CN113872684A - Optical time delay measuring method and device - Google Patents
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Abstract
The invention discloses an optical time delay measuring method, which uses two paths of microwave signals with different frequencies to carry out multi-sideband modulation on the same path of narrow linewidth optical carrier, wherein the product of the frequency difference of the two paths of microwave signals and the optical time delay to be measured is less than or equal to one half; dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, and the other path does not pass through the optical link to be measured to serve as a reference path, and respectively performing photoelectric conversion on the optical signal of the measuring path and the optical signal of the reference path to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters and each wavelength cluster comprises a plurality of dense frequency components; and extracting phase differences of a plurality of different frequency components in at least two adjacent sparse wavelength clusters in two paths of multi-frequency microwave signals in a digital domain, and solving the optical time delay to be measured by using a phase extrapolation method according to the phase differences. The invention also discloses an optical time delay measuring device. Compared with the prior art, the invention has the advantages of high measurement stability, high measurement speed and simple structure.
Description
Technical Field
The invention relates to an optical time delay measuring method, in particular to a rapid optical time delay measuring method, and belongs to the technical field of optical measurement and microwave photon.
Background
The optical link has been widely used in information systems due to advantages such as small transmission loss, large bandwidth, and anti-electromagnetic interference, and is an important component of novel array radar, laser communication, distributed radar, and 5G base station. The optical time delay is used as a basic parameter in the generation, transmission and control of optical signals, and the measurement and characterization of the optical time delay run through the whole processes of production, application and maintenance of optical link products. With the development of 5G communication, light-controlled phased arrays, distributed radar networks and laser link systems, higher requirements are put forward on the measurement precision and speed of optical time delay. For example, the 5G communication base station needs a high-speed high-precision optical time delay measurement technology to realize signal matching and cooperation among distributed base stations, and the communication performance of the 5G base station is improved.
The commonly used optical time delay measurement methods mainly include a pulse method, a frequency sweep interference method and a phase-push method. The pulse method is also called as a time domain method, and the time interval between the emission and the reception of the optical pulse signal is directly recorded in the time domain to obtain the optical delay to be measured. The method usually uses a backscattering signal of a pulse in an optical link as a receiving signal, but the backscattering signal is weaker, and the signal-to-noise ratio of a system is not high, so that the measurement precision is limited, the backscattering signal is usually meter-level, and the requirement of high-precision time delay measurement is difficult to meet.
The sweep frequency interference method is also called as a frequency domain method, and by utilizing a continuous sweep frequency laser and an interference structure, beat frequencies of reference light and measuring light are obtained, and an optical time delay is mapped into beat frequencies, so that higher measuring precision (millimeter magnitude) can be obtained. The method has higher requirements on the phase noise performance of the swept-frequency laser, and the longer the measurement distance is, the poorer the precision is; and limited by the linewidth of the laser and the linearity of the sweep frequency, an auxiliary interferometer is often needed to correct the frequency modulation nonlinearity of the light source, increasing the system complexity.
The phase-subtraction method uses the phase change of signals before and after link transmission to calculate the optical time delay, and the accuracy of submillimeter level can be achieved. In order to ensure the measurement accuracy, the phase shift of the high-frequency signal needs to be measured, and because the high-frequency phase demodulation often adopts frequency conversion, extra noise is easily introduced, and errors are brought. Meanwhile, in order to solve the whole cycle ambiguity of the phase, the frequency sweep is needed to obtain the phases of a plurality of frequency points, so that the system cost and complexity are improved, and the measuring speed of the method is limited.
In summary, the prior art has the following disadvantages: (1) the time domain method has poor precision, is only meter-level and has a blind area; (2) the frequency domain method has a complex system structure, high requirements on photoelectric devices, a short measurement range and mutual restriction with precision; (3) the phase-contrast method needs frequency sweeping, the measurement speed is limited, phase-contrast errors are easy to introduce under the high-frequency condition, and the time delay measurement precision is finally reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art and provide an optical time delay measuring method which has the advantages of high measuring stability, high measuring speed and simple structure.
The invention specifically adopts the following technical scheme to solve the technical problems:
an optical time delay measurement method is characterized in that two paths of microwave signals with different frequencies are used for carrying out multi-sideband modulation on the same path of narrow linewidth optical carrier, and the product of the frequency difference of the two paths of microwave signals and the optical time delay to be measured is less than or equal to one half; dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, and the other path does not pass through the optical link to be measured to serve as a reference path, and respectively performing photoelectric conversion on the optical signal of the measuring path and the optical signal of the reference path to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters and each wavelength cluster comprises a plurality of dense frequency components; and extracting the phase difference of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals in the digital domain, and calculating the optical time delay to be measured by using a phase extrapolation method according to the phase difference.
Preferably, the method for calculating the time delay of the light to be measured specifically includes:
τ1＝(k1/2π)-τ0
wherein k is0The slope, k, of a phase difference-frequency fitting straight line of a plurality of different frequency components in a low-order sparse wavelength cluster in two paths of multi-frequency microwave signals1The slope of a phase difference-frequency fitting straight line in two paths of multi-frequency microwave signals is formed by a frequency component selected from a high-order first-order sparse wavelength cluster and a plurality of different frequency components in a low-order sparse wavelength cluster, and f and N (f)m)、
Respectively the frequency, integer ambiguity and phase difference of the frequency component selected from the first-order sparse wavelength cluster]For the operator of rounding, τ0Is the time delay difference, tau, of the two paths of modulated optical signals when the optical link to be measured is not added1To solve the calculated delay of the light to be measured.
Further, the method for calculating the time delay of the light to be measured further includes: based on the obtained time delay difference tau1Iterating n high-order sparse wavelength clusters according to the method, wherein n is an integer larger than 1, and thus obtaining a time delay measurement value tau with higher precisionn。
Preferably, the multi-sideband modulation is performed using a dual parallel mach-zehnder modulator.
Preferably, the phase difference of a certain frequency component in the two paths of multi-frequency microwave signals is extracted in the digital domain by the following method: firstly, fast Fourier transform is respectively carried out on time domain signals in the two paths of multi-frequency microwave signals to obtain the phase of the frequency component in the two paths of multi-frequency microwave signals, and further the phase difference is obtained.
Based on the same inventive concept, the following technical scheme can be obtained:
an optical time delay measuring device comprising:
the double-frequency multi-sideband modulation module is used for carrying out multi-sideband modulation on the same narrow linewidth optical carrier by using two paths of microwave signals with different frequencies, and the product of the frequency difference of the two paths of microwave signals and the optical delay to be measured is less than or equal to one half;
the photoelectric conversion module is used for dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, the other path does not pass through the optical link to be measured to serve as a reference path, and the optical signals of the measuring path and the reference path are respectively subjected to photoelectric conversion to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters, and each wavelength cluster comprises a plurality of dense frequency components;
and the resolving module is used for extracting the phase difference of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals in the digital domain and resolving the optical delay to be measured by using a phase-deduction method according to the phase difference.
Preferably, the method for calculating the time delay of the light to be measured specifically includes:
τ1＝(k1/2π)-τ0
wherein k is0The slope, k, of a phase difference-frequency fitting straight line of a plurality of different frequency components in a low-order sparse wavelength cluster in two paths of multi-frequency microwave signals1The slope of a phase difference-frequency fitting straight line in two paths of multi-frequency microwave signals is formed by a frequency component selected from a high-order first-order sparse wavelength cluster and a plurality of different frequency components in a low-order sparse wavelength cluster, and f and N (f)m)、
Respectively the frequency, integer ambiguity and phase difference of the frequency component selected from the first-order sparse wavelength cluster]For the operator of rounding, τ0Is the time delay difference, tau, of the two paths of modulated optical signals when the optical link to be measured is not added1To solve the calculated delay of the light to be measured.
Further, the method for calculating the time delay of the light to be measured further includes: based on the obtained time delay difference tau1And overlapping the n sparse wavelength clusters of higher order according to the methodN is an integer greater than 1, so as to obtain a higher-precision time delay measurement value taun。
Preferably, the dual-frequency multi-sideband modulation module performs the multi-sideband modulation using a dual parallel mach-zehnder modulator.
Preferably, the phase difference of a certain frequency component in the two paths of multi-frequency microwave signals is extracted in the digital domain by the following method: firstly, fast Fourier transform is respectively carried out on time domain signals in the two paths of multi-frequency microwave signals to obtain the phase of the frequency component in the two paths of multi-frequency microwave signals, and further the phase difference is obtained.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
based on the basic principle of a phase-push method, the invention adopts a double-frequency multi-sideband modulation mode to generate a modulated optical signal with a plurality of sparse wavelength clusters, generates a multi-frequency microwave signal with a plurality of sparse wavelength clusters after photoelectric detection, wherein each wavelength cluster comprises a plurality of dense frequency components, and simultaneously obtains two paths of phase differences of each frequency component at one time in a digital domain, thereby solving the problem of slow measurement speed caused by continuous frequency sweep in the traditional phase-push delay system, and having the advantages of high measurement speed, no frequency sweep and one-time measurement completion.
According to the invention, through digital domain phase discrimination, frequency conversion is not needed, and extra noise is not introduced; meanwhile, the invention does not need frequency sweep, and the error caused by environmental fluctuation is further avoided by the characteristic of single measurement, and the measurement result is stable and reliable.
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FIG. 1 is a schematic structural diagram of an embodiment of an optical time delay measuring apparatus according to the present invention;
fig. 2 is a signal spectrum diagram of a modulated optical signal before and after photoelectric conversion.
Detailed Description
Aiming at the defects of the existing phase-push method for measuring optical time delay, the solution idea of the invention is based on the basic principle of the phase-push method, a mode of double-frequency multi-sideband modulation is adopted to generate a modulated optical signal with a plurality of sparse wavelength clusters, a multi-frequency microwave signal with a plurality of sparse wavelength clusters and each wavelength cluster containing a plurality of dense frequency components is generated after photoelectric detection, and two paths of phase differences of each frequency component are simultaneously obtained in a digital domain at one time, so that the problem of slow measurement speed caused by continuous frequency sweeping in the traditional phase-push time delay measurement system is solved.
The optical time delay measuring method provided by the invention comprises the following specific steps:
performing multi-sideband modulation on the same narrow linewidth optical carrier by using two paths of microwave signals with different frequencies, wherein the product of the frequency difference of the two paths of microwave signals and the optical delay to be measured is less than or equal to one half; dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, and the other path does not pass through the optical link to be measured to serve as a reference path, and respectively performing photoelectric conversion on the optical signal of the measuring path and the optical signal of the reference path to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters and each wavelength cluster comprises a plurality of dense frequency components; and extracting the phase difference of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals in the digital domain, and calculating the optical time delay to be measured by using a phase extrapolation method according to the phase difference.
The optical time delay measuring device provided by the invention comprises:
the double-frequency multi-sideband modulation module is used for carrying out multi-sideband modulation on the same narrow linewidth optical carrier by using two paths of microwave signals with different frequencies, and the product of the frequency difference of the two paths of microwave signals and the optical delay to be measured is less than or equal to one half;
the photoelectric conversion module is used for dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, the other path does not pass through the optical link to be measured to serve as a reference path, and the optical signals of the measuring path and the reference path are respectively subjected to photoelectric conversion to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters, and each wavelength cluster comprises a plurality of dense frequency components;
and the resolving module is used for extracting the phase difference of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals in the digital domain and resolving the optical delay to be measured by using a phase-deduction method according to the phase difference.
The measuring range and the precision of the measuring device can be flexibly controlled by changing the frequency interval and the size of two paths of microwave signals: when large-scale time delay is measured, the frequency interval of a wavelength cluster needs to be controlled to be small so as to ensure that the phase difference-angular frequency can be expanded; meanwhile, the sideband number is limited, the maximum frequency aperture which can be obtained is limited by the size of the sideband number and the modulation frequency, and the final measurement precision depends on the phase discrimination precision and the frequency aperture. Therefore, under the condition of ensuring that the phases among dense frequency components can be spread, the modulation frequency is improved, and the final time delay measurement precision of the system can be improved.
For the public understanding, the technical scheme of the invention is explained in detail by a specific embodiment and the accompanying drawings:
the structure of the optical time delay measuring device in this example is shown in fig. 1, and includes a narrow linewidth laser, a microwave source, a dual-frequency multi-sideband modulation module, a photoelectric detection module, a dual-channel acquisition module, a resolving module, and a plurality of optical couplers. An optical carrier output by the narrow linewidth laser is sent to a multi-frequency multi-sideband modulation module, two microwave signals with small frequency difference are respectively modulated onto the optical carrier, and finally a modulated optical signal with multi-order sidebands is generated, wherein each non-zero-order sideband is provided with a wavelength cluster containing two frequency components; then, the modulated optical signal is divided into two paths, wherein one path is used as a reference path and directly enters the photoelectric detection module, and the other path passes through the optical link to be detected and then enters the photoelectric detection module to be used as a detection path; after photoelectric conversion, the two paths of modulated optical signals can respectively obtain multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters, and each wavelength cluster comprises a plurality of dense frequency components; the method comprises the steps of carrying out digital sampling quantification on two paths of multi-frequency microwave signals, then sending the two paths of multi-frequency microwave signals into a resolving module, extracting phase differences of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals by the resolving module, and resolving the optical delay to be measured of an optical link to be measured by using a phase-subtraction method according to the phase differences.
The dual-frequency multi-sideband modulation module can adopt a cascade form of two Mach-Zehnder modulators, and two paths of microwave signals are respectively input into microwave signal input ports of the two Mach-Zehnder modulators; or two paths of microwave signals can be coupled into one path and then input into a microwave signal input port of a Mach-Zehnder modulator; the dual-frequency multi-sideband modulation module in this embodiment adopts a dual-parallel mach-zehnder modulator (DPMZM), and two microwave signals are respectively input to two microwave signal input ports of the DPMZM. The modulator consists of three MZMs, an upper sub MZM and a lower sub MZM are embedded on two arms of a third MZM, so that the modulation state of each modulation signal is controllable, the insertion loss is small, the problem that the signal is too small after photoelectric conversion due to too large optical insertion loss caused by cascade modulation can be solved, and the problem that dense cluster signals are too small after photoelectric conversion due to the fact that the modulation state of a single modulation signal cannot be controlled when two paths of microwave signals are coupled and input is solved.
Let the frequency of the optical carrier be f0Strength of E0(ii) a The frequencies of the two microwave sources are respectively fm1、fm2The difference between the two is Δ f, and the initial phases of the optical carrier and the modulated signal are not considered for simplicity of discussion. The modulated output light can be expressed as:
wherein
And
phase difference between the two arms, beta, of MZM modulators on the upper and lower sub-arms, respectively1And beta2For the modulation depth of the two modulation signals,
is the phase difference between the upper and lower sub-arms, Jn(β1) And Jn(β2) Being the nth order function of Bessel functions of the first kind, AnAnd BnIs an integration coefficient, n is an integer; the spectrum is shown as a in fig. 2, with wavelength clusters containing two frequency components at each non-zero order sideband.
After passing through the photodetector, the electrical signal can be expressed as:
where eta is the response of the photodetector, alpha is the link transmission loss, and tauoFor the time delay introduced in the link transmission process, | | is an absolute value operation symbol. The available electrical signals contain: d, direct current; a cluster of zeroth order wavelengths Δ f, 2 Δ f, 3 Δ f … …; first order wavelength cluster fm1，fm1±Δf，fm1±2Δf，fm1± 3 Δ f … …; second order wavelength cluster 2fm1，2fm1±Δf，2fm1±2Δf，2fm13 af … …, and higher order wavelength clusters, each containing a plurality of closely spaced frequency components. The spectrum of the electrical signal output by the photodetection module is shown as b in fig. 2.
The time domain waveforms of the electric signals of the measuring path and the reference path are acquired and quantized through an acquisition module, and two paths of phase differences of each frequency component are obtained in a digital domain. If the time delay difference of two paths is tau, the phase difference between two paths of each frequency component
Comprises the following steps:
wherein N (f) is integer ambiguity corresponding to the selected frequency, and theta (f) is phase obtained by phase discrimination, and is in the interval of [0,2 pi ].
The invention obtains a modulated optical signal with a plurality of sparse wavelength clusters by utilizing a dual-frequency multi-sideband modulation structure, obtains a multi-frequency microwave signal with a plurality of sparse wavelength clusters after photoelectric conversion, can obtain the phase difference between measurement paths and reference paths of different frequency components by acquiring data once, and further solves the time delay of an optical link to be measured according to the phase-extrapolation principle. Because the digital domain phase demodulation is adopted and only single acquisition is needed, the time delay measurement speed is greatly improved, and the measurement stability is greatly improved.
The calculation method is specifically as follows:
the method comprises the steps of conventionally expanding two paths of phase differences of a low-order wavelength cluster, fitting the expanded phase differences to a frequency to form a straight line, wherein the slope of the straight line is k0(ii) a Then, phase expansion is carried out on any frequency component in the high-order wavelength cluster, phase difference-frequency straight line fitting is carried out on the phase difference of the expanded frequency component and the phase difference of the low-order wavelength cluster, and the slope is set to be k1(ii) a Therefore, the time delay tau of the optical link to be measured can be calculated1The formula is specifically expressed as follows:
τ1＝(k1/2π)-τ0 (7)
wherein k is0The slope, k, of a phase difference-frequency fitting straight line of a plurality of different frequency components in a low-order sparse wavelength cluster in two paths of multi-frequency microwave signals1The slope of a phase difference-frequency fitting straight line in two paths of multi-frequency microwave signals is formed by a frequency component selected from a high-order first-order sparse wavelength cluster and a plurality of different frequency components in a low-order sparse wavelength cluster, and f and N (f)m)、
Respectively selected frequency components from the first-order sparse wavelength clustersFrequency, integer ambiguity, phase difference of (2)]For the operator of rounding, τ0Is the time delay difference, tau, of the two paths of modulated optical signals when the optical link to be measured is not added1To solve the calculated delay of the light to be measured.
The time delay measurement precision can also be obtained by continuously expanding the phase of a higher-order wavelength cluster by adopting the formula and iterating to obtain a time delay measurement value tau with higher precisionnThe method comprises the following steps: based on the obtained time delay difference tau1Iterating n high-order sparse wavelength clusters according to the method, wherein n is an integer larger than 1, and thus obtaining a time delay measurement value tau with higher precisionn(ii) a The specific formula is expressed as follows:
τn＝(kn/2π)-τ0 (8)
in order to ensure that the phase difference-frequency of the dense frequency components in the sparse wavelength cluster can be accurately fitted into a straight line, the phase difference between the frequency components needs to be ensured to be less than pi, and the interval of the dense frequency components in the wavelength cluster is delta f, so that the frequency difference delta f of two modulation frequencies can meet the following requirements: the product of the frequency difference delta f and the optical time delay tau to be measured is less than or equal to one half, namely:
in conclusion, the measuring device has the advantages of simple structure, strong system stability and extremely simple and convenient resolving process, so that the rapid and high-stability optical time delay measurement can be realized.
Claims (10)
1. The optical time delay measuring method is characterized in that two paths of microwave signals with different frequencies are used for carrying out multi-sideband modulation on the same path of narrow linewidth optical carrier, and the product of the frequency difference of the two paths of microwave signals and the optical time delay to be measured is less than or equal to one half; dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, and the other path does not pass through the optical link to be measured to serve as a reference path, and respectively performing photoelectric conversion on the optical signal of the measuring path and the optical signal of the reference path to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters and each wavelength cluster comprises a plurality of dense frequency components; and extracting phase differences of a plurality of different frequency components in at least two adjacent sparse wavelength clusters in two paths of multi-frequency microwave signals in a digital domain, and solving the optical time delay to be measured by using a phase extrapolation method according to the phase differences.
2. The optical time delay measurement method according to claim 1, wherein the solution method of the optical time delay to be measured is specifically as follows:
N(f)＝[k0f/2π]，
τ1＝(k1/2π)-τ0
wherein k is0The slope, k, of a phase difference-frequency fitting straight line of a plurality of different frequency components in a low-order sparse wavelength cluster in two paths of multi-frequency microwave signals1The slope of a phase difference-frequency fitting straight line in two paths of multi-frequency microwave signals is formed by a frequency component selected from a high-order first-order sparse wavelength cluster and a plurality of different frequency components in a low-order sparse wavelength cluster, and f and N (f)m)、
Respectively the frequency, integer ambiguity and phase difference of the frequency component selected from the first-order sparse wavelength cluster]For the operator of rounding, τ0Is the time delay difference, tau, of the two paths of modulated optical signals when the optical link to be measured is not added1To solve the calculated delay of the light to be measured.
3. The optical time delay measurement method according to claim 2, wherein the calculation method of the optical time delay to be measured further comprises: based on the obtained time delay difference tau1Iterating n high-order sparse wavelength clusters according to the method, wherein n is an integer larger than 1, and thus obtaining a time delay measurement value tau with higher precisionn。
4. The method for optical time delay measurement according to claim 1, wherein the multi-sideband modulation is performed using a dual parallel mach-zehnder modulator.
5. The optical time delay measurement method according to any one of claims 1 to 4, wherein the phase difference of a certain frequency component in the two multi-frequency microwave signals is extracted in the digital domain by the following method: firstly, fast Fourier transform is respectively carried out on time domain signals in the two paths of multi-frequency microwave signals to obtain the phase of the frequency component in the two paths of multi-frequency microwave signals, and further the phase difference is obtained.
6. An optical time delay measuring device, comprising:
the double-frequency multi-sideband modulation module is used for carrying out multi-sideband modulation on the same narrow linewidth optical carrier by using two paths of microwave signals with different frequencies, and the product of the frequency difference of the two paths of microwave signals and the optical delay to be measured is less than or equal to one half;
the photoelectric conversion module is used for dividing the generated modulated optical signal into two paths, wherein one path passes through an optical link to be measured to serve as a measuring path, the other path does not pass through the optical link to be measured to serve as a reference path, and the optical signals of the measuring path and the reference path are respectively subjected to photoelectric conversion to obtain two paths of multi-frequency microwave signals which are provided with a plurality of sparse wavelength clusters, and each wavelength cluster comprises a plurality of dense frequency components;
and the resolving module is used for extracting the phase difference of a plurality of different frequency components of at least two adjacent sparse wavelength clusters in the two paths of multi-frequency microwave signals in the digital domain and resolving the optical delay to be measured by using a phase-deduction method according to the phase difference.
7. The optical delay measuring device according to claim 1, wherein the method for calculating the optical delay to be measured is specifically as follows:
N(f)＝[k0f/2π]，
τ1＝(k1/2π)-τ0
wherein k is0The slope, k, of a phase difference-frequency fitting straight line of a plurality of different frequency components in a low-order sparse wavelength cluster in two paths of multi-frequency microwave signals1The slope of a phase difference-frequency fitting straight line in two paths of multi-frequency microwave signals is formed by a frequency component selected from a high-order first-order sparse wavelength cluster and a plurality of different frequency components in a low-order sparse wavelength cluster, and f and N (f)m)、
Respectively the frequency, integer ambiguity and phase difference of the frequency component selected from the first-order sparse wavelength cluster]For the operator of rounding, τ0Is the time delay difference, tau, of the two paths of modulated optical signals when the optical link to be measured is not added1To solve the calculated delay of the light to be measured.
8. The optical delay measuring apparatus according to claim 7, wherein the method of calculating the optical delay to be measured further comprises: based on the obtained time delay difference tau1Iterating n high-order sparse wavelength clusters according to the method, wherein n is an integer larger than 1, and thus obtaining a time delay measurement value tau with higher precisionn。
9. The optical delay measurement device of claim 6, wherein the dual-frequency multi-sideband modulation module performs the multi-sideband modulation using a dual parallel mach-zehnder modulator.
10. The optical delay measuring device according to any one of claims 6 to 9, wherein the phase difference of a certain frequency component in the two multi-frequency microwave signals is extracted in the digital domain by the following method: firstly, fast Fourier transform is respectively carried out on time domain signals in the two paths of multi-frequency microwave signals to obtain the phase of the frequency component in the two paths of multi-frequency microwave signals, and further the phase difference is obtained.
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