CN117968864A - Nonlinear continuous sweep frequency light source accurate calibration system and method based on FP etalon - Google Patents

Abstract

The system and the method for precisely calibrating the nonlinear continuous sweep-frequency light source based on the FP etalon are characterized in that broadband continuous sweep-frequency light with nonlinear changes of frequency and wavelength along with time is generated by the sweep-frequency light source, the emitted light signals respectively pass through the FP etalon I and the FP etalon II after passing through a shunt coupler, transmission light with the transmission peak position which is unevenly changed along with time is generated, the transmission light respectively enters the PD I and the PD II, the PD I and the PD II convert two paths of transmission light signals into two paths of voltage signals which are an electric signal I and an electric signal II, and the electric signals are recorded on an oscilloscope. Trigger signals are generated at the starting and ending positions of the light source sweep and at the channel switching position, and are synchronously recorded on the oscilloscope. According to the method, after the three paths of electric signals on the oscilloscope are subjected to fitting, peak searching, interpolation, smooth connection and the like, the change of the wavelength and the frequency of the nonlinear sweep frequency light emitted by the sweep frequency light source along with time can be obtained, calibration is completed, and the calibration is simple and efficient and is not influenced by the step size of the wavelength and the sweep frequency speed.

Description

Nonlinear continuous sweep frequency light source accurate calibration system and method based on FP etalon

Technical Field

The invention belongs to the field of optical sensing, and particularly relates to a nonlinear continuous sweep-frequency light source accurate calibration system and method based on an FP etalon.

Background

Along with the rapid development and innovation progress of new technologies of the Internet and the Internet of things such as 5G, artificial intelligence, virtual reality, metauniverse and the like, the intellectualization gradually becomes the necessary trend of development and upgrading in the fields of a plurality of industries. The accurate sensing of the information is a precondition for realizing the intellectualization, so that the sensing technology plays an important supporting role in various intelligent processes. The optical sensing is based on the advantages of rapidness, stability, interference resistance and the like, and is widely applied to various industries, including but not limited to the fields of gas sensing, biological sensing, optical fiber sensing including Fiber Bragg Grating (FBG) sensing and the like. The sweep frequency light source is used as a key device in the field of optical sensing, and the performance of the sweep frequency light source determines a plurality of key parameters such as detection speed, detection range, detection precision, resolution and the like of a sensing system.

When the sweep frequency light source is used in the field of optical sensing, the time-dependent change relation between the frequency and the wavelength of the sweep frequency light needs to be obtained, so that the mapping of the sensing signal from the frequency domain to the time domain can be realized, and the process of accurately measuring the time-dependent change relation between the frequency and the wavelength of each sweep frequency light source is called calibration. At present, the main stream light source in the market is calibrated in a complicated point-by-point calibration mode, the mode can be reduced along with the step reduction of wavelength and the improvement of the frequency sweeping speed, the workload is multiplied, and the frequency sweeping light source calibrated by the mode is not a real continuous frequency sweeping, but a large number of independently-excited lasers are lighted in sequence, so that an effect similar to the continuous frequency sweeping is formed. For example, the calibration method is adopted by a Distributed Bragg Reflection (DBR) laser based on the 'Vernier' effect, which is a mainstream light source used in the field of fiber grating sensing at present.

The point-by-point calibration method is cumbersome, complex and time consuming, and is not suitable for continuous frequency sweep and nonlinear frequency sweep light sources. Such as integrated Distributed Feedback (DFB) semiconductor lasers, which can emit continuously stable swept light by applying a continuously varying current signal, there is currently a lack of an efficient calibration method for such swept light sources.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a nonlinear continuous sweep-frequency light source accurate calibration system and method based on FP etalons, which can accurately calibrate the change of the frequency and wavelength of nonlinear continuous sweep-frequency light along with time by utilizing the matching of a plurality of FP etalons and performing data processing on transmitted light signals, thereby being effectively used in the field of optical sensing.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

the nonlinear continuous sweep frequency light source accurate calibration system based on the FP etalon is characterized by comprising: the system comprises a sweep frequency light source, a shunt coupler, an FP etalon I, a photoelectric detector I, an FP etalon II, a photoelectric detector II, an acquisition device and a computer;

The sweep light source generates broadband continuous sweep light with nonlinear change of frequency and wavelength along with time, and generates trigger signals at the starting position, the ending position and the channel switching position of each sweep period; in a sweep period, the change of the frequency and the wavelength of sweep light along with time is irregular;

The shunt coupler divides the sweep frequency light into two paths of optical signals, namely an optical signal I and an optical signal II; the first FP etalon and the second FP etalon respectively convert the first optical signal and the second optical signal into first transmission light and second transmission light; the first photoelectric detector and the second photoelectric detector respectively convert the first transmission light and the second transmission light into an electric signal I and an electric signal II; the acquisition device records an electric signal I, an electric signal II and a trigger signal;

The computer fits and peak-finding the first and second electric signals recorded by the acquisition device, and finds out the abscissa of the peak position of each transmission peak, wherein the abscissa represents time; marking the starting and ending positions of the sweep frequency period and the channel switching position according to the trigger signal; identifying the frequency and the wavelength of flyback according to the position relation of transmission peaks corresponding to the first electric signal and the second electric signal; and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time.

In order to optimize the technical scheme, the specific measures adopted further comprise:

further, two flat plates plated with high reflection films are arranged in the first FP etalon and the second FP etalon, so that transmission spectrums of the flat plates are a plurality of transmission peaks with equal frequency intervals, and the frequency intervals among the peaks are equal.

Further, the free spectral range of FP etalon one is at least 10 times greater than the free spectral range of FP etalon two, and the free spectral range of FP etalon one is not equal to an integer multiple of the free spectral range of FP etalon two.

Further, the computer identifies the frequency and the wavelength of the flyback according to the position relation of the transmission peaks corresponding to the first electric signal and the second electric signal, specifically:

The transmission peaks corresponding to the first electric signal and the second electric signal are respectively defined as a big peak and a small peak, the two sides of the center position of each big peak are respectively provided with the small peaks, and the ratio of the distance between the small peak on one side and the center position of the big peak to the distance between the small peak on the other side and the center position of the big peak is defined as a double peak ratio; and (3) sequentially calculating the bimodal ratio of each large peak, if two large peaks with identical bimodal ratio exist, indicating that the two large peaks are the same large peak, wherein the middle part is a flyback part, and identifying the flyback frequency and wavelength.

Further, the computer performs smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time, specifically:

And recording the abscissa of the position of the small peak, combining the absolute frequency and the absolute wavelength represented by the small peak to obtain the time-dependent change relation of the frequency and the wavelength of the sweep frequency light, and drawing a time-dependent change curve of the frequency and the wavelength.

In addition, the invention also provides a nonlinear continuous sweep frequency light source accurate calibration method based on the FP etalon, which is characterized by comprising the following steps:

s1: generating a broadband continuous swept light with nonlinear variation of frequency and wavelength with time using a swept light source, and generating a trigger signal at a start position, an end position, and a channel switching position of each sweep period; in a sweep period, the change of the frequency and the wavelength of sweep light along with time is irregular;

s2: dividing the sweep frequency light into two paths of optical signals, namely an optical signal I and an optical signal II by using a branching coupler; converting the first and second optical signals into first and second transmitted light, respectively, using a first FP etalon and a second FP etalon;

S3: the first photoelectric detector and the second photoelectric detector are used for respectively converting the first transmission light and the second transmission light into the first electric signal and the second electric signal, and the first electric signal and the second electric signal are recorded in the acquisition device through radio frequency conduction; the acquisition device also synchronously records the trigger signal;

S4: fitting and peak searching are carried out on the first electric signal and the second electric signal recorded by the acquisition device by using a computer, and the abscissa of the peak position of each transmission peak is found out, wherein the abscissa represents time; marking the starting position, the ending position and the channel switching position of the sweep frequency period according to the trigger signal; identifying the frequency and the wavelength of flyback according to the position relation of transmission peaks corresponding to the first electric signal and the second electric signal;

S5: and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time.

Further, two flat plates plated with high reflection films are arranged in the first FP etalon and the second FP etalon, so that transmission spectrums of the flat plates are a plurality of transmission peaks with equal frequency intervals, and the frequency intervals among the peaks are equal.

Further, the free spectral range of FP etalon one is at least 10 times greater than the free spectral range of FP etalon two, and the free spectral range of FP etalon one is not equal to an integer multiple of the free spectral range of FP etalon two.

Further, the identifying the frequency and the wavelength of the flyback according to the position relation of the transmission peaks corresponding to the first electric signal and the second electric signal specifically includes:

The transmission peaks corresponding to the first electric signal and the second electric signal are respectively defined as a big peak and a small peak, the two sides of the center position of each big peak are respectively provided with the small peaks, and the ratio of the distance between the small peak on one side and the center position of the big peak to the distance between the small peak on the other side and the center position of the big peak is defined as a double peak ratio; and (3) sequentially calculating the bimodal ratio of each large peak, if two large peaks with identical bimodal ratio exist, indicating that the two large peaks are the same large peak, wherein the middle part is a flyback part, and identifying the flyback frequency and wavelength.

Further, the smoothing connection and interpolation processing are performed on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal, so as to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time, specifically:

And recording the abscissa of the position of the small peak, combining the absolute frequency and the absolute wavelength represented by the small peak to obtain the time-dependent change relation of the frequency and the wavelength of the sweep frequency light, and drawing a time-dependent change curve of the frequency and the wavelength.

The beneficial effects of the invention are as follows:

1. the invention can accurately calibrate the nonlinear continuous sweep frequency light source in the true sense, the change of the frequency and the wavelength of the sweep frequency light along with time in the sweep frequency period can not have any regularity, the calibration method is simple to operate and has higher efficiency, and the calibration workload is not influenced by the step size of the wavelength;

2. The frequency and wavelength calibration accuracy of the invention can be directly regulated and controlled by the FP etalon II, and the smaller the free spectrum range is, the higher the calibration accuracy is, so the invention can be used for scenes with different accuracy requirements;

3. the calibration efficiency and the calibration accuracy of the invention are not influenced by the sweep frequency speed, and the magnitude of the sweep frequency speed can not influence the calibration in theory, so the calibration method can be used for the calibration of the ultra-high-speed sweep frequency light source.

Drawings

FIG. 1 is a schematic diagram of the connection of a nonlinear continuous swept light source precision calibration system based on an FP etalon.

Fig. 2 is a schematic diagram of the transmittance of the FP etalon as a function of frequency.

FIG. 3 is a schematic diagram of a nonlinear swept light source structure used in the examples.

FIG. 4 is a schematic diagram of a calibration system used in the examples.

FIG. 5 is a schematic diagram illustrating the processing of the first, second and third signals recorded on the oscilloscope during the calibration process according to the embodiment.

Fig. 6 is an enlarged view of the data in the block of fig. 5.

FIG. 7 is a graph showing the recorded frequency and wavelength over time after processing the first, second and third data of the electrical signal according to the embodiment.

FIG. 8 is a plot of the frequency and wavelength of a nonlinear swept light source versus time for calibration results of an example.

Detailed Description

The invention will now be described in further detail with reference to the accompanying drawings.

As shown in fig. 1, the invention provides a nonlinear continuous sweep frequency light source frequency and wavelength accurate calibration system based on an FP etalon, comprising: a swept light source, a first FP (fabry-perot) etalon, a first Photodetector (PD), a second FP etalon, a second Photodetector (PD), an oscilloscope, and a computer. The oscilloscope can also be any device capable of collecting electric signals in real time, such as a high-speed collecting circuit board.

The sweep frequency light source is used for generating broadband continuous sweep frequency light with nonlinear change of frequency and wavelength along with time, three electric signals can be finally left on the oscilloscope, the change of the frequency and the wavelength along with time of the sweep frequency light can be accurately calibrated by processing data, and the specific calibration steps are as follows:

S1: the sweep frequency light source emits broadband continuous sweep frequency light with nonlinear change of frequency and wavelength along with time, and the change of the frequency and the wavelength of the light along with time does not have any rule in one sweep frequency period.

S2: the swept light is divided into two paths of optical signals, namely an optical signal I and an optical signal II, by the aid of a branching coupler, the optical signal I generates transmitted light I by the aid of an FP etalon I, and the optical signal II generates transmitted light II by the aid of the FP etalon II; since the frequency of the sweep light varies unevenly over time, the positions of the transmission peaks of the first and second generated transmitted light vary unevenly over time, and each transmission peak position has a determined frequency value, so that the transmitted light also contains information about the frequency variation over time.

S3: the transmitted light I and the transmitted light 2 enter a PD I and a PD II respectively, and the PD I and the PD II respectively convert the transmitted light I and the transmitted light II into corresponding electric signals I and electric signals II; the first electric signal and the second electric signal are conducted through a relatively stable radio frequency wire and recorded in an oscilloscope;

The sweep light source generates trigger signals (pulling the level high/low) at the start and end positions of each sweep period, which is an electrical signal three, which is also synchronously recorded on the oscilloscope for marking the start and end positions of the sweep period.

S4: fitting and peak searching are carried out on the first electric signal and the second electric signal recorded by the oscilloscope by the computer, and the abscissa of the peak position of each transmission peak is found out; comparing the starting and ending of the frequency sweep with the signal three marks and the channel switching time; since the first transmitted light represented by the first electrical signal is generated by the first FP etalon, the second transmitted light represented by the second electrical signal is generated by the second FP etalon, and FSRl of the first FP etalon is more than ten times greater than the FSR2 of the second FP etalon, and FSRl is not equal to an integer multiple of FSR 2. Thus, at different transmission peak positions, the relative positional relationship of the two peaks is different, and such positional relationship can be calculated in advance, so that the frequency and wavelength of "flyback" can be identified and resolved using such positional relationship.

S5: and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of each transmission peak in the second electric signal to obtain the change of the frequency and the wavelength of the sweep frequency light along with time.

In the FP etalon, after the broadband laser is injected into the FP etalon, since the inside of the FP etalon is provided with two flat plates coated with the highly reflective film, light rays entering the flat plates are reflected for multiple times and interfere, so that the transmission spectrum of the FP etalon is a plurality of transmission peaks with equal frequency intervals, and the frequency intervals among the peaks are equal.

Fig. 2 shows the change in transmittance of the transmitted light of the FP etalon with frequency, and the same amount of frequency change between two adjacent transmission peaks, which is also called the Free Spectral Range (FSR), i.e., the peak-to-peak spacing of each two adjacent transmission peaks. The FSR1 of the first FP etalon is far greater than the FSR2 of the second FP etalon, so that the transmission peak of a transmission light signal generated by the first FP etalon is sparse and the half-width is large, namely a large peak is short; the transmission light signals generated by the FP etalon II are dense, and the half-width is smaller, and the half-width is short as a small peak.

If the sweep frequency light with nonlinear change of the frequency along with time is injected, the density of the transmission peak of the generated transmission spectrum is changed along with time, the transmission peak is denser at the position with high sweep speed, and the position with low sweep speed is sparser, so that the transmission light signal accurately carries the information of the frequency change along with time.

FSRl of the FP etalon one is more than ten times greater than FSR2 of FP etalon two, and FSRl is not equal to an integer multiple of FSR 2. The purpose is to identify the frequency and wavelength of "flyback" by using the positional relationship of the two transmitted light transmission peaks. Because FSR1 can not be divided by FSR2, when the first and second electric signals are overlapped together by taking time as the abscissa, two small peaks of the second electric signal with a smaller distance are arranged on two sides of each large peak of the first electric signal, the ratio of the center of the two small peaks to the center of the middle large peak is called as a double peak ratio, the double peak ratio can not be repeated in a certain frequency range, and the double peak ratio can be calculated in advance. It is thus possible to identify whether the sweep light is "flyback" by the magnitude of the bimodal ratio.

Because the FSR2 of the FP etalon II is smaller, a small peak in the electrical signal II is finer and is used for recording the peak coordinates subsequently and carrying out data processing so as to ensure that higher calibration accuracy is obtained.

In the FP etalon two, because the "small peak" in the electrical signal two generated by the transmitted light thereof, the adjacent peak represents the optical frequency variation FSR2, and the absolute frequency and the absolute wavelength represented by each small peak are known, only the abscissa (time) of the small peak is recorded, so that the information of the frequency and the wavelength variation of the sweep light with time can be accurately obtained, and the curve of the frequency and the wavelength variation with time is drawn.

The system and method provided by the present invention are described below in connection with specific embodiments.

As shown in fig. 3, the embodiment adopts a monolithically integrated 24-channel array DFB semiconductor laser, and integrates 24 DFB lasers together in a matrix, and simultaneously integrates a Y-wave and a Semiconductor Optical Amplifier (SOA). The wavelength interval of the adjacent 2 DFB lasers is 2nm, a triangular wave current signal which is changed from 50mA to 180mA is applied to the lasers with the shortest wavelength, sweep light which covers about 2.2nm is generated, the lasers are switched to the adjacent next DFB lasers after the completion of the process, after the 24 DFB lasers are swept in sequence, nonlinear continuous sweep which covers more than 48nm and has the sweep speed of 100Hz is realized, in order to ensure that the wavelengths are completely covered when the DFB lasers of different channels are switched, gaps are not formed, the sweep range of the single DFB laser is ensured to be more than 2nm, and a part of flyback phenomenon is inevitably generated at the joint of the channels.

By utilizing the method and the device for calibrating the frequency and wavelength variation of the nonlinear sweep light source, which are used in the embodiment, the time variation of the frequency and wavelength of the nonlinear sweep light source is accurately calibrated, and two FP etalons with FSRs of 130GHz and 12.5GHz respectively are selected as the FP etalon I and the FP etalon II respectively in combination with the wavelength range characteristics of the nonlinear sweep light source, as shown in figure 4.

In the process of calibrating the embodiment, the first, second and third electric signals recorded on the oscilloscope are processed, as shown in fig. 5. The electrical signal three is switched by high and low levels, so that the switching time points of 24 DFB lasers can be identified, and the level of the electrical signal three is inverted (pulled high/pulled low) every moment the DFB lasers are switched.

The electrical signals one and two represent the transmitted light signal produced by the swept light passing through a 130GHz and 12.5GHz FP etalon, which has a FSR and full width at half maximum that are much greater than the 12.5GHz FP etalon, so that the "large peak" and "small peak" are clearly visible, each peak having a known center wavelength and frequency according to the etalon characteristics. And because the sweep speed of the sweep light source is different at different moments in the sweep period, the uniformity of the 'large peak' and the 'small peak' along with the time change is also different, the time transmission peak with high sweep speed is denser, and the time transmission peak with low sweep speed is sparser.

In order to obtain the accurate change of the frequency and the wavelength of the nonlinear sweep-frequency light source along with time in the embodiment, the abscissa (time) of the peak positions of the first and second electric signals needs to be accurately recorded through a peak searching algorithm, so that the mapping from the frequency domain to the time domain is completed. And the "flyback" portion can be judged and identified by the relative positional relationship of the "large peak" and the "small peak". To clearly illustrate this process, the position at which the 10 th DFB laser switches to the 11 th DFB laser is locally enlarged (square box portion in fig. 5), as shown in fig. 6. It can be seen that there are two small peaks spaced apart from each other on the left and right sides of the center of each large peak, so that the ratio of the distance between the left small peak and the center of the large peak to the ratio of the distance between the right small peak and the center of the large peak is defined as the "double peak ratio". The bimodal ratios of the large peaks 1,2, 3 and 4 can be calculated as: 0.44, 3.12, 0.15. Since the "large peak" 2 and 3 double peak ratios are identical, these two peaks represent the same absolute wavelength and frequency, and the portion in the middle of the "large peak" 2 and 3 is the "flyback" portion. These two large peaks are the same reflection peak, representing the same frequency and wavelength.

After identifying the "flyback" portion of each DFB laser channel switch, the peak abscissa (time) of the electrical signal two is recorded, as shown in fig. 7, with the absolute wavelength and frequency represented by the center position of each peak known.

After fitting, interpolating and smoothing the data, the relationship between the frequency and the wavelength of the nonlinear sweep-frequency light source in the embodiment can be obtained, as shown in fig. 8.

The method and the device can be used for finally realizing the accurate calibration of the nonlinear sweep frequency light source, are simple to operate and high in efficiency, and the calibration workload is not influenced by the sweep frequency speed, so that the method and the device have stronger universality.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the invention without departing from the principles thereof are intended to be within the scope of the invention as set forth in the following claims.

Claims (10)

1. The nonlinear continuous sweep frequency light source accurate calibration system based on the FP etalon is characterized by comprising: the system comprises a sweep frequency light source, a shunt coupler, an FP etalon I, a photoelectric detector I, an FP etalon II, a photoelectric detector II, an acquisition device and a computer;

The sweep light source generates broadband continuous sweep light with nonlinear change of frequency and wavelength along with time, and generates trigger signals at the starting position, the ending position and the channel switching position of each sweep period; in a sweep period, the change of the frequency and the wavelength of sweep light along with time is irregular;

The shunt coupler divides the sweep frequency light into two paths of optical signals, namely an optical signal I and an optical signal II; the first FP etalon and the second FP etalon respectively convert the first optical signal and the second optical signal into first transmission light and second transmission light; the first photoelectric detector and the second photoelectric detector respectively convert the first transmission light and the second transmission light into an electric signal I and an electric signal II; the acquisition device records an electric signal I, an electric signal II and a trigger signal;

The computer fits and peak-finding the first and second electric signals recorded by the acquisition device, and finds out the abscissa of the peak position of each transmission peak, wherein the abscissa represents time; marking the starting position, the ending position and the channel switching position of the sweep frequency period according to the trigger signal; identifying the frequency and the wavelength of flyback according to the position relation of transmission peaks corresponding to the first electric signal and the second electric signal; and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time.

2. The FP etalon based nonlinear continuous sweep light source precision calibration system of claim 1 wherein: the FP etalon I and the FP etalon II are internally provided with two flat plates plated with high-reflection films, so that the transmission spectrum of the FP etalon I and the FP etalon II is a plurality of transmission peaks with equal frequency intervals, and the frequency intervals among the peaks are equal.

3. The FP etalon based nonlinear continuous sweep light source precision calibration system of claim 1 wherein: the free spectral range of the FP etalon one is at least 10 times greater than the free spectral range of the FP etalon two, and the free spectral range of the FP etalon one is not equal to an integer multiple of the free spectral range of the FP etalon two.

4. The FP etalon based nonlinear continuous sweep light source precision calibration system of claim 3 wherein: the computer identifies the frequency and the wavelength of flyback according to the position relation of transmission peaks corresponding to the first electric signal and the second electric signal, and specifically comprises the following steps:

The transmission peaks corresponding to the first electric signal and the second electric signal are respectively defined as a big peak and a small peak, the two sides of the center position of each big peak are respectively provided with the small peaks, and the ratio of the distance between the small peak on one side and the center position of the big peak to the distance between the small peak on the other side and the center position of the big peak is defined as a double peak ratio; and (3) sequentially calculating the bimodal ratio of each large peak, if two large peaks with identical bimodal ratio exist, indicating that the two large peaks are the same large peak, wherein the middle part is a flyback part, and identifying the flyback frequency and wavelength.

5. The FP etalon based nonlinear continuous sweep light source precision calibration system of claim 4 wherein: the computer carries out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time, and the method specifically comprises the following steps:

And recording the abscissa of the position of the small peak, combining the absolute frequency and the absolute wavelength represented by the small peak to obtain the time-dependent change relation of the frequency and the wavelength of the sweep frequency light, and drawing a time-dependent change curve of the frequency and the wavelength.

6. The nonlinear continuous sweep frequency light source accurate calibration method based on the FP etalon is characterized by comprising the following steps of:

s1: generating a broadband continuous swept light with nonlinear variation of frequency and wavelength over time using a swept light source, and generating a trigger signal at a start, an end, and a channel switch of each sweep period; in a sweep period, the change of the frequency and the wavelength of sweep light along with time is irregular;

s2: dividing the sweep frequency light into two paths of optical signals, namely an optical signal I and an optical signal II by using a branching coupler; converting the first and second optical signals into first and second transmitted light, respectively, using a first FP etalon and a second FP etalon;

S3: the first photoelectric detector and the second photoelectric detector are used for respectively converting the first transmission light and the second transmission light into the first electric signal and the second electric signal, and the first electric signal and the second electric signal are recorded in the acquisition device through radio frequency conduction; the acquisition device also synchronously records the trigger signal;

s4: fitting and peak searching are carried out on the first electric signal and the second electric signal recorded by the acquisition device by using a computer, and the abscissa of the peak position of each transmission peak is found out, wherein the abscissa represents time; marking the starting and ending positions of the sweep frequency period and the channel switching position according to the trigger signal; identifying the frequency and the wavelength of flyback according to the position relation of transmission peaks corresponding to the first electric signal and the second electric signal;

S5: and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time.

7. The FP etalon based nonlinear continuous sweep light source accurate calibration method of claim 6, wherein: the FP etalon I and the FP etalon II are internally provided with two flat plates plated with high-reflection films, so that the transmission spectrum of the FP etalon I and the FP etalon II is a plurality of transmission peaks with equal frequency intervals, and the frequency intervals among the peaks are equal.

8. The FP etalon based nonlinear continuous sweep light source accurate calibration method of claim 6, wherein: the free spectral range of the FP etalon one is at least 10 times greater than the free spectral range of the FP etalon two, and the free spectral range of the FP etalon one is not equal to an integer multiple of the free spectral range of the FP etalon two.

9. The FP etalon based nonlinear continuous sweep light source accurate calibration method of claim 8, wherein: the identification of the flyback frequency and wavelength according to the position relation of the transmission peaks corresponding to the first electric signal and the second electric signal specifically comprises the following steps:

The transmission peaks corresponding to the first electric signal and the second electric signal are respectively defined as a big peak and a small peak, the two sides of the center position of each big peak are respectively provided with the small peaks, and the ratio of the distance between the small peak on one side and the center position of the big peak to the distance between the small peak on the other side and the center position of the big peak is defined as a double peak ratio; and (3) sequentially calculating the bimodal ratio of each large peak, if two large peaks with identical bimodal ratio exist, indicating that the two large peaks are the same large peak, wherein the middle part is a flyback part, and identifying the flyback frequency and wavelength.

10. The FP etalon based nonlinear continuous sweep light source accurate calibration method of claim 9, wherein: and carrying out smooth connection and interpolation processing on the frequency and time represented by the peak position of the transmission peak corresponding to the second electric signal to obtain the change relation between the frequency and the wavelength of the sweep frequency light along with time, wherein the change relation comprises the following specific steps:

And recording the abscissa of the position of the small peak, combining the absolute frequency and the absolute wavelength represented by the small peak to obtain the time-dependent change relation of the frequency and the wavelength of the sweep frequency light, and drawing a time-dependent change curve of the frequency and the wavelength.