CN100505590C - NRZ clock signal reinforcing method - Google Patents

Abstract

The invention provides an enhancement scheme for non-return-to-zero code data clock signal in optical communication, which comprises: two segments of nonlinear optical fiber, two optical bandpass filters, two wavelength division multiplexers, and two continuous wave optical sources with different wave length. Wherein, with cross-phase modulation effect in optical fiber, the non-return-to-zero code data takes frequency modulation to continuous wave signal; the said filter converts the signal into amplitude modulation; it forms burned holes opposite to said data, and obtains pseudo-return-to-zero code with very strong clock signal component by a reverse optical fiber wavelength converter.

Description

A kind of Enhancement Method of NRZ clock signal

Affiliated technical field

The invention belongs to technical field of optical fiber communication, it is particularly related to the enhancement techniques of nonreturn to zero code data clock signal in the optical communication.

Background technology

In communication system, it is that signal processing is done time reference that clock signal be arranged, and optical fiber telecommunications system is no exception.So the clock recovery technology that goes out clock signal from extracting data becomes a key technology the optical communication system.The clock recovery scheme major part that has proposed all can only be at the effect of NRZ data competence exertion, because in the modulation spectrum of return-to-zero coding data, contain very strong clock signal component, and for the nonreturn to zero code data, its faint clock signal component makes that directly it being carried out clock recovery becomes very difficult.

At present, the scheme of the nonreturn to zero code data being carried out all-optical clock recovery all is to adopt to add a light signal processing module before clock recovery module, is used for strengthening the clock signal of nonreturn to zero code data.People such as H.K.Lee have proposed to constitute full light XOR gate with the Mach-Zehnder interferometer and have carried out nonreturn to zero code and strengthen clock signal to the conversion of pseudo-NRZ and (see document H.K.Lee, J.T.Ahn, M.-Y.Jeon, K.H.Kim, D.S.Lim, and C.-H.Lee, " All-optical clock recoveryfrom NRZ data of 10Gb/s; " IEEE Photon.Technol.Lett., vo1.11, pp.730-732, June1999), because it is 20Gb/s or more in the system at the end that the restriction of XOR gate processing speed, this technical scheme only are applicable to bit rate; People such as H.J.Lee have proposed the frequency chirp that utilizes the nonreturn to zero code signal to cause because of self phase modulation in semiconductor optical amplifier, cooperate high pass filter that non-return-to-zero is changed to pseudo-NRZ and realize that the enhancing of clock signal (sees document H.J.Lee, H.G.Kim, J.Y.Choi, and H.K.Lee, " All-optical clock recovery from NRZ datawith simple NRZ-to-PRZ converter based on self-modulation of semiconductor opticalamplifier; " Electron.Lett., vol.35, no.12, pp.989-990,1999), though this scheme can be applicable under the higher bit rate system, but only stay the rising edge part of former nonreturn to zero code because wherein filter can filter out most of signal energy, so performance is unsatisfactory and depend critically upon a yard type; W.Mao, people such as M.Al-Mumin use light belt resistance filter instead and filter nonreturn to zero code signal mid portion on the basis of the scheme of this H.J.Lee, the enhancing of clock and the compacting of data have been finished simultaneously, making that the clock signal component further improves in the pseudo-NRZ data of gained (sees document W.Mao, M.Al-Mumin, X.Wang, and G.Li, " All-optical enhancement of clock and clock-to-datasuppression ratio of NRZ data; " IEEE Photon.Technol.Lett., vol.13, no.3, pp.239-141, March 2001), still, the pseudo-NRZ data pulse variable power that it produces is very big, be unfavorable for the clock recovery in later stage, performance improvement is limited.

As can be seen, the common shortcoming of these technical schemes can not be operated under the high bit rate data flow exactly, so can not be applicable to following high speed optical communication system.

Summary of the invention

In order to overcome the deficiency of technique scheme, the clock that solves high bit rate nonreturn to zero code data flow strengthens problem, the invention provides a kind of Enhancement Method of nonreturn to zero code data clock signal, this method can be finished the clock signal enhancing of bit rate up to the nonreturn to zero code data flow of 140Gb/s well.

For the present invention program is described easily, at first make term definition:

Cross-phase modulation: a kind of nonlinear effect, show as when the light signal of two or more wavelength transmits in optical fiber simultaneously, the change in signal strength of arbitrary wavelength all can cause the change of optical fiber effective refractive index, thereby makes the light signal generation phase change of other wavelength.

Frequency chirp: be subjected to the influence of fiber nonlinear effect, certain change can take place in the frequency of the light signal each several part in the transmission.

Dispersion shifted optical fiber: i.e. itu standard optical fiber G.653, it has moved on to the 1550nm window with zero-dispersion wavelength.

The Enhancement Method of a kind of nonreturn to zero code data clock signal provided by the invention, step realized below it adopted:

Step 1. obtains the light signal that first contains two wavelength with the continuous wave detectable signal of the nonreturn to zero code pump signal of wavelength 1532.18nm, power 21.03dBm and wavelength 1537.67nm, power 17dBm through first wavelength division multiplexer is multiplexing;

Step 2. obtains first light signal that contains two wavelength with step 1 and is injected in first section dispersion shifted optical fiber, because cross-phase modulation effect makes the continuous wave detectable signal of wavelength 1537.67nm, power 17dBm produce frequency chirp; First section dispersion shifted optical fiber major parameter is: zero-dispersion wavelength 1535nm, chromatic dispersion gradient 0.086ps/ (nm ²* km), length 500m, effective area 24*10 ^-12m ², nonlinear refractive index 4.5*10 ^-20m ²/ W;

Step 3. is that the optical band pass filter that the signal of 1537.67nm is injected into centre wavelength 1537.67nm, bandwidth 300Ghz filters with the wavelength with frequency chirp of step 2 gained, obtains having the continuous wave signal of spatial hole burning;

Step 4. has step 3 gained the continuous wave signal of spatial hole burning and amplifies via erbium-doped fiber amplifier, make the power of continuous wave signal reach 22.17dBm with spatial hole burning, this signal is 1532.18nm by second wavelength division multiplexer and wavelength, power is that the continuous wave of 13dBm is multiplexing, obtains second light signal that contains two wavelength;

Step 5. is injected into second section dispersion shifted optical fiber with second light signal that contains two wavelength of step 4 gained, because cross-phase modulation effect makes that wavelength is that 1532.18nm, power are the continuous wave generation phase modulated of 13dBm.The major parameter of second section dispersion shifted optical fiber is: zero-dispersion wavelength 1535nm, chromatic dispersion gradient 0.086ps/ (nm ²* km), length 200m, effective area 24*10 ^-12m ², nonlinear refractive index 4.5*10 ^-20m ²/ W;

After the signal of step 6. after with the process phase modulated of step 5 gained carries out demultiplexing via the band pass filter of centre wavelength 1532.18nm, bandwidth 300GHz to signal, continuous wave with wavelength 1532.18nm produces interference in coupler again, just can obtain pseudo-NRZ signal, this signal promptly is the nonreturn to zero code signal after oversampling clock strengthens.

The present invention is by being converted to the NRZ data enhancing that pseudo-NRZ data are finished clock signal, and cardinal principle is according to the nonlinear effect of optical fiber---the cross-phase modulation.

As everyone knows, it is interpulse owing to the variation that exists cross-phase modulation effect to interact to cause frequency domain and time domain (is seen [U.S.] Govind P.Agrawal work that two frequencies transmitting in the optical fiber do not overlap, Jia Dongfang etc. translate. nonlinear optical fiber optical principle and application. and Beijing: publishing house of the Ministry of Electronics Industry, 2002).Concretely, when a detectable signal and a pump signal are injected in the optical fiber simultaneously, because the cross-phase modulation effect between them, pump signal can make the frequency of detectable signal produce and warble: the rising edge of pump signal and trailing edge can allow the difference detectable signal produce the red shift blue shift of frequency.The maximum of warbling is directly proportional with the signal injecting power.

According to this phenomenon, if adopt continuous wave signal as detectable signal, the nonreturn to zero code data-signal is as pump signal, and the rising edge of nonreturn to zero code and trailing edge can produce the frequency chirp of different directions respectively to continuous wave signal so, promptly it have been carried out frequency modulation(FM).By using a band pass filter that centre frequency is identical with continuous wave signal, this frequency modulation(FM) is transformed into amplitude modulation(PAM): continuous wave can produce hole burning in the position of frequency chirp, and these hole burning time intervals equal the integral multiple of the minimum pulse width of nonreturn to zero code pump signal.Again by (the spectrum counter-rotating of output signal and input signal of a counter-rotating wavelength shifter that constitutes by optical fiber, as input signal is 101, then through behind the counter-rotating wavelength shifter, output signal is 010), just can obtain containing the pseudo-NRZ signal of very strong clock signal component, thereby reach the purpose that clock strengthens.

This technical method can strengthen carry out clock up to 140Gb/s nonreturn to zero code data flow, and good performance performance is arranged.Confirm through Computer Simulation: the clock signal component that 64Gb/s and 140Gb/s nonreturn to zero code data are comprised is through after strengthening, and clock data can reach 22.94dB and 15dB than respectively, and in length for being respectively 2 ⁷-1,2 ¹⁵-1,2 ²¹-1,2 ³¹Under-1 the pseudo-random binary nonreturn to zero code data, all do not show dependence, export pseudo-NRZ signal pulse energy basically identical the sign indicating number type.

Description of drawings

Fig. 1 is the inventive method system flow chart

Fig. 2 is the structural representation of the inventive method

Wherein, the 1st, the nonreturn to zero code data-in port; 2 and 6 is continuous wave signal input ports; 3 and 9 is wavelength division multiplexers; 4 and 10 is dispersion shifted optical fibers; 5 and 11 is optical band pass filters; 8 and 12 is couplers; The 7th, fiber amplifier.

Fig. 3 is the system's each several part oscillogram under the 64Gb/s nonreturn to zero code data flow

Wherein, a) be original nonreturn to zero code data waveform;

B) for producing the continuous wave signal waveform of spatial hole burning;

C) be the continuous wave signal waveform after the counter-rotating;

Wherein, abscissa is the time, and ordinate is an amplitude

Fig. 4 is the radio spectrum figure of system's input and output signal under the 64Gb/s nonreturn to zero code data flow

Wherein, a) be original nonreturn to zero code data radio spectrum;

B) strengthen the pseudo-NRZ signal RF frequency spectrum in back for clock;

Wherein, abscissa is a frequency, and ordinate is a radio-frequency power

Fig. 5 carries out the pseudo-NRZ signal waveforms that obtains after clock strengthens to 140Gb/s nonreturn to zero code data flow

Wherein, abscissa is the time, and ordinate is an amplitude

Fig. 6 carries out the pseudo-NRZ signal RF frequency spectrum that obtains after clock strengthens to 140Gb/s nonreturn to zero code data flow

Wherein, abscissa is a frequency, and ordinate is a radio-frequency power

Claims (1)

1, a kind of Enhancement Method of nonreturn to zero code data clock signal, step realized below it adopted:

Step 1. obtains the light signal that first contains two wavelength with the continuous wave detectable signal of the nonreturn to zero code pump signal of wavelength 1532.18nm, power 21.03dBm and wavelength 1537.67nm, power 17dBm through first wavelength division multiplexer is multiplexing;

Step 2. obtains first light signal that contains two wavelength with step 1 and is injected in first section dispersion shifted optical fiber, because cross-phase modulation effect makes the continuous wave detectable signal of wavelength 1537.67nm, power 17dBm produce frequency chirp; First section dispersion shifted optical fiber major parameter is: zero-dispersion wavelength 1535nm, chromatic dispersion gradient 0.086ps/ (nm ²* km), length 500m, effective area 24*10 ^-12m ², nonlinear refractive index 4.5*10 ^-20m ²/ W;

Step 3. is that the optical band pass filter that the signal of 1537.67nm is injected into centre wavelength 1537.67nm, bandwidth 300Ghz filters with the wavelength with frequency chirp of step 2 gained, obtains having the continuous wave signal of spatial hole burning;

Step 4. has step 3 gained the continuous wave signal of spatial hole burning and amplifies via erbium-doped fiber amplifier, make the power of continuous wave signal reach 22.17dBm with spatial hole burning, this signal is 1532.18nm by second wavelength division multiplexer and wavelength, power is that the continuous wave of 13dBm is multiplexing, obtains second light signal that contains two wavelength;

Step 5. is injected into second section dispersion shifted optical fiber with second light signal that contains two wavelength of step 4 gained, because cross-phase modulation effect makes that wavelength is that 1532.18nm, power are the continuous wave generation phase modulated of 13dBm.The major parameter of second section dispersion shifted optical fiber is: zero-dispersion wavelength 1535nm, chromatic dispersion gradient 0.086ps/ (nm ²* km), length 200m, effective area 24*10 ^-12m ², nonlinear refractive index 4.5*10 ^-20m ²/ W;

After the signal of step 6. after with the process phase modulated of step 5 gained carries out demultiplexing via the band pass filter of centre wavelength 1532.18nm, bandwidth 300GHz to signal, continuous wave with wavelength 1532.18nm produces interference in coupler again, just can obtain pseudo-NRZ signal, this signal promptly is the nonreturn to zero code signal after oversampling clock strengthens.

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