A microwave photon frequency measurement method and device based on fixed frequency detection

Abstract

A microwave photon frequency measurement method and device based on fixed frequency point detection belongs to the field of microwave photonics technology. It is composed of an adjustable laser, a coupler 1, a coupler 2, an intensity modulator 1, an intensity modulator 2, an adjustable filter 1, an adjustable filter 2, an erbium-doped fiber amplifier, an isolator, a single-mode optical fiber, a circulator, a microwave signal source 1, a microwave signal source 2, a DC stabilized power supply, a photoelectric converter and a spectrum analyzer. The present invention is based on down-conversion beat frequency technology to keep the measurement error of single and multiple signal frequency values ​​below 6MHz, has multi-frequency detection capability, and the multi-frequency resolution is 15MHz; the local oscillator signal of the present invention is generated by the all-optical stimulated Brillouin effect, does not require the input of electrical signals, and makes the system structure simple and low-loss. The present invention uses down-conversion technology to detect signals at a fixed intermediate frequency, which greatly alleviates the pressure of subsequent ADC sampling and avoids the use of expensive electronic measurement devices.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave photonics, and in particular relates to a microwave photon frequency measurement device based on stimulated Brillouin scattering down-conversion and fixed frequency point detection. Background Art

[0002] High-performance perception, reception and processing of radio frequency signals in complex electromagnetic environments have important application value in the fields of civilian broadband multi-service access, communication navigation identification, electronic countermeasures, spectrum monitoring, and communication intelligence in information warfare, and have received extensive attention and research from scholars at home and abroad. Traditional receivers cannot support ultra-wideband and multi-band radio frequency signal processing capabilities due to the great loss of radio frequency devices in high frequency bands. It is difficult to achieve uniform high performance in a wide frequency range, and the anti-electromagnetic interference capability is poor. Therefore, due to these limitations, the performance of broadband signal receiving systems in the traditional electrical domain is limited, which seriously affects the improvement of system performance and is difficult to cope with the current complex electromagnetic environment and military and civilian needs. With the development of optical fiber technology, microwave photonics, which integrates microwave technology and photonic technology, has shown great advantages and potential in broadband microwave signal transmission, perception and processing. Photonics-assisted microwave reception methods have the characteristics of wide frequency range, large instantaneous bandwidth, high sensitivity, high perception accuracy, and low power consumption. The advantages of photonic technology also include parallel processing, ultra-wideband tuning, long-distance transmission, and anti-electromagnetic interference. Therefore, microwave photonic technology has opened up a new way of thinking for microwave signal reception, laying the foundation for my country's comprehensive breakthroughs in astronomy, satellite communications, electronic warfare and other fields. Summary of the invention

[0003] The purpose of the present invention is to provide a microwave photon frequency measurement device based on stimulated Brillouin scattering down-conversion and fixed frequency point detection. The Brillouin effect is used to down-convert the unknown signal so that the system receives information at a fixed intermediate frequency point. The structure is simple and does not require the use of high-speed electronic equipment, which relieves the subsequent processing pressure, and finally obtains a high-precision, simple and easy-to-implement microwave photon frequency measurement device.

[0004] The structure of the microwave photon frequency measuring device of the present invention is as follows: Figure 1 As shown, it consists of an adjustable laser, a coupler 1, a coupler 2, an intensity modulator 1, an intensity modulator 2, an adjustable filter 1, an adjustable filter 2, an erbium-doped fiber amplifier, an isolator, a single-mode optical fiber, a circulator, a microwave signal source 1, a microwave signal source 2, a DC regulated power supply, a photoelectric converter and a spectrum analyzer.

[0005] The continuous light output by the tunable laser is used as the optical carrier f c1The optical signal is divided into two branches through coupler 1, namely the first branch and the second branch. In the first branch, the optical signal is amplified by the erbium-doped fiber amplifier and then input into the isolator. The function of the isolator is to ensure the unidirectional transmission of the optical signal. The amplified optical signal is input through port 1 of the circulator and output from port 2 (the working direction of the circulator is as shown in FIG. Figure 1 As shown in the figure, that is, the optical signal is input from port 1 and output from port 2, and is input from port 2 and output from port 3) into the single-mode optical fiber, serving as the pump light of the stimulated Brillouin scattering effect; when the optical power of the pump light reaches a certain power threshold, the stimulated Brillouin scattering effect occurs, and the lower sideband is 1 / 4 of the carrier wave. c1 A Brillouin frequency shift V B A Lorentz-shaped gain spectrum is generated at the point, that is, single-sideband modulation with suppressed carrier is realized; the optical signal processed by the stimulated Brillouin scattering effect is input from port 2 of the circulator and output from port 3, and enters coupler 2; the second branch optical signal output by coupler 1 enters intensity modulator 1 and is modulated by a series of swept-frequency microwave signals f output by microwave signal source 1 s Modulation is performed; the signal output by intensity modulator 1 is filtered out by adjustable filter 1 to remove the right band and carrier, and then enters intensity modulator 2 as a new optical carrier; then the frequency is f x The microwave signal to be measured is generated by a microwave signal source 2 and input through the RF input port of the intensity modulator 2. The DC bias end of the intensity modulator 2 is connected to a DC regulated power supply. A DC bias voltage is applied to the intensity modulator 2 through the DC regulated power supply, so that the intensity modulator 2 works at the minimum transmission point to achieve a double-sideband modulation state in which the carrier is suppressed. The output signal of the intensity modulator 2 is coupled with the optical signal from the first branch in the coupler 2 and then enters the tunable filter 2. The tunable filter 2 is set to a certain bandwidth to filter out the upper sideband signal and other clutter. The optical signal processed by the tunable filter 2 is down-converted by the photoelectric converter and then input into the spectrum analyzer. As the frequency-sweeping microwave signal f s The frequency value gradually increases, and the signal spectrum is obtained at the fixed intermediate frequency point, and the swept frequency signal f is recorded. s The value of the microwave signal f x The frequency measurement value.

[0006] After the system is connected, turn on the device to put it into working state; the continuous optical signal f output by the tunable laser c1 The optical signal is divided into the first branch and the second branch by the coupler 1. After being amplified by the erbium-doped fiber amplifier in the first branch, it is input into the isolator. After unidirectional transmission, the optical signal enters the single-mode optical fiber through the circulator's port 1 input and port 2 output, and serves as the pump light of the stimulated Brillouin scattering effect. When the pump light reaches a certain power threshold, the stimulated Brillouin scattering effect occurs, generating a gain spectrum with a center frequency of f c1 -VB (like Figure 2 (1) As shown, V B is the stimulated Brillouin frequency shift); the suppressed carrier single-sideband optical signal realized by the stimulated Brillouin scattering effect enters the coupler 2 from the 2-port input and 3-port output of the circulator; the optical signal of the second branch output by the coupler 1 enters the intensity modulator 1 and is output by a series of microwave signal sources including a frequency of f s The swept frequency microwave signal modulation (f s 、f s1 、f s2 …、f sn …、f sm etc. s1 =f s +Δv,f s2 =f s +2Δv…,f sn =f s +nΔv…,f sm =f s +mΔv, n, m are positive integers, and m≥n), the frequency interval of these sweep signals is set to Δv (Δv is the minimum resolution of the microwave signal source output signal, less than MHz), so as to ensure that the frequency information will not be lost during measurement; the signal f output by the intensity modulator 1 c1 、f c1 ±f s 、f c1 ±f s1 、f c1 ±f s2 …、f c1 ±f sn …、f c1 ±f sm The right band and the carrier f are filtered out by adjustable filter 1 c1 After (such as Figure 2 As shown in (2), f c1 The effect is suppressed, which is equivalent to no effect and will not interfere with subsequent experiments). The signal f c2 (f c2 Yes c2-1 、f c2-2 …、f c2-n …、f c2-m The general term for c2-1 = = f c1 -f s , f c2-2 =f c1 -2f s …, f c2-n =f c1 -nf s …, f c2-m =f c1 -mfs ) enters intensity modulator 2 as an optical carrier; the frequency is f x The microwave signal to be measured is generated by a microwave signal source 2 and input through the RF input port of the intensity modulator 2. The DC bias terminal of the intensity modulator 2 is connected to a DC regulated power supply. A DC bias voltage is applied to the intensity modulator 2 through the DC regulated power supply, so that the intensity modulator 2 works at the minimum transmission point to achieve a double-sideband modulation state in which the carrier is suppressed. The output frequency value of the intensity modulator 2 is f c2 -f x and f c2 +f x The lower and upper sideband signals (f c2 and f c1 It has been suppressed, almost to the point of non-existence, such as Figure 2 (3)); the output signal is coupled with the first branch signal by the coupler 2 and enters the adjustable filter 2, and the bandwidth of the adjustable filter 2 is set to 0 = ~ (V B +1 / 2ΔV B ), ΔV B is the Brillouin gain spectrum bandwidth, filtering out the upper sideband signal f c2 +f x and other clutter to prevent frequency ambiguity after the input multi-frequency signal beats; the lower sideband signal f before entering the photoelectric converter c2 -f x The spectrum diagram is as follows Figure 2 As shown in (4), as the frequency of the sweep signal gradually increases from fs to f sn When the corresponding f c2 Gradually from f c2-1 Change to f c2-n , at this time the frequency value is f c2-n -f x The signal gradually approaches the Brillouin gain spectrum f c1 -V B ; When the frequency difference between the two signals is Δf = 828MHz, f c2-n -f x The signal is down-converted by the photoelectric converter and input into the spectrum analyzer. The signal spectrum (such as Figure 2 (5)), record the value of the frequency sweep signal f sn , we can get the unknown signal f x The measured value f′ x (f′ x =V B -Δf-f sn), thereby realizing the frequency measurement of the unknown signal from the microwave signal source 2. After the measurement is completed, the measured value f′ x With the actual input value f x The measurement error is obtained by comparison, and then unknown signals of other frequencies are input in turn. After obtaining the measured values, the corresponding measurement error is obtained. When measuring with multiple frequency inputs, the above measurement steps are still repeated, and the measurement error is kept below 6MHz.

[0007] The present invention uses a tunable laser with a wavelength of 1530nm to 1565nm as a carrier light source; the coupler 1 and the coupler 2 are 5:5 couplers; the bandwidth of the intensity modulator 1 and the intensity modulator 2 is 20GHz; the adjustable bandwidth of the adjustable filter 1 and the adjustable filter 2 is 50pm to 800pm; the length of the single-mode optical fiber is 10000m to 15000m, and the stimulated Brillouin frequency shift V B The frequency range of the microwave signal source 1 and the microwave signal source 2 is 1 GHz to 70 GHz. The output voltage of the DC regulated power supply is adjustable within the range of 1V to 20V.

[0008] The device of the present invention is characterized by:

[0009] (1) Based on the down-conversion beat frequency technology, the measurement error of single and multiple signal frequency values ​​is kept below 6MHz.

[0010] (2) It has multi-frequency detection capability with a multi-frequency resolution of 15MHz.

[0011] (3) The local oscillator signal is generated by the all-optical stimulated Brillouin effect, which does not require the input of electrical signals, making the system structure simple and low-loss.

[0012] (4) Applying down-conversion technology to detect the signal at a fixed intermediate frequency greatly alleviates the pressure of subsequent ADC sampling and avoids the use of expensive electronic measurement devices, thus reducing system costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 :Microwave photon frequency measurement device based on fixed frequency detection;

[0014] Figure 2 : Spectrum processing diagram of frequency measurement device;

[0015] Figure 3 :Brillouin frequency shift measurement spectrum (1) and frequency spectrum (2);

[0016] Figure 4 : Signal spectrum diagram of single frequency input at a fixed frequency point;

[0017] Figure 5 : Measurement error diagram for microwave signal frequencies within the range of 1=GHz to 9.5GHz;

[0018] Figure 6 : Signal spectrum diagram of multi-frequency input at fixed frequency points;

[0019] Figure 7 : Relationship diagram between multi-frequency input frequency difference and measurement error; DETAILED DESCRIPTION

[0020] Example 1:

[0021] The tunable laser is Santec's TSL-510 tunable laser, and the wavelength range of the laser is 1510nm~1630nm; coupler 1 and coupler 2 are 5:5 couplers; the erbium-doped fiber amplifier is WZEDFA-SO-PS-0-1-2 from Wuxi Zhongxing Optoelectronics Technology Co., Ltd.; intensity modulator 1 and intensity modulator 2 use Photline's MXAN-LN-20, with a bandwidth of 20GHz, and the minimum operating point bias voltage measured before the experiment is 6.7V; the isolation of the isolator is greater than 40dB; the single-mode optical fiber uses the same single-mode optical fiber from Changfei Technology Co., Ltd., with a length of 14km. When the optical carrier wavelength is 1550nm, the stimulated Brillouin frequency shift V B =10.828GHz; microwave signal source 1 adopts Agilent's microwave signal generator E8257D, with an output frequency range of 100kHz to 70GHz; microwave signal source 2 adopts Keysight's M8195A; the photoelectric converter is Optilab's PD-40-M, with a bandwidth of 40GHz; the DC regulated power supply is Goodwill's GPS-4303C, with an output voltage amplitude adjustable from 1V to 20V; the circulator is Shenzhen Zhiyuan Optical Communication Technology Co., Ltd.'s CIR-3-1550-900um-1m-FC / APC; adjustable filter 1 and adjustable filter 2 are Yenista's Yenista=XTM-50, with an adjustable bandwidth of 50pm-800pm; the spectrum analyzer is Agilent's N9010A, with a measurement signal range bandwidth of 10Hz to 26.5GHz.

[0022] After the system is connected, turn on the device to put it into working state. First, the tunable laser output frequency is f c1=193.414THz (corresponding to a wavelength of 1550nm) is divided into a first branch and a second branch by a 5:5 coupler 1. In the first branch, the optical signal is amplified to 15mW by an erbium-doped fiber amplifier and then input into the isolator. After unidirectional transmission, the optical signal enters the single-mode fiber through the circulator's port 1 input and port 2 output, serving as pump light for stimulated Brillouin scattering. When the pump light reaches a certain power threshold, stimulated Brillouin scattering occurs, generating a gain spectrum, the spectrum of which is shown in the figure below. Figure 3 As shown in (1), the Brillouin frequency shift V is obtained after the beat frequency B =10.828GHz (such as Figure 3 (2)). Therefore, the suppressed carrier single-sideband optical signal f is realized by stimulated Brillouin scattering effect. c1 The -10.828 GHz signal output from port 3 of the circulator is coupled to the signal of the second branch through coupler 2.

[0023] The optical signal of the second branch output by the coupler 1 enters the intensity modulator 1 and is modulated by a series of microwave signals output by the microwave signal source including a frequency of f s The swept frequency microwave signal modulation, the swept frequency signal f s Starting from 500MHz (because f x =V B (10.828GHz)-Δf(828MHz)-f s , = where f s When the frequency is 500MHz, the unknown signal f can be measured. x The range reaches 9.5GHz, so set f s The frequency information is not lost during measurement. The signal f output by intensity modulator 1 is c1 、f c1 ±500MHz, f c1 ±500.1MHz…、f c1 ±5GHz, f c1 ±5.0001GHz…、f c1 ±9GHz passes through the adjustable filter 1 to remove the right band and carrier, and the signal f c1 -500MHz, f c1 -500.1MHz…、f c1 -5GHz, f c1 -5.0001GHz…、f c1 -9GHz as the optical carrier and set it to f c2 Enter intensity modulator 2. Then the frequency is f x=1GHz microwave signal to be tested is generated by microwave signal source 2 and input through the RF input port of intensity modulator 2. The DC bias terminal of intensity modulator 2 is connected to the DC regulated power supply. A DC bias voltage of 6.7V is applied to intensity modulator 2 through the DC regulated power supply, so that the intensity modulator works at the minimum transmission point, realizing the double-sideband modulation state with carrier suppressed, and the output frequency value is f c2 -1GHz and f c2 +1GHz lower and upper sideband signals, and the carrier f c2 The output signal is coupled with the first branch signal through the coupler 2 and enters the tunable filter 2, and the bandwidth of the tunable filter 2 is set to 0 = ~ = (10.828GHz + 1 / 2 * 0.1GHz = 10.878GHz, ΔV B =0.1GHz is the Brillouin gain spectrum bandwidth), filter out the upper sideband signal f c2 +1GHz and other clutter to prevent frequency ambiguity after the input multi-frequency signal beats. Before passing through the photoelectric converter, as the sweep signal f s The frequency value gradually increases, and the frequency value is f c2-n -1GHz signal gradually approaches the Brillouin gain spectrum f c1 -10.828GHz. When the frequency difference between the two signals is Δf = 828MHz, after being down-converted by the photoelectric converter and input into the spectrum analyzer, the signal spectrum can be obtained at the fixed intermediate frequency point Δf = 828MHz (such as Figure 4 As shown), the frequency sweep signal f is recorded at this time sn =8.9989GHz (n is 84989) can get the measurement value f' of the unknown signal x is 1.0011GHz(f′ x =10.828GHz-828MHz-8.9989GHz).

[0024] Data recording is completed, the actual input value f x =1GHz and the frequency value f′ of the unknown signal obtained experimentally x = 1.0011GHz, the absolute error is 1.1MHz (such as Figure 5 As shown in Figure 2.1.1.1.2. By inputting unknown signals of other frequencies in turn and obtaining the measured values, the corresponding measurement errors are still as follows: Figure 5 As shown, the absolute value of the measurement error in the frequency range of 1 to 9.5 GHz is less than 5 MHz (some are positive errors, some are negative errors). The measurement process and results in the frequency range of 1-9.5 GHz show that the proposed frequency measurement system can accurately measure single-frequency unknown signals.

[0025] Repeat the above measurement steps and input the frequency f x1=8GHz, f x2 =8.015GHz, f x1 = = 8GHz, f x2 = = 8.02GHz and f x1 = = 8GHz, f x2 = = Three groups of multiple signals with a frequency difference of 15MHz, 20MHz, and 30MHz, respectively. After beating the frequency, the corresponding spectrum diagram is obtained at the fixed frequency point of 828MHz (such as Figure 6 Then, the minimum resolution of multi-frequency input is analyzed. When the frequency difference is 20MHz, the two peaks can be clearly separated. When the frequency difference is 15MHz, they can still be separated, but the effect is biased. Therefore, the frequency resolution of this frequency measurement system is 15MHz. Similar to single-frequency measurement, multi-frequency unknown signals can be accurately measured. The measurement error changes with the frequency difference curve (as shown in Figure 7 As shown), the multi-frequency measurement error is finally obtained within 6MHz.

Claims

1. A microwave photon frequency measurement device based on fixed frequency detection, characterized in that: The invention comprises an adjustable laser, a coupler 1, a coupler 2, an intensity modulator 1, an intensity modulator 2, an adjustable filter 1, an adjustable filter 2, an erbium-doped fiber amplifier, an isolator, a single-mode fiber, a circulator, a microwave signal source 1, a microwave signal source 2, a DC regulated power supply, an optoelectronic converter and a spectrum analyzer; the continuous light output by the adjustable laser is divided into two branches as an optical carrier through the coupler 1, namely the first branch and the second branch; in the first branch, the optical signal is amplified by the erbium-doped fiber amplifier and then input into the isolator, the function of the isolator is to ensure the unidirectional transmission of the optical signal; the amplified optical signal is input through port 1 of the circulator and output from port 2 to enter the single-mode fiber as the pump light of the stimulated Brillouin scattering effect; when the optical power of the pump light reaches a certain power threshold, the stimulated Brillouin scattering effect occurs, and the distance between the lower sideband and the carrier is small. A Brillouin frequency shift A Lorentz-shaped gain spectrum is generated at the point, that is, single-sideband modulation with suppressed carrier is realized; the optical signal processed by the stimulated Brillouin scattering effect is input from port 2 of the circulator and output from port 3, and enters coupler 2; the second branch optical signal output by coupler 1 enters intensity modulator 1 and is modulated by a series of swept-frequency microwave signals output by microwave signal source 1 Modulation is performed; the signal output by the intensity modulator 1 is filtered out by the adjustable filter 1 to remove the right band and the carrier, and then enters the intensity modulator 2 as a new optical carrier; then the frequency is The microwave signal to be measured is generated by a microwave signal source 2 and input through the RF input port of the intensity modulator 2. The DC bias end of the intensity modulator 2 is connected to a DC regulated power supply. A DC bias voltage is applied to the intensity modulator 2 through the DC regulated power supply, so that the intensity modulator 2 works at the minimum transmission point to achieve a double-sideband modulation state in which the carrier is suppressed. The output signal of the intensity modulator 2 is coupled with the optical signal from the first branch in the coupler 2 and then enters the tunable filter 2. The tunable filter 2 is set to a certain bandwidth to filter out the upper sideband signal and other clutter. The optical signal processed by the tunable filter 2 is down-converted by the photoelectric converter and then input into the spectrum analyzer. As the frequency-sweeping microwave signal The frequency value gradually increases, the signal spectrum is obtained at the fixed intermediate frequency point, and the swept frequency signal is recorded The value of the microwave signal to be measured can be obtained The frequency measurement value.

2. A microwave photon frequency measurement device based on fixed frequency detection as claimed in claim 1, characterized in that: A tunable laser with a wavelength of 1530nm~1565nm is selected as the carrier light source; coupler 1 and coupler 2 are 5:5 couplers; the bandwidth of intensity modulator 1 and intensity modulator 2 is 20GHz; the adjustable bandwidth of adjustable filter 1 and adjustable filter 2 is 50pm~800pm; the length of single-mode fiber is 10000m~15000m, and the stimulated Brillouin frequency shift is The frequency range of the microwave signal source 1 and the microwave signal source 2 is 1GHz~70GHz; the output voltage of the DC regulated power supply is adjustable from 1V to 20V.

3. A microwave photon frequency measurement device based on fixed frequency detection as claimed in claim 1, characterized in that: Used to measure a single-frequency unknown signal or a multi-frequency unknown signal from a microwave signal source 2.

4. A microwave photon frequency measurement method based on the microwave photon frequency measurement device with fixed frequency detection according to any one of claims 1 to 3, characterized in that: After the device is connected, turn on the device to put it in working state; Continuous optical signal output by a tunable laser The optical signal is divided into the first branch and the second branch by the coupler 1. After being amplified by the erbium-doped fiber amplifier in the first branch, it is input into the isolator. After unidirectional transmission, the optical signal enters the single-mode optical fiber through the circulator's port 1 input and port 2 output, serving as the pump light for stimulated Brillouin scattering effect. When the pump light reaches a certain power threshold, stimulated Brillouin scattering effect occurs, generating a gain spectrum with a center frequency of , is the stimulated Brillouin frequency shift; the suppressed carrier single-sideband optical signal realized by the stimulated Brillouin scattering effect enters the coupler 2 from the circulator's port 2 input and port 3 output; the optical signal of the second branch output by coupler 1 enters the intensity modulator 1 and is output by a series of microwave signal sources including a frequency of f s Frequency-swept microwave signal modulation , = + , = +2 …, = +n , = +m , n, m are positive integers, and m ≥ n, the frequency intervals of these sweep signals are set to , The minimum resolution of the microwave signal source output signal is less than MHz, which can ensure that the frequency information is not lost during measurement; the signal output by the intensity modulator 1 , ..., after the adjustable filter 1 removes the right band and the carrier, the signal As an optical carrier enters the intensity modulator 2, the signal yes , …, A general term for = , The frequency is The microwave signal to be measured is generated by a microwave signal source 2 and input through the RF input port of the intensity modulator 2. The DC bias terminal of the intensity modulator 2 is connected to a DC regulated power supply. A DC bias voltage is applied to the intensity modulator 2 through the DC regulated power supply, so that the intensity modulator 2 works at the minimum transmission point to achieve a double-sideband modulation state in which the carrier is suppressed. The output frequency value of the intensity modulator 2 is The output signal is coupled with the first branch signal through coupler 2 and enters the adjustable filter 2, and the bandwidth of the adjustable filter 2 is set to 0 ~ is the Brillouin gain spectrum bandwidth, filtering out the upper sideband signal and other clutter to prevent frequency ambiguity after the input of multi-frequency signal beat frequency; as the frequency value of the sweep signal changes from s gradually increases to When Gradually from Change to , the frequency value is The signal gradually approaches the Brillouin gain spectrum ; When the frequency difference between the two signals is =828MHz, The signal is down-converted by the photoelectric converter and then input into the spectrum analyzer. Get the signal spectrum and record the value of the swept frequency signal , then we can get the unknown signal The measured value , thereby realizing the frequency measurement of the unknown signal from the microwave signal source 2.

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