lens nonlinear phase response characteristic, namely, the dispersion element with a dispersion value just opposite to the dispersion value of the time lens is introduced in front of the time lens to eliminate the time lens nonlinear phase response characteristic. The phase modulator is used to generate periodic frequency responses and the intensity modulator is used to achieve a flattening of these frequency responses. FSROFCDetermined 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. The transfer function of the time lens can be seen as a superposition of a series of impulse functions in frequency, the convolution with the impulse function in the frequency domain corresponding to the down-conversion operation in the system. The time lens thus functions to perform a plurality of different down-conversion operations on the input frequency components, the frequency spacing of the converted spectral components being FSROFC。
The discrete frequency components output by the periodic optical filter are down-converted by a time lens, the frequency interval is greatly reduced, and a plurality of groups of compressed frequency spectrum components are obtained.
In embodiments of the present invention, the delay of the electro-optic modulator implementing the time lens may be designed to be on the order of ten nanoseconds, much less than the transmission delay in a dispersive optical fiber.
The second optical filter is used for filtering out frequency components of a predetermined frequency value from the plurality of sets of compressed spectral components. And outputting a plurality of groups of compressed frequency components after passing through the time lens, wherein the frequency components do not overlap on the frequency spectrum, and the frequency spectrum information contained in each group is the same. The second optical filter is used for extracting one group from a plurality of components with the same frequency information and filtering other frequency components,
a continuous light laser is used to generate a laser signal of a continuous wavelength.
The photoelectric detector is used for carrying out coherent detection on the optical pulse signal output by the second optical filter and the optical signal output by the continuous optical laser, and down-converting the detected signal to a radio frequency domain, so that the compression of the bandwidth of the optical pulse signal is realized. In an embodiment of the present invention, a coherent detection method is adopted in the signal receiving process, that is, the local oscillator light and the signal light are mixed and then received by the photodetector. Since coherent detection is used here, the photodetector used in the embodiments of the present invention is a balanced photodetector.
The time domain is widened after the bandwidth compression, so that the frequency acquisition of high-speed and transient optical signals can be realized by using a commercial analog-to-digital converter.
In the embodiment of the invention, the frequency sampling of the periodic optical filter and the bandwidth compression of the time lens can keep the initial phase, so that the bandwidth compression process is coherent and no additional phase information is introduced.
In addition, in the embodiment of the invention, no additional nonlinear phase is introduced in the processes of frequency domain sampling, time-lapse lens modulation, optical filtering and coherent detection. Therefore, in the output result, not only the stretching of the time-domain envelope of the input signal can be realized, but also the phase information of the input pulse is preserved. Therefore, the time-domain envelope shape and phase information of the optical pulse to be measured can be directly measured through the system without relying on a complex algorithm and additional digital signal processing. This makes possible a fast continuous observation of transient physical phenomena.
In the embodiment of the invention, the frequency interval of the initial input signal of the optical pulse to be measured is FSRVCFIs compressed to (FSR) after passing through the measurement systemVCF-FSROFC) The bandwidth compression factor can be expressed as FSRVCF/(FSRVCF-FSRoFC) For a fourier transform limited pulse, i.e., a pulse in which the frequency-phase response of the pulse is linear, the bandwidth compression is equal to the time domain stretch. The multiple of the time domain stretch can thus be expressed as:
based on the formula, the FSR can be passed in the test system of the inventionVCFOr ((FSR)VCF-FSROFC) To control the time domain stretch factor.
In an embodiment of the invention, the time lens is co-generated using an intensity modulator and a phase modulator stage. In fig. 1, a dispersive element is used to cancel the time lens nonlinear phase response characteristic. The phase modulator is used to generate periodic frequency responses and the intensity modulator is used to achieve a flattening of these frequency responses. From the frequency domain, the time lens has a quadratic phase response characteristic, which is consistent with the expression form of dispersion. The dispersion is determined by the driving frequency and driving power of the phase modulator and the intensity modulator, and can be expressed as V on the formulaπ/(πVmFSROFC 2) In which V isπIs the half-wave voltage, V, of the phase modulatormIs the peak-to-peak value of the drive signal on the intensity modulator. The time lens nonlinear phase response characteristic is eliminated by introducing a dispersive element in front of the time lens, the dispersive element having a dispersion value exactly opposite to that of the time lens. The radio frequency signals 1 and 2 are generated by an external microwave source, the driving frequency and power of the radio frequency signals 1 and 2 determine the free spectral range and the nonlinear phase response characteristic of the time lens, or the driving frequency and power of the first radio frequency signal and the second radio frequency signal are used for adjusting the free spectral range and the nonlinear phase response characteristic of the time lens. The bandwidth range of the frequency response can be increased by increasing the number of the phase modulators connected in series or increasing the driving power of the phase modulators, so that in the embodiment of the invention, one phase modulator or a plurality of phase modulators connected in series can be arranged in the time lens. When the intensity modulator is operated in the RZ-50 modulation format, the drive frequency of the intensity modulator and the drive frequency of the phase modulator coincide to produce a time lens. When the intensity modulator operates in the RZ-33 modulation format, the driving frequency of the intensity modulator is the driving frequency of the phase modulator oneHalf to create a time lens. In the embodiment of the invention, only one intensity modulator is provided, but a plurality of phase modulators connected in series can be arranged to improve the observation bandwidth of the system.
The system proposed in the embodiments of the present invention has good integration potential due to the well-established integration schemes of both the periodic optical filter and the electro-optical modulator used to implement the time lens. The defect that the volume is overlarge when ultra-short light pulses are measured by utilizing the envelope stretching effect of dispersion on the ultra-short pulses in the prior art can be overcome.
Fig. 2-4 illustrate input pulse versus output pulse comparison results in some embodiments of the invention. Fig. 2 (a) and (b) are frequency spectrum and time domain waveforms of an input pulse according to an embodiment of the present invention, respectively, where the input pulse is obtained by simulation. Fig. 3 (a) and (b) show the spectrum and time domain waveform of the output pulse, respectively, according to an embodiment of the present invention, where the spectrum compression factor is 73 and the time domain envelope stretching factor is 73. Fig. 4 (a) and (b) show the frequency spectrum and time domain waveform of the output pulse, respectively, according to an embodiment of the present invention, where the frequency spectrum compression factor is 85 and the time domain envelope stretching factor is 85. Both fig. 3 and fig. 4 are experimental results and the output signals are both digitally converted to the fundamental frequency for the convenience of phase and envelope comparison.
As can be seen from the comparison of fig. 2 to 4, the system can well complete the time-domain envelope stretching of the ultrashort pulse, and the phase information of the input signal can be retained in the stretching process, and the output result shows good consistency with the theoretical analysis.
In the traditional scheme, the measurement of the ultrashort light pulse is realized by utilizing the envelope stretching effect of dispersion on the ultrashort pulse. This solution relies on a large dispersion medium, making the system bulky and the transmission delay large. Also, the dispersion-based scheme cannot directly measure the phase information of the input optical pulse. The invention completely gets rid of the dependence on large dispersion and greatly reduces the transmission delay of the system. The invention can directly measure the phase of the input signal without additional digital signal processing, thereby greatly improving the real-time property of the ultrashort pulse measurement.
Correspondingly to the foregoing system, the present invention further provides an ultrashort optical pulse measuring method, as shown in fig. 5, including the following steps:
step S110, performing spectrum sampling on the ultrashort optical pulse to be detected by using the first optical filter to obtain discrete frequency components. Wherein the first optical filter is a periodic optical filter.
And step S120, carrying out down-conversion on the discrete frequency components obtained by the frequency spectrum sampling in the step S110 through a time lens to obtain a plurality of groups of compressed frequency spectrum components.
In step S130, frequency components of predetermined frequency values are filtered out from the plurality of groups of compressed spectral components by using a second optical filter.
In step S140, a laser signal with continuous wavelength is generated by using a continuous light laser to mix with the optical pulse output by the second optical filter.
Step S150, a photodetector (e.g., a balanced photodetector) is used to perform coherent detection on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser, and down-convert the detected signal to the radio frequency domain.
Thereby, a compression of the bandwidth of the optical pulse signal is achieved.
The ultrashort optical pulse measuring system and method of the present invention as described above implement stretching the duration of the signal by performing bandwidth compression on the signal, thereby implementing measurement of the ultrashort optical pulse. In addition, the frequency of the input light pulse is sampled by a periodic optical filter, and then discrete frequency components are converged by a time lens based on an electro-optical modulator, so that the bandwidth compression is equivalently realized. Wherein the frequency-phase response of the time lens is linear and the non-linear phase response is cancelled by the dispersive medium. Furthermore, the output after the optical filter can be mixed with the continuous optical laser for coherent detection, so that the measurement of the input pulse intensity and the phase position is realized. The invention can also directly detect through the photoelectric detector in the occasion without measuring phase information, and can realize the stretching of the pulse time domain envelope.
It should be noted that the exemplary embodiments of 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-described steps, that is, the steps may be performed in the order mentioned in the embodiments, may be performed in an order different from the order in the embodiments, or may be performed simultaneously.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments in the present invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made to the embodiment of the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A system for measuring ultrashort light pulses, the system comprising:
the first optical filter is used for carrying out frequency spectrum sampling on the ultrashort optical pulse to be detected to obtain discrete frequency components, and the first optical filter is a periodic optical filter;
the time lens is used for carrying out down-conversion on discrete frequency components obtained by the frequency spectrum sampling of the periodic optical filter to obtain a plurality of groups of compressed frequency spectrum components;
a second optical filter for filtering frequency components of a predetermined frequency value from the plurality of sets of compressed spectral components;
the continuous light laser is used for generating a laser signal with continuous wavelength;
and the balanced photoelectric detector is used for performing coherent detection on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser, and down-converting a signal obtained by detection to a radio frequency domain, so that the compression of the bandwidth of the optical pulse signal is realized.
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 for eliminating 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 is used for generating a periodic frequency response for the signal from the dispersive element;
the intensity modulator is used to flatten the generated periodic frequency response.
3. The system of claim 2,
the driving frequency of the intensity modulator is identical to the driving frequency of the phase modulator, or is half of the driving frequency of the phase modulator.
4. The system of claim 2,
the phase modulator also receives a first radio frequency signal, and the intensity modulator also receives a second radio frequency signal;
the driving frequency and power of the first radio frequency signal and the second radio frequency signal are used for adjusting the free spectral range and the nonlinear phase response characteristic of the time lens.
5. The system of claim 2,
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,
the frequency response characteristic of the periodic optical filter is in accordance with: sigmakH(ω-k·2πFSRVCF)；
Wherein k is a positive integer and representsNumber of transmission peak of periodic optical filter, omega is angular frequency, FSRVCFRepresents the free spectral range of the periodic optical filter, H being the shape of each transmission peak;
the frequency transfer function of the time lens is:
∑mδ(ω-m·2πFSROFC)；
where δ is the impulse function, FSROFCRepresenting a free spectral range of the frequency response characteristic of the time lens, wherein m is a positive integer and represents the corresponding series of the frequency response characteristic of the time lens;
the time domain stretching multiple of the system is as follows:
7. a method of measuring ultrashort light pulses, the method comprising the steps of:
and performing spectrum sampling on the ultrashort optical pulse to be detected by using the first optical filter to obtain discrete frequency components. Wherein the first optical filter is a periodic optical filter;
carrying out down-conversion on discrete frequency components obtained by the frequency spectrum sampling through a time lens to obtain a plurality of groups of compressed frequency spectrum components;
filtering out frequency components of predetermined frequency values from the plurality of groups of compressed spectral components using a second optical filter;
generating a laser signal with a single wavelength by using a continuous light laser to be mixed with the optical pulse output by the second optical filter;
and coherent detection is carried out on the optical pulse output by the second optical filter and the optical pulse output by the continuous optical laser by using the photoelectric detector, and the detected signal is down-converted to a 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 for eliminating 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 is used for generating a periodic frequency response for the signal from the dispersive element;
the intensity modulator is used to flatten the generated periodic frequency response.
9. The method of claim 7,
the driving frequency of the intensity modulator is identical to the driving frequency of the phase modulator, or is half of the driving frequency of the phase modulator.
10. The method of claim 7,
the phase modulator also receives a first radio frequency signal, and the intensity modulator also receives a second radio frequency signal;
the driving frequency and power of the first radio frequency signal and the second radio frequency signal are used for adjusting the free spectral range and the nonlinear phase response characteristic of the time lens.
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