CN101867435A - An all-optical OFDM symbol generator - Google Patents

Abstract

An all-optical OFDM symbol generator, including on the circuit: a serial-to-parallel conversion chip to convert high-speed bi-level data signals into N-way sub-channel signals with a relatively low rate; N-way duobinary precoders to The sub-channel signal is pre-coded; the optical path includes: a laser light source to output an optical carrier; a 1:N optical splitter to equally divide the optical carrier into N beams; an N-channel optical modulator to modulate the signal strength according to the duo-binary pre-coding Optical carrier to obtain duobinary optical signals; LiNbO ₃ waveguide integrated chip to perform quadrature modulation on N channels of duobinary optical signals to obtain optical OFDM symbols and directly enter optical fiber for transmission; drive signal generator to generate LiNbO ₃ waveguide integrated The driving signal of the chip. The invention realizes optical Fourier inverse transformation in an all-optical manner, thereby obtaining optical OFDM symbols, eliminates the electronic bottleneck problem of traditional optical OFDM systems, and improves the transmission rate of optical communication systems.

Description

A kind of fully optical orthogonal frequency division multiplexing symbol generator

Technical field

The present invention relates to a kind of light positive and hand over fully optical orthogonal frequency division multiplexing (the being full light OFDM) symbol generator of Frequency Division Multiplexing system (being optical OFDM system), transmitting terminal at optical OFDM system, two level data signals are converted to the light OFDM symbol that is fit to Optical Fiber Transmission through behind the full light OFDM symbol generator.

Background technology

(frequencydivision multiplexing, FDM) the technology comparing class seemingly with the frequency division multiplexing of widespread usage for OFDM (OFDM) technology.Identical with the FDM principle, OFDM is assigned to data flow at a high speed in the relatively low experimental process channel of speed by serial to parallel conversion and transmits; Different is that the frequency interval that existence is bigger between the FDM adjacent channel has so just reduced the availability of frequency spectrum of whole system with the interference between preventing mutually.And OFDM adopts subcarrier orthogonal multiplex technology, and adjacent sub-channel spectra is mutually orthogonal, has so not only reduced crosstalking of interchannel, has also improved the channel spectrum utilance.

Because the OFDM technology has solved the intersymbol interference that dispersive channel causes effectively, it is widely used in a lot of emerging broadband cabled and wireless communication systems, has been asserted mature technique.The orthogonal frequency division multiplexi of light (light OFDM) is recent years emerging a kind of optical transport technology, the especially application facet of communicating by letter with multimode fiber at high speed optical communication.Light OFDM adopts OFDM technology ripe in the radio communication, only the carrier wave of symbol has been moved light carrier from radio frequency.Because the OFDM technology is that data flow at a high speed is decomposed into the relatively low mutually orthogonal subchannel of a plurality of speed, therefore possess the not available characteristics of a lot of traditional dense wave division multipurpose (DWDM) mode in the application of optical fiber communication: band efficiency improves, and chromatic dispersion tolerance limit, polarization mode tolerance limit improve.

Fig. 1 shows the embodiment of traditional optical OFDM system, and it extensively adopts the implementation based on electronic chip, and this system comprises: the serial to parallel conversion chip is converted to the relatively low N of a speed sub-channel signal with two level data signals at a high speed; Discrete inverse Fourier transform (IDFT) chip is used for N sub-channel signal carried out inverse Fourier transform, obtaining electric OFDM symbol, and then electric OFDM symbol is carried out digital-to-analogue conversion; Carrier modulator is used for electric OFDM symbol-modulated obtaining light OFDM symbol to light carrier, transmits to enter in the optical fiber.At receiving terminal: light OFDM symbol passes through photodetector in proper order, detects to obtain electric OFDM symbol; Discrete Fourier transform (DFT) chip, with electric OFDM symbol discretization, demodulation obtains N sub-channel signal through Fourier transform then; The parallel serial conversion chip recovers original two level data signals.

The reflector of tradition in the optical OFDM system is made up of IDFT chip and carrier modulator, and it mainly is subject to the processing speed of electronic chip, exists some bottleneck problems, is difficult in the optical communication system of two-forty to be used widely.In addition, traditional light OFDM reflector need encode transmission signals before communication mostly in advance, thereby its application in real-time optical communication system also exists some problems.Therefore traditional light OFDM reflector is at processing speed, complexity, the cost of device or be to have some inevitable shortcomings on the real-time.

Summary of the invention

The object of the present invention is to provide a kind of light positive to hand over fully optical orthogonal frequency division multiplexing symbol generator in the Frequency Division Multiplexing system, can obtain light OFDM symbol, transmit directly to enter in the optical fiber with the mode of full light.Thereby saved a series of electronic chip, simplified system, reduced cost; Solve the electronic bottleneck problem that exists in the existing optical OFDM system simultaneously, improve the transmission rate of optical OFDM system.

The technical scheme that is adopted is as follows for achieving the above object:

A kind of fully optical orthogonal frequency division multiplexing symbol generator, handing over Frequency Division Multiplexing system at light positive is to produce light positive in the mode of full light in the optical OFDM system to hand over frequency division multiplexing symbol be light OFDM symbol, transmits directly to enter in the optical fiber, this symbol generator comprises on circuit:

The serial to parallel conversion chip is used for two level data signals at a high speed are converted to the relatively low N subchannels signal of speed, and wherein N is a number of subchannels;

N road duobinary system precoder so that above-mentioned N subchannels signal is carried out precoding, obtains N road duobinary system precoded signal;

On light path, comprise:

LASER Light Source is used to export light carrier;

The 1:N optical branching device is used for above-mentioned light carrier is divided into the N bundle;

N road optical modulator carries out intensity modulated to above-mentioned N bundle light carrier respectively according to described N road duobinary system precoded signal, obtains corresponding N road duobinary optical signal;

LiNbO ₃The waveguide integrated chip is used for above-mentioned N road duobinary optical signal is carried out quadrature modulation, obtains light OFDM symbol, and then directly enters in the optical fiber and transmit; With

Drive signal generator is used to produce LiNbO ₃The drive signal of waveguide integrated chip.

Further improve described LiNbO as the present invention ₃The waveguide integrated chip comprises N road LiNbO ₃Waveguide Phase Modulator is used for respectively described N road duobinary optical signal being carried out phase modulated; The optical coupler of N:1 is used for the above-mentioned N road signal that carries out after the phase modulated is carried out orthogonalization process, to obtain light OFDM symbol.

Further improve as the present invention, the drive signal that described drive signal generator produces is the N road, drives each road LiNbO respectively ₃Waveguide Phase Modulator.

Further improve as the present invention, above-mentioned N road drive signal is that frequency is respectively Δ f, 2 Δ f, and L, N Δ f, the voltage span is 0～2V _πThe periodicity sawtooth waveforms, wherein, Δ f is the frequency of light OFDM symbol, V _πBe LiNbO ₃The half-wave voltage of Waveguide Phase Modulator.

Further improve as the present invention, this optical modulator comprises Mach-Zehnder light intensity modulator, inverter, first driving amplifier, second driving amplifier and electric delayer,

Described duobinary system precoded signal is at first divided equally is two-way, and wherein one the tunnel is anti-phase by inverter, is designated as

Another road remains unchanged, and is designated as Q, and Q amplifies through first driving amplifier, obtains modulator driving signal V ₁,

After second driving amplifier amplifies, carry out the time-delay of 1 bit through electric delayer again, obtain modulator driving signal V ₂, said modulator drive signal V ₁And V ₂Drive described Mach-Zehnder light intensity modulator, the signal after the light carrier of described LASER Light Source output is modulated and will be modulated is exported as duobinary optical signal.

Further improve as the present invention, described Mach-Zehnder light intensity modulator is Z-cut both arms light intensity modulators.

Further improve as the present invention, described duobinary system precoder can adopt XOR gate and electric delayer to realize.

A kind of light positive is handed over Frequency Division Multiplexing system, comprises described fully optical orthogonal frequency division multiplexing symbol generator.

The present invention at first utilizes N optical modulator that N subchannels signal is carried out the duobinary system modulation, obtains N road duobinary optical signal; Utilize LiNbO then ₃The waveguide integrated chip is realized the quadrature modulation of N road duobinary optical signal, finally obtains light OFDM symbol, directly enters in the optical fiber and transmits.The present invention utilizes drive signal generator to produce N road frequency to be increased successively, is respectively Δ f, 2 Δ f, and L, N Δ f, range of voltage values is constant, is 0～2V _πThe periodicity sawtooth waveforms as LiNbO ₃The drive signal of waveguide integrated chip obtains light OFDM symbol in the mode of full light, has eliminated the restriction of traditional optical OFDM system electronic bottleneck problem, has simplified system greatly.

Description of drawings

Fig. 1 is traditional optical OFDM system structure;

Fig. 2 forms structural representation for the full light OFDM of the present invention symbol generator;

Fig. 3 is the structural representation of duobinary system precoder and optical modulator in the full light OFDM symbol generator;

Fig. 4 is the modulated process of Mach-Zehnder light intensity modulator in the optical modulator;

Fig. 5 is a duobinary system light modulation process in the full light OFDM symbol generator;

Fig. 6 is LiNbO ₃The N road drive signal schematic diagram of waveguide integrated chip;

Fig. 7 is a receiving terminal structural representation of the present invention.

Embodiment

In the ofdm system, each subchannel is mutually orthogonal, and then frequency interval Δ f is the inverse in each sub-channel signal cycle between subchannel, that is:

$\mathrm{\Δf}=\frac{1}{T}---\left(1\right)$

Here T=NT _SBe the cycle of OFDM symbol, T _SBe two level data signal cycle at a high speed, N is an integer, the expression number of subchannels, and its value is decided according to the system transmissions demand.A typical light OFDM symbol can be expressed as:

$S\left(t\right)=\underset{l=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\left[\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{X}_{l,k}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HDA0000022532580000012.png,HDA0000022532580000031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\right]U_T(t-\mathrm{lT})$ (2)

$U_T\left(t\right)=\left\{\begin{array}{cc}1& 0\&le;t\&le;\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="HDA0000022532580000021.png"\; state="\{\{state\}\}">T</figure-callout>}\\ 0& \mathrm{else}\end{array}\right.$

X in the formula _{L, k}Be the sub-channel data symbol behind the process serial to parallel conversion, it is in k sub-channel of l light OFDM symbol; f _cBe optical carrier frequency; Δ f is the frequency interval between the subchannel of being determined by formula (1), and T is the time cycle of aforementioned lights OFDM symbol.

So usually single smooth OFDM symbol is written as:

$S_l^{\%}\left(t\right)=\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{X}_{\mathrm{<figure-callout\; id="2"\; label="k\; e\; j"\; filenames="HDA0000022532580000012.png,HDA0000022532580000031.png"\; state="\{\{state\}\}">k</figure-callout>}}{e}^j{2\mathrm{\&pi;}(f_c+\mathrm{k\&Delta;f})t}^{},0\&le;t\&le;T---\left(3\right)$

From formula (3), we at first carry out the duobinary system modulation to the two level data signals on each subchannel, and it is modulated on the light carrier, and the mathematical expression of process is: 0≤t≤T.As long as realize the phase modulated e on remaining each subchannel ^{J2 π k Δ ft}, O≤t≤T with all sub-channel signal coupling additions, can obtain light OFDM symbol again.

Preferred embodiment of the present invention 2-6 with reference to the accompanying drawings is described.In these accompanying drawings, same element although occur, is noted as same Reference numeral or symbol in different accompanying drawings.Wherein, channel number N is taken as 4, realize the full light OFDM symbol generator of 10Gb/s * 4, can the present invention is further described in conjunction with the accompanying drawings:

Fig. 2 is the full light OFDM symbol generator constructional device in the optical OFDM system of the present invention.

As shown in Figure 2, the present invention comprises serial to parallel conversion chip 1, N road duobinary system precoder 2 on circuit; On light path, comprise LASER Light Source 3,1:N optical branching device 4, N road optical modulator 5 and a LiNbO ₃Waveguide integrated chip 6, drive signal generator 7.It is the continuous light laser of 193.1THz that described LASER Light Source 3 can adopt centre frequency; Serial to parallel conversion chip 1 can adopt the CO40VNS10 chip of coreoptics company.

Two level data signals at a high speed at first are converted into the relatively low N subchannels signal of speed through serial to parallel conversion chip 1; N subchannels signal passes through N road duobinary system precoder 2 respectively, obtains N road duobinary system precoded signal, is input in the corresponding N road optical modulator 5.Wherein, duobinary system precoder 2 can adopt XOR gate 210 and electric delayer 220 to realize, as shown in Figure 3.

And on light path, the light carrier that sends from LASER Light Source 3 is divided into the N road through 1:N optical branching device 4, passes through N road optical modulator 5 again.Every road optical modulator 5 is changed the phase place of continuous light under the effect of duobinary system precoded signal, and exports modulated duobinary optical signal by modulation continuous light intensity.

Wherein, every road optical modulator 5 comprises Mach-Zehnder light intensity modulator 510, inverter 520, driving amplifier 531 and driving amplifier 532 and electric delayer 540.The precoded signal that comes out from duobinary system precoder 2 is at first divided equally is two-way, and wherein one the tunnel is reverse by inverter 520, is designated as

Another road remains unchanged, and is designated as Q.Q is admitted to driving amplifier 531 and amplifies, and obtains modulator driving signal V ₁

After being admitted to driving amplifier 532 amplifications, carry out the time-delay of 1 bit through electric delayer 540 again, obtain modulator driving signal V ₂V ₁And V ₂Be used as the both arms 511 of Mach-Zehnder light intensity modulator 510 and 512 drive signal.Like this, by two drive signal V of Mach-Zehnder interfere type light intensity modulator 510 ₁And V ₂Change from the phase place of the light carrier of LASER Light Source 3 outputs.At last, the signal after the luminous intensity of this light carrier is modulated and will be modulated is exported as duobinary optical signal.

In an embodiment, this Mach-Zehnder interfere type light intensity modulator is Z-cut both arms light intensity modulators.

The modulated process of Mach-Zehnder light intensity modulator 510 as shown in Figure 4.

In duobinary system light modulation process, " 1 " sign indicating number level is zero, and " 0 " sign indicating number level is "+1 " or " 1 ".We use three value Z, and A and B represent duobinary three kinds of logic states; Z represents " 0 ", and A represents "+1 ", and B represents " 1 ".In the implementation case, we adopt duobinary system Modulation and Amplitude Modulation phase keying (AM-PSK), combine the characteristics of intensity modulated and phase modulated, Z=0 then, A=1=e ^J0, B=-1=e ^{J π}, promptly the phase place of A is 0, the phase place of B is π.In conjunction with Fig. 5, duobinary system light modulation process as shown in Figure 5.In the AM-PSK duobinary system that this mode generates, " 1 " sign indicating number light intensity is zero, and " 0 " sign indicating number light intensity is " 1 ".When odd number " 1 " was arranged between two " 0 ", phase place can be switched.And when there was even number " 1 " centre, then phase place can not switched.

Enter LiNbO again from the N road duobinary optical signal that N road optical modulator 5 comes out ₃Waveguide integrated chip 6 so that N road duobinary optical signal is carried out quadrature modulation, obtains light OFDM symbol, and then directly enters in the optical fiber and transmit.

Wherein, LiNbO ₃Waveguide integrated chip 6 is by N road LiNbO ₃Connecing N:1 optical coupler 620 after the Waveguide Phase Modulator 610 constitutes.N road LiNbO ₃ Waveguide Phase Modulator 610 under the effect of the N road drive signal that drive signal generator 7 produces, changes the phase place of N road duobinary optical signal successively, thereby on frequency domain this N road duobinary optical signal is carried out quadrature modulation respectively on time domain.

Above-mentioned LiNbO ₃The waveguide integrated chip needs N road drive signal, known again LiNbO ₃Waveguide Phase Modulator modulation equation is:

$E_{\mathrm{out}}=E_{\mathrm{in}}{e}^{\mathrm{j\&pi;}\frac{V\left(t\right)}{V_{\mathrm{\&pi;}}}}---\left(4\right)$

V wherein _πBe LiNbO ₃The half-wave voltage of Waveguide Phase Modulator, V (t) is for being carried in LiNbO ₃Drive signal on the Waveguide Phase Modulator, with reference to formula (3), k (1≤k≤N) the road drive signal is:

$V_k\left(t\right)=\frac{V_{\mathrm{\&pi;}}}{\mathrm{\&pi;}}2\mathrm{\&pi;k\&Delta;ft}=2V_{\mathrm{\&pi;}}\mathrm{k\&Delta;ft},0\&le;t\&le;T---\left(5\right)$

Wherein Δ f is the frequency of light OFDM symbol, LiNbO again ₃Waveguide Phase Modulator modulation equation satisfies:

$\exp \left(\mathrm{j\&pi;}\frac{V\left(t\right)}{V_{\mathrm{\&pi;}}}\right)=\exp \left(\mathrm{j\&pi;}\frac{V\left(t\right)+{2V}_{\mathrm{\&pi;}}}{V_{\mathrm{\&pi;}}}\right)---\left(6\right)$

So the drive signal magnitude of voltage reaches 2V when the k road _π, magnitude of voltage makes zero, as shown in Figure 6.

Fig. 6 illustrates the N road drive signal that drive signal generator 7 produces, the magnitude of voltage of horizontal ordinate difference express time and drive signal.Its Smalt line is a first via drive signal, and frequency is Δ f; Red line is the second tunnel drive signal, and frequency is 2 Δ f, and the rest may be inferred for each road drive signal of back, and promptly N road drive signal is that frequency is respectively Δ f, 2 Δ f, and L, N Δ f, the voltage span is 0～2V _πThe periodicity sawtooth waveforms.

Wherein, drive signal generator 7 can adopt the AWG (Arbitrary Waveform Generator) (Tyke AWG7122B) of Imtech, generates N road LiNbO with the mode of encoding ₃The Waveguide Phase Modulator drive signal.

Fig. 7 is a receiving terminal module map of explaining full light OFDM symbol generator of the present invention, this structure comprises: array waveguide grating (AWG) 8, with sub-channel signal after the modulation that separates N road quadrature, respectively from N the light delivery outlet output of AWG, (1≤k≤N) centre frequency of individual optical output port light signal is f to k then _c+ k Δ f; N photodetector 9 with the sub-channel signal demodulation after the modulation of N road, obtains the charged signal of N roadbed; And string conversion chip 10, so that N subchannels signal is carried out serial to parallel conversion, recover two original level data signals.This parallel serial conversion chip can adopt the CO40MRS10 chip of coreoptics company.

In addition, owing at transmitting terminal two level data signals have been carried out doubinary encoding, its signal bandwidth is half of all the other modulation formats, encodes as RZ.N road duobinary optical signal is at process LiNbO ₃Behind the waveguide integrated chip, the lucky quadrature of the frequency spectrum between the different subchannels, LiNbO ₃The output of waveguide integrated chip is light OFDM symbol.Just because of the duobinary optical signal bandwidth has reduced half, at receiving terminal, we only need AWG, N photodetector, and sub-channel signal that can the N road is mutually orthogonal separates, and by the parallel serial conversion chip, can recover to demodulate original two level data signals again.Compare with O-OFDM system demodulation mode, also simplified system complexity largely based on electronic chip.

The invention allows for a kind of optical OFDM system, it comprises described full light OFDM symbol generator.

Claims (8)

1. fully optical orthogonal frequency division multiplexing symbol generator, handing over Frequency Division Multiplexing system at light positive is to produce light positive in the mode of full light in the optical OFDM system to hand over frequency division multiplexing symbol be light OFDM symbol, transmit directly to enter in the optical fiber, this symbol generator comprises on circuit:

Serial to parallel conversion chip (1) is used for two level data signals at a high speed are converted to the relatively low N subchannels signal of speed, and wherein N is a number of subchannels;

N road duobinary system precoder (2) so that above-mentioned N subchannels signal is carried out precoding, obtains N road duobinary system precoded signal;

On light path, comprise:

LASER Light Source (3) is used to export light carrier;

1:N optical branching device (4) is used for above-mentioned light carrier is divided into the N bundle;

N road optical modulator (5) carries out intensity modulated to above-mentioned N bundle light carrier respectively according to above-mentioned N road duobinary system precoded signal, obtains corresponding N road duobinary optical signal;

LiNbO ₃Waveguide integrated chip (6) is used for above-mentioned N road duobinary optical signal is carried out quadrature modulation, obtains light OFDM symbol, and then directly enters in the optical fiber and transmit; With

Drive signal generator (7) is used to produce LiNbO ₃The drive signal of waveguide integrated chip.

2. fully optical orthogonal frequency division multiplexing symbol generator according to claim 1 is characterized in that, described LiNbO ₃Waveguide integrated chip (6) comprises N road LiNbO ₃Waveguide Phase Modulator (610) is used for respectively described N road duobinary optical signal being carried out phase modulated; And the optical coupler of N:1 (620), be used for the above-mentioned N road signal that carries out after the phase modulated is carried out orthogonalization process, to obtain light OFDM symbol.

3. fully optical orthogonal frequency division multiplexing symbol generator according to claim 2 is characterized in that, the drive signal that described drive signal generator (7) produces is the N road, drives each road LiNbO respectively ₃Waveguide Phase Modulator (610).

4. fully optical orthogonal frequency division multiplexing symbol generator according to claim 3 is characterized in that, above-mentioned N road drive signal is that frequency is respectively Δ f, 2 Δ f, and L, N Δ f, the voltage span is 0～2V _πThe periodicity sawtooth waveforms, wherein, Δ f is the frequency of light OFDM symbol, V _πBe LiNbO ₃The half-wave voltage of Waveguide Phase Modulator (610).

5. according to the described fully optical orthogonal frequency division multiplexing symbol generator of one of claim 1-4, it is characterized in that, this optical modulator (5) comprises Mach-Zehnder light intensity modulator (510), inverter (520), first driving amplifier (531), second driving amplifier (532) and electric delayer (540)

Described duobinary system precoded signal is at first divided equally is two-way, and wherein one the tunnel is anti-phase by inverter (520), is designated as , another road remains unchanged, and is designated as Q, and Q amplifies through first driving amplifier (531), obtains modulator driving signal V ₁, After second driving amplifier (532) amplifies, pass through electric delayer (540) again and carry out the time-delay of 1 bit, obtain modulator driving signal V ₂, said modulator drive signal V ₁And V ₂Drive described Mach-Zehnder light intensity modulator (510), the signal after the light carrier of described LASER Light Source (3) output is modulated and will be modulated is exported as duobinary optical signal.

6. according to the described a kind of fully optical orthogonal frequency division multiplexing symbol generator of one of claim 1-5, it is characterized in that described Mach-Zehnder light intensity modulator (510) is Z-cut both arms light intensity modulators.

7. according to the described a kind of fully optical orthogonal frequency division multiplexing symbol generator of one of claim 1-6, it is characterized in that described duobinary system precoder (2) can adopt XOR gate (210) and electric delayer (220) to realize.

8. a light positive is handed over Frequency Division Multiplexing system, comprises one of aforesaid right requirement 1-7 described fully optical orthogonal frequency division multiplexing symbol generator.

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