CN101902278A - Microwave signal generation scheme capable of adjusting frequency and pulse width - Google Patents

Abstract

The invention discloses a microwave signal generation scheme capable of adjusting frequency and pulse width, which is based on a broadband light source, an adjustable differential group delay element, an optical filter with adjustable bandwidth and a microwave generation device consisting of a frequency domain-to-time domain mapping module; and the microwave signal generation method is as follows: injecting wide-spectrum light produced by the light source into an optical spectrum constructing module, using the adjustable differential group delay module and the optical filter for constructing a target optical spectrum, and finally utilizing the frequency domain-to-time domain mapping module for generating a microwave signal with the designated frequency and the pulse width. The method of the invention can realize the adjustability of the frequency and the pulse width of the signal on the basis of ensuring the high-frequency performance of the produced microwave signal and enhance the flexibility of the ordinary microwave signal generation method.

Description

The microwave signal generation scheme capable that a kind of frequency and pulsewidth are adjustable

Technical field

The present invention relates to microwave photon, microwave signal generation field, especially photon type microwave generation technique.

Background technology

The high-frequency microwave generation technique is at light carrier radio communication system, plays key effect in radar system and the sensing network always.At present, the microwave frequency band that adopts in microwave technology and the application and intend adopting is constantly soaring, and this is a great challenge to the traditional microwave device, and therefore utilizing optical means to produce microwave signal becomes an extremely attractive research focus.Compare with traditional microwave production method, the photonic propulsion method has low-loss, the high bandwidth characteristic, and can not be subjected to electromagnetic interference.It is worthy of note that the microwave signal frequency of utilizing optical means to generate often only is subjected to the restriction of photodetector bandwidth, therefore, generate the field at high-frequency microwave signal, optical means has certain advantage.

With regard to present progress, the multiple scheme of utilizing optical means to produce microwave signal is arranged.Wherein, utilizing difference frequency light to carry out beat frequency and utilize the spectrum structure is two kinds of main microwave signal generation scheme capables in conjunction with the method for time domain frequency domain mapping.The former is close with two bundle frequencies, and the light wave that polarization state is identical incides simultaneously and carries out beat frequency on the high frequency light detector, and the microwave signal frequency that obtains is by the difference on the frequency decision of two-beam.The The latter comb filter is carried out the spectrum structure to wide spectrum light source, then carries out the frequency domain to time domain mapping by dispersive medium and photo-detector, and then obtains the microwave signal of certain frequency.

Need to such an extent that be pointed out that: above-mentioned two kinds of technology paths all can only exist limitation separately.The microwave signal frequency that the former produces is influenced by wavelength stability, and the minor shifts of input optical wavelength all can cause generating the variation of microwave signal frequency, and is higher to selecting requirement on devices for use.And the latter can only produce the microwave signal of fixed frequency, in case select for use comb optical filter to fix, it is also fixing thereupon to generate signal frequency.The present invention has provided a kind of frequency and the adjustable microwave signal of pulsewidth produces scheme, provides the bigger degree of freedom for high-frequency microwave signal produces.

Summary of the invention

In view of the deficiency of the existing program of above statement, the present invention aims to provide a kind of frequency and the adjustable microwave signal of pulsewidth produces scheme, strengthens the flexibility that produces microwave signal characteristic (comprising frequency and pulsewidth) under the prerequisite that guarantees microwave signal frequency stability.

Purpose of the present invention realizes by following means.

Microwave signal that a kind of frequency and pulsewidth are adjustable produces scheme, based on by a wideband light source, an adjustable Differential Group Delay element, and the optical filter that bandwidth is adjustable, and the microwave generation device that the frequency domain to time domain mapping block constitutes; Microwave signal generating method is: the wide range light beam that light source produces is gone in the spectrum constructing module, use adjustable Differential Group Delay module and optical filter structure target optical spectrum, utilize the frequency domain to time domain mapping device to produce the microwave signal of assigned frequency and pulsewidth at last.

After the wide range light process light intensity modulator down modulation that ultrashort pulse source or other wideband light source produce, the ultrashort pulse sequence that the cycle that obtains is lower, be entered in the spectrum constructing module to obtain target optical spectrum, then the monomode fiber by adding one section length-specific is to introduce chromatic dispersion and to use photodetector to convert light signal to microwave signal.Wherein, the spectrum constructing module is by two adjustable Polarization Controllers, an adjustable differential group time delay element, and a bandwidth tunable optical filter, a polarizer is formed.Wide range light reduces the pulse repetition period through low frequency signal modulation back, make spectrum more smooth, then import the group velocity retardation element and between two orthogonal polarisation state, introduce a certain size time delay, and at polarizer place generation polarization interference, produce the comb filtering effect, make broadband spectral be longitudinal cosine type and change, use optical filter restriction spectral width thereafter, carry out the time domain frequency domain mapping through a section single-mould fiber at last, can obtain required microwave signal.Owing to generate Differential Group Delay and optical fiber dispersion amount that microwave signal frequency depends on introducing, therefore under the situation that the rear end fiber lengths is determined, can control the signal frequency of generation by changing the Differential Group Delay amount; Same, the microwave symbol width of generation depends on spectral width and dispersion measure size, can control the signal pulsewidth of generation by changing optical filter bandwidth.

Through after the above design, the inventive method has following advantage: on the basis that does not change the system configuration device, the microwave signal frequency of generation and pulsewidth can be regulated according to system requirements, have increased the flexibility of photoproduction microwave technology.

Description of drawings is as follows:

Fig. 1. the present invention program's system block diagram.

Fig. 2. the structured flowchart of spectrum constructing module.

Fig. 3. at Differential Group Delay is 40ps, and filter bandwidht is under the 3nm situation, (a) signal spectrum that obtains; (b) microwave signal.

Fig. 4. keep Differential Group Delay at 40ps, change the microwave signal that optical filter bandwidth obtains: (a) filter bandwidht is 2.1nm; (b) filter bandwidht is 1.2nm.

Fig. 5. the microwave signal of the different frequency that change Differential Group Delay size obtains: (a) Differential Group Delay is 18ps; (b) Differential Group Delay is 95ps.

Fig. 6. (a) microwave signal frequency of Sheng Chenging is with the change curve of Differential Group Delay; (b) the signal pulsewidth is with the change curve of optical filter bandwidth.

Embodiment

Below in conjunction with accompanying drawing enforcement of the present invention is further described.

As shown in Figure 1, the present invention program is by 10, one optical modulators 20 of a ultra-short pulse source, and spectrum constructing module 30, one section single-mould fibers 40 and a photodetector 50 constitute.

Light pulse by ultrashort pulse laser 10 outputs has the Gaussian envelope, and its time-domain description can be represented with following formula:

$A\left(\mathrm{\ω}\right)=\mathrm{Cexp}(-\frac{{\mathrm{\ω}}^2}{{\mathrm{\τ}}^2})---\left(1\right)$

Wherein, τ represents the ultrashort pulse laser bandwidth.This signal is input to (as Fig. 2) behind the spectrum structure device, front end Polarization Controller 31 with signal state of polarization keep with Differential Group Delay element 32 main shafts in angle of 45 degrees, between the flashlight of two main shafts transmission, will produce sizable time delay T, rear end Polarization Controller 33 adjustment output polarization states and polarizer 34 main shafts are in angle of 45 degrees, make flashlight that polarization interference take place herein, thereby generation comb filtering effect, make signal spectrum have the cosine spectral pattern, after passing through optical filter filtering 35 at last, spectral width is limited by optical filter bandwidth, and the signal that obtains is described by following formula:

A ' (ω)=A (ω) [1+cos (ω T)], (ω _l＜ω＜ω _h) (2) wherein T represent Differential Group Delay size, ω _lAnd ω _hRepresent limitting frequently up and down of optical filter respectively.

Then, use a section single-mould fiber 40 to introduce chromatic dispersion and realize the frequency domain to time domain mapping, finally the signal of telecommunication that is obtained by photodetector 50 can be expressed as:

$\begin{array}{c}a\left(t\right)=C^{\text{'}}\exp \left(\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000188469800021.png,HSA00000188469800022.png"\; state="\{\{state\}\}">j</figure-callout>}}{2{\mathrm{\&Phi;}}_2}{t}^2\right)A^{\text{'}}{\left(\mathrm{\&omega;}\right)}_{\mathrm{\&omega;}=t/{\mathrm{\&Phi;}}_2}\\ =C^{\text{'}}\exp \left(\frac{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000188469800021.png,HSA00000188469800022.png"\; state="\{\{state\}\}">j</figure-callout>}}{2{\mathrm{\&Phi;}}_2}{t}^2\right)\exp \left(\frac{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HSA00000188469800021.png,HSA00000188469800022.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}{{{\mathrm{\&Phi;}}_2}^2{\mathrm{\&tau;}}^2}\right)[1+\cos \frac{\mathrm{Tt}}{{\mathrm{\&Phi;}}_2}],(t_l<t<t_h)\end{array}---\left(3\right)$

In the formula, Φ ₂Be the GVD (Group Velocity Dispersion) coefficient, C ' is a constant coefficient, (t _l, t _h) corresponding to the time domain scope of microwave signal.Can obtain determining the relational expression of microwave signal frequency and pulsewidth from following formula:

f＝T/(2πΦ ₂)(4)

$\mathrm{Vt}=({\mathrm{\&omega;}}_h-{\mathrm{\&omega;}}_l)g{\mathrm{\&Phi;}}_2>>\frac{2\mathrm{\&pi;c}}{{\mathrm{\&lambda;}}^2}\mathrm{V\&lambda;g}{\mathrm{\&Phi;}}_2---\left(5\right)$

Can see that from formula microwave signal frequency and pulsewidth can be respectively by setting the control of Differential Group Delay and optical filter bandwidth.

According to the such scheme principle, we provide the validity that 3 groups of experimental example illustrate this scheme.The setting Differential Group Delay is 40ps, and optical filter bandwidth is 3nm, obtains one group of timely domain waveform figure of signal spectrum, as Fig. 3.Wherein, signal frequency is 12.7GHz, and pulse duration is 1.18ns; Then change optical filter bandwidth, make it be respectively 2.1nm and 1.2nm, the microwave signal pulsewidth that obtains is respectively 0.86ns and 0.52ns, as Fig. 4; At last, by changing the Differential Group Delay size of introducing, be respectively 18ps and 95ps, we have obtained the microwave signal of 7.1GHz and 30.8GHz, as Fig. 5.Wherein, the 95ps Differential Group Delay is produced by one section guarantor optical fiber that shakes.At last, Fig. 6 has provided the microwave signal frequency that generates and the pulsewidth change curve with Differential Group Delay and filter bandwidht respectively.Source of error wherein is offset the mistake meter error that reaches the optical fiber dispersion amount in the output valve of Differential Group Delay element.

In sum, feature of the present invention mainly contains following 2 points: (1) uses tunable Differential Group Delay device that flashlight is produced the comb filtering effect of variable cycle, thereby control is by the microwave signal frequency size of frequency domain to time domain mapping generation; (2) the tunable optical filter spare of utilized bandwidth is with the width of restricting signal spectrum, the microwave signal pulsewidth that obtains with change.

Claims (4)

1. the adjustable microwave signal of frequency and pulsewidth produces scheme, based on by a wideband light source, an adjustable Differential Group Delay element, and the optical filter that bandwidth is adjustable, and the microwave generation device that the frequency domain to time domain mapping block constitutes; Microwave signal generating method is: the wide range light beam that light source produces is gone in the spectrum constructing module, use adjustable Differential Group Delay module and optical filter structure target optical spectrum, utilize the frequency domain to time domain mapping device to produce the microwave signal of assigned frequency and pulsewidth at last.

2. produce scheme according to claim 1 described frequency and the adjustable microwave signal of pulsewidth, it is characterized in that, use the Differential Group Delay element between input light pairwise orthogonal polarization state, to produce adjustable delay time, cause polarization interference with structure sinusoidal periodic spectral shape with the polarizer, by regulating the Differential Group Delay size to change sinusoidal spectral period; In addition, the adaptive-bandwidth optical filter of rear end adding is in order to limit spectral width; Microwave signal frequency that produces and pulsewidth are changed by regulating introducing differential delay size and optical filter bandwidth.

3. produce scheme according to claim 1 described frequency and the adjustable microwave signal of pulsewidth, it is characterized in that described wideband light source can be spontaneous radiation incoherent light source ASE.

4. produce scheme according to claim 1 described frequency and the adjustable microwave signal of pulsewidth, it is characterized in that described wideband light source is the ultra-short pulse laser source.

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