CN101252396B

CN101252396B - Adjustable multi-order polarization module color dispersion emulator

Info

Publication number: CN101252396B
Application number: CN2008100445033A
Authority: CN
Inventors: 闫连山; 潘炜; 罗斌
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2008-04-02
Filing date: 2008-04-02
Publication date: 2010-08-18
Anticipated expiration: 2028-04-02
Also published as: CN101252396A

Abstract

The invention discloses an adjustable multi-order polarization mode dispersion emulator which realizes the emulations of the single-order and the multi-order polarization mode dispersion. The optical combination comprises at least an optical unit which is composed of the combination of an optical birefringence element and a polarization rotator pair; the birefringence elements and the polarization rotator pair are in staggered arrangement along the optical axis; the polarization rotator pair is composed of at least two saturated polarization rotators whose angels can be rotated. Two or more than two polarization rotators between the birefringence elements are rotated with different fixed angels to generate adjustable single-order or second-order polarization mode dispersion which is applied to the emulation or compensation of the polarization mode dispersion.

Description

Adjustable multi-order polarization module color dispersion emulator

Technical field

The present invention relates in fiber optic communication field emulation and compensation to polarization mode dispersion.

Background technology

To high performance optical fiber telecommunications system, when the speed of transmission surpasses 10-Gb/s, (Polarization ModeDispersion, PMD) caused degradation effects becomes the subject matter of system in the polarization mode dispersion that components and parts had in optical fiber itself and the transmission link.In general, polarization mode dispersion is because the fibre core of optical fiber itself is not desirable circle, thereby causes when light signal during along Optical Fiber Transmission two polarized component institute transmitting speed differences.After through a segment distance, produce relative delay between two polarized components.The polarization mode dispersion effect of this single order is referred to as Differential Group Delay (Differential Group Delay).On the other hand, because other factor causes the generation of high-order polarization mode dispersion effect, can further worsen signal.(Second-order PMD, simple understanding SOPMD) can be thought to cause producing with the relevant Differential Group Delay of wavelength to the second order polarization mode dispersion.

Because the importance of polarization mode dispersion, not only need research that it is compensated, and need in actual experiment, carry out emulation.The necessity of emulation mainly is because the optical fiber that has a big polarization mode dispersion value all has been laid on real system to have suffered, and the state that can not wait as long for optical fiber itself in the experiment variation fast takes place is simulated polarization mode dispersion.Therefore, provide the emulation of polarization mode dispersion and compensation arrangement to have very important Practical significance.

Polarization mode dispersion emulator (in general at present, simulator also can be used as compensator greatly, therefore, we mainly discuss simulator) comprise several structures: adopt birefringece crystal and magneto-optic shutter realize adjustable single order PMD emulation (L.-S.Yan, et al, " Programmable groupdelay module using binary polarization switching; " J.Lightwave Technol., vol.21, no.7,2003); Adopt the multistage polarization maintaining optical fibre to be equipped with the multistage PMD emulation (R.Khosravani of intermediate polarisation controller coupling, et al, " Time and frequency domaincharacteristics of polarization-mode dispersion emulators; " IEEE Photon.Technol.Lett., vol.13, no.2,2001); Micro-heater change phase place reaches PMD emulation (M.C.Hauer on the polarization maintaining optical fibre of employing multistage fixed coupling, et al, " Electricallycontrollable all-fiber PMD emulator using a compact array of thin-filmmicroheaters; " J.Lightw.Technol., vol.22, no.4,2004); Adopt the high accuracy phase control to produce PMD (J.N.Damask, et al, " Demonstration of a coherent PMDsource, " IEEE Photon.Technol.Lett., vol.15, no.11,2003); And adopt a plurality of adjustable single order DGD simulators to form the adjustable PMD simulator (L.-S.Yan of high-order, et al, " Polarization-mode-dispersion emulator using variable differential groupdelay (DGD) elements and its use for experimental importance sampling; " J.Lightwave Technol., vol.22, no.3,2004).

Above structure adopts the mode of birefringence element and Polarization Controller or single polarization rotator, and the problem of existence comprises: perhaps be unsuitable for doing compensator; Perhaps speed is too slow; Perhaps there is not adjustability; Perhaps repeated bad.(L.-S.Yan as previously mentioned, C.Yeh, G.Yang, L.Lin, Z.Chen, Y.Q.Shi, A.E.Willner, and X.Steve Yao, " Programmable groupdelay module using binary polarization switching, " J.Lightwave Technol., vol.21, no.7, what 2003) single polarization rotator adopted is 90 ° of anglecs of rotation, and therefore, the state (0 ° or 90 ° of rotations) that changes polarization rotator can be so that correlation between the birefringece crystal or addition (PMD increase) or disappear mutually (PMD reduces), thereby what make output is adjustable single order polarization mode dispersion (DGD just), does not have second-order effects.

Summary of the invention

In view of the above shortcoming of prior art, the objective of the invention is to design a kind of adjustable multi-order polarization module color dispersion emulator or compensator, below narration is as no special circumstances, and we are referred to as simulator.The objective of the invention is to realize by following means:

Adjustable multi-order polarization module color dispersion emulator is realized the emulation of single order and multi-order polarization module color dispersion, the light path combination comprise at least one by optical birefringence element and polarization rotator the optical unit to constituting; Birefringence element and polarization rotator are to arranging along preface between optical axis; Described polarization rotator constitutes the saturation type polarization rotator by at least two angle rotatables.

With the same part that also adopts birefringence element (as birefringece crystal or polarization maintaining optical fibre etc.) to constitute simulator of other design, and design different with other is that what we adopted between birefringence element is not Polarization Controller or single polarization rotator (can produce 90 ° the anglec of rotation).We adopt is the polarization rotator (or polarization switch) that two (or more than, as long as satisfy similar rotation relationship) can produce 45 ° the anglec of rotation.The characteristic that this circulator has as shown in Figure 1.Under certain drive current (or voltage) situation, its anglec of rotation reaches stable saturation condition, for example, and when drive current is lower than I ₁The time, its angle is a fixing value, electric current is low more also to be like this.And, be higher than I when the drive current increase ₂The time, it is saturated to continuing after 45 ° of polarization state of incident rotations, and increasing electric current more also is so.Adopt such saturation type polarization rotator can guarantee the value unanimity (repeatability) of each polarization mode dispersion that produces.

As shown in Figure 2, two DGD vector (τ ₁With τ ₂) (Fig. 2 a), the τ of generation addition the time _TotalSingle order PMD for linear, additive; When two DGD vectors subtract each other (Fig. 2 b), the τ of generation _TotalThe single order PMD that subtracts each other for linearity.Here it is adopts the effect of 90 ° of polarization rotators.And under the situation that adopts 45 ° of circulators, two vector superposed effects (Fig. 2 c) have just produced except single order τ _TotalOutward, the high-order that still has (being mainly second order) component, i.e. dash area among the figure.

Adopt 45 ° polarization rotator operation principle as shown in Figure 3, corresponding two intrinsic optical axises of birefringece crystal (fast axle and slow axis), the original position of polarization rotator is placed on the centre (i.e. 45 ° place) of two axles, and a polarization rotator of polarization rotator centering can produce+rotation of 22.5 ° or-22.5 °.So, in the time of two such polarization rotator cascades, such three kinds of situations will occur: (1) produces+45 ° rotation (corresponding diagram 3 when two circulators simultaneously to a direction rotation time, parallel with slow axis), perhaps-45 ° rotation (parallel) with fast axle; Corresponding diagram 2a and Fig. 2 b, such situation is exactly a first-order effects, and is the same with the purpose of the adjustable DGD simulator principle of front and realization; (2) when two circulator direction of rotation are opposite (one+22.5 °, one-22.5 °), the resultant effect of generation is not have deflection, polarization coupled still rests on the centre (45 °) of two intrinsic axles of birefringece crystal.Corresponding diagram 2c, that at this moment produce is exactly second-order effects (SOPMD).

Adopt the solution of the present invention, by the combination of different polarization rotators, we both can realize the adjustable PMD of single order completely (being DGD) emulation, can realize the emulation of corresponding second order (perhaps more high-order) PMD again as required.Because the speed of polarization rotator can very fast (as magneto-optic shutter at a high speed), such device both can be used for emulation, can be used in the real-time compensation system again.In addition, because the polarization rotator of magneto-optic class is operated in saturation condition, its repeatability is very high, and therefore the PMD simulation result that produces is also highly stable, and can repeat.

Description of drawings is as follows:

Fig. 1 is the characteristic schematic diagram of the used polarization rotator of the present invention.

Fig. 2 is single order and the vector superposed schematic diagram of second order PMD.

Fig. 3 the present invention utilizes 45 ° of polarization rotators to realize the principle schematic of adjustable PMD simulator.

Fig. 4 is exemplary block diagram of the invention process.

Fig. 5 is the application schematic diagram of the present invention as the PMD simulator.

Fig. 6 is the application schematic diagram of the present invention as the PMD compensator.

Fig. 7 is typical single order PMD (being a DGD) measurement result.

Fig. 8 is corresponding typical second order PMD measurement result.

Embodiment

The invention will be further described below in conjunction with accompanying drawing.

Fig. 4 has expressed an exemplary block diagram of the invention process.Adjustable multi-order PMD simulator 100 of the present invention is by a series of

birefringence element

102 ₁, 102 ₂102 _N+1With polarization rotator 103 _A1, 103 _B1103 _AN, 103 _BNForm, polarization rotator adopts the saturation classes magneto-optic shutter.When input optical signal 101 when an end enters simulator, first birefringence element of process is (normally along the middle one 45 ° of direction incidents of two intrinsic axles of element earlier, sometimes also before first birefringence element, add polarization rotator, but this is not principle main points of the present invention, but the fine setting of carrying out according to different situations in the practical application), through first pair of polarization rotator, enter second birefringence element more then.According to the described principle of Fig. 3, adjust two corresponding anglecs of rotation of polarization rotator, can realize the linear, additive of the DGD that first and second birefringence elements itself have or disappear mutually (remaining single order PMD, i.e. DGD), also can produce the PMD (during 45 ° of anglecs of rotation) of second order.As a same reason, a series of birefringence elements of back can be realized different single orders and the emulation (promptly adjustable) of second order PMD by different combinations with polarization rotator.It should be noted that we can so that all or part birefringence element all with 45 ° of couplings, but that realize like this is not only second order PMD, has also comprised the more component of high-order, and has calculated also more complicated, needs more consideration in practicality.We considered is only to select as far as possible wherein that one group of polarization rotator remains on 45 °, and other all is or 0 °, perhaps 90 °, the resultant effect of Chan Shenging is equivalent to two adjustable single order PMD simulators and carries out cascade (Fig. 2 c) with 45 ° coupling like this, easily control with calculate.Such design also has an other benefit: in polarization mode dispersion (PMD) compensation, especially in the two-forty system, the effect of high-order PMD (being often referred to second order PMD) also clearly, but optical compensation also lacks means.The structure that adopts us to invent can produce under the situation of same single order PMD (DGD), and PMD adjusts to second order, thereby compensation effect is further optimized.

Fig. 5 has enumerated this structure as the application of PMD simulator in system.The light signal that transmitter 201 produces enters into simulator 203 after Polarization Controller 202 is adjusted, and then enters in the Transmission Fibers link 204, at last receiver 205 place's acknowledge(ment) signals and deliver to checkout equipment 206 and carry out the PMD effect analysis again.

Fig. 6 has enumerated this structure as the application of PMD compensator in system.The light signal that transmitter 301 produces is by behind the Transmission Fibers link 302, enters into by Polarization Control and plays 303 and the PMD compensator formed of this structure 304.By control, make signal-quality optimization, and deliver in receiver 305 and the final checkout equipment 306 compensator.

Fig. 7 and Fig. 8 then are examples of test result of the present invention, we have adopted similar (L.-S.Yan, C.Yeh, G.Yang, L.Lin, Z.Chen, Y.Q.Shi, A.E.Willner, and X.Steve Yao, " Programmable group delay module using binarypolarization switching, " J.Lightwave Technol., vol.21, no.7,2003) structure in, but 90 ° of polarization switches of inciting somebody to action wherein change two 45 ° polarization rotator into, and a pair of polarization rotator is adjusted to the emulation that intermediateness realizes second order PMD by inciting somebody to action wherein.That Fig. 7 shows is the single order PMD that measures, and Fig. 8 then is corresponding second order PMD value.Can see that the single order PMD of generation no longer fixes, and the PMD of second order has been arranged.We have also further verified by different combinations, can reach under the situation that produces identical single order PMD, and second order PMD can adjust.

Claims

1. adjustable multi-order polarization module color dispersion emulator is realized the emulation of single order and multi-order polarization module color dispersion, the light path combination comprise at least one by optical birefringence element and polarization rotator the optical unit to constituting; Birefringence element and polarization rotator are to arranging along preface between optical axis; Described polarization rotator is to by at least two cascades that produce the polarization rotator of 45 ° of anglecs of rotation only, corresponding two intrinsic optical axises of birefringece crystal, the centre that the original position of polarization rotator is placed on two axles i.e. 45 ° position, and a polarization rotator of polarization rotator centering can produce ± 22.5 ° rotation.

2. the adjustable multi-order polarization module color dispersion emulator according to claim 2 is characterized in that, described polarization rotator is the saturation classes magneto-optic shutter.