CN101567723B - Microwave frequency measuring method based on optical power detection and device thereof - Google Patents

Abstract

The invention discloses a microwave frequency measuring method based on optical power detection and a device thereof, which conducts real-time measurement on microwave frequency by adopting a system consisting of an electro-optical modulating module and a frequency demodulating module. A continuous microwave signal is loaded on a continuous light source in the modulating module in the modulating manner of carrier suppressed small signals, and only generates two plus or minus 1 stage optical margin strips; the modulated optical signal is divided into two paths, wherein one path is injected intoa comb-like filter with sine-function transmission spectrum while the other path is injected into a tunable optical attenuator; the output optical power of the two paths are detected and compared wit h each other and the microwave frequency is obtained from the demodulation of power ratio. The invention lowers the complexity and cost of the system, eliminates the influence of fluctuation of outputpower of the light source on the measurement of the frequency and enlarges the measuring frequency band of frequency linear demodulation.

Description

A kind of microwave frequency measuring method and device thereof that detects based on luminous power

Technical field

The present invention relates to communication and signal processing field, the real-time microwave frequency measuring method of especially a kind of photon technology type.

Background technology

Microwave frequency measurement in real time is an important content in dual-use microwave communication and the signal processing field, relates to frequency-tracking, communication intercept etc.Early stage microwave frequency measuring technique is mostly based on electronic technology, like electric spectrometer.The electricity spectrometer carries out work under a kind of scan pattern.When the life period of microwave signal to be measured during less than a scan period, electric spectrometer can't normally obtain its frequency information.And in some key areas (such as electronic warfare), the time that is sudden very strong, that exist of communication or signal is very short, and scan pattern type frequency measurement mode is difficult to prove effective, and broadband, real-time microwave frequency measuring method seem particularly important.Such as, the frequency range of using in the modern electronic warfare is approaching or surpass 100GHz, thereby need in big band limits, realize real-time microwave frequency measurement, and this is the insoluble problem of conventional electrical method.

Along with the rise that microwave photon is learned, utilize photon technology to handle the focus that microwave signal becomes research gradually and uses, it has broadband disposal ability, light weight, loss is little and anti-electromagnetic interference capability is strong characteristics.At present, photon technology type real time frequency measurement technology mainly contains two kinds: the channel device of cutting apart based on frequency range and based on the frequency measurement technology of power contrast.

Channel device based on frequency range is cut apart can be constructed by following elements: electric light delayed linear array, high-resolution free space diffraction grating, phase-shifted grating array; The integrated system of fiber grating and Fresnel prism; The system of combined standard tool and wavelength division multiplexer (F.A.Volkening, Photonic channelized RF receiver employing dense wavelength divisionmultiplexing, U.S.Patent 7 245 833B1; July 17,2007).The operation principle of these schemes is roughly the same: under the small-signal modulation, optical sideband and the light carrier interval on frequency domain is microwave frequency to be measured.Depart from the distance of light carrier through detecting optical sideband, thereby detect the microwave frequency of measured signal.This channel device of cutting apart based on frequency range is normally roughly confirmed the present wave band of microwave frequency (is 2GHz such as resolution), obtains more accurate frequency values with parallel arrowband processing method then.

Measuring technique based on the power contrast can be divided into two types again: based on the measurement scheme of microwave power detection and the measurement scheme that detects based on luminous power.Using the microwave power attenuation effect that effect of dispersion causes mostly based on the measurement scheme of microwave power detection realizes; Such as adopting fiber grating (Linh V.T.Nguyen and David B.Hunter.A photonic technique formicrowave frequency measurement.IEEE Photonics Technology Letters; 2006, vol.18, no.10; 1188-1190); Or dispersive optical fiber (Xihua Zou and JianpingYao.An optical approach to microwave frequency measurement withadjustable measurement range and resolution.IEEE Photonics TechnologyLetters, 2008, vol.20; No.23,1989-1991).Frequency measurement scheme based on microwave power detection needs two high-speed photodetectors, is used to detect the high-frequency microwave power of two channel outputs.

Frequency measurement scheme based on the luminous power detection: under the modulation of carrier suppressed type small-signal, utilize filter that the microwave frequency information translation is intensity signal.Detect and contrast the luminous power of two-way; Counter separating obtains microwave frequency to be measured (Hao Chi, Xihua Zou, andJianping Yao.An approach to the measurement of microwave frequencybased on optical power monitoring.IEEE Photonics Technology Letters from power ratio; 2008; Vol.20, no.14,1249-1251).Though this scheme only needs the photo-detector or the light power meter of low speed, this measurement scheme needs two continuous light sources, and the complexity of system and cost are still higher, and in addition, the fluctuation meeting of two continuous light source power outputs brings negative effect to frequency measurement; Corresponding relation between luminous power ratio and the microwave frequency is the tan shape, and the broadband with linear frequency demodulation frequency range is limited.

Summary of the invention

In view of the above shortcoming of prior art, the purpose of this invention is to provide a kind of real-time microwave frequency measuring method that detects based on luminous power, make it to overcome the above deficiency of prior art.

The objective of the invention is to realize through following means:

A kind of microwave frequency measuring method that detects based on luminous power; The system that employing is made up of electrooptic modulation module and frequency demodulation module is measured real-time microwave frequency; The continuous microwave signal is loaded on the continuous light source in the modulation module with carrier suppressed type small-signal modulation system, only generates two optical sidebands in ± 1 rank; The modulation module light signal is divided into two-way after injecting demodulation module, and one the tunnel is injected into the comb filter with SIN function shape transmission spectrum, the variation of microwave frequency is converted into the variation of optical sideband intensity; Another road is injected into variable optical attenuator, with the loss of balance two branch roads; Through detecting and contrast the Output optical power of said two branch roads, demodulation obtains microwave frequency from power ratio.

Another object of the present invention provides the practical implementation device of realizing above-mentioned method of measurement.Mainly form by carrier suppressed type small-signal electrooptic modulation module and microwave frequency demodulation module with arcsin function shape demodulation curve; In said demodulation module, be divided into two light branch roads after modulated light signal injects: the one tunnel is injected into the optical comb filter with SIN function shape transmission spectrum and the light path of a low speed photo-detector; Another road is injected in the light path of a variable optical attenuator and a low speed photo-detector; The output of said two light branch roads is connected with the digital processing comparing unit.

After design as above, compared with prior art, the present invention has following advantage: adopt low speed photo-detector or light power meter to detect luminous power; Only need single continuous light source, reduced the complexity and the cost of system, and eliminated the influence of the fluctuation of light source output power frequency measurement; Have arcsin function type microwave frequency demodulation curve, enlarged the measurement frequency range of frequency linearity demodulation.

Description of drawings is following:

The system schematic of Fig. 1 the inventive method.

Fig. 2 optical comb filter power transmission spectrum.

Fig. 3 light source output frequency places the crest or the wave trough position figure of pectination spectrum.

Fig. 4 crest (solid line), trough (dotted line) position power ratio are with the changing trend diagram of microwave frequency.

The microwave frequency distribution map that Fig. 5 crest (solid line), trough (dotted line) position are obtained by the power ratio demodulation.

Fig. 6 combines the modulation system sketch map of electric light light polarization modulator and polarization beam apparatus.

Fig. 7 is based on the time delay interferometer structure figure of polarization maintaining optical fibre.

Fig. 8 crest (solid line), trough (dotted line) position luminous power are with the changing trend diagram of microwave frequency.

Embodiment

Below in conjunction with accompanying drawing the present invention is done further description.

As shown in Figure 1, measuring system comprises the electrooptic modulation module 10 and the demodulation module 11 with arcsin function shape frequency demodulation curve of carrier suppressed type small-signal modulation.In the electrooptic modulation module, the microwave signal that receives from the external world is through electrooptic modulator, and the mode of modulating with small-signal is loaded on the continuous light source; Introduce the carrier suppressed condition, the light signal after the modulation only generates ± two optical sidebands in 1 rank.

The output light signal of modulation module is injected into demodulation module.In demodulation module, the light signal of being made up of ± 1 rank optical sideband is divided into two-way: the one tunnel is injected in the comb filter with SIN function type transmission spectrum, the variation of microwave frequency is converted into the variation of optical sideband intensity; Another road is injected in the variable optical attenuator, with the insertion loss of balance two branch roads.The power transmission spectrum T of optical comb filter sees Fig. 2, and its free spectrum region is FSR.The FSR of the inventive method medium frequency measuring range and optical comb filter is closely related, and the limit range of frequency measurement is: 0～FSR/2.

Detect and contrast the Output optical power of two branch roads, the frequency demodulation module converts the variation of microwave frequency to the variation of luminous intensity.The output frequency of light source is arranged on the crest location or the wave trough position (see figure 3) of optical comb filter, obtains the corresponding relation that is sine function shape between luminous power ratio R and the microwave frequency f, see Fig. 4.

The microwave frequency that demodulation obtains from luminous power ratio presents arcsin function shape corresponding relation (see figure 5), is expressed as with mathematical form:

$f=\mathrm{Arcsin}\left[\sqrt{R}\right]\×\frac{\mathrm{FSR}}{\mathrm{\π}}$ Or $f=\mathrm{Arccos}\left[\sqrt{R}\right]\×\frac{\mathrm{FSR}}{\mathrm{\π}}.$

At this moment, microwave frequency measurement result and microwave power are irrelevant, because do not comprise any factor that relates to microwave power in the microwave frequency expression formula that demodulates; And, from luminous power ratio, demodulate in this process of microwave frequency, exist approximately linear corresponding relation preferably between luminous power ratio and the microwave frequency, i.e. the arcsin function relation; This corresponding relation has been simplified the demodulating process of microwave frequency, has enlarged the scope of frequency measurement.

The method for microwave measurement that the present invention announces is formed (see figure 1) by the electrooptic modulation module 10 of carrier suppressed type small-signal modulation with the demodulation module 11 with arcsin function shape frequency demodulation curve.

In the electrooptic modulation module, the microwave signal that receives from the external world is loaded on the continuous light source through the mode of carrier suppressed type double-sideband modulation device 101 with the modulation of carrier suppressed type small-signal through electrooptic modulator.Light signal after the modulation only keeps ± two optical sidebands in 1 rank, two luminous power P that optical sideband carries ₀Be expressed as:

P ₀＝2αP[J ₁(β)] ²

Wherein: α representes the various losses in the light path, comprises the loss that insertion loss, the junction loss in the link and the photo-detector response coefficient of modulator cause; P representes light source output power; β representes modulation depth, and is relevant with the half-wave voltage of microwave power and modulator; J ₁() expression 1 rank first kind Bessel function.

When reality was implemented, carrier suppressed type small-signal modulation system can realize through three kinds of approach: connect the narrowband reflection fiber grating after intensity modulator is applied half-wave bias voltage, phase-modulator, combine light polarization modulator and analyzer.One of enforcement approach: intensity modulator is applied dc offset voltage; Intensity modulator is operated in the minimum point of transfer function, thereby realizes the effect of carrier suppressed.Two of enforcement approach: connect the narrowband reflection fiber grating after the phase-modulator; The narrowband reflection grating is connected after the phase-modulator, and light carrier is reflected, and ± 1 rank optical sideband passes through, thereby realizes the effect of suppressed carrier.Three of enforcement approach: combine light polarization modulator and polarization beam apparatus, see Fig. 6; Light polarization modulator and polarization beam apparatus common down, strange time optical sideband is able to separate on the polarization state of two quadratures with the inferior optical sideband of idol, has promptly realized the effect that light carrier separates with ± 1 rank optical sideband, thereby has reached the purpose of suppressed carrier.

The output signal of electrooptic modulation module is injected in the demodulation module.In demodulation module, modulated light signal (only having kept ± 1 rank optical sideband) is divided into two-way: the one tunnel is injected in the optical comb filter with SIN function shape transmission spectrum; Another road is injected into a variable optical attenuator, with the insertion loss of balance two branch roads.

Optical comb filter with SIN function shape transmission spectrum, its power transmission spectrum T sees Fig. 2, is expressed as with mathematical formulae:

$T={\left[\cos \left(\frac{\mathrm{\&pi;}{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="H2009100595073E00012.png,H2009100595073E00021.png"\; state="\{\{state\}\}">f</figure-callout>}}_0}{\mathrm{FSR}}\right)\right]}^2,$

Wherein: f ₀The expression light frequency, FSR representes the free spectrum region of comb filter.It is to be noted: the FSR of frequency measurement scope in the methods of the invention and optical comb filter is closely related, and the limit range of frequency measurement is: 0～FSR/2.

Optical comb filter 111 practical implementations with SIN function shape transmission spectrum can be adopted the non-equilibrium Mach-Zehner interferometer of single-stage, or based on the single-stage time delay interferometer of polarization maintaining optical fibre, or based on three kinds of approach of single-stage time delay interferometer of birefringece crystal.One of enforcement approach: the non-equilibrium Mach-Zehnder interferometer of single-stage; It is made up of two 3dB optical couplers and a pair of nonequilibrium brachium, and the free spectrum region of its comb filtering spectrum is by the relative light path difference decision of two arms.Two of enforcement approach:, see Fig. 7 based on the time delay interferometer of polarization maintaining optical fibre; It is made up of one section polarization maintaining optical fibre, two Polarization Controllers and an analyzer, and the free spectrum region of its comb filtering spectrum is by the length and the long common decision of bat of polarization maintaining optical fibre; Three of enforcement approach: based on the time delay interferometer of birefringece crystal; It is made up of a birefringece crystal and two polarization beam apparatus, and the free spectrum region of its comb filtering spectrum is determined by the double refractive inde and the length of crystal jointly.

The output frequency of continuous light source is arranged on the crest location or the wave trough position of optical comb filter SIN function shape transmission spectrum, sees Fig. 3.Through the filter action of comb filter, the variation of microwave frequency converts into ± the variation (see figure 8) of 1 rank optical sideband intensity, represent output intensity P with mathematical form ₁:

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009100595073E00021.png,H2009100595073E00022.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=2\mathrm{\&alpha;\; P}{\left[J_1\left(\mathrm{\&beta;}\right)\right]}^2{\left[\mathrm{Sin}\left(\frac{\mathrm{\&pi;\; f}}{\mathrm{FSR}}\right)\right]}^2$ Or ${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009100595073E00021.png,H2009100595073E00022.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=2\mathrm{\&alpha;\; P}{\left[J_1\left(\mathrm{\&beta;}\right)\right]}^2\{1-{\left[\mathrm{Sin}\left(\frac{\mathrm{\&pi;\; f}}{\mathrm{FSR}}\right)\right]}^2\}.$

The modulated light signal in another road (only having kept ± 1 rank optical sideband) is input in the variable optical attenuator.The attenuation of adjustment light is with the loss difference of compensation two ways of optical signals.Thereby, the light intensity P of optical attenuator output ₂Expression

P ₂＝2αP[J ₁(β)] ²

Detect and contrast the Output optical power of two branch roads, obtain the corresponding relation between luminous power ratio R and the microwave frequency f:

$R=\frac{P_1}{P_2}={\left[\mathrm{Sin}\left(\frac{\mathrm{\&pi;\; f}}{\mathrm{FSR}}\right)\right]}^2$ Or $R=\frac{P_1}{P_2}=1-{\left[\mathrm{Sin}\left(\frac{\mathrm{\&pi;\; f}}{\mathrm{FSR}}\right)\right]}^2.$

Form with figure provides the corresponding relation between luminous power ratio R and the microwave frequency f, sees Fig. 4.Demodulation obtains microwave frequency to be measured from luminous power ratio:

$f=\mathrm{Arcsin}\left[\sqrt{R}\right]\&times;\frac{\mathrm{FSR}}{\mathrm{\&pi;}}$ Or $f=\mathrm{Arccos}\left[\sqrt{R}\right]\&times;\frac{\mathrm{FSR}}{\mathrm{\&pi;}}.$

Thus it is clear that, do not comprise any factor that relates to microwave power, luminous power in the microwave frequency expression formula that demodulation obtains, so microwave frequency measurement result and microwave power are irrelevant.And, present the arcsin function shape by luminous power ratio to the frequency demodulation curve of microwave frequency, see Fig. 5; Therefore exist approximately linear corresponding relation preferably between luminous power ratio and the microwave frequency, this corresponding relation has been simplified the demodulating process of microwave frequency, has enlarged the scope of frequency measurement.

Comprehensive above statement, the present invention has following characteristic: 1). and adopt photon technology that the frequency of microwave signal is measured, because photon technology itself has the incomparable superiority bandwidth of electronic technology, the present invention has the wideband frequency measurement capability; 2). adopt the form of luminous power contrast to carry out frequency measurement, do not need the photo-detector and the scanning work pattern in high speed, broadband, reduced cost, and realized real time frequency measurement; 3). good by power ratio to the demodulation curve linear degree of microwave frequency, make the frequency demodulation process more easy; 4). adopt single source, reduced the cost of method of measurement, and eliminated the negative effect of light source output power fluctuation fully frequency measurement.

It is above that what state only is the preferred implementation of the inventive method; Should be understood that; Under the prerequisite that does not break away from the inventive method principle, can also make some improvement and the local example that becomes in the specific implementation, these also should be included in protection scope of the present invention.

Claims (3)

1. microwave frequency measuring method that detects based on luminous power; The system that employing is made up of electrooptic modulation module and frequency demodulation module is measured microwave frequency in real time; Adopt following working method: the continuous microwave signal is loaded on the continuous light source in the modulation module with carrier suppressed type small-signal modulation system, only generates two optical sidebands in ± 1 rank; Be divided into two-way after the light signal of modulation module output is input in the demodulation module, the one tunnel is injected into the comb filter with SIN function shape transmission spectrum, the variation of microwave frequency is converted into the variation of optical sideband intensity; Another road is injected into variable optical attenuator, with the loss of balance two branch roads; Detect and contrast the Output optical power of said two branch roads; Demodulation obtains microwave frequency from luminous power ratio; Microwave frequency f is drawn by

In the formula: P ₁And P ₂Be respectively the Output optical power of two branch roads, R is a luminous power ratio, and FSR is the free spectrum region of said optical comb filter.

2. realize the device of a kind of microwave frequency measuring method that detects based on luminous power that claim 1 is said; It is characterized in that, form by the continuous light source and the Double Sideband Suppressed Carrier modulating device of serial connection carrier suppressed type small-signal electrooptic modulation module of being formed and microwave frequency demodulation module with arcsin function shape demodulation curve; The coupler rear end that receives modulated light signal in the said demodulation module has the light branch road of two parallel connections: the one tunnel connects in proper order has the optical comb filter and a low speed photo-detector of SIN function shape transmission spectrum; Another road connect in proper order a variable optical attenuator and a low speed photo-detector; The output of said two light branch roads is connected with digital processing element.

3. a kind of microwave frequency measurement mechanism that based on luminous power detect according to claim 2; It is characterized in that one of following three kinds of modes are adopted in the realization of the optical comb filter of SIN function shape transmission spectrum: the non-equilibrium Mach-Zehner interferometer of single-stage that a) constitutes by two 3dB optical couplers and a pair of nonequilibrium brachium; B) by one section polarization maintaining optical fibre, two Polarization Controllers and analyzer constitute based on polarization maintaining optical fibre time delay interferometer; C) by a birefringece crystal and two time delay interferometers that polarization beam apparatus constitutes based on birefringece crystal.

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