CN102544985A - Optical fiber type terahertz wave generation device and method based on modulation instability - Google Patents

Abstract

The invention discloses an optical fiber type terahertz wave generation device and method based on modulation instability. The terahertz wave generation device based on modulation instability in optical fiber comprises a monomode laser, a phase modulation, a microwave source, an intensity modulator, an optical amplifier, a tunable filter, a photoelectric detector and an antenna. The optical fiber type terahertz wave generation device disclosed by the invention has simple and compact structure, can realize generation of tunable terahertz waves by adjusting the frequency of a microwave drive signal and has the advantages of greatly reducing the bandwidth requirements of the device and saving the cost of a system.

Description

Optical-fiber type THz wave generation device and method based on modulational instability

Technical field

The present invention relates to photoproduction THz wave technology in the microwave photon field, specifically is a kind of optical-fiber type THz wave generation device and method based on modulational instability.

Background technology

Be in the Terahertz frequency range among microwave frequency band and the light wave frequency range at present, receive the concern of numerous scientific research institutions and company.And at the THz wave of 0.1-0.3THz frequency range because less relatively with to produce power higher relatively in the propagation in atmosphere loss; In applications such as high-speed radiocommunication, military radar, imagings huge development potentiality being arranged, is a very popular emerging research field.Since more near microwave frequency band, more often adopt the electronics technology to produce THz wave in this frequency range at present, such as electron laser, electronics Solid State Source etc.But because the restriction of electronic bottleneck, along with the raising of output frequency range, the complexity of electronic system and cost increase significantly, hamper further developing and using of Terahertz Technology.

It is the research field that microwave combines with photonic propulsion that microwave photon is learned.Wherein producing THz wave based on photonic propulsion is one of them important research direction, through the high bandwidth of combination optical frequencies and the advantage of the optic communication device of maturation, can significantly improve the situation that the Terahertz system receives electronic device bandwidth and system cost restriction.What the photoproduction THz wave was comparatively commonly used at present is the technology that adopts external modulation; Utilize intensity modulator to produce new relevant plain edge and bring the realization optical sccond-harmonic generation; Its sideband frequency difference can reach the Terahertz magnitude; Produce terahertz wave signal through opto-electronic conversion again, the THz wave signal to noise ratio that produces in this way is higher, stable performance.But the nonlinear response efficient of the intensity modulator of single commercialization is limited; The general generation single order optical sideband that is fit to is realized light two frequencys multiplication, because it is lower to produce high-order optical sideband conversion efficiency; Frequency is low; Can only reduce half the bandwidth of a device demand, this kind method Terahertz system cost is comparatively expensive, is unfavorable for practicality.

Summary of the invention

Technical problem to be solved by this invention is; Not enough to prior art, a kind of optical-fiber type THz wave generation device and method based on modulational instability is provided, improve the optical sccond-harmonic generation multiple in the photoproduction THz wave technology effectively; Reduce the requirement of system device greatly, reduce system cost.

For solving the problems of the technologies described above; The technical scheme that the present invention adopted is: based on the optical-fiber type THz wave generation device of modulational instability; Comprise single-mode laser, phase-modulator, intensity modulator, image intensifer, tunable optic filter, photodetector and antenna; Single-mode laser, phase-modulator, intensity modulator, image intensifer connect successively; Image intensifer is connected with tunable optic filter through monomode fiber, and tunable optic filter, photodetector, antenna connect successively, and intensity modulator is connected with microwave source.

Said single-mode laser is a distributed feed-back formula laser, and image intensifer is an erbium-doped fiber amplifier.

Corresponding with said apparatus, the invention allows for optical-fiber type THz wave production method based on modulational instability, it comprises following basic step:

1) utilizes single-mode laser to produce the continuous light signal of a wavelength, optical signal spectrum is carried out broadening through described phase-modulator for 1550nm.

2) microwave source of a tunable output 10-30GHz frequency of employing; With this microwave frequency signal and continuous light signal behind said phase-modulator broadening input intensity modulator in the lump, with the light signal of the double-sideband modulation that drives these two single order sidebands of intensity modulator output and centered carrier;

3) light signal with said intensity modulator output inputs to said fiber amplifier, and power amplification is to 0.45W.

2) light signal after the output of described fiber amplifier is amplified inputs to 5 kilometers long monomode fibers and transmits, and produces two to five new rank sidebands, the microwave frequency that the frequency interval between the new sideband of said generation equals to drive.

3) the output signal of monomode fiber entering tunable optic filter carries out filtering, leaches two five rank sidebands;

The light five rank sidebands that 4) will obtain carry out beat frequency through a photodetector, produce the THz wave signal of telecommunication, launch THz wave by antenna.

The efficient that the present invention is directed to single commercial intensity modulator generation high-order optical sideband is lower; Be difficult to realize that high optical sccond-harmonic generation produces the problem of THz wave; With the double-sideband signal of intensity modulator output after power amplifier amplifies; Insert the long monomode fiber of 5km, utilize the modulational instability effect in the optical fiber to produce the five rank optical sidebands of signal to noise ratio up to 30dB.Obtain the THz wave of high s/n ratio again through photodetector beat frequency and antenna emission.This scenario-frame compact, the frequency of the microwave-driven signal through regulating intensity modulator can produce tunable THz wave, and greatly reduces the bandwidth requirement of device, has practiced thrift the cost of system.

Description of drawings

Fig. 1 is the optical-fiber type THz wave generation device structural representation of one embodiment of the invention based on modulational instability;

Wherein:

1: distributed feed-back formula laser (DFB-LD); 2: phase-modulator; 3: intensity modulator; 4: microwave source; 5: erbium-doped fiber amplifier (EDFA); 6: monomode fiber (SMF); 7: tunable optic filter; 8: photodetector (PD); 9: antenna; 10: THz wave.

Embodiment

As shown in Figure 1; One embodiment of the invention device comprises distributed feed-back formula laser 1, phase-modulator 2, intensity modulator 3, microwave source 4, erbium-doped fiber amplifier 5, monomode fiber 6, tunable optic filter 7, photodetector 8 and antenna 9; Said reaction type laser 1 output continuous light signal is input to phase-modulator 2, and after said phase-modulator carried out broadening to its continuous light live width, its microwave-driven signal of exporting with microwave source 4 was in the lump as the input signal of intensity modulator 3; Said intensity modulator 3 outputs contain the light double-sideband signal of centered carrier and two single order sidebands; After erbium-doped fiber amplifier 5 amplifies, be input to monomode fiber (SMF) again, above-mentioned monomode fiber transmission back produces new second order, three rank, quadravalence, five rank light signals; Again through adjustable light wave-filter 7; Output only contains the input signal of five rank light signals as photodetector 8, and the output signal of said photodetector 8 inserts antenna 9 at last, output THz wave 10.

Specifying of above-mentioned each module is described below:

Distributed feed-back formula laser 1 is used to produce the optical carrier of specifying narrow linewidth;

Phase-modulator 2 carries out broadening to the light signal of narrow linewidth, to suppress the Brillouin scattering effect in the optical fiber;

Intensity modulator 3 is used for producing two single order sideband signals to specifying optical carrier to carry out double-sideband modulation, with as modulating unsettled modulation signal in the next stage optical fiber;

Microwave source 4: the microwave source signal that is used to produce tunable 10～30GHz frequency;

Erbium-doped fiber amplifier 5 is to the power amplification of carrying out of light double-sideband signal;

Monomode fiber 6 is used for the single order sideband signals is produced modulational instability, to produce the high-order optical sideband;

Tunable optic filter 7 is used to keep two light, the five rank sideband signals that modulational instability produces, other sideband of filtering and centered carrier light signal;

Photodetector 8 is used for the beat frequency that carries out of two five rank light signals is produced the Terahertz signal of telecommunication;

Antenna 9 is launched the Terahertz signal of telecommunication with the electromagnetic wave form.

THz wave 10, the THz wave of generation.

Utilize single-mode laser 1 to produce a continuous light signal, carry out broadening through 2 pairs of light signal live widths of a phase-modulator.Adopt the microwave source 4 of a tunable output 10-30GHz frequency; Be input to an intensity modulator in the lump with the continuous light signal behind the phase-modulator broadening, to drive the light signal that this intensity modulator produces the double-sideband modulation that contains two single order sidebands and centered carrier; The light signal of said intensity modulator output is inputed to said erbium-doped fiber amplifier (EDFA) 5, and power amplification is to 0.45W.The output light signal of described EDFA inputs to monomode fiber 6 through after amplifying, and through 5 kilometers Optical Fiber Transmission, produces new a series of high-order optical sidebands, the microwave frequency that the frequency interval between the new sideband of said generation equals to drive.The output signal of monomode fiber gets into tunable optic filter 7 and carries out filtering, has to two light, five rank sidebands; The light that obtains five rank sidebands are carried out beat frequency through a photodetector 8, produce the high-frequency THz wave signal of telecommunication, launch THz wave 10 by antenna 9.

Operation principle of the present invention and process are: produce a continuous light signal E by single-mode laser ₀=Ecos (ω _cT), wavelength is 1550nm, as light carrier, through phase-modulator its live width is carried out broadening earlier, can effectively suppress Brillouin scattering effect in the optical fiber, again with microwave signal E _RF(t)=V _FRCos (ω _RFT) drive strength modulator, and be modulated on the light carrier and just can produce the light double-sideband modulation signal, i.e. a light carrier and two single order sideband light signals, expression formula can be:

$E_{\mathrm{DSB}}\left(t\right)=\frac{E}{2}\{J_0\left(\mathrm{\χ}\right)\cos \left({\mathrm{\ω}}_{c}t\right)-J_1\left(\mathrm{\χ}\right)[\sin \left(({\mathrm{\ω}}_c-{\mathrm{\ω}}_{\mathrm{RF}})t\right)+\sin \left(({\mathrm{\ω}}_c+{\mathrm{\ω}}_{\mathrm{RF}})t\right)\left]\right\}$

(1)

ω wherein _cBe optical carrier frequency, E representes the amplitude of light carrier, ω _RFThe frequency of expression microwave signal, 10GHz≤ω _RF≤30GHz,

The expression modulation depth.

Double-sideband signal through the image intensifer power amplification to P ₀Behind=the 0.45W, input to monomode fiber and transmit, ignore the loss of optical fiber, its communication satisfaction non-linear Schrodinger equation in optical fiber is:

$i\frac{\&PartialD;A}{\&PartialD;z}+\frac{{\mathrm{\&beta;}}_2}{2}\frac{{\&PartialD;}^{2}A}{{\&PartialD;\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000127728080000011.png"\; state="\{\{state\}\}">T</figure-callout>}}^2}+\mathrm{\&gamma;}{\left|A\right|}^{2}A=0$

(2)

A (z, the T) amplitude of expression light field envelope, β wherein ₂Expression GVD parameter, γ representes the nonlinear fiber coefficient.

We are ω with frequency ₀Optical carrier as pump light, two frequencies are respectively ω _c-ω _RF, ω _c+ ω _RFThe single order sideband as surveying light, be in the anomalous dispersion zone of optical fiber this moment, when luminous power when producing the power threshold of modulational instability, according to phase matched and law of conservation of energy, can produce new n rank optical sideband, ω _c-n ω _RFAnd ω _c+ n ω _RF, n>=2.It is that the accurate Analysis of non-linear Schrodinger equation is separated that Akhmediev Breather (AB) separates, to AB separate carry out Fourier transform after, can be used to represent of the variation of light n rank sideband with the Optical Fiber Transmission distance:

$A_n\left(\mathrm{\&xi;}\right)=\frac{\mathrm{ib}\sinh \mathrm{b\&xi;}+{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA0000127728080000011.png"\; state="\{\{state\}\}">p</figure-callout>}}^2\cosh \mathrm{b\&xi;}}{\sqrt{{\mathrm{<figure-callout\; id="2"\; label="cosh"\; filenames="HDA0000127728080000011.png"\; state="\{\{state\}\}">cosh</figure-callout>}}^2\mathrm{b\&xi;}-2a}}\&times;{\left[\frac{\cosh \mathrm{b\&xi;}-\sqrt{{\mathrm{<figure-callout\; id="2"\; label="cosh"\; filenames="HDA0000127728080000011.png"\; state="\{\{state\}\}">cosh</figure-callout>}}^2\mathrm{b\&xi;}-2a}}{\sqrt{2a}}\right]}^n$

(3)

Wherein,

B=[8a (1-2a) ^1/2], p=2 (ω _RF/ ω _c) ^1/2, L _NL=(γ P ₀) ^-1, ξ=z/L _NLRepresent normalized transmission range, sinh, cosh are respectively hyperbolic sine and hyperbolic cosine.

The monomode fiber parameter that we adopt is β ₂=-21ps ²Km ^-1, γ=1W ^-1Km ^-1, z=5km can get through calculating, and the five rank sideband signal to noise ratios that modulational instability produces have very high signal to noise ratio greater than 30dB.Leach two five rank sidebands through tunable optical filter, produce the terahertz wave signal that decuples the microwave-driven signal through the high-speed photodetector beat frequency:

E _out＝μ·A ₅(ξ)·cos(10ω _RFt)

(4)

Wherein μ representes the response coefficient of photodetector.

Modulational instability in the optical fiber is the coefficient result of optical fiber dispersion and nonlinear effect, shows continuous or quasi-continuous laser is split into a row ultrashort pulse string.In the anomalous dispersion district, at enough big state, non-linear effect is enough as if luminous power, and for continuous laser, frequency can divide, and observes at frequency spectrum and finds to have a series of frequency peak.But because passive modulation instability is uncontrollable, thereby division has randomness, and is wayward.As before satisfying the unsettled condition of modulation, introduce a stronger modulation, then can make the modulation instability occur in existing modulating frequency place.Thereby initiatively regulate and control modulational instability, produce a series of stabilized frequency frequency peak at interval that have.The phase place of these frequency peak locks; We produce two single order sidebands through low frequency microwave signal drive strength modulator, through image intensifer with power amplification after, through the monomode fiber transmission of certain-length; Because the modulational instability effect in the optical fiber; The single order sideband can divide a plurality of high-order sidebands, can also reach the signal to noise ratio of 30dB during to five rank sidebands, leaches the frequency peak of five rank sidebands through tunable optical filter; Utilize the emission of photodetector beat frequency and antenna, just can obtain decupling the electromagnetic wave of microwave signal.Thereby adopt this method to produce the 0.1-0.3THz THz wave, and only needing the 10-30G microwave signal, the modulator bandwidth is as long as 30G is convenient and practical.

Claims (8)

1. optical-fiber type THz wave generation device based on modulational instability; Comprise single-mode laser, phase-modulator, microwave source, intensity modulator, image intensifer, tunable optic filter, photodetector and antenna; It is characterized in that; Single-mode laser, phase-modulator, intensity modulator, image intensifer connect successively; Image intensifer is connected with tunable optic filter through monomode fiber, and tunable optic filter, photodetector, antenna connect successively, and intensity modulator is connected with microwave source.

2. the optical-fiber type THz wave generation device based on modulational instability according to claim 1 is characterized in that said single-mode laser is a distributed feed-back formula laser, and image intensifer is an erbium-doped fiber amplifier.

3. the optical-fiber type THz wave production method based on modulational instability is characterized in that, steps of the method are:

1) utilizes single-mode laser to produce a continuous light signal, be input to phase-modulator, the live width of continuous light signal is carried out broadening;

2) light signal of phase-modulator output and the microwave signal of microwave source generation are input to intensity modulator in the lump, produce the double-sideband modulation device signal of two single order sideband signals;

3) double-sideband modulation device signal input image intensifer and amplification are transmitted through monomode fiber, produce two five rank sideband signals;

4) with the humorous filter of tunable optical to five rank sideband signals filtering, choosing two difference on the frequencies is the five rank sidebands that decuple microwave signal;

5) two five rank sidebands are carried out beat frequency through photodetector, produce the THz wave signal of telecommunication, launch THz wave by antenna again.

4. the optical-fiber type THz wave production method based on modulational instability according to claim 3 is characterized in that, in the said step 1), and light signal E ₀Expression formula be: E ₀=Ecos (ω _cT) its wavelength is 1550nm; ω wherein _cBe optical carrier frequency, E representes the amplitude of light carrier.

5. the optical-fiber type THz wave production method based on modulational instability according to claim 3 is characterized in that said step 2) in, double-sideband modulation device signal E _DSBExpression formula do $E_{\mathrm{DSB}}\left(t\right)=\frac{E}{2}\{J_0\left(\mathrm{\&chi;}\right)\mathrm{Cos}\left({\mathrm{\&omega;}}_{c}t\right)-J_1\left(\mathrm{\&chi;}\right)[\mathrm{Sin}\left(({\mathrm{\&omega;}}_c-{\mathrm{\&omega;}}_{\mathrm{RF}})t\right)+\mathrm{Sin}\left(({\mathrm{\&omega;}}_c+{\mathrm{\&omega;}}_{\mathrm{RF}})t\right)\left]\right\};$ Wherein: ω _RFThe frequency of expression microwave signal, 10GHz≤ω _RF≤30GHz, The expression modulation depth, J ₀Expression first kind zero Bessel function, J ₁Expression first kind first-order bessel function, V _RFExpression microwave-driven voltage of signals amplitude, V _πThe half-wave voltage of expression modulator.

6. the optical-fiber type THz wave production method based on modulational instability according to claim 3 is characterized in that in the said step 3), image intensifer is amplified to 0.45W with the output signal of intensity modulator.

7. the optical-fiber type THz wave production method based on modulational instability according to claim 3 is characterized in that, in the said step 3), and the signal to noise ratio＞30dB of five rank sideband signals.

8. the optical-fiber type THz wave production method based on modulational instability according to claim 3 is characterized in that, in the said step 5), and THz wave signal of telecommunication E _OutExpression formula be: E _Out=μ A ₅(ξ) cos (10 ω _RFT); Wherein: A _n(ξ) expression light n rank sideband is with the variation of Optical Fiber Transmission distance, and ξ representes normalized transmission range, and μ representes the response coefficient of photodetector.

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