CN1489320A - Method for suppressing coherent crosstalk in optical transmission system and optical transmission system - Google Patents
Method for suppressing coherent crosstalk in optical transmission system and optical transmission system Download PDFInfo
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- CN1489320A CN1489320A CNA021438870A CN02143887A CN1489320A CN 1489320 A CN1489320 A CN 1489320A CN A021438870 A CNA021438870 A CN A021438870A CN 02143887 A CN02143887 A CN 02143887A CN 1489320 A CN1489320 A CN 1489320A
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Abstract
Transmission process is as following. Optical signals in multichannel through optical multiplexing unit are combined into one transmission optical fiber. Passing through one or more optical transmission units, signals are transferred to optical demultiplexing unit. Through optical demultiplexing unit, optical signals in different channels are assigned to different optical receiver so as to realize transmission of optical signal. The characters are that generated optical signal in each channel is modulated by same electric signal by using multiline light source. Transmission of optical signal is realized by using multiline light source instead of narrowband light source so as to reduce coherent length of signal, and restrain non-linear cross talk and noise of beat frequency between transmission channels. The invention raises performances of transferring optical signal, lowers performance requirement for parts used in optical network. Thus, it reduces system cost.
Description
Technical field:
The present invention relates to a kind of method and optical transmission system that suppresses coherent crosstalk in the optical transmission system.
Background technology:
Dense wavelength division multiplexing system (DWDM) has been widely used in the optical transport network, along with further raising to the optical-fiber network performance requirement, multiplexing (OADM) and optical cross connect (OXC) equipment and technology begin to use gradually about the light, because the prolongation of transmission range and the raising of optical-fiber network flexibility, being lowered into to the restriction optical-fiber network of optical transmission signal quality used and the key factor of scale.
Dense wave division multipurpose optical communication system (DWDM) partly is made up of optical sender, interference filter, fiber grating or waveguide grating, optical receiver etc. usually, because the nearly 100nm of the bandwidth utilized of optical fiber, in same optical fiber, can transmit the signal of multichannel different wave length simultaneously, 80 or more the system of multi-wavelength begun to use wavelength interval normally 50,100 or 200GHz.Realize multiplexing, light source and filter for receiver must have higher frequency stability and precision, and the light source of using mostly is that control realizes stable Distributed Feedback Laser by temperature now, and frequency bandwidth has only several MHz.The light source of narrow spectrum like this has long coherence length, the coherent crosstalk that brings has thus but limited the prolongation of transmission range of dwdm system and the increase of transmission channel, also limited the application of OADM and OXC, to the demands for higher performance of devices such as OADM, OXC, thereby manufacture difficulty and system cost have been increased.
Summary of the invention:
Purpose of the present invention is exactly in order to overcome the above problems, and a kind of method and optical transmission system that suppresses coherent crosstalk in the optical transmission system is provided, and suppresses the nonlinear crosstalk between the transmission channel.
For achieving the above object, the present invention proposes a kind of method and optical transmission system that suppresses coherent crosstalk in the optical transmission system.
The method of coherent crosstalk comprises the steps: multi channel light signal is multiplexed in the same optical fiber by optical multiplex unit and transmits in the described inhibition optical transmission system; Be transferred to the Optical Demultiplexing unit through one or more optical transmission units; Through the Optical Demultiplexing unit light signal of different channels is assigned to different optical receivers, realizes the transmission of light signal; It is characterized in that: the light signal of described each channel utilizes multi-thread light source to be modulated and produce by the same signal of telecommunication.
Described optical transmission system, comprise optical sender, optical multiplex unit, optical transmission unit, Optical Demultiplexing unit and optical receiver, the multi channel optical multiplexed signal that optical multiplex unit sends optical sender is used in the same optical fiber and is transmitted, and is transferred to the Optical Demultiplexing unit through one or more optical transmission units; The Optical Demultiplexing unit is assigned to different optical receivers to the light signal of different channels, realizes the transmission of light signal; It is characterized in that: the light source of the light signal of described each channel is multi-thread light source.
Owing to adopted above scheme, replace narrow-band light source to realize the transmission of light signal with multi-thread light source, each bar line what carry is identical information, can be owing to not crosstalking between the relevant generation signal, that is: reduce the coherence length of signal, thereby suppressed nonlinear crosstalk and beat frequency noise between the transmission channel, improved the performance of transmitting optical signal, reduced the performance requirement of optical-fiber network, thereby reduced system cost with used device.
Description of drawings:
Fig. 1 is the multi-thread light source DWDM of a present invention optical network system embodiment schematic diagram.
Fig. 2 is the optical transmission unit schematic diagram.
Embodiment:
Also the present invention is described in further detail in conjunction with the accompanying drawings below by specific embodiment.
Main points of the present invention are to utilize multi-thread light source to replace single line narrow-band light source commonly used in the optical transport network to realize the transmission of signal, reach the purpose that suppresses nonlinear crosstalk.Comprise the multi-thread light source that produces in the particular range of wavelengths, with the signal of telecommunication modulate modulated light signal that multi-thread light source produces different wave length, these light signals are by the transmission of DWDM optical transmission system and receive, nonlinear crosstalk is suppressed in this process.Wherein, the feature of the many line spectrum of generation be each bar spectral line spectrum width less than spectral line at interval, and much smaller than the wavelength interval between the multi wave length illuminating source, spectral line is at interval greater than the bandwidth of the modulator signal of telecommunication; Every spectral line in multi-thread light source is modulated by the same signal of telecommunication simultaneously, the light signal of picked up signal modulation.
Be elaborated from theory analysis below.
The coherent crosstalk that narrow spectroscopic light source causes derives from two aspects, and the firstth, nonlinear effect, the secondth, the extinction ratio that optical device is limited.
Nonlinear effect in the dwdm system between the adjacent channel mainly contains four wave mixing and cross-phase modulation, four wave mixing is meant to interact between the different transmission wavelengths (frequency) and produces new wavelength (frequency) component, this frequency component drops within the bandwidth of optical receiver, produces beat frequency noise with other interchannels.The cross-phase modulation is another kind of nonlinear effect, is meant interchannel because Kerr effect causes variations in refractive index, thereby causes the transmitted waveform distortion.Four wave mixing and cross-phase modulation are the key constraints that maximum single channel launched power improves in the wdm system, have also determined the minimum optical fiber dispersion of minimum frequency space and permission simultaneously.
Another kind is crosstalked and is derived from the limited extinction ratio of used device in the WDM optical-fiber network (OADM, OXC etc.), even bigger extinction ratio is as-20dB, if signal is concerned with, the noise power that produces that interacts between the last lower channel still reaches-10dB, therefore the performance to OADM and OXC proposes requirements at the higher level, particularly in wdm system of future generation, optical switch and wavelength route have been introduced, each up and down and crossover node all can produce and crosstalk, the inhibition of coherent crosstalk is particularly important to optical-fiber network of future generation.
Nonlinear crosstalk can be expressed as in the DWDM optical-fiber network:
ε=Δ P
NL/ P is P and Δ P wherein
NLBe respectively the power that transmitting power and nonlinear crosstalk produce, with reference to [OpticalFiber Communication Systems, Vol.IIIA, Ed.I.P.Kaminow and T.L.Koch, Academic Press, San Diego, 1997], following formula can be expressed as:
ε=4 (γ PL
e)
2η wherein γ is a non linear coefficient, is determined by fiber type.Le is the optical fiber effective length [with reference to " nonlinear optical fiber optics ", G.P.AGRAWAL work, publishing house of University Of Tianjin] of nonlinear effect decision, is generally about 20 kilometers.η is the interaction coefficient of optical fiber dispersion and channel spacing decision.
For waiting channel spacing WDM optical transmission system, the nonlinear crosstalk that four wave mixing produces drops within the receiver bandwidth, and to the light signal generating influence, because the effect of chromatic dispersion has only the signal of adjacent channel just to have obvious effect, the effect of other channels is less.Under the situation of using multi-thread wideband light source, luminous power is distributed on the different N bar spectral lines, and the noise that produces on receiver of crosstalking that four wave mixing produces reduces N doubly.Be the dwdm system of 1mw (milliwatt) for 100GHz channel spacing, launched power for example, because the effect of four wave mixing, the single line narrow-band light source can produce the Power penalty of 1dB, and for multi-thread wideband light source, the Power penalty of generation has only 0.05dB.
For the DWDM optical network system that has OADM or OXC, deciliter wave filter in different DWDM signal allocation to different ports, part signal just is leaked to other ports, signal to other ports exerts an influence, when these signals being coupled to again in the same optical fiber, because the coherence between the signal, the signal of originally revealing away is the signal interaction generation beat frequency noise in the channel again and originally.Because the limited extinction ratios of device such as OADM, OXC also have part signal to reveal, when original Wavelength reuse, produce beat frequency noise in addition with the signal interaction of revealing.With reference to [E.L.Goldstein et al., " Scaling limitations in Transparant Opticalnetworks Duo to Low Level Crosstalk " IEEE PTL, Vol.7, P.93,1995]:
Wherein Pc is the beat frequency generation Power penalty of crosstalking, ε
DBFor OADM the levels of crosstalk that produces such as OXC, N is the port number of optical device, q be the system parameters corresponding to the error rate, q=5.9, the error rate of correspondence is 10
-9
When using multi-thread light source, the interference between the light field reduces, and the Power penalty when incoherent is:
For the identical error rate, Pi is than the about little 20dB of Pc.For example, the optical network system of 40 path 10s OADM node supposes that the power leakage of each website is identical, and then producing the unit of crosstalking under the worst case is 400, be concerned with if crosstalk, and be 10 in the error rate
-10, Power penalty is under the situation of 1dB, the crosstalking of requirement less than-52dB, and then the non-adjacent channel interference of multiplex/demultiplex filter device must be less than-26dB.Consider the requirement such as low noise, polarization irrelevant of multiplex/demultiplex filter, existing device can't meet the demands.If but light source is noncoherent, the crosstalking of non-adjacent channel of multiplex/demultiplex filter required to be reduced to-16dB.Therefore multi-thread light source has reduced the requirement to the multiplexing and demultiplexing filter.
The method that realizes multi-thread light source has following several method, and (1) regulates the stable laser of several temperature respectively on different frequencies, and this requires laser must have high degree of regulation.(2) with continuous-wave laser of two or three external modulators (as the LiNbO3 modulator) modulation, produce 3 spectral lines, more if desired spectral line, must produce narrower pulse, with reference to [J.JVeselka etc., ＂ Pulse Generation for Soliton systems using lithiumniobate modulators ＂, IEEE J.Sel.Topics in Quantum Electronics, Vol.2, P.300,1996].
Utilize DWDM optical network system that the present invention realizes as shown in Figure 1.The light source of the optical sender among Fig. 1 is multi-thread light source, can realize with method mentioned above, it also can be additive method, multi channel light signal is multiplexed in the same optical fiber with filter by recovery and transmits, be transferred to the Optical Demultiplexing filter cell through some optical transmission units, through the Optical Demultiplexing filter light signal of different channels is assigned to different optical receivers, realizes the transmission of light signal.Used smooth multiplex/demultiplex filter in this realization, optical receiver are with now general consistent.The composition of optical transmission unit as shown in Figure 2, be respectively Transmission Fibers, image intensifer, dispersion compensation unit, OADM, OXC etc., these devices have been formed the optical transmission unit of difference in functionality, it can be part, also can be whole, because multi-thread light source has suppressed nonlinear crosstalk, Transmission Fibers in this realization can be dispersion shifted optical fiber, general single mode fiber, non-zero dispersion displacement optical fiber etc., devices such as OADM and OXC there is not the property requirement, improve the transmission performance of DWDM optical-fiber network, reduced cost and manufacture difficulty.
The present invention utilizes multi-thread light source to form the DWDM optical transmission system can suppress nonlinear crosstalk and beat frequency noise effectively, improves the performance of transmitting optical signal, has reduced the performance requirement of optical-fiber network with used device, thereby has reduced system cost.
Claims (10)
1, a kind of method that suppresses coherent crosstalk in the optical transmission system comprises the steps: multi channel light signal is multiplexed in the same optical fiber by optical multiplex unit and transmits; Be transferred to the Optical Demultiplexing unit through one or more optical transmission units; Through the Optical Demultiplexing unit light signal of different channels is assigned to different optical receivers, realizes the transmission of light signal;
It is characterized in that: the light signal of each channel utilizes multi-thread light source to be modulated and produce by the same signal of telecommunication.
2, a kind of method that suppresses coherent crosstalk in the optical transmission system as claimed in claim 1 is characterized in that: adjusts the spectrum width of every spectral line in the described multi-thread light source, makes it at interval less than spectral line, and much smaller than the wavelength interval between the multi wave length illuminating source.
3, a kind of method that suppresses coherent crosstalk in the optical transmission system as claimed in claim 1 or 2, the method that it is characterized in that producing multi-thread light source is one of following method: (1) regulates the stable laser of several temperature respectively on different frequencies; (2) with continuous-wave laser of two or more external modulator modulation, produce 3 or many spectral lines, wherein the spectral line of multi-thread light source interval is greater than the bandwidth of the modulator signal of telecommunication.
4, a kind of method that suppresses coherent crosstalk in the optical transmission system as claimed in claim 1 or 2 is characterized in that: light signal is by dispersion shifted optical fiber, general single mode fiber or non-zero dispersion displacement optical fiber transmission.
5, a kind of method that suppresses coherent crosstalk in the optical transmission system as claimed in claim 3, it is characterized in that: described optical transmission system is the DWDM optical transmission system, wherein contains light add-drop multiplexer spare, optical cross connect device.
6, a kind of optical transmission system, comprise optical sender, optical multiplex unit, optical transmission unit, Optical Demultiplexing unit and optical receiver, the multi channel optical multiplexed signal that optical multiplex unit sends optical sender is used in the same optical fiber and is transmitted, and is transferred to the Optical Demultiplexing unit through one or more optical transmission units; The Optical Demultiplexing unit is assigned to different optical receivers to the light signal of different channels, realizes the transmission of light signal; It is characterized in that: the light source of the light signal of described each channel is multi-thread light source.
7, optical transmission system as claimed in claim 6 is characterized in that: in the described multi-thread light source spectrum width of every spectral line less than spectral line at interval, and much smaller than the wavelength interval between the multi wave length illuminating source.
8, as claim 6 or 7 described optical transmission systems, it is characterized in that: the generation device of described multi-thread light source is one of following apparatus: the laser of the temperature stabilization of (1) scalable frequency; (2) two or more external modulators and a continuous-wave laser that is subjected to its modulation.
9, as claim 6 or 7 described optical transmission systems, it is characterized in that: described optical transmission unit comprises dispersion shifted optical fiber, general single mode fiber or non-zero dispersion displacement optical fiber transmission.
10, as claim 6 or 7 described optical transmission systems, it is characterized in that: described optical transmission system is the DWDM optical transmission system, wherein contains light add-drop multiplexer spare, optical cross connect device.
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| CN101167318B (en) * | 2005-05-13 | 2012-12-19 | 泰克诺沃斯公司 | Method and system for mitigating Raman crosstalk in an Ethernet passive optical network |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101167318B (en) * | 2005-05-13 | 2012-12-19 | 泰克诺沃斯公司 | Method and system for mitigating Raman crosstalk in an Ethernet passive optical network |
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