Broadband multi-signal instantaneous frequency measuring device and method based on simple three optical combs
The broadband multi-signal instantaneous frequency measurement device using a simple three-optical comb structure addresses the limitations of existing systems by generating optical combs for accurate frequency determination of multi-tone signals, reducing complexity and cost while maintaining high accuracy.
Patent Information
- Application Number
- CN202411369054.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-29
- Publication Date
- 2024-12-06
AI Technical Summary
Existing microwave frequency measurement systems face challenges in achieving high accuracy and flexibility due to the limitations of electronic bottlenecks, particularly in measuring multi-tone signals, with current methods either being inaccurate, costly, or requiring complex topologies.
A broadband multi-signal instantaneous frequency measurement device using a simple three-optical comb structure, which divides optical and RF signals into multiple paths, employs modulators and local oscillator signal sources to generate optical combs, and utilizes photodetectors to convert signals for accurate frequency determination.
The device achieves high measurement accuracy and flexibility by generating intermediate frequency signals, reducing complexity and cost, and enabling unambiguous measurement of multi-frequency signals with minimal error, independent of optical comb flatness.
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Figure CN119087035A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of frequency measurement, and in particular to a broadband multi-signal instantaneous frequency measurement device and method based on a simple three-optical comb. Background Art
[0002] In electronic countermeasures, wireless communications and other systems, it is often necessary to measure the parameters of unknown microwave signals. The measured parameters mainly include RF signal frequency, arrival angle, signal type, etc. Among them, the measurement of microwave signal frequency is crucial.
[0003] Instantaneous Frequency Measurement (IFM) technology refers to the rapid measurement of the frequency of an unknown signal within a short period of time. As the working bandwidth of the RF system gradually increases, traditional electronic systems are unable to complete the task of broadband IFM due to the limitation of "electronic bottleneck".
[0004] The IFM method based on microwave photonic technology utilizes the large bandwidth and anti-electromagnetic interference characteristics of microwave photonic technology to process signals in the optical domain, which can greatly expand the system bandwidth and has the advantages of large instantaneous bandwidth, wide operating frequency range, and anti-electromagnetic interference. At present, the microwave frequency measurement systems based on microwave photonic technology mainly include frequency-power mapping type, frequency-time mapping type, and frequency-space mapping type. The frequency-power mapping type utilizes the different amplitude response characteristics of different frequency signals in a specific system. By measuring the power of the output signal, the frequency of the signal to be measured is calculated. This type of scheme has a relatively simple structure, but it usually cannot measure multi-tone signals. The frequency-time mapping type utilizes the different transmission time characteristics of optical signals of different frequencies in the medium, separates signals of different frequencies in the time domain, and calculates the signal frequency by measuring the signal delay. This type of scheme can measure multi-frequency signals, but the accuracy is generally poor; the frequency-space mapping type divides the spectrum into multiple small intervals, separates signals of different frequencies in space, and detects them. This type of scheme can measure multi-tone signals and is easy to topology, but the topology cost is high and the accuracy is relatively poor. The scanning frequency measurement scheme continuously changes the frequency of the optical local oscillator signal to scan it within the entire frequency measurement range, and receives and measures the signal through a down-conversion structure. This type of scheme requires frequency scanning within the entire frequency measurement range, with high measurement accuracy but slow speed. Summary of the invention
[0005] The main purpose of the present application is to provide a broadband multi-signal instantaneous frequency measurement device and method based on a simple three-light comb, aiming to solve the problem of poor measurement accuracy of existing measurement methods.
[0006] To achieve the above-mentioned purpose, the present application provides a broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb, comprising: a laser, the laser is used to output an optical carrier signal; an optical power splitter, the input end of which is connected to the output end of the laser; at least two modulators, the input end of each modulator is correspondingly connected to the output end of the optical power splitter, the radio frequency end is connected to a local oscillator signal source, and the output end is connected to a photodetector; an electrical power splitter, the input end is connected to the RF signal to be measured, and the output end is connected to the radio frequency end of each modulator; a spectrum processor, connected to all photodetectors, the spectrum processor is used to determine the frequency of the RF signal to be measured according to the signal output by the photodetector; wherein the frequency of each local oscillator signal source is different.
[0007] Optionally, the modulators include three.
[0008] The present application also provides a broadband multi-signal instantaneous frequency measurement method based on a simple three-optical comb, which adopts the measurement device of claim 1, including: a laser outputs a continuous optical carrier divided into multiple optical paths through an optical power divider, and the optical signal on each optical path enters the input end of the corresponding modulator; the RF signal to be measured is divided into electrical signals with the same number as the optical paths through an electrical power divider, and each electrical signal enters a radio frequency port of the corresponding modulator; the output signal of each electrical local oscillator signal source is input into another radio frequency port of the corresponding modulator, and the modulator uses the output signal of the electrical local oscillator signal source and the optical signal to modulate the RF signal to be measured to obtain a modulated signal; each modulated signal is input into a corresponding photodetector, and the photodetector converts the modulated signal into an electrical signal; all electrical signals enter a spectrum processor, and the spectrum processor determines the position of the optical comb that beats with the RF signal to be measured according to the electrical signal, and determines the frequency of the RF signal to be measured according to the position of the optical comb, the electrical signal and the relationship between the preset parameters.
[0009] Optionally, the preset parameter relationship includes a first preset parameter relationship and a second preset parameter relationship, and the first preset parameter relationship is:
[0010] f RF =kf LO1 -f IF1
[0011] The second preset parameter relationship is:
[0012] f RF =kf LO1 +f IF1
[0013] In the formula, f LO1 is the frequency of the electric local oscillator signal source, f IF1 is the frequency of the electrical signal output by the photodetector corresponding to the electrical local oscillator signal source, and k is the position of the optical comb.
[0014] Optionally, the position of an optical comb that beats with the RF signal to be measured is determined according to the electrical signal, and the frequency of the RF signal to be measured is determined according to the position of the optical comb, the electrical signal and the relationship between preset parameters, including: taking any two adjacent optical paths as the first optical path and the second optical path; determining the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path, and the difference in the optical comb intervals of the two modulators, and determining the position of the optical comb that beats with the RF signal to be measured according to the ratio of the two differences; determining the frequency of the RF signal to be measured according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and the relationship between preset parameters.
[0015] Optionally, when it is determined that the number of frequency spectra output by any photodetector in the first optical path and the second optical path is inconsistent with the number of frequencies of the RF signal to be measured, the method also includes: using any optical path in the remaining optical paths as a third optical path; determining the position of the optical comb that beats with the RF signal to be measured according to the ratio of the difference in the frequencies of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path, and the difference in the optical comb intervals of the two modulators; and determining the frequency of the RF signal to be measured according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and a preset parameter relationship.
[0016] Optionally, determining the position of the optical comb that beats the RF signal to be measured according to the electrical signal, and determining the frequency of the RF signal to be measured according to the position of the optical comb, the electrical signal and the relationship between the preset parameters, includes: taking any three adjacent optical paths as the first optical path, the second optical path and the third optical path; determining the difference in the frequency of the electrical signal output by the photoelectric detector corresponding to the first optical path and the second optical path, and the difference in the optical comb intervals of the two modulators, and determining the position of the optical comb that beats the RF signal to be measured according to the ratio of the two differences; determining the position of the optical comb that beats the RF signal to be measured according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, and the photoelectric detector corresponding to the first optical path; The method comprises the following steps: determining a first measurement result based on the frequency of the electrical signal output by the photodetector corresponding to the first optical path and the third optical path, and determining a position of the optical comb that beats with the RF signal to be measured based on the ratio of the two differences, according to the difference in the frequencies of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path, and the difference in the optical comb intervals of the two modulators; determining a second measurement result based on the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and the preset parameter relationship; and taking the same frequency in the first measurement result and the second measurement result as the frequency of the RF signal to be measured.
[0017] Optionally, if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is positive, the preset parameter relationship is the first preset parameter relationship; if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is negative, the preset parameter relationship is the second preset parameter relationship.
[0018] Optionally, if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path is negative, the preset parameter relationship is the first preset parameter relationship; if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is positive, the preset parameter relationship is the second preset parameter relationship.
[0019] Compared with the prior art, the present invention has the following beneficial effects:
[0020] The broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb of the present invention divides the optical carrier signal output by the laser into multiple optical paths through an optical power divider, and simultaneously divides the RF signal to be measured into multiple components through an electrical power divider, and correspondingly sets a modulator and a local oscillator signal source. When the modulator receives the multi-tone signal, signals of different frequencies will beat with the corresponding optical comb teeth, thereby generating different intermediate frequency signals in a two-dimensional spectrum. According to the frequency of each intermediate frequency signal, the frequency of each signal in the multi-tone signal can be calculated; by changing the frequency and power of the local oscillator signal, the measurement bandwidth of the system can be changed without adding additional devices, thereby retaining the advantage of high topological flexibility and solving the disadvantage of high topological cost; using a photoelectric detector to beat the RF signal to be measured with the optical comb, it is only to convert a large bandwidth frequency into a small bandwidth, which is easy to directly measure. The introduced error is very small and is only related to the frequency accuracy of the local oscillator signal source. Therefore, as long as the sampling accuracy of the subsequent ADC is improved, a very high measurement accuracy can be achieved; the device has a simple structure and a large bandwidth. The broadband multi-signal instantaneous frequency measurement method based on a simple three-optical comb of the present invention divides the RF signal to be measured into multiple components, and correspondingly sets multiple modulators and local oscillator signal sources. Multiple different local oscillator signal sources can generate multiple groups of optical combs with different free frequency intervals, which are respectively coupled with the RF signal to be measured. After independent beat frequency detection, the frequency of the RF signal to be measured is calculated according to the intermediate frequency component of the detection output. Since the process of solving the radio frequency frequency only uses the frequency component of the intermediate frequency, there is no requirement for the flatness of the optical comb; a third signal is introduced, and the beat frequency result of the third photodetector is used to further determine the relationship between the frequency of the RF signal to be measured and the corresponding optical comb frequency, thereby accurately determining the frequency of the RF signal to be measured, and realizing unambiguous measurement of multi-frequency signals. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 This is a schematic diagram of the structure of a broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb in this application;
[0022] Figure 2 This is a flow chart of a broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb in this application;
[0023] Figure 3 This is an output spectrum diagram of the first modulator in a broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb in this application;
[0024] Figure 4 This is an output spectrum diagram of the first photodetector in a broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb in this application;
[0025] Figure 5 This is an output spectrum diagram of the second photodetector in a broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb in this application;
[0026] Figure 6 This is an output spectrum diagram of the third photodetector in a broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb in this application;
[0027] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0028] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.
[0029] The first embodiment of the present invention provides a broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb, such as Figure 1 As shown, it includes a laser L, an optical power splitter OPS, at least two modulators MZM, an electric power splitter EPS and a spectrum processor SP, the laser L is used to output an optical carrier signal; the optical power splitter OPS is located at the optical output end of the laser source; at least two modulators (in this embodiment, they may include a first modulator MZM1 and a second modulator MZM2), the input end of each modulator is correspondingly connected to the output end of the optical power splitter OPS, any RF end is connected to a local oscillator signal source, and the output end is connected to a photodetector; the electric power splitter EPS, the input end is connected to the RF signal to be measured, and the output end is connected to the other RF end of each modulator; the spectrum processor SP is connected to all the photodetectors, and the spectrum processor SP is used to determine the frequency of the RF signal to be measured according to the signal output by the photodetector; wherein the frequency of each local oscillator signal source is different.
[0030] Exemplarily, the modulators may include three, four, five, or more modulators, and the modulators may be dual-drive Mach-Zehnder modulators (MZM). The following describes the measuring device by taking three modulators as an example.
[0031] The modulators may be a first modulator MZM1, a second modulator MZM2 and a third modulator MZM3; the corresponding local oscillator signal sources may be a first local oscillator signal source 1, a second local oscillator signal source 2 and a third local oscillator signal source 3; the photodetectors may be a first photodetector PD1, a second photodetector PD2 and a third photodetector PD3.
[0032] The input ends of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3 are correspondingly connected to the output end of the optical power divider OPS, one RF port of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3 is correspondingly connected to the first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3, and the output ends are correspondingly connected to the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3; the output end of the electrical power divider EPS is connected to another RF port of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3; the spectrum processor SP is connected to the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3, and the frequencies of the first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3 are different.
[0033] The second embodiment of the present invention provides a broadband multi-signal instantaneous frequency measurement method based on a simple three-optical comb, using the above-mentioned measurement device, such as Figure 2 As shown, the specific steps include:
[0034] Step S1, the continuous optical carrier output by the laser is divided into multiple optical paths through an optical power divider, and the optical signal on each optical path enters the input end of the corresponding modulator;
[0035] Specifically, the continuous optical carrier output by the laser L is divided into three optical paths through the optical power splitter OPS, and the optical signal on each optical path enters the input end of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3 respectively; the continuous optical carrier output by the laser L is expressed by the following formula:
[0036] E in (t) = E0exp(j2πf c t)
[0037] The bias voltages of the three modulators are set according to Calculate, V π is the half-wave voltage of the modulator.
[0038] Step S20, the RF signal to be tested is divided into electrical signals having the same number as the optical paths by an electrical power divider, and each electrical signal enters a radio frequency port of the modulator;
[0039] Specifically, the RF signal to be measured is divided into three electrical signals by the electrical power divider EPS, and each electrical signal enters a radio frequency port of the input end of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3 respectively, and the DC bias angles of the first modulator MZM1, the second modulator MZM2 and the third modulator MZM3 are α1, α2 and α3 respectively, which can be controlled by their DC voltages respectively;
[0040] Step S30, the output signal of each electric local oscillator signal source is input to another RF port of the corresponding modulator, and the modulator modulates the RF signal to be measured using the output signal of the electric local oscillator signal source and the optical signal to obtain a modulated signal;
[0041] Specifically, the output signals of the first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3 are correspondingly input to another RF port of the first modulator MZM1, the second modulator MZM2, and the third modulator MZM3, and the phase difference between the RF signal to be measured and the optical frequency comb is adjusted through the output signals of the first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3 and the optical signals of the corresponding optical paths, so that the RF signal to be measured can beat with any optical comb, and three modulated signals are obtained; the RF signal to be measured is:
[0042] V RF (t) = V RF cos(j2πf RF t)
[0043] The first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3 are respectively:
[0044] V LO1 (t) = V LO cos(j2πf LO1 t)
[0045] V LO2 (t) = V LO cos(j2πf LO2 t)
[0046] V LO3 (t) = V LO cos(j2πf LO3 t)
[0047] Where E0 is the light field amplitude of the laser source output light signal, f c is the frequency of the optical carrier, V RFis the amplitude of the RF signal, f RF is the frequency of the RF signal, V LO is the amplitude of the local oscillator signal, f LO1 、f LO2 and f LO3 are the frequencies of the first local oscillator signal source 1, the second local oscillator signal source 2, and the third local oscillator signal source 3, respectively. The difference between the three is a small frequency f0, that is, f LO1 =f LO2 -f0=f LO3 +f0.
[0048] Step S50, each modulated signal is input into a corresponding photodetector, and the photodetector converts the modulated signal into an electrical signal;
[0049] Specifically, the three modulation signals are respectively input into the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 to convert the modulation signals into electrical signals. The principle is: the optical signal output by the photodetector is sent to the low-frequency DC isolation PD for beat frequency detection. For the spectrum of the beat frequency signal, the analysis frequency is less than f LO1 / 2 part and the DC component is suppressed, so only the RF first-order sideband and the beat frequency component of the adjacent optical frequency comb signal can be observed. Since the interval of the optical comb is f LO1 , so only one frequency of the optical comb and the component obtained by the beat frequency of the signal to be measured will be received. The optical comb is used to down-convert the high-frequency signal to a lower-frequency intermediate-frequency signal, and the error introduced is small, and the error is independent of the frequency. Therefore, the frequency measurement error can be reduced while the frequency measurement bandwidth is increased. This solution greatly reduces the complexity and cost of the system by optimizing the optical comb generation and coupling structure, and can achieve unambiguous measurement of multi-tone signals.
[0050] In step S50, all electrical signals enter the spectrum processor SP, which determines the position of the optical comb that beats the RF signal to be measured according to the electrical signals, and determines the frequency of the RF signal to be measured according to the relationship between the position of the optical comb, the electrical signals and preset parameters.
[0051] Step S51, taking any two adjacent optical paths as the first optical path and the second optical path; in this embodiment, the modulator and the photodetector corresponding to the first optical path are the first modulator MZM1 and the first photodetector PD1, respectively, and the modulator and the photodetector corresponding to the second optical path are the second modulator MZM2 and the second photodetector PD2, respectively; the outputs of the first modulator MZM1 and the second modulator MZM2 can be expressed as:
[0052]
[0053] Where m1 = πV LO / V πRepresents the LO signal modulation index, m2=πV RF / V π represents the RF signal modulation index, J n (·) represents the first-order n-order Bessel function. The local oscillator signal drives the modulator with high power, so multiple sidebands need to be considered; the power of the RF signal is generally small, and only the first-order sideband needs to be considered when the Bessel function is expanded. Therefore, the output of the first modulator MZM1 and the second modulator MZM2 can be further expressed as follows:
[0054]
[0055] Assuming that the first-order sideband obtained by the RF modulated signal is near the kth optical comb, the beat frequency signal output by the first photodetector PD1 and the second photodetector PD2 can be simplified as:
[0056]
[0057] η represents the responsiveness of PD. From the above formula, it can be seen that no matter which interval the signal to be measured is in, it can beat with the optical comb to generate an intermediate frequency signal. The frequency of this intermediate frequency signal is the frequency difference between the signal to be measured and the nearest optical comb.
[0058] Step S52, determining the difference in frequency of the electrical signal output by the first photodetector PD1 and the second photodetector PD2, and the difference in the optical comb intervals of the first modulator MZM1 and the second modulator MZM2, and calculating the ratio of the two differences to determine the position of the optical comb that beats the RF signal to be measured, that is, the number of the optical comb;
[0059] Specifically, assuming that the frequency of the signal to be measured is near the kth optical comb, the frequency difference of the intermediate frequency signal generated by the beat frequency of PD1 and PD2 can be expressed as:
[0060] |Δf|=|f IF1 -f IF2 |=k(f LO2 -f LO1 )=kf0
[0061] Among them, f IF1 and f IF2Represents the frequency of the output signal of PD1 and PD2. It can be seen that after the signal to be measured beats with different optical combs, the frequency difference of the intermediate frequency signals generated by PD1 and PD2 is different and must be equal to an integer multiple of f0. By measuring the frequency difference of the output signals of PD1 and PD2, and calculating the difference between the optical comb intervals of the first modulator MZM1 and the second modulator MZM2, that is, the frequency difference f0 between the first local oscillator signal source 1 and the second local oscillator signal source 2, the k value can be obtained, that is, the position of the optical comb that beats with the RF signal to be measured. After determining the position of the optical comb, it is also necessary to determine whether the frequency of the RF signal to be measured is higher than the frequency of the optical comb, that is, whether the RF signal to be measured is located on the left or right side of the optical comb. Specifically, it can be judged according to the following principles:
[0062] Assuming that the frequency of the RF signal to be measured is lower than the frequency of the optical comb, that is, it is on the left side of the optical comb, when the signal beats with the optical comb of the downstream, since the frequency of the corresponding optical comb of the downstream increases by kf0, the frequency difference between the signal and the downstream optical comb will increase by kf0 compared with the upstream, that is, f IF1 Less than f IF2 , the difference is negative. When the signal frequency is higher than the optical comb frequency, that is, on the right side of the optical comb, since the frequency of the corresponding optical comb in the downstream increases by kf0, the frequency difference between the signal and the downstream optical comb will decrease by kf0, that is, f IF1 Greater than f IF2 , the difference is positive. Therefore, we can use f IF1 and f IF2 The positive or negative value of the difference determines whether the frequency of the RF signal to be measured is higher than the frequency of the optical comb.
[0063] Step S53, determining the frequency of the RF signal to be measured according to the position of the optical comb, the optical comb interval of the first modulator MZM1, the frequency of the electrical signal output by the first photodetector PD1, and a preset parameter relationship;
[0064] Specifically, the preset parameter relationship includes a first preset parameter relationship and a second preset parameter relationship. Based on whether the frequency of the RF signal to be measured is higher than the frequency of the optical comb, the preset parameter relationship is determined to be the first preset parameter relationship or the second preset parameter relationship, that is, by f IF1 and f IF2 The positive or negative value of the difference determines the preset parameter relationship. Specifically, if the difference in the frequency of the electrical signal output by the first photodetector PD1 and the second photodetector PD2 is negative, the preset parameter relationship is the first preset parameter relationship, and the first preset parameter relationship is;
[0065] f RF =kf LO1 -f IF1
[0066] If the difference between the frequencies of the electrical signals output by the first photodetector PD1 and the second photodetector PD2 is positive, the preset parameter relationship is the second preset parameter relationship, which is:
[0067] f RF =kf LO1 +f IF1
[0068] In the formula, f LO1 is the frequency of the first electrical local oscillator signal source, f IF1 is the frequency of the electrical signal output by the first photodetector PD1, and k is the position of the optical comb.
[0069] Step S54, if the number of frequencies of the RF signal to be measured outputted at this time is consistent with the number of spectra outputted by the first photodetector PD1 or the second photodetector PD2, the current output is the final measurement result. When the frequency of the RF signal is close to the center frequency of the optical comb or the two optical comb frequencies, that is, when the number of spectra outputted by the first photodetector PD1 or the second photodetector PD2 is inconsistent with the number of frequencies of the RF signal to be measured, it is impossible to distinguish whether the RF signal changes directly or exceeds the current interval and moves to another frequency interval, so there will be ambiguity in some frequency points, and further calculation needs to be performed by introducing a third optical path. The specific steps are as follows.
[0070] Step S55, determining the optical comb position that beats with the RF signal to be measured according to the ratio of the frequency difference of the electrical signals output by the first photodetector PD1 and the third photodetector PD3 to the difference between the optical comb intervals of the first modulator MZM1 and the third modulator MZM3;
[0071] Step S56, determining the frequency of the RF signal to be measured according to the optical comb position, the optical comb interval of the first modulator MZM1, the frequency of the electrical signal output by the first photodetector PD1 and the preset parameter relationship, wherein the principle of selecting the preset parameter relationship is: if the difference in frequency between the electrical signals output by the first photodetector PD1 and the second photodetector PD2 is positive, the preset parameter relationship is the first preset parameter relationship; if the difference in frequency between the electrical signals output by the first photodetector PD1 and the second photodetector PD2 is negative, the preset parameter relationship is the second preset parameter relationship.
[0072] The method for determining the frequency of the RF signal to be measured may also be determined based on the electrical signals of any three adjacent optical paths. Step S50 specifically includes the following steps:
[0073] Step S510, determining the position of the optical comb that beats with the RF signal to be measured according to the ratio of the frequency difference of the electrical signals output by the first photodetector PD1 and the second photodetector PD2 to the difference between the optical comb intervals of the first modulator MZM1 and the second modulator MZM2;
[0074] Step S520, determining a first measurement result according to the position of the optical comb, the optical comb interval of the first modulator MZM1, the frequency of the electrical signal output by the first photodetector PD1, and a preset parameter relationship;
[0075] Step S530, determining the position of the optical comb that beats with the RF signal to be measured according to the ratio of the frequency difference of the electrical signals output by the first photodetector PD1 and the third photodetector PD3 to the difference between the optical comb intervals of the first modulator MZM1 and the third modulator MZM3;
[0076] Step S540, determining a second measurement result according to the position of the optical comb, the optical comb interval of the first modulator MZM1, the frequency of the electrical signal output by the first photodetector PD1, and a preset parameter relationship;
[0077] Step S550: taking the same frequency in the first measurement result and the second measurement result as the frequency of the RF signal to be measured.
[0078] Among them, the formula of the preset parameter relationship is the same as the formula of the preset parameter relationship mentioned above, and will not be repeated here.
[0079] Example 1
[0080] Step 1, the continuous optical carrier output frequency generated by the laser source is 193.1THz and the power is 16dBm; the dual-tone RF signal to be tested generated by the RF signal source has a frequency of 6.8GHz and 16.8GHz and a power of -20dBm; the local oscillator signal frequency generated by the first local oscillator signal source 1 passed into the first modulator MZM1 is 4GHz and the power is 25dBm. The spectrum output by the first modulator MZM1 is shown in Figure 3 ; The second local oscillator signal source 2 passed into the second modulator MZM2 generates a local oscillator signal with a frequency of 4.1 GHz and a power of 25 dBm; the third local oscillator signal source 3 passed into the third modulator MZM3 generates a local oscillator signal with a frequency of 3.9 GHz and a power of 25 dBm; the half-wave voltage of the three modulators is 5 V, the insertion loss is 6 dB, and the extinction ratio is 35 dB; the responsivity of the three photodetectors is 0.65 A / W.
[0081] Step 2, adjusting the DC bias voltage to satisfy the output of the first modulator MZM1 and the second modulator MZM2, so that the RF modulated signal can beat the frequency with each optical comb;
[0082] Step 3, observe the outputs of the first photodetector PD1 and the second photodetector PD2, such as Figure 4 and Figure 5 As shown in the figure, it can be seen that there are two frequency components in the first photodetector PD1 and the second photodetector PD2 respectively. The component in the first photodetector PD1 is recorded as IF 1,1 and IF 1,2 , the component in the second photodetector PD2 is recorded as IF 2,1 and IF 2,2 IF 1,1 The frequency of is 0.8GHz, and it moves to the left to 0.4GHz in the second photodetector PD2, which is reduced by 0.4GHz. k is calculated to be 4, so it is judged to be on the right side of the fourth optical comb, that is, 16~18GHz, and IF is generated. 1,1 The RF signal frequency of the signal is 16+0.8=16.8GHz; IF 1,2 The frequency of is 1.2GHz, and it moves to the right to 1.4GHz in PD2, increasing by 0.2GHz. k is calculated to be 2, so it is judged to be on the left side of the second optical comb, that is, 6~8GHz, which generates IF 1,2 The RF signal frequency of the signal is 8-1.2=6.8 GHz. Since the RF signal frequency consistent with the input has been obtained at this time, there is no need to perform further measurement through the third optical path.
[0083] If the RF signal frequency is inconsistent with the input, further measurement is performed through the third optical path; observe the output of the third photodetector PD3, see Figure 6 It can be found that the change law of the second photodetector PD2 is exactly opposite, so the measurement method is the same as above, except that when selecting the preset parameter relationship, it is just opposite to the second optical path. By combining the three photodetectors, the unambiguous instantaneous measurement of the multi-tone signal frequency can be achieved.
[0084] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.
Claims
1. A broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb, characterized in that: include: A laser, wherein the laser is used to output an optical carrier signal; An optical power splitter, the input end of which is connected to the output end of the laser; At least two modulators, each modulator has an input end correspondingly connected to the output end of the optical power divider, a radio frequency end connected to a local oscillator signal source, and an output end connected to a photodetector; An electric power divider, the input end of which is connected to the RF signal to be measured, and the output end of which is connected to the RF end of each of the modulators; A spectrum processor connected to all the photodetectors, the spectrum processor being used to determine the frequency of the RF signal to be measured according to the signal output by the photodetectors; Wherein, the frequency of each local oscillator signal source is different.
2. The broadband multi-signal instantaneous frequency measurement device based on a simple three-optical comb according to claim 1 is characterized in that: The modulators include three.
3. A broadband multi-signal instantaneous frequency measurement method based on a simple three-optical comb, characterized in that: The measuring device according to claim 1 comprises: The continuous optical carrier output by the laser is divided into multiple optical paths through an optical power splitter, and the optical signal on each optical path enters the input end of the corresponding modulator; The RF signal to be measured is divided into electrical signals of the same number as the optical paths by an electrical power divider, and each of the electrical signals enters a RF port corresponding to the modulator; The output signal of each electric local oscillator signal source is input into another RF port of the corresponding modulator, and the modulator modulates the RF signal to be measured using the output signal of the electric local oscillator signal source and the optical signal to obtain a modulated signal; Each of the modulated signals is input into a corresponding photodetector, and the photodetector converts the modulated signal into an electrical signal; All the electrical signals enter the spectrum processor, which determines the position of the optical comb that beats the RF signal to be measured based on the electrical signals, and determines the frequency of the RF signal to be measured based on the position of the optical comb, the electrical signals and the relationship between preset parameters.
4. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 3 is characterized in that: The preset parameter relationship includes a first preset parameter relationship and a second preset parameter relationship, wherein the first preset parameter relationship is: f RF =kf LO1 -f IF1 The second preset parameter relationship is: f RF =kf LO1 +f IF1 In the formula, f LO1 is the frequency of the electric local oscillator signal source, f IF1 is the frequency of the electrical signal output by the photodetector corresponding to the electrical local oscillator signal source, and k is the position of the optical comb.
5. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 4 is characterized in that: The step of determining the position of the optical comb that beats the RF signal to be measured according to the electrical signal, and determining the frequency of the RF signal to be measured according to the position of the optical comb, the electrical signal and a relationship between preset parameters, includes: Taking any two adjacent light paths as the first light path and the second light path; Determine the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path, and the difference in the intervals of the optical combs of the two modulators, and determine the position of the optical comb that beats the RF signal to be measured according to the ratio of the two differences; The frequency of the RF signal to be measured is determined according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and a preset parameter relationship.
6. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 5 is characterized in that: When it is determined that the number of frequency spectra output by any photodetector in the first optical path and the second optical path is inconsistent with the number of frequencies of the RF signal to be measured, the method further includes: Using any one of the remaining light paths as the third light path; According to the difference in the frequencies of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path, and the difference in the optical comb intervals of the two modulators, and according to the ratio of the two differences, determining the position of the optical comb that beats the RF signal to be measured; The frequency of the RF signal to be measured is determined according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and a preset parameter relationship.
7. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 3 is characterized in that: The step of determining the position of the optical comb that beats the RF signal to be measured according to the electrical signal, and determining the frequency of the RF signal to be measured according to the position of the optical comb, the electrical signal and a relationship between preset parameters, includes: Taking any three adjacent light paths as a first light path, a second light path and a third light path; Determine the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path, and the difference in the intervals of the optical combs of the two modulators, and determine the position of the optical comb that beats the RF signal to be measured according to the ratio of the two differences; Determine a first measurement result according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and a preset parameter relationship; According to the difference in the frequencies of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path, and the difference in the optical comb intervals of the two modulators, and according to the ratio of the two differences, determining the position of the optical comb that beats the RF signal to be measured; Determine a second measurement result according to the position of the optical comb, the optical comb interval of the modulator corresponding to the first optical path, the frequency of the electrical signal output by the photodetector corresponding to the first optical path, and a preset parameter relationship; The same frequency in the first measurement result and the second measurement result is used as the frequency of the RF signal to be measured.
8. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 4 or 7, characterized in that: If the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is positive, the preset parameter relationship is the first preset parameter relationship; if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is negative, the preset parameter relationship is the second preset parameter relationship.
9. The broadband multi-signal instantaneous frequency measurement method based on a simple three-light comb according to claim 5 or 7, characterized in that: If the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the third optical path is negative, the preset parameter relationship is the first preset parameter relationship; if the difference in frequency of the electrical signals output by the photodetectors corresponding to the first optical path and the second optical path is positive, the preset parameter relationship is the second preset parameter relationship.