A ranging device and method incorporating pseudo code and dual optical combs

Abstract

This invention discloses a ranging device and method combining pseudocode and dual optical combs, belonging to the field of dual optical comb ranging technology. The light from the signal optical comb is modulated by a pseudocode through an acousto-optic modulator. One path of the modulated light serves as the reference light, and the other as the measurement light. Both paths pass through a beam splitter and enter a photodetector. The photodetector converts the optical signal into an electrical signal. An electrical filter filters out a sinusoidal signal with the repetition frequency of the optical comb as the carrier. Since this signal contains pseudocode modulation information, the time-of-flight of the pseudocode can be obtained by performing an autocorrelation operation on the filtered signals from the first and second photodetectors, thus yielding the distance to be measured. This invention provides a simple and easy-to-use method for effectively extending the unambiguous range of dual-comb ranging systems, and has certain application value in ultra-large-scale measurement scenarios.

Description

Technical Field

[0001] This invention belongs to the field of dual-comb ranging technology, and more specifically, relates to a ranging device and method that combines pseudocode and dual-comb. Background Technology

[0002] Distance measurement is of great significance in both scientific and technological fields, such as equipment manufacturing, biomedical imaging, and gravitational wave detection. Generally, there are two different methods for measuring distance: incremental measurement and absolute measurement. In the former, the target mirror moves along the measurement beam, and the photodetector continuously receives the returned signal without interruption. Therefore, the incremental distance can be read out from the fringes of the interference signal. Absolute measurement, on the other hand, does not require continuous detection of the returned signal and can determine the distance absolutely, such as using the time-of-flight method or multi-wavelength interferometry.

[0003] With the development of optical frequency comb technology, the precision measurement of large-scale absolute distances has made a qualitative leap. Among these, absolute distance measurement using a dual-comb asynchronous sampling method can achieve sub-micrometer accuracy, but due to limitations in the interval between pulses, the unambiguous range of dual-comb ranging is on the order of meters. Pseudo-code ranging technology, utilizing the good autocorrelation of pseudo-codes and their relatively long chip width, is widely used in large-scale measurements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a ranging device and method that combines pseudo-code and dual optical comb, thereby solving the problem of a small non-ambiguous range in dual optical comb ranging.

[0005] To achieve the above objectives, this invention provides a ranging device combining pseudocode and dual optical combs, comprising a signal optical comb, a sampling optical comb, an acousto-optic modulator, a first beam splitter, a circulator, a first collimator, a measuring mirror, a second beam splitter, a first photodetector, a third beam splitter, a second photodetector, a first beam combiner, a second beam combiner, a second collimator, an optical bandpass filter, a third photodetector, and a high-speed oscilloscope. The signal light emitted from the signal optical comb passes through the acousto-optic modulator, which is used to apply pseudocode modulation. The modulated signal light can then be written as: Where A(t) is the amplitude of the pseudocode modulation, f rep1 It is the repetition frequency of the signal light. This is the initial phase. The modulated signal light is then split into two beams by the first beam splitter. One beam serves as the reference beam, and the other as the measurement beam. The measurement beam enters the circulator, the first collimator, and the distance to be measured L1, and is reflected by the measuring mirror, returning to the first collimator and the circulator. At this point, the measurement beam can be written as: The measurement light is split into a dual-comb measurement light and a pseudo-code measurement light by a second beam splitter, and the pseudo-code measurement light enters the second photodetector. The reference light can be written as: The reference light is split into a dual-comb reference light and a pseudo-code reference light by a third beam splitter. The pseudo-code reference light enters the first photodetector. The dual-comb measurement light and the dual-comb reference light are combined by a first beam combiner, and then combined with the sampling light emitted from the sampling comb to form a dual-comb interference light. The dual-comb interference light passes through a second collimator and an optical bandpass filter before entering the third photodetector. The first, second, and third photodetectors are connected to electrical filters and then enter a high-speed oscilloscope. By performing autocorrelation on the pseudo-code reference path data after the first photodetector and the pseudo-code measurement path data after the second photodetector, a coarse large number L of the distance to be measured can be calculated. PRN Then, the decimal distance to be measured is obtained from the interference fringes of the two-comb light: Lcomb = c × Δt × Δf rep / 2 / f rep1 Where Δt is the time difference between the two-comb interference fringes, and Δf rep The difference lies in the signal optical comb and the sampling optical comb. Because the pseudo code has a longer pseudo code period, the pseudo code ranging has a larger unambiguous ranging range, which can broaden the unambiguous ranging range of the dual optical comb.

[0006] Furthermore, the acousto-optic modulator is used to load pseudo-code modulation, and the modulation method is amplitude modulation. The pseudo-code symbol width and chip length can be designed according to actual needs.

[0007] The circulator has a unidirectional conduction function.

[0008] The height and tilt angle of the collimator and the measuring mirror are set so that the light is on the same horizontal plane.

[0009] The sampling optical comb and the measurement optical comb are locked to the same stable reference source.

[0010] The sampling optical comb and the measuring optical comb have a certain difference in repetition frequency.

[0011] The high-speed oscilloscope has a sampling frequency of 100MHz-20GHz and a sampling time of 100us to 10ms.

[0012] The ranging result is determined by the pseudocode ranging value and the dual-comb ranging value:

[0013]

[0014] Where round means rounding down.

[0015] This invention also provides a ranging method combining pseudocode and dual optical comb, comprising the following steps:

[0016] The signal light is modulated with a pseudocode, and then split into two beams: a reference beam and a measurement beam. The measurement beam is reflected after passing the distance to be measured, L1, and then split into a dual-comb measurement beam and a pseudocode measurement beam. The pseudocode measurement beam is measured to obtain pseudocode measurement path data. The reference beam is split into a dual-comb reference beam and a pseudocode reference beam. The pseudocode reference beam is measured to obtain pseudocode reference path data. The dual-comb measurement beam and the dual-comb reference beam are combined, and then combined with the sampling beam to form a dual-comb interference beam. The dual-comb interference beam is collimated and filtered, and the dual-comb interference fringes are measured. By performing autocorrelation on the pseudocode reference path data and the pseudocode measurement path data, a large number greater than the ambiguity range of dual-comb ranging is obtained. Then, by the time difference between the dual-comb interference fringes, a small number of the distance to be measured is obtained. By combining the large number and the small number, the distance to be measured is obtained, thus widening the unambiguous range of dual-comb ranging.

[0017] The process involves acquiring data from the pseudocode measurement light and the pseudocode reference light using a high-speed oscilloscope. Then, an autocorrelation operation is performed on these two sets of data. The time corresponding to the maximum peak of the autocorrelation operation is the flight time of the pseudocode, which allows the distance to be measured to be obtained. Since the pseudocode has a relatively long chip width, the unambiguous range of the dual-comb ranging can be widened.

[0018] Furthermore, the expression for the pseudocode reference light acquired by the oscilloscope is written as follows:

[0019]

[0020] The expression for measuring light using pseudocode acquired by the oscilloscope is written as follows:

[0021]

[0022] Perform an autocorrelation operation on the data from the pseudocode reference light and the data from the pseudocode measurement light:

[0023]

[0024] The time corresponding to the maximum autocorrelation value is the pseudocode's time of flight:

[0025] τ PRN =max(Ryy(τ))

[0026] Where A(t) is the amplitude of the pseudocode modulation, c is the speed of light, and f is the amplitude of the pseudocode modulation. rep1 It is the repetition frequency. It is the initial phase, and τ is the data translation time;

[0027] A rough estimate of the distance to be measured can be obtained from the flight time of the pseudocode:

[0028] LPRN=cτPRN / 2

[0029] A more accurate ranging value is obtained from the interference fringes of the two-comb optical array:

[0030] Lcomb=c×Δt×Δf rep / 2 / f rep1

[0031] Where Δt is the time difference between the two-comb interference fringes, and Δf rep The difference lies in the signal optical comb and the sampling optical comb.

[0032] The final ranging result is obtained by combining the large number determined by the pseudocode ranging and the small number determined by the dual-comb ranging:

[0033]

[0034] Where round means rounding down.

[0035] Compared with the prior art, the present invention provides a practical device and method for expanding the unambiguous range of dual-comb ranging using pseudo-code. By applying pseudo-code modulation to the optical comb using an acousto-optic modulator, and performing autocorrelation calculations on the signals of the pseudo-code reference path and the pseudo-code measurement path, the flight time of the pulse can be obtained. Since the pseudo-code has a relatively long period, the blind zone of pseudo-code ranging is tens of kilometers. The ranging accuracy of the pseudo-code is limited by the signal-to-noise ratio and sampling rate, reaching the millimeter level, effectively covering the blind zone of dual-comb ranging, thereby expanding the unambiguous range of dual-comb ranging and enabling large-scale absolute distance measurement. Attached Figure Description

[0036] Figure 1 This is a structural block diagram of a ranging device combining pseudocode and dual optical comb provided in an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0038] See Figure 1In one embodiment, a ranging device combining pseudocode and dual optical combs is provided. The device includes a signal optical comb 1, a sampling optical comb 2, an acousto-optic modulator 3, a first beam splitter 4, a circulator 5, a first collimator 6, a measuring mirror 7, a second beam splitter 8, a first photodetector 9, a third beam splitter 10, a second photodetector 11, a first beam combiner 12, a second beam combiner 13, a second collimator 14, an optical bandpass filter 15, a third photodetector 16, and a high-speed oscilloscope 17. The signal light emitted from the signal optical comb 1 passes through the acousto-optic modulator 2. Since the acousto-optic modulator 2 requires an external radio frequency signal as its trigger, the amplitude of the signal light can be modulated by switching it on and off. A pseudo-code is injected into the acousto-optic modulator in the form of voltage through a signal source. When the voltage is less than the driving threshold of the acousto-optic modulator, the signal light is zero, corresponding to the 0 value of the pseudo-code. When the voltage is greater than the driving threshold of the acousto-optic modulator, there is signal light, corresponding to the 1 value of the pseudo-code. Therefore, a sequence of 0101 pseudo-code is modulated onto the signal light in the form of voltage. The modulated signal light can be written as: Where A(t) is the amplitude of the pseudocode modulation, f rep1 It is the repetition frequency of the signal light. This is the initial phase. The modulated light then passes through the first beam splitter and is divided into two beams: one as the reference beam and the other as the measurement beam. The measurement beam enters the circulator, the first collimator, and the distance to be measured L1, is reflected by the object under test, and returns to the first collimator and the circulator. The measurement beam at this point is written as: Next, the measurement light is split into a dual-comb measurement light and a pseudo-code measurement light by the second beam splitter, with the pseudo-code measurement light entering the second photodetector. The reference light is split into a dual-comb reference light and a pseudo-code reference light by the third beam splitter. The reference light is written as: The pseudo-code reference light enters the first photodetector. The dual-comb measurement light and the dual-comb reference light are combined by the first beam combiner, and then combined with the sampling light comb to form a dual-comb interference light. This interference light then passes through the second collimator and an optical bandpass filter before entering the third photodetector. The first, second, and third photodetectors are each connected to an electrical filter before entering a high-speed oscilloscope. By performing autocorrelation on the pseudo-code reference path data obtained from the first photodetector and the pseudo-code measurement path data obtained from the second photodetector, the time corresponding to the maximum autocorrelation peak is the flight time of the light comb. A rough measurement distance can be calculated from the flight time, and the precise measurement distance value is obtained from the dual-comb interference fringes: Lcomb = c × Δt × Δf rep / 2 / f rep1 Where Δt is the time difference between the two-comb interference fringes, and Δf repThe difference lies in the signal optical comb and the sampling optical comb. Because the pseudo code has a longer pseudo code period, the pseudo code ranging has a larger unambiguous ranging range, which can broaden the unambiguous ranging range of the dual optical comb.

[0039] Furthermore, the acousto-optic modulator is used to load pseudo-code modulation, and the modulation method is amplitude modulation. The pseudo-code symbol width and chip length can be designed according to actual needs.

[0040] The circulator has a unidirectional conduction function.

[0041] The height and tilt angle of the collimator and the measuring mirror are set so that the light is on the same horizontal plane.

[0042] The sampling optical comb and the measurement optical comb are locked to the same stable reference source.

[0043] The high-speed oscilloscope has a sampling frequency of 100MHz-50GHz and a sampling time of 100us to 10ms.

[0044] The ranging result is determined by the pseudocode ranging value and the dual-comb ranging value:

[0045]

[0046] Where round means rounding down.

[0047] A ranging method combining pseudocode and dual optical comb is disclosed, wherein data of the pseudocode measurement light and pseudocode reference light are acquired by a high-speed oscilloscope, and then autocorrelation is performed on the two sets of data. The time corresponding to the maximum peak of the autocorrelation operation is the flight time of the pseudocode, thereby obtaining the distance to be measured. Since the pseudocode has a relatively long chip width, the unambiguous range of dual optical comb ranging can be widened.

[0048] Furthermore, the expression for the pseudocode reference light acquired by the oscilloscope is written as follows:

[0049]

[0050] The expression for measuring light using pseudocode acquired by the oscilloscope is written as follows:

[0051]

[0052] Perform an autocorrelation operation on the data from the pseudocode reference light and the data from the pseudocode measurement light:

[0053]

[0054] The time corresponding to the maximum autocorrelation value is the pseudocode's time of flight:

[0055] τ PRN =max(Ryy(τ))

[0056] Where A(t) is the amplitude of the pseudocode modulation, c is the speed of light, and f is the amplitude of the pseudocode modulation. rep1 It is the repetition frequency. It is the initial phase, and τ is the data translation time;

[0057] A rough estimate of the distance to be measured can be obtained from the flight time of the pseudocode:

[0058] LPRN=cτ PRN / 2

[0059] The precise ranging value is obtained from the interference fringes of the two-comb optical filter:

[0060] Lcomb=c×Δt×Δf rep / 2 / f rep1

[0061] Where Δt is the time difference between the two-comb interference fringes, and Δf rep The difference lies in the signal optical comb and the sampling optical comb.

[0062] The final ranging result is obtained by combining the large number determined by the pseudocode ranging and the small number determined by the dual-comb ranging:

[0063]

[0064] Where round means rounding down.

[0065] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A ranging device combining pseudocode and dual optical comb, characterized in that, The system includes a signal optical comb, a sampling optical comb, an acousto-optic modulator, a first beam splitter, a circulator, a first collimator, a measuring mirror, a second beam splitter, a first photodetector, a third beam splitter, a second photodetector, a first beam combiner, a second beam combiner, a second collimator, an optical bandpass filter, a third photodetector, and a high-speed oscilloscope. The signal light emitted from the signal optical comb passes through the acousto-optic modulator, which is used to load pseudo-code modulation. The modulated signal light is split into two beams by the first beam splitter: one beam is a reference beam, and the other is a measurement beam. The measurement beam passes sequentially through the circulator, the first collimator, and the distance to be measured L1, and is then reflected by the measuring mirror, returning to the first collimator and the circulator. It then enters the second beam splitter and is split into a dual-comb measurement beam and a pseudo-code measurement beam. The pseudo-code measurement beam enters the second photodetector. The reference light is split into a dual-comb reference light and a pseudo-code reference light by a third beam splitter. The pseudo-code reference light enters the first photodetector. The dual-comb measurement light and the dual-comb reference light are combined by a first beam combiner and then combined with the sampling light emitted from the sampling comb to form a dual-comb interference light. The dual-comb interference light enters the third photodetector after passing through a second collimator and an optical bandpass filter. The first, second, and third photodetectors are connected to electrical filters and then enter a high-speed oscilloscope. By performing autocorrelation on the pseudo-code reference path data obtained from the first photodetector and the pseudo-code measurement path data obtained from the second photodetector, a large number greater than the ambiguity range of dual-comb ranging is obtained. Then, by using the time difference between the dual-comb interference fringes obtained from the third photodetector, a small number of the distance to be measured is obtained. By combining the large number and the small number, the distance to be measured is obtained, thus widening the unambiguous range of dual-comb ranging.

2. The apparatus according to claim 1, characterized in that, The signal light, reference light, pseudocode reference light, and dual-comb reference light are: The dual-comb measurement light and the pseudocode measurement light are: Where A(t) is the amplitude of the pseudocode modulation, c is the speed of light, and f is the amplitude of the pseudocode modulation. rep1 It is the repetition frequency of the signal light. It is the initial phase.

3. The apparatus according to claim 2, characterized in that, The autocorrelation of the pseudocode reference path data obtained by the first photodetector and the pseudocode measurement path data obtained by the second photodetector is expressed as follows: The time corresponding to the maximum autocorrelation value is the pseudocode's time of flight: τ PRN = max(Ryy(τ)) We obtain a large number greater than the ambiguity range of dual-comb ranging: LPRN = cτ PRN / 2 Where τ is the time of data translation.

4. The apparatus according to claim 3, characterized in that, The dual-comb measuring light, dual-comb reference light, and sampling light undergo dual-comb interference to form dual-comb interference light. The decimal of the distance to be measured is obtained by the time difference between the dual-comb interference fringes. Lcomb = c x At x Df rep / 2 / f rep1 Where Δt is the time difference between the two-comb interference fringes, and Δf rep It is the frequency difference between the signal optical comb and the sampling optical comb.

5. The apparatus according to claim 4, characterized in that, The distance to be measured is: Here, round means rounding down.

6. A ranging method combining pseudocode and dual optical comb based on the device according to any one of claims 1 to 5, characterized in that, Includes the following steps: The signal light is modulated with a pseudocode, and then split into two beams: a reference beam and a measurement beam. The measurement beam is reflected after passing the distance to be measured, L1, and then split into a dual-comb measurement beam and a pseudocode measurement beam. The pseudocode measurement beam is measured to obtain pseudocode measurement path data. The reference beam is split into a dual-comb reference beam and a pseudocode reference beam. The pseudocode reference beam is measured to obtain pseudocode reference path data. The dual-comb measurement beam and the dual-comb reference beam are combined, and then combined with the sampling beam to form a dual-comb interference beam. The dual-comb interference beam is collimated and filtered, and the dual-comb interference fringes are measured. By performing autocorrelation on the pseudocode reference path data and the pseudocode measurement path data, a large number greater than the ambiguity range of dual-comb ranging is obtained. Then, by the time difference between the dual-comb interference fringes, a small number of the distance to be measured is obtained. By combining the large number and the small number, the distance to be measured is obtained, thus widening the unambiguous range of dual-comb ranging.

7. The method according to claim 6, characterized in that, The signal light, reference light, pseudocode reference light, and dual-comb reference light are: The dual-comb measurement light and the pseudocode measurement light are: Where A(t) is the amplitude of the pseudocode modulation, c is the speed of light, and f is the amplitude of the pseudocode modulation. rep1 It is the repetition frequency of the signal light. It is the initial phase.

8. The method according to claim 7, characterized in that, The autocorrelation of the pseudocode reference path data and the pseudocode measurement path data is expressed as follows: The time corresponding to the maximum autocorrelation value is the pseudocode's time of flight: t PRN =max(Ryy(τ)) We obtain a large number greater than the ambiguity range of dual-comb ranging: LPRN=cτ PRN / 2 Where τ is the time of data translation.

9. The method according to claim 8, characterized in that, The dual-comb measuring light, dual-comb reference light, and sampling light undergo dual-comb interference to form dual-comb interference light. The decimal of the distance to be measured is obtained by the time difference between the dual-comb interference fringes. Lcomb=c×Δt×Δf rep / 2 / f rep1 Where Δt is the time difference between the two-comb interference fringes, and Δf rep It is the frequency difference between the signal optical comb and the sampling optical comb.

10. The method according to claim 9, characterized in that, The distance to be measured is: Here, round means rounding down.

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