CN116379945A - Coherent ranging system and method - Google Patents
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Abstract
The application is applicable to the technical field of coherent ranging, and provides a coherent ranging system and a method, wherein the system comprises a sweep frequency light source, a first coupler, a circulator, a second coupler, a third coupler and a cache ring, and the cache ring comprises an optical delay line and a first intensity modulator; the sweep frequency light source is used for generating a sweep frequency light signal with a preset duty cycle, a preset duration and a preset scanning waveform; the first intensity modulator is used for controlling the switching time and the buffering times of the buffering ring according to the first modulation signal generated by the waveform generator. According to the method, the distance to be measured is divided into a plurality of small fragments for measurement based on the optical caching principle, the problem that the measurement distance is limited by the measurement bandwidth and the coherence length is solved, and meanwhile, the measurement distance is improved on the premise of little loss of the measurement rate in the optical caching time division multiplexing mode.
Description
Technical Field
The application belongs to the technical field of coherent ranging, and particularly relates to a coherent ranging system and a method.
Background
The coherent ranging is widely applied to the fields of automatic driving, medical examination, 3D printing, industrial detection and the like. The common coherent ranging mode is to acquire distance information of an object to be measured by detecting and analyzing interference signals between reference light and reflected light of the object to be measured by means of a sweep frequency light source. In a coherent ranging system, the maximum measurement distance is proportional to the instantaneous coherence length of the light source, so to achieve a large distance measurement, a narrow linewidth light source is theoretically required. In addition, in the conventional scheme, the measurement speed, the measurement distance and the required measurement bandwidth of the system are mutually restricted, so that on the premise of ensuring the system accuracy, a large measurement bandwidth is generally required to realize rapid measurement of a large distance.
Disclosure of Invention
The embodiment of the application provides a coherent ranging system and a coherent ranging method, which are used for solving the problem that the measurement speed, the measurement distance and the required measurement bandwidth of the conventional coherent ranging system are mutually restricted, and realizing the rapid measurement of a large distance on the premise of ensuring the resolution of the system, and meanwhile, only needing smaller detection bandwidth.
A first aspect of an embodiment of the present application provides a coherent ranging system, including a swept-frequency light source, a first coupler, a circulator, a second coupler, a third coupler, and a buffer ring, where the buffer ring includes an optical delay line and a first intensity modulator;
the sweep frequency light source is used for generating a sweep frequency light signal with a preset duty cycle, a preset duration and a preset scanning waveform;
the first intensity modulator is used for controlling the switching time and the buffering times of the buffering ring according to a first modulation signal generated by the waveform generator;
the sweep frequency optical signal is split into a measuring optical signal and a reference optical signal through the first coupler;
the measuring light signal is transmitted to an object to be measured through the circulator;
the reflected light signals reflected by the object to be detected are transmitted to the second coupler through the circulator;
the reference optical signal is transmitted to the buffer ring through the third coupler, and after being respectively delayed by the optical delay line and modulated by the first intensity modulator, one part of the reference optical signal is transmitted to the buffer ring again through the third coupler, and the other part of the reference optical signal is transmitted to the second coupler through the third coupler;
the reflected light signal and the other part of reference light signal are transmitted to the measuring equipment after interference occurs in the second coupler to generate a first interference light signal;
the measuring device is used for measuring time domain information of the first interference optical signal.
In one embodiment, the swept optical source comprises a continuous optical source, a second intensity modulator, and a phase modulator;
the continuous light source is used for generating a continuous light signal;
the second intensity modulator is used for adjusting the duration time and the time domain waveform of the continuous optical signal according to the second modulation signal generated by the waveform generator;
the phase modulator is used for adjusting the phase of the continuous optical signal adjusted by the second intensity modulator according to a third modulation signal generated by the waveform generator;
and after the continuous optical signals are modulated by the second intensity modulator and the phase modulator respectively, sweep-frequency optical signals with preset duty ratios, preset duration time and preset scanning waveforms are formed.
In one embodiment, the swept optical source comprises a distributed feedback laser.
In one embodiment, the buffer loop further comprises an optical amplifier and an optical bandpass filter;
the reference optical signal is transmitted to the buffer ring through the third coupler, and is amplified by the optical amplifier, filtered by the optical band-pass filter, delayed by the optical delay line and modulated by the first intensity modulator respectively, one part of the reference optical signal is transmitted to the buffer ring again through the third coupler, and the other part of the reference optical signal is transmitted to the second coupler through the third coupler.
In one embodiment, the buffer ring further comprises a first polarization controller;
the first polarization controller is used for controlling the polarization state of the reference light signal.
In one embodiment, the coherent ranging system further comprises at least one of a second polarization controller and a collimator;
the second polarization controller is used for controlling the polarization state of the measurement light signal;
the measurement light signal is transmitted to the circulator after the polarization state of the measurement light signal is regulated by the second polarization controller;
and the measuring light signal is transmitted to the collimator through the circulator to be collimated and then transmitted to the object to be measured.
In one embodiment, the coherent ranging system further comprises a scanning galvanometer;
the scanning galvanometer is used for adjusting the incidence position of a measuring light signal transmitted to an object to be measured so as to scan the object to be measured in two dimensions or three dimensions.
A second aspect of embodiments of the present application provides a coherent ranging method, implemented based on the coherent ranging system provided in the first aspect, the method including:
controlling the sweep frequency light source to generate a sweep frequency light signal with a preset duty ratio, a preset duration and a preset scanning waveform;
controlling the waveform generator to generate a first modulation signal so that the first intensity modulator controls the switching time and the buffering times of the buffering ring according to the first modulation signal;
and obtaining the distance information of the object to be measured according to the time domain information of the first interference light signal measured by the measuring equipment.
In one embodiment, the swept optical signal comprises a first swept optical signal and a second swept optical signal within a single period;
the delay time between two adjacent caches of the cache ring is as follows:
wherein DeltaT represents the delay time, L represents the optical length of the buffer ring, and n represents the bufferThe refractive index of the light transmitting material in the storage ring, c represents the speed of light in vacuum, δt 1 Representing the duration of the first swept optical signal in a single period δt 2 Representing the duration of the second swept optical signal in a single period δt 3 Representing the duration of the first modulated signal, L c Representing the instantaneous coherence length of the swept optical signal.
In one embodiment, the distance information of the object to be measured is:
wherein d represents the absolute distance of the object to be measured, m represents the cache times of the cache ring, and δd represents the relative distance.
The coherent ranging system provided in the first aspect of the embodiments of the present application includes a swept source, a first coupler, a circulator, a second coupler, a third coupler, and a buffer ring, where the buffer ring includes an optical delay line and a first intensity modulator; the sweep frequency light source is used for generating a sweep frequency light signal with a preset duty cycle, a preset duration and a preset scanning waveform; the first intensity modulator is used for controlling the switching time and the buffering times of the buffering ring according to the first modulation signal generated by the waveform generator; the sweep frequency optical signal is split into a measuring optical signal and a reference optical signal through a first coupler; transmitting the measuring optical signal to an object to be measured through a circulator; transmitting a reflected light signal reflected by the object to be detected to the second coupler through the circulator; the reference optical signal is transmitted to the buffer ring through the third coupler, and after being modulated by the optical delay line delay and the first intensity modulator respectively, one part of the reference optical signal is transmitted to the buffer ring again through the third coupler, and the other part of the reference optical signal is transmitted to the second coupler through the third coupler; the reflected light signal and the other part of the reference light signal are interfered in the second coupler to generate a first interference light signal, and then the first interference light signal is transmitted to the measuring equipment; the measuring equipment is used for measuring time domain information of the first interference optical signal, and based on an optical caching principle, the distance to be measured is divided into a plurality of small fragments for measurement, so that the problem that the measurement distance is limited by measurement bandwidth and coherence length is solved; meanwhile, the measurement distance is improved on the premise of little loss of the measurement rate by the time division multiplexing mode of the optical buffer.
It will be appreciated that the advantages of the second aspect may be found in the relevant description of the first aspect, and will not be described in detail herein.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following description will briefly introduce the drawings that are needed in the embodiments or the description of the prior art, it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a first structure of a coherent ranging system according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a second configuration of a coherent ranging system according to an embodiment of the present application;
FIG. 3 is a schematic diagram of a third configuration of a coherent ranging system according to an embodiment of the present application;
fig. 4 is a schematic diagram of a fourth structure of a coherent ranging system according to an embodiment of the present application;
fig. 5 is a flow chart of a coherent ranging method according to an embodiment of the present application;
fig. 6 is a waveform diagram of a second modulation signal and a first modulation signal provided in an embodiment of the present application;
FIG. 7 is a waveform diagram of a reference optical signal provided in an embodiment of the present application;
FIG. 8 is a waveform diagram of a first interference optical signal and a Fourier transform thereof provided in an embodiment of the present application;
fig. 9 is a waveform chart of fourier transform of a first interference optical signal at different distances to be measured according to an embodiment of the present application.
Detailed Description
In order to make the present application solution better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, shall fall within the scope of the present application.
The term "comprising" in the description of the present application and the claims and in the above figures, as well as any variants thereof, is intended to cover a non-exclusive inclusion. For example, a process, method, or system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed but may optionally include additional steps or elements not listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "first," "second," and "third," etc. are used for distinguishing between different objects and not for describing a particular sequential order.
As shown in fig. 1, the embodiment of the present application provides a coherent ranging system, which includes a Swept-frequency light Source (sweep Source) 1, a first coupler 21, a circulator (Optical Circulator) 3, a second coupler 22, a third coupler 23, and a buffer ring 4, where the buffer ring 4 includes an optical delay line (Optical Delay Line, ODL) 41 and a first intensity modulator (Amplitude Modulation) 42;
the sweep frequency light source 1 is used for generating a sweep frequency light signal with a preset duty cycle, a preset duration and a preset scanning waveform;
the first intensity modulator 42 is configured to control the switching time and the buffering times of the buffer ring 4 according to the first modulation signal generated by the waveform generator (Arbitrary Waveform Generator, AWG) 5;
the sweep frequency optical signal is split into a measuring optical signal and a reference optical signal through the first coupler 21;
the measuring optical signal is transmitted to an object 6 to be measured through the circulator 3;
the reflected light signal reflected by the object to be measured 6 is transmitted to the second coupler 22 through the circulator 3;
the reference optical signal is transmitted to the buffer ring 4 through the third coupler 22, is respectively delayed by the optical delay line 41 and modulated by the first intensity modulator 42, one part of the reference optical signal is transmitted to the buffer ring 4 again through the third coupler 23, and the other part of the reference optical signal is transmitted to the second coupler 22 through the third coupler 23;
the reflected light signal and the other part of the reference light signal interfere in the second coupler 22 to generate a first interference light signal, and then the first interference light signal is transmitted to the measuring device 7;
the measuring device 7 is used for measuring time domain information of the first interference light signal.
In application, all components in the coherent ranging system can be connected through optical fibers to form an all-fiber connection ranging system, so that the whole system is beneficial to movement, and transmission light paths cannot be interrupted due to small position changes among the components.
As shown in fig. 1, the connection structure of each component in the coherent ranging system when connected by an optical fiber is exemplarily shown as follows:
the output end of the sweep frequency light source 1 is connected with the input end of the first coupler 21 through an optical fiber;
the first output end of the first coupler 21 is connected with the input end of the circulator 3 through an optical fiber, and the second output end of the first coupler 21 is connected with the first input end of the third coupler 23 through an optical fiber;
the output end of the circulator 3 is connected with the first input end of the second coupler 22 through an optical fiber, and the input and output ends of the circulator 3 face the object 6 to be measured;
the first output end of the third coupler 23 is connected with the input end of the optical delay line 41 through an optical fiber, the output end of the optical delay line 41 is connected with the first input end of the first intensity modulator 42 through an optical fiber, the second input end of the first intensity modulator 42 is electrically connected with the first output end of the waveform generator 5, the output end of the first intensity modulator 42 is connected with the input end of the third coupler 23 through an optical fiber, and the second output end of the third coupler 23 is connected with the second input end of the second coupler 22 through an optical fiber;
the output of the second coupler 22 is connected to the input of the measuring device 7 by means of an optical fiber.
In application, the connection sequence of the optical delay line and the first intensity modulator in the buffer ring may be set according to actual needs, for example, the first output end of the third coupler, the input end of the optical delay line, the output end of the optical delay line, the first input end of the first intensity modulator, the output end of the first intensity modulator and the input end of the third coupler are sequentially connected through optical fibers; alternatively, the first output end of the third coupler, the first input end of the first intensity modulator, the output end of the first intensity modulator, the input end of the optical delay line, the output end of the optical delay line, and the input end of the third coupler are sequentially connected through optical fibers, one of which is illustrated in fig. 1 by way of example.
In application, the duty cycle, duration and scanning waveform of the swept optical signal can be preset according to actual needs. The first intensity modulator is used for adjusting the intensity of the reference optical signal according to the first modulation signal generated by the waveform generator so as to realize control of the switching time and the buffering times of the buffer ring, for example, when the intensity of the reference optical signal is 0, the buffer ring is closed, otherwise, the buffer ring is opened, and the reference optical signal is transmitted in the buffer ring through the third coupler for one circle (transmitted from the first output end of the third coupler to the buffer ring and then returned to the first output end of the third coupler), namely, one buffer is obtained.
In application, the first coupler and the second coupler may be implemented by a Beam Splitter (BS) for splitting or combining an incident optical signal.
In application, the measuring device may be implemented by any device capable of photoelectrically converting an optical signal and measuring time domain information thereof, for example, a photodetector and an oscilloscope, or a photodetector and a spectrometer, etc.
As shown in fig. 2, in one embodiment, the swept optical source 1 includes a continuous optical source 11, a second intensity modulator 12, and a Phase modulator 13;
a continuous light Source (Continuous Wave Source, CW Source) 11 for generating a continuous light signal;
the second intensity modulator 12 is used for adjusting the duration and the time domain waveform of the continuous optical signal according to the second modulation signal generated by the waveform generator 5;
the phase modulator 13 is used for adjusting the phase of the continuous optical signal adjusted by the second intensity modulator 12 according to the third modulation signal generated by the waveform generator;
the continuous optical signal is modulated by the second intensity modulator 12 and the phase modulator 13, respectively, to form a swept optical signal having a predetermined duty cycle, a predetermined duration, and a predetermined sweep waveform.
In application, all components in the sweep frequency light source can be connected through optical fibers, so that the coherent ranging system forms an all-fiber connection ranging system, the whole system is beneficial to movement, and transmission light paths are not interrupted due to small position changes among all the components.
As shown in fig. 2, the connection structure of the components in the swept-frequency light source when the components are connected by optical fibers is exemplarily shown as follows:
the output end of the continuous light source 11 is connected to a first input end of a second intensity modulator 12 via an optical fiber, a second input end of the second intensity modulator 12 is electrically connected to a second output end of the waveform generator 5, an output end of the second intensity modulator 12 is connected to a first input end of a phase modulator 13 via an optical fiber, a second input end of the phase modulator 13 is electrically connected to a third output end of the waveform generator 5, and an output end of the phase modulator 13 is connected to an input end of a first coupler 21 via an optical fiber.
In application, the connection sequence of the second intensity modulator and the phase modulator in the sweep frequency light source can be set according to actual needs, for example, the output end of the continuous light source, the first input end of the second intensity modulator, the output end of the second intensity modulator, the first input end of the phase modulator, the output end of the phase modulator and the input end of the first coupler are sequentially connected through optical fibers; alternatively, the output end of the continuous light source, the first input end of the phase modulator, the output end of the phase modulator, the first input end of the second intensity modulator, the output end of the second intensity modulator, and the input end of the first coupler are sequentially connected through optical fibers, one of which is illustrated in fig. 2 by way of example.
In application, the continuous light source may be implemented by any laser that can continuously emit an optical signal. The sweep frequency light source can also be realized by a distributed feedback laser to equivalently replace the continuous light source, the second intensity modulator and the phase modulator so as to simplify the system structure. The second intensity modulator is used for adjusting the intensity of the continuous optical signal according to the second modulation signal generated by the waveform generator so as to realize adjustment of the duration time of the continuous optical signal and the scanning waveform, for example, when the intensity of the continuous optical signal is 0, the continuous optical signal is interrupted, otherwise, the continuous optical signal is normally transmitted, and the duration time of the continuous optical signal is the duration time when the light intensity of the continuous optical signal is greater than 0; the adjustment of the scanning waveform can be achieved by adjusting the light intensity at each instant in the duration of the continuous light signal, the scanning waveform being a square wave when the light intensity at each instant in the duration of the continuous light signal is the same. The phase modulator is used for adjusting the phase of the continuous optical signal output by the second intensity modulator according to the third modulation signal generated by the waveform generator so as to realize the adjustment of the phase of the continuous optical signal.
As shown in fig. 3, in one embodiment, the buffer ring 4 further includes an optical amplifier (Optical Amplifier, OA) 43 and an optical band pass filter (Optical Band Pass Filter, OBPF) 44;
the reference optical signal is transmitted to the buffer ring 4 through the third coupler 21, and is amplified by the optical amplifier 43, filtered by the optical bandpass filter 44, delayed by the optical delay line 41 and modulated by the first intensity modulator 42, one part of the reference optical signal is transmitted to the buffer ring 4 again through the third coupler 23, and the other part of the reference optical signal is transmitted to the second coupler 22 through the third coupler 23.
In application, the connection sequence of the optical delay line, the first intensity modulator, the optical amplifier and the optical band-pass filter in the buffer ring can be set according to actual needs.
As shown in fig. 3, an optical amplifier 43, an optical band-pass filter 44, an optical delay line 41, and a first intensity modulator 42 are exemplarily shown as follows:
the first output end of the third coupler 23 is connected to the input end of the optical amplifier 43 by an optical fiber, the output end of the optical amplifier 43 is connected to the input end of the optical band pass filter 44 by an optical fiber, the output end of the optical band pass filter 44 is connected to the input end of the optical delay line 41 by an optical fiber, the output end of the optical delay line 41 is connected to the first input end of the first intensity modulator 42 by an optical fiber, and the output end of the first intensity modulator 42 is connected to the input end of the third coupler 23 by an optical fiber.
In applications, the optical Amplifier may be a semiconductor Amplifier (Semiconductor Optical Amplifier, SOA) or a Fiber Amplifier (FA), e.g., an erbium doped fiber Amplifier (Erbium Doped Optical Fiber Amplifier, EDFA), etc.
In application, the internal gain coefficient of the buffer ring is adjusted through the optical amplifier, so that the internal loss of the buffer ring can be compensated, the spatial transmission loss of a measurement optical signal transmitted to an object to be measured can be approximately compensated by means of the interference heterodyne amplification effect during measurement, and the signal-to-noise ratio of system measurement is improved. The optical band-pass filter filters out the spontaneous emission of the optical amplifier, and a good signal-to-noise ratio can also be achieved.
As shown in fig. 4, in one embodiment, the buffer ring 4 further includes a first polarization controller 45;
the first polarization controller 45 is used to control the polarization state of the reference light signal.
In application, the first polarization controller can be arranged at any position in the buffer ring according to actual needs. The first polarization controller ensures the intensity modulation effect of the first intensity modulator on the reference light signal by controlling the polarization state of the reference light signal.
As shown in fig. 4, an optical amplifier 43, an optical band-pass filter 44, an optical delay line 41, a first polarization controller 45, and a first intensity modulator 42 are exemplarily shown as follows:
the first output end of the third coupler 23 is connected to the input end of the optical amplifier 43 through an optical fiber, the output end of the optical amplifier 43 is connected to the input end of the optical band pass filter 44 through an optical fiber, the output end of the optical band pass filter 44 is connected to the input end of the optical delay line 41 through an optical fiber, the output end of the optical delay line 41 is connected to the input end of the first polarization controller 45 through an optical fiber, the output end of the first polarization controller 45 is connected to the first input end of the first intensity modulator 42 through an optical fiber, and the output end of the first intensity modulator 42 is connected to the input end of the third coupler 23 through an optical fiber.
As shown in fig. 4, in one embodiment, the coherent ranging system provided in the embodiments of the present application further includes a second polarization controller 8;
the input end of the second polarization controller 8 is connected with the first output end of the first coupler 21, and the output end of the second polarization controller 8 is connected with the input end of the circulator 3;
the second polarization controller 8 is used for controlling the polarization state of the measurement light signal;
the measurement light signal is transmitted to the circulator 3 after the polarization state is adjusted by the second polarization controller 8.
As shown in fig. 4, in one embodiment, the coherent ranging system provided in the embodiments of the present application further includes a collimator 9;
the input end of the collimator 9 is connected with the input and output ends of the circulator 3, and the output end of the collimator 9 faces the object 6 to be measured;
the measuring light signal is transmitted to the collimator 9 through the circulator 3 for collimation and then transmitted to the object 6 to be measured.
In application, the collimator can be realized by a collimating lens, and is used for collimating the measurement light signal, so that the measurement light signal can be accurately incident to the object to be measured.
In one embodiment, the coherent ranging system provided in the embodiments of the present application further includes a scanning galvanometer;
when the coherent ranging system does not comprise a collimator, the scanning galvanometer is arranged between the input end and the output end of the circulator and an object to be measured;
when the coherent ranging system comprises a collimator, the scanning galvanometer is arranged between the output end of the collimator and an object to be measured;
the scanning galvanometer is used for adjusting the incident position of the measuring light signal transmitted to the object to be measured so as to realize two-dimensional or three-dimensional scanning of the object to be measured.
In application, the scanning galvanometer can be composed of a motor and a reflecting mirror which move in a two-dimensional space so as to realize two-dimensional scanning of the surface profile of an object to be detected; the scanning galvanometer can also be composed of a motor and a reflecting mirror which move in a three-dimensional space so as to realize three-dimensional scanning of the surface profile of the object to be detected. By arranging the scanning galvanometer, the coherent ranging system not only can be used for measuring the distance of an object to be measured, but also can be used for measuring the surface profile of the object to be measured, thereby being capable of being used for two-dimensional imaging or three-dimensional imaging of the surface profile of the object to be measured.
As shown in fig. 5, the embodiment of the present application further provides a coherent ranging method implemented based on a coherent ranging system, which may be specifically executed by a processor of a control device when running a corresponding computer program, where the method includes steps S1 to S3 as follows:
s1, controlling a sweep frequency light source to generate a sweep frequency light signal with a preset duty ratio, a preset duration and a preset scanning waveform;
s2, controlling a waveform generator to generate a first modulation signal so that a first intensity modulator controls the switching time and the buffering times of a buffering ring according to the first modulation signal;
s3, obtaining the distance information of the object to be measured according to the time domain information of the first interference light signal measured by the measuring equipment.
In application, the control device can be electrically connected with at least one of a continuous light source, a distributed feedback laser, a waveform generator, a measuring device and a scanning galvanometer to control the working states of the components, so as to realize the measurement of the distance information of the object to be measured. The continuous light source, the distributed feedback laser, the waveform generator, and the measurement device may also operate independently of the control device.
In application, the control device may be a computing device capable of implementing data processing functions, such as a desktop computer, a notebook computer, a netbook, a personal digital assistant (Personal Digital Assistant, PDA), or the like.
In application, the processor may be implemented by a central processing unit (Central Processing Unit, CPU), other general purpose processor, digital signal processor (Digital Signal Processor, DSP), application specific integrated circuit (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, or the like. The general purpose processor may be a microprocessor or any conventional processor or the like.
In application, the coherent ranging system and control device may include, but are not limited to, the components described above. It will be appreciated by those skilled in the art that the illustrations of fig. 1-4 are merely examples of coherent ranging systems and are not limiting of coherent ranging systems, and may include more or fewer components than illustrated, or may combine certain components, or different components, e.g., the control device may also include a memory, an input-output device, a network access device, etc.
In an application, the control device may further comprise a memory electrically connected to the processor for storing a computer program executable by the processor, which when executed, effects control of the operating states of the components electrically connected to the control device. The memory may in some embodiments be an internal storage unit of the control device, e.g. a hard disk or a memory of the control device. The memory may in other embodiments also be an external storage device of the control device, for example a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash Card (Flash Card) or the like, provided on the control device. Further, the memory may also include both an internal memory unit of the control device and an external memory device. The memory is used to store an operating system, application programs, boot Loader (Boot Loader), data, and other programs, etc., such as program code for a computer program, etc. The memory may also be used to temporarily store data that has been output or is to be output.
In one embodiment, the swept optical signal comprises a first swept optical signal and a second swept optical signal within a single period;
the delay time between two adjacent caches of the cache ring is as follows:
wherein DeltaT represents the delay time, L represents the optical length of the buffer ring, n represents the refractive index of the light transmission material in the buffer ring, c represents the speed of light in vacuum, deltat 1 Representing the duration of the first swept optical signal in a single period δt 2 Representing the duration of the second swept optical signal in a single period δt 3 Representing the duration of the first modulated signal, L c Representing the instantaneous coherence length of the swept optical signal.
In application, the swept optical signal has two modulated signals of different durations within a single period, namely a first swept optical signal and a second swept optical signal, the second swept optical signal having a duration δt within a single period 2 Much longer than the duration δt of the first swept optical signal in a single period 1 The first sweep frequency optical signal is used for calibrating the cache times of the cache ring, and the second sweep frequency optical signal is mainly used for measuring distance information. In addition, the buffer time delta t of the buffer ring is required 3 As large as possible, the duration delta t of the second sweep optical signal in a single period is required to be longer than that of the second sweep optical signal 2 To ensure a sufficient number of caches. And meanwhile, different modulation signals meet a certain time sequence.
As shown in fig. 6, a waveform diagram of the second modulation signal and the first modulation signal is exemplarily shown; wherein the horizontal axis represents time and the vertical axis represents intensity.
As shown in fig. 7 (a), the reference optical signal output after each buffering by the buffering ring is exemplarily shown; wherein the horizontal axis represents time and the vertical axis represents intensity.
In application, the delay time delta T between two adjacent caches of the cache ring is related to the optical length L of the cache ring, namely: Δt=l/(nc). In order to realize the measurement of the cache times and the expansion of the measurement distance under the small detection bandwidth, the following conditions are required to be satisfied: δt 1 <ΔT<δt 2 . In addition, to ensure by means of short coherence lengthThe light source can realize large distance measurement, and the conditions are also required to be satisfied: l (L)<L c /2. In application, because of DeltaT<δt 2 There is an overlap between the reference optical signals output from the buffer ring, so that interference occurs between the plurality of reference optical signals output from the buffer ring at different times.
As shown in fig. 7 (b), the superposition result of a plurality of reference optical signals output by the buffer ring at different times is exemplarily shown.
In one embodiment, the frequency of the second interference signal generated by the interference between the plurality of reference optical signals output by the buffer ring at different times is:
wherein B is 1 Represents the frequency of the second interference signal, m represents the buffer number of the buffer ring, and Deltaf 1 Representing the sweep bandwidth, Δt, of the second swept optical signal 1 Representing the duration of a single period of the second swept optical signal, δt 2 。
In application, in theory, interference between multiple reference optical signals may disturb the actual measurement, but since the fundamental frequency of the second interference optical signal is Δf 1 L/(Δt 1 c) Therefore, the influence can be eliminated at the receiving end (i.e. the input end of the measuring device) by means of low-pass filtering, and the filtering bandwidth is the fundamental frequency of the second interference optical signal.
As shown in fig. 7 (c), the low-pass filtered reference optical signal is exemplarily shown.
In application, the delay of the reference optical signal is realized through the buffer ring, and meanwhile, the division of the distance to be measured is approximately realized, and the division unit is half of the optical length of the buffer ring. In a traditional coherent ranging system, the detection bandwidth is proportional to the measurement distance, and the application of the system in remote measurement is greatly limited. The coherent ranging system provided by the embodiment of the application utilizes the delay mode of the buffer ring to make the measurement optical signal interfere with the reference optical signal of the specific buffer times (nearest in time) (other interference signals cannot be measured due to overlarge bandwidth), so that the segmentation of the measurement distance is approximately realized, and the limit relation that the detection bandwidth is in direct proportion to the measurement distance in the coherent ranging system can be eliminated.
In one embodiment, the distance information of the object to be measured is:
wherein d represents the absolute distance of the object to be measured, m represents the number of times of buffering of the buffering ring, δd represents the relative distance, B 2 Representing the frequency of the first interference signal.
In application, by directly measuring the first interference light signal, according to the formula: b (B) 2 ＝2δdΔf 1 /(cΔt 1 ) The relative distance information δd may be recovered. And the absolute distance d finally measured can be obtained from the relative distance δd and the number of times the cache ring is cached to obtain m, expressed as the formula: d=ml/2+δd.
In the application, the relative distance information δd includes positive and negative. When the distance to be measured is larger, the actually measured relative distance is half of the optical length of the buffer ring, so that the instantaneous coherence length of the sweep frequency optical signal is only required to be larger than half of the optical length of the buffer ring, and the limitation of the coherence length on the measured distance in the traditional coherence ranging system can be eliminated. In the coherent ranging system provided by the embodiment of the application, the buffered reference light signals overlap with each other, so that the buffer process has little influence on the system measurement rate, and large-distance measurement can be realized at a faster rate.
In application, when performing large-distance measurement, the conventional coherent ranging system reduces the intensity of the measurement optical signal for interferometry with increasing measurement distance due to increasing transmission and reception loss, resulting in a decrease in the signal-to-noise ratio of the interference optical signal finally output to the measurement device with increasing measurement distance. The coherent ranging system provided by the embodiment of the application can realize gradual intensity increase of the reference optical signal along with the increase of the buffer times by adjusting the relation between the gain and the loss in the buffer ring, so as to approximately compensate the loss of the measurement optical signal.
As shown in fig. 8 (a), measurement results of the first interference optical signal at different distances to be measured are exemplarily shown; the horizontal axis represents time, the vertical axis represents intensity, the distance to be measured is 20.04m, 1020.04m and 1920.04m, the count of the buffering times is the first interference optical signal when the buffering times are 0, 10 and 19 respectively, the duration of the signal is 50 mu s, the corresponding measuring speed is 20kHz, and the time positions of the reference optical signals corresponding to the buffering times under different distances to be measured are different.
As shown in fig. 8 (b), the frequency and relative distance information of the first interference optical signal is exemplarily shown after fourier transformation with the measurement result of the first interference optical signal shown in fig. 8 (a); wherein the horizontal axis represents distance and frequency and the vertical axis represents intensity.
As can be seen from fig. 8 (b), the frequencies of the measurement results of the first interference light signals at different distances to be measured are substantially identical. Because the length of the buffer ring is set to be 200m in simulation, the theoretical non-fuzzy distance of measurement is 100m, and because the differences among different distances to be measured are integral multiples of the non-fuzzy distance, the relative distances obtained after Fourier transformation are nearly the same and are 20.039m, 20.041m and 20.044m respectively, so that the measurement deviation of the coherent ranging system provided by the embodiment of the application in a 2000m measurement range is less than 5mm, consistent system resolution is kept in the whole measurement range, and the required detection bandwidth is less than 1.33GHz, which is reduced by one order of magnitude compared with the traditional coherent ranging system. In addition, in the coherent ranging system provided by the embodiment of the application, the required detection bandwidth can be reduced by reducing the length of the buffer ring.
In application, the measuring device in the embodiment of the application may include a coherent receiver, and by adopting the coherent receiver to demodulate the first interference optical signal, the positive and negative of the frequency can be distinguished, and meanwhile, the dynamic range of system measurement can be further improved, and based on the coherent receiver, the non-blind area measurement of the system under different measurement distances within the range of 2000m can be realized.
As shown in fig. 9, measurement results after fourier transform of the first interference optical signal at different distances to be measured are exemplarily shown; wherein the horizontal axis represents depth, the vertical axis represents intensity, the distances to be measured are set to be 100m, 249.95m, 550.05m, 1530m and 1870m, the measured relative distance information is-0.001 m, 49.95m, -49.948m, 30.003m and-29.995 m, and the absolute measured distances are obtained by combining the number of times of buffering and are 99.999m, 249.95m, 550.052m, 1530.003m and 1870.005m, respectively, which are completely consistent with the set distances to be measured. Therefore, the coherent ranging system provided by the embodiment of the application can realize the measurement without blind areas in a measurement range of 2000 m. Meanwhile, the measurement range of the system can be further increased within the allowable range of the optical power and the measurement time, and the buffer ring can realize the buffer quantity of more than 100 times.
In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.
Those of ordinary skill in the art will appreciate that the devices of the examples described in connection with the embodiments disclosed herein can be implemented as electronic hardware, or as a combination of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
In the embodiments provided in the present application, it should be understood that the disclosed apparatus may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of units is merely a logic function division, and there may be another division manner in actual implementation, for example, a plurality of devices may be combined or may be integrated.
The above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.
Claims (10)
1. The coherent ranging system is characterized by comprising a sweep frequency light source, a first coupler, a circulator, a second coupler, a third coupler and a buffer ring, wherein the buffer ring comprises an optical delay line and a first intensity modulator;
the sweep frequency light source is used for generating a sweep frequency light signal with a preset duty cycle, a preset duration and a preset scanning waveform;
the first intensity modulator is used for controlling the switching time and the buffering times of the buffering ring according to a first modulation signal generated by the waveform generator;
the sweep frequency optical signal is split into a measuring optical signal and a reference optical signal through the first coupler;
the measuring light signal is transmitted to an object to be measured through the circulator;
the reflected light signals reflected by the object to be detected are transmitted to the second coupler through the circulator;
the reference optical signal is transmitted to the buffer ring through the third coupler, and after being respectively delayed by the optical delay line and modulated by the first intensity modulator, one part of the reference optical signal is transmitted to the buffer ring again through the third coupler, and the other part of the reference optical signal is transmitted to the second coupler through the third coupler;
the reflected light signal and the other part of reference light signal are transmitted to the measuring equipment after interference occurs in the second coupler to generate a first interference light signal;
the measuring device is used for measuring time domain information of the first interference optical signal.
2. The coherent ranging system of claim 1, wherein the swept optical source comprises a continuous optical source, a second intensity modulator, and a phase modulator;
the continuous light source is used for generating a continuous light signal;
the second intensity modulator is used for adjusting the duration time and the time domain waveform of the continuous optical signal according to the second modulation signal generated by the waveform generator;
the phase modulator is used for adjusting the phase of the continuous optical signal adjusted by the second intensity modulator according to a third modulation signal generated by the waveform generator;
and after the continuous optical signals are modulated by the second intensity modulator and the phase modulator respectively, sweep-frequency optical signals with preset duty ratios, preset duration time and preset scanning waveforms are formed.
3. The coherent ranging system of claim 1, wherein the swept optical source comprises a distributed feedback laser.
4. A coherent ranging system according to any one of claims 1 to 3, wherein the buffer loop further comprises an optical amplifier and an optical bandpass filter;
the reference optical signal is transmitted to the buffer ring through the third coupler, and is amplified by the optical amplifier, filtered by the optical band-pass filter, delayed by the optical delay line and modulated by the first intensity modulator respectively, one part of the reference optical signal is transmitted to the buffer ring again through the third coupler, and the other part of the reference optical signal is transmitted to the second coupler through the third coupler.
5. A coherent ranging system according to any of claims 1-3, wherein the buffer loop further comprises a first polarization controller;
the first polarization controller is used for controlling the polarization state of the reference light signal.
6. A coherent ranging system according to any one of claims 1-3, further comprising at least one of a second polarization controller and a collimator;
the second polarization controller is used for controlling the polarization state of the measurement light signal;
the measurement light signal is transmitted to the circulator after the polarization state of the measurement light signal is regulated by the second polarization controller;
and the measuring light signal is transmitted to the collimator through the circulator to be collimated and then transmitted to the object to be measured.
7. A coherent ranging system according to any one of claims 1 to 3, further comprising a scanning galvanometer;
the scanning galvanometer is used for adjusting the incidence position of a measuring light signal transmitted to an object to be measured so as to scan the object to be measured in two dimensions or three dimensions.
8. A method of coherent ranging implemented based on the coherent ranging system of any of claims 1 to 7, the method comprising:
controlling the sweep frequency light source to generate a sweep frequency light signal with a preset duty ratio, a preset duration and a preset scanning waveform;
controlling the waveform generator to generate a first modulation signal so that the first intensity modulator controls the switching time and the buffering times of the buffering ring according to the first modulation signal;
and obtaining the distance information of the object to be measured according to the time domain information of the first interference light signal measured by the measuring equipment.
9. The coherent ranging method of claim 8, wherein said swept optical signal comprises a first swept optical signal and a second swept optical signal within a single period;
the delay time between two adjacent caches of the cache ring is as follows:
wherein DeltaT represents the delay time, L represents the optical length of the buffer ring, n represents the refractive index of the light transmission material in the buffer ring, c represents the speed of light in vacuum, deltat 1 Representing the duration of the first swept optical signal in a single period δt 2 Representing the duration of the second swept optical signal in a single period δt 3 Representing the duration of the first modulated signal, L c Representing the instantaneous coherence length of the swept optical signal.
10. The coherent ranging method according to claim 9, wherein the distance information of the object to be measured is:
wherein d represents the absolute distance of the object to be measured, m represents the cache times of the cache ring, and δd represents the relative distance.
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