An instantaneous frequency measurement device and method based on an unbalanced dual-arm MZI
By using an optical link based on unbalanced double-arm MZI for phase modulation and signal processing in electronic warfare, the shortcomings of traditional electronic instantaneous frequency measurement methods in complex electromagnetic environments are solved, and efficient and simplified microwave signal frequency measurement is achieved, which is suitable for modern electronic warfare needs.
Patent Information
- Application Number
- CN202211010398.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-23
- Publication Date
- 2025-06-20
- Estimated Expiration
- 2042-08-23
AI Technical Summary
When facing complex electromagnetic environments and high-frequency and large bandwidth signals, the traditional electronic instantaneous frequency measurement method is huge in size, complex structure, expensive in construction and susceptible to electromagnetic interference, and cannot meet the needs of modern electronic warfare.
An optical link based on unbalanced double-arm MZI is adopted to modulate the microwave signal to be measured onto the optical wave through a phase modulator, and the signal processing is performed using the differential delay of MZI to realize instantaneous frequency measurement of the microwave signal.
This method has no intrinsic 3dB optical loss, the signal intensity remains unchanged, and the bias control is eliminated. The front end of the system is simplified, suitable for military occasions, and the frequency measurement error is less than 60MHz.
Smart Images
Figure CN115459861B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electronic reconnaissance, and particularly to an instantaneous frequency measurement device and method based on an unbalanced dual-arm MZI. Background Art
[0002] In modern electronic warfare, it is necessary to first detect the electromagnetic radiation information of the enemy for interference, deception, etc. The electromagnetic pulse density on the battlefield is extremely high, and modern electronic support reconnaissance systems already have the ability to work in a signal environment of millions of pulses per second. Instantaneous frequency measurement is an important technology developed to meet the requirements of electronic warfare support systems for high intercept probability, large instantaneous bandwidth, and fast pulse measurement. Traditional instantaneous frequency measurement receivers are based on electronic methods and can complete the frequency measurement of signals within a certain bandwidth, but they are bulky, complex in structure, expensive in cost, and vulnerable to electromagnetic interference. Facing the increasingly complex electromagnetic environment, especially the frequency measurement of high-frequency and large-bandwidth signals, the traditional electronic frequency measurement methods face great challenges due to their own bottlenecks and cannot meet the requirements of modern electronic warfare. Due to the advantages of large bandwidth, low loss, small size, light weight, and anti-electromagnetic interference of optical fibers, the photon-assisted instantaneous frequency measurement technology has attracted much attention.
[0003] The photon-assisted instantaneous frequency measurement system mainly modulates the intercepted microwave signal onto an optical wave, and through certain optical processing, generates a mapping relationship related to the frequency of the signal to be measured, such as constructing an amplitude comparison function (ACF) related to the frequency f. In current conventional methods, it is inevitable to use a Mach-Zehnder intensity modulator, but the intensity modulation-based link has the following problems: (1) A bias circuit is required for bias point control, such as the commonly used quadrature bias point. Sometimes, in a harsh working environment, it is impossible to maintain it at the required bias point, which seriously affects the operation of the system. (2) The intensity modulator operating at the quadrature bias point has an inherent 3dB loss, thus failing to effectively utilize the input optical power and reducing the signal intensity. (3) The optical intensity in the intensity modulation link changes, so it is susceptible to nonlinear effects during transmission. These factors limit the application scenarios of the intensity modulation-based link, especially in military applications. Summary of the Invention
[0004] Aiming at the deficiencies of the prior art, the present invention provides a simple instantaneous frequency measurement device based on an unbalanced dual-arm MZI. The present invention only requires conventional, simple, and fewer devices to build an instantaneous frequency measurement device, and can achieve the instantaneous frequency measurement of microwave signals without bias voltage control.
[0005] The technical solution of the present invention is: An instantaneous frequency measurement device based on an unbalanced dual-arm MZI, comprising a laser, a phase modulator, a beam splitter, an MZI, an optical fiber, and a photodetector. The electrical input interface of the phase modulator is connected to the signal to be measured; the optical input interface of the phase modulator is connected to the laser; it is characterized in that: the output light of the phase modulator is evenly divided into two paths by the beam splitter. One path of light is connected to the first photodetector after passing through the first MZI, and the other path of light is connected to the second photodetector after passing through the second MZI. The first photodetector and the second photodetector are connected to the signal processing module, where the differential delays of the first MZI and the second MZI are τ1 and τ2 respectively, and τ1≠τ2.
[0006] For an instantaneous frequency measurement device based on an unbalanced dual-arm MZI as described above, it is characterized in that: the signal processing module calculates the frequency f of the signal to be measured according to the formula where P rf1 and P rf2 are the electrical signal intensities output by the first and second photodetectors respectively, and τ1 and τ2 are the differential delays of the first and second MZIs respectively.
[0007] The present invention also discloses an instantaneous frequency measurement method based on an unbalanced dual-arm MZI, which is characterized in that: it includes the following steps:
[0008] Step 1: After the laser (optical carrier) emitted by the laser is incident on the phase modulator, the phase modulator modulates the microwave signal to be measured onto the optical carrier and outputs a modulated optical wave signal (modulated light). The optical field of the modulated light is where v is the frequency of the laser, l p is the loss coefficient of the phase modulator, P o is the average optical power corresponding to the optical field E o , A is the cross-sectional area of the optical fiber core, μ is the magnetic permeability of the optical fiber core, ε is the dielectric constant of the optical fiber core, φ(t) is the phase shift of the phase modulator, and its relationship with the signal to be measured V i (t) = V rf sin(ωt) is where V rf is the amplitude of the signal to be measured, ω is the angular frequency of the signal to be measured, ω = 2πf, f is the frequency of the signal to be measured, and V π is the half-wave voltage of the phase modulator;
[0009] Step 2: The beam splitter evenly divides the modulated light into two paths. The two paths of light respectively enter the photodetector after passing through the MZI, and convert the modulated optical signal into an electrical signal to demodulate the information of the signal to be measured; the differential delays of the two MZIs are different, and the theoretical values of the electrical signal intensities of the two branches are and where is the DC photocurrent of the corresponding link. is the responsivity of the photodetector, l b is the optical loss coefficient of the beam splitter, l m is the optical loss coefficient additionally introduced by the MZI, g o is the net gain of the link, P is the incident optical power of the photodetector, Z i 、Z o are the input and output impedances of the link respectively, H pd is the frequency response function of the photodetector;;
[0010] Step 3: The signal processing module reads the electrical signal intensities P rf1,s and P rf2,s output by the two photodetectors and processes them to obtain the amplitude comparison function of the 2 branches And from the above analysis and derivation, the theoretical value of the ACF is Combining the two gives In the formula, the frequency f of the signal to be measured is related to the electrical signal intensities P rf1,s 、P rf2,s of the two branches and the differential delays τ1, τ2 of the two MZIs. And τ1, τ2 are known, P rf1,s 、P rf2,s are measured values. The frequency f of the signal to be measured can be obtained by inversion calculation from this formula.
[0011] According to an instantaneous frequency measurement method based on an unbalanced dual-arm MZI as described above, it is characterized in that: the two photodetectors have the same performance.
[0012] According to an instantaneous frequency measurement method based on an unbalanced dual-arm MZI as described above, it is characterized in that: it further includes Step 4: The signal processing modules can be connected in multiple stages for extended use. The measurement accuracy of the first-stage processing module is the lowest (coarse measurement), which is used for the preliminary positioning of the frequency, and the subsequent ones are used for precise measurement.
[0013] The beneficial effects of the present invention are: Compared with the conventional intensity modulation method, the optical link using an unbalanced dual-arm MZI based on phase modulation has the following advantages: (1) There is no intrinsic 3dB optical loss, so the input optical power can be effectively utilized to increase the signal intensity; (2) The intensity of the phase modulation signal remains unchanged, so it is not easily affected by nonlinear effects during transmission; (3) There is no need to use a bias circuit for bias point control (required for the intensity modulation link), which greatly simplifies the front end of the system, so it can be flexibly designed and deployed, and thus has good potential in military applications. Description of the Drawings
[0014] Figure 1 is the structural schematic diagram of the instantaneous frequency measurement device based on the unbalanced dual-arm MZI.
[0015] Figure 2 is based on the response of the first branch of the unbalanced dual-arm MZI link (τ1 = 100 ps).
[0016] Figure 3 is based on the response of the second branch of the unbalanced dual-arm MZI link (τ2 = 375 ps).
[0017] Figure 4 is the variation relationship of the amplitude comparison function (ACF) of the unbalanced dual-arm MZI link with the signal frequency f.
[0018] Figure 5 is the frequency measurement result of the instantaneous frequency measurement device based on the unbalanced dual-arm MZI.
[0019] Figure 6 is the frequency measurement error of the instantaneous frequency measurement device based on the unbalanced dual-arm MZI.
[0020] Figure 7 is the schematic diagram of the remote connection based on the structure of the instantaneous frequency measurement device of the unbalanced dual-arm MZI.
[0021] Explanation of terms: MZI - Mach-Zehnder interferometer. Specific implementation mode
[0022] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.
[0023] As Figure 1 shown, an instantaneous frequency measurement device based on an unbalanced dual-arm MZI of the present invention includes a laser, a phase modulator, a beam splitter, an MZI, an optical fiber, and a photodetector. The electrical input interface of the phase modulator is connected to the signal to be measured, and the optical input interface of the phase modulator is connected to the laser; the phase modulator modulates the information of the signal to be measured onto the laser (optical carrier) emitted by the laser; the output light (modulated light) of the phase modulator is evenly divided into two paths by the beam splitter, one path of light passes through the first MZI and is connected to the first photodetector, and the other path of light passes through the second MZI and is connected to the second photodetector. The first photodetector and the second photodetector are connected to the signal processing module. The differential delays of the first MZI and the second MZI are τ1 and τ2 respectively, and τ1 ≠ τ2. In the present invention, the fiber lengths between the phase modulator and the optical beam splitter, and between the phase modulator and the laser can be several kilometers (up to dozens of kilometers with the addition of optical compensation and amplification devices), as Figure 7 shown. In this way, it can be ensured that the detection point (remote control unit) where the phase modulator is located and the processing point position (local unit) have a relatively long distance, enabling personnel to stay away from the battlefield. And the phase modulator, beam splitter, and MZI in the present invention are passive devices and do not require power supply, which can not only simplify the design (without power supply and bias control), but also make the operation and use convenient, enabling long-distance measurement and long-term operation.
[0024] An instantaneous frequency measurement method based on an unbalanced dual-arm MZI of the present invention includes the following steps:
[0025] Step 1: After the laser (optical carrier) emitted by the laser is incident on the phase modulator, the phase modulator modulates the microwave signal to be measured onto the optical carrier and outputs a modulated optical wave signal (modulated light). The output optical field of the modulated light is where ν is the frequency of the laser, l p is the loss coefficient of the phase modulator, P o is the average optical power corresponding to the optical field E o , A is the cross-sectional area of the optical fiber core, μ is the magnetic permeability of the optical fiber core, ε is the dielectric constant of the optical fiber core, φ(t) is the phase shift of the phase modulator, and its relationship with the signal V i (t) = V rf sin(ωt) is where V rf is the amplitude of the signal to be measured, ω is the angular frequency of the signal to be measured, ω = 2πf, f is the frequency of the signal to be measured, and V π is the half-wave voltage of the phase modulator.
[0026] Step 2: The beam splitter equally divides the modulated light into two paths. The two paths of light enter the photodetector after passing through the MZI respectively, and the modulated optical signal is converted into an electrical signal to demodulate the information of the signal to be measured. The differential delays of the two MZIs are different, and the performances of the two photodetectors are the same. The theoretical values of the signal intensities of the two branches are and where corresponds to the DC photocurrent output by the link, is the responsivity of the photodetector, l b is the optical loss coefficient of the beam splitter, l m is the optical loss coefficient additionally introduced by the MZI, g o is the net gain of the link, P is the incident optical power of the photodetector, Z i , Z o are the input and output impedances of the link respectively, and H pd is the frequency response function of the photodetector.
[0027] Step 3: The signal processing module reads the electrical signal intensities P rf1,s and P rf2,s output by the two photodetectors and processes them to obtain the amplitude comparison function of the two branches And from the above analysis and derivation, the theoretical value of the ACF is By combining the two, we get In the formula, the frequency f of the signal to be measured and the electrical signal intensities P rf1,s , P rf2,sIt is related to the differential delays τ1 and τ2 of two MZIs, and τ1 and τ2 are known, P rf1,s 、P rf2,s are measurement values, and the frequency f of the signal to be measured can be obtained by inversion calculation through this formula.
[0028] Step 4: Further, the signal processing modules can be connected in multiple stages for extended use. When multiple-stage processing modules are adopted, the measurement accuracy of the first-stage processing module is the lowest and is used for the preliminary positioning (coarse measurement) of the frequency, and the subsequent ones are used for precise measurement. By using multiple stages in combination, the measurement error can be further reduced.
[0029] The present invention has verified the frequency measurement of signals from 0.5 GHz to 18.5 GHz, and the frequency error of the coarse measurement is less than 60 MHz. Due to the large bandwidth characteristic of photon technology, as long as the operating frequencies of the devices in the device support it, its frequency measurement range can be extended. The method for expanding the frequency measurement range is: adopting a phase modulator and a photodetector with a wider operating frequency band without replacing other devices. The present invention can quickly determine the frequency range of the signal to be measured within a wide frequency band, and then further precisely measure the frequency by other means within the wide frequency band, such as the precise frequency measurement in Step 4.
[0030] Measures to improve the accuracy of coarse frequency measurement: (1) There are certain differences in the responses of the detector to signals of different frequencies, and the frequency measurement error can be reduced by calibrating it; (2) The half-wave voltage V of the phase modulator is different at different frequencies, and the frequency measurement error can also be reduced by calibrating it; (3) Improve the anti-environmental disturbance ability of the MZI, such as adopting measures such as constant temperature and vibration resistance; (4) Select a laser with low relative intensity noise. π is different, and the frequency measurement error can also be reduced by calibrating it; (3) Improve the anti-environmental disturbance ability of the MZI, such as adopting measures such as constant temperature and vibration resistance; (4) Select a laser with low relative intensity noise.
[0031] The beneficial effects of the present invention are: (1) An instantaneous frequency measurement device can be built only with conventional, simple, and fewer devices, including 1 laser, 1 phase modulator, 1 beam splitter, 2 MZIs (which can be constituted by a beam splitter and a delay line), 2 photodetectors, optical fibers, and a signal processing module, etc. There is no need for a large number of complex devices, such as optical frequency combs, dual-polarization Mach-Zehnder modulators, and demanding light sources, nor is there a need for complex control, such as polarization control and dispersion management. (2) There is no need for bias control. Compared with the commonly used intensity modulation method (which requires a bias control circuit to control its bias point), the front end of this device is greatly simplified. In some occasions, especially in military scenarios, there is greater design freedom and it can be flexibly deployed and used, such as deploying the front end of the device closer to the target and pulling the other parts farther away, so it is extremely attractive. (3) On the premise of simplifying the device, it can still maintain a small error (the error of the coarse frequency measurement is within 60 MHz).
[0032] Description of the drawings: Figure 1It is a schematic structural diagram of an instantaneous frequency measurement device based on an unbalanced dual-arm MZI. Figure 2 It is the response of the first branch (τ1 = 100 ps). The circles and solid lines represent the experimental results and theoretical results respectively, and the experimental measurement results are basically in line with the theory. Figure 3 It is the response of the first branch (τ2 = 375 ps). The circles and solid lines represent the experimental results and theoretical results respectively, and the two are in good agreement. From bottom to top, they correspond to the incident optical powers of different photodetectors, 8 dBm, 10 dBm, and 11.5 dBm respectively. By changing the incident optical power of the detector, the gain of the microwave signal increases, which is beneficial to improving the signal-to-noise ratio and measurement accuracy. Figure 4 It is the variation relationship of the amplitude comparison function (ACF) based on the dual-arm unbalanced MZI link with respect to the signal frequency f. The circles and solid lines represent the experimental results and theoretical results respectively, and the two are in good agreement. Figure 5 It is the comparison between the true frequency and the experimentally measured frequency, where the circles and solid lines represent the experimental measurement results and the true frequency respectively, and the measurement results are relatively consistent with the true values. Figure 6 It is the frequency error obtained from experimental measurement (within ±60 MHz).
Claims
1. An instantaneous frequency measurement device based on an unbalanced dual-arm MZI, comprising a laser, a phase modulator, a beam splitter, an MZI, an optical fiber, a photodetector, and a signal processing module. The electrical input interface of the phase modulator is connected to the signal to be measured; the electrical input interface of the phase modulator is connected to the laser. It is characterized in that: The output light of the phase modulator is evenly divided into two paths by a beam splitter. One path of light is connected to a first photodetector after passing through a first MZI, and the other path of light is connected to a second photodetector after passing through a second MZI. The first photodetector and the second photodetector are connected to a signal processing module, where the differential delays of the first MZI and the second MZI are respectively and , and ; The signal processing module calculates the frequency of the signal to be measured according to the formula where , and are the electrical signal intensities output by the first and second photodetectors respectively, , are the differential delay parameters of the first and second MZIs respectively.
2. An instantaneous frequency measurement method based on an unbalanced dual-arm MZI, characterized in that: It includes the following steps: Step 1: The laser emitted by the laser source is incident on the phase modulator. The phase modulator modulates the microwave signal to be measured onto the optical carrier and outputs the modulated optical wave signal. The optical field of the modulated light ; where is the frequency of the laser,[[]] is the loss coefficient of the phase modulator,[[]] is the average optical power corresponding to the optical field ; is the cross-sectional area of the fiber core,[[]] is the magnetic permeability of the fiber core,[[]] is the dielectric constant of the fiber core,[[]] is the phase shift of the phase modulator, and its relationship with the signal to be measured is ; where is the amplitude of the signal to be measured,[[]] is the angular frequency of the signal to be measured,[[]] , is the frequency of the signal to be measured,[[]] is the half-wave voltage of the phase modulator. Step 2: The beam splitter divides the modulated light into two equal paths. The two paths of light enter the photodetector after passing through the MZIs respectively, and the modulated optical signal is converted into an electrical signal to demodulate the information of the signal to be measured. The differential delays of the two MZIs are different, and the theoretical values of the electrical signal intensities of the two branches are and ; where is the DC optical current of the corresponding link, is the responsivity of the photodetector, is the optical loss coefficient of the beam splitter, is the optical loss coefficient additionally introduced by the MZI, is the net gain of the link, is the incident optical power of the photodetector, 、 are the input and output impedances of the link respectively, is the frequency response function of the photodetector; Step 3: The signal processing module reads the electrical signal strength output by the two photoelectric detectors and And process it to get the amplitude comparison function of the two branches ; From the above analysis, we can deduce The theoretical value is ; Combining the two, we get ; The frequency of the signal to be measured in the formula The electrical signal strength of the two branches , And the differential delay of the two MZIs , about, and , is known, , is the measured value. The frequency of the signal to be measured can be obtained by inverse calculation using this formula. .
3. The instantaneous frequency measurement method based on an unbalanced dual-arm MZI according to claim 2, characterized in that: The two photodetectors have the same performance.
4. The instantaneous frequency measurement method based on an unbalanced dual-arm MZI according to claim 2, characterized in that: It further includes Step 4. The signal processing modules can be connected in multiple levels for extended use. The measurement accuracy of the first-level processing module is the lowest and it is used for the preliminary positioning of the frequency, while the subsequent ones are used for precise measurement.