All-fiber range-extended frequency-domain interferometric ranging method and device based on optical microwave mapping

Abstract

A method and apparatus for all-fiber range-extended frequency-domain interferometric ranging based on optical microwave mapping are disclosed. The method is used to measure the distance information of a target. The method includes: Step S1, sending a broadband spectrum to a ranging probe, which splits the broadband spectrum into a reference beam and a signal beam; Step S2, the ranging probe sends the signal beam to the target and receives the reflected signal beam, coupling it with the reference beam to form an interference signal; Step S3, analyzing the interference signal to obtain the distance information to the target; and the apparatus is used for ranging the target. This invention has the advantages of simple structure, long range, and micron-level accuracy.

Description

Technical Field

[0001] This invention relates to the field of optical ranging technology, and in particular to an all-fiber range-extended frequency domain interferometric ranging method and apparatus based on optical microwave mapping. Background Technology

[0002] Optical interferometry is widely used in fields such as spatial distance measurement, thin film thickness measurement, precision machining of workpieces, and precision control of displacement machinery due to its advantages such as high precision, strong anti-interference ability, and suitability for complex environments.

[0003] Currently, many optical interferometric ranging techniques have been proposed, such as laser heterodyne interferometry displacement measurement, frequency modulated continuous wave (FMCW) ranging, and broadband optical interferometry. Among them, laser heterodyne interferometry can measure the frequency or phase change of the Doppler frequency shift signal caused by displacement. In recent years, by using methods such as nonlinear phase compensation, improved signal processing circuits, and electronic subdivision, displacement measurement capabilities with resolutions of tens to hundreds of picometers have been achieved within a range of hundreds of millimeters. However, the laser heterodyne interferometry method cannot interrupt fringe counting during the measurement process, making it impossible to achieve absolute distance measurement. FMCW ranging, by measuring the frequency difference between emitted and reflected frequency-modulated lasers, can achieve micrometer-level precision ranging within a meter-level range. When high ranging accuracy is required, the large bandwidth and high linearity of the light source lead to high cost and complex structure. Furthermore, key technologies such as frequency sweep nonlinear correction and spectrum analysis also affect the ranging range and accuracy, increasing the complexity of system design. For optical frequency domain interferometric ranging methods based on spectrometers, the superposition of light waves with different optical paths can form interference fringes to analyze distance information. Currently, the engineering measurement range can reach 17 cm, and the ranging accuracy can reach the micrometer level. Since the period of the interference fringes is inversely proportional to the distance to be measured, and the resolution bandwidth of spectrometers is generally 0.02 nm, the theoretical measurement distance can only reach 24 cm. Once the distance to be measured is too long, the spectrometer cannot identify and record the complete period. High requirements for improving the resolution bandwidth of optical instruments limit the range expansion in engineering fields. To date, optical absolute distance measurement technology with simple structure, long range, and micrometer-level accuracy remains one of the most pressing frontier directions in this field. Summary of the Invention

[0004] The purpose of this invention is to provide an all-fiber range-extended frequency domain interferometric ranging method and device based on optical microwave mapping, which has the advantages of simple structure, long range and micron-level accuracy.

[0005] To achieve the above objectives, the present invention provides an all-fiber extended-range frequency-domain interferometric ranging method based on optical microwave mapping. The method is used to measure the distance information of a target. The method includes: step S1, sending a broadband spectrum to a ranging probe, which divides the broadband spectrum into a reference beam and a signal beam; step S2, the ranging probe sending the signal beam to the target and receiving the reflected signal beam, coupling it with the reference beam to form an interference signal; and step S3, analyzing the interference signal to obtain the distance information to the target.

[0006] Preferably, step S1 includes: step S11, sending a broadband spectrum to the ranging probe to obtain the light intensity of the reference beam at time t. and the intensity of the signal beam at time t ;

[0007]

[0008]

[0009] in, t represents the total intensity of the broadband spectrum; A represents the percentage of the total intensity of the broadband spectrum occupied by the reference beam; B represents the percentage of the total intensity of the broadband spectrum occupied by the signal beam. This is a time delay.

[0010] Step S12: Obtain the electric field signal of the reference beam. With signal beam electric field signal ;

[0011]

[0012]

[0013] in, It is the broadband spectral electric field signal at time t;

[0014] Preferably, step S2 includes: step S21, the ranging probe sends a signal beam to the target and receives the reflected signal beam, couples it with a reference beam to form an interference signal, and obtains a time-domain interference signal. ;

[0015]

[0016] Step S22, for the time-domain interferometric signal Perform a Fourier transform to obtain the frequency domain interference signal. ;

[0017]

[0018] in, It is the frequency of light.

[0019] Preferably, step S3 includes: step S31, performing photodetector analysis on the time-domain interferometric signal, and obtaining the current expression. for:

[0020]

[0021] in, This represents the DC term of the photocurrent at time t; This represents the interference signal term of the photocurrent at time t; Indicates the responsivity of the photodetector;

[0022] Step S32, obtain spectral density ;

[0023]

[0024] in, The spectral intensity of the broadband spectrum;

[0025] Step S33: Obtain the current spectral density ;

[0026]

[0027] ,

[0028] in, It is the effective bandwidth of the photodetector; This represents the phase shift of the sinusoidal interference signal;

[0029] Step S34, verify the current spectral density With spectral density Does the self-convolution satisfy: If the condition is met, proceed to step S35; otherwise, return to step S1.

[0030] Step S35, according to Obtain the distance to be measured ;

[0031] in, It is the speed of light.

[0032] A full-fiber range-extended frequency-domain interferometric ranging device based on optical microwave mapping is described above. The device is used to measure the distance to a target and includes: a light source transmitter for emitting a broadband spectrum; an optical fiber circulator connected to the light source transmitter to receive and transmit the broadband spectrum; a ranging probe connected to the optical fiber circulator to receive the broadband spectrum from the circulator; a first broadband spectrum forming a reference beam inside the ranging probe, and a second broadband spectrum emitted towards the target, receiving the signal beam reflected from the target; the reference beam and the signal beam coupling within the ranging probe to form an interference signal, which is transmitted to the optical fiber circulator; and an analysis module connected to the optical fiber circulator to receive and analyze the interference signal to obtain the distance to be measured.

[0033] Preferably, the ranging probe consists of a single-mode fiber, a focusing lens, and a metal housing; when the broadband spectrum enters the single-mode fiber of the ranging probe through the fiber circulator, the broadband spectrum is reflected at the end face of the single-mode fiber due to the Fresnel effect, serving as a reference beam.

[0034] Preferably, the analysis module includes: a photodetector connected to an optical fiber circulator to receive interference signals from the optical fiber circulator, analyze the interference signals using the photodetector, and obtain a converted interference signal; a spectrum analyzer connected to the photodetector to receive the converted interference signal and perform spectral density analysis and current spectral density analysis on it; and a computer connected to the spectrum analyzer to receive the spectral density analysis results and current spectral density analysis results, and then calculate the distance information.

[0035] Preferably, the fiber optic circulator includes: a first port connected to a light source transmitter to receive a broadband spectrum; a second port connected to the first port and connected to a ranging probe to transmit the broadband spectrum to the ranging probe and receive interference signals; and a third port connected to the first and second ports and connected to a photodetector to receive interference signals and transmit them to the photodetector.

[0036] In summary, compared with the prior art, the all-fiber range-extended frequency domain interferometric ranging method and device based on optical microwave mapping provided by the present invention has the following beneficial effects:

[0037] First, this invention overcomes the limitations on the measurement range imposed by factors such as the resolution and bandwidth of spectrometers in traditional optical ranging technology in principle.

[0038] Secondly, the technology described in this invention patent can achieve high-precision absolute distance measurement over a large range without the need for additional precision optical components. Compared with ranging methods such as femtosecond lasers or optical frequency combs, the system has a simpler structure, lower cost, and is easier to construct.

[0039] Third, this invention uses only a simple FFT (Fast Fourier Transform) to process the frequency domain signal, resulting in a low signal-to-noise ratio in the interferogram, making it suitable for complex engineering environments. Attached Figure Description

[0040] Figure 1 This invention relates to an all-fiber range-extended frequency domain interferometric ranging device based on optical microwave mapping.

[0041] Figure 2 The interference fringes are preserved by two instruments in this embodiment of the invention.

[0042] Figure 3 The frequency domain interference fringes in the range of 5.08 m are shown in this embodiment of the invention.

[0043] Figure 4 The data results of 100 measurements were performed on the target object in this embodiment of the invention.

[0044] Figure 5 This is a flowchart illustrating the all-fiber range-extended frequency domain interferometric ranging method based on optical microwave mapping proposed in this invention.

[0045] Figure label:

[0046] 101-Light source emitter, 102-Fiber optic circulator, 103-Range measuring probe, 104-Photodetector, 105-Spectrum analyzer, 106-Computer, 107-Target under test, 1-First port, 2-Second port, 3-Third port. Detailed Implementation

[0047] The following will be combined with the appendix in the embodiments of the present invention. Figure 1 ~Appendix Figure 5 The technical solutions, structural features, objectives and effects achieved in the embodiments of the present invention will be described in detail.

[0048] It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions. They are only used to facilitate and clarify the purpose of illustrating the embodiments of the present invention, and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationship, or adjustments to the size should still fall within the scope of the technical content disclosed in the present invention, provided that they do not affect the effects and objectives that the present invention can produce.

[0049] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only the expressly listed elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0050] This invention proposes an all-fiber range-extended frequency-domain interferometric ranging method and device based on optical microwave mapping. For example... Figure 5 As shown, the method is used to measure the distance information of the target to be measured, and the method includes:

[0051] Step S1: Send a broadband spectrum to the ranging probe, which divides the broadband spectrum into a reference beam and a signal beam;

[0052] The reference beam is the beam of light produced by reflection within the ranging probe due to the Fresnel effect after the broadband spectrum enters the probe. The signal beam is the beam of light transmitted to the target after the broadband spectrum enters the probe.

[0053] Step S2: The ranging probe sends a signal beam to the target and receives the reflected signal beam, which couples with the reference beam to form an interference signal.

[0054] Step S3: Analyze the interference signal to obtain the distance information to the target.

[0055] Specifically, step S1 includes:

[0056] Step S11: Send a broadband spectrum to the ranging probe to obtain the light intensity of the reference beam at time t. and the intensity of the signal beam at time t ;

[0057]

[0058]

[0059] in, t represents the total intensity of the broadband spectrum; A represents the percentage of the total intensity of the broadband spectrum occupied by the reference beam; B represents the percentage of the total intensity of the broadband spectrum occupied by the signal beam; the signal beam experiences a time delay because its optical path is longer than that of the reference beam by the measured distance. .

[0060] Step S12: Obtain the electric field signal of the reference beam. With signal beam electric field signal ;

[0061]

[0062]

[0063] in, It is the electric field signal of the broadband spectrum at time t.

[0064] Specifically, step S2 includes:

[0065] Step S21: The ranging probe sends a signal beam to the target and receives the reflected signal beam, which couples with the reference beam to form an interference signal, thus acquiring the time-domain interference signal. ;

[0066]

[0067] Step S22, for the time-domain interferometric signal Perform a Fourier transform to obtain the frequency domain interference signal. ;

[0068]

[0069] in, It is the frequency of light.

[0070] Specifically, step S3 includes:

[0071] Step S31: Perform photodetector analysis on the time-domain interferometric signal, current expression. for:

[0072]

[0073] in, This represents the DC term of the photocurrent at time t; This represents the interference signal term of the photocurrent at time t; Indicates the responsivity of the photodetector;

[0074] Step S32, obtain spectral density ;

[0075]

[0076] in, The spectral intensity of the broadband spectrum;

[0077] Step S33: Obtain the current spectral density ;

[0078]

[0079] ,

[0080] in, It is the effective bandwidth of the photodetector; This indicates the phase shift of the sinusoidal interference signal.

[0081] Step S34, verify the current spectral density With spectral density Does the self-convolution satisfy: If the condition is met, proceed to step S35; otherwise, return to step S1.

[0082] The principle here is that if the current spectral density With spectral density The self-convolution is proportional; this indicates that the current spectral density function after photoelectric conversion is... Within the effective response range of the photodetector and the spectral density function The fact that they have the same periodicity demonstrates the feasibility of converting optical interference fringes into microwave interference fringes.

[0083] Step S35, according to Obtain the distance to be measured ;

[0084] in, It is the speed of light.

[0085] The above analysis shows that frequency-domain interferometric absolute distance measurement based on optical microwave mapping only requires obtaining the frequency-domain interferometric spectrum over a wide bandwidth. After photoelectric conversion, the transmission time difference can be obtained using inverse Fourier transform, and the absolute distance information of the target object can then be calculated. Assuming that the sinusoidal AC components of the current spectral density function carrying distance information and the spectral density function have the same period, this demonstrates the feasibility of mapping the optical wave interferometric signal to the microwave frequency band after photoelectric conversion for signal processing.

[0086] In addition, this invention also proposes an all-fiber extended-range frequency domain interferometric ranging device based on optical microwave mapping; the device is used to measure the distance to the target 107, and the device includes:

[0087] Light source emitter 101 is used to emit broadband spectrum;

[0088] The fiber optic circulator 102 is connected to the light source transmitter 101, receives the broadband spectrum from the light source transmitter 101, and transmits it.

[0089] The ranging probe 103 is connected to the fiber optic circulator 102 and receives the broadband spectrum from the fiber optic circulator 102; the first broadband spectrum forms a reference beam inside the ranging probe 103, and the second broadband spectrum is emitted toward the target 107 and receives the signal beam reflected by the target 107; the reference beam and the signal beam are coupled in the ranging probe 103 to form an interference signal, which is transmitted to the fiber optic circulator 102.

[0090] The analysis module is connected to the fiber optic circulator 102, receives the interference signal from the fiber optic circulator 102, analyzes it, and obtains the distance to be measured.

[0091] In a specific embodiment, the ranging probe 103 consists of a single-mode optical fiber, a focusing lens, and a metal housing. When a broadband spectrum enters the single-mode optical fiber of the ranging probe 103 through the fiber optic circulator 102, the broadband spectrum is reflected at the end face of the single-mode optical fiber due to the Fresnel effect, serving as a reference beam. The specific structure of the ranging probe 103 is prior art and is sufficient to achieve the aforementioned technical effects; therefore, it will not be elaborated upon here.

[0092] Specifically, the analysis module includes:

[0093] The photodetector 104 is connected to the fiber optic circulator 102, receives the interference signal from the fiber optic circulator 102, analyzes the interference signal through the photodetector 104, and obtains the converted interference signal.

[0094] The spectrum analyzer 105 is connected to the photodetector 104, which receives the converted interference signal and performs spectral density analysis and current spectral density analysis on it.

[0095] Computer 106 is connected to spectrum analyzer 105 to receive spectral density analysis results and current spectral density analysis results, and then calculates distance information.

[0096] At the same distance, after multiple verifications as described above, the transmission time difference can be obtained directly by performing an inverse Fourier transform on the interference signal in the photodetector 104 (equivalent to skipping the verification part of the spectral density analysis results and current spectral density analysis results), and then the distance information can be calculated.

[0097] Specifically, in a preferred embodiment, the fiber optic circulator 102 includes:

[0098] The first port 1 is connected to the light source emitter 101 to receive broadband spectrum;

[0099] The second port 2 is connected to the first port 1 and to the ranging probe 103. It transmits broadband spectrum to the ranging probe 103 and receives interference signals.

[0100] The third port 3 is connected to the first port 1 and the second port 2, and is connected to the photodetector 104 to receive interference signals and transmit them to the photodetector 104.

[0101] By distributing three ports within the fiber optic circulator 102, independent operation between the ports and components is achieved, reducing the impact of optical path transmission between them.

[0102] The following are specific examples.

[0103] Because the spectrum analyzer 105 in this system has a resolution bandwidth of 1 MHz within a 20 GHz passband, it is far superior to the fiber optic spectrometer with a resolution bandwidth of 0.62 GHz in previous studies. The minimum resolution bandwidth of the spectrum analyzer 105 is 1 Hz, and theoretically, the ranging range can be increased to hundreds of thousands of kilometers or more. Meanwhile, the measurement accuracy depends on the signal-to-noise ratio of the interferometric spectrum and the accuracy of the inverse Fourier transform. Optimal signal-to-noise ratio is achieved when the power ratio of the reference beam to the signal beam is equal; and micrometer-level measurement accuracy is achieved when the inverse Fourier transform calculation length reaches the order of 226. This allows for an expansion of the ranging range by several orders of magnitude while maintaining micrometer-level ranging accuracy.

[0104] Based on the device, Figure 1 The structure shown is used as an example to illustrate the optimal implementation scheme. The broadband spectrum used in the figure is generated by an ASE (Amplified Spontaneous Emission Source) source produced by an EDFA (Erbium-Doped Fiber Amplifier). This source passes through the first port 1 and the second port 2 of the fiber optic circulator 102, and then through the ranging probe 103. Through the Fresnel effect and optical frequency domain interference, a broadband sinusoidal interference signal with a frequency of 192-196 THz is generated. Finally, it is injected into a photodetector 104 with an effective bandwidth of 20 GHz through the third port 3 of the fiber optic circulator 102. The fiber optic circulator 102 has a center wavelength of 1550 nm, a passband of 30 nm, an insertion loss of 1 dB, and an isolation of 52 dB. The ranging probe 103 is connected to a single-mode fiber with a numerical aperture of 0.14, a probe diameter of 12 mm, and an imaging focal length of 5 m. The target 107 is a silver-plated mirror with a diameter of 30 mm. The microwave signal acquired after photoelectric conversion was recorded by a spectrum analyzer 105 with a frequency range of 10 Hz-30 GHz and a resolution bandwidth of 1 MHz. The distance to be measured was approximately 5 m.

[0105] Furthermore, at the same distance, after multiple verifications as described above, and after repeatedly completing the transition from optical frequency domain to microwave frequency domain ranging, optical frequency domain interference fringes (spectral density) are recorded within the effective measurement range of the photodetector 104. Then, with the distance to be measured remaining constant, microwave frequency domain interference fringes (current spectral density) are observed using a spectrum analyzer 105. Figure 2 As shown. By comparing the interference fringes preserved by the two instruments, it can be found that although the carrier frequencies of the fringes are different, the periods of the two cosine signals are exactly the same. This indicates that it is feasible to convert the interference signal from the optical frequency domain to the microwave frequency domain for fringe analysis within the effective operating range of the photodetector.

[0106] The frequency domain interference fringes (current spectral density) obtained in the 5.08 m range in the experiment are as follows: Figure 3 As shown. 100 measurements were performed on the target object, and the results are as follows. Figure 4 As shown, the distance measurement accuracy at 5.08 m is calculated to be 6.4 µm.

[0107] In summary, this invention, based on the principle of frequency domain interference, constructs a simple and compact extended-range optical-microwave mapping absolute distance measurement device, which extends the measurement range of the distance to be measured by 29.9 times while ensuring micrometer-level measurement accuracy.

[0108] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A full-fiber range-extended frequency-domain interferometric ranging method based on optical microwave mapping, characterized in that, The method is used to measure the distance information of the target under test, and the method includes: Step S1: Send a broadband spectrum to the ranging probe, which divides the broadband spectrum into a reference beam and a signal beam; Step S2: The ranging probe sends a signal beam to the target and receives the reflected signal beam, which couples with the reference beam to form an interference signal. Step S3: Analyze the interference signal to obtain distance information to the target. Step S1 includes: Step S11: Send a broadband spectrum to the ranging probe to obtain the light intensity of the reference beam at time t. and the intensity of the signal beam at time t ; in, t represents the total intensity of the broadband spectrum; A represents the percentage of the total intensity of the broadband spectrum occupied by the reference beam; B represents the percentage of the total intensity of the broadband spectrum occupied by the signal beam. For time delay; Step S12: Obtain the electric field signal of the reference beam. With signal beam electric field signal ; in, It is the broadband spectral electric field signal at time t. Step S2 includes: Step S21: The ranging probe sends a signal beam to the target and receives the reflected signal beam, which couples with the reference beam to form an interference signal, thus acquiring the time-domain interference signal. ; Step S22, for the time-domain interferometric signal Perform a Fourier transform to obtain the frequency domain interference signal. ; in, It is the frequency of light. Step S3 includes: Step S31: Perform photodetector analysis on the time-domain interferometric signal, current expression. for: in, This represents the DC term of the photocurrent at time t; This represents the interference signal term of the photocurrent at time t; Indicates the responsivity of the photodetector; Step S32, obtain spectral density ; in, The spectral intensity of the broadband spectrum; Step S33: Obtain the current spectral density ; , in, It is the effective bandwidth of the photodetector; This represents the phase shift of the sinusoidal interference signal; Step S34, verify the current spectral density With spectral density Does the self-convolution satisfy: If the condition is met, proceed to step S35; otherwise, return to step S1. Step S35, according to Obtain the distance to be measured ; in, It is the speed of light.

2. A full-fiber range-extended frequency-domain interferometric ranging device based on optical microwave mapping, characterized in that, Used to implement the all-fiber range-extended frequency domain interferometric ranging method based on optical microwave mapping as described in claim 1; The device is used for ranging the target (107) to be measured, and includes: A light source emitter (101) is used to emit a broadband spectrum; An optical fiber circulator (102) is connected to a light source transmitter (101) to receive and transmit the broadband spectrum from the light source transmitter (101). The ranging probe (103) is connected to the fiber optic circulator (102) and receives the broadband spectrum from the fiber optic circulator (102); the first broadband spectrum forms a reference beam inside the ranging probe (103), and the second broadband spectrum is emitted toward the target (107) and receives the signal beam reflected by the target (107); the reference beam and the signal beam are coupled in the ranging probe (103) to form an interference signal and are transmitted to the fiber optic circulator (102). The analysis module is connected to the fiber optic circulator (102), receives the interference signal from the fiber optic circulator (102), analyzes it, and obtains the distance to be measured.

3. The all-fiber range-extended frequency domain interferometric ranging device based on optical microwave mapping according to claim 2, characterized in that, The ranging probe (103) consists of a single-mode fiber, a focusing lens, and a metal shell. When the broadband spectrum enters the single-mode fiber of the ranging probe (103) through the fiber circulator (102), the broadband spectrum is reflected at the end face of the single-mode fiber due to the Fresnel effect, serving as a reference beam.

4. The all-fiber range-extended frequency-domain interferometric ranging device based on optical microwave mapping according to claim 3, characterized in that, The analysis module includes: A photodetector (104) is connected to an optical fiber circulator (102) to receive interference signals from the optical fiber circulator (102), and analyzes the interference signals using the photodetector (104) to obtain the converted interference signals. A spectrum analyzer (105) is connected to a photodetector (104) to receive the converted interference signal and perform spectral density analysis and current spectral density analysis on it. The computer (106) is connected to the spectrum analyzer (105) to receive the spectral density analysis results and the current spectral density analysis results, and then calculates the distance information.

5. The all-fiber range-extended frequency-domain interferometric ranging device based on optical microwave mapping according to claim 4, characterized in that, The fiber optic circulator (102) includes: The first port (1) is connected to the light source emitter (101) to receive broadband spectrum; The second port (2) is connected to the first port (1) and connected to the ranging probe (103) to transmit broadband spectrum to the ranging probe (103) and receive interference signals; The third port (3) is connected to the first port (1) and the second port (2), and is connected to the photodetector (104) to receive interference signals and transmit them to the photodetector (104).

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