CN103558688A - Broadband double-refraction phase compensator - Google Patents

Abstract

The invention is suitable for the optical technical field, and provides a broadband variable double-refraction phase compensator. The broadband double-refraction phase compensator comprises a first optical wedge pair, a second optical wedge pair and a double-refraction flat plate. The first optical wedge pair comprises a wedge angle, a first optical wedge and a second optical wedge, the optical axis directions of the first optical wedge and the second optical wedge are same and opposite, and the first optical wedge pair is made of a first double-refraction crystal. The second optical wedge pair comprises a wedge angle, a third optical wedge and a fourth optical wedge, the optical axis directions of the third optical wedge and the fourth optical wedge are same and opposite, the second optical wedge pair is made of a second double-refraction crystal, and the double-refraction flat plate is made of a third double-refraction crystal. Types of the first double-refraction crystal, the second double-refraction crystal and the third double-refraction crystal are different, the variable proportions of materials and thicknesses of the first double-refraction crystal, the second double-refraction crystal and the third double-refraction crystal meet first-order double-refraction dispersion compensation conditions, and the second optical wedge and the third optical wedge are fixed together to synchronously move to conduct linear regulation on a double-refraction phase of the compensator. According to the broadband double-refraction phase compensator, different double-refraction phases of incident light can be compensated according to the needed broadband, and operation can be conveniently achieved.

Description

A kind of broadband birefringent phase compensator

Technical field

The invention belongs to optical technical field, relate in particular to a kind of broadband birefringent phase compensator.

Background technology

Can make two field vectors that vibrate in mutually perpendicular direction produce certain optical path difference or the device of phase differential, be called phase compensator.Traditional continuously changing the orthogonal two bunch polarized lights generations of direction of vibration is that controllable phase difference compensation has Babinet and Suo Lier-Babinet phase compensator: Babinet compensator is split and formed by the quartz crystal of two homogeneities, these two optical axises of splitting are mutually vertical, its shortcoming is to use superfine incident beam, because the different piece of wide light beam can produce different phase differential; And Suo Lier-Babinet phase compensator can make up this deficiency, it is comprised of two parallel quartz wedges and a quartzy surface plate, the optical axis that the optical axis of quartz plate is split with two is vertical, on split and can make it parallel by fine adjustment screw, thereby change light, by two gross thickness of splitting, obtain the phase value of certain wavelength.

The birefringent phase that compensator can compensating optical element produces also can be introduced a fixing delay biasing in an optical device.After calibration calibration, can also be used to measure the phase delay of wave plate to be asked.Therefore be widely used.But due to the effect of dispersion of birefringece crystal, the bandwidth of operation of traditional phase compensator is all narrow, this can have a strong impact on its working effect in broad band laser and application system thereof.

Summary of the invention

The object of the present invention is to provide a kind of simple in structure and broadband birefringent phase compensator of being easy to regulate.

The present invention is achieved in that a kind of broadband birefringent phase compensator, comprises that the first wedge, the second wedge, the 3rd wedge, the 4th wedge and the birefringence that sequentially arrange are dull and stereotyped; Described the first wedge and the second wedge are made by the first birefringece crystal, and their angle of wedge and optical axis direction are identical, and both place in opposite directions and form the first wedge pair; Described the 3rd wedge and the 4th wedge are made by the second birefringece crystal, and their angle of wedge and optical axis direction are identical, and both place in opposite directions and form the second wedge pair; Described birefringence flat board is made by the 3rd birefringece crystal, described the first birefringece crystal, the second birefringece crystal and the 3rd birefringece crystal inequality aspect material formation.

The present invention cuts into the angle of wedge and identical the first wedge and the second wedge of optical axis direction by the first birefringece crystal, and both place in opposite directions and form the first wedge pair; The second birefringece crystal is cut into the angle of wedge and identical the 3rd wedge and the 4th wedge of optical axis direction, and both place in opposite directions and form the second wedge pair; The 3rd birefringece crystal is cut into birefringence flat board, wherein said the first birefringece crystal, the second birefringece crystal and the 3rd birefringece crystal inequality aspect material formation.By described the second wedge and the 3rd wedge synchronizing moving that is fixed together, when moving, they will make the right thickness equal proportion of the right thickness of described the first wedge and the second wedge change.The selection of this ratio need meet the first wedge to and the second wedge pair between single order birefringence dispersion compensation condition.Selected birefringence plate material and thickness thereof need coordinate and also meet single order birefringence dispersion compensation condition being operated in the thickness at zero birefraction phase place place with selected first and second wedge.This phase compensator is the different birefringent phases of broadband compensation incident light as required, easy to operate.Be applicable to broad band laser and application system thereof.

Accompanying drawing explanation

Fig. 1 is the structural representation of the broadband birefringent phase compensator that provides of the embodiment of the present invention;

Fig. 2 is the KDP/MgF that the embodiment of the present invention provides ₂+ ADP(d _c=4000 μ m) phase place of phase compensator and the graph of relation of wavelength.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

As shown in Figure 1, the broadband birefringent phase compensator that the embodiment of the present invention provides comprises the first wedge 1, the second wedge 2, the 3rd wedge 3, the 4th wedge 4 and the birefringence flat board 5 sequentially arranging.Wherein, described the first wedge 1 is identical with the angle of wedge and the optical axis direction of the second wedge 2, by the first birefringece crystal, makes, and both arrange the optical flat that is equivalent to a variable thickness in opposite directions; Described the 3rd wedge 3 is identical with the angle of wedge and the optical axis direction of the 4th wedge 4, by the second birefringece crystal, makes, and both arrange the optical flat that is equivalent to another variable thickness in opposite directions.Described birefringence flat board 5 is made by the 3rd birefringece crystal, described the first birefringece crystal, the second birefringece crystal and the 3rd birefringece crystal inequality aspect material formation.For example, described the first birefringece crystal can be selected KDP crystal, and the first wedge 1 and the second wedge 2 are KDP crystal; Described the second birefringece crystal can be selected MgF ₂crystal, the 3rd wedge 3 and the 4th wedge 4 are MgF ₂crystal; Described the 3rd birefringece crystal can be selected ADP crystal, i.e. birefringence dull and stereotyped 5 is ADP crystal.

For this phase compensator can be operated near zero phase, make the first wedge pair with the second wedge, the birefringent phase sum producing and the birefringent phase of the dull and stereotyped generation of birefringence be disappeared mutually, so have

${\mathrm{\η}}_A\left({\mathrm{\λ}}_0\right)\·d_{A_0}+{\mathrm{\η}}_B\left({\mathrm{\λ}}_0\right)\·d_{B_0}+{\mathrm{\η}}_C\left({\mathrm{\λ}}_0\right)\·d_C=0---\left(1\right)$

Simultaneously for making bandwidth of operation optimization, selected birefringece crystal and each wedge must meet single order birefringence dispersion compensation condition to the thickness of, birefringence flat board,

${\mathrm{\η}}_A^{\left(1\right)}\left({\mathrm{\λ}}_0\right)\·d_{A_0}+{\mathrm{\η}}_B^{\left(1\right)}\left({\mathrm{\λ}}_0\right)\·d_{B_0}+{\mathrm{\η}}_C^{\left(1\right)}\left({\mathrm{\λ}}_0\right)\·d_C=0---\left(2\right)$

D wherein _a0, d _b0and d _cbe respectively the first wedge of being operated in zero phase place to, the second wedge to the thickness with birefringence flat board.η _i(λ) (i=A, B or C) be birefringece crystal in the minimum and maximum refringence of af at wavelength lambda, be defined as

η _i(λ)=n _o(λ)-n _e(λ), （3）

And η _i ^(m)(λ ₀) (i=A, B; M=1,2 ...) expression η _iin wavelength X ₀the m level derivative at place.According to formula (1), (2), can obtain d _a0, d _b0and d _cratio.Like this when the right thickness of the first wedge pair and the second wedge departs from d _a0and d _b0time, the birefringent phase of compensator is with regard to offset from zero, so should have

η _A(λ ₀)·d _A+η _B(λ ₀)·d _B=nλ ₀ （4）

(4) n λ in formula ₀for the birefringence delay of compensator, for example, n=0.5 is half-wave plate, and n=0.25 is quarter-wave plate.D wherein _a, d _bbe respectively the first wedge to, the second wedge to respect to d _a0, d _b0thickness bias.For realizing broadband birefringent phase, need meet single order birefringence dispersion compensation condition

${\mathrm{\η}}_A^{\left(1\right)}\left({\mathrm{\λ}}_0\right)\·d_A+{\mathrm{\η}}_B^{\left(1\right)}\left({\mathrm{\λ}}_0\right)\·d_B=n---\left(5\right)$

Obviously, for given n value, from (4), (5) two formulas, can ask d _a, d _bvalue.And as long as increase on year-on-year basis or reduce d _a, d _bvalue can regulate n value to realize the compensation of variable bandwidth birefringent phase on year-on-year basis.For example, regulate in proportion d _a, d _bvalue can change n value between-0.5 to 0.5, just can make compensator compensates scope be increased to 180 ° from-180 °.If d in above-mentioned calculating _a, d _bvalue, for jack per line, show that their optical axis of crystal directions are identical, otherwise their optical axis of crystal direction each other at an angle of 90.According to Theoretical Design principle above, for KDP/MgF ₂the compensator of/ADP combination of materials, can calculate when n=0.5 d _a=39.1 μ m, d _b=162.1 μ m.If select d _c=2000 μ m, d _a0=-1816.8 μ m, d _b0=2671.2 μ m.D _a0and d _b0the optical axis direction that the negative sign of value shows them at an angle of 90, but d _b0value and d _cjack per line illustrates that the second birefringece crystal is consistent with the optical axis direction of the 3rd birefringece crystal.Hence one can see that, the right thickness of first and second wedge is adjustable, in the embodiment of the present invention, the first wedge is 1816.8～1816.8+2 * 39.1 μ m to thickness adjustable extent, the second wedge is 2671.2～2671.2+2 * 162.1 μ m to thickness adjustable extent, and designed phase compensator can be realized the scope birefringent phase compensation from 0 ° to 360 °.

For simplifying, regulate, convenient use, the second wedge 2 described here and the 3rd wedge 3 arrange in the same way, and are placed in same linear translation platform, make the described right thickness bias d of first and second wedge when they move like this _aand d _bvalue changes equal proportion.If

tg(α _A)/tg(α _B)=μ=d _A/d _B （6）

Need only by mobile described translation stage, just can be by changing in proportion d _aand d _bvalue regulates birefringent phase, and (4), (5) two formulas meet all the time.

If the centre wavelength of designed phase compensator is 800nm, the spectral range of work is 650nm～950nm.The birefringent phase that Fig. 2 provides Theoretical Design central wavelength compensator is respectively 0,90 °, and 180 °, 270 ° (corresponding n value is respectively 0,0.25,0.5,0.75).In 650nm～950nm spectral region, maximum skew is respectively 5.52 °, and 3.91 °, 2.41 ° and 0.86 °.What in Fig. 2, a line was corresponding is the Babinet compensator that single quartz crystal is made, and its maximum deviation is up to 44.3 °.Visible the present invention has dwindled maximum deviation greatly, thereby can significantly increase work live width.And in Fig. 2, all curves have same rule: the closer to centre wavelength, digital baseband input signal is just less, and this illustrates that phase compensator of the present invention is relatively applicable to ultrashort laser pulse, and most of energy of this pulse all concentrates near centre wavelength.

Design as for first and second wedge to the angle of wedge, from the known d of calculating above _a/ d _b=0.2412, if select α _b=3 °, α so _a=0.7245 °.Its angular resolution depends on the minimum step of aforementioned translation stage.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (4)

1. a broadband birefringent phase compensator, is characterized in that, described phase compensator comprises that the first wedge, the second wedge, the 3rd wedge, the 4th wedge and the birefringence that sequentially arrange are dull and stereotyped; Described the first wedge and the second wedge are made by the first birefringece crystal, and their angle of wedge and optical axis direction are identical, and both place in opposite directions and form the first wedge pair; Described the 3rd wedge and the 4th wedge are made by the second birefringece crystal, and their angle of wedge and optical axis direction are identical, and both place in opposite directions and form the second wedge pair; Described birefringence flat board is made by the 3rd birefringece crystal, and described the first birefringece crystal, the second birefringece crystal and the 3rd birefringece crystal kind are different.

2. broadband as claimed in claim 1 birefringent phase compensator, it is characterized in that, the selection of bi-material that first and second selected wedge is right and the selection of thickness must meet single order birefringence dispersion compensation condition, selected birefringence plate material and thickness thereof need coordinate and also meet single order birefringence dispersion compensation condition being operated in the thickness at zero birefraction phase place place with selected first and second wedge, so that bandwidth of operation optimization.

3. broadband as claimed in claim 1 birefringent phase compensator, is characterized in that, is fixed together, thereby can in fixing ratio, regulates the first wedge to the thickness right with the second wedge easily after described the 3rd wedge and the second wedge arrange in the same way.

4. broadband as claimed in claim 1 birefringent phase compensator, is characterized in that, described the first wedge is to depending on that with the right angle of wedge of the second wedge the first wedge is to the ratio μ with the right variation in thickness of the second wedge, and tg (α _a)/tg (α _b)=μ, wherein α _abe the angle of wedge of the second wedge, α _bit is the angle of wedge of the 3rd wedge.

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