CN110702985B - Beat frequency type frequency spectrum detecting system - Google Patents
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Abstract
A beat frequency type frequency spectrum detection system comprises a sweep frequency light source, a phase modulator, an optical filter, an optical fiber, a photoelectric detector, a power divider, an electric amplifier, a combiner, an electric filter, an oscilloscope and a signal source to be detected; the sweep frequency light source, the phase modulator, the optical filter, the optical fiber, the photoelectric detector and the electric amplifier form an annular photoelectric oscillator resonant cavity together; when the Fourier domain mode locking condition is met, the photoelectric oscillator resonant cavity can generate a frequency sweeping signal with adjustable broadband. According to the invention, a signal to be detected is coupled into the Fourier domain mode-locked photoelectric oscillator, the beat frequency of the signal to be detected is oscillated in a loop and the photoelectric oscillator, and the time domain waveform of the output signal is observed through the oscilloscope after being filtered by the electric filter, so that the frequency information of the signal to be detected can be obtained by utilizing the characteristics related to the output frequency and time of the Fourier domain mode-locked photoelectric oscillator and the appearance time of the waveform observed by the oscilloscope.
Description
Technical Field
The invention relates to the technical field of microwave photonics, in particular to a beat frequency type frequency spectrum detection system.
Background
In radar and other electronic warfare systems, the ability to measure the intercepted unknown microwave signal with high accuracy is critical. Modern electronics technology can realize high-precision frequency detection, but the frequency of a signal to be detected may be distributed in a wider frequency band, and the bandwidth is limited when the pure electronics method is adopted for measurement, and the electromagnetic interference is easily caused during measurement.
The above-mentioned disadvantages of electronics can be avoided by using photonics. In principle, photonic-based microwave signal frequency detection schemes can be broadly classified into three categories, namely photonic-based channelization techniques, frequency-to-power-based mapping, and frequency-to-time-based mapping. The frequency measurement with large bandwidth can be realized based on the photonics channelization technology, but the frequency measurement error is very large and is usually larger than 1GHz, so that the application requirements of most electronic warfare systems cannot be met; the method based on mapping from frequency to power can realize frequency detection with relatively higher precision, but the method can only detect microwave signals with single frequency, and cannot simultaneously detect a plurality of dot frequency signals, so that the application is limited. While the method based on frequency-to-time mapping can realize the detection of multi-point frequency signals, the frequency resolution of the method is limited by the precision of an optical time gate in the system, and is about in the order of hundreds of MHz.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, it is therefore a primary object of the present invention to provide a beat frequency spectrum detection system, which at least partially solves at least one of the above-mentioned problems.
In order to achieve the above object, the present invention provides a beat frequency spectrum detection system, comprising: the device comprises a sweep frequency light source, a phase modulator, an optical filter, an optical fiber, a photoelectric detector, a power divider, an electric amplifier, a combiner, an electric filter, an oscilloscope and a signal source to be detected;
the swept-frequency light source, the phase modulator, the optical filter, the optical fiber and the photoelectric detector are connected through optical fiber jumpers; the photoelectric detector, the power divider, the electric amplifier, the combiner and the phase modulator are connected through cables; the power divider, the electric filter and the oscilloscope are connected through cables; the combiner and the signal source to be detected are connected through a cable;
the sweep frequency light source, the phase modulator, the optical filter, the optical fiber, the photoelectric detector and the electric amplifier form an annular photoelectric oscillator resonant cavity together; and when the Fourier domain mode locking condition is met, the photoelectric oscillator resonant cavity can generate a frequency sweeping signal with adjustable bandwidth and center frequency.
Based on the above scheme, the beat frequency spectrum detection system of the present invention has the following beneficial results:
(1) acquiring information of a signal to be detected by observing the signal to be detected and a beat frequency result of a sweep frequency signal in a Fourier domain mode-locked optoelectronic oscillator by using an electric filter and an oscilloscope; due to the high-precision frequency sweeping characteristic of the Fourier domain mode-locked photoelectric oscillator, high-precision detection of signals can be realized;
(2) the detectable signal frequency range is related to the sweep frequency bandwidth of the Fourier domain mode-locked photoelectric oscillator, and the Fourier domain mode-locked photoelectric oscillator can output sweep frequency signals with adjustable broadband, so that the broadband spectrum detection can be realized;
(3) for a high-frequency signal to be detected, by means of square law characteristics of a photoelectric detector, frequency characteristics of the high-frequency signal to be detected and a difference frequency of a sweep frequency signal in a Fourier domain mode-locked photoelectric oscillator can be obtained by observing, so that detection of a high-frequency microwave signal can be realized;
(4) the precision of the frequency spectrum detection method is determined by the bandwidth of the optical filter and the electric filter; by adopting a high-performance narrow-band filter, the spectrum detection with the precision in the magnitude of MHz or dozens of MHz can be realized.
Drawings
FIG. 1 is a schematic diagram of a beat frequency spectrum detection system according to the present invention;
FIG. 2 is a schematic diagram illustrating the principle of spectrum detection when observing the sum frequency of the signal to be detected and the unidirectional frequency sweep signal; wherein, fig. 2(a) is a relative spectrum relationship of a frequency sweep signal, a signal to be measured and a passband of the electrical filter, fig. 2(b) is a frequency sweep characteristic of the fourier domain mode-locked optoelectronic oscillator, and fig. 2(c) is an output signal waveform of the electrical filter observed by an oscilloscope;
FIG. 3 is a schematic diagram illustrating the principle of spectrum detection when observing the sum frequency of the signal to be detected and the bidirectional frequency sweeping signal; fig. 3(a) is a relative spectrum relationship between a frequency sweep signal, a signal to be measured, and a passband of the electrical filter, fig. 3(b) is a frequency sweep characteristic of the fourier domain mode-locked optoelectronic oscillator, and fig. 3(c) is an output signal waveform of the electrical filter observed by an oscilloscope.
In the above figures, the reference numerals have the following meanings:
1 sweep frequency light source 2 phase modulator 3 optical filter
4 optical fiber 5 photoelectric detector 6 power divider
7 electric amplifier 8 combiner 9 electric filter
10 oscilloscope 11 signal source to be measured
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
The method is based on the microwave photon technology, couples the signal to be detected into the Fourier domain mode-locked photoelectric oscillator, utilizes a proper electric filter for filtering, and utilizes the corresponding relation between the output frequency and the time of the Fourier domain mode-locked photoelectric oscillator, namely, the sweep frequency characteristic of the Fourier domain mode-locked photoelectric oscillator to realize the high-precision detection of the unknown microwave signal. Furthermore, the invention also utilizes the sweep frequency microwave generation performance of the Fourier domain mode-locked photoelectric oscillator, the modulation characteristic of the phase modulator and the square law characteristic of the photoelectric detector to realize the large-bandwidth and high-precision spectrum detection of unknown microwave signals.
Specifically, the beat frequency spectrum detection system of the present invention includes: the device comprises a sweep frequency light source, a phase modulator, an optical filter, an optical fiber, a photoelectric detector, a power divider, an electric amplifier, a combiner, an electric filter, an oscilloscope and a signal source to be detected; the sweep frequency light source, the phase modulator, the optical filter, the optical fiber and the photoelectric detector are connected through optical fiber jumpers, and the photoelectric detector, the power divider, the electric amplifier, the combiner and the phase modulator are connected through cables; the power divider, the electric filter and the oscilloscope are connected through cables; the combiner and the signal source to be detected are connected through a cable.
The sweep light source, the phase modulator, the optical filter, the optical fiber, the photoelectric detector and the electric amplifier form an annular photoelectric oscillator resonant cavity together. When the Fourier domain mode locking condition is met, the resonant cavity can generate a frequency sweeping signal with adjustable bandwidth and center frequency.
Wherein the Fourier domain mode locking condition is as follows: nT ═ Tr；
Wherein n is a positive integer, T is a variation period of the microwave photonic filter, and TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop.
The swept-frequency light source is a swept-frequency semiconductor laser driven by current or a swept-frequency light source based on single-sideband modulation, and the light-emitting wavelength of the swept-frequency light source periodically changes.
Wherein the optical filter is a notch filter with an ultra-narrow bandwidth or an ultra-narrow optical filter based on a stimulated brillouin scattering effect gain spectrum, for example, the bandwidth is tens of MHz.
The beat frequency type spectrum detection system can realize spectrum detection in different frequency measurement ranges by changing the magnitude relation among the frequency sweeping signal, the signal to be detected and the frequency of the electric filter.
The power divider in the beat frequency spectrum detection system may be a one-to-three power divider, or may also be two-to-two power dividers.
The beat frequency spectrum detection system further comprises a polarization controller for controlling the polarization state of the optical signal.
The beat frequency spectrum detection system also comprises an optical amplifier or an electric amplifier for amplifying signals.
The photoelectric oscillator loop can be replaced by a single loop into a plurality of loops which are more than or equal to 2.
When the device works, a signal to be detected is input to the combiner by the signal source to be detected, the combiner combines the signal to be detected and a sweep frequency signal generated by self-oscillation of the photoelectric oscillator and inputs the combined signal and the sweep frequency signal to the electric signal input end of the phase modulator, and the phase modulator modulates the combined electric signal to the sweep frequency optical signal emitted by the sweep frequency light source. The optical signal of the double-sideband phase modulation output by the phase modulator is selectively attenuated or amplified by an optical filter, and then is input into the photoelectric detector through an optical fiber. Due to the square-law characteristic of the photoelectric detector, a signal to be measured modulated onto the optical carrier wave can beat with the sweep frequency signal in the resonant cavity. The signal after beat frequency is output to a power divider by a photoelectric detector, the power divider divides the signal into three paths, one path of signal returns to an electric amplifier for coupling a signal to be detected, the other path of signal is input to an oscilloscope for detecting and determining the corresponding relation between the frequency and the time of the output signal of the Fourier domain mode-locked photoelectric oscillator, and the other path of signal is input to an electric filter with known passband, so that the signal to be detected is detected, and the detection of the signal to be detected is completed.
The working principle of the whole beat frequency type high-precision frequency spectrum detection system is as follows: the sweep frequency light source, the phase modulator, the optical filter and the photoelectric detector form a high-precision sweep frequency microwave photon filter, the sweep frequency period of the microwave photon filter is matched with the delay of one cycle of signal transmission in a photoelectric oscillator loop, and the Fourier domain mode locking condition is met. Under the drive of a definite periodic signal, the frequency and the time of a frequency sweep microwave signal output by the Fourier domain mode-locked optoelectronic oscillator have a definite corresponding relation. The microwave signal to be measured is coupled to the Fourier domain mode-locked photoelectric oscillator which completely starts oscillation, and due to the square law characteristic of the photoelectric detector, the signal to be measured modulated on the optical carrier wave can beat with the sweep frequency signal in the resonant cavity. And an electric filter with a known passband is added at the output end of the Fourier domain mode-locked photoelectric oscillator, so that the information of the signal to be detected can be obtained through the observed information of the beat frequency signal of the filter, and the detection of the signal to be detected is completed.
The technical solution of the present invention is explained in detail by the specific embodiments with reference to the attached drawings.
As shown in fig. 1, which is a schematic structural diagram of the present invention, mainly includes: 1 sweep frequency light source 1, 1 phase modulator 2, 1 optical filter 3, 1 section of optical fiber 4, 1 photoelectric detector 5, 1 power divider 6, 1 electric amplifier 7, 1 combiner 8, 1 electric filter 9, 1 oscilloscope 10 and 1 signal source 11 to be measured. The sweep frequency light source 1, the phase modulator 2, the optical filter 3, the optical fiber 4 and the photoelectric detector 5 are connected in sequence through optical fiber jumpers. The photoelectric detector 5, the power divider 6, the electric amplifier 7, the combiner 8 and the phase modulator 2 are connected in sequence through cables; the power divider 6, the electric filter 9 and the oscilloscope 10 are connected in sequence through cables; the combiner 8 and the signal source 11 to be measured are connected through a cable.
The swept-frequency light source 1, the phase modulator 2, the optical filter 3, the optical fiber 4, the photoelectric detector 5, the electric amplifier 7, the power divider 6 and the combiner 8 form a Fourier domain mode-locked photoelectric oscillator. In a Fourier domain mode-locked optoelectronic oscillator, a sweep frequency light source 1, a phase modulator 2, an optical filter 3 and a photoelectric detector 5 form a high-precision sweep frequency microwave photon filter, the sweep frequency period of the microwave photon filter is matched with the delay of a signal transmitted for one circle in an optoelectronic oscillator loop, and the Fourier domain mode-locked condition is met: nT ═ Tr；
Wherein n is a positive integer, T is a variation period of the microwave photonic filter, and TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop. As shown in the upper graph of fig. 2, when the microwave photonic filter is driven by a sawtooth wave, the fourier domain mode-locked optoelectronic oscillator outputs a periodic chirp signal, and the frequency and time of the signal have a periodic correspondence.
The microwave signal to be measured is coupled to the fourier domain mode-locked optoelectronic oscillator through the combiner 8. Due to the square-law characteristic of the photoelectric detector, a signal to be measured modulated onto the optical carrier wave can beat with the sweep frequency signal in the resonant cavity. In FuAn electric filter with a known passband is added at the output end of the inner-leaf mode-locked photoelectric oscillator, so that the information of the signal to be detected can be obtained through the observed information of the beat frequency signal of the filter, and the detection of the signal to be detected is completed. Assuming that the frequency of the signal to be measured is higher than the frequency of the sweep signal and the center frequency of the electrical filter is higher than the frequency of the signal to be measured, as shown in fig. 2, if the actual frequency of the signal to be measured is finUsing a passband centered at ffilterWhen the frequency of the sweep frequency signal in the Fourier domain mode-locked optoelectronic oscillator is foIn time, the output signal of the electrical filter can be observed on an oscilloscope; when the frequency of the sweep signal is not equal to foThe sum frequency term cannot pass through the electrical filter. Therefore, the frequency information of the signal to be detected can be obtained by the frequency sweeping characteristic of the known Fourier domain mode-locked optoelectronic oscillator and the characteristic of the electric filter and the appearance time of the output signal of the electric filter observed by the oscilloscope. The corresponding relation between the frequency and the time of the output signal of the Fourier domain mode-locked photoelectric oscillator can be obtained by a sweep frequency output signal which is measured by an oscilloscope and is divided by the power divider 6.
Furthermore, the frequency spectrum detection in different frequency measurement ranges can be realized by changing the magnitude relation among the frequency sweeping signals, the signals to be detected and the frequencies of the electric filters. For example, similar to the method of observing sum frequency shown in the lower graph of FIG. 2, when the frequency of the signal to be measured satisfies ffilter＝fin-f0And in the process, the frequency characteristic can be obtained by observing the difference frequency of the signal to be measured and the sweep frequency signal in the Fourier domain mode-locked photoelectric oscillator.
Considering that the frequency sweeping manner of the frequency sweeping signal generated by the fourier domain mode-locked optoelectronic oscillator is not limited to the unidirectional frequency sweeping as shown in fig. 2, in some alternative embodiments, as shown in fig. 3, the two-way frequency sweeping fourier domain mode-locked optoelectronic oscillator may be used for performing the beat frequency spectrum detection. At this time, within one sweep period, two pulse output signals can be obtained at the output end of the electrical filter by using the oscilloscope. Due to the frequency sweep characteristic of the Fourier domain mode-locked photoelectric oscillator, the time intervals of the two pulse output signals correspond to the frequency of the signal to be detected one by one, and therefore frequency spectrum detection can be achieved. At this time, the one-to-three power divider 6 can also be replaced by a one-to-two power divider, one path is sent to the electric amplifier after being divided, and the other path is directly sent to the electric filter for filtering. Similarly, the frequency spectrum detection in different frequency measurement ranges can be realized by changing the magnitude relation among the frequency sweep signal, the signal to be detected and the frequency of the electric filter.
Furthermore, the above definitions of the various elements and methods are not limited to the specific structures, shapes or modes mentioned in the embodiments, and those skilled in the art may simply well-know substitutions for their structures, such as: the one-to-three power divider 6 can be replaced by two one-to-two power dividers; a polarization controller can be added to control the polarization state of the optical signal so as to achieve better spectrum detection performance; an optical amplifier or an electrical amplifier can be added in the optical path to amplify the signal. Also, the attached drawings are simplified and are for illustration purposes. The number, shape, and size of the devices shown in the drawings may be modified depending on the actual situation, and the arrangement of the devices may be more complicated.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A beat frequency spectrum detection system, comprising: the device comprises a sweep frequency light source, a phase modulator, an optical filter, an optical fiber, a photoelectric detector, a power divider, an electric amplifier, a combiner, an electric filter, an oscilloscope and a signal source to be detected;
the swept-frequency light source, the phase modulator, the optical filter, the optical fiber and the photoelectric detector are connected through optical fiber jumpers; the photoelectric detector, the power divider, the electric amplifier, the combiner and the phase modulator are connected through cables; the power divider, the electric filter and the oscilloscope are connected through cables; the combiner and the signal source to be detected are connected through a cable;
the sweep frequency light source, the phase modulator, the optical filter, the optical fiber, the photoelectric detector and the electric amplifier form an annular photoelectric oscillator resonant cavity together; and when the Fourier domain mode locking condition is met, the photoelectric oscillator resonant cavity can generate a frequency sweeping signal with adjustable bandwidth and center frequency.
2. The system according to claim 1, wherein the swept-frequency light source is a current-driven swept-frequency semiconductor laser or a swept-frequency light source based on single-sideband modulation, which emits light with a periodic variation in wavelength.
3. The beat frequency spectrum detection system according to claim 1, wherein the optical filter is a notch filter with ultra-narrow bandwidth or an ultra-narrow optical filter based on stimulated brillouin scattering effect gain spectrum.
4. The beat frequency spectrum detection system according to claim 1, wherein said swept frequency light source, phase modulator, optical filter, and photodetector together comprise a high precision swept frequency microwave photonic filter; and
the sweep frequency period of the microwave photon filter is matched with the delay of a signal transmitted for one circle in a photoelectric oscillator loop, and the following Fourier domain mode locking conditions are met:
nT＝Tr；
wherein n is a positive integer, T is a variation period of the microwave photonic filter, and TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop.
5. The system according to claim 1, wherein the system is capable of performing spectrum sensing in different frequency measurement ranges by changing the relationship between the frequency of the electrical filter and the frequency of the sweep signal.
6. The system according to claim 1, wherein the power divider in the system is a one-to-three power divider or two-to-two power dividers.
7. The system according to claim 1, further comprising a polarization controller for controlling the polarization state of the optical signal.
8. The system according to claim 1, further comprising an optical amplifier or an electrical amplifier for amplifying the signal.
9. The system according to claim 1, wherein the optoelectronic oscillator loop in the system is replaced by a single loop with a loop equal to or greater than 2.
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| CN110518975B (en) | 2019-08-30 | 2021-10-15 | 中国科学院半导体研究所 | Frequency spectrum detection system |
| CN111313983B (en) * | 2020-02-17 | 2021-10-26 | 湖南工学院 | Microwave instantaneous frequency extraction and amplification method and instantaneous frequency measurement method and system |
| CN115015630B (en) * | 2022-05-31 | 2023-06-09 | 天津大学 | Ultra-weak frequency offset signal detection system and method based on photoelectric oscillator |
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