CN2766258Y - Optical time domain depolarizer - Google Patents

Abstract

The utility model relates to an optical time domain depolarizer applied in optical fiber communication systems to transform transmission polarized light signals into fading polarized light signals. The utility model is characterized in that the optical time domain depolarizer comprises two 1/2 wavelength plate arrays and one 1/4 wavelength plate. The 1/4 wavelength plate is arranged between the two 1/2 wavelength plate arrays, and the two adjacent 1/2 wavelength plates at both of the two sides have opposite rotary directions. Each 1/2 wavelength plate is equal in rotary velocity, but the adjacent wavelength plates have opposite rotary directions. The 1/4 wavelength plate is two times of the 1/2 wavelength plate in rotary velocity. Crystal shafts of wavelength plate of all the wavelength plates are always perpendicular to an incidence ray during a rotary process. The utility model has the advantages that low velocity element cascade connection is adopted to remove the influence of polarization effects such as polarization dependent loss, polarization dependent gain, etc., which is favorable for reducing cost and manufacture difficulties.

Description

Light time territory depolarizer

Technical field

The utility model relates to a kind of device of realizing light signal time domain depolarization in the optical fiber telecommunications system.

Technical background

The light depolarizer is widely used in long-distance speed fiber optic communication systems and the light measurement system.Usually the light depolarizer is designed to complete light beam and partial polarization light beam are transformed into the depolarization light beam that shakes.In long-distance high speed optical communication system, because being extensive use of of broadband Erbium-Doped Fiber Amplifier (EDFA) (EDFA), when its cascade number reaches hundreds of, will the gain of light of some polarization state be reached capacity and produce polarization hole burning (PHB) effect, Raman Amplifier Gain territory inside-pumping polarisation of light directional correlation etc.In test instrumentation is made,, also need light signal is carried out depolarization for eliminating the polarization correlated Polarization Dependent Loss that produces (PDL) of some optical elements (as catoptron, grating, prism, photo-detector etc.).

Existing smooth depolarizer can be divided into spatial domain depolarization, frequency domain depolarization and time domain depolarization three major types on principle.

Light spatial domain depolarization is processed into certain angle of wedge birefringece crystal or gyrotropi crystal crystal by employing, light is passed through behind the crystal in diverse location phase differential difference or rotation angle difference, thereby the polarization state that output light is reached on the space on average realizes depolarization.This structure depolarization effect is relatively poor, so can only satisfy reducing its occasion such as polarization correlated before the not high detector of depolarization effect requirements.

Optical frequency territory depolarizer comprises the Lyot depolarizer, fiber optic loop etc., and this structural requirement input light must have certain spectral width.This structure depolarization effect is medium, generally is used for Raman Pump laser instrument depolarization, light source depolarization etc. in the optical fibre gyro.

Light time territory depolarizer then is by to input polarization state of light fast modulation, makes the SOP of output light change the identical depolarization effect that reaches of probability of occurrence of the feasible various polarization states of on average getting off within a certain period of time in time fast.This structure can be to the monochromatic light depolarization, and its depolarization effect is best, is used for the depolarization of light signal in the High Speed System more.From the implementation method branch electric accent mode and mechanical system are arranged, dividing from principle has phase modulation (PM) and optical axis rotation modulation.Wherein mainly contain following several mode: 1, use the LN waveguide of Z-cut or X-cut, after adding modulation voltage, be equivalent to a phase place or the variable wave plate of optical axis direction, the output polarization state is changed.2, earlier input light is carried out polarization spectro, to wherein one the tunnel modulating, export after closing ripple, its principle is the same with adjusting wave plate phase place.3, rotating wave plate.4, the use piezoelectric ceramics is controlled the birefringence of optical fiber (or polarization maintaining optical fibre) etc.

Territory depolarization structure of above light time in fact all is the time domain depolarizations that realize light signal by phase place that changes equivalent wave plate or optical axis direction.Wherein, comparatively typical high speed depolarization structure is that Fred Heismann is at article " CompactElectro-Optic Polarization Scramblers for Optically Amplified Lightwave Systems " (J.Lightwave Technol., vol.14, pp.1801-1813,1996) middle a kind of two 1/2 wave plates and time domain depolarization structure that the quarter wave plate structure is formed utilized of introducing.As shown in Figure 3, this structure realizes depolarization effect preferably by selecting specific wave plate rotating speed.But as shown in Figure 5, the minimum depolarization cycle of this structure remains 1.5 times of minimum speed of wave plate in the structure.As seen, though select the specific wave plate rotating speed shortcut that improves the depolarizer performance of can yet be regarded as,, still need comprehensively consider from selecting specific wave plate combined mode and rotation mode two aspects in order further to optimize the depolarization performance of depolarizer.

Summary of the invention

The purpose of this utility model provides a kind of territory depolarizer of improved light time, be applied in the optical fiber telecommunications system, to transmit polarized light signal and be transformed into the depolarization light signal that shakes, it utilizes the low speed devices cascade to realize the high speed depolarization of light signal, efficient influence of removing polarization effects such as Polarization Dependent Loss, Polarization-Dependent Gain helps reducing cost and manufacture difficulty.

The technical solution of the utility model is: territory depolarizer of a kind of light time, it is characterized in that comprising two 1/2 wave plate arrays and a quarter wave plate, quarter wave plate is placed between the two 1/2 wave plate arrays, tight two the 1/2 adjacent wave plate sense of rotation in its both sides are opposite, each 1/2 wave plate speed of rotation equates but adjacent wave plate switched in opposite, the quarter wave plate speed of rotation is the twice of 1/2 wave plate speed, and the crystallographic axis of all wave plates wave plate in rotary course is vertical with incident ray all the time.

Territory depolarizer of aforesaid light time is characterized in that two 1/2 wave plate arrays have identical wave plate number.

Territory depolarizer of aforesaid light time, the wave plate number that it is characterized in that 1/2 wave plate array is 3～7.

Territory depolarizer of aforesaid light time is characterized in that second 1/2 wave plate array can substitute with light path commutator and first 1/2 wave plate array.

Territory depolarizer of aforesaid light time is characterized in that the light path commutator is the catoptron or the prism of 180 degree commutations.

Principle of the present utility model is: the time domain depolarization that adopts two 1/2 wave plate arrays and a quarter wave plate combination realization light signal.The utility model structure has two key components: equates but array that a plurality of 1/2 wave plates of adjacent wave plate switched in opposite are formed by speed of rotation, and by such two arrays and the light time territory depolarization structure that quarter wave plate combines.Wherein, quarter wave plate is placed between the two 1/2 wave plate arrays, and tight two the 1/2 adjacent wave plate sense of rotation in its both sides are opposite, and the quarter wave plate speed of rotation is the twice of each 1/2 wave plate speed, but it turns to and can choose wantonly.And the crystallographic axis of all wave plates wave plate in rotary course is vertical with incident ray all the time.In addition, for optimizing the depolarization effect, two 1/2 wave plate arrays can be selected identical wave plate number, and the wave plate number in the array can require to select in 〉=2 according to designs, consider effect, cost and manufacturing factor, general wave plate number is selected to satisfy various request for utilizations between 3～7.

The related utility model structure of the utility model can be selected different implementations according to the difference of depolarizer manufactured materials.For example, when adopting waveguide material to realize,, can directly adopt the mode of 1/2 a wave plate array and a quarter wave plate combination because need not substantially to consider that wave plate increases and decreases the material cost problem of being brought; And when adopting crystalline material (as birefringece crystal, electro-optic crystal or magneto-optical crystal) to realize, for economical with materials, can be by adding the completely reflecting mirror that pair of orthogonal is placed behind first 1/2 wave plate array and the quarter wave plate in light path, the minute surface direction of pairwise orthogonal completely reflecting mirror is all at 45 with the light transmission direction, makes light signal more again oppositely by first 1/2 wave plate array.This can realize same depolarization effect.

The advantage of the time domain depolarizer that use the utility model relates to is:

1. adopt the high speed depolarization of the polarized light signal in the low speed devices cascade realization system, the degree of polarization of light signal is controlled at below 4% after the depolarization.Therefore the influence that can efficiently remove polarization effects such as Polarization Dependent Loss, Polarization-Dependent Gain.

2. the spectrum width of this depolarization structure depolarization effect and light signal is irrelevant, and because can utilize the low speed devices cascade to realize the high speed depolarization of light signal, helps reducing cost and manufacture difficulty.

Description of drawings

Fig. 1 is first kind of specific implementation of light time of the present utility model territory depolarizer.

Fig. 2 is second kind of specific implementation of light time of the present utility model territory depolarizer.

Fig. 3 is a kind of specific implementation of traditional light time territory depolarizer.

Fig. 4 is the depolarization design sketch of structure shown in Figure 1.

Fig. 5 is the depolarization effect of traditional time domain depolarizer shown in Figure 3.

Embodiment

For realizing the purpose of this utility model, we provide method and the implement device thereof of realizing this purpose.Further specify embodiment of the present utility model and principle of work below in conjunction with drawings and Examples:

If the Stokes form of certain passage input polarization light is in the dwdm system:

$S_{\mathrm{in}}(\mathrm{\&beta;},\mathrm{\&theta;})=\left(\begin{array}{c}{S}_0\\ S_1\\ S_2\\ {\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="Y20042005780500091.png"\; state="\{\{state\}\}">S</figure-callout>}}_3\end{array}\right)=\left(\begin{array}{c}1\\ \cos \left(2\mathrm{\&beta;}\right)\cos \left(2\mathrm{\&theta;}\right)\\ \cos \left(2\mathrm{\&beta;}\right)\sin \left(2\mathrm{\&theta;}\right)\\ \sin \left(2\mathrm{\&beta;}\right)\end{array}\right)$

Wherein, θ is the position angle of elliptically polarized light, promptly elliptically polarized light on the Poincere ball with S ₁S ₂The angle on plane, and-pi/2≤θ≤pi/2; β is the ellipticity angle ,-π/4≤β≤π/4.On time domain, because the degree of polarization of light signal (DOP) in fact refers to the r.m.s. that interior three stokes of light signal of one concrete period divide energy normalization quadratic sum after carrying out time average, promptly DOP can be expressed as

$\mathrm{DOP}=\sqrt{{\left[{\&Integral;}_0^T{S}_1\left(t\right)\mathrm{dt}\right]}^2+{\left[{\&Integral;}_0^T{S}_2\left(t\right)\mathrm{dt}\right]}^2+{\left[{\&Integral;}_0^T{S}_3\left(t\right)\mathrm{dt}\right]}^2}/\left[{\&Integral;}_0^T{S}_0\left(t\right)\mathrm{dt}\right].$

According to above-mentioned formula as can be known, the principle of light time territory high speed depolarizer time domain depolarization is exactly to make three Stokes components of light signal be divided into 0 in certain integration period T inner product.That is:

${\&Integral;}_0^T{S}_1\left(t\right)\mathrm{dt}={\&Integral;}_0^T{S}_2\left(t\right)\mathrm{dt}={\&Integral;}_0^T{S}_3\left(t\right)\mathrm{dt}=0$

Certainly, if we are by adopting certain depolarization structure, make light signal that n the point that degree of polarization is extremely low be arranged within the integration period that we select in advance, these original depolarization cycles of selecting of naming a person for a particular job are divided into n-1 depolarization subcycle again, so just can realize the depolarization acceleration by selecting the littler depolarization cycle.That is to say, compare, in this specific depolarization structure, just can obtain same depolarization performance with low speed devices more with traditional depolarization structure.

In addition, because the random polarization state in the Stokes space all can be expressed as three basic polarization states, i.e. 0 ° of linear polarization (1,1,0,0) ^T, 45 ° of linear polarization (1,0,1,0) ^TAnd circular polarization state (1,0,0,1) ^TLinear superposition, so as long as the DOP value of these three basic polarization states less than designing requirement, just can guarantee that random polarization state all can obtain effective depolarization.Further specify embodiment of the present utility model and principle of work below in conjunction with accompanying drawing:

Fig. 1 is a kind of specific implementation of the light time territory depolarizer that relates to of the utility model.Can make up the time domain depolarization that realizes light signal by array and quarter wave plate that a plurality of 1/2 wave plates are formed.Wherein, 1/2 wave plate can change the azimuth angle theta of polarized light on the Poincere ball, and quarter wave plate can be converted to circularly polarized light the line polarisation that shakes.And, adopt a plurality of 1/2 wave plate cascades can quicken rotation to azimuth angle theta.If the crystallographic axis speed of rotation of all 1/2 wave plates (being the rate of change of θ) is v, the direction of rotation of per two adjacent wave plates (" ⊙ " expression turns to vertical paper inside, and it is outside that "  " represents to turn to vertical paper).Turning to arbitrarily of quarter wave plate, but rotating speed is the twice of each 1/2 wave plate rotating speed.The crystallographic axis of all wave plates wave plate in rotary course is vertical with incident ray all the time.

Fig. 2 is second kind of specific implementation of the light time territory depolarizer that relates to of the utility model.Compared to Figure 1, many pair of orthogonal catoptrons in this structure, the minute surface direction of pairwise orthogonal completely reflecting mirror is all at 45 with the light transmission direction.By this direction of propagation to quadrature catoptron change light signal, two 1/2 wave plate arrays that experienced before and after the quarter wave plate in the structure shown in Figure 1 can adopt same 1/2 wave plate array to finish.

Fig. 3 is a kind of specific implementation of traditional light time territory depolarizer.Wherein, it is identical that light signal enters turning to of three wave plates that this depolarizer successively passes through, but rotating speed is respectively 10v/3,3v/2 and v.

Fig. 4 is when each 1/2 wave plate array in the structure shown in Figure 1 (also being structure shown in Figure 2, because Fig. 1 and the equivalence of Fig. 2 light path) is formed by 5 1/2 wave plates, the depolarization design sketch of this depolarizer.Wherein, Fig. 4 (a) turns to depolarization effect when identical when quarter wave plate in the structure shown in Figure 1 turns to its adjacent 1/2 wave plate in left side; Fig. 4 (b) turns to depolarization effect when identical when quarter wave plate in the structure shown in Figure 1 turns to adjacent 1/2 wave plate with its right side.On the one hand, can adopting more, low speed devices obtains same depolarization performance much smaller than the design cycle depolarization cycle of structure shown in Figure 1; On the other hand, comparison diagram 4 (a) and (b) as can be known, turning to the depolarization influential effect of total of quarter wave plate is very little.

Fig. 5 is the depolarization effect of traditional time domain depolarizer shown in Figure 3.As shown in Figure 5, the minimum depolarization cycle of this structure remains 1.5 times of its design cycle.

The utility model relates to a kind of improvement of optical facilities.We can realize the time domain depolarization of polarized light signal by the utility model, and the spectrum width of depolarization effect and light signal is irrelevant.Though the time domain depolarization structure that number of devices is more traditional in the related depolarization structure of the utility model is slightly many, but comparing its depolarization speed of tens of times promotes, adopt more the device of low speed just can realize and the identical depolarization effect of traditional time domain depolarization structure, so not only manufacturing cost can be reduced, and the serviceable life of depolarizer can be improved.

According to top description, make those of ordinary skills make and to use the utility model, to those skilled in the art, multiple modification of the present utility model is conspicuous, and universal principle herein can be applied to other embodiment.Therefore, the utility model is not limited to illustrated embodiment, and consistent with the wide region that meets principle described herein and feature.

Claims (5)

1, light time territory depolarizer, it is characterized in that comprising two 1/2 wave plate arrays and a quarter wave plate, quarter wave plate is placed between the two 1/2 wave plate arrays, tight two the 1/2 adjacent wave plate sense of rotation in its both sides are opposite, each 1/2 wave plate speed of rotation equates but adjacent wave plate switched in opposite, the quarter wave plate speed of rotation is the twice of 1/2 wave plate speed, and the crystallographic axis of all wave plates wave plate in rotary course is vertical with incident ray all the time.

2, light time territory depolarizer as claimed in claim 1 is characterized in that two 1/2 wave plate arrays have identical wave plate number.

3, light time territory depolarizer as claimed in claim 2, the wave plate number that it is characterized in that 1/2 wave plate array is 3～7.

4,, it is characterized in that second 1/2 wave plate array substitutes with light path commutator and first 1/2 wave plate array as claim 1 or 3 territory depolarizers of described light time.

5, light time territory depolarizer as claimed in claim 4 is characterized in that the light path commutator is the catoptron or the prism of 180 degree commutations.

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