Imaging system with simple structure and adjustable depth measurement range

Abstract

The application provides an imaging system with simple structure and adjustable depth measurement range, which comprises a laser, a first dispersive medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope. The imaging device divides the pulsed laser after time domain stretching by the first dispersive medium into multiple incident light signals with different wavelengths, and makes each incident light signal vertically incident on different positions of a sample to be measured. Each imaging light signal output from different positions of the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer. When the wavelength division multiplexer is provided with at least a corresponding number of output ends, the overlapped imaging light signals with different wavelengths received can be respectively divided into different light paths. The detector converts each spatial imaging light signal divided into a spatial imaging electrical signal and sends the spatial imaging electrical signal to the oscilloscope for resolution. The number of output ends provided on the wavelength division multiplexer is related to the depth measurement range of the system on the sample to be measured. The application has simple structure and small volume.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast time stretch imaging, specifically relating to an imaging system with a simple structure and adjustable depth measurement range. Background Technology

[0002] For optical time-coded imaging, there are two main types of correspondences: one is the correspondence between time and spectrum; the other is the correspondence between spectrum and spatial position. Time-domain stretching imaging systems typically first use a dispersive medium to stretch the laser signal in the time domain, achieving a correspondence between time and spectrum. Then, the time-stretched pulsed laser is split into multiple incident light signals of different wavelengths, and these different wavelengths are perpendicularly incident on different positions on the sample under test, achieving a correspondence between spectrum and spatial position. Finally, imaging is achieved based on the spatial imaging light signals reflected back from different positions on the sample. The objective factors affecting time-domain stretching imaging systems include the selection of the dispersion coefficient of the dispersion compensation fiber and the repetition frequency of the pulsed laser, among others.

[0003] Ideally, using a dispersion compensation medium with a large dispersion coefficient to perform time-domain stretching of pulsed lasers can broaden the pulses of different wavelengths in the time-stretched laser (e.g., ...). Figure 1 As shown in the figure, this can improve the resolution of different wavelength pulses in the spatial imaging optical signal. However, since different wavelength pulses in the spatial imaging optical signal correspond to different positions on the sample under test, and these different positions on the sample under test have varying depths, this will cause the temporal sequence of different wavelength pulses in the spatial imaging optical signal to change. For example... Figure 1 In mid-space imaging, the following pulse may exceed the preceding pulse, resulting in temporal overlap between pulses. To improve the resolution of the spatial imaging signal, wavelength division multiplexing (WDM) can be used to split pulses of different wavelengths into different optical paths. However, due to the rich spectral composition of pulsed lasers, splitting each pulse of a different wavelength into a different optical path would require not only maximizing the number of output ports on the WDM but also necessitating a large number of WDMs, making the imaging system extremely complex and bulky. Furthermore, existing imaging systems typically have a fixed depth measurement range for the sample, making it difficult to adjust the depth measurement range of the sample by simply replacing components while maintaining the resolution of the spatial imaging signal. Summary of the Invention

[0004] The application provides an imaging system with simple structure to solve the problem of complex structure and large volume of a time-domain stretching imaging system in ensuring spatial imaging light signal resolution, and provides an imaging system with adjustable depth measurement range to solve the problem that the depth measurement range of a sample to be measured cannot be adjusted by simply replacing devices while ensuring spatial imaging light signal resolution.

[0005] According to a first aspect of the embodiment of the application, an imaging system with simple structure is provided, which comprises a laser, a first dispersion medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersion medium performs time-domain stretching on pulsed laser provided by the laser; the imaging device divides the pulsed laser after time-domain stretching into multiple incident light signals with different wavelengths, and makes each incident light signal vertically incident on different positions of a sample to be measured, and each imaging light signal reflected or transmitted from the different positions of the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer.

[0006] When at least a corresponding number of output ends are arranged on the wavelength division multiplexer, the multiple imaging light signals with different wavelengths and overlapping in time domain received by the wavelength division multiplexer can be respectively divided into different light paths, so that the imaging light signals with different wavelengths in each divided spatial imaging light signal do not overlap in time domain, for each spatial imaging light signal, the wavelength division multiplexer transmits the spatial imaging light signal to a corresponding detector, the detector converts the spatial imaging light signal into a spatial imaging electrical signal, and sends the spatial imaging electrical signal to the oscilloscope for resolution, wherein the number of output ends arranged on the wavelength division multiplexer is related to the depth measurement range of the system to the sample to be measured.

[0007] In an optional implementation, the number of output ends arranged on the wavelength division multiplexer is also related to the dispersion coefficient of the first dispersion medium, and by increasing the dispersion coefficient of the first dispersion medium, the resolution of the spatial imaging light signal can be improved; when adjacent incident light signals output by the imaging device are discontinuous or continuous in time domain, the number of output ends arranged on the wavelength division multiplexer can be minimized.

[0008] When the dispersion coefficient of the first dispersion medium is increased until each adjacent incident light signal output by the imaging device is continuous in time domain, the resolution of the spatial imaging light signal can reach the highest when the number of output ends on the wavelength division multiplexer is minimized.

[0009] In another optional implementation, assuming that the time interval of adjacent incident light signals output by the imaging device is t, the light speed is c, and the maximum measurement depth of the system to the sample to be measured is h, then first, is calculated. an integer n, and then calculates the number N = n + 1 of at least the output ends provided on the wavelength division multiplexer;

[0010] wherein, when the adjacent incident light signals are discontinuous in time domain, the time interval t is the sum of the duration of a pulse in the incident light signal and the discontinuous time; when the adjacent incident light signals are continuous in time domain, the time interval t is the duration of a pulse in the incident light signal.

[0011] In another optional implementation, the overlapping of the different wavelength imaging light signals includes complete overlapping or partial overlapping, when the overlapping is complete, the wavelength division multiplexer divides the overlapping different wavelength imaging light signals into different light paths and outputs from different ports; when the overlapping is partial, the wavelength division multiplexer divides a previous imaging light signal into a light path, and then, for the overlapping part, divides the imaging light signal with the same wavelength as the previous imaging light signal into the same light path as the previous one, and divides the imaging light signal with a different wavelength from the previous imaging light signal into a different light path.

[0012] According to the second aspect of the present application, there is also provided an imaging system with adjustable depth measurement range, comprising a laser, a first dispersion medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersion medium time-domain stretches the pulsed laser provided by the laser; the imaging device divides the time-domain stretched pulsed laser into multiple incident light signals with different wavelengths, so that each incident light signal is perpendicularly incident on different positions of a sample to be measured, and each imaging light signal reflected or transmitted from the different positions of the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer.

[0013] The wavelength division multiplexer divides the multiple different wavelength imaging light signals received thereby into different light paths, so that the different wavelength imaging light signals in each divided light path do not overlap in time domain, for each light path, the wavelength division multiplexer transmits the light path to a corresponding detector, the detector converts the light path into a spatial imaging electrical signal and sends the spatial imaging electrical signal to the oscilloscope for resolution, and the depth measurement range of the system for the sample to be measured is adjusted by changing the dispersion coefficient of the first dispersion medium and / or the number of output ends on the wavelength division multiplexer.

[0014] In an optional implementation, the maximum measurement depth h = (N - 1) * t * c in the depth measurement range of the system for the sample to be measured, where t is the time interval of adjacent incident light signals output by the imaging device after the pulsed laser is time-domain stretched by the first dispersion medium and transmitted to the imaging device, c is the speed of light, and N is the number of output ends on the wavelength division multiplexer.

[0015] In another optional implementation, when the depth measurement range of the system to the sample to be measured and the dispersion coefficient of the first dispersive medium are fixed, i.e., the maximum measurement depth h in the depth measurement range and the time interval t of the adjacent incident light signals are fixed, the depth measurement range is ensured by changing the number of output ends on the wavelength division multiplexer. First, the integer n of the following formula is calculated: Then, the number N of output ends at least provided on the wavelength division multiplexer is calculated as N=n+1. When there are N output ends at least provided on the wavelength division multiplexer, the multiple different wavelength imaging light signals overlapping in the time domain received by the wavelength division multiplexer can be respectively divided into different optical paths.

[0016] In another optional implementation, when the maximum measurement depth h in the depth measurement range of the system to the sample to be measured and the number N of output ends on the wavelength division multiplexer are fixed, the depth measurement range is ensured by changing the dispersion coefficient of the first dispersive medium. The dispersion coefficient of the first dispersive medium can be changed to make the time interval of the adjacent incident light signals between [t min , t max ], the minimum pulse width t min is The maximum pulse width t max is the time interval of the adjacent incident light signals when the adjacent incident light signals are continuous in the time domain. At this time, the wavelength division multiplexer can divide the multiple different wavelength imaging light signals overlapping in the time domain into different optical paths.

[0017] When the dispersion coefficient of the first dispersive medium is changed to make the time interval of the adjacent incident light signals t max , the resolution of the spatial imaging light signal reaches the highest when N output ends are provided on the wavelength division multiplexer.

[0018] In another optional implementation, when the depth measurement range is adjusted by changing the dispersion coefficient of the first dispersive medium and the number of output ends on the wavelength division multiplexer, the dispersion coefficient of the first dispersive medium is first changed until the adjacent incident light signals output by the imaging device are continuous in the time domain. In this way, when the wavelength division multiplexer divides the multiple different wavelength imaging light signals overlapping in the time domain into different optical paths, the number of output ends used is the least, and the resolution of the spatial imaging light signal can reach the highest when the number of output ends used is the least. Then, the number N of output ends on the wavelength division multiplexer is changed to ensure the depth measurement range. First, the integer n of the following formula is calculated: Then, the number N of output ends at least provided on the wavelength division multiplexer is calculated as N=n+1.

[0019] In another alternative implementation, the overlapping of the different wavelength imaging light signals includes complete overlapping or partial overlapping, when the overlapping is complete, the wavelength division multiplexer divides the overlapping different wavelength imaging light signals into different optical paths and outputs from different ports; when the overlapping is partial, the wavelength division multiplexer divides a previous imaging light signal into an optical path, and then, for the overlapping part, divides the imaging light signal with the same wavelength as the previous imaging light signal into the same optical path as the previous one and divides the imaging light signal with a different wavelength from the previous imaging light signal into a different optical path.

[0020] The present application has the following advantages:

[0021] 1. The simple imaging system of the present application divides the different wavelength imaging light signals overlapping in time domain into different optical paths through the wavelength division multiplexer, so that the different wavelength imaging light signals in each divided spatial imaging light signal do not overlap in time domain, thus when the spatial imaging light signal resolution is improved by increasing the dispersion coefficient of the dispersion medium, the spatial imaging light signal resolution is not reduced due to the overlapping of the pulses in the spatial imaging light signal caused by the too large dispersion coefficient; secondly, the present application divides the different wavelength imaging light signals overlapping in time domain into different optical paths, rather than dividing each different wavelength imaging light signal into a different optical path, thus the structure is simple and the volume is small; thirdly, the present application can determine the number of at least the output ends of the wavelength division multiplexer according to the depth measurement range of the system to the sample to be measured, the determination method is simple, and the imaging system structure can be further simplified and the volume can be further reduced; in addition, the present application can realize the acquisition of the sample surface topography information by single pulse; the dispersion Fourier transform (DFT) technology is used to record the spectrum, compared with the traditional spectrometer, the spectrum resolution can be ensured at the same time, the spectrum information can be directly collected by the detector, so that the sampling rate is improved to megahertz; the imaging device can make the spatial position and the spectrum correspond, so that the spectrum intensity of the reflected light or the transmitted light can reflect the information of different spatial positions of the sample;

[0022] 2. In the simple imaging system of the present application, the number of the output ends of the wavelength division multiplexer is the least only when the time intervals of the adjacent incident light signals are discontinuous or continuous to ensure that the multiple different wavelength imaging light signals overlapping in time domain are divided into different optical paths respectively;

[0023] 3、The imaging system with adjustable depth measurement range of the present application can separate the different wavelength imaging light signals which are overlapped in time domain into different light paths through the wavelength division multiplexer, so that the different wavelength imaging light signals in each separated light path will not be overlapped in time domain, thus when the resolution of the spatial imaging light signal is improved by increasing the dispersion coefficient of the dispersion medium, the pulse in the spatial imaging light signal will not be overlapped due to the too large dispersion coefficient, which can avoid the resolution reduction of the spatial imaging light signal; secondly, the depth measurement range of the system to the sample to be measured can be adjusted by changing the dispersion coefficient of the first dispersion medium and / or the number of the output ends of the wavelength division multiplexer, that is, the depth measurement range of the sample to be measured can be adjusted by simply replacing the device while ensuring the resolution of the spatial imaging light signal; in addition, the present application can realize the acquisition of the sample surface topography information by single pulse; the dispersion Fourier transform (DFT) technology is used to record the spectrum, compared with the traditional spectrometer, the spectrum information can be directly collected by the detector while ensuring the spectrum resolution, so as to improve the sampling rate to megahertz; the imaging device can make the spatial position and the spectrum correspond, so that the spectral intensity of the reflected light or the transmitted light can reflect the information of different spatial positions of the sample;

[0024] 4、When the depth measurement range of the imaging system to the sample to be measured is adjusted, if the dispersion coefficient of the first dispersion medium is constant, the actual depth measurement range can be ensured within the required depth measurement range by changing the number of the output ends of the wavelength division multiplexer, and the present application can also determine the minimum number of the output ends required when the wavelength division multiplexer separates the multiple different wavelength imaging light signals which are overlapped in time domain into different light paths, so that the wavelength division multiplexer and its output ends can be avoided to be blindly added, thereby the structure of the imaging system can be simplified and the volume can be reduced;

[0025] 5、When the depth measurement range of the imaging system to the sample to be measured is adjusted, if the number of the output ends of the wavelength division multiplexer is constant, the actual depth measurement range can be ensured within the required depth measurement range by changing the dispersion coefficient of the first dispersion medium, and as long as the time interval of the adjacent incident light signals is within [t min , t max ] when the first dispersion medium is selected, the wavelength division multiplexer can separate the multiple different wavelength imaging light signals which are overlapped in time domain into different light paths when the corresponding number of the output ends is provided; the present application provides a time interval range, and the dispersion coefficient of the first dispersion medium also has a range, so that the flexibility of selecting the first dispersion medium can be improved;

[0026] 6. When adjusting the depth measurement range by changing the dispersion medium of the first dispersion medium and the number of output terminals on the wavelength division multiplexer, the present invention first changes the dispersion coefficient of the first dispersion medium until each adjacent incident light signal output by the imaging device is continuous in the time domain, ensuring that the number of output terminals used on the wavelength division multiplexer is minimized and the resolution of the spatial imaging light signal reaches the highest level when the number of output terminals used is minimized. Then, the minimum number of output terminals that should be set on the wavelength division multiplexer is calculated according to the corresponding formula. This not only ensures that the number of output terminals used on the wavelength division multiplexer is minimized, but also ensures that the resolution of the spatial imaging light signal is maximized as much as possible.

[0027] 7. In this invention, regardless of whether the imaging optical signals of different wavelengths completely overlap or partially overlap, the wavelength division multiplexer can completely divide the imaging optical signals of different wavelengths into different optical paths. Therefore, it can be guaranteed that the imaging optical signals of different wavelengths will not overlap in the time domain among the divided spatial imaging optical signals. Attached Figure Description

[0028] Figure 1 This is a waveform comparison diagram of the pulsed laser, the time-stretched pulsed laser, the incident light signal, and the spatial imaging light signal of the present invention;

[0029] Figure 2 This is a structural block diagram of an embodiment of the imaging system of the present invention, which has a simple structure and adjustable depth measurement range;

[0030] Figure 3 This is a structural block diagram of another embodiment of the imaging system of the present invention, which has a simple structure and adjustable depth measurement range;

[0031] Figure 4 This is a schematic diagram of the depth measurement range in an imaging system;

[0032] Figure 5 (a) to (d) show the correspondence between the range of the forward shift of the later pulse and the time interval between the adjacent incident light signals and the temporal overlap of imaging light signals of different wavelengths when each adjacent incident light signal is discontinuous or continuous in the time domain.

[0033] Figure 6 It is the correspondence between the range of the forward shift of the subsequent pulse and the time interval between the adjacent incident light signals and the temporal overlap of imaging light signals of different wavelengths when each adjacent incident light signal is discontinuous in the time domain;

[0034] Figure 7 It is the correspondence between the forward shift range of the later pulse and the time interval between adjacent incident light signals and the temporal overlap of imaging light signals of different wavelengths when each adjacent incident light signal overlaps in the time domain.

[0035] Figure 8is a schematic diagram of different wavelength imaging light signal partially overlapped;

[0036] Figure 9 is a structural block diagram of another embodiment of the imaging system with simple structure and adjustable depth measurement range;

[0037] Figure 10 is Figure 9 is a specific structural schematic diagram of the embodiment shown in

[0038] Figure 11 is Figure 9 is another specific structural schematic diagram of the embodiment shown in DETAILED DESCRIPTION

[0039] In order to make the technical personnel in the art better understand the technical solutions in the embodiments of the present application, and make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings.

[0040] In the description of the present application, unless otherwise specified and limited, it is necessary to explain that the term "connection" should be understood broadly, for example, it can be mechanical connection or electrical connection, or the internal communication of two elements, which can be directly connected or indirectly connected through intermediate medium. For those skilled in the art, the specific meaning of the above-mentioned term can be understood according to the specific circumstances.

[0041] Referring to Figure 2 and Figure 3 are two structural schematic diagrams of the imaging system with simple structure of the present application. The imaging system can include a laser, a first dispersive medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersive medium time domain stretches the pulsed laser provided by the laser and transmits the time domain stretched pulsed laser to the imaging device, the imaging device divides the time domain stretched pulsed laser into multiple incident light signals with different wavelengths, so that each incident light signal is vertically incident on different positions of the sample to be measured, and the reflected light (as shown in Figure 2 or transmitted light (as shown in Figure 3Each imaging optical signal (as shown) is transmitted by the imaging device to the wavelength division multiplexer. Only when the wavelength division multiplexer has at least a corresponding number of output terminals can it split the multiple imaging optical signals of different wavelengths that overlap in the time domain to different optical paths, so that the imaging optical signals of different wavelengths in the split spatial imaging optical signals will not overlap in the time domain. For each spatial imaging optical signal, the wavelength division multiplexer transmits the spatial imaging optical signal to the corresponding detector. The detector converts the spatial imaging optical signal into a spatial imaging electrical signal and sends the spatial imaging electrical signal to the oscilloscope for resolution (e.g., waveform resolution). The number of output terminals provided on the wavelength division multiplexer is related to the depth measurement range of the sample to be tested by the system.

[0042] In this embodiment, the laser is connected to the input terminal of the imaging device through a first dispersive medium, the output terminal of the imaging device is connected to a wavelength division multiplexer, and the output terminal of the wavelength division multiplexer is connected to an oscilloscope through a detector. Figure 2 and Figure 3 In both embodiments shown, the output of the wavelength division multiplexer is connected to an oscilloscope via a corresponding detector. The time-stretched pulsed laser can include multiple pulses of different wavelengths. The pulses in the time-stretched pulsed laser have the same width, and their widths are increased compared to those in the pulsed laser provided by the laser source. Furthermore, the multiple incident light signals with different wavelengths divided by the imaging device can be parallel to each other and have equal pulse widths. Each imaging light signal can correspond to a wavelength and a position on the sample under test. The set of light signals composed of multiple imaging light signals constitutes the spatial imaging light signal, and each imaging light signal corresponds to a pulse in this spatial imaging light signal.

[0043] like Figure 4 As shown, the depth varies across different areas of the sample under test, with both depressions and protrusions. This invention uses the lowest permissible depression position on the sample as the 0 value of the depth measurement range, and the highest permissible protrusion position as the maximum measurement depth h of the depth measurement range. When all positions on the sample are at the lowest permissible depression position, Figure 1 The spatial imaging light signal is still the same as the incident light signal, but as... Figure 1 In the mid-space imaging optical signal, the height of the position corresponding to the subsequent pulse increases continuously. In the time domain, the subsequent pulse will gradually surpass the preceding pulse, and in this process, they will overlap in the time domain.

[0044] When adjacent incident light signals are continuous in the time domain (i.e., there are no pulse interruptions in the incident light signals), the correspondence between the subsequent pulse forward shift range, the time interval between adjacent incident light signals, and the temporal overlap of imaging light signals of different wavelengths is as follows:Figure 5 (a) to (d), the range indicated by the double arrow T in the figure is the range of the forward shift in time domain of the later pulse in the spatial imaging light signal from the lowest position of the allowed recess to the highest position of the allowed protrusion, and since the light speed c is fixed, the range of the forward shift can reflect the depth measurement range of the system to the sample under test, and the maximum measurement depth of the depth measurement range can be represented as h = T * c. Let the difference between the occurrence time of adjacent incident light signals be the time interval t of adjacent incident light signals (the time interval of each adjacent incident light signal is equal), as shown in Figure 5 (a), when the range of the forward shift in time domain of the later pulse in the spatial imaging light signal is greater than 0 and less than or equal to 1 t, at most only 2 pulses can overlap in time domain; for example Figure 5 (b), when the range of the forward shift in time domain of the later pulse in the spatial imaging light signal is greater than 1 t and less than or equal to 2 t, the 1st to 3rd pulses from right to left can overlap in time domain, that is, at most 3 pulses can overlap in time domain; for example Figure 5 (c), when the range of the forward shift in time domain of the later pulse in the spatial imaging light signal is greater than 2 t and less than or equal to 3 t, the 1st to 4th pulses from right to left can overlap in time domain, that is, at most 4 pulses can overlap in time domain; for example Figure 5 (d), when the range of the forward shift in time domain of the later pulse in the spatial imaging light signal is greater than 3 t and less than or equal to 4 t, the 1st to 5th pulses from right to left can overlap in time domain, that is, at most 5 pulses can overlap in time domain.

[0045] When each adjacent incident light signal is interrupted in time domain (that is, there is a pulse interruption segment in the incident light signal), the corresponding relationship between the forward shift range of the later pulse, the time interval of adjacent incident light signals, and the time domain overlap of different wavelength imaging light signals is as shown in Figure 6 , similarly, the range indicated by the double arrow T in the figure is used to represent the range of the forward shift in time domain of the later pulse in the spatial imaging light signal from the lowest position of the allowed recess to the highest position of the allowed protrusion. Let the difference between the occurrence time of adjacent incident light signals be the time interval t of adjacent incident light signals, when the range of the forward shift in time domain of the later pulse in the spatial imaging light signal is greater than 1 t and less than or equal to 2 t, the 1st to 3rd pulses from right to left can overlap in time domain, that is, at most 3 pulses can overlap in time domain, which is the same as Figure 5 (b) under the same condition.

[0046] When each adjacent incident light signal is overlapped in time domain, the corresponding relationship between the forward shift range of the later pulse, the time interval of adjacent incident light signals, and the time domain overlap of different wavelength imaging light signals is as shown in Figure 7As shown, similarly, the range shown by the double arrow T in the figure is used to represent the time-domain forward shift range T in the process of the trailing pulse in the spatial imaging light signal increasing from the lowest position of the allowed recess to the highest position of the allowed protrusion. Assuming that the difference between the occurrence time of adjacent incident light signals is the time interval t of adjacent incident light signals, when the time-domain forward shift range T of the trailing pulse in the spatial imaging light signal is greater than 1 t and less than or equal to 2 t, the first to fourth pulses from right to left can have time-domain overlap, i.e., at most 4 pulses have time-domain overlap, while in the same case Figure 5 (b) At most 3 pulses have time-domain overlap.

[0047] It can be seen that when each adjacent incident light signal output by the imaging device is discontinuous or continuous in the time domain, the wavelength division multiplexer is provided with an equal and small number of output ends to ensure that the multiple different wavelength imaging light signals overlapping in the time domain received thereby are respectively divided into different light paths, and when each adjacent incident light signal is overlapping in the time domain, the wavelength division multiplexer is provided with a larger number of output ends to ensure that the multiple different wavelength imaging light signals overlapping in the time domain received thereby are respectively divided into different light paths. Therefore, only when the adjacent incident light signals output by the imaging device are discontinuous or continuous in the time domain, the number of output ends provided on the wavelength division multiplexer can be minimized. When the dispersion coefficient of the first dispersion medium is increased until each adjacent incident light signal output by the imaging device is continuous in the time domain, the resolution of the spatial imaging light signal can reach the highest when the number of output ends on the wavelength division multiplexer is minimized.

[0048] In addition, as can be seen from the above description, the time-domain overlap of the pulses in the spatial imaging light signal is related to the time interval t of the adjacent incident light signals. Since the pulsed laser is transmitted to the imaging device after being time-domain stretched by the first dispersion medium, and the incident light signal is output by the imaging device, the characteristics of the incident light signal, including the difference between the occurrence time of adjacent incident light signals (i.e., the time interval t of adjacent incident light signals), are related to the dispersion coefficient of the first dispersion medium. In addition, the wavelength division multiplexer is provided with at least a number of output ends equal to the maximum number of pulses that can have time-domain overlap in the spatial imaging light signal, so the number of output ends provided on the wavelength division multiplexer is also related to the dispersion coefficient of the first dispersion medium. By increasing the dispersion coefficient of the first dispersion medium, the resolution of the spatial imaging light signal can be improved.

[0049] According to the above Figure 5According to the relevant description, when T is greater than 0 and less than or equal to t, there are at most 2 pulses overlapping in the spatial imaging optical signal in the time domain; when T is greater than t and less than or equal to 2t, there are at most 3 pulses overlapping in the time domain; when T is greater than 2t and less than or equal to 3t, there are at most 4 pulses overlapping in the time domain; and when T is greater than 3t and less than or equal to 4t, there are at most 5 pulses overlapping in the time domain. From this, it can be deduced that when T is greater than m*t and less than or equal to (m+1)*t, i.e., (m+1)*t ≥ T > m*t, there are at most m+2 pulses overlapping in the time domain in the corresponding spatial imaging optical signal. Since h = T*c, multiplying both sides of the inequality about T by c, we get (m+1)*t*c ≥ h > m*t*c, thus the range of values ​​for m can be determined as follows: At this point, a maximum of m+2 pulses in the spatial imaging optical signal will overlap in the temporal domain. Let n = m+1, then the range of values ​​for n is... At that time, at most n+1 pulses in the spatial imaging optical signal will overlap in the temporal domain.

[0050] Therefore, when determining the minimum number of output terminals on a wavelength division multiplexer, we can first calculate... The integer n is used to calculate the minimum number of output terminals N = n + 1 on the wavelength division multiplexer, where t is the time interval between adjacent incident light signals output by the imaging device, c is the speed of light, and h is the maximum measurement depth of the sample under test by the system. Specifically, when the adjacent incident light signals are discontinuous in the time domain, the time interval t is the sum of the pulse duration and the interruption time in the incident light signal; when the adjacent incident light signals are continuous in the time domain, the time interval t is the pulse duration in the incident light signal. The above formula verifies that the minimum number of output terminals on the wavelength division multiplexer is indeed related to the maximum measurement depth h in the depth measurement range of the sample under test and the dispersion coefficient of the first dispersive medium indirectly reflected by t.

[0051] The overlap of imaging optical signals of different wavelengths can include complete overlap or partial overlap. When it is complete overlap, the wavelength division multiplexer splits the overlapping imaging optical signals of different wavelengths into different optical paths and outputs them from different ports; when it is partial overlap, such as... Figure 8As shown, the wavelength division multiplexer divides the previous imaging light signal into an optical path, and for the overlapping part, divides the imaging light signal with the same wavelength as the previous imaging light signal into the same optical path, divides the imaging light signal with different wavelength from the previous imaging light signal into a different optical path, and so on. Since the wavelength division multiplexer can completely divide the imaging light signals with different wavelengths into different optical paths no matter whether the imaging light signals completely overlap or partially overlap, it can ensure that the imaging light signals with different wavelengths in each divided spatial imaging light signal do not overlap in time domain.

[0052] As can be seen from the above embodiment, the present application divides the imaging light signals with different wavelengths overlapping in time domain into different optical paths by setting the wavelength division multiplexer, so that the imaging light signals with different wavelengths in each divided spatial imaging light signal do not overlap in time domain, and thus when the spatial imaging light signal resolution is improved by increasing the dispersion coefficient of the dispersion medium, the spatial imaging light signal resolution will not be reduced due to the overlapping of the pulses in the spatial imaging light signal caused by the too large dispersion coefficient. Secondly, the present application divides the imaging light signals with different wavelengths overlapping in time domain into different optical paths, rather than dividing each imaging light signal with different wavelength into a different optical path, so that the structure is simple and the volume is small. Thirdly, the present application can determine the number of at least output ends of the wavelength division multiplexer according to the depth measurement range of the system to the sample to be measured, and the determination method is simple, which can further simplify the structure of the imaging system and reduce the volume. In addition, the present application can realize the acquisition of the sample surface topography information by single pulse. The dispersion Fourier transform (DFT) technology is used to record the spectrum, and compared with the traditional spectrometer, this method can directly collect the spectrum information by the detector while ensuring the spectrum resolution, so that the sampling rate is improved to megahertz. The imaging device can make the spatial position and the spectrum correspond to each other, so that the spectral intensity of the reflected light or the transmitted light can reflect the information of different spatial positions of the sample.

[0053] In addition, the present application also provides an imaging system with adjustable depth measurement range, which has the same structure as the above-mentioned simple imaging system, and similarly, the depth measurement range of the imaging system can be adjusted by adjusting the number of output ends of the wavelength division multiplexer. Figure 2 and Figure 3As shown, the imaging system can include a laser, a first dispersive medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersive medium time-domain stretches the pulsed laser provided by the laser; the imaging device divides the time-domain stretched pulsed laser into multiple incident light signals with different wavelengths, and makes each incident light signal vertically incident on different positions of the sample to be measured, and each imaging light signal reflected or transmitted from the different positions of the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer; the wavelength division multiplexer divides the multiple different wavelength imaging light signals received thereby and overlapping in time domain into different light paths, so that the different wavelength imaging light signals in each divided light path do not overlap in time domain, and for each light path, the wavelength division multiplexer transmits the light path to a corresponding detector, the detector converts the light path into a spatial imaging electrical signal, and sends the light path to the oscilloscope for resolution, and the depth measurement range of the system for the sample to be measured is adjusted by changing the dispersion coefficient of the first dispersive medium and / or the number of output ends of the wavelength division multiplexer.

[0054] In the embodiment, the maximum measurement depth in the depth measurement range of the system for the sample to be measured can be represented as h=(N-1)*t*c, where t is the time interval of adjacent incident light signals output by the imaging device after the pulsed laser is time-domain stretched by the first dispersive medium and transmitted to the imaging device, c is the speed of light, and N is the number of output ends of the wavelength division multiplexer.

[0055] When the depth measurement range of the system for the sample to be measured and the dispersion coefficient of the first dispersive medium are constant, i.e., the maximum measurement depth h in the depth measurement range and the time interval t of adjacent incident light signals are constant, the number of output ends of the wavelength division multiplexer is changed to ensure the depth measurement range, and first, the integer n is calculated, and then the number of output ends N of the wavelength division multiplexer is calculated as N=n+1, and when the wavelength division multiplexer has at least N output ends, the multiple different wavelength imaging light signals received thereby and overlapping in time domain are divided into different light paths. When the depth measurement range of the imaging system for the sample to be measured is adjusted, if the dispersion coefficient of the first dispersive medium is constant, the number of output ends of the wavelength division multiplexer can be changed to ensure that the actual depth measurement range is within the required depth measurement range, and the present application can also determine the minimum number of output ends required when the wavelength division multiplexer divides the multiple different wavelength imaging light signals received thereby and overlapping in time domain into different light paths within the required depth measurement range, thereby avoiding blindly adding the wavelength division multiplexer and its output ends, so as to simplify the structure of the imaging system and reduce its volume.

[0056] Since the wave division multiplexer can only set the least output ends to respectively divide the received multiple different wavelength imaging light signals which overlap in time domain into different light paths when the adjacent incident light signals outputted by the imaging device are discontinuous or continuous (i.e. not overlapping) in time domain, correspondingly, when the wave division multiplexer is provided with corresponding number of output ends, the dispersion coefficient of the first dispersion medium is not the larger the better, when the dispersion coefficient of the first dispersion medium is increased to make the adjacent incident light signals overlapping, the wave division multiplexer cannot divide the received multiple different wavelength imaging light signals which overlap in time domain into different light paths. Therefore, the present application ensures the depth measurement range by changing the dispersion coefficient of the first dispersion medium when the maximum measurement depth h (i.e. depth measurement range) in the depth measurement range of the sample to be measured by the system and the number N of output ends on the wave division multiplexer are certain, and the dispersion coefficient of the first dispersion medium can be changed to make the time interval of the adjacent incident light signals between [t min , t max ], wherein the minimum pulse width t min is the maximum pulse width t max is the time interval of the adjacent incident light signals when the adjacent incident light signals are continuous in time domain (i.e. the duration of the pulse in the incident light signal), at this time, the wave division multiplexer can divide the received multiple different wavelength imaging light signals which overlap in time domain into different light paths. When the dispersion coefficient of the first dispersion medium is changed to make the time interval of the adjacent incident light signals t max , the resolution of the spatial imaging light signal reaches the highest when the wave division multiplexer is provided with N output ends. When the depth measurement range of the sample to be measured by the imaging system is adjusted, if the number of output ends on the wave division multiplexer is certain, the actual depth measurement range can be ensured within the required depth measurement range by changing the dispersion coefficient of the first dispersion medium, and when the first dispersion medium is selected, as long as the time interval of the adjacent incident light signals is between [t min , t max ], it can be ensured that the wave division multiplexer can divide the received multiple different wavelength imaging light signals which overlap in time domain into different light paths when the wave division multiplexer is provided with corresponding number of output ends; the present application provides a time interval value range, and correspondingly, the dispersion coefficient of the first dispersion medium also exists in a range, so that the flexibility of selecting the first dispersion medium can be improved.

[0057] When adjusting the depth measurement range by changing the dispersion medium of the first dispersive medium and the number of output terminals on the wavelength division multiplexer, the dispersion coefficient of the first dispersive medium is first changed until the adjacent incident light signals output by the imaging device are continuous in the time domain. This ensures that the wavelength division multiplexer uses the fewest number of output terminals when it distributes the multiple overlapping imaging light signals of different wavelengths received in the time domain to different optical paths, and that the resolution of the spatial imaging light signal reaches the highest level when the number of output terminals is minimized. Then, the depth measurement range is ensured by changing the number N of output terminals on the wavelength division multiplexer. At this time, the first step is to determine... The integer n is used to calculate the minimum number of output terminals N = n + 1 on the wavelength division multiplexer. Only when the wavelength division multiplexer has at least N output terminals can the multiple overlapping imaging light signals of different wavelengths received in the time domain be distributed to different optical paths. In this invention, when adjusting the depth measurement range by changing the dispersion medium of the first dispersive medium and the number of output terminals on the wavelength division multiplexer, the dispersion coefficient of the first dispersive medium is first changed until the adjacent incident light signals output by the imaging device are continuous in the time domain. This ensures that the number of output terminals used on the wavelength division multiplexer is minimized and the resolution of the spatial imaging light signal reaches its maximum when the number of output terminals used is minimized. Then, the minimum number of output terminals that should be set on the wavelength division multiplexer is calculated according to the corresponding formula. This not only ensures that the number of output terminals used on the wavelength division multiplexer is minimized but also ensures that the resolution of the spatial imaging light signal is maximized.

[0058] The overlap of imaging optical signals of different wavelengths can include complete overlap or partial overlap. When it is complete overlap, the wavelength division multiplexer splits the overlapping imaging optical signals of different wavelengths into different optical paths and outputs them from different ports; when it is partial overlap, such as... Figure 8 As shown, the wavelength division multiplexer (WDM) distributes the initial imaging optical signal to one optical path. For overlapping portions, it distributes the imaging optical signal with the same wavelength as the initial imaging optical signal to the same optical path, and the imaging optical signal with a different wavelength to a different optical path, and so on. Since the WDM can completely distribute the imaging optical signals of different wavelengths to different optical paths, whether the overlap is complete or partial, it can ensure that the imaging optical signals of different wavelengths will not overlap in the time domain among the divided spatial imaging optical signals.

[0059] As can be seen from the above embodiments, the application sets the wavelength division multiplexer to divide the different wavelength imaging light signals overlapping in time domain into different light paths, so that the different wavelength imaging light signals in each divided spatial imaging light signal do not overlap in time domain, and thus when the spatial imaging light signal resolution is improved by increasing the dispersion coefficient of the dispersion medium, the spatial imaging light signal resolution is not reduced due to the overlapping of the pulses in the spatial imaging light signal caused by the too large dispersion coefficient; secondly, the depth measurement range of the system for the sample to be measured can be adjusted by changing the dispersion coefficient of the first dispersion medium and / or the number of output ends of the wavelength division multiplexer, that is, the depth measurement range of the sample to be measured can be adjusted by simply replacing the device while ensuring the spatial imaging light signal resolution; in addition, the application can realize the acquisition of the sample surface topography information by single pulse; the dispersion Fourier transform (DFT) technology is used to record the spectrum, and compared with the traditional spectrometer, the spectrum information can be directly collected by the detector while ensuring the spectrum resolution, so that the sampling rate is improved to megahertz; the imaging device is used to correspond the spatial position and the spectrum, so that the spectrum intensity of the reflected light or the transmitted light can reflect the information of different spatial positions of the sample.

[0060] In addition, as shown in Figure 9 the structural block diagram of another embodiment of the imaging system with simple structure and adjustable depth measurement range. The second dispersion medium is further arranged between the output end of the wavelength division multiplexer and the input end of the detector in the two imaging systems, the second dispersion medium performs time domain stretching on each spatial imaging light signal output by the wavelength division multiplexer, and transmits each spatial imaging light signal after time domain stretching to the corresponding detector; for each spatial imaging light signal after time domain stretching, the detector converts the spatial imaging light signal after time domain stretching into a spatial imaging electrical signal, and sends the spatial imaging electrical signal to the oscilloscope for resolution. The dispersion characteristics of the second dispersion medium for performing time domain stretching on each spatial imaging light signal are completely the same.

[0061] In addition, the optical amplifier is further arranged between the first dispersion medium and the imaging device in the two imaging systems, the optical amplifier amplifies the pulse laser after time domain stretching into a flat-top pulse, so that the background noises of the different wavelength pulses in the pulse laser are the same, to ensure the sample topography recovery accuracy based on the spatial imaging light signal; the optical amplifier transmits the flat-top pulse to the imaging device, the imaging device divides the flat-top pulse into a plurality of incident light signals with different wavelengths, each incident light signal is vertically incident to different positions on the sample to be measured, and each imaging light signal reflected or transmitted from the different positions on the sample to be measured is transmitted to the wavelength division multiplexer by the imaging device.

[0062] Referring toFigure 10 ,for Figure 9 The illustrated embodiment presents a specific structural diagram. In this system, the laser is connected to the imaging device via a first dispersive medium, and the imaging device is connected to the wavelength division multiplexer (WDM). For each pair of output terminals of the WDM, a second dispersive medium is provided. One output terminal of the WDM is connected to the first terminal of a first circulator, the second terminal of the first circulator is connected to the second terminal of a second circulator via the second dispersive medium, and the third terminal is connected to the corresponding input terminal of the oscilloscope via a first detector. The other output terminal of the WDM is connected to the first terminal of the second circulator, and the third terminal is connected to the corresponding input terminal of the oscilloscope via a second detector.

[0063] The first dispersive medium performs temporal stretching on the pulsed laser provided by the laser. The imaging device splits the temporally stretched pulsed laser into multiple incident light signals with different wavelengths, so that each incident light signal is perpendicularly incident on different positions on the sample under test. The imaging light signals reflected or transmitted from different positions on the sample under test are transmitted by the imaging device to the wavelength division multiplexer. When multiple imaging light signals of different wavelengths that overlap in the temporal domain are received, the wavelength division multiplexer splits the overlapping imaging light signals of different wavelengths into different optical paths, so that the imaging light signals of different wavelengths in the split spatial imaging light signals do not overlap in the temporal domain. For each pair of outputs of the wavelength division multiplexer (WDM), one spatial imaging optical signal is transmitted to the second dispersive medium via the first circulator. After time-domain stretching by the second dispersive medium, it is transmitted to the second detector via the second circulator. The second detector converts the time-domain stretched spatial imaging optical signal into a spatial imaging electrical signal and sends it to the oscilloscope for resolution. The other spatial imaging optical signal is transmitted to the second dispersive medium via the second circulator. After time-domain stretching by the second dispersive medium, it is transmitted to the first detector via the first circulator. The first detector converts the time-domain stretched spatial imaging optical signal into a spatial imaging electrical signal and sends it to the oscilloscope for resolution. This invention uses a single second dispersive medium for each pair of outputs of the WDM, achieving dispersion compensation for both spatial imaging optical signals with identical compensation values. This reduces the number of second dispersive media required and simplifies the structure.

[0064] If the second dispersive medium used for each pair of outputs of a wavelength division multiplexer (WDM) has different dispersive characteristics, then the oscilloscope needs to use different dispersion compensation standards to resolve the spatial imaging light signals divided by the WDM. Therefore, in this invention, the second dispersive medium used for time-domain stretching of each spatial imaging light signal needs to be exactly the same. This ensures high resolution efficiency of the oscilloscope for spatial imaging light signals, thus facilitating the recovery of the surface morphology of the sample under test. To ensure that the dispersive characteristics of each second dispersive medium are the same, the dispersive characteristics of each second dispersive medium need to be calibrated before use. Therefore, this invention uses a single second dispersive medium for each pair of outputs of the WDM, which also reduces the number of calibrations required for the second dispersive medium in this system.

[0065] See Figure 11 ,for Figure 9 Another specific structural diagram of the illustrated embodiment. In this system, the laser is connected to the input of the imaging device through a first dispersive medium, and the output of the imaging device is connected to a wavelength division multiplexer; for each output of the wavelength division multiplexer, a second dispersive medium is provided, and each output of the wavelength division multiplexer is connected to a corresponding detector through a second dispersive medium; each detector is connected to an oscilloscope.

[0066] The first dispersive medium time-domain stretches the pulsed laser provided by the laser; the imaging device divides the time-domain stretched pulsed laser into multiple incident light signals with different wavelengths, and makes each incident light signal vertically incident on different positions on the sample to be measured, and each imaging light signal reflected or transmitted from the different positions on the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer. When receiving multiple different wavelength imaging light signals overlapping in time domain, the wavelength division multiplexer divides the overlapping different wavelength imaging light signals into different light paths respectively, so that the divided different wavelength imaging light signals in each light path do not overlap in time domain. Each spatial imaging light signal output by the wavelength division multiplexer is time-domain stretched by the corresponding second dispersive medium, and is transmitted to the corresponding detector. The detector converts the time-domain stretched spatial imaging light signal into a spatial imaging electrical signal, and sends the spatial imaging electrical signal to the oscilloscope for resolution. Similarly, if the second dispersive medium provided for each output end of the wavelength division multiplexer has different dispersion characteristics, the oscilloscope needs to use different dispersion compensation standards when resolving the spatial imaging light signals divided by the wavelength division multiplexer. Therefore, the dispersion characteristics of the second dispersive medium used to time-domain stretch each spatial imaging light signal in the present application are completely the same, which can ensure the resolution efficiency of the high oscilloscope for the spatial imaging light signal, thereby facilitating the recovery of the surface topography of the sample to be measured. In order to ensure that the dispersion characteristics of each second dispersive medium are the same, the dispersion characteristics of each second dispersive medium need to be calibrated before use.

[0067] In one example, in conjunction with Figure 10 and Figure 11As shown, the imaging device can include a main ring, a collimator, a diffraction grating and a lens, the main ring is connected to the optical amplifier at a first end, the pulsed laser provided by the laser is transmitted to the first end of the main ring through the first dispersive medium and the optical amplifier in turn, the pulsed laser after time domain stretching through the first dispersive medium and amplification through the optical amplifier is transmitted to the collimator from the second end of the main ring, after collimation through the collimator, it is transmitted to the diffraction grating, the diffraction grating divides the pulsed laser into a plurality of incident light signals with different wavelengths, the plurality of incident light signals form linear incident light signals after the lens, the linear incident light signals are perpendicular to different positions on the sample to be measured, the linear incident light signals are composed of a plurality of parallel incident light signals with different wavelengths, thereby realizing line scanning of the sample to be measured; the spatial imaging light signals reflected from different positions on the sample to be measured are transmitted to the second end of the main ring according to the original path, and then transmitted to the wavelength division multiplexer from the third end of the main ring. In order to realize surface scanning, a stepping motor can be provided, the straight line where the linear incident light signal is located is defined as the x-axis, and the y-axis is perpendicular to the x-axis, the sample to be measured is moved along the y-axis by the stepping motor.

[0068] It should be noted that after receiving each spatial imaging light signal, the oscilloscope can collect and distinguish the spatial imaging light signal and transmit the collected data to the computer, and the computer can recover the surface topography of the sample to be measured according to the collected data. The pulsed laser can be a wide-spectrum ultrafast pulsed laser with high pulse repetition frequency, so as to ensure the imaging frame rate of the system, for example, a pulsed laser with a spectral range of tens of nanometers and a pulse repetition frequency greater than 1 MHz. The wavelength resolution capability of the system is mainly determined by the following factors: one is the dispersion capability of the dispersive element, two is the spectral resolution capability of the dispersive Fourier transform (DFT), and three is the spectral resolution capability determined by the bandwidth of the detector, high-speed oscilloscope and other digital devices. The total spectral resolution capability of the system is determined by the largest parameter among the above three parameters. The imaging frame rate of the system is mainly determined by the pulse frequency of the light source, and the pulse frequency of the ultrafast laser is usually greater than 1 MHz; the effective frame rate of the imaging also depends on the moving speed of the sample; the pixel points of the image are mainly determined by the spectral width of the light source, the dispersion coefficient of the dispersion compensation fiber and the sampling rate of the oscilloscope. The first dispersive medium and the second dispersive medium can be dispersion compensation fibers, and the oscilloscope can be a high-speed oscilloscope.

[0069] For Figure 10In the shown embodiment, the pulse laser outputted by the ultrafast pulsed laser with a center wavelength of 1565nm, a spectral bandwidth of 15nm and a repetition frequency of 50MHz is time-stretched by a first dispersion compensation fiber with a dispersion coefficient of 1.2ns / nm, amplified to 40mW by an optical amplifier, then injected into a collimator through a port of a main circulator, and the spatial light outputted by the collimator is dispersed by a 1200-line diffraction grating, the first-order diffracted light of the grating is collimated by a plano-convex lens and irradiated onto a sample to be measured, the light signal carrying the sample information returns to the main circulator in the original path, and the light signal is outputted from a three-port of the main circulator to a wavelength division multiplexer, the incident laser is divided into two paths by the wavelength division multiplexer (WDM) and outputted: one path of light is transmitted to a two-port of a first circulator after passing through a one-port of the first circulator, then injected into a second dispersion compensation fiber through a two-port of the first circulator, dispersed and compensated by the second dispersion compensation fiber, transmitted to a two-port of a second circulator, and then outputted from a three-port of the second circulator, the outputted light is converted into an electrical signal by a second photodetector and inputted into a port of a high-speed oscilloscope; the other path of light is transmitted to a two-port of the second circulator after passing through a one-port of the second circulator, then injected into the second dispersion compensation fiber through a two-port of the second circulator, dispersed and compensated by the second dispersion compensation fiber, transmitted to a two-port of the first circulator, and then outputted from a three-port of the first circulator, the outputted light is converted into an electrical signal by a first photodetector and inputted into another port of the high-speed oscilloscope. The signals inputted into the two ports of the high-speed oscilloscope are collected and stored, and then the collected signals are processed by a computer, so that the surface topography information of the sample is recovered.

[0070] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0071] It is to be understood that the application is not limited to the precise construction here described and as illustrated in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is to be defined by the claims appended hereto.

Claims

1. An imaging system of simple construction, characterized in that The system comprises a laser, a first dispersion medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersion medium time-stretching the pulsed laser provided by the laser, the imaging device dividing the time-stretched pulsed laser into multiple incident light signals with different wavelengths, each incident light signal being perpendicularly incident on different positions of a sample to be measured, each imaging light signal reflected or transmitted from the different positions of the sample being transmitted by the imaging device to the wavelength division multiplexer. When the wavelength division multiplexer is provided with at least a corresponding number of output ends, the multiple different wavelength imaging light signals received by the wavelength division multiplexer can be respectively divided into different light paths, so that the different wavelength imaging light signals in each divided light path do not overlap in time domain, for each light path, the wavelength division multiplexer transmits the light path to a corresponding detector, the detector converts the light path into a spatial imaging electrical signal, and sends the spatial imaging electrical signal to the oscilloscope for resolution, wherein the number of output ends provided on the wavelength division multiplexer is related to the depth measurement range of the system for the sample to be measured. The time interval of the adjacent incident light signals input by the imaging device is t, the light speed is c, the maximum measuring depth of the system to the sample to be measured is h, and the integer n is first calculated, and then the number N of the output ends arranged on the wavelength division multiplexer is calculated. ​​ When the adjacent incident light signals are discontinuous in time domain, the time interval t is the sum of the duration of the pulses in the incident light signals and the discontinuous time; when the adjacent incident light signals are continuous in time domain, the time interval t is the duration of the pulses in the incident light signals. The different wavelength imaging light signals are completely overlapped or partially overlapped, when they are completely overlapped, the wavelength division multiplexer divides the overlapped different wavelength imaging light signals into different light paths and outputs them from different ports; when they are partially overlapped, the wavelength division multiplexer divides the previous imaging light signal into a light path, and for the overlapping part, divides the imaging light signal with the same wavelength as the previous imaging light signal into the same light path, and divides the imaging light signal with a different wavelength from the previous imaging light signal into a different light path.

2. The simple structured imaging system of claim 1, wherein The number of output ends provided on the wavelength division multiplexer is also related to the dispersion coefficient of the first dispersion medium, by increasing the dispersion coefficient of the first dispersion medium, the spatial imaging light signal resolution can be improved; when the adjacent incident light signals input by the imaging device are discontinuous or continuous in time domain, the number of output ends provided on the wavelength division multiplexer can be minimized. When the dispersion coefficient of the first dispersion medium is increased until the adjacent incident light signals input by the imaging device are continuous in time domain, the spatial imaging light signal resolution can reach the highest when the number of output ends on the wavelength division multiplexer is minimized.

3. An imaging system with adjustable depth measurement range, characterized in that The system comprises a laser, a first dispersive medium, an imaging device, a wavelength division multiplexer, a detector and an oscilloscope, the first dispersive medium time-stretches the pulsed laser provided by the laser, the imaging device divides the time-stretched pulsed laser into multiple incident light signals with different wavelengths, each incident light signal is perpendicularly incident on different positions of a sample to be measured, and each imaging light signal reflected or transmitted from the different positions of the sample to be measured is transmitted by the imaging device to the wavelength division multiplexer; The wavelength division multiplexer divides the multiple different wavelength imaging light signals received by the wavelength division multiplexer into different optical paths, so that the different wavelength imaging light signals in each divided spatial imaging light signal do not overlap in time domain, for each spatial imaging light signal, the wavelength division multiplexer transmits the spatial imaging light signal to a corresponding detector, the detector converts the spatial imaging light signal into a spatial imaging electrical signal, and sends the spatial imaging electrical signal to the oscilloscope for resolution, the depth measurement range of the system for the sample to be measured is adjusted by changing the dispersion coefficient of the first dispersive medium and / or the number of output ends of the wavelength division multiplexer. The system has a maximum measurement depth in a depth measurement range of a sample to be measured Wherein t is the time interval of the adjacent incident light signals input by the imaging device after the pulsed laser is time domain stretched by the first dispersive medium and transmitted to the imaging device, c is the speed of light, and N is the number of output ends of the wavelength division multiplexer. The different wavelength imaging light signals are completely overlapped or partially overlapped, when the different wavelength imaging light signals are completely overlapped, the wavelength division multiplexer divides the overlapped different wavelength imaging light signals into different optical paths and outputs from different ports, when the different wavelength imaging light signals are partially overlapped, the wavelength division multiplexer divides a previous imaging light signal into an optical path, and for the overlapped part, divides the imaging light signal with the same wavelength as the previous imaging light signal into the same optical path as the previous imaging light signal, and divides the imaging light signal with a different wavelength from the previous imaging light signal into a different optical path.

4. The depth of field range adjustable imaging system of claim 3, wherein, When the depth measurement range of the sample under test and the dispersion coefficient of the first dispersive medium are fixed, i.e., the maximum measurement depth h and the time interval t between adjacent incident light signals are fixed, and the depth measurement range is ensured by changing the number of output terminals on the wavelength division multiplexer, the following steps are first taken: Given an integer n, calculate the minimum number of output terminals N that must be set on the wavelength division multiplexer. Only when the wavelength division multiplexer has at least N output terminals can it distribute the multiple imaging optical signals of different wavelengths that are superimposed in the time domain to different optical paths.

5. The depth of measurement range adjustable imaging system according to claim 3 or 4, characterized in that, With the maximum measurement depth h and the number N of output terminals on the wavelength division multiplexer fixed within the depth measurement range of the sample to be measured in the system, when ensuring the depth measurement range by changing the dispersion coefficient of the first dispersive medium, the dispersion coefficient of the first dispersive medium can be changed so that the time interval between adjacent incident light signals is within [t]. min , t max The value ranges between ], with the minimum pulse width t. min for Maximum pulse width t max The time interval between adjacent incident light signals is when they are continuous in the time domain. Only then can the wavelength division multiplexer distribute the multiple imaging light signals of different wavelengths that are superimposed in the time domain to different optical paths. wherein when the dispersion coefficient of the first dispersion medium is changed to make the time interval of the adjacent incident light signals t max , the resolution of the spatial imaging light signals reaches the highest when N outputs are set on the wavelength division multiplexer.

6. The depth measurement range adjustable imaging system of claim 5, wherein, When the depth measurement range is adjusted by changing the dispersion medium of the first dispersive medium and the number of output ends of the wavelength division multiplexer, first, the dispersion coefficient of the first dispersive medium is changed until each adjacent incident light signal input by the imaging device is continuous in time domain, so that when the wavelength division multiplexer divides the multiple different wavelength imaging light signals received by the wavelength division multiplexer into different optical paths, the number of output ends used is the least, and the resolution of the spatial imaging light signal can reach the highest when the number of output ends used is the least. The depth measurement range is then ensured by varying the number N of outputs of the wavelength division multiplexer, for which the integer n is first determined, and then the number N of outputs of the wavelength division multiplexer is calculated .​

Images