CN1659809A - System for higher-order dispersion compensation including a delay line - Google Patents
System for higher-order dispersion compensation including a delay line Download PDFInfo
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- CN1659809A CN1659809A CN 02826430 CN02826430A CN1659809A CN 1659809 A CN1659809 A CN 1659809A CN 02826430 CN02826430 CN 02826430 CN 02826430 A CN02826430 A CN 02826430A CN 1659809 A CN1659809 A CN 1659809A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
- G02B6/278—Controlling polarisation mode dispersion [PMD], e.g. PMD compensation or emulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/2519—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using Bragg gratings
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2569—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to polarisation mode dispersion [PMD]
Abstract
A high-order dispersion compensator having a first order and a second-order polarization mode dispersion compensation elements including a polarization beam splitter coupled to receive the polarization controlled signal and split it into a first polarization component and a second orthogonal polarization component. A first waveguide having a first non-linearly chirped grating receives the first polarization signal. A second waveguide having a second non-linearly chirped grating receives the second polarization signal. A first tuning mechanism tunes both the first and the second grating simultaneously and a second tuning mechanism tunes the second grating independently. The compensator also may have a static chromatic dispersion compensation element.
Description
Background of invention
The present invention relates to be used for the method and system of signal chromatic dispersion compensation.Specifically, the present invention relates to a kind of method that is used for higher-order dispersion compensation, this method adopts Prague (Bragg) grating of at least two high-frequency impulses, with the pip of decomposed two polarization signals of selectively harmonizing, causes and variable higher-order delay associated.
Current telecommunications systems need transmit light signal on very long distance.In the signal of an optical communication, data are sent with a series of light pulse.Signal pulse is made up of the distribution of light wavelength and polarization, and each pulse is with its feature velocity transmission.This variation on speed causes pulse stretching, thereby makes signal degradation.Degenerating of causing owing to speed is relevant with wavelength is referred to as chromatic dispersion, because relevant with polarization degenerating of causing then is referred to as polarization mode dispersion (OMD).
On mathematics, the light velocity v in waveguide is provided by following formula:
C is the light beam in the free space in the formula, and n is the effective refractive index in waveguide.
Under normal situation, the effective refractive index n of optical media, relevant with the wavelength of light component.Therefore, the component with light of different wave length will be propagated with different speed.
Effective refractive index in waveguide also can be relevant with the polarization of light signal except with wavelength is relevant.Even in " single mode " optical fiber, keeping the polarised light of two quadratures, and, existing under the birefringent situation, these two polarised lights are propagated with different speed.Birefringent reason in optical fiber may comprise the two many reasons of manufacture deviation and the environmental factor relevant with the time.Speed difference causes the propagation time relevant with polarization between two different polarization patterns in birefringence fiber, i.e. " differential group delay " (differential group delay) (DGD).In the fibre system of reality, the orientation of birefringent size and birefringence axis is different everywhere along optical fiber.So just cause more complicated effect on light signal, it is to be that the notion of PSP is represented its feature by " the basic attitude of polarization ".PSP is defined as being subjected to two polarization states of maximum relevant DGD, and their unique instantaneous states that characterizes this system.
When signal is propagated by the different portions section of optical communication system, by the statistics of two polarized component distinct group speed and the distortion that causes the time, measure polarization mode dispersion (PMD).PMD comprises single order PMD and higher-order PMD, and right and wrong are deterministic.On a given wavelength, single order PMD is a differential polarization group delay.The instantaneous value of long optical fibers can for a long time at interval and the interval of short time change on the two, the former is owing to cause such as changing slowly of temperature drift, and the latter is owing to vibrate the polarization fluctuating of inducting such as mechanics and cause.Describe single order PMD mean value coefficient can to the poor PMD optical fiber of performance greater than 2ps/km
1/2Change to the reasonable PMD optical fiber of performance less than 0.1ps/km
1/2
Second order PMD is mainly caused by two reasons: (i) the single order PMD that becomes with wavelength; (ii) the orientation of the PSP of system (the basic attitude of polarization) is with the change of wavelength, and it causes PMD with wavelength change.Second order PMD causes the group delay relevant with wavelength, in fact, is of equal value to variable dispersion, and symbol can or negative or positive.Speed that rises and falls and the fluctuating velocity of single order PMD are same magnitude.
Two class chromatic dispersions are arranged: deterministic and variable.The certainty chromatic dispersion is the fixedly chromatic dispersion that has on the fixed refraction waveguide unit length.To one group of given environmental condition, the certainty chromatic dispersion is relatively fixing (for example, to standard single-mode fiber～17ps/nmkm).For example, 17ps/nmkm refers to (10km) system of 10 kms, and dedicated bandwidth is 0.1 nanometer (nm) when carrying data, will often arrive the chromatic dispersion of about 17 picoseconds (ps).
Variable chromatic dispersion is by owing to for example add or remove optical fiber that channel causes and connect the change of length and cause by tensile stress and/or temperature fluctuation.The prediction of the amount that will change chromatic dispersion, reasonably value be arrive at-500ps/nm+scope of 500ps/nm in.
Except the independent effect of PMD and chromatic dispersion, also have that there is the higher-order dispersion cross term that causes simultaneously in the two owing to chromatic dispersion and PMD.It is zero mean value that this cross term between institute's chromatic dispersion and the second order PMD has, but root mean square (RMS) contribution of non-zero can be arranged.Be similar to second order PMD item, this RMS value can have the contribution of plus or minus.Be similar to second order PMD item, this RMS value can have the contribution of plus or minus.The contribution of RMS can be from less than 1% the magnitude identical with chromatic dispersion that be dispersed into according to the PMD coefficient of optical fiber.
Chromatic dispersion has applied strict restriction to transmission bandwidth, is particularly crossing on the long distance such such as transoceanic link.When higher bit rates, it is more important that chromatic dispersion problem becomes, and this spacing that is between light pulse is less, and short herein pulse causes the signal spectrum bandwidth of broad, increases the weight of chromatic dispersion and effect higher-order PMD.In bit rate during, even to the optical fiber (≤0.1ps/km of " good " more than or equal to 40Gb/s
1/2The PMD coefficient), long length connects the dynamic compensation that also needs higher-order.Owing to need the position of additional light-electro-optical signal conversion,, perhaps limit total system length or improve system cost, the factor that chromatic dispersion may be become-suppress to allow signal of telecommunication regeneration.
Higher-order dispersion is measured and explained to unsuitable understanding in the dispersion compensation device in the past.In the solution of higher-order dispersion compensation is provided, be important to the understanding of reason in the higher-order dispersion and factor.
(the PMD coefficient is 0.1ps/km to " good " optical fiber
1/2) exemplary calculated show:
| Dispersion term | ??17ps/nm·km |
| Single order PMD coefficient | ??0.1ps/km 1/2 |
| Second order PMD coefficient | ??0.006ps/nm·km |
| The size of cross term RMS | ??0.37ps/nm·km |
To " difference " optical fiber (1ps/km
1/2) exemplary calculated show:
| Dispersion term | ??17ps/nm·km |
| Single order PMD coefficient | ??1ps/km 1/2 |
| Second order PMD coefficient | ??0.6ps/nm·km |
| The size of cross term RMS | ??3.7ps/nm·km |
The second order coefficient of PMD can be according to " second order polarization mode dispersion: the influence in analog-and digital-transmission " literary composition (IEEE J.of Lightwave Tech, JLT-16, NO 5 pp 757-771, May 1998) described in theory calculate, this article is combined in this by reference.
Second order PMD coefficient=(single order PMD coefficient)
2/ 1.73 (2)
Equation 2 is only taken into account the root mean square (RMS) of last chromatic dispersion.The calculating cross term is:
Cross term=17
1/2* (single order PMD coefficient)
1/2* 1.16 (3)
So, can understand: for to having the optical fiber of high PMD coefficient, because when only adopting fixing dispersion compensation by the chromatic dispersion of second order PMD item and cross term accumulation, PMD may cause a problem.Like this, become big or when bit rate reaches higher, will cause having the uncompensated chromatic dispersion of high value when the PMD of optical fiber coefficient.
Analyze from this, adopt the current best optical fiber of producing (to suppose～0.025ps/km even can calculate
1/2), eliminate under the situation of effect of second order PMD and cross term not carrying out dynamic dispersion compensation, to 10Gb/s transmission, propagation distance be mostly be limited to≤(chromatic dispersion＜0.3 * 100ps) to 40Gb/s then is≤200km (chromatic dispersion＜0.3 * 25ps) 3000km.
Many document papers attempt to explain the problem of higher-order dispersion compensation.A method is to adopt multi-section section PMD compensator.A kind of like this method is expensive mostly, and also will be subject to the quantity of accessible variable dispersion.Other method is selectively to add the various piece of special-purpose linear chrip (chirped) to pulse, and transmits this pulse by the high dispersion element with calibration marker and compress this pulse.A kind of like this method can be taken into account all types of chromatic dispersions.But a kind of like this method is owing to need clock recovery and phase modulated, thus be expensive mostly, and only can just can use at receiver terminal.And if residual dispersion is low, it could be worked.
The needs that Dispersion Compensation Systems is stayed not only will be to PMD, but also dynamic the adjusting done in chromatic dispersion and the chromatic dispersion of higher-order look.The needs of the telecommunications systems that has improved, such as to temperature fluctuation compensation and soon with prospect not because the needs of the possibility of the variable path length that the interpolation/system of removing of light causes, require one dynamic and be the bucking-out system of reality on cost.
Brief summary of the invention
The present invention relates to a kind of higher order dispersion compensator, be used for tuning one and have the first polarization mode dispersion component, the signal of second order polarization mode dispersion component and variable dispersion component.
This compensator comprises first tuned cell of the single order polarization mode dispersion component of regulating the Polarization Control signal and regulates second tuned cell of the variable dispersion component of second order polarization mode dispersion component and Polarization Control signal.This compensator also can comprise the Polarization Controller that the incident light of random polarization is changed into the Polarization Control signal with required polarization state.
In one embodiment, first tuned cell can comprise differential higher-order delay line, this line comprises the beam splitter/combiner that is coupled to the signal that receives Polarization Control, and this polarization beam splitter becomes first polarized component and second orthogonal polarization components to the Signal Separation of Polarization Control herein.Have be tuned to first waveguide of reflection first grating of this first polarized component and first reference reflection point be optically coupled to and receive this first polarization signal.Have be tuned to second grating of this second polarized component of reflection, and have second waveguide of second reference reflection point to be optically coupled to receive this second polarization signal.First waveguide have be tuned to reflect first chirp grating of this first polarization signal in first reference reflection point.Second waveguide is optically coupled and aligned to second delivery outlet of separator.Second waveguide have be tuned to the second frequency modulation on pulse grating of this second polarization signal of reflection, and second reference reflection point is arranged.According to this embodiment of the invention, the frequency modulation on pulse of grating can be linear, nonlinear, maybe can have complicated spatial relationship.Some is used, and the length of grating can be to be equal to or greater than 1 meter.
In this first one exemplary embodiment, two gratings all are to finish the single order PWD compensation and the fixing Bragg grating of chromatic dispersion colour table compensation with linear chrip.First tuner is such as come a grating in the tuning grating by making grating be in stress on mechanics.
In other embodiments, all available non-linear chirp of two gratings is finished except these two compensation of fixing and variable dispersion, also will finish the compensation of single order and second order PMD.In addition, can select the more complicated figure of warbling to finish more special is the compensation of higher-order (three, fourth class rank).
The two all can have substantially the same reflection external form and substantially the same chirp rate first grating and second grating; And first and second pip can be at substantially the same optical path length place.Perhaps, before regulating by tuner, in the grating reflection point a bit may than second pip from optical path length place that burble point is lacked.
Second tuned cell can comprise the 3rd waveguide of second tuner of Bragg grating with the 3rd non-linear chirp and tuning the 3rd grating.The scope of the value of warbling in this 3rd nonlinear FM pulse Bragg grating can determine the respective range of variable dispersion compensation.
This system also may comprise static dispersion element, and it comprises the speed of on average warbling corresponding to first and second gratings of fixedly dispersion measure to be compensated.
Can adopt circulator to come the route of regulation light signal.One embodiment comprises the circulator of four-way, this circulator has the input port that couples light to reception Polarization Control signal, couple light to and controller output signal is transferred to differential off-delay line and receives first belt again mouthful that this delay line is exported, the delay line output signal is transferred to second tuned cell and goes in ring again mouthful with coupling light to, and fill the delivery outlet that is coupled to the transmission final output signal to second of the second tuned cell output signal.
In another one exemplary embodiment, first tuned cell and second tuned cell comprise and are coupled to the polarization beam splitter that receives the signal be subjected to Polarization Control, here, this separator is being subjected to the Signal Separation of Polarization Control to become first polarized component and second orthogonal polarization components.First waveguide is optically coupled to and receives first polarization signal, this first waveguide have be tuned to this first polarization signal of reflection and the first non-linear chirp grating with first reference reflection point.Second waveguide is optically coupled to and receives second polarization signal, this second waveguide have be tuned to this second polarization signal of reflection and the second non-linear chirp grating with second reference reflection point.First tuner simultaneously tuning first and second gratings the two, second tuner then with irrespectively tuning second grating of first grating.Compensator can have static dispersive compensation element, and wherein the speed of on average warbling of first and second gratings is corresponding to the amount of fixedly chromatic dispersion to be compensated.
In this embodiment, single order polarization mode dispersion compensating element, comprises second tuner and second grating, and the single order polarization mode dispersion by obtain with the tuning dividually second non-linear chirp grating of first grating, second order polarization mode dispersion compensation and variable dispersion compensating element, comprise first and second gratings and first tuner, variable dispersion compensation and higher-order polarization mode dispersion compensate then to be obtained by tuning first and second gratings as one man.
In another embodiment, higher order dispersion compensator comprises the dispersion compensator that is coupled to receiving inputted signal; Couple light to the phase-modulator of this dispersion compensator, wherein this phase-modulator sends warbling of part selectively; And the dynamic dispersion element that is coupled to this phase-modulator signal of reception.This is adjustable the dynamic dispersion element comprises have be tuned to reflection this be subjected to the first non-linear chirp grating of the signal of Polarization Control, and have first waveguide of first reference reflector; And first tuner of tuning this first grating.
This compensator can comprise and couples light to judgement by the signal of optical grating reflection and the signal analyzer of control signal to tuner correspondingly is provided.This signal analyzer also can provide control signal to arrive phase-modulator.
This waveguide is exemplary optical fiber.In specific embodiment, this waveguide can be that the light single mode is kept polarization (PM) optical fiber, polarizing (PZ) optical fiber, and/or make the optical fiber of certain shape.
This compensator can be the compensator that adapts to, and it also comprises the signal analyzer that control signal one of is provided in the tuner at least.
This dispersion compensator can be at least partially integrated in the integrated optics chip such as lithium niobate.This waveguide can be a channel waveguide.Another tuner can be used acoustics, calorifics, electrical-optical, or the method for mechanics is come tuning grating.
A kind of being used for compensates single order polarization mode dispersion signal the compensation method of the higher-order dispersion of incident light signal of communication according to the present invention; The second order polarization mode dispersion signal is compensated; And the step of the variable dispersion signal being done compensation.In addition, this method can comprise the step of solid tame chromatic dispersion being made the polarization of compensation and control incoming signal.After compensation process, can monitor this signal, and according to monitoring the degree of regulating compensation.
The step of single order polarization mode dispersion signal being done compensation can comprise the polarization of controlling this signal; This Signal Separation is become first and second orthogonal polarization components; In fixing linear chrip grating, reflect this first polarized component; In tuned linear chrip grating, reflect this second polarized component; And the step that reconfigures this first and second polarized component.
The step of the signal of second order polarization mode dispersion being done compensation can be included in the step that reflects this signal in the tuned non-linear chirp grating.
In a certain embodiments of the present invention, this method comprises the steps:
The polarization state of regulating the communicate optical signal of incident makes the basic attitude of polarization of signal of communication be registered to the basic attitude of polarization of compensator system exactly;
Signal of communication is separated into the basic attitude of polarization of first and second quadratures at burble point;
First attitude of polarization state is transferred to first waveguide with first non-linear chirp grating, and this grating has first reference reflection point;
Second attitude of polarization state is transferred to second waveguide with second non-linear chirp grating, and this grating has the figure of warbling that is similar to first chirp grating substantially, and has second reference reflection point;
By changing along the position of first and second pips of grating, adjustable ground changes the chromatic dispersion of first and second reflections;
Adjustable ground changes corresponding optical path length between first and second pip and the burble point and compensates polarization dispersion between first and second orthogonal states of polarization; And
First and second polarization states are reassembled into output signal.
This method also comprises the step to the quality of output signals sampling.Adopt this quality reading, the present invention can comprise the steps:
Adapt to that the polarization state of incoming signal is regulated on ground and with respect to the optical path length of second pip of burble point, the quality of response output signal and the single order polarization mode dispersion is compensated, and/or
Adapting to ground regulates with respect in first and second pips of burble point one or two, so that the chromatic dispersion in signal is compensated.
Changing before the step of the optical path length of second pip adjustablely, at least in the grating can regulate like this, makes that second pip is on a desirable point, for example, as first pip, from substantially the same optical path length of burble point or different optical path lengths.Its difference can be selected according to the polarization dispersion of an expectation between first and second orthogonal polarisation state.
At another embodiment that is used for the higher-order dispersion of communicate optical signal is done the method for compensation according to the present invention, this method comprises the following steps:
Signal of communication is separated into the basic polarization state of first and second quadratures,
First polarization state is transferred to the first high birefringence fiber waveguide with first linear chrip grating, and this first fiber waveguide has first pip at the first optical path length place;
Second polarization state is transferred to the second adjustable high birefringence fiber waveguide with second linear chrip grating, and this second fiber waveguide has second pip at the second optical path length place;
This first and second polarization state is reassembled into output signal;
This output signal is transferred to the 3rd high birefringence fiber waveguide with non-linear chirp grating, and wherein this grating has a pip;
Adjustable ground changes second optical path length of the second linear chrip grating, so that the polarization dispersion between first and second orthogonal polarisation state is compensated; And
Adjustable ground changes light path in the 3rd grating so that the higher-order dispersion in output signal is compensated.
Second chirp grating can have the figure of warbling that is substantially similar to first chirp grating, and this second grating has the same with first pip basically at second pip on the identical optical path length of burble point.Again, can be to output signal sampling, the optical path length of the polarization state of incoming signal and second pip can respond the quality of output signal and regulate.
The accompanying drawing summary
Fig. 1 is to part schematic flow sheet dynamic according to the present invention, the higher-order dispersion compensation method;
Fig. 2 is the representative schematic diagram of first embodiment of, higher-order dispersion compensation system dynamic according to the present invention;
Fig. 3 is the representative schematic diagram of second embodiment of, higher order dispersion compensator dynamic according to the present invention; And
Fig. 4 is the representative schematic diagram of the 3rd embodiment of, higher order dispersion compensator dynamic according to the present invention.
Detailed description of the present invention
The objective of the invention is to be used for a kind of method and a kind of system of higher-order dispersion compensation (HDC), it can make compensation simultaneously to the higher-order dispersion effect of being made up of chromatic dispersion, polarization mode dispersion, higher-order polarization mode dispersion and variable dispersion, and optical loss and equipment are on the whole reduced to minimum.Higher-order dispersion compensation is defined as and comprises the diffusing compensation of chromatic dispersion, polarization mode dispersion compensation, second order polarization mode dispersion compensation and variable dispersion compensation.
An one exemplary embodiment of the present invention relates to a kind of higher order dispersion compensator system of adaptation.This system comprises Polarization Controller, differential polarization delay unit, dynamic dispersion compensation element and fixing dispersion element.In various forms of the present invention, these work are by two, three, or four elements are finished.For example, in one embodiment, all these four work can be finished by the element that separates, and in another embodiment, all working except Polarization Control is finished by a compensating element.
Resemble the such reflection-type grating of warbling of Bragg grating (FBG) and be used to generation time delay between the polarization of quadrature.In an one exemplary embodiment of the present invention, between the polarization of quadrature, come generation time to postpone with two Chirp Bragg gratings at least, comprise warbling and the correcting value of the chromatic dispersion of the tuning level of grating simultaneously according to grating.A kind of signal analysis method is pointed out the level of concrete dispersive component, or the level of the diffusing component of institute's chromatic dispersion, and a controlling schemes will adopt this signal analysis to cause this system optimization.
Signal to be compensated can comprise the first polarization mode dispersion component, second order (and/or higher-order) the polarization mode dispersion component, variable (promptly dynamic) dispersive component, and/or static (promptly fixing) dispersive component, and/or static (promptly fixing) dispersive component.Fig. 1 is the flow chart that is used for signal is provided all steps of one exemplary embodiment of higher-order dispersion compensation according to the present invention.Incoming signal 142 Polarization Controllers 140, it is transformed into the output signal that is controlled 144 with required polarization state to any incident polarized light.This controlled output signal is gone out through total pulse distortion being reduced to minimum fixedly dispersion compensator 112.The negative dispersion amount of being introduced is relevant with the expectation connection length of progressively leading to compensator.To a plurality of embodiment that discussed, because the use of chirped fiber Bragg grating, this functional relation will be finished simultaneously with following step.
The output of signal sends by single order PMD compensator 114.Then, last signal sends by Variable Dispersion Compensator 116, and it also compensates any dynamic dispersion the compensation except any residue second order PMD is done.At last, this final output signal that has compensated 148 is subjected to signal analyse block 120 monitoring by light signal tap 118, and this module outputs to control element such as Polarization Controller 140 and suitable dispersion compensating element, 110 to control signal 128.
To vacuum wavelength is that the grating periods lambda that the light signal of λ is made strong reflection is provided by following formula:
Λ＝λ/2n???????????????????????????????(4)
Here n is the effective refractive index of waveguide.Therefore,, just can be controlled in the pip of signal pulse in the grating by control Λ (x), thus the may command propagation time.And, pass to from the cycle be the be reflected chromatic dispersion of signal of the chirp grating of Λ (x), (this cycle has corresponding cyclic gradient d Λ/dx or " warbling " provided by following formula along this grating
By the periods lambda (x) of normal design and tuning this grating, people can be controlled in the chromatic dispersion that is subjected to by pulse in the grating and total delay the two.
Type that the chromatic dispersion measurement technology is used and number can according to circumstances change.Fig. 1 illustrates the three kinds of technology that adopted: DOP mensuration 122, subharmonic filtering 124, and/or frequency modulation(FM) 126.To adopting two kinds or more may be advantageous simultaneously such as the measuring technique of the subfrequency filtering of polarization monitoring degree and electricity.But, may increase the cost of compensator like this, thereby wish only to adopt a kind of technology.The modification technology of shown other measuring technique or these technology may be advantageous.Some example is: laterally filtering; The DOP mensuration that has scanning filter; Or the direct inspectional analysis or the digital communication analyzer of use bit error rate tester.The two all can be used for analytic signal suitably feedforward and rear feed measuring technique.
Can combine to obtain extra functionality with various feed forward methods or with the phase modulated compensation method from some compensating element, of embodiment shown in Fig. 1.
Fig. 2 is the schematic diagram of first embodiment of higher-order bucking-out system 200 according to the present invention, and 2nd order chromatic dispersion herein is to do compensation by the compensating element, that separates with 1st order chromatic dispersion.Signal of communication 242 enters this system by Polarization Controller 240, and wherein the polarization state of incoming signal 242 was corrected.
Then, last controller input signal 244 is gone out by first circulator 250.Circulator 250 has the input port of being coupled to reception controller output signal 244, couple light to controller output signal is transferred to and comprise, (in this example), the going in ring again mouthful of the single order PMD of differential delay line 260 and static chromatic dispersion compensation element (and return path is provided for this reflected signal), and be coupled to the delivery outlet that reflected signal 246 is transferred to another circulator 252.
Signal is being reflected corresponding to the grating 274 of signal wavelength and the pip place of 284 inside.This o'clock, available tuner 286 tuning gratings 184 in second waveguide 282 changed.
Tuning 286 can be by changing optical grating element effective period regulate long-distance changeably with respect to the light path of one or two reference point of burble point with the reference reflection point that changes signal.The device that is used for the tuned light grid cycle can comprise: apply axial mechanics tension force to uphold or the compression grating, apply electric field and control grating index with electrical-optical, apply heat and control grating index with heat-light, or adopt other known in the art tuner such as method (for example, by upholding or the compression grating) with acoustics and/or mechanics.
After reflection, when signal is got back to circulator 250, to compensate this moment to single order PMD, this is because the optical path difference between these two optical grating reflection points, with fixing chromatic dispersion is compensated because these two gratings have the predetermined chirp rate corresponding to fixedly dispersion measure to be compensated.Therefore, the average chirp rate of first grating 274 and second grating 284 determines the fixedly amount of dispersion compensation.
In this one exemplary embodiment, first grating and second grating the two all have substantially the same reflection to distribute and substantially the same chirp rate; And first and second reference reflection point basically at identical optical path length place.
Perhaps, by and before a tuner regulates, first reflection of first grating can than second pip on the short or long optical path length of the burble point of beam splitter.With respect to the initial position (that is, the optical path length of this section) of first and second reference reflection point of burble point, can should be as finishing to specific.In the application of the expectation DGD that is no more than the tuner scope, the one the second reference reflection point can be at the optical path length place substantially the same with respect to burble point.Perhaps, a certain reference reflection point can be departed from (can have different optical path lengths) so that single order PMD all or part is made compensation.
The parts that the present invention is different can be integrated into such as lithium niobate (LiNbO
3) one on the chip comprise the integrated optical device of birefringent waveguide.In one embodiment, Polarization Controller and differential delay are integrated into single LiNbO
3Chip on.In another embodiment, can be integrated into single LiNbO to polarization dispersion compensator in wavelength division multiplexing (WDM) system from adjacent channel
3Chip on.Obviously, also can adopt integrated optical device based on other material system.
So signal 246 comes out by second circulator 252, it is to from variable dispersion, and the signal after 264 reflections of higher-order pmd compensator provides the path of recurrence.Compensator 264 comprises the 3rd delay element 290, and it comprises the waveguide 292 that contains the 3rd tuned grating 294.In this example, grating 294 is non-linearly sent warbles.
Exemplarily, waveguide 272,282 and 292 is the optical fiber of single mode.In an one exemplary embodiment, these optical fiber are the optical fiber of keeping polarization.By using tuner 296 tuning gratings 294 suitably, (such as by applying tension force or temperature gradient) will the two all does dynamic compensation to variable dispersion and higher-order polarization mode dispersion.Must consider that the mean dispersion of being inducted by non-linear chirp grating 294 is adjusted in the chirp value of linear chrip grating 274 and 284 in the section of back.So the scope of the value of warbling will determine the relevant range of variable dispersion compensation in the non-linear chirp waveguide optical grating.
Since write different warble and the grating of bandwidth in flexibility, shown in three optical grating constructions can make the loose amount of compensation of PMD, chromatic dispersion and variable dispersion that a scope is very flexibly arranged, and don't change configuration.
With reference to figure 2, can be coupled to the delivery outlet of circulator to optical axis head coupler so that the sampling of output signal is provided to analyzer 220 again.The quality of 220 pairs of delay line output signals of analyzer is assessed, and control signal offered compiles shake controller and differential polarization delay unit.Control signal 228 from the signal analyse block 220 that output signal 248 is sampled passes to Polarization Controller 240, is used for the tuner of linear chrip waveguide optical grating 284 and tuned non-linear frequency-modulated wave guide grating 294.As above-mentioned, preferable detection method can according to circumstances be decided.
The configuration of the dispersive compensation element in Fig. 2 is exemplary.For example, people can be placed on single order PMD/ to variable dispersion/higher-order PMD compensator fixedly before the dispersion compensator 260.If this tuned non-linear chirp waveguide optical grating is to have write the Fiber Bragg Grating FBG (FBG) of keeping polarization fiber (PMF), by because the single order PMD that added compensation, people also can use the second Polarization Controller (not shown) to reach higher functionality before variable dispersion/higher-order PMD compensator 264.Also have, the circulator of available single four ports replaces the circulator 250 and 252 of two three ports, can save an element.
Another compensator 300 shown in Figure 3, it can finish dynamic higher-order dispersion compensation.In compensator 300, signal at first passes through fixedly dispersion compensator 312, makes and has only single order PMD and higher-order dispersion component (second order PMD and variable dispersion) keeping.So it is gone out through single order and second order PMD and dynamic dispersion compensation device that comprises phase-modulator 380 and the waveguide 392 that comprises non-linear chirp Bragg grating 394.Phase-modulator 380 is added to part signal to warble [ps/nm] on time selectively.Phase correction module 382 provides control signal 327 for phase-modulator.The purpose of phase correction module 382 is the phase place of warbling that is provided by this module and cycle and incoming signal suitable phase place and cycle are aimed at, for example the signal of a nrz encoding.So this chirp signal is gone out through circulator 350, and enters the waveguide 392 that comprises non-linear chirp Bragg grating 394.Non-linear chirp Bragg grating 392 is tuning by tuner 396, makes it have normal chromatic dispersion [ps/nm] level.The combination that is applied to the chromatic dispersion of warbling and being given by tuned grating 394 of part signal will have the effect at compression pulse edge on time, thereby any remaining and/or higher-order dispersion component is compensated.
After Bragg grating 394 returns, signal 348 leaves circulator 350 for belt again mouthful by an output, and is taken a sample by signal analyse block 320.Signal analyse block 320 supplies to tuner 396 to suitable control signal to adapt to the tuning non-linear chirp grating 394 in ground.Because the combination of the element (non-linear chirp FBG) of phase-modulator and chromatic dispersion is made compensation to all types of chromatic dispersions, so be the subharmonic filter to the exemplary candidate of signal analysis.Equally, be receiving terminal to the example location of this penalty method, from the electrical representation signal tap to occurring here at attachment.Down, will be a receiver after circulator 350 on this occasion, make that signal 348 will be the signal of telecommunication rather than light signal.
This method can be used in conjunction with other element.For example, can connect together use to single order PMD compensator and compensator 300 to reduce polarization dispersion to be compensated.This should be very favorable connecting together when reducing the necessary compensation range of dynamic higher order dispersion compensator with high PMD.
Another interchangeable embodiment of Fig. 3, the two optimizes the composite behaviour that is added to chromatic dispersion on the warbling of signal and that be subjected to by tuner in grating will to have signal analyse block 320 to control tuned grating 392 and phase correction module 380.
Another one exemplary embodiment will adopt no static chromatic dispersion compensation element 312 or adopt one basically to the suitable value more or less of the fixed compensation of static chromatic dispersion compensation element 312.If like this, can be adjusted to normal level to the relevant range of adjustable chromatic dispersion element 394 so that all dispersion term are compensated.In other words, can be adjusted to adjustable chromatic dispersion element 394 fixing and variable chromatic dispersion is done compensation and can be transferred to phase-modulator 380 phase place of having added and the combination of dispersion element 394 can be compensated the chromatic dispersion of remainder.This may give whole bucking-out systems with many more flexibility and scope in compensation program.
Another one exemplary embodiment will have the non-linear tuning grating 394 in the high birefringence waveguide that has been written to the optical fiber of for example keeping polarization, and comprise that also Polarization Controller enters the polarization of the signal of non-linear chirp grating 394 with control.This embodiment may be implemented in previously described two kinds of methods a kind of usefulness or without static chromatic dispersion compensation element 312.The static chromatic dispersion compensation element 312 that occurs under the occasion of Polarization Control and non-linear chirp Xi Lage grating combination can be used to all or part single order polarization mode dispersion are compensated.Fixedly dispersion element 312 will compensate the fixedly chromatic dispersion that occurs in incoming signal.So the combination of the instantaneous value of phase-modulator and chromatic dispersion can optimised next dispersive component to remainder compensate.Under static chromatic dispersion compensation element 312 absent variable occasions, also will comprise fixedly dispersion term to remaining item to be compensated by phase modulated and dispersion element combination.
Fig. 4 illustrates another embodiment of the bucking-out system 400 according to the present invention.System 400 is convenient to make the higher-order dispersion compensation notion integrated with less level.Input signal 442 enters system 400 by Polarization Controller 440, and this controller converts the signal state of polarization of incident to the signal 444 with required polarization state.After signal 444 was gone out by the mouth that goes in ring again of circulator 450, it was optically coupled to the beam splitter/combiner 462 of Delay Element 460.This Delay Element also comprises first delay element 470 and second delay element 480.Signal 444 is separated into the component of its quadrature, and each component is transferred to the delivery outlet of splitter/combiner 462.These two signals crossed first delay element 470 and second delay element 480 simultaneously, first delay element comprises that first waveguide 472 that comprises the first non-linear chirp grating 474 then comprises second waveguide 482 that comprises the second non-linear chirp grating 484 with second waveguide, 482, the second delay cells 480 that comprise the second non-linear chirp grating 484.
First grating 474 and second grating 484 have the tuner 490 of controlling these two gratings simultaneously.Second grating 484 has the additional tuner 492 of independent tuning grating 484.Fixedly dispersion compensation is to finish by the correct mean value of warbling is write non-linear chirp waveguide optical grating 474 and 484.It is by as one man tuning 474 and 484 that variable dispersion compensation and higher-order PMD compensate, and for example, the temperature of both same amounts that changes them only obtains.Single order PMD compensation is by the tuning second non-linear chirp grating 484 dividually, for example by making it be in that stress obtains.Can adopt tuning type to be not limited to temperature or stressed tuning, and each all can be used for a harmonic tuning or separately tuning.
After optical grating reflection, the signal 446 that has compensated is reconfigured by polarization separator combiner 462, and continues to turn back to the delivery outlet of this circulator by circulator 450 at once.An one exemplary embodiment of the present invention can comprise light tap coupler 452, and in the signal analyse block 420 of circulator 450 back.According to selected detection method with whether adopt the feedforward or the algorithm of rear feed, tap coupler 452 can be placed on the different place of system.Signal analyse block 420 is provided to tuner 490 and 492 to control signal 428, and to Polarization Controller 440.
Above-mentioned method and system may cause the fixedly chromatic dispersion of a small amount of residue of inducting between two polarized components of signal.For a spot of single order PMD, this is receptible mostly, as based on shown in below the calculating in the example system of Fiber Bragg Grating FBG.
| Fixing dispersion measure: | ????700ps/nm |
| The variable dispersion amount: | -500ps/nm arrives+500ps/nm |
| Actual chirped grating scope: | 200ps/nm is to 1200ps/nm (or 50pm/mm to 8.33pm/mm cycle warble) |
| Grating length (example): | 1 meter |
| The unit length rapid change of warbling: | The every cm of 10ps/nm |
| DGD scope (example): | 100ps (or the 1cm pip changes) |
| The every DGD maximum magnitude of chirped grating rapid change | ????10ps/nm |
In an example system, if (PMD (DGD) is that maximum expected value is 100ps to the incident single order, and then the grating of above-mentioned design can preferentially add the residual dispersion of 10ps/nm between the pairwise orthogonal polarized component of signal.Because Mike's Si prestige that PMD has in time distributes, if make that maximum expected value is 100ps, the actual amount branch that most of time is seen is less, so this amount should be low more usually.And, increase grating length or change design, otherwise can further reduce this quantity.Above structure will cause being used for making a kind of very flexible, the low-loss method of compensation to any kind chromatic dispersion or in tight any combination of the factor chromatic dispersion type of mode.
In the one exemplary embodiment of Fig. 4, waveguide 472 and 482 is to be made by the optical fiber of keeping polarization.In an interchangeable embodiment, can be integrated in this waveguide on the integrated optics chip such as lithium niobate chip.In addition, being attached in the integrated optics chip, may be good such as more bucking-out system parts such as more bucking-out system device/combiner 462 such as polarization splitter/combiner 462 and Polarization Controller 440 and Polarization Controllers 440.Can be placed on Polarization Controller 440 on the position between circulator 450 and the polarization splitter/combiner 462 the interchangeable configuration of Fig. 4.This will make things convenient for certain or all these parts to integrate on the optical chip together.For example, an one exemplary embodiment can be Polarization Controller 440, and polarization splitter/combiner 462 and waveguide 472 and 482 are integrated in a substrate.
Technical staff in the art will understand the present invention and can be used in all optical application that need the higher-order compensation.Although the present invention has used the reference of preferable all embodiment is described, the present invention can realize with other concrete form in the case without departing from the scope of the present invention.Therefore, it only is exemplary will be appreciated that here all embodiment that describe and illustrate of institute, can not be thinking limitation of the scope of the invention.Can make other variation and modification according to the scope of the invention.
Claims (24)
1. higher order dispersion compensator (400) that is used to regulate the Polarization Control signal, the signal of being regulated has the first polarization mode dispersion component, second rank polarization mode dispersion component and the variable dispersion component, and described compensator comprises:
A) first regulating element, the first rank polarization mode dispersion component of adjusting Polarization Control signal; With
B) second regulating element, second rank polarization mode dispersion component and the variable dispersion component of adjusting Polarization Control signal.
2. dispersion compensator as claimed in claim 1 is characterized in that, first regulating element and second regulating element comprise:
A) polarization beam splitter (462), its coupling receives Polarization Control signal, therein polarization beam splitter with the Polarization Control Signal Separation in first polarizer and the second cross-polarization element;
B) first waveguide (472), optical coupling receives first polarization signal, and first waveguide has the first non-linear chirp grating (474) and first reference reflection point of accommodation reflex first polarization signal;
C) second waveguide (482), optical coupling receives second polarization signal, and second waveguide has the second non-linear chirp grating (484) and second reference reflection point of accommodation reflex second polarization signal;
D) first tuner (490) is regulated first and second gratings simultaneously; With
E) second tuner (492) is independent of first grating and regulates second grating.
3. dispersion compensator as claimed in claim 2, the Polarization Control signal also comprises fixedly chromatic dispersion polarized component, this compensator comprises fixedly chromatic dispersion polarizer, wherein compensation and the fixedly speed of on average warbling of corresponding first and second gratings of dispersion measure.
4. dispersion compensator as claimed in claim 2, it is characterized in that, the first rank polarization mode dispersion compensating element, comprises second tuner and second grating, and obtains the first rank polarization mode dispersion compensation by regulating the second non-linear chirp grating separately with first grating.
5. dispersion compensator as claimed in claim 2, it is characterized in that, the second rank polarization mode dispersion compensation and variable dispersion polarization compensation element comprise first and second gratings and first tuner, and obtain variable dispersion polarization compensation and the compensation of higher-order polarization mode dispersion by as one man regulating first and second gratings.
6. dispersion compensator as claimed in claim 2 is characterized in that compensator is an adaptive compensator, and also comprising provides control signal to arrive the signal analyzer of one of tuner (420) at least.
7. dispersion compensator as claimed in claim 2 is characterized in that waveguide is an optical fiber.
8. dispersion compensator as claimed in claim 2 is characterized in that, waveguide is the single mode polarization-maintaining fiber.
9. dispersion compensator as claimed in claim 2 is characterized in that, waveguide is the single mode polarization fiber.
10. dispersion compensator as claimed in claim 2 is characterized in that, waveguide is the optical fiber of certain shape.
11. dispersion compensator as claimed in claim 2 is characterized in that, grating is an optical fiber Bragg optical fiber.
12. dispersion compensator as claimed in claim 2 is characterized in that dispersion compensator is at least partially integrated in the integrated optics chip.
13. dispersion compensator as claimed in claim 2 is characterized in that, waveguide is the channel waveguide in the integrated optics chip.
14. dispersion compensator as claimed in claim 13 is characterized in that, integrated optics chip is a lithium niobate chip.
15. dispersion compensator as claimed in claim 2 is characterized in that, separator be will reflection separation/composite set of reconfiguring of first and second polarizers.
16. dispersion compensator as claimed in claim 2 is characterized in that, first grating and second grating all have essentially identical reflection external form and essentially identical chirp rate; And first and second reference reflection point are on the identical optical path length substantially.
17. dispersion compensator as claimed in claim 2 is characterized in that, before being regulated by tuner, first pip of first grating is in from the short optical path length of ratio second pip of burble point.
18. dispersion compensator as claimed in claim 2 is characterized in that tuner applies mechanical tension to optical fiber.
19. dispersion compensator as claimed in claim 2 is characterized in that, tuner comprises the device of acoustics, heat, electrical-optical or mechanical adjustment grating.
20. dispersion compensator as claimed in claim 2 is characterized in that, at least one rice of first and second grating measurings.
21. be used to regulate the higher-order compensator of random polarization signal, this compensator comprises:
A) Polarization Controller is transformed into the Polarization Control signal with required polarization state with the incident light of random polarization; With
B) compensator as claimed in claim 2.
22. the adaptability higher order dispersion compensator is characterized in that, comprising:
A) Polarization Controller converts the random polarization incident light to the Polarization Control signal with required polarization state;
B) differential higher-order delay line, optical coupling receives the Polarization Control signal, and this delay line comprises:
I) polarization beam splitter, coupling receives the Polarization Control signal, and polarization beam splitter becomes first polarization signal and second orthogonal polarization signals with the Polarization Control Signal Separation herein,
The ii) first nonlinear fiber Chirp Bragg grating, coupling receives first polarization signal,
The iii) second nonlinear fiber Chirp Bragg grating, coupling receives second polarization signal,
Iv) first tuner is regulated first grating independently,
V) second tuner, as one man regulate two gratings and
Vi) composite set is exported the orthogonal polarization signals recombinant of two reflections to delay line; And
C) signal analyzer couples light to sampling delay line output, wherein analyzer computing relay line output signal and control Polarization Controller and tuner.
23. the adaptability higher order dispersion compensator is characterized in that, comprising:
A) Polarization Controller converts the random polarization incident light to the Polarization Control signal with required polarization state;
B) differential higher-order delay line, optical coupling receives the controller output signal from Polarization Controller, and this delay line comprises:
I) polarization beam splitter, having coupling receive controller output signal output, burble point, first and second outputs, this is in the burble point controller output signal and is separated into first and second orthogonal polarization signals, first and second polarization signals are guided to first and second outputs respectively
Ii) first waveguide, optocoupler merge aims at first output, and first waveguide has the first non-linear chirp grating of accommodation reflex first polarization signal and has first reference reflection point,
Iii) second waveguide, optocoupler merge aims at second output, and second waveguide has the second non-linear chirp grating of accommodation reflex second polarization signal and has second reference reflection point,
Iv) first tuner comprises first and second tuners, all is coupled to first and second gratings, and tuner is regulated two gratings with essentially identical amount here,
V) second tuner comprises second tuner, and wherein second tuner is regulated one of grating independently,
Vi) composite set is exported the orthogonal polarization signals recombinant of two reflections to delay line; And
C) signal quality analyzer couples light to sampling delay line output, wherein the quality of analyzer computing relay line output signal and provide control signal to arrive Polarization Controller and differential delay line.
24. a higher order dispersion compensator that is used to regulate the Polarization Control signal, the signal of being regulated has the first polarization mode dispersion component, and second rank polarization mode dispersion component and the variable dispersion component is characterized in that this compensator comprises:
A) coupling receives the polarization beam splitter of Polarization Control signal, and wherein polarization beam splitter is first polarized component and second orthogonal polarization components with the Polarization Control Signal Separation;
B) first fiber waveguide, optical coupling is to receive first polarization signal, and first waveguide has adjusting to reflect the first non-linear chirp grating and first reflection reference point of first polarization signal;
C) second fiber waveguide, optical coupling is to receive second polarization signal, and second waveguide has second non-linear chirp grating and second reflection reference point of adjusting with reverse second polarization signal;
D) first tuner is regulated first and second gratings simultaneously; With
E) second tuner is independent of first grating and regulates second grating.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US34496501P | 2001-12-31 | 2001-12-31 | |
| US60/344,965 | 2001-12-31 | ||
| US10/323,301 US6829409B2 (en) | 2001-12-31 | 2002-12-18 | Method for higher-order dispersion compensation |
| US10/323,301 | 2002-12-18 | ||
| US10/323,952 US7016567B2 (en) | 2001-12-31 | 2002-12-18 | System for higher-order dispersion compensation including a delay line |
| US10/323,952 | 2002-12-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN1659809A true CN1659809A (en) | 2005-08-24 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 02826430 Pending CN1659809A (en) | 2001-12-31 | 2002-12-19 | System for higher-order dispersion compensation including a delay line |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1461880A2 (en) |
| CN (1) | CN1659809A (en) |
| AU (1) | AU2002358259A1 (en) |
| WO (1) | WO2003058857A2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7454092B2 (en) | 2006-10-24 | 2008-11-18 | Kailight Photonics, Inc. | Systems and methods for polarization mode dispersion mitigation |
| US20080095538A1 (en) | 2006-10-24 | 2008-04-24 | Kailight Photonics, Inc. | Optical transponders with reduced sensitivity to polarization mode dispersion (PMD) and chromatic dispersion (CD) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6647180B2 (en) * | 2000-09-21 | 2003-11-11 | Teraxion Inc. | Tunable optical dispersion by using two fiber Bragg gratings with nonlinear group delays |
| US6271952B1 (en) * | 1998-08-18 | 2001-08-07 | Nortel Networks Limited | Polarization mode dispersion compensation |
| DE19903523A1 (en) * | 1999-01-29 | 2000-08-03 | Ernst Brinkmeyer | Delay system for an optical transmission system includes Bragg grating with variable positioning |
| US6658215B1 (en) * | 1999-09-24 | 2003-12-02 | Fitel Usa Corp. | Arrangement for mitigating first order and second-order polarization mode dispersion in optical fiber communication systems |
| US20010028760A1 (en) * | 2000-03-03 | 2001-10-11 | Yaffe Henry H. | Methods and apparatus for compensating chromatic and polarization mode dispersion |
-
2002
- 2002-12-19 CN CN 02826430 patent/CN1659809A/en active Pending
- 2002-12-19 AU AU2002358259A patent/AU2002358259A1/en not_active Abandoned
- 2002-12-19 WO PCT/US2002/040959 patent/WO2003058857A2/en not_active Application Discontinuation
- 2002-12-19 EP EP02792497A patent/EP1461880A2/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP1461880A2 (en) | 2004-09-29 |
| WO2003058857A3 (en) | 2003-10-16 |
| WO2003058857A2 (en) | 2003-07-17 |
| AU2002358259A1 (en) | 2003-07-24 |
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