CN1367593A - Birefringent cascade polarization interference odd-even signal separator and preparation method thereof - Google Patents

Abstract

A birefringent cascade polarization interference odd-even signal separator and a preparation method thereof are mainly used for two-channel separation of odd-even signals in wavelength division multiplexing signals in a wavelength division multiplexing communication system and all filters needing flattening spectral transmittance functions. The core element is a filter formed by K ≧ 1 analog wave plates with the same structure. Controlling the birefringence retardation and polarization orientation of the analog waveplate allows the order of the spectral transmittance function to approach the Fourier order of the ideal periodic rectangular transmittance function. And obtaining matched combination angles of the K mode polarization rotating plates in the K analog wave plates closest to the periodic rectangular transmittance function by adopting a Fourier series comparison method and a searching method. Compared with the prior art, the separator of the invention is easy to realize the odd-even separation of the wavelength division signals with various spectral frequency intervals, and can achieve the small spectral frequency interval which cannot be achieved by the prior art. The method is simple, and the number of analog wave plates in the filter can be reduced.

Description

Birefingent cascade polarized interference old-even signal separator and preparation method thereof

Technical field:

The present invention is odd-even signal separator of a kind of birefringence cascade polarized interference and preparation method thereof, demultiplexer mainly as two channel separation (English name interleaver) of odd and even number signal in the wavelength-division multiplex signals in the wavelength division multiplexing communications systems, also can be used for the filter that all need planarization spectral-transmission favtor function.

Background technology:

Wavelength-division multiplex signals is made up of a series of equifrequents single CF signal at interval, adopts demodulation multiplexer wavelength-division multiplex signals can be separated by the difference of wavelength.Along with the development of close wavelength-division multiplex technology, frequency interval is more and more little, and this has proposed higher spectrally resolved requirement for demodulation multiplexer.The effect of odevity wavelength division multiplexing separator (hereinafter to be referred as the odd even separator) is that wavelength-division multiplex signals is separated into odd number series and serial two channels of even number according to the order of wavelength-division carrier frequency, corresponding the doubling of wavelength-division frequency interval in each channel, so just reduced the requirement of Wave division multiplexer/demultiplexer, therefore the odd even separator is a kind of important optical communication core devices, and in order to be adapted to more and more highdensity wavelength division multiplexing, the developing direction of odd even separator is to realize that little to the greatest extent spectral frequency at interval.Separate for the odd even that realizes low cross interference, the odd even separator must possess smooth and the passband of high-contrast and the spectrum transmitting characteristic of stopband.

Be the structure that a kind of spectrum transmitting function that utilizes long period fiber grating is realized the fiber amplifier flat gainization described in the technology [1] (referring to Opt.Lett., A.M.Vengsarkar et al., 21,336-338,1996) formerly.Be used for erbium-doped fiber amplifier and can achieve flat gainization, the fluctuating of gain spectral is less than 0.2dB in the 25-30nm bandwidth.In optical WDM communication system, can make 20 channels spaced apart in the bandwidth of 1550.4-1561.8nm with 0.6nm.Can be used for the separation of neat even signaling channel equally.But this formerly technology have some limitation in actual applications, very responsive to bending as it, a very little bending all can be moved its peak wavelength to short wavelength regions, and peak value also can drop to about 3dB from 20dB, thereby loses former characteristic.

Be that a kind of array waveguide grating (English be called for short AWG) that utilizes produces the flat spectral response function described in the technology [2] (referring to Journal of Lightwave Technology, Thomas Kamalakis et al., 19 (11), 1716,2001) formerly.It is to realize at the relative position on free propagation region border by the length of adjusting Waveguide array and they.Can realize the multiplex/demultiplex function in the wavelength-division multiplex technique, insert functions such as dividing multiplexing function and wavelength route.But this necessary in actual applications employing of technology formerly other method and apparatus elimination polarization and Temperature Influence, thereby limited its application.

Be a kind of cascade birefringence interference technique that produces planarization spectral-transmission favtor function described in the technology [3] (referring to Eltctron.Lett., W.J.Carlsen and C.F.Buhrer, 23 (3), 106-107,1987) formerly.Its optical system structure that adopts is that the thickness ratio that places among both polarizer and analyzer and they is three blocks of birefringece crystal wave plates of 1: 2: 2.Calculated the drift angle value of each required piece crystal by the backstepping computational methods with respect to the polarizer.But it is not more than at 1% o'clock in the shake of passband and stopband, has only obtained one group of crystal drift angle value, and is not more than at 0.1% o'clock at passband and stopband shake, and the ratio of the width δ f of passband or stopband and cycle Δ f is less than 3%.Therefore this structure needs large scale, high optical quality, and the crystal of high birefringence, this crystalloid kind is seldom.Used in addition is the high-order wave plate, manufactures difficulty.

Formerly technology [4] is (referring to Journal of the Optical Society of American., S.E.Harris etal., 54 (10), 1267-1279,1964) described in is that required filter construction need be tried to achieve with reverse computational methods when cascade birefringence filter was produced specific filtering spectral waveform, though this reverse just anti-pushing manipulation has universality in theory, but the necessary thickness of crystal that requires formation cascade birefringence filter to be adopted is identical, therefore when having the spectral waveform of high order rank cosine series, simulation need use than polycrystal, and the projectional technique complexity.

Summary of the invention:

The core parts filter of odd-even signal separator of the present invention is to be made of the identical K of structure 〉=1 simulation wave plate, and the birefringence delay of control simulation wave plate and the progression that polarization orientation can make the spectral-transmission favtor function are near the fourier series of desirable cycle rectangular transmission rate.Employing fourier series method of comparison and searching method are tried to achieve the combination angle that is complementary near K analog polarization rotary plate in K the simulation wave plate of ideal period rectangular transmission rate function, to obtain the structure of analog polarization rotary plate.Method is simple, reliable.

The structure of demultiplexer of the present invention, comprise collimating lens 2, output end face places the input optical fibre 1 on collimating lens 2 front focus, first condenser lens 12 that arranged side by side storing arranged and second condenser lens 14 relative on the light path of input optical fibre 1 output beam with collimating lens 2, there is input end face to place first output optical fibre 13 on first condenser lens, 12 back focuses, has input end face to place second output optical fibre 15 on second condenser lens, 14 back focuses; On the light path between collimating lens 2 and two condenser lenses 12,14, be equipped with input polarization beam splitter 3, on the light path between input polarization beam splitter 3 and two condenser lenses 12,14, be equipped with output polarization bundling device 11; On the light path between input polarization beam splitter 3 and the output polarization bundling device 11, input polarization circulator 4 is arranged, on the light path between input polarization circulator 4 and the output polarization bundling device 11, output polarization circulator 10 is arranged, on the light path between input polarization circulator 4 and the output polarization circulator 10, output polarization beam splitter 9 is arranged; On the light path between input polarization circulator 4 and the output polarization beam splitter 9, be equipped with by the identical K of structure 〉=1 filter 16 that simulation wave plate 5,6,7 constitutes; On the light path in filter 16 between K simulation wave plate and the output polarization beam splitter 9 or be equipped with intermediate polarisation circulator 8.

Demultiplexer concrete structure of the present invention such as above-mentioned shown in Figure 1, comprise input optical fibre 1, be equipped with collimating lens 2 successively on the light path on the direction of advancing by input optical fibre 1 emission light beam, input polarization beam splitter 3, input polarization circulator 4, by the first identical simulation wave plate 5 of structure, the second simulation wave plate 6, the 3rd simulation wave plate 7, total K 〉=1 filter 16 that the simulation wave plate constitutes perhaps has intermediate polarisation circulator 8, output polarization beam splitter 9, output polarization circulator 10, output polarization bundling device 11, first condenser lens 12 and first output optical fibre 13 and second condenser lens 14 and second output optical fibre of putting 15 side by side.

The simulation wave plate 5 of said formation filter 16,6,7, comprise analog polarization rotary plate 501 with incident polarized light rotation-180 °＜θ＜180 ° angle, have the plane of incidence of light beam and mould polarization that exit facet is parallel to each other to close bundle sheet 505, two parallel beam incident surfaces of analog polarization rotary plate 501 all close the central axis OO of bundle sheet 505 both coincidences perpendicular to analog polarization rotary plate 501 and mould polarization with two parallel beam incident surface and the exit facets that exit facet and mould polarization close bundle sheet 505 ₂, close between the bundle sheet 505 at analog polarization rotary plate 501 and mould polarization, two parallel beam incident surfaces and exit facet are arranged perpendicular to central axis OO ₂, and center O ₁At central axis OO ₂On mould polarization beam splitter 502, mould polarization beam splitter 502 and mould polarization close be equipped with between the bundle sheet 505 refractive index inequality along its length with central axis OO ₂ First medium 503 of parallel storing arranged side by side and second medium 504.As shown in Figure 2.Close between the bundle sheet 505 or be equipped with second analog polarization rotary plate 506 at two media 503,504 and mould polarization.As shown in Figure 3.

Said above-mentioned simulation wave plate 5,6,7 (all simulate wave plate) in fact has two kinds of structures.Fig. 2 is first kind of structure, and by analog polarization rotary plate 501, mould polarization beam splitter 502, the first media 503, the second media 504, mould polarization close bundle sheet 505 and form.Incident polarized light rotates with respect to incident polarization light direction θ angle through analog polarization rotary plate 501, be decomposed into spatially that separate up and down and two bundle collimated light beams cross-polarization by mould polarization beam splitter 502 again, these two light beams pass through refractive index first medium 503 inequality and second medium 504 respectively, close bundle sheet 505 through the mould polarization at last and synthesize a branch of output beam again.The effect of therefore simulating wave plate is equivalent to the birefringece crystal wave plate, has promptly produced the different phase delay of two orthogonal polarization components in the same light beam.Fig. 3 is second kind of structure, by analog polarization rotary plate 501, mould polarization beam splitter 502, first medium 503, first medium 504, analog polarization rotary plate 506, the mould polarization closes bundle sheet 505 and forms, Duoed one second analog polarization rotary plate 506 than first kind of structure, incident polarized light rotates with respect to incident polarization light direction θ angle through analog polarization rotary plate 501, be decomposed into parallel separation and two light beams polarized orthogonal on the space by mould polarization beam splitter 502 again, they pass through the first different medium 503 of refractive index and first medium 504 respectively, polarization direction by these two light beams of second analog polarization rotary plate 506 rotation is 90 ° then, closes bundle sheet 505 through the mould polarization at last and synthesizes an output beam, and its effect also is equivalent to the birefringece crystal wave plate.In first kind of structure, ordinary light beam in the mould polarization beam splitter 502 and abnormal polarization light beam close at the mould polarization and still are ordinary deflected beam and unusual deflected beam in the bundle sheet 505, ordinary polarised light is different with the light path of abnormal polarization light, so mould polarization beam splitter 502 and mould polarization close bundle sheet 505 and produce an additional birefringence and postpone.In second kind of structure, ordinary light beam in the mould polarization beam splitter 502 and abnormal polarization light beam close in the bundle sheet 505 at the mould polarization and become abnormal polarization light beam and ordinary light beam respectively, and it can eliminate mould polarization beam splitter 502 and the mould polarization closes the additional birefringence delay that bundle sheet 505 is introduced.

Collimating lens 2 is used for random polarized wave division multiplex signal light beam to input optical fibre 1 emission and collimates and expand bundle, through the parallel light pencil A of collimating lens 2 outputs, it incides the collimated light beam that is broken down into the two bundle polarized orthogonals that separate about equicohesive behind the input polarization beam splitter 3 in the horizontal direction, work through 4 of input polarization circulators unusual light beam for one of them (left side among Fig. 1) vertical polarization, and 90 ° in rotatory polarization direction, thereby through behind the input polarization circulator 4 being the collimated light beam a that two bundle polarizations are all horizontal polarization direction ₁And a ₂, again by entering output polarization beam splitter 9 behind the filter 16 that constitutes by K simulation wave plate 5,6,7.

Output polarization beam splitter 9 is for from a ₁And a ₂And the two bundle collimated light beams that come respectively are decomposed into two bundle collimated light beams on vertical direction, promptly produce four light beams, wherein (top) two bundle b ₁, c ₁Be the ordinary light of horizontal polarization, in addition (following) two bundle b ₂, c ₂Unusual light for vertical polarization.Enter output polarization circulator 10 backs for last right light beam b ₁With bottom left light beam c ₂Produce additional 90 ° polarization direction rotation, therefore by four light beam b before output polarization circulator 10 backs and the irradiation output polarization bundling device 11 ₁, c ₁, b ₂, c ₂Polarization state be: light beam b ₁Vertical polarization, light beam c ₁Horizontal polarization, light beam b ₂Vertical polarization, light beam c ₂Horizontal polarization enters the synthetic in the horizontal direction light beam of output polarization bundling device 11, and it makes light beam b ₁And c ₁Synthesize output beam C, make light beam b ₂And c ₂Synthesize output beam B.First condenser lens 12 focuses on and is coupled into for B road output beam among first output optical fibre 13, and second condenser lens 14 focuses on and is coupled among second output optical fibre 15 for C road output beam.

Said input polarization beam splitter 3 and input polarization circulator 4 are used to decompose the input beam of random polarization, output polarization beam splitter 9, output polarization circulator 10 and output polarization bundling device 11 are used for filtered light beam is synthesized again the output beam of random polarization, and main purpose is the operating characteristic of realization and input beam polarization irrelevant.Therefore, all simulation wave plates have certain width, and permission can be carried out identical processing simultaneously for two light beams that input polarization beam splitter 3 decomposes.

Be the simulation of first in the filter 16 wave plate 5, the second simulation wave plates 6, the three simulation wave plate 7 and intermediate polarisation circulators 8 successively between input polarization circulator 4 and output polarization beam splitter 9.The simulation wave plate of cascade has K, thus wherein also just comprise K analog polarization rotary plate 501,601 ... K01, they are θ with respect to the incident polarization light direction polarization anglec of rotation ₁, θ ₂..., θ _KLight beam a ₁And a ₂Incident is also passed through the simulation wave plate 6,7 that simulation wave plate 5 reaches K-1 cascade subsequently ..., their are θ through intermediate polarisation circulator 8 rotatory polarization orientation angles _PCore key element of the present invention is the polarization interference filter of the equivalent birefringent wave plate of filter 16 equivalences that K simulation wave plate the constitutes cascade of having formed K different birefringence delays and different orientation, the polarization interference filter of a wave plate produces the spectral transmittance function of cosine-shaped, and its basic spectral frequency cycle is inversely proportional to birefringence and postpones.Therefore, the spectral transmittance function that the cascade of a plurality of wave plates produces not only comprise they separately the fundamental frequency item and also they are arranged with the subtractive combination item, the spectral transmittance function is a progression of being made up of different spectral frequency items.Can make this progression approach the fourier series of cycle rectangular function so adjust and control the birefringence delay and the polarization orientation of simulation wave plate, thereby produce smooth seeing through passband and see through stopband, keep maximum transmission and minimum transmitance to be respectively 1 and 0 simultaneously.

Above-mentioned said polarization rotator 4,8,10 and analog polarization rotary plate 501 ... K01 can adopt optical rotation plate or half-wave plate.Wherein optical rotation plate is made of the gyrotropi crystal of twin polishing, and the specific rotatory power of gyrotropi crystal is ζ (a degree/millimeter), and when the required incident light polarization direction polarization anglec of rotation with respect to being incident in first circulator was θ, the logical light length D (mm) of optical rotation plate was: $D=\frac{\mathrm{\θ}}{\mathrm{\ζ}}.---\left(1\right)$ When using half-wave plate, when the required polarization anglec of rotation was θ, then the fast axle of half-wave plate or the angle ξ of slow axis and input polarisation of light direction were: $\mathrm{\ξ}=\frac{\mathrm{\θ}}{2}.----\left(2\right)$ Above-mentioned said polarization beam apparatus 3,9 and mould polarization beam splitter 502, ... K02 and polarization beam combiner 11 and mould polarization close bundle sheet 505, ... K05 can adopt birefringece crystal piece or ahrens prism combination, refractive index in the above-mentioned said simulation wave plate inequality first, second medium 503,504 can adopt isotropic material such as glass or anisotropic material such as crystal, and crystal must cut along main shaft.The analog polarization rotary plate 501,601,701 of simulation in the wave plate 5,6,7 can, at this moment simulate wave plate combined and need rotate corresponding θ angle along optical axis.The equivalent birefringence delay of its generation can change when the medium in the simulation wave plate rotated 503,504, and this can be used for the fine tuning of spectral bandwidth.

For being analyzed as follows of the invention described above structure:

One, about simulation wave plate 5,6,7

For above-mentioned no matter be the simulation wave plate of first kind or second kind structure when adopting the birefringece crystal piece to close bundle sheet 505 as mould polarization beam splitter 502 and mould polarization, the deviation angle alpha degree of extraordinary ray e is: $\mathrm{tg\α}=(\frac{n_o^2}{n_e^2}-1)\frac{\mathrm{ctg}{\mathrm{\β}}_1}{1+\frac{n_o^2}{n_e^2}{\mathrm{ct}g}^2{\mathrm{\β}}_1},-------\left(3\right)$ Wherein, n _oBe ordinary refraction index, n _eBe extraordinary (different) optical index, β ₁Angle for optical axis and crystal interface.

For the simulation wave plate of first kind of structure, the phase delay of o-ordinary light and e-extraordinary ray is:

Work as L _{A, k}=L _{B, k}And L _{C, k}=L _{D, k}The time, have: Wherein, n _aIts length of refractive index that is first medium 503 is L _a, n _{A, K}Be the refractive index of K the first medium K03 in the simulation wave plate, its length is L _{A, K}, n _bIts length of refractive index that is second medium 504 is L _b, same, n _{B, K}Be the refractive index of K the second medium K04 in the simulation wave plate, its length is L _{B, K}, L _{C, K}Be the length of mould polarization beam splitter K02 in K the simulation wave plate, L _{D, K}Be the length that the mould polarization closes bundle sheet K05 in K the simulation wave plate, β ₂Be the angle of the o-light and the optical axis of crystal in the mould polarization beam splitter, n _e(β ₂) be e-light equivalent refractive index: $n_e^2=\frac{n_o^2{n}_e^2}{n_o^2{\sin }^2{\mathrm{\β}}_2+n_e^2{\cos }^2{\mathrm{\β}}_2}.---------\left(5\right)$ For the simulation wave plate of second kind of structure, be for the phase delay of o-light and e-light:

Work as L _{A, k}=L _{B, k}And L _{C, k}=L _{D, k}In time, have

The phase delay of each simulation wave plate can be expressed as the spectral period Δ f of polarization interference _kOr equivalent delay γ _k:

Wherein: C is the light velocity, and λ is the incident light wavelength.

Two, the spectral-transmission favtor function of odd even separator

The polarization optics problem adopts the Jones matrix formula analysis usually, and the Jones matrix of optical element and device is respectively in the structure as shown in Figure 1:

The Jones matrix P of polarization beam apparatus (horizontal polarization) ₁ ${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">P</figure-callout>}}_1=\left[\begin{array}{cc}1& 0\\ 0& 0\end{array}\right],-------\left(8\right)$

The simulation wave plate 5,6,7....K Jones matrix W _K

Orientation θ _sThe Jones matrix P of polarization beam combiner ₂ $P_2=\left[\begin{array}{cc}1& 0\\ 0& 0\end{array}\right]R\left({\mathrm{\&theta;}}_s\right),----\left(10\right)$ Wherein $R\left(\mathrm{\&theta;}\right)=\left[\begin{array}{cc}\cos \mathrm{\&theta;}& \sin \mathrm{\&theta;}\\ -\sin \mathrm{\&theta;}& \cos \mathrm{\&theta;}\end{array}\right].--------\left(11\right)$

Therefore, containing K Jones matrix M that simulates the filter of wave plate is expressed as:

M＝P ₂W _K....W ₂W ₁P ₁。(12)

For simulation wave plate incident light and emergent light following relation is arranged: $\left[\begin{array}{c}{E_x}^{\&prime;}\\ {E_y}^{\&prime;}\end{array}\right]=M\left[\begin{array}{c}{E}_x\\ E_y\end{array}\right],------\left(13\right)$ When emergent light in the horizontal polarization direction analyzing, its field amplitude E _x'=M ₁₁E _xM wherein ₁₁Diagonal matrix for M.Because of incident light is the linearly polarized light of horizontal direction, then the spectral-transmission favtor of the filter of this simulation wave plate is: T=|M ₁₁| ², perhaps be expressed as T (f)=T with common progression ₀+ T ₁Cos (2 π γ ' ₁F)+T ₂Cos (2 π γ ' ₂F)+T ₃Cos (2 π γ ' ₃F)+... .+T _nCos (2 π γ ' _nF)+....,

(14) wherein, T _nBe and angle θ ₁, θ ₂, θ ₃...., θ _KWith angle θ _PRelevant coefficient, γ ' _nBe (γ ₁, γ ₂, γ ₃...., γ _K) separately or the difference of its combination in any and or and difference, thereby the equivalent spectrum cycle of n item be: $\mathrm{\&Delta;}{f_n}^{\&prime;}=\frac{1}{{{\mathrm{\&gamma;}}^{\&prime;}}_n}.-------\left(15\right)$ For example, it is as follows to calculate the spectral-transmission favtor progression of filter from (8)-(14) formula when K=3: $T\left(f\right)={\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_0+{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_1\cos \left(2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;}{f}_1}\right)+T_2\cos (2\mathrm{\&pi;}\frac{f}{{\mathrm{\&Delta;f}}_2})+T_3\cos (2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;}{f}_3})+$ $+T_4\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}+\frac{1}{{\mathrm{\&Delta;f}}_2})\right)+{\mathrm{<figure-callout\; id="5"\; label="T"\; filenames="A0211098400212.png"\; state="\{\{state\}\}">T</figure-callout>}}_5\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}+\frac{1}{\mathrm{\&Delta;}{f}_3})\right)+T_6\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{\mathrm{\&Delta;}{f}_3})\right)+$ $+T_7\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{{\mathrm{\&Delta;f}}_2})\right)+T_8\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{\mathrm{\&Delta;}{f}_1})\right)+T_9\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_2}-\frac{1}{\mathrm{\&Delta;}{f}_1})\right)+,\left(16\right)$ $+T_{10}\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{{\mathrm{\&Delta;f}}_2}+\frac{1}{{\mathrm{\&Delta;f}}_1})\right)+T_{11}\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{\mathrm{\&Delta;}{f}_2}-\frac{1}{{\mathrm{\&Delta;f}}_1})\right)+$ $+T_{12}\cos \left(2\mathrm{\&pi;f}(\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{{\mathrm{\&Delta;f}}_2}+\frac{1}{{\mathrm{\&Delta;f}}_1})\right)+T_{13}\cos \left(2\mathrm{\&pi;f}(-\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{{\mathrm{\&Delta;f}}_1})\right)$ Comprise that zero level has 14.By above-mentioned (8)-(13) formula as can be known, T _nBe and angle θ ₁, θ ₂, θ ₃..., θ _kAnd θ _PRelevant coefficient can draw following T ₀-T ₁₃The progression coefficient be:

T ₀＝1/2[1+cos2θ ₁cos2(θ ₂-θ ₁)cos2(θ ₃-θ ₂)cos2(θ _p-θ ₃)]

T ₁＝(-1/2)cos2(θ _p-θ ₃)cos2(θ ₃-θ ₂)sin2θ ₁sin2(θ ₂-θ ₁)

T ₂＝(-1/2)cos2θ ₁cos2(θ _p-θ ₃)sin2(θ ₃-θ ₂)sin2(θ ₂-θ ₁)

T ₃＝(-1/2)cos2θ ₁sin2(θ _p-θ ₃)sin2(θ ₃-θ ₂)cos2(θ ₂-θ ₁)

T ₄＝(-1/2)cos ²(è ₂-è ₁)cos2(è _p-è ₃)sin2(è ₃-è ₂)sin2è ₁

T ₅＝(1/4)sin2θ ₁sin2(θ _p-θ ₃)sin2(θ ₃-θ ₂)sin2(θ ₂-θ ₁)

T ₆＝(-1/2)cos2θ ₁cos ²(θ ₃-θ ₂)sin2(θ _p-θ ₃)sin2(θ ₂-θ ₁)

T ₇＝(1/2)cos2θ ₁sin ²(θ ₃-θ ₂)sin2(θ _p-θ ₃)sin2(θ ₂-θ ₁)????(17)

T ₈＝(1/4)sin2θ ₁sin2(θ ₃-θ ₂)sin2(θ _p-θ ₃)sin2(θ ₂-θ ₁)

T ₉＝1/2sin2θ ₁sin ²(θ ₂-θ ₁)cos2(θ _p-θ ₃)sin2(θ ₃-θ ₂)

T ₁₀＝(-1/2)cos ²(θ ₂-θ ₁)cos ²(θ ₃-θ ₂)sin2(θ _p-θ ₃)sin2θ ₁

T ₁₁＝(1/2)cos ²(θ ₃-θ ₂)sin ²(θ ₂-θ ₁)sin2(θ _p-θ ₃)sin2θ ₁

T ₁₂＝(-1/2)sin ²(θ ₂-θ ₁)sin ²(θ ₃-θ ₂)sin2(θ _p-θ ₃)sin2θ ₁

T ₁₃=(1/2) cos ²(θ ₂-θ ₁) sin ²(θ ₃-θ ₂) sin 2 (θ _p-θ ₃) sin2 θ ₁Have simultaneously: ${\mathrm{\&gamma;}}_1=\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ ${\mathrm{\&gamma;}}_2=\frac{1}{{\mathrm{\&Delta;f}}_2}$ ${\mathrm{\&gamma;}}_3=\frac{1}{{\mathrm{\&Delta;f}}_3}$ ${\mathrm{\&gamma;}}_4=\frac{1}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}+\frac{1}{{\mathrm{\&Delta;f}}_2}$ ${\mathrm{\&gamma;}}_5=\frac{1}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}+\frac{1}{{\mathrm{\&Delta;f}}_3}$ ${\mathrm{\&gamma;}}_6=\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{{\mathrm{\&Delta;f}}_3}$ ${\mathrm{\&gamma;}}_7=\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{{\mathrm{\&Delta;f}}_2}$ ${\mathrm{\&gamma;}}_8=\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ ${\mathrm{\&gamma;}}_9=\frac{1}{\mathrm{\&Delta;}{f}_2}-\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ ${\mathrm{\&gamma;}}_{10}=\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ ${\mathrm{\&gamma;}}_{11}=\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{\mathrm{\&Delta;}{f}_2}-\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1},-------------\left(18\right)$ ${\mathrm{\&gamma;}}_{12}=\frac{1}{\mathrm{\&Delta;}{f}_3}-\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ ${\mathrm{\&gamma;}}_{13}=-\frac{1}{\mathrm{\&Delta;}{f}_3}+\frac{1}{\mathrm{\&Delta;}{f}_2}+\frac{1}{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="f"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">f</figure-callout>}}_1}$ Three, see that again expressing a desirable cycle rectangle spectrum transmittance function (see figure 4) for the fourier series of ideal period rectangle spectrum transmittance function is $T\left(f\right)=\underset{n}{\mathrm{\&Sigma;}}\mathrm{rect}\left(\frac{f-\mathrm{n\&Delta;f}}{\mathrm{\&delta;f}}\right),-----\left(19\right)$ Wherein δ f is the spectrum transmitting A/F, for demultiplexer, is through passband width.This cycle rectangle spectrum transmittance function can be expressed as with fourier series $T\left(f\right)={\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_0+{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_1\cos \left(2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;f}}\right)+T_2\cos \left(2\mathrm{\&pi;}\frac{2f}{\mathrm{\&Delta;f}}\right)+T_3\cos \left(2\mathrm{\&pi;}\frac{3f}{\mathrm{\&Delta;f}}\right)+....+T_n\cos \left(2\mathrm{\&pi;}\frac{\mathrm{nf}}{\mathrm{\&Delta;f}}\right)+....,-----\left(20\right)$ Wherein fourier coefficient is ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_0=\frac{\mathrm{\&delta;f}}{\mathrm{\&Delta;f}},-----\left(21-1\right)$ $T_n=2\frac{\mathrm{\&delta;f}}{\mathrm{\&Delta;f}}\sin c\left(\frac{\mathrm{n\&delta;f}}{\mathrm{\&Delta;f}}\right)---(n\&NotEqual;0).--------(21-2)$

Four, obtain preparing the method for demultiplexer of the present invention according to above-mentioned analysis, particularly prepare the preparation method of core key element simulation wave plate

In order to obtain arbitrary aperture efficiency Rectangle spectrum transmittance function (referring to formula 19), can adopt K simulation wave plate and control their the mould polarization anglec of rotation and θ ₁, θ ₂, θ ₃...., θ _K, intermediate polarisation anglec of rotation θ _PWith spectral period Δ f ₁, Δ f ₂, Δ f ₃...., Δ f _K, make that the progression (formula 14) of the spectral-transmission favtor function that it produced is close with fourier series (formula 20) contrast of above-mentioned ideal period rectangular function, promptly obtain the spectral-transmission favtor function close with the ideal period rectangular function.This is called the fourier series method of comparison.

Specific practice is:

＜1〉selects the fourier series expression formula (20) of above-mentioned desirable cycle rectangle spectrum transmittance function for use $T\left(f\right)={\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_0+{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_1\cos \left(2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;f}}\right)+T_2\cos \left(2\mathrm{\&pi;}\frac{2f}{\mathrm{\&Delta;f}}\right)+T_3\cos \left(2\mathrm{\&pi;}\frac{3f}{\mathrm{\&Delta;f}}\right)+....+T_n\cos \left(2\mathrm{\&pi;}\frac{\mathrm{nf}}{\mathrm{\&Delta;f}}\right)+....,$ When being used for the accurate curve that calculates ideal period rectangle spectrum transmittance function, get n 〉=30, when be used for the progression coefficient ratio than the time progression got keep count of identical with the actual stage of the spectral-transmission favtor function of the filter (16) of simulation wave plate formation;

＜2〉spectral-transmission favtor function series expression formula (14) T (the f)=T of the filter (16) of foundation simulation wave plate formation ₀+ T ₁Cos (2 π γ ' ₁F)+T ₂Cos (2 π γ ' ₂F)+T ₃Cos (2 π γ ' ₃F)+... .+T _nCos (2 π γ ' _nF)+...., T wherein _nBe with the simulation wave plate in the angle θ of the relative incident polarization light direction of analog polarization rotary plate rotation ₁, θ ₂, θ ₃...., θ _KRelevant, also with intermediate polarisation circulator 8 rotatory polarization angle θ _PRelevant coefficient, Δ f _n' be the equivalent spectrum cycle of n item;

Desired spectral-transmission favtor period of a function Δ f has determined the spectral period of polarization interference of the maximum of simulation wave plate, therefore the spectral period of at least one simulation wave plate should equal Δ f, the spectral period of the simulation wave plate of all the other K-1 should equal Δ f or doubly dwindle for the integer ratio of Δ f, at this moment the relevant γ ' in the following formula (being formula 14) _nValue be γ _bOr its integral multiple (0,1,2,3......),

Identical γ ' (γ _b) item of value merges, the series statement that finally obtains approaching the spectral-transmission favtor function of the filter (16) that the simulation wave plate of desirable cycle rectangle spectrum transmittance function (formula 20) constitutes is: T (f)=T ' ₀+ T ' ₁Cos (2 π γ _bF)+T ' ₂Cos (2 * 2 π γ _bF)+T ' ₃Cos (3 * 2 π γ _bF)+; (22)

+ ... .+T ' _nCos (n * 2 π γ _bF)+.... in (22) formula, T ' _nAs above-mentioned T _nBe with K simulation wave plate in K analog polarization rotary plate angle θ that the incident polarization light direction is rotated ₁, θ ₂, θ ₃..., θ _KAbout and with intermediate polarisation circulator 8 rotatory polarization angle θ _PRelevant coefficient;

＜3〉simplify to calculate variable, when the aperture efficiency of the spectral-transmission favtor function of the filter (16) that constitutes when the simulation wave plate is integral multiple (P＞1), P * 1 of ideal period rectangle spectrum transmittance function, P * 2, P * 3 ... the progression coefficient be zero, therefore can select specific and fixing θ for use _PValue and θ ₁, θ ₂-θ ₁, θ ₃-θ ₂...., θ _K-θ _K-1Among some be the particular fixed value, this will simplify following search and calculate;

＜4〉determine parameter: select for use maximum summit value of transmissivity and smallest peaks valley to be respectively 1 and 0, because the actual simulation wave plate number that uses is limited, the progression item of the transmittance function that it produces also is limited, therefore can not form as above-mentioned so desirable cycle rectangular function, but can realize smooth seeing through passband and see through stopband.Put before this and to have defined flatness, set peak-peak and reduced the width of s% for seeing through the spectral width δ f of passband, set minimum peak and increase the width of s% for seeing through the stopband spectral width, when s=0.1, reach-cross interference of 30dB, reach during s=1-20dB, determine the aperture efficiency in smooth passband and cycle

, the quantity K of the simulation wave plate that is adopted (5,6,7) and transmission are made the curve of desirable spectrum transmittance function by the frequency of light wave f of the simulation filter that wave plate constituted according to the expression formula (formula 20) of the first step;

＜5〉adopt searching method, seek the angle θ of K analog polarization rotary plate incident polarization light direction rotation in K the simulation wave plate ₁, θ ₂, θ ₃...., θ _KAnd θ _P, θ _kAnd θ _PCan be starting point with polarization direction of importing first simulation wave plate time bundle, perhaps the direction of rotation with the analog polarization rotary plate in the previous simulation wave plate be a starting point, in full-shape-180 °＜θ＜180 ° scope, obtains θ every specific angle value Δ θ≤5 ° ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary;

＜6〉with above-mentioned definite parameter and the θ that obtains ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that the is complementary coefficient T of trying to achieve ' _nIn the fourier series expression formula (22) of the above-mentioned spectral transmittance function by the filter that constitutes of simulation wave plate of substitution, and draw the curve of spectral transmittance function, with fourier series (20) the formula contrast of above-mentioned desirable cycle rectangle spectral-transmission favtor, find out the θ that satisfies the approaching desirable cycle rectangle transmittance function curve that flatness requires ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary at angle;

＜8〉θ of the above-mentioned acquisition of foundation ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary determine analog polarization rotary plate in the simulation wave plate.When analog polarization rotary plate is that the logical light length of analog polarization rotary plate is when adopting gyrotropi crystal:

Wherein ζ is the specific rotatory power of gyrotropi crystal; Perhaps when analog polarization rotary plate was half-wave plate, the angle ξ of the fast axle of half-wave plate or slow axis and input polarisation of light direction was:

What the technology [1] formerly compared with technology formerly adopted is optical fiber and fiber grating, what formerly technology [2] adopted is the plane integrated optics, what the present invention adopted is the filter that the identical simulation wave plate of structure constitutes, it is the simulation wave plate that discrete optical element is fitted together, can use the traditional optical process technology to process each optical element, it is simple to have equipment, the reliable advantage of technology.And compare with technology [1] [2] formerly, the present invention adopts medium and the mould polarization beam splitter in the simulation wave plate to close bundle sheet etc., has avoided the influence of curvature effect and stress polarization.What formerly technology [3] adopted is the birefringence of crystal, in contrast to this present invention adopt the simulation wave plate be two media 503, therefore 504 refringence can not only the very big equivalent birefringence difference of formation range, and can reach the equivalent birefringence more much bigger than monolithic crystal birefringence.The refractive index of optical glass is 1.45-1.8, the refractive index of optical crystal is 1.5-2.2, for example in first of 1550nm wavelength BK7 glass and lithium columbate crystal combination, second medium 503,504 birefringence can reach 0.7, much larger than single quartz crystal birefringence 0.0084, lithium columbate crystal birefringence 0.073, calcite crystal birefringence 0.156 and yttrium vanadate crystal birefringence 0.209, therefore analog wave chip architecture of the present invention is simple, the high-quality medium is easy to get, the choice of dielectric material is big and price is low, be easy to realize the odd even separation of all size spectral frequency wavelength-division signal at interval, be specially adapted to the highly dense wavelength-division multiplex signals and realize the crystal interferometric method with and formerly the inaccessible very little spectral frequency of technology is at interval, simultaneously when debuging, as long as rotating media is realized the fine tuning of spectral bandwidth to changing light path, device is easy to adorn the school.Only obtain one group θ with technology [3] formerly ₁, θ ₂, θ ₃...., θ _KAnd θ _PCompare, the present invention adopts the fourier series method of comparison can access through the more smooth more θ of peak value ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary.Compare with technology [4] formerly, the present invention adopts the search method of forward, and method is simpler, and it is different dielectric thicknesses that the simulation wave plate can use different spectrum fundamental frequencies, reduces the usage quantity of simulation wave plate.

Description of drawings:

Fig. 1 is the structural representation of the neat even signal separator of the present invention.

Fig. 2 is first kind of structural representation of simulation wave plate among Fig. 1.

Fig. 3 is second kind of structural representation of simulation wave plate among Fig. 1.

Fig. 4 is the curve waveform figure of desirable cycle rectangle transmittance function.

Fig. 5 is the curve waveform figure of the planarization spectral-transmission favtor function that produces in the embodiment.

Embodiment:

Structure as shown in Figure 1, enforcement be that to be used for input signal be that 50GHz spectral frequency wavelength-division multiplex signals odevity at interval is separated into 100GHz spectral frequency odd even wavelength-division demultiplexer at interval, be used for λ=1550nm wave band.

One, according to above-mentioned specific practice preparation simulation wave plate

Concrete way as mentioned above.

When definite odd even separator produces the aperture efficiency in smooth passband and cycle Be 2: 1 the smooth passband of cycle and the spectrum transmitting function of stopband, what obtained by the formula in the above-mentioned first step (20) is that the fourier series of ideal period rectangular function has only odd number frequency item, for $T\left(f\right)=0.5+\frac{2}{\mathrm{\&pi;}}\cos \left(2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;f}}\right)-\frac{2}{3\mathrm{\&pi;}}\cos \left(2\mathrm{\&pi;}\frac{3f}{\mathrm{\&Delta;f}}\right)+\frac{2}{5\mathrm{\&pi;}}\cos \left(2\mathrm{\&pi;}\frac{5f}{\mathrm{\&Delta;f}}\right)-....+...,-----\left(23\right)$

Be that three simulations of employing wave plates are K=3 in the present embodiment, concrete structure sees Fig. 1, and its spectral-transmission favtor function and relevant parameters thereof are provided by formula (16)-(18), have 14.

For producing, set Δ f near the expressed desirable cycle rectangular function of formula (15) ₁=2 Δ f ₂=2 Δ f ₃=Δ f, θ ₁=45 ° and θ _p=0 °, at this moment the form that embodies of (22) formula of the spectral-transmission favtor function of odd even separator is: $T\left(f\right)=0.5+({\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A0211098400221.png"\; state="\{\{state\}\}">T</figure-callout>}}_1+T_8+T_9+T_{12}+T_{13})\cos \left(\frac{2\mathrm{\&pi;f}}{\mathrm{\&Delta;f}}\right)+(T_4+{\mathrm{<figure-callout\; id="5"\; label="T"\; filenames="A0211098400212.png"\; state="\{\{state\}\}">T</figure-callout>}}_5+T_{11})\cos \left(\frac{6\mathrm{\&pi;f}}{\mathrm{\&Delta;f}}\right)+T_{10}\cos \left(\frac{10\mathrm{\&pi;f}}{\mathrm{\&Delta;f}}\right).---\left(24\right)$

With search method every Δ θ=1 ° to θ ₂And θ ₃In-180 ° to 180 °, do the circulation searching and satisfy the desired θ of planarization spectral-transmission favtor function ₂And θ ₃, require except zero level since 1 grade, should be the progression of alternate positive and negative, so be T for 1 grade of above-mentioned (24) formula ₁+ T ₈+ T ₉+ T ₁₂+ T ₁₃＞0,5 grades is T ₁₀＞0 and 3 grades be T ₄+ T ₅+ T ₁₁＜0, and limit seeing through of passband be 1 and stopband to see through be 0, the shake of passband and stopband be not more than 0.1% (30dB), the result that can adopt is as follows:

????θ 2°	????θ 3°	The ratio of pass band width and spectrum interval	The ratio of bandwidth of rejection and spectrum interval
				????-72	????84	????0.185185
????-18	????6
		????-71	????83	????0.199199
????-19	????7
		????-70	????82			????0.202202
????-20	????8
		????-70	????83	????0.190190
????-20	????7
		????-69	????81			????0.192192
????-21	????9
		????-69	????82	????0.189189
????-21	????8

Fig. 5 is that the structure that adopts in the present embodiment is θ ₁=45 °, θ ₂=-71 °, θ ₃=83 °, θ _PPlanarization spectrum transmitting rate curve under=θ °, the most approaching with the curve waveform of desirable cycle rectangular transmission rate function shown in Figure 4.

Two, about device architecture

Overall structure sees Fig. 1.Three simulation wave plates 5,6,7 of K=3 all adopt second kind of structure shown in Figure 3, and two media all adopts optical glass, and the trade mark of first medium 503 is SF11, and second medium 504 is the glass of BK7, the refractive index n of first medium 503 _aBe n _aThe refractive index n of=1.74474, second medium 504 _bBe n _b=1.50065, equivalent birefringence n=0.24409.Because Δ f ₁=2 Δ f ₂=2 Δ f ₃So, 2L ₁=L ₂=L ₃(L wherein _{A, 1}=L _{B, 1}=L ₁, L _{A, 2}=L _{B, 2}=L ₂, L _{A, 3}=L _{B, 3}=L ₃).Obtain L by formula (4-2) and (5) ₁=12.282mm and L ₂=L ₃=24.564mm.

Incident be through the collimation optical fiber beam, bore is Φ 0.5mm, two light beam (a in device ₁And a ₂) central optical axis be spaced apart 1.5mm, therefore four light beam (b ₁, b ₂, c ₁, c ₂) central optical axis be spaced apart 1.5mm * 1.5mm.In order to guarantee the whole logical light of four light beams, the logical light face of optical element is of a size of 2.5 * 2.5mm ²The calcite crystal piece that the beam incident surface that all polarization beam apparatus and polarization beam combiner all adopt monolithic to cut naturally parallels with exit facet, be the ordinary light of generation 1.5mm and separating of unusual light two central optical axis, the logical light length of calcite crystal is～13.5mm.Polarization rotator and analog polarization rotary plate all are quartzy half-wave plates, the analog polarization rotary plate 501 of first simulation in the wave plate 5 with respect to incident polarized light a ₁, a ₂Polarization anglec of rotation θ ₁Be 45 °, angle ξ=22.5 of the fast axle (or slow axis) of half-wave plate and input polarisation of light direction ° then.The polarization anglec of rotation θ of the analog polarization rotary plate 601 in the second simulation wave plate 6 ₂Be-71 °, angle ξ=-35.5 of the fast axle (or slow axis) of its half-wave plate and input polarisation of light direction °.The polarization anglec of rotation θ of the analog polarization rotary plate 701 in the 3rd simulation wave plate 7 ₃Be 83 °, angle ξ=41.5 of the fast axle (or slow axis) of its half-wave plate and input polarisation of light direction °.Because θ _P=0, intermediate polarisation circulator 8 can not wanted.In a word, the general shape size of the odd even separation filter of present embodiment is approximately 2.5mm * 2.5mm * 180mm (long * wide * dark).

Claims (3)

1. Birefingent cascade polarized interference old-even signal separator specifically includes:

＜1〉collimating lens (2), output end face places the input optical fibre (1) on collimating lens (2) front focus, first condenser lens (12) that arranged side by side storing arranged and second condenser lens (14) relative on the light path of input optical fibre (1) output beam with collimating lens (2), input end face places has first output optical fibre (13) on first condenser lens (12) back focus, and input end face places has second output optical fibre (15) on second condenser lens (14) back focus;

＜2〉on the light path between collimating lens (2) and two condenser lenses (12,14), be equipped with input polarization beam splitter (3), on the light path between input polarization beam splitter (3) and two condenser lenses (12,14), be equipped with output polarization bundling device (11);

It is characterized in that:

＜3〉on the light path between input polarization beam splitter (3) and the output polarization bundling device (11), input polarization circulator (4) is arranged, on the light path between input polarization circulator (4) and the output polarization bundling device (11), output polarization circulator (10) is arranged, on the light path between input polarization circulator (4) and the output polarization circulator (10), output polarization beam splitter (9) is arranged;

＜4〉on the light path between input polarization circulator (4) and the output polarization beam splitter (9), be equipped with filter (16) by the identical K of structure 〉=1 simulation wave plate (5,6,7) constitutes;

＜5〉in filter (16) on the light path between K simulation wave plate and the output polarization beam splitter (9) or be equipped with intermediate polarisation circulator (8).

2. Birefingent cascade polarized interference old-even signal separator according to claim 1, the simulation wave plate (5 that it is characterized in that said formation filter (16), 6,7), comprise incident polarized light rotation-180 °＜θ＜180 ° angle, the analog polarization rotary plate that the plane of incidence of light beam and exit facet are parallel to each other (501), the mould polarization that has beam incident surface and exit facet to be parallel to each other closes bundle sheet (505), and analog polarization rotary plate (501) two parallel beam incident surfaces close bundle sheet (505) two parallel beam incident surface and exit facets with exit facet and mould polarization and all close the central axis (OO of both coincidences of bundle sheet (505) perpendicular to analog polarization rotary plate (501) and mould polarization ₂), close between the bundle sheet (505) at analog polarization rotary plate (501) and mould polarization, two parallel beam incident surfaces and exit facet are arranged perpendicular to central axis (OO ₂), and center (O ₁) at central axis (OO ₂) on mould polarization beam splitter (502), mould polarization beam splitter (502) and mould polarization close be equipped with between the bundle sheet (505) refractive index inequality along its length with central axis (OO ₂) first medium (503) and second medium (504) of parallel storing arranged side by side, close between the bundle sheet (505) or be equipped with second analog polarization rotary plate (506) at two media (503,504) and mould polarization.

3. the preparation method of Birefingent cascade polarized interference old-even signal separator according to claim 1 and 2, it is characterized in that preparing core parts simulation wave plate (5,6,7) be to adopt by simulation wave plate (5,6,7) the close fourier series method of comparison of fourier series contrast of the progression of the spectral-transmission favtor function that produced of the filter of Gou Chenging (16) and desirable cycle rectangle spectrum transmittance function, specific practice is:

＜1〉select for use the fourier series expression formula of desirable cycle rectangle spectrum transmittance function to be: $T\left(f\right)=T_0+T_1\cos \left(2\mathrm{\&pi;}\frac{f}{\mathrm{\&Delta;f}}\right)+T_2\cos \left(2\mathrm{\&pi;}\frac{2f}{\mathrm{\&Delta;f}}\right)+T_3\cos \left(2\mathrm{\&pi;}\frac{3f}{\mathrm{\&Delta;f}}\right)+...+T_n\cos \left(2\mathrm{\&pi;}\frac{\mathrm{nf}}{\mathrm{\&Delta;f}}\right)+...\left(1\right)$ (1) fourier coefficient is in the formula

Wherein f is the frequency of light wave of transmission, Δ f-and be spectral period, δ f-be to see through passband width, -be aperture efficiency, n is that level is inferior, positive integer;

＜2〉determine the spectral period parameter of simulation wave plate: the maximum cycle of determining the spectral-transmission favtor function of a simulation wave plate is that the spectral period of all the other K-1 of Δ f simulation wave plate should equal Δ f or doubly dwindles for the integer ratio of Δ f, when

Be γ _bOr its integral multiple (0,1,2, in the time of 3......), identical γ _bThe item of value merges, the series statement of the spectral-transmission favtor function of the filter (16) that the simulation wave plate of the cycle rectangle spectrum transmittance function that (1) formula that finally approached is desirable constitutes: T (f)=T ' ₀+ T ' ₁Cos (2 π γ _bF)+T ' ₂Cos (2 * 2 π γ _bF)+T ' ₃Cos (3 * 2 π γ _bF)+

(2)

+ ... .+T ' _nCos (n * 2 π γ _bF)+.... T ' in (2) formula _nBe with K simulation wave plate in K analog polarization rotary plate angle θ that the incident polarization light direction is rotated ₁, θ ₂, θ ₃..., θ _KAbout and with intermediate polarisation circulator 8 rotatory polarization angle θ _PRelevant coefficient;

＜3〉simplify to calculate variable in advance: when the aperture efficiency of the spectral-transmission favtor function of the filter (16) that constitutes when the simulation wave plate is integral multiple (P＞1), P * 1 of ideal period rectangle spectrum transmittance function, P * 2, P * 3, ... the progression coefficient of item is zero, therefore can select the θ of particular fixed _PValue and θ ₁, θ ₂-θ ₁, θ ₃-θ ₂...., θ _K-θ _K-1Among some be the particular fixed value;

＜4〉determine parameter: select for use maximum summit value of transmissivity and smallest peaks valley to be respectively 1 and 0, the aperture efficiency in smooth passband and cycle , quantity K 〉=1 of the simulation wave plate that comprises in the filter that is adopted, transmission requires the s% value by the frequency of light wave f and the flatness of the filter that the simulation wave plate constitutes, and makes the curve of desirable spectrum transmittance function according to the expression formula (1) of the first step;

＜5〉adopt search method, seek the angle θ of K the relative incident polarization direction rotation of analog polarization rotary plate in K the simulation wave plate ₁, θ ₂, θ ₃...., θ _KRotatory polarization angle θ with the intermediate polarisation circulator _P, θ _kAnd θ _PCan be starting point with polarization direction of importing first simulation wave plate time bundle, perhaps the direction of rotation with analog polarization rotary plate in the previous simulation wave plate be a starting point, in full-shape-180 °＜θ＜180 ° scope, obtains θ every specific angle value Δ θ≤5 ° ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary;

＜6〉with above-mentioned definite parameter and the θ that obtains ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe coefficient T that the combination angle that is complementary is tried to achieve ' _nIn the above-mentioned expression formula of substitution (2) formula, draw the curve of the spectral-transmission favtor function of the filter that constitutes by the simulation wave plate, with the curve contrast of above-mentioned desirable cycle rectangle spectrum transmittance function, satisfying under the flatness s% situation, select the most akin combination angle θ that is complementary ₁, θ ₂, θ ₃...., θ _KAnd θ _P

＜7〉θ that obtains according to above-mentioned the 6th step ₁, θ ₂, θ ₃...., θ _KAnd θ _PThe combination angle that is complementary is determined analog polarization rotary plate and intermediate polarisation circulator in the simulation wave plate, and when adopting gyrotropi crystal, the logical light length of analog polarization rotary plate and intermediate polarisation circulator is: Wherein ζ is the specific rotatory power of gyrotropi crystal, and perhaps when analog polarization rotary plate and intermediate polarisation circulator were half-wave plate, the fast axle or the slow axis of half-wave plate with the angle ξ that imports the polarisation of light direction were:

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