Optical device time delay measurement method and device based on coherent reception

Abstract

The present invention discloses a method and device for measuring the delay of an optical device based on coherent reception, wherein the method comprises: dividing the optical signal output by a single-wavelength light source into a detection path signal and a local oscillator path signal, wherein the detection path signal is modulated by an electro-optical modulation module and sent to the optical device to be measured, and the local oscillator path signal is frequency-shifted by a frequency shift module; combining the first optical signal output by the optical device to be measured with the second optical signal after frequency shifting and performing photoelectric conversion to generate a photocurrent carrying delay information and optical phase noise; extracting the phase information of a specified frequency component from the photocurrent, and eliminating the common-mode phase noise in the phase information to determine the delay of the optical device to be measured. The technical solution provided by the present invention can significantly improve the sensitivity of the existing optical device delay measurement system, thereby achieving high-precision measurement of the delay of optical links with large insertion loss.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a method and device for measuring optical device delay based on coherent reception. Background Art

[0002] With the rapid application of optical devices in information systems due to their advantages such as large bandwidth, low loss, electromagnetic interference resistance, and easy integration, high-precision optical delay measurement technology has become a key technology for the development, production, and application of high-performance information systems such as 5 / 6G wireless communication networks, optical phased arrays, and distributed radar networks. However, in many practical applications, the presence of significant attenuation in optical links affects the accuracy of delay measurements and limits the implementation of high-precision optical delay measurement. For example, optical phased array chips require precise control of the phase shift (i.e., delay) for each channel of the phased array unit, but their insertion loss is generally greater than 20dB, which places high demands on the sensitivity of the delay measurement system.

[0003] At present, there are three main methods for measuring the delay of optical devices: the pulse method, the frequency scanning interferometry method, and the phase push method. The measurement accuracy of the pulse method is limited by the pulse width, which is generally in the nanosecond level. On the one hand, this technology cannot meet the needs of high-precision delay measurement. On the other hand, for measuring optical devices with large insertion loss, it is necessary to increase the peak power of the pulse, but this is easy to stimulate nonlinear effects in the optical link, affecting the accuracy of optical delay measurement and the normal performance of the optical information system. The frequency scanning interferometry method achieves high-precision delay measurement by scanning a large frequency range combined with an interference structure. Although the system can achieve high measurement sensitivity, its essence is to exchange frequency domain bandwidth for high measurement accuracy. It cannot measure narrowband optical devices (such as in 5G ultra-dense wavelength division multiplexing systems, the adjacent channel spacing may be less than 6.25GHz), and its application scenarios are limited. The phase-pushing method uses phase changes during transmission to calculate fiber delay, achieving sub-picosecond measurement accuracy within a narrowband measurement range of several GHz. However, this approach uses a direct beat frequency signal from the optical device under test to generate a photocurrent for processing in the electrical domain. The received power at the receiver is proportional to the signal intensity, significantly degrading the signal-to-noise ratio when measuring optical devices with high insertion loss, severely impacting system sensitivity. Using erbium-doped fiber to amplify the signal light introduces additional spontaneous emission noise, impacting measurement accuracy. Therefore, this approach cannot simultaneously improve system sensitivity and guarantee measurement accuracy. Summary of the Invention

[0004] The purpose of the present invention is to propose a method and device for measuring optical device delay based on coherent reception, so as to significantly improve the sensitivity of existing optical device delay measurement systems, thereby achieving high-precision measurement of optical link delay with large insertion loss.

[0005] In one aspect, the present invention provides a method for measuring optical device delay based on coherent reception, the method comprising:

[0006] The optical signal output by the single-wavelength light source is divided into a detection path signal and a local oscillator path signal, wherein the detection path signal is modulated by the electro-optical modulation module and sent to the optical device to be measured, and the local oscillator path signal is frequency-shifted by the frequency shift module;

[0007] Combining the first optical signal output by the optical device to be measured with the second optical signal after frequency shifting and performing photoelectric conversion to generate a photocurrent carrying time delay information and optical phase noise;

[0008] Phase information of a specified frequency component is extracted from the photocurrent, and common-mode phase noise in the phase information is eliminated to determine the time delay of the optical device to be measured; wherein the specified frequency component is generated by the frequency of the modulation signal of the electro-optical modulation module and the frequency shift amount of the frequency shift module.

[0009] Furthermore, the phase information extracted from the photocurrent is expressed as:

[0010]

[0011]

[0012] Among them, ω m is the frequency of the modulation signal of the electro-optical modulation module, ω c is the central wavelength of the optical signal output by the single-wavelength light source, τ is the time delay of the optical device to be measured, is the phase noise of the laser, Ω is the frequency shift of the frequency shift module, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information.

[0013] Furthermore, the method utilizes frequency shift coherence to improve the signal-to-noise ratio of the measurement system.

[0014] Furthermore, the method can achieve suppression of common-mode phase noise.

[0015] Furthermore, the time delay τ of the optical device to be measured is expressed by the following formula:

[0016]

[0017] in, and are the specified frequency components (ω m +Ω) and (ωm -Ω) phase information, ω m is the frequency of the modulation signal of the electro-optical modulation module, and Ω is the frequency shift amount of the frequency shift module.

[0018] In another aspect, the present invention provides an optical device delay measurement device based on coherent reception, the device comprising:

[0019] A light source module, configured to output a single-wavelength optical signal;

[0020] An optical beam splitter, configured to split the single-wavelength optical signal into a detection path signal and a local oscillator path signal;

[0021] A frequency shift module, configured to perform frequency shift processing on the local oscillator signal with a fixed frequency shift amount;

[0022] A swept-frequency microwave source is used to output a series of frequency-adjustable microwave signals to achieve integer ambiguity resolution;

[0023] an electro-optical modulation module, configured to modulate the detection path signal using the microwave signal;

[0024] An optical device to be tested, used for receiving the signal modulated by the electro-optical modulation module;

[0025] an optical beam combiner, configured to combine the first optical signal output by the optical device to be measured with the second optical signal after frequency shift processing;

[0026] an optical detection module, configured to perform beat frequency processing on the first optical signal and the second optical signal to generate a photocurrent carrying delay information and optical phase noise;

[0027] a phase measurement unit, configured to measure phase information of a specified frequency component in the photocurrent; wherein the specified frequency component is generated by the frequency of the modulation signal of the electro-optical modulation module and the frequency shift amount of the frequency shift module;

[0028] A solving unit is used to eliminate common-mode phase noise in the phase information to determine the time delay of the optical device to be measured.

[0029] Further, the phase information measured by the phase measurement unit is expressed as:

[0030]

[0031]

[0032] Among them, ω m is the frequency of the modulation signal of the electro-optical modulation module, ω c is the central wavelength of the optical signal output by the single-wavelength light source, τ is the time delay of the optical device to be measured, is the phase noise of the laser, Ω is the frequency shift of the frequency shift module, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information.

[0033] Furthermore, the device utilizes frequency shift coherence to improve the signal-to-noise ratio of the measurement system.

[0034] Furthermore, the device can suppress common-mode phase noise.

[0035] Furthermore, the time delay τ of the optical device to be measured is expressed by the following formula:

[0036]

[0037] in, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information, ω m is the frequency of the modulation signal of the electro-optical modulation module, and Ω is the frequency shift amount of the frequency shift module.

[0038] Compared with the prior art, the present invention adopts the above technology and has the following gains: the present invention adopts coherent reception technology. Since the equivalent received optical power at the optical receiving input end is the square root of the product of the signal optical power and the local oscillator optical power, when using a higher-power local oscillator light, the system can obtain a local oscillator gain of 10 to 25 dB, thereby improving the receiver sensitivity and thus improving the optical delay measurement accuracy; in addition, the present invention eliminates the influence of optical phase noise through positive and negative sidebands, thereby improving the measurement accuracy under the coherent reception system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of a method for measuring optical device delay based on coherent reception in an embodiment of the present invention;

[0040] Figure 2 Schematic diagram of the structure principle of an optical device delay measurement device based on coherent reception in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] To address the limitations of existing delay measurement solutions for high-insertion-loss devices, this invention employs a coherent reception measurement solution. This solution uses a photocurrent derived from the beat frequency of the local oscillator (LO) optical signal to improve receiver sensitivity and achieve a LO gain of 10-25dB. To minimize relative phase noise between the LO light and the signal light, phase cancellation of the ±1st-order sidebands of the signal light eliminates the optical signal's phase noise, ensuring measurement accuracy.

[0043] See also Figure 1 The present application provides a method for measuring optical delay based on coherent reception, the method comprising:

[0044] S1: The optical signal output by the single-wavelength light source is divided into a detection path signal and a local oscillator path signal, wherein the detection path signal is modulated by the electro-optical modulation module and sent to the optical device to be measured, and the local oscillator path signal is frequency-shifted by the frequency shift module.

[0045] S2: Combining the first optical signal output by the optical device to be measured with the second optical signal after frequency shifting and performing photoelectric conversion to generate a photocurrent carrying time delay information and optical phase noise.

[0046] S3: Extracting phase information of a specified frequency component from the photocurrent and eliminating common-mode phase noise in the phase information to determine the time delay of the optical device to be measured; wherein the specified frequency component is generated by the frequency of the modulation signal of the electro-optical modulation module and the frequency shift amount of the frequency shift module.

[0047] The following combination Figure 2 The technical solution of the present invention is further described in detail:

[0048] like Figure 2 As shown, the light source module emits a central wavelength of ω c Signal light E i (t), its expression is:

[0049]

[0050] Among them, E o is the signal light amplitude, is the phase noise of the laser. Then the signal light is divided into two paths through the optical beam splitter, the upper path is the detection path signal, and the lower path is the local oscillator path signal. The detection path signal first passes through the electro-optical modulation module and is modulated by the frequency ω m When the microwave signal is subjected to suppressed carrier double-sideband modulation and only the ±1-order sidebands are considered, the expression is:

[0051]

[0052] Where M is the electro-optical modulation coefficient. After passing through the optical device to be measured, the optical signal expression is expressed as:

[0053]

[0054] Where τ and α are the delay and insertion loss of the optical device under test, respectively. For the local oscillator path, the optical signal is frequency-shifted by the frequency shift module, and its expression can be written as:

[0055]

[0056] Wherein, Ω is the frequency shift amount of the frequency shift module.

[0057] Then the local oscillator signal and the measurement signal are combined by the optical combiner, which can be further written as:

[0058]

[0059] The optical signal is converted into photoelectricity by the optical detection module, and the DC component is removed. The resulting current is:

[0060]

[0061] The current passes through the phase measurement unit and the frequency components ω are extracted respectively. m The phase of ±Ω can be obtained:

[0062]

[0063] Then the optical delay can be calculated as:

[0064]

[0065] In general, since the measurement range of the phase measurement unit is [-π, π], the delay calculated according to formula (8) has an integer ambiguity term. The integer ambiguity can be expanded using the general phase inference method, such as the paper (SPLi, T.Qing, JBFu, XCWang, SLPan, "High-Accuracy and Fast Measurement of Optical Transfer Delay," IEEE Transactions on Instrumentation and Measurement, vol. 70, 8000204, 2021.), which calculates the true delay value by tuning the microwave swept frequency source and setting different microwave frequencies.

[0066] Through the above method and device, the signal-to-noise ratio of the measurement system can be improved by using frequency shift coherence, and the common-mode phase noise can be suppressed.

[0067] Compared with the prior art, the present invention adopts the above technology and has the following gains: the present invention adopts coherent reception technology. Since the equivalent received optical power at the optical receiving input end is the square root of the product of the signal optical power and the local oscillator optical power, when using a higher-power local oscillator light, the system can obtain a local oscillator gain of 10 to 25 dB, thereby improving the receiver sensitivity and thus improving the optical delay measurement accuracy; in addition, the present invention eliminates the influence of optical phase noise through positive and negative sidebands, thereby improving the measurement accuracy under the coherent reception system.

Claims

1. A method for measuring optical delay based on coherent reception, characterized in that: The method comprises: The optical signal output by the single-wavelength light source is divided into a detection path signal and a local oscillator path signal, wherein the detection path signal is modulated by the electro-optical modulation module and sent to the optical device to be measured, and the local oscillator path signal is frequency-shifted by the frequency shift module; Combining the first optical signal output by the optical device to be measured with the second optical signal after frequency shifting and performing photoelectric conversion to generate a photocurrent carrying time delay information and optical phase noise; Phase information of a specified frequency component is extracted from the photocurrent, and common-mode phase noise in the phase information is eliminated to determine the time delay of the optical device to be measured; wherein the specified frequency component is generated by the frequency of the modulation signal of the electro-optical modulation module and the frequency shift amount of the frequency shift module.

2. The optical delay measurement method based on coherent reception according to claim 1, wherein: The phase information extracted from the photocurrent is expressed as: Among them, ω m is the frequency of the modulation signal of the electro-optical modulation module, ω c is the central wavelength of the optical signal output by the single-wavelength light source, τ is the time delay of the optical device to be measured, is the phase noise of the laser, Ω is the frequency shift of the frequency shift module, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information.

3. The optical delay measurement method based on coherent reception according to claim 1, wherein: The method utilizes frequency shift coherence to improve the signal-to-noise ratio of the measurement system.

4. The optical delay measurement method based on coherent reception according to claim 1, wherein: The method can suppress common-mode phase noise.

5. The optical delay measurement method based on coherent reception according to claim 1, wherein: The time delay τ of the optical device to be measured is expressed by the following formula: in, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information, ω m is the frequency of the modulation signal of the electro-optical modulation module, and Ω is the frequency shift amount of the frequency shift module.

6. An optical device delay measurement device based on coherent reception, characterized in that: include: A light source module, configured to output a single-wavelength optical signal; An optical beam splitter, configured to split the single-wavelength optical signal into a detection path signal and a local oscillator path signal; A frequency shift module, configured to perform frequency shift processing on the local oscillator signal with a fixed frequency shift amount; A swept-frequency microwave source is used to output a series of frequency-adjustable microwave signals to achieve integer ambiguity resolution; an electro-optical modulation module, configured to modulate the detection path signal using the microwave signal; An optical device to be tested, used for receiving the signal modulated by the electro-optical modulation module; an optical beam combiner, configured to combine the first optical signal output by the optical device to be measured with the second optical signal after frequency shift processing; an optical detection module, configured to perform beat frequency processing on the first optical signal and the second optical signal to generate a photocurrent carrying delay information and optical phase noise; a phase measurement unit, configured to measure phase information of a specified frequency component in the photocurrent; wherein the specified frequency component is generated by the frequency of the modulation signal of the electro-optical modulation module and the frequency shift amount of the frequency shift module; A solving unit is used to eliminate common-mode phase noise in the phase information to determine the time delay of the optical device to be measured.

7. The optical device delay measurement device based on coherent reception according to claim 6, characterized in that: The phase information measured by the phase measurement unit is expressed as: Among them, ω m is the frequency of the modulation signal of the electro-optical modulation module, ω c is the central wavelength of the optical signal output by the single-wavelength light source, τ is the time delay of the optical device to be measured, is the phase noise of the laser, Ω is the frequency shift of the frequency shift module, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information.

8. The optical device delay measurement device based on coherent reception according to claim 6, characterized in that: The device utilizes frequency shift coherence to improve the signal-to-noise ratio of the measurement system.

9. The optical device delay measurement device based on coherent reception according to claim 6, characterized in that: The device can achieve suppression of common-mode phase noise.

10. The optical device delay measurement device based on coherent reception according to claim 6, characterized in that: The time delay τ of the optical device to be measured is expressed by the following formula: in, and are the specified frequency components (ω m +Ω) and (ω m -Ω) phase information, ω m is the frequency of the modulation signal of the electro-optical modulation module, and Ω is the frequency shift amount of the frequency shift module.

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