CN101051124A - Super wide band single period pulse optical producing method based on double refraction time delay - Google Patents

Abstract

The optical generation method of ultra-wideband single-cycle pulses based on birefringence time delay belongs to the field of optical fiber communication technology, especially relates to the single-cycle pulse generation technology in ultra-wideband communication technology. Pulses with opposite polarities are generated on the two vertical polarization states of the polarization-maintaining fiber, and then the birefringence phenomenon of the polarization-maintaining fiber is used to make the two vertically polarized lights produce a certain delay, and then the electrical signal can be obtained through optical signal amplification, attenuation, and photoelectric conversion. Ultrawideband single-cycle pulses over the domain. The invention has the advantages of only needing a single light source, no need of complex filtering devices, and simple structure.

Description

Optical generation method based on the super wide band single period pulse of double refraction time delay

Technical field

The invention belongs to photoelectron technology and technical field of optical fiber communication.Being particularly related to the monocycle impulse that carries in ultra broadband (UWB) communication system at light produces.

Background technology

From twentieth century seventies, ultra broadband (UWB) technology is widely used among radar, sensing and the military communication.Along with the regulation UWB of FCC (FCC) technology in 2002 can be used among the commercial communication, the system of UWB can insert and share the 7500MHz bandwidth of 3.1 ~ 10.6GHz, and this technology has caused extensive concern.Advantages such as UWB communication is low in energy consumption with it, transfer rate is high, antijamming capability is strong are just becoming the strong competition technology of short-distance wireless communication.But, because microwave electronic device is limited to the processing power of high-frequency signal, making that the UWB monocycle impulse relative bandwidth that produces is narrower, efficient is not high.It is that utilize optical processing method and the optical fiber that grows up recently produces new technology with the Transmission Microwave signal that light carries microwave (ROF) transmission technology.The ROF technology is utilized the big bandwidth and the low loss characteristic of Optical Fiber Transmission, has improved the microwave transmission channel greatly.Optical processing device also has big bandwidth characteristic simultaneously, can realize the ultra-wideband microwave signal processing function that the traditional microwave device can't be realized.Based on this, the idea that light carries radio ultra wide band system (UWB over fiber) is also arisen at the historic moment, and improves the spreading range of UWB system by efficient, low-loss fiber distribution network, becomes the basic imagination of following BRAN.

The generation of UWB waveform is the gordian technique that light carries the UWB system arbitrarily.In the recent period some institutes have carried out the optical generation method of the monocycle impulse that is applied to the UWB system in the world, and this method has very wide bandwidth of operation, waveform regulates easily and be easy to and transmit in optical fiber, with the combination of optical fiber system.Therefore, this method is the technical foundation that following UWB over fiber uses, and has a wide range of applications.The method of at present main photoproduction UWB monocycle impulse is mainly used the cross-phase in optical fiber or the semiconductor optical amplifier to modulate and is realized, but this method requires to use two lasing light emitters and a plurality of fiber grating filter spare, and system architecture is very complicated.

Summary of the invention

The object of the present invention is to provide a kind of need to use a light source and optical system simple in structure to produce method based on the super wide band single period pulse of double refraction time delay.

We adopt based on LiNbO ₃The phase-modulator of crystal is realized Polarization Modulation.The benefit of this modulation is to use single phase-modulator just can realize Polarization Modulation, and scheme is fairly simple, is easy to realize, is equivalent to discrete function element is incorporated into together, has better stability.Input signal light enters LiNbO through the polarizer ₃In the crystal.Because crystal has only and applies voltage on the direction and carry out phase modulation (PM), and not modulation on the another one vertical direction so will produce interference effect at the output terminal of phase-modulator, changes the input signal polarization state of light.Set LiNbO ₃The modulation voltage of crystal is V _π, then on the polarization direction of ovennodulation, signal is equivalent to postpone the π phase differential.Its effect is equal to the slow axis of signal through 1/2 wave plate.Signal is at LiNbO ₃Polarization state changes as shown in Figure 1 in the crystal.The Jones matrix of 1/2 wave plate is:

$H_{\mathrm{\&theta;}}=\left(\begin{array}{cc}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}& \sin 2\mathrm{\&theta;}\\ \sin 2\mathrm{\&theta;}& -\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}\end{array}\right)---\left(1\right)$

Wherein θ is the x axle of incident light and the angle of the fast axle of wave plate.Suppose that incident light is the linearly polarized light along the x axle:

${\stackrel{\&RightArrow;}{E}}_{\mathrm{in}}\left(t\right)=A\left(t\right)e^{j{\mathrm{\&omega;}}_{0}t}\left(\begin{array}{c}1\\ 0\end{array}\right)---\left(2\right)$

Then emergent light can be expressed as:

${\stackrel{\&RightArrow;}{E}}_{\mathrm{out}}=H_{\mathrm{\&theta;}}\&times;{\stackrel{\&RightArrow;}{E}}_{\mathrm{in}}=A\left(t\right)e^{j{\mathrm{\&omega;}}_0\mathrm{<figure-callout\; id="2"\; label="t\; cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">t</figure-callout>}}\left(\begin{array}{c}\cos \end{array}\right)\left(\begin{array}{c}2\mathrm{\&theta;}\\ \sin 2\mathrm{\&theta;}\end{array}\right)---\left(3\right)$

When θ=45 °,

${\stackrel{\&RightArrow;}{E}}_{\mathrm{out}}\left(t\right)=A\left(t\right)e^{j{\mathrm{\&omega;}}_{0}t}\left(\begin{array}{c}0\\ 1\end{array}\right)---\left(4\right)$

As seen, behind 1/2 wave plate, the polarization direction of emergent light is vertical with the incident light polarization direction.Promptly working as modulation signal is V _πThe time, the polarization direction that just can realize flashlight is revolved and is turn 90 degrees, i.e. orthogonal directions.

The principle that monocycle impulse produces as shown in Figure 2, at first utilize the photoelectricity principle of polarizing modulation, the opposite pulse of polarization on two mutually orthogonal vertical polarization attitudes utilizes the birefringent phenomenon in optical fiber or the optical device then, makes two vertical polarization attitude pulses produce certain time delay.Adopt polarization maintaining optical fibre to cause time-delay in embodiment of the present invention as the birefringence device.The length of supposing polarization maintaining optical fibre is L, claps the long B that is, then along the light of two main shafts time delay after through the polarization maintaining optical fibre transmission is:

$\mathrm{\&tau;}=\frac{\mathrm{L\&lambda;}}{\mathrm{BC}}---\left(5\right)$

Wherein λ is a communication wavelengths, is generally 1550nm, and C is the light velocity in the vacuum.Like this, polarization maintaining optical fibre through suitable length, the bit of two polarization state pulse daleys that makes transmission just can be combined into the light pulse of super wide band single period pulse shape, utilizes photodetector just to produce the monocycle impulse in the electric territory of suitable UWB system requirements again.

The invention is characterized in that this method realizes successively according to the following steps:

Step (1): the laser beam of laser instrument Laser output outputs to the first Polarization Controller PC1, makes and exports polarisation of light direction and LiNbO ₃The quick shaft direction angle of phase-modulator is 45 degree, and is input to this LiNbO ₃Phase-modulator;

Step (2): described LiNbO ₃Phase-modulator obtains two polarization states that repeat mutually under the electric pulse generator Pulse Generator modulation of setting repetition frequency, its emergent light is expressed as:

$\stackrel{\&RightArrow;}{E_{\mathrm{out}}}=H_{\mathrm{\&theta;}}\&times;\stackrel{\&RightArrow;}{E_{\mathrm{in}}}=A\left(t\right)e^{\mathrm{j\&omega;\&Delta;t}}\left(\begin{array}{c}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}\\ \sin 2\mathrm{\&theta;}\end{array}\right)$

Wherein, H _θBe the Jones matrix, $H_{\mathrm{\&theta;}}=\left(\begin{array}{cc}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}& \sin 2\mathrm{\&theta;}\\ \sin 2\mathrm{\&theta;}& -\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20071009940300062.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}\end{array}\right)$

θ is the X-axis and the described LiNbO of incident light ₃The quick shaft direction angle of phase-modulator

Incident light ${\stackrel{\&RightArrow;}{E}}_{\mathrm{in}}\left(t\right)=A\left(t\right)e^{j{\mathrm{\&omega;}}_{0}t}\left(\begin{array}{c}1\\ 0\end{array}\right)$

Step (3): the light signal of two orthogonal polarized lights of the middle process of step (2) Polarization Modulation is not by the adjustment of the modulator PC of the second polarizer PC, make two spindle alignments of two orthogonal polarized lights and polarization maintaining optical fibre PMF, make light signal obtain birefringence through polarization maintaining optical fibre PMF and postpone, its time-delay is calculated as follows:

$\mathrm{\&tau;}=\frac{\mathrm{L\&lambda;}}{\mathrm{BC}}$

Wherein, λ is a communication wavelengths, is 1550nm, and c is a vacuum light speed, and L is the length on the polarization maintaining optical fibre PMF, and β is long for clapping;

Step (4): the light signal of polarization maintaining optical fibre PMF output is successively through sending into photodetector PIN behind Erbium-Doped Fiber Amplifier EDFA, the attenuator ATT, the output of this photodetector PIN enters receiver, and is measured by digital sample oscillograph DSO and electric spectrometer ESA.

Our the super wide band single period pulse production method based on double refraction time delay of design is simple in structure, only needs to use single light source and does not need complicated filtering device.Utilize polarization modulation characteristics, and produce super wide band single period pulse by birefringence fiber.

Description of drawings

Fig. 1, LiNbO ₃Phase-modulator is realized the schematic diagram of Polarization Modulation.

Fig. 2, monocycle impulse produces schematic diagram (DGD: the Differential Group Delay device).

Fig. 3, the optical system schematic diagram (Laser: laser instrument that the present invention adopts; Pulse Generator: electric pulse generator; PC: Polarization Controller; PM: phase-modulator; PMF: polarization maintaining optical fibre; EDFA: Erbium-Doped Fiber Amplifier (EDFA); ATT: attenuator; PIN: photodetector; ESA: frequency spectrograph; DSO: the digital sample oscillograph).

Fig. 4, the time-domain diagram of electric pulse.

Fig. 5, the positive polarity monocycle impulse figure of generation.

Fig. 6, the negative polarity monocycle impulse figure of generation.

Fig. 7, positive polarity monocycle impulse spectrogram.

Embodiment

Specific embodiments as shown in Figure 3.The output of laser instrument is adjusted through Polarization Controller (PC), makes polarization direction and LiNbO ₃The quick shaft direction angle of phase-modulator is 45 degree.The signal rate of modulation is 8.2Gb/s, and it is V that modulation code is classified " 10,000,000 0,000 0000 " modulation amplitude as _πLike this, the repetition rate of pulse signal is exactly 512MHz.Fig. 3 has shown that the full width at half maximum of pulse is for being about 122ps.Adjust by Polarization Controller (PC) through the light signal of Polarization Modulation, make two spindle alignments of two vertical polarization attitudes and polarization maintaining optical fibre (PMF).Like this, signal just can experience the double refraction time delay in the polarization maintaining optical fibre.The length of polarization maintaining optical fibre is 90m in the scheme, claps the long 3.8mm that is, double refraction time delay is about 122ps, just in time is the full width at half maximum of pulse.Be equivalent to bit stack of the pulse daley of two polarization directions.Utilize suitable decay to enter receiver behind the signal process Erbium-Doped Fiber Amplifier (EDFA) (EDFA), and measure by digital sample oscillograph (DSO) and electric spectrometer (ESA).

The installation drawing that adopts in this example as shown in Figure 3, wherein:

That CSRZ optical signal generator A.43Gb/s and receiver use is the MI4010ST of Mintera company

B. Polarization Controller adopts the PolarRITE of General Photonics company.

That C. wave filter uses is the OTF-300-03S3 of Santac company.

D.LiNbO ₃Phase-modulator adopts the LN_053-065 modulator of Covega company.

E.EDFA adopts the EDFA-BA of Shanghai Luminous Networks, Inc..

That number generator F.8.2Gb/s and receiver use respectively is the D3186 PULSE PATTERNGENERATOR and the D3286 ERROR DETECTOR of ADVANTEST company.

G. photo-detector adopts the PD1100 of Yi Ou company.

H. the digital sample oscillograph adopts the TDS8200 of Tektronix company.

I. electric frequency spectrograph adopts the E4446A of Agilent company.

Fig. 5 shown through Polarization Modulation and the time delay the super wide band single period pulse (resolution is 200ps/div) of acquisition.In fact, can know,, can so just be easy to obtain reverse monocycle impulse, as shown in Figure 6 so that different polarized pulses obtains opposite time delay by regulating the polarization state of input polarization maintaining optical fibre by the principle of this programme.The binary phase that this mode can be applied in the ultra-wideband communications is modulated in the middle of (BPSK).Fig. 7 has shown the spectrogram of the super wide band single period pulse that is produced.As can be seen, centre frequency is 4.2GHz, and effective bandwidth is about 150%, and each frequency component equals the repetition frequency of pulse, i.e. 512MHz at interval.

Claims (1)

1. The optical generation method of the ultra-broadband single-period pulse based on birefringence time delay, it is characterized in that, this method realizes by following steps successively: Step (1): The laser beam output by the laser Laser is output to the first polarization controller PC1, so that the polarization direction of the output light and the fast axis direction of the LiNbO ₃ phase modulator have an angle of 45 degrees, and input to the LiNbO ₃ phase modulator device; Step (2): The LiNbO ₃ phase modulator obtains two mutually repeating polarization states under the modulation of the electric pulse generator Pulse Generator with a set repetition frequency, and its outgoing light is expressed as: $\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; \&times;</span>\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j\&omega;\&Delta;t</span>}}\left(\begin{array}{c}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right)$ Among them, H _θ is Jones matrix, $h_{\mathrm{\&theta;}}=\left(\begin{array}{cc}\cos 2\mathrm{\&theta;}& \sin 2\mathrm{\&theta;}\\ \sin 2\mathrm{\&theta;}& -\cos 2\mathrm{\&theta;}\end{array}\right)$ θ is the angle between the X axis of the incident light and the fast axis direction of the LiNbO ₃ phase modulator ${\stackrel{\&Right\; Arrow;}{\mathrm{E.}}}_{\mathrm{in}}\left(t\right)=A\left(t\right)e^{{\mathrm{j\&omega;}}_{0}t}\left(\begin{array}{c}1\\ 0\end{array}\right)$ Step (3): The optical signals of the two vertically polarized lights that have been polarization-modulated in step (2) are adjusted by the second polarizer PC so that the two vertically polarized lights are aligned with the two main axes of the polarization-maintaining fiber PMF , so that the optical signal passes through the polarization-maintaining fiber PMF to obtain a birefringence delay, and the delay is calculated by the following formula: $\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L\&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; BC</span>}}$ Among them, λ is the communication wavelength, which is 1550nm, c is the speed of light in vacuum, L is the length on the polarization maintaining fiber PMF, β is the beat length; Step (4): The optical signal output by the polarization-maintaining optical fiber PMF passes through the erbium-doped optical fiber amplifier EDFA and the attenuator ATT in turn, and then is sent to the photodetector PIN. Electrospectrometer ESA measurement.

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