CN102096217B - Adjustable dispersion compensation device based on liquid crystal array technology - Google Patents

Abstract

The invention relates to an adjustable dispersion compensation device based on the liquid crystal array technology, and the adjustable dispersion compensation device is composed of a fiber collimator, a polarizing beam splitter, a half wave plate, a PMD (polarization mode dispersion) compensator, a liquid crystal array and a total reflection prism which are sequentially arranged on an optical path, and is capable of realizing adjustable dispersion compensation on multiple channels. The fiber collimator comprises an input terminal collimator and a receiving terminal collimator, the polarizing beam splitter and the half wave plate cause the light incident to the liquid crystal array to be linear polarized light, and the polarization direction is parallel to the plane formed by an optical axis and an incident signal light ray; the total reflection prism is used for eliminating the deviation of a reflected signal light ray produced by adjusting the liquid crystal array on the surface of the liquid crystal array; and the PMD compensator carries out PMD compensation on signal light passing through the polarizing beam splitter and the half wave plate. In the invention, the liquid crystal array is utilized to realize dispersion control; the response speed of the device is greatly improved; the PDL (polarization dependent loss) and PMD are reduced; the structure is simple, no movable mechanical part is adopted, the performance is stable, and the reliability is high.

Description

Tunable Dispersion Compensator spare based on the liquid crystal array technology

Technical field

The present invention relates to a kind of Tunable Dispersion Compensator spare.Particularly relate to a kind of Tunable Dispersion Compensator spare based on the liquid crystal array technology that can carry out dispersion compensation to the light signal of a plurality of wavelength/passages in the dense wavelength division multiplexing system.

Background technology

Along with the high speed development of internet, the dense wavelength division multiplexing system of two-forty has become main flow.The continuous increase of system's speed has improved the requirement of system to the chromatic dispersion compensation precision, and the development of reconfigurable network also requires dispersion compensation to adjust dynamically according to the circuit situation, so the adjustable dispersion compensating technology becomes a kind of inexorable trend.

The speed of single wavelength/passage has risen to present 10Gb/s and 40Gb/s by previous 2.5Gb/s, along with the continuous lifting of speed, chromatic dispersion for the influence of system also become more obvious.Because square being inversely proportional to of dispersion tolerance and speed lifting multiple, when system's speed of 2.5Gb/s rose to 10Gb/s and 40Gb/s, its dispersion tolerance had only original 1/16 and 1/256.That is to say that when then speed rose to 10Gb/s and 40Gb/s, the dispersion tolerance of system will drop to 56km and 3.5km if speed is the dispersion tolerance of the system of 2.5Gb/s is 900km.If still adopt fixing dispersion compensation device to compensate; The fixedly dispersion compensation device that then need lay in a large amount of different numerical value is added and subtracted permutation and combination and is satisfied tens even the demand of several kilometers dispersion compensation precision, has not only increased the complexity of engineering debug but also brought extra burden to system.If adopt Tunable Dispersion Compensator spare; Not only can satisfy the demand of hundreds of kilometer dispersion measure; Also can satisfy the demand of the chromatic dispersion precision at several kilometers of zero points, both reduce the stock of various fixedly dispersion compensation device, also make things convenient for the engineering staff in system, to debug.

In addition, along with the development of network structure, reconfigurable network will become following main flow.Unexpected variation takes place in the chromatic dispersion that can cause this wavelength/passage of redistributing of reconfigurable network medium wavelength/passage; Traditional fixedly dispersion compensation device is powerless to this, and only the dispersion compensation device of reliable Fast Adjustable could satisfy the demand of reconfigurable network.

Mentioned a kind of spatial mode Tunable Dispersion Compensator spare at U.S. Pat 7039261B2 " Etalon Based Compact Dispersion Module " based on Etalon; Utilize several polarization beam apparatus (Polarization Beam Splitter; PBS) realize the cascade of several Etalon; Utilize temperature to control and realize control, realized the function of adjustable dispersion compensating the chromatic dispersion of Etalon etalon.But its complex structure needs a plurality of PBS, and need carry out dispersion adjustment through temperature control, and the time of adjusting is difficult to satisfy the requirement of Millisecond in the communication system.

Summary of the invention

Technical matters to be solved by this invention is, provides a kind of simple in structure, do not have the mobile machine parts, and stable performance has the Tunable Dispersion Compensator spare based on the liquid crystal array technology of good reliability.

The technical scheme that the present invention adopted is: a kind of Tunable Dispersion Compensator spare based on the liquid crystal array technology; Be to be arranged in order to be provided with by light path by optical fiber collimator, an inclined to one side beam splitter, half-wave plate, PMD compensating plate, first, second liquid crystal array and total reflection prism to constitute; The concrete connection is: optical fiber collimator is connected through light path with an inclined to one side beam splitter; The output light that plays inclined to one side beam splitter divides two-way to connect half-wave plate and PMD compensating plate through light path respectively; The output light of half-wave plate and PMD compensating plate is connected first liquid crystal array through light path, and the described first liquid crystal array light connects second liquid crystal array, and between first liquid crystal array and second liquid crystal array, repeatedly reflects; Said second liquid crystal array connects total reflection prism through light path; Realization is to the adjustable dispersion compensating of a plurality of passages, and wherein, described optical fiber collimator includes input end collimating apparatus and receiving end collimating apparatus; It is the line polarisation that described inclined to one side beam splitter and half-wave plate make the light that incides on the liquid crystal array, and the polarization direction is parallel to the plane that optical axis and incoming signal light constitute; Described total reflection prism makes the former road of flashlight return liquid crystal array, eliminates owing to regulating the skew on the liquid crystal array surface of reflected signal light that liquid crystal array produces with this; Described PMD compensating plate carries out the PMD compensation to the flashlight that has passed through inclined to one side beam splitter and half-wave plate.

Described a plurality of passage is the standard channel of ITU-T designated centers wavelength, or is the passage of centre wavelength with any wavelength in the device working range.

Described liquid crystal array includes first liquid crystal array and second liquid crystal array that interlaces and be arranged in parallel, and described first liquid crystal array is identical with the second liquid crystal array structure, all has the liquid crystal cells of equal number.

Described liquid crystal cells includes liquid crystal cells front-reflection face, liquid crystal cells back reflection face and the liquid crystal layer between liquid crystal cells front-reflection face and liquid crystal cells back reflection face.

Different liquid crystal cells produce different chromatic dispersion compensation quantities, and described chromatic dispersion compensation quantity is to be decided by the surface reflectivity of liquid crystal cells, optical axis direction and refractive index, and the adjusting of said chromatic dispersion compensation quantity is to realize through changing optical axis direction.

Described each liquid crystal cells surface reflectivity is to have different reflectivity and support 10 degree to decide with the film system of upper angle incident by plating at this liquid crystal cells front-reflection face and liquid crystal cells back reflection face.

Be coated with one deck on the described liquid crystal cells front-reflection face and support the semi-transparent semi-reflecting film of 10 degree with upper angle incident; Be coated with one deck on the described liquid crystal cells back reflection face and support the high-reflecting film of 10 degree with upper angle incident.

The axial change of described each liquid crystal cells surface light is to realize through changing the voltage that loads on the liquid crystal cells.

The refractive index of described each liquid crystal cells liquid crystal layer is to be decided by voltage that is loaded on the liquid crystal cells and selected liquid crystal material.

The total dispersion compensation rate of this Tunable Dispersion Compensator spare is by the chromatic dispersion compensation quantity that each liquid crystal cells the produces acquisition that adds up; The mode that adds up is that light rays reflects mutually through the liquid crystal cells on 2 parallel liquid crystal arrays, and adding up of a chromatic dispersion compensation quantity once just accomplished in wherein every reflection.

Tunable Dispersion Compensator spare based on the liquid crystal array technology of the present invention has following characteristics:

1, utilize liquid crystal array to realize chromatic dispersion control;

2, the response speed of liquid crystal array is at Millisecond, raising greatly response device speed;

3, adopt the light path design of polarization irrelevant, reduced PDL and PMD;

4, simple in structure, there are not the mobile machine parts, stable performance has good reliability.

Description of drawings

Fig. 1 is a light channel structure synoptic diagram of the present invention

Wherein (a) is front view, (b) is vertical view;

Fig. 2 is the formation and the work synoptic diagram of liquid crystal cells of the present invention

Wherein, (a) being the liquid crystal cell structure synoptic diagram, (b) is liquid crystal cells light path synoptic diagram;

Fig. 3 is the skew synoptic diagram that different electric is depressed dispersion curve;

Fig. 4 is a Tunable Dispersion Compensator spare dispersion curve synoptic diagram

Wherein, (a) being the curve of control chromatic dispersion compensation quantity, (b) is the curve of control chromatic dispersion compensation quantity centre wavelength.

Wherein:

Embodiment

Below in conjunction with embodiment and accompanying drawing the Tunable Dispersion Compensator spare based on the liquid crystal array technology of the present invention is made detailed description.

As shown in Figure 1; Tunable Dispersion Compensator spare based on the liquid crystal array technology of the present invention; Be by optical fiber collimator 11,18, play inclined to one side beam splitter 12, half-wave plate 13, PMD (polarization mode dispersion) compensating plate 14, liquid crystal array 15,16 and total reflection prism 17 and be arranged in order by light path formation is set; Realization is to the adjustable dispersion compensating of a plurality of passages, and described a plurality of passages are standard channel of ITU-T appointment, or is the passage of centre wavelength with any wavelength in the device working range.Wherein, Described optical fiber collimator includes input end collimating apparatus 11 and receiving end collimating apparatus 18; It is the line polarisation that described inclined to one side beam splitter 12 makes the light that incides on the liquid crystal array with half-wave plate 13, and the polarization direction is parallel to the plane of optical axis and incoming signal light formation; Described total reflection prism 17 is eliminated owing to regulate reflected signal light that liquid crystal array produces in the surperficial skew of liquid crystal array; The flashlight that 14 pairs of processes of described PMD compensating plate play inclined to one side beam splitter 12 and half-wave plate 13 carries out the PMD compensation.

Described liquid crystal array includes first liquid crystal array 15 and second liquid crystal array 16 that interlaces and be arranged in parallel, and described first liquid crystal array 15 is identical with second liquid crystal array, 16 structures, all has the liquid crystal cells of equal number.

Shown in Fig. 2 (a), described liquid crystal cells includes liquid crystal cells front-reflection face 31, liquid crystal cells back reflection face 32 and the liquid crystal layer 33 between liquid crystal cells front-reflection face 31 and liquid crystal cells back reflection face 32.

Different liquid crystal cells produce different chromatic dispersion compensation quantities, and described chromatic dispersion compensation quantity is to be decided by the surface reflectivity of liquid crystal cells, optical axis direction and refractive index, and when work, the adjusting of chromatic dispersion compensation quantity is to realize through changing optical axis direction.Described each liquid crystal cells surface reflectivity is to have different reflectivity and support 10 degree to decide with the film system of upper angle incident by plating at this liquid crystal cells front-reflection face 31 and liquid crystal cells back reflection face 32.Be coated with one deck on the described liquid crystal cells front-reflection face 31 and support the semi-transparent semi-reflecting film of 10 degree with upper angle incident; Be coated with one deck on the described liquid crystal cells back reflection face 32 and support the high-reflecting film of 10 degree with upper angle incident.The axial change of described each liquid crystal cells surface light is to realize through changing the voltage that loads on the liquid crystal cells.The refractive index of described each liquid crystal cells liquid crystal layer is to be decided by voltage that loads on the liquid crystal cells and selected liquid crystal material.

The total dispersion compensation rate of this Tunable Dispersion Compensator spare is by the chromatic dispersion compensation quantity that each liquid crystal cells the produces acquisition that adds up; The mode that adds up is that light rays reflects mutually through the liquid crystal cells on 2 parallel liquid crystal arrays, and adding up of a chromatic dispersion compensation quantity once just accomplished in wherein every reflection.

Principle based on the technological Tunable Dispersion Compensator spare of liquid crystal array of the present invention is following: the flashlight that comprises a plurality of wavelength transmits the back and gets into input end collimating apparatus 11 in an optical fiber; Flashlight through collimation is divided into two bunch polarisations by an inclined to one side beam splitter 12, and the polarization state of this two-beam is parallel to xz plane and yz plane respectively.Wherein, the flashlight that is parallel to the yz plane through a half-wave plate 13, makes its polarization direction rotate 90 degree and identical with the flashlight polarization direction that is parallel to the xz plane after having left inclined to one side beam splitter.Like this, before inciding 2 parallel liquid crystal arrays, played that inclined to one side beam splitter opened in 2 minutes two restraint flashlights the polarization direction all with the xz plane parallel.That a branch of flashlight of process half-wave plate 13 has not passed through a PMD compensating plate 14 simultaneously, and the PMD compensating plate can be a glass sheet here.Because after having passed through inclined to one side beam splitter and half-wave plate 13; The light path of two bundle polarized light processes is different; So here need compensate to that short a branch of flashlight of light path, make that two bundle flashlights optical path difference before inciding liquid crystal array is 0, reduce PMD with this.

Two bundle flashlights at first incide on first liquid crystal cells 21 of first liquid crystal array 15; And reflexed on first liquid crystal cells 22 of second liquid crystal array 16 by first liquid crystal cells 21; Flashlight is reflexed on second liquid crystal cells 23 of first liquid crystal array 15 by first liquid crystal cells 22 of second liquid crystal array 16 more then; By that analogy; Through the repeatedly reflection 16 of first liquid crystal array 15 and second liquid crystal arrays, last two bundle flashlights are reflected liquid crystal array by last piece liquid crystal cells of second liquid crystal array 16.

The two bundle flashlights that reflect from second liquid crystal array 16 incide liquid crystal array once more through the total reflection that places liquid crystal array total reflection prism 17 at the back; Same through the repeatedly reflection between liquid crystal array above being similar to, last two bundle flashlights are reflected liquid crystal array by first liquid crystal cells, the 21 former roads of first liquid crystal array 15.

Once reflexed on the half-wave plate 13 by liquid crystal array once more through a branch of flashlight of half-wave plate 13, its polarization direction rotated once more 90 degree and with the yz plane parallel.Once a branch of flashlight through PMD compensating plate 14 was reflexed on the PMD compensating plate 14 by liquid crystal array once more, in advance light path was compensated.The two bundle flashlights that incided inclined to one side beam splitter this moment all are the line polarisations, and the polarization direction is orthogonal.Passed through the light that closes of inclined to one side beam splitter, the mutually perpendicular flashlight in two bundle polarization directions has been synthesized a branch of flashlight identical with the incoming signal polarization state, gets into optical fiber through receiving end collimating apparatus 18 then.

The Principles of Regulation of single liquid crystal cells can be realized by following mode: shown in Fig. 2 (a); Liquid crystal cells front-reflection face 31 is coated with the semi-transparent semi-reflecting film that one deck is supported the above wide-angle incident of 10 degree; The size of semi-transparent semi-reflecting film reflectivity directly has influence on the chromatic dispersion compensation quantity of this liquid crystal cells, and reflectivity can be 20% here.Liquid crystal cells back reflection face 32 is coated with the high-reflecting film that one deck is supported the above wide-angle incident of 10 degree, and the reflectivity of this layer high-reflecting film will can be 99.5% as far as possible near 100% here.Instinct liquid crystal material in the liquid crystal layer 33 of liquid crystal cells can be nematic liquid crystal E44 here.When the voltage that is carried between liquid crystal cells front-reflection face 31 and the liquid crystal cells back reflection face 32 is V ₁The time, the optical axis direction of liquid crystal (long axis direction) is parallel to reflecting surface, and this moment, incoming signal light was 34, and reflected signal light is 35.When the voltage that is carried between liquid crystal cells front-reflection face 31 and the liquid crystal cells back reflection face 32 becomes V ₂The time, because electro-optic birefringent effect, the optical axis direction of liquid crystal (long axis direction) will deflect around the y axle, and this moment, incoming signal light was 34, and reflected signal light has become 36.

For single liquid crystal array, its phase function does

$\mathrm{\ψ}(r,\mathrm{\ΔOPL})=-2\arctan \left(\frac{1-r}{1+r}\tan \left(\frac{\mathrm{\π}}{\mathrm{\λ}}\mathrm{\ΔOPL}\right)\right)$

Wherein r is the reflection coefficient of liquid crystal front-reflection face, and Δ OPL is two optical path differences between the reflecting surface

The time delay function of liquid crystal cells does

$\mathrm{\τ}=\frac{\mathrm{d\ψ}(r,\mathrm{\ΔOPL})}{\mathrm{d\ω}}$

The chromatic dispersion function of liquid crystal cells does

$D=\frac{\mathrm{d\τ}}{\mathrm{d\λ}}=-\frac{{\mathrm{\λ}}^2}{2\mathrm{\πc}}\frac{\mathrm{d\ψ}(r,\mathrm{\ΔOPL})}{\mathrm{d\λ}}$

Optical path difference wherein

ΔOPL=nd?cos(θ)+n′d?cos(θ′)

It is thus clear that the chromatic dispersion of liquid crystal cells depends primarily on the reflection coefficient r of liquid crystal cells front-reflection face, the effective refractive index n and the n ' of liquid crystal material, the long d in the chamber of liquid crystal cells and light angle θ and θ '.Because liquid crystal is a kind of anisotropic material, so light is propagated birefringent phenomenon can take place in liquid crystal.Because the existence of birefringent phenomenon is arranged, and when the optical axis direction of liquid crystal changes, the angle θ of the non-ordinary light in the liquid crystal and effective refractive index n will change.

Shown in Fig. 2 (b), when incoming signal light 34 incided on the liquid crystal cells, because the polarization direction of incoming signal light 34 is parallel to the xz plane, incoming signal light 34 was exactly non-ordinary light concerning liquid crystal cells, when the voltage that is carried on the liquid crystal cells is V ₁The time, the optical axis of liquid crystal is parallel with the z axle, and this moment, the non-ordinary light effective refractive index from first reflecting surface to the second reflecting surface direction was n ₁, light angle is θ ₁, the non-ordinary light effective refractive index from second reflecting surface to the first reflecting surface direction is n ₂, light angle is θ ₂So optical path difference is Δ OPL=n ₁Dcos (θ ₁)+n ₂Dcos (θ ₂).When the voltage that is carried in liquid crystal cells by V ₁Become V ₂The time, because the optical axis of liquid crystal has rotated an angle around the y axle, this moment, the non-ordinary light effective refractive index from first reflecting surface to the second reflecting surface direction was n ₁', light angle is θ ₁', the non-ordinary light effective refractive index from second reflecting surface to the first reflecting surface direction is n ₂', light angle is θ ₂', so optical path difference is Δ OPL=n ₁' dcos (θ ₁')+n ₂' dcos (θ ₂').It is thus clear that be carried in the optical axis direction that voltage on the liquid crystal cells changes liquid crystal cells, just can change optical path difference Δ OPL, thereby realize control the liquid crystal cells chromatic dispersion through change.As shown in Figure 3, when the voltage that is carried in liquid crystal array is respectively V ₁, V ₂The time, skew has taken place in dispersion curve.

Whenever flashlight reflects once on a liquid crystal cells; Its chromatic dispersion just by this liquid crystal cells compensation once; When the flashlight order successively through 2 liquid crystal arrays on the reflection of liquid crystal cells, its chromatic dispersion that is compensated is quite whole chromatic dispersion sums of producing of liquid crystal cells just.If each liquid crystal cells all adds the voltage of an appointment; Just can control the dispersion compensation curve that whole liquid crystal cells produces an appointment; And the shape of this dispersion compensation curve can change; Also can squint in the position, so just realized the adjustable dispersion compensating function of any centre wavelength.Dispersion compensation curve as shown in Figure 4, that a plurality of liquid crystal cells are combined into, wherein (a) is the curve of control chromatic dispersion compensation quantity, (b) is the curve of control chromatic dispersion compensation quantity centre wavelength.

As shown in Figure 2; When changing chromatic dispersion through voltage, because the change of non-ordinary light light angle θ, the reflected signal light 35 through the liquid crystal cells reflection had become 36 originally; Make the reflected signal facula position produce a skew; And after repeatedly reflecting, this skew is increasing through stack, and can change along with the change in voltage that is carried in liquid crystal cells.In order to eliminate this skew, can add a reflection unit in the back of liquid crystal array, this reflection unit can be a total reflection prism 17 here.Total reflection prism makes the flashlight that reflects liquid crystal array return liquid crystal array with same direction, because the former road of flashlight is returned, skew is eliminated, shown in Fig. 1 (a).Simultaneously, this reflection unit also makes flashlight on the y direction, produce a translation, through the flashlight after the translation through the reflection of 2 liquid crystal arrays and rise inclined to one side beam splitter close light after incide the receiving end collimating apparatus, shown in Fig. 1 (b).

Claims (10)

1. Tunable Dispersion Compensator spare based on liquid crystal array technology; It is characterized in that; Be to be arranged in order by light path by optical fiber collimator, an inclined to one side beam splitter (12), half-wave plate (13), PMD compensating plate (14), first, second liquid crystal array (15,16) and total reflection prism (17) formation is set; The concrete connection is: optical fiber collimator is connected through light path with an inclined to one side beam splitter (12); The output light that plays inclined to one side beam splitter (12) divides two-way to connect half-wave plate (13) and PMD compensating plate (14) through light path respectively; The output light of half-wave plate (13) and PMD compensating plate (14) is connected first liquid crystal array (15) through light path, and described first liquid crystal array (15) light connects second liquid crystal array (16), and between first liquid crystal array (15) and second liquid crystal array (16), repeatedly reflects; Said second liquid crystal array (16) connects total reflection prism (17) through light path; Realization is to the adjustable dispersion compensating of a plurality of passages, and wherein, described optical fiber collimator includes input end collimating apparatus (11) and receiving end collimating apparatus (18); It is the line polarisation that described inclined to one side beam splitter (12) and half-wave plate (13) make the light that incides on the liquid crystal array, and the polarization direction is parallel to the plane of optical axis and incoming signal light formation; Described total reflection prism (17) makes the former road of flashlight return liquid crystal array, eliminates owing to regulating the skew on the liquid crystal array surface of reflected signal light that liquid crystal array produces with this; Described PMD compensating plate (14) carries out the PMD compensation to the flashlight that has passed through inclined to one side beam splitter (12) and half-wave plate (13).

2. the Tunable Dispersion Compensator spare based on liquid crystal array technology according to claim 1 is characterized in that described a plurality of passages are standard channel of ITU-T designated centers wavelength, or is the passage of centre wavelength with any wavelength in the device working range.

3. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 1; It is characterized in that; Described liquid crystal array includes first liquid crystal array (15) and second liquid crystal array (16) that interlaces and be arranged in parallel; Described first liquid crystal array (15) is identical with second liquid crystal array (16) structure, all has the liquid crystal cells of equal number.

4. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 3; It is characterized in that, described liquid crystal cells include liquid crystal cells front-reflection face (31), liquid crystal cells back reflection face (32) and be positioned at liquid crystal cells front-reflection face (31) and liquid crystal cells back reflection face (32) between liquid crystal layer (33).

5. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 3; It is characterized in that; Different liquid crystal cells produce different chromatic dispersion compensation quantities; Described chromatic dispersion compensation quantity is to be decided by the surface reflectivity of liquid crystal cells, optical axis direction and refractive index, and the adjusting of said chromatic dispersion compensation quantity is to realize through changing optical axis direction.

6. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 5; It is characterized in that described each liquid crystal cells surface reflectivity is to have different reflectivity and support 10 degree to decide with the film system of upper angle incident by plating at this liquid crystal cells front-reflection face (31) and liquid crystal cells back reflection face (32).

7. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 6 is characterized in that, is coated with one deck on the described liquid crystal cells front-reflection face (31) and supports the semi-transparent semi-reflecting film of 10 degree with upper angle incident; Be coated with one deck on the described liquid crystal cells back reflection face (32) and support the high-reflecting film of 10 degree with upper angle incident.

8. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 5 is characterized in that, the axial change of described each liquid crystal cells surface light is to realize through changing the voltage that loads on the liquid crystal cells.

9. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 5 is characterized in that the refractive index of described each liquid crystal cells liquid crystal layer is to be decided by voltage that is loaded on the liquid crystal cells and selected liquid crystal material.

10. the Tunable Dispersion Compensator spare based on the liquid crystal array technology according to claim 3; It is characterized in that; The total dispersion compensation rate of this Tunable Dispersion Compensator spare is by the chromatic dispersion compensation quantity that each liquid crystal cells the produces acquisition that adds up; The mode that adds up is that light rays reflects mutually through the liquid crystal cells on 2 parallel liquid crystal arrays, and adding up of a chromatic dispersion compensation quantity once just accomplished in wherein every reflection.

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