CN101286801A - Optical fiber transmission system in light frequency domain - Google Patents

Abstract

The invention relates to an optical fiber transmission system in an optical frequency domain, pertaining to high-speed optical fiber communication devices and aiming at conveniently solving the effect and limitation caused by the inherent loss of the optical fiber on the high-speed optical pulse transmission. The optical fiber transmission system in a light transmission link comprises a transmitter, a cycle all-optical Fourier inverting converter, a first erbium-doped optical fiber amplifier, a single-mode transmission optical fiber, a second erbium-doped optical fiber amplifier, a cycle all-optical Fourier converter and a receiver in sequence. By adopting the optical fiber transmission system of the invention, the waveform of the pulse sequence of an original light signal is not influenced by inherent linear perturbations in an optical communication system, such as the group velocity dispersion of the optical fiber, polarization mode dispersion, time jitter, etc., thereby being capable of realizing the high-speed optical signal transmission with the speed rate of more than 40Gbit/s.

Description

A kind of optical fiber transmission system in light frequency domain

Technical field

The invention belongs to the high speed optical fiber communication device, be specifically related to a kind of adopt continuous Fourier transform of full light and inverse transformation realize the high-speed frequency-domain fiber optic transmission system of transmission rate greater than 40Gbit/s.

Background technology

In the optical fiber telecommunications system, the transmission of optical signal pulses in optical fiber carried out on time domain at present, and the waveform of its time domain, phase place etc. all can change along with the change of transmission range.Its transmitting speed B and distance L satisfy following formula:

B ²L＜(16| β ₂|) ^-1, β wherein ₂Be the spread fiber parameter;

Along with the sharp increase of multimedia communication demand, more and more urgent for extra long distance, vast capacity and ultrahigh speed optical fiber telecommunications system and technical need thereof in the key optical transport network.But distinctive linearity of optical fiber and nonlinear impairments have but limited ultrahigh speed, the optical fiber telecommunications system of ultra broadband and the application of network greatly.For capacity and the performance that improves system transmissions, comparative maturity and reliable technique mainly concentrate at present:

For the spontaneous emission noise ASE that amplifier produces, can adopt the erbium-doped fiber amplifier EDFA of Raman distributed fiber amplifier or low-noise factor, reduce by the reasonable disposition optical transmission section simultaneously.For 2nd order chromatic dispersion, can adopt technology such as dispersion compensating fiber/module to come segmented compensation, still, because the CHROMATIC DISPERSION IN FIBER OPTICS slope causes compensation and not exclusively, simultaneously, these dispersion compensation modules can bring loss, and just needing increases EDFA, has also increased the ASE noise; Increased simultaneously the cost of system greatly.For third-order dispersion, i.e. chromatic dispersion gradient, present compensation technique is incomplete, and what the wavelength that has was owed to mend, have makes amends for one's faults; Simultaneously, these compensation can cause in the non-linear restriction cross-phase modulation XPM, from the accumulation of the phase noise of phase modulated SPM to intensity noise, be unfavorable for the application of the direct detection system IM-DD of intensity modulated.For the above system of 40Gbit/s, need compensating polarization mode dispersion PMD, increase the system transmissions cost.Mainly show for nonlinear noise unmatched phase noise is become intensity noise, adopting the accumulation that becomes intensity noise under EDFA and the incomplete situation of dispersion compensation, directly reduce and transmit Q value and signal to noise ratio snr as XPM, this class of SPM.For the nonlinear noise of this class of four wave mixing FWM, show that mainly phase place does not match on, can pass through the reasonable disposition channel, the frequency that increases interchannel reduces at interval.But, in the network of ultrahigh speed, ultra broadband, because the restriction of the flat gain of EDFA spectrum causes spendable wavelength number and wavelength interval to be limited.

Can see that the mode of existing raising transmission performance (SNR and Q value) is to adopt the damage of direct compensation Optical Fiber Transmission, owing to a large amount of optics that use cause the surging of cost.

Simultaneously, people also propose the capacity that adopts new modulation and coding techniques to improve system transmissions from transmitting terminal, the technology of comparative maturity is to adopt the lower carrier suppressed-NRZ of carrier power to reduce the luminous power that light pulse is transmitted in optical fiber at present, thereby the minimizing nonlinear effect reduces phase place and intensity noise.Be applied.But, need the two-stage external modulator, increased the cost of system.

The employing pulse duration is narrower, frequency spectrum is narrower and better phase modulated of anti-hot-tempered acoustic performance and return-to-zero coding technology, such as: ODB sign indicating number, PSK sign indicating number and QPSK sign indicating number wait the capacity that improves system, also reduce simultaneously specification requirement for recovery usefulness and demodulation multiplexer etc., but need the two-stage external modulator at least, increased cost.

Above-mentioned these technology all must adopt the external modulation technology, and what have needs the secondary external modulator, such as two Mach-Zehnder interferometers of needs, has increased the cost of technical sophistication and system.

Simultaneously, people can also adopt forward error correction coding mode FEC to improve the SNR of system at transmitting terminal, and this mode needs the signal of telecommunication to handle, and cost is not high, and still, its performance that improves system is limited.

In sum, the prior art scheme respectively has pluses and minuses, cuts both ways, and can not fundamentally solve the signal transmission restriction that all optical fiber damages bring.

Summary of the invention

The invention provides a kind of optical fiber transmission system in light frequency domain, purpose is to solve conveniently, at low cost influence and the restriction of the inherent loss of present optical fiber for the high-speed optical pulse transmission.

A kind of optical fiber transmission system in light frequency domain of the present invention, order comprises transmitter, first erbium-doped fiber amplifier, single-mode transmission optical fiber, second erbium-doped fiber amplifier and receiver on the optical transmission chain, it is characterized in that:

Light path connects cycle full-optical Fourier inverse transformer between the described transmitter and first erbium-doped fiber amplifier; Light path connects cycle full-optical Fourier converter between described second erbium-doped fiber amplifier and the receiver;

Described transmitter carries out the electric light conversion to original electric data bit flow, becomes the optical signal pulses sequence by intensity modulated again and sends into cycle full-optical Fourier inverse transformer;

Cycle full-optical Fourier inverse transformer is carried out inverse fourier transform to the optical signal pulses sequence of input, output light signal time domain waveform, and the spectrum envelope of light signal time domain waveform is the time domain waveform of the optical signal pulses sequence of input; Emission entered and grows the distance High-speed transmission in the single-mode transmission optical fiber after this light signal time domain waveform was amplified through first erbium-doped fiber amplifier;

Through after the single-mode transmission optical fiber transmission, after the light signal time domain waveform of distortion amplified through second erbium-doped fiber amplifier, be input to cycle full-optical Fourier converter and carry out Fourier transform;

Cycle full-optical Fourier converter output optical signal pulses sequence, this optical signal pulses sequence is identical with transmitter output, sends into receiver, realizes recovery, regeneration and the differentiation of raw electrical signal in receiver.

Described a kind of optical fiber transmission system in light frequency domain is characterized in that:

Described cycle full-optical Fourier inverse transformer is connected to form by the dispersion compensating fiber light path by two negative sense cycle square phase-modulators, two negative sense cycle square phase-modulators have identical cycle and identical modulation parameter, and the expression formula of negative sense cycle square phase-modulator is:

$B_{\mathrm{out}}=B_{\mathrm{in}}\exp \left(\mathrm{<figure-callout\; id="1"\; label="i"\; filenames="A20081004766200131.png"\; state="\{\{state\}\}">i</figure-callout>}\frac{1}{2{\mathrm{L\&beta;}}_2}{t}^2\right)*\underset{m=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}(t-m{T}_w)$

B wherein _InAnd B _OutBe respectively the input time domain waveform and the output time domain waveform of negative sense cycle square phase-modulator; L and β ₂Length and the dispersion parameters of representing dispersion compensating fiber respectively; δ (t) is an impulse function; T _wBe the cycle of negative sense cycle square phase-modulator, t is the time, and m is an integer, and the required synchronizing signal of negative sense cycle square phase-modulator is provided by the clock of transmitter.

Described a kind of optical fiber transmission system in light frequency domain is characterized in that:

Described cycle full-optical Fourier converter is connected to form by the dispersive optical fiber light path by two forward cycle square phase-modulators, two forward cycle square phase-modulators have identical cycle and identical modulation parameter, and the expression formula of forward cycle square phase-modulator is:

${B^{\&prime;}}_{\mathrm{out}}={B^{\&prime;}}_{\mathrm{in}}\exp \left(\mathrm{<figure-callout\; id="1"\; label="i"\; filenames="A20081004766200131.png"\; state="\{\{state\}\}">i</figure-callout>}\frac{1}{2L^{\&prime;}{{\mathrm{\&beta;}}_2}^{\&prime;}}{t}^2\right)*\underset{m=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}(t-m{T_w}^{\&prime;})$

B ' wherein _InAnd B ' _OutBe respectively the input time domain waveform and the output time domain waveform of forward cycle square phase-modulator; L ' and β ₂' represent the length and the dispersion parameters of dispersive optical fiber respectively; δ (t) is an impulse function; T _w' be the cycle of forward cycle square phase-modulator, t is the time, and m is an integer, and the required synchronizing signal of forward cycle square phase-modulator is provided by the clock that clock recovery module extracts from single-mode transmission optical fiber;

The length of the dispersion compensating fiber of described dispersive optical fiber and described cycle full-optical Fourier inverse transformer and dispersion parameters satisfy relation:

L β ₂=-L ' β ₂', L β ₂Span 23ps ²～200ps ²

Forward cycle square phase-modulator is identical with the cycle of negative sense cycle square phase-modulator:

T _w'=T _w, T _wSpan 100ps～200ps.

In the system of the present invention:

Original electric data bit flow is modulated into the optical signal pulses sequence after the transmitter process is by electric light conversion and intensity modulated, be expressed as:

$A_{\mathrm{in}}\left(t\right)=g\left(t\right)*\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}(t-\mathrm{kT})---\left(1\right)$

A in the formula _In(t) be the optical signal pulses sequence after the modulation, T is the time cycle of optical signal pulses, and k is a positive integer, and g (t) is the expression formula of individual pulse, and δ (t) is an impulse function;

Every N light pulse is in one group of input cycle full-optical Fourier inverse transformer in the above-mentioned optical signal pulses sequence, be converted to a light signal time domain waveform, and the Cycle Length of N light pulse be with the cycle in the Fourier transform as long measure, the transformation for mula of inverse fourier transform is:

A _IFT-out(t)＝F ^-1[A _in(t)]

＝F ^-1[A _in(k′·ω)] (2)

＝∫A _in(k′·ω)e ^jωtdω

A in the formula _IFT-out(t) the light signal time domain waveform after the expression conversion, F ^-1The arithmetic sign of expression inverse fourier transform, k ' is a constant, and with the parameter correlation of cycle full-optical Fourier inverse transformer, ω is an optical pulse frequency, and the required synchronizing signal of inverse fourier transform is provided by the clock of transmitter.

The time domain expression formula of the light signal time domain waveform after the conversion is F ^-1[A _In(k ' ω)], frequency-domain expression is:

$A_{\mathrm{IFT}-\mathrm{out}}=\left(\mathrm{\&omega;}\right)=A_{\mathrm{in}}\left(k^{\&prime;}\mathrm{\&omega;}\right)$

$=g\left(t\right)*\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}(t-\mathrm{kT})---\left(3\right)$

The frequency-domain expression of this light signal time domain waveform is consistent with the time waveform of the optical signal pulses sequence of the input of formula (1) expression.

Light signal time domain waveform after the process cycle full-optical Fourier inverse transformation is with F ^-1[A _In(k ' ω)] form, send in the single-mode transmission optical fiber through first erbium-doped fiber amplifier and to transmit, after one section transmission, this light signal time domain waveform will be by optical fiber attenuation and distortion.Then, being sent to second erbium-doped fiber amplifier amplifies, send into cycle full-optical Fourier converter again, this cycle full-optical Fourier converter carries out Fourier transform to the light signal symbol, and the needed clock signal of Fourier transform need be extracted from single-mode transmission optical fiber by clock recovery module.

Through the light signal symbol of transmission, its time domain waveform can be subjected to the influence of optic fiber polarization mould dispersion, chromatic dispersion and high-order dispersion etc., has superposeed noise and is out of shape, and still, its frequency-domain waveform is constant, remains: $g\left(t\right)*\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}(t-\mathrm{kT});$

The light signal symbol that transmits in the optical fiber frequency domain is sent into cycle full-optical Fourier converter, the process Fourier transform:

A _FT-out(t)＝F[A _IFT-OUT(k′·ω)] (4)

Obtain $g\left(t\right)*\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}(t-\mathrm{kT}),$ The optical signal pulses sequence of formula (1) input just;

In the formula, F represents the arithmetic sign that Fourier changes.

The present invention can not be subjected in the optical fiber such as chromatic dispersion when utilizing the spectrum envelope of light pulse to transmit in optical fiber, polarization mode dispersion, the influence of linear perturbations such as time jitter, the spectrum envelope of light pulse this fundamemtal phenomena that in the optical pulse propagation process, can not change.

The cycle of supposing Fourier transform be original input the optical signal pulses sequence time cycle N doubly, to expand to the time period the inside of an identical light signal time domain waveform so through the primary light pulse of N after the periodic full-optical Fourier inverse transformer adjacent bit, and can determine the time of this light signal time domain waveform by the parameter that cycle full-optical Fourier inverse transformer is set.After the conversion time span of light signal time domain waveform with respect to original single light pulse to N doubly with broadening N/2, thereby reduced transmission rate, improved the interference free performance of system for linear perturbations such as GVD (Group Velocity Dispersion), polarization mode dispersion, time jitters.

In addition, because being input to the time domain waveform of the pulse in the cycle full-optical Fourier inverse transformer is the spectrum envelope of light pulse symbol after the conversion, so no matter which kind of yard type the inceptive impulse of input adopts, as long as the time cycle of its inverse-Fourier transform does not become, after the parameter of inverse fourier transform device was determined, the spectrum width that conversion produces the light signal time domain waveform just can not become.So when the pulse train of input when adopting the pulse of NRZ modulation, can obtain by analysis, the light signal time domain waveform of passing through behind the inverse-Fourier transform of actual transmissions will be higher than original intensity modulated NRZ in the optical fiber aspect band efficiency.And approach to adopt the band efficiency of nonreturn to zero code.

The clock signal that to extract from system of the present invention just can be recovered original optical signal pulses sequence as the timing clock signal of receiving terminal.In whole system, original optical signal pulses sequence waveform will can not be subjected to the influence of the intrinsic linear perturbation of optical fiber GVD (Group Velocity Dispersion), polarization mode dispersion, time jitter etc. in the optical communication system.Can realize the high-speed optical signal transmission of the above speed of 40Gbit/s.

Parameter by appropriate design Fourier and inverse fourier transform device comprises the T that chooses the conversion time cycle _wLength, the length of dispersive optical fiber and dispersion parameters L, β ₂, and the length of dispersion compensating fiber and dispersion parameters L ', β ₂', transmission rate be can obtain and the no any chromatic dispersion of 40Gbit/s and the long Distance Transmission of light pulse of polarization mode dispersion (PMD) compensation are higher than.

Description of drawings

Fig. 1 is a system configuration schematic diagram of the present invention, is labeled as among the figure: transmitter 1, cycle full-optical Fourier inverse transformer 2, first erbium-doped fiber amplifier 3, single-mode transmission optical fiber 4, the second erbium-doped fiber amplifiers 5, cycle full-optical Fourier converter 6, receiver 7, clock recovery module 8.

Fig. 2 is a cycle full-optical Fourier inverse transformer structural representation of the present invention, is labeled as among the figure: negative sense cycle square phase-modulator 9, dispersion compensating fiber 10;

Fig. 3 is a cycle full-optical Fourier transformer configuration schematic diagram of the present invention, is labeled as among the figure: forward cycle square phase-modulator 11, dispersive optical fiber 12.

Embodiment

The present invention is further described below in conjunction with accompanying drawing

As shown in Figure 1, the present invention includes transmitter 1, cycle full-optical Fourier inverse transformer 2, the first erbium-doped fiber amplifiers 3, single-mode transmission optical fiber 4, the second erbium-doped fiber amplifiers 5, cycle full-optical Fourier converter 6, receiver 7, clock recovery module 8.At first sending a string pulse train via intensity modulated (NRZ or nonreturn to zero code) by transmitter 1 is input in the cycle full-optical Fourier inverse transformer 2.Then with the Fourier transform period T _w=NT is that integer (N) adjacent pulse of long measure is converted to a new impulse code through conversion, and transmits.The synchronizing signal of this cycle full-optical Fourier inverse transformer is provided by the clock of transmitter.N original after conversion pulse train is with regard to the spectrum envelope as new impulse code.Because coming out to enter into the pulse train of inverse-Fourier transform system from transmitting terminal is real-time, a continuous process.So after the conversion repetition period of this new impulse code will be the original conversion pre-pulse sequence pulse repetition period N doubly.By the parameter L β of cycle full-optical Fourier inverse transformer is set ₂Can make the time span of transmission symbol be controlled at Fourier transform within the cycle.

At transmission cycle full-optical Fourier converter place,, must make the time span of transmission pulse symbol be controlled within the one-period of cycle full-optical Fourier converter for original signal being recovered out by Fourier transform.So need carry out synchronously to the transmission pulse symbol, synchronous needed clock signal need be extracted from single-mode transmission optical fiber by clock recovery module, this clock signal is exactly the cycle of transmission pulse symbol, and this clock cycle has prolonged N doubly with respect to the pulse train clock cycle before the inverse-Fourier transform.Just can Fourier transform cycle and symbol period be coincided control cycle full-optical Fourier converter after the Clock Extraction.Original like this pulse train just can be recovered out accurately.Whole system does not need to consider the influence such as chromatic dispersion, polarization mode dispersion and time jitter.

Figure 2 shows that the structural representation of cycle full-optical Fourier inverse transformer of the present invention, connect to form by the dispersion compensating fiber light path by two negative sense cycle square phase-modulators, two negative sense cycle square phase-modulators have identical cycle and identical modulation parameter, and modulation parameter is the length of dispersion compensating fiber and the inverse of dispersion parameters product.Modulator can adopt lithium niobate (LiNbO ₃) waveguide and constitute as the r-f generator of its driving.The synchronizing signal of negative sense cycle square phase-modulator is provided by the clock of transmitter.

Figure 3 shows that the structural representation of cycle full-optical Fourier converter of the present invention, connect to form by the dispersive optical fiber light path by two forward cycle square phase-modulators, two forward cycle square phase-modulators have identical cycle and identical modulation parameter, and modulation parameter is the length of dispersive optical fiber and the inverse of dispersion parameters product.Forward cycle square phase-modulator can adopt lithium niobate (LiNbO ₃) waveguide and constitute as the r-f generator of its driving.The synchronizing signal of forward cycle square phase-modulator is provided by the clock that adopts clock recovery module to extract from single-mode transmission optical fiber, and clock recovery module can adopt the clock recovery module of model C DR-O125.

The length of the dispersion compensating fiber of described dispersive optical fiber and described cycle full-optical Fourier inverse transformer and dispersion parameters satisfy relation:

L β ₂=-L ' β ₂', as an embodiment, L β ₂Value is 37.7ps ²,

L=0.4km wherein; β ₂=94.3ps ²/ km; L '=8km; β ₂The 4.7ps of '=- ²/ km

Forward cycle square phase-modulator is identical with the cycle of negative sense cycle square phase-modulator:

T _w'=T _w, among the embodiment, T _wGet 100ps.

Obtaining transmission rate is the no any chromatic dispersion of 100Gbit/s and the long Distance Transmission of light pulse of polarization mode dispersion (PMD) compensation.

Claims (3)

1. an optical fiber transmission system in light frequency domain comprises transmitter, first erbium-doped fiber amplifier, single-mode transmission optical fiber, second erbium-doped fiber amplifier and receiver on the optical transmission chain in proper order, it is characterized in that:

Light path connects cycle full-optical Fourier inverse transformer between the described transmitter and first erbium-doped fiber amplifier; Light path connects cycle full-optical Fourier converter between described second erbium-doped fiber amplifier and the receiver;

Described transmitter carries out the electric light conversion to original electric data bit flow, becomes the optical signal pulses sequence by intensity modulated again and sends into cycle full-optical Fourier inverse transformer;

Cycle full-optical Fourier inverse transformer is carried out inverse fourier transform to the optical signal pulses sequence of input, output light signal time domain waveform, and the spectrum envelope of light signal time domain waveform is the time domain waveform of the optical signal pulses sequence of input; Emission entered and grows the distance High-speed transmission in the single-mode transmission optical fiber after this light signal time domain waveform was amplified through first erbium-doped fiber amplifier;

Through after the single-mode transmission optical fiber transmission, after the light signal time domain waveform of distortion amplified through second erbium-doped fiber amplifier, be input to cycle full-optical Fourier converter and carry out Fourier transform;

Cycle full-optical Fourier converter output optical signal pulses sequence, this optical signal pulses sequence is identical with transmitter output, sends into receiver, realizes recovery, regeneration and the differentiation of raw electrical signal in receiver.

2. a kind of optical fiber transmission system in light frequency domain as claimed in claim 1 is characterized in that:

Described cycle full-optical Fourier inverse transformer is connected to form by the dispersion compensating fiber light path by two negative sense cycle square phase-modulators, two negative sense cycle square phase-modulators have identical cycle and identical modulation parameter, and the expression formula of negative sense cycle square phase-modulator is:

$B_{\mathrm{out}}=B_{\mathrm{in}}\exp \left(i\frac{1}{2{\mathrm{L\&beta;}}_2}{t}^2\right)*\underset{m=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}(t-m{T}_w)$

B wherein _InAnd B _OutBe respectively the input time domain waveform and the output time domain waveform of negative sense cycle square phase-modulator; L and β ₂Length and the dispersion parameters of representing dispersion compensating fiber respectively; δ (t) is an impulse function; T _wBe the cycle of negative sense cycle square phase-modulator, t is the time, and m is an integer, and the required synchronizing signal of negative sense cycle square phase-modulator is provided by the clock of transmitter.

3. a kind of optical fiber transmission system in light frequency domain as claimed in claim 1 or 2 is characterized in that:

Described cycle full-optical Fourier converter is connected to form by the dispersive optical fiber light path by two forward cycle square phase-modulators, two forward cycle square phase-modulators have identical cycle and identical modulation parameter, and the expression formula of forward cycle square phase-modulator is:

${B^{\&prime;}}_{\mathrm{out}}={B^{\&prime;}}_{\mathrm{in}}\exp \left(i\frac{1}{2L^{\&prime;}{{\mathrm{\&beta;}}_2}^{\&prime;}}{t}^2\right)*\underset{m=-\&infin;}{\overset{\&infin;}{\mathrm{\&Sigma;}}}(t-m{T_w}^{\&prime;})$

B ' wherein _InAnd B ' _OutBe respectively the input time domain waveform and the output time domain waveform of forward cycle square phase-modulator; L ' and β ₂' represent the length and the dispersion parameters of dispersive optical fiber respectively; δ (t) is an impulse function; T _w' be the cycle of forward cycle square phase-modulator, t is the time, and m is an integer, and the required synchronizing signal of forward cycle square phase-modulator is provided by the clock that clock recovery module extracts from single-mode transmission optical fiber;

The length of the dispersion compensating fiber of described dispersive optical fiber and described cycle full-optical Fourier inverse transformer and dispersion parameters satisfy relation:

L β ₂=-L ' β ₂', L β ₂Span 23ps ²～200ps ²

Forward cycle square phase-modulator is identical with the cycle of negative sense cycle square phase-modulator:

T _w'=T _w, T _wSpan 100ps～200ps.

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