Optical ranging method and device based on coherent phase push system

Abstract

The present invention discloses an optical ranging method of a coherent phase-pushing system, which uses a single-frequency microwave signal to perform double-sideband modulation on an optical carrier signal. After the generated modulated optical signal passes through the optical link to be measured, it is polarized and split into two beams of detection optical signals in the horizontal and vertical polarization directions, and the local oscillator optical signal is polarized and split into two beams of local oscillator optical signals in the horizontal and vertical polarization directions; the local oscillator optical signal in the horizontal polarization direction and the detection optical signal, and the local oscillator optical signal in the vertical polarization direction and the detection optical signal are respectively combined, photoelectrically detected, and envelope detected, and then the two obtained electrical signals are combined to generate the electrical signal to be measured; the phase difference between the doubled frequency signal of the single-frequency microwave signal and the corresponding frequency component in the electrical signal to be measured is detected, and the distance of the optical link to be measured is calculated based on the phase difference. The present invention also discloses an optical ranging device of a coherent phase-pushing system. The present invention can effectively improve the optical ranging accuracy of the coherent phase-pushing system.

Description

Technical Field

[0001] The present invention relates to an optical distance measurement method, and in particular to an optical distance measurement method and device based on a coherent phase-pushing system. Background Art

[0002] Optical ranging is a non-contact measurement technology characterized by high directivity, high monochromaticity, high accuracy, and fast measurement speed. It is widely used in scenarios such as dimensional measurement, position measurement, deformation detection, sensor positioning, and active optical imaging. Optical phase inference ranging is a laser ranging method that achieves high precision and wide range. Its principle is to modulate the intensity of a laser signal. After passing through the optical link to be measured, this intensity-modulated signal will produce a corresponding phase shift. The phase shift of the modulated signal can be used to calculate the distance of the corresponding optical link to be measured. Because the accuracy is traceable to the phase of the modulated signal, ranging accuracy can be improved by 3 to 4 orders of magnitude compared to pulse and triangulation methods.

[0003] Current optical phase estimation ranging systems are primarily implemented using two methods: incoherent and coherent. The incoherent system directly converts the detection optical signal into photoelectricity. The measurement signal-to-noise ratio of this scheme is proportional to the square of the loss of the link under test, resulting in a sharp drop in accuracy when measuring links with high loss. In certain measurement scenarios, such as atmospheric turbulence and diffuse reflection from rain and fog, which can cause severe power jitter in the measurement link, the incoherent optical phase estimation ranging system can no longer maintain high-precision ranging capabilities. The coherent system, on the other hand, compensates for the power loss during photoelectric conversion by using the local oscillator optical signal. Its measurement sensitivity is superior to that of the incoherent system and it is insensitive to power jitter in the measurement path. However, coherent optical phase estimation systems face three major problems: First, the polarization states of the probe light and the local oscillator light differ, resulting in polarization fading and introducing additional amplitude jitter during photoelectric conversion. Second, when the probe light and the local oscillator light are not locked, there is relative phase noise between them. The difference in phase noise between the two is converted into phase jitter in the electrical signal during photoelectric conversion, introducing additional phase measurement errors. Third, when there is relative motion in the probe light link, the probe light will introduce Doppler frequency shift, and the electrical signal after photoelectric conversion will retain this Doppler frequency shift, further introducing additional phase measurement errors. Most existing technologies can only specifically eliminate or suppress one of these measurement errors. Currently, there is no method to eliminate all three measurement errors simultaneously, which seriously restricts the performance and application scope of coherent optical phase estimation systems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method that can simultaneously eliminate the influence of laser phase noise, Doppler effect and polarization fading on the optical phase-guessing ranging system under the coherent receiving system, thereby effectively improving the optical ranging accuracy of the coherent phase-guessing system.

[0005] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0006] A coherent phase-pushing optical distance measurement method is disclosed. A single-frequency microwave signal is used to perform double-sideband modulation on an optical carrier signal. After the generated modulated optical signal passes through an optical link to be measured, it is polarization-split into two probe optical signals in horizontal and vertical polarization directions. The local oscillator optical signal is also polarization-split into two local oscillator optical signals in horizontal and vertical polarization directions. The frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal. The local oscillator optical signal in the horizontal polarization direction and the probe optical signal, and the local oscillator optical signal in the vertical polarization direction and the probe optical signal are sequentially combined, photoelectrically detected, and envelope detected. The two resulting electrical signals are then combined to generate an electrical signal to be measured. The phase difference between the doubled frequency signal of the single-frequency microwave signal and the corresponding frequency component in the electrical signal to be measured is detected, and the distance of the optical link to be measured is calculated based on the phase difference.

[0007] Preferably, the distance of the optical link to be measured is calculated using the following formula:

[0008]

[0009] Where R is the distance of the optical link to be measured; c is the speed of light; n is the refractive index of the optical link to be measured; ω m is the frequency of the single-frequency microwave signal; It is the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured.

[0010] Preferably, the double sideband modulation is carrier suppressed double sideband modulation.

[0011] Based on the same inventive concept, the following technical solutions can also be obtained:

[0012] An optical distance measuring device of a coherent phase-pushing system, comprising:

[0013] A detection optical path unit is used to perform double-sideband modulation on an optical carrier signal using a single-frequency microwave signal, and to polarize-split the generated modulated optical signal into two detection optical signals in a horizontal polarization direction and a vertical polarization direction after passing through the optical link to be measured;

[0014] A local oscillator optical path unit is used to polarization-split the local oscillator optical signal into two local oscillator optical signals in a horizontal polarization direction and a vertical polarization direction, wherein the frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal;

[0015] A coherent demodulation unit is used to combine the horizontally polarized local oscillator optical signal and the detection optical signal, and the vertically polarized local oscillator optical signal and the detection optical signal, respectively, perform photoelectric detection, and envelope detection, and then combine the two obtained electrical signals to generate an electrical signal to be measured;

[0016] The measuring unit is used to detect the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured, and calculate the distance of the optical link to be measured based on the phase difference.

[0017] Preferably, the measuring unit calculates the distance of the optical link to be measured by the following formula:

[0018]

[0019] Where R is the distance of the optical link to be measured; c is the speed of light; n is the refractive index of the optical link to be measured; ω m is the frequency of the single-frequency microwave signal; It is the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured.

[0020] Preferably, the double sideband modulation is carrier suppressed double sideband modulation.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] The present invention eliminates the influence of polarization fading on measurement through polarization diversity and electrical signal beam combining. Through the envelope detection process, it eliminates the phase noise of the local oscillator optical signal and the detection optical signal and the error of the Doppler effect introduced on the optical link to be measured, which can effectively improve the optical ranging accuracy of the coherent phase-pushing system. The system structure is simple and the implementation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic diagram of the structural principle of a specific embodiment of the optical distance measuring device of the present invention. DETAILED DESCRIPTION

[0024] Coherent receiving systems can significantly improve the receiving sensitivity of measurement systems, enabling the system to achieve higher local oscillator gain, thereby improving measurement accuracy. However, current optical phase inference ranging solutions based on coherent receiving systems still have unresolved issues such as polarization fading and Doppler sensitivity, which seriously restrict their use in measurement scenarios. To address this issue, the present invention adopts polarization diversity and envelope detection technology to simultaneously cancel errors such as the phase noise of the local oscillator light source, polarization fading in the measurement path, and Doppler frequency shift in the analog domain, thereby realizing a high-precision optical phase inference ranging system based on coherent receiving systems.

[0025] The optical ranging method of the coherent phase push system proposed in the present invention is as follows:

[0026] A single-frequency microwave signal is used to perform double-sideband modulation on an optical carrier signal. After the generated modulated optical signal passes through the optical link to be measured, it is polarized and split into two probe optical signals in horizontal and vertical polarization directions. The local oscillator optical signal is also polarized and split into two local oscillator optical signals in horizontal and vertical polarization directions. The frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal. The local oscillator optical signal in the horizontal polarization direction and the probe optical signal, and the local oscillator optical signal in the vertical polarization direction and the probe optical signal are sequentially combined, photoelectrically detected, and envelope detected. The two resulting electrical signals are then combined to generate the electrical signal to be measured. The phase difference between the doubled frequency signal of the single-frequency microwave signal and the corresponding frequency component in the electrical signal to be measured is detected, and the distance of the optical link to be measured is calculated based on the phase difference.

[0027] The optical distance measuring device of the coherent phase-pushing system proposed in the present invention comprises:

[0028] A detection optical path unit is used to perform double-sideband modulation on an optical carrier signal using a single-frequency microwave signal, and to polarize-split the generated modulated optical signal into two detection optical signals in a horizontal polarization direction and a vertical polarization direction after passing through the optical link to be measured;

[0029] A local oscillator optical path unit is used to polarization-split the local oscillator optical signal into two local oscillator optical signals in a horizontal polarization direction and a vertical polarization direction, wherein the frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal;

[0030] A coherent demodulation unit is used to combine the horizontally polarized local oscillator optical signal and the detection optical signal, and the vertically polarized local oscillator optical signal and the detection optical signal, respectively, perform photoelectric detection, and envelope detection, and then combine the two obtained electrical signals to generate an electrical signal to be measured;

[0031] The measuring unit is used to detect the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured, and calculate the distance of the optical link to be measured based on the phase difference.

[0032] To facilitate public understanding, the technical solution of the present invention is described in detail below through a specific embodiment with reference to the accompanying drawings:

[0033] The basic structure of the optical distance measuring device of this embodiment is as follows: Figure 1As shown, it includes a detection optical path unit, a local oscillator optical path unit, a coherent demodulation unit and a measurement unit; wherein the local oscillator optical path unit includes a light source module 1, a polarization controller and a polarization beam splitter 1; the detection optical path unit includes a light source module 2, an electro-optical modulation module and a polarization beam splitter 2; the coherent demodulation unit includes a photoelectric detection module 1, a photoelectric detection module 2, an envelope detection module 1, an envelope detection module 2, and a microwave power splitter; the measurement unit includes a microwave source module, a double frequency module, a phase detection module and a solution module.

[0034] Light source module 1 is a local oscillator light source, and its emitted light supplements the power of the measurement link. The light signal emitted by light source module 2 is the detection signal. For the local oscillator optical path unit, the emission center frequency of light source module 1 is ω c1 The local oscillator light signal is expressed as:

[0035]

[0036] Among them, E o1 is the amplitude of the light signal emitted by the light source module 1, The phase noise of the light signal emitted by the light source module 1. The polarization state of the local oscillator light signal is controlled and stabilized at a 45-degree angle to the horizontal polarization state by the polarization controller. The light signal enters the polarization beam splitter 1, generating two linearly polarized lights with perpendicular polarization directions, which are recorded as E rs (t) and E rp (t), the optical signal output by the polarization beam splitter 1 can be expressed as:

[0037]

[0038] For the detection optical path, the emission center frequency of the light source module 2 is ω c2 Optical carrier E i (t), its expression is:

[0039]

[0040] Among them, E o2 is the amplitude of the optical carrier emitted by the light source module 2, is the phase noise of the optical carrier emitted by the light source module 2. The optical signal is then subjected to double-sideband modulation by the electro-optical modulation module. The modulation signal is a single-frequency microwave signal output by the microwave source module. The double-sideband modulation can be either double-sideband modulation with the carrier retained or double-sideband modulation with carrier suppressed. Preferably, double-sideband modulation with carrier suppressed is used. The suppressed carrier double-sideband modulation signal is expressed as:

[0041] E m (t) = E i (t)[Mcos(ω m t)] (4)

[0042] Where M is the modulation coefficient of the electro-optical modulation module; ω m is the frequency of the microwave signal output by the microwave source module, and satisfies ω m >|ω c2 -ω c1 After passing through the optical link to be tested, the optical signal is expressed as:

[0043]

[0044] Where n is the refractive index of the optical link to be measured, R is the distance of the optical link to be measured, c is the speed of light, ω d is the Doppler frequency introduced by the optical link to be measured. Subsequently, the optical signal enters the polarization beam splitter 2, generating two linearly polarized beams with perpendicular polarization directions, denoted as E is (t) and E ip (t), assuming that the angle between the optical signal and the horizontal polarization state before entering the polarization beam splitter 2 is θ(t), the two detection optical signals output by the polarization beam splitter 2 can be expressed as:

[0045]

[0046] Then, the vertically polarized light of the local oscillator signal and the vertically polarized light of the measurement signal are combined, and the parallel polarized light of the local oscillator signal and the parallel polarized light of the measurement signal are combined, which can be further written as:

[0047]

[0048] Photoelectric detection module 1 and photoelectric detection module 2 respectively detect the optical signal E s (t) and E p (t) Perform photoelectric conversion and remove the DC component. The resulting photocurrent signal is:

[0049]

[0050] Where * represents the complex conjugate, and η1 is the responsivity of the photoelectric detection module. The photocurrent output by the photoelectric detection module is envelope-detected in the envelope detection module and the envelope detection module 2, respectively, to obtain:

[0051]

[0052] Among them, η2 is the response of the envelope detector. From the above formula, we can see that 2ω m The signal phase of the frequency component is only related to the distance to be measured and the modulation frequency, eliminating the influence of laser phase noise and Doppler frequency shift introduced by the link to be measured on the measurement results.

[0053] The two microwave signals are then combined using a microwave power splitter. The resulting electrical signal eliminates the effect of polarization state changes on the measurement results.

[0054]

[0055] The microwave signal output by the microwave source module enters the double frequency module to generate 2ω m The phase detector module detects the 2ω of the two signals at the same time. m The components are phase-detected and the phase-detection results can be obtained:

[0056]

[0057] Finally, the distance of the optical link to be measured can be calculated based on the phase comparison result:

[0058]

[0059] Through the above-mentioned method and device, a highly reliable optical phase estimation ranging technology of a coherent system can be realized, the receiving signal-to-noise ratio of the measurement system can be improved, and the influences of laser phase noise, polarization fading, Doppler effect, etc. can be eliminated.

Claims

1. An optical ranging method based on coherent push-pull system, characterized in that: A single-frequency microwave signal is used to perform double-sideband modulation on an optical carrier signal. After the generated modulated optical signal passes through the optical link to be measured, the modulated optical signal is polarized and split into two probe optical signals in horizontal and vertical polarization directions. The local oscillator optical signal is polarized and split into two local oscillator optical signals in horizontal and vertical polarization directions, wherein the frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal. The local oscillator optical signal in the horizontal polarization direction and the probe optical signal, and the local oscillator optical signal in the vertical polarization direction and the probe optical signal are sequentially combined, photoelectrically detected, and envelope detected. The two resulting electrical signals are then combined to generate the electrical signal to be measured. The phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured is detected, and the distance of the optical link to be measured is calculated based on the phase difference.

2. The optical distance measurement method of the coherent phase push system as claimed in claim 1, characterized in that: The distance of the optical link to be measured is calculated using the following formula: Where R is the distance of the optical link to be measured; c is the speed of light; n is the refractive index of the optical link to be measured; ω m is the frequency of the single-frequency microwave signal; It is the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured.

3. The optical distance measurement method of the coherent phase push system as claimed in claim 1, characterized in that: The double sideband modulation is carrier suppressed double sideband modulation.

4. An optical distance measuring device based on a coherent push-pull system, characterized in that: include: A detection optical path unit is used to perform double-sideband modulation on an optical carrier signal using a single-frequency microwave signal, and to polarize-split the generated modulated optical signal into two detection optical signals in a horizontal polarization direction and a vertical polarization direction after passing through the optical link to be measured; A local oscillator optical path unit is used to polarization-split the local oscillator optical signal into two local oscillator optical signals in a horizontal polarization direction and a vertical polarization direction, wherein the frequency difference between the optical carrier signal and the local oscillator optical signal is less than the frequency of the single-frequency microwave signal; A coherent demodulation unit is used to combine the horizontally polarized local oscillator optical signal and the detection optical signal, and the vertically polarized local oscillator optical signal and the detection optical signal, respectively, perform photoelectric detection, and envelope detection, and then combine the two obtained electrical signals to generate an electrical signal to be measured; The measuring unit is used to detect the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured, and calculate the distance of the optical link to be measured based on the phase difference.

5. The optical distance measuring device of the coherent phase push system as claimed in claim 4, characterized in that: The measurement unit calculates the distance of the optical link to be measured using the following formula: Where R is the distance of the optical link to be measured; c is the speed of light; n is the refractive index of the optical link to be measured; ω m is the frequency of the single-frequency microwave signal; It is the phase difference between the double frequency signal of the single frequency microwave signal and the corresponding frequency component in the electrical signal to be measured.

6. The optical distance measuring device of the coherent push-pull system as claimed in claim 4, characterized in that: The double sideband modulation is carrier suppressed double sideband modulation.

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