CN101034190A - Odevity demultiplexer based on cascaded ring-shaped cavity pairs structure - Google Patents

Abstract

This invention relates to a cascade odd and even number demultiplexer that is on the basis of toroid cavity structure. The invention includes an input optical fiber, a first output optical fiber and a second output optical fiber. The invention includes standard placed lens, a polarizing beam splitter, an input half wave plate and a cascade toroid cavity along antegrade direction of output beam of input optical fiber in order; the invention includes a first input half wave plate, a first polarizing combining beam equipment, a first focusing lens and a stated first output optical fiber along antegrade direction of output horizontal beam of cascade toroid cavity in order; the invention includes a second output half wave plate, a second polarizing combining beam equipment, a second focusing lens and a stated second output optical fiber along antegrade direction of output perpendicular light beam of cascade toroid cavity in order. This invention is mainly used in wave separating reused communication system to separate double chain of odd and even number of wave separating reused signal and for absorber that needs to smooth spectral transmission rate function.

Description

Based on the odd-even signal separator of cascade ring cavity to structure

Technical field:

The present invention is a kind of odd-even signal separator, and particularly a kind of mainly can be used in the wavelength-division multiplex technique separated the odevity signaling channel (interleaver) and also be can be used for the wave filter that all need planarization spectral-transmission favtor function.

Background technology:

Along with developing rapidly of close wavelength-division multiplex technology, signal frequency is more and more little at interval, needs to adopt the wavelength division multiplex device of narrower frequency interval to come dilatation, and this has also just proposed higher spectrally resolved requirement to multiplexing demultiplexing device.And the very ripe multiplexing demultiplexing device of original technology, reaching more as the dielectric film wave filter to 50GHz, small frequency channel signal at interval is difficult to continue to use.Odevity wavelength-division multiplex signals separation vessel (hereinafter to be referred as the odd even separation vessel) can be separated into one group of wavelength-division multiplex signals serial and two channels of even number series of one group of odd number of sigtnal interval multiplication, so just reduced the burden that Wave division multiplexer/demultiplexer requires the wavelength interval, improved system transmission capacity, so the odd even separation vessel is a kind of important optical communication core devices.In order effectively to separate the odevity signal, realize the low pass intertrack crosstalk, the odd even separation vessel must possess smooth and the passband of high-contrast and the spectrum transmitting characteristic of stopband.In addition, along with improving constantly of system transmissions speed, the odd even separation vessel also must have low dispersion characteristics.

Formerly technology [1] (referring to optical communication technique, Feng Dejun etc., 2000, (1), what 29-32) describe is the wavelength-division multiplex system device of a kind of full optical fiber mach-Ze De (Mach-Zehnder) interferometer type structure.This formerly technology can be used as odd-even signal separator equally, require the splitting ratio of first fiber coupler this moment is 1: 1, interferes the length difference of arm and the splitting ratio of second fiber coupler can make the output two-port obtain odd number set of wavelengths flashlight and even number set of wavelengths flashlight respectively by controlling two.But formerly technology is to the having relatively high expectations of two arm optical path differences and second coupling mechanism splitting ratio for this, and existing coupling mechanism drawing process is to second the difficult control of coupling mechanism beam splitting.In addition, formerly technology is comparatively responsive to temperature, polarization etc. for this, and such device also should solve the influence that this type of problem is brought simultaneously.

Formerly technology [2] (referring to Opt.Commu., C.W.Lee, R.Wang, R.Yeh et al., 2006,260, what 311-317) describe is a kind of birefringence odd-even signal separator of ring cavity structure.Its ring cavity structure that adopts is made of a prism and two catoptrons, and two light beams of S and P polarization state are different in this ring cavity boundary reflection rate, thereby produces different equal the diverting from one use to another in the spectral-transmission favtor that obtains planarization in position.The maximum characteristics of this structure are to have avoided using the coating process of the pinpoint accuracy requirement in the traditional endless cavity configuration in its ring cavity structure.But the odd-even signal separator of this structure has high dispersion characteristics, is unfavorable for using in the transmission system of two-forty.

Formerly technology [3] (referring to Opt.Lett., K.Okamoto and H.Yamada, 20 (1), 1995, described in 43-45) is that a kind of array waveguide grating (the English AWG of abbreviation) that utilizes produces the spectral response functions of planarization.Its design concept by the simulation beam propagation, has realized the smooth SPECTRAL REGION greater than 57.2Ghz of 100GHz channel spacing based on discrete Fourier transform (DFT).Can realize the multiplex/demultiplex function in the wavelength-division multiplex technique, insert functions such as dividing multiplexing function and wavelength route.But this formerly technology exist to insert loss bigger, the Polarization Dependent Loss height, shortcoming such as temperature stability is bad must adopt other method and apparatus to eliminate the influence of polarization and temperature etc., thereby limit its application in the practical application.

Formerly technology [4] (referring to Opt.Commu., X.Ye, M.Zhang and P.Ye, 2006,257, what 255-260) describe is a kind of odd-even signal separator of cascade M-Z interferometer type of ring cavity structure.Its ring cavity structure that adopts is made of beam splitter and catoptron, thus two have the ring cavity of beam splitter splitting ratio not place respectively position that two arms of M-Z interferometer are used for light beam mutually modulation produce the spectral-transmission favtor function of high flat characteristic and isolation.Adopt extra ring cavity to be used for dispersion compensation at two output terminals again to improve the dispersion characteristics of entire device.Though the odd-even signal separator dispersion characteristics of this structure are improved, all contain beam splitter in its each ring cavity, the thin-film technique that this just inevitably still will use pinpoint accuracy to require, thereby do not utilize practical application.

Summary of the invention:

The objective of the invention is to overcome the difficulty of above-mentioned technology formerly, provide a kind of based on the odd-even signal separator of cascade ring cavity to structure, that this separation vessel has is simple in structure, technology is reliable, cost is low, performance is good, high reliability features.

For achieving the above object, design of the present invention is to adopt 2 ring cavitys to the structure cascade, two right prism boundary of each ring cavity are coated with semi-transparent semi-reflecting film, respectively to the light beam beam splitting with close bundle, ring cavity plays light beam is carried out the position effect of modulation mutually, the refractive index of control first order ring cavity centering two prisms can obtain big flat-top passband (or stopband) width and high channel isolation, separates reliably thereby form the odevity signal; Adopt second level ring cavity to being used for dispersion compensation to improve dispersion characteristics.

According to above-mentioned inventive concept, concrete technical solution of the present invention is as follows:

A kind of based on the odd-even signal separator of cascade ring cavity to structure, comprise an input optical fibre, first output optical fibre and one second output optical fibre; It is characterized in that: it is right that the direction of advancing along described input optical fibre output beam is provided with a collimation lens, a polarization beam apparatus, an input half-wave plate and a cascade ring cavity successively; Along the cascade ring cavity output horizontal light beam working direction is provided with one first described first output optical fibre of exporting half-wave plate, first polarization beam combiner, first condenser lens and being positioned at this first condenser lens focus successively; Along the cascade ring cavity output normal beam working direction is provided with one second described second output optical fibre of exporting half-wave plate, second polarization beam combiner, second condenser lens and being positioned at this second condenser lens focus successively.

The cascade ring cavity is to being that ring cavity by two same structures constitutes cascade, wherein two of each ring cavity centering ring cavity structures are identical, each ring cavity is formed by a prism and two catoptrons, two catoptrons and prism symmetry are placed, and promptly prism equates with two catoptron angulations.Identical, the equal and opposite in direction of two prisms structure of each ring cavity centering, the planar structure of prism is a pentagon, be with the base angle equal 45 ° isosceles trapezoid cut away go to the bottom for this is trapezoidal pentagon of isosceles right triangle of a part of a hypotenuse at a base angle; In addition, the two prisms cross surface of each ring cavity centering is coated with semi-transparent semi-reflecting film.

The prism of each ring cavity centering adopts isotropic material or the glass of different refractivity is arranged.Polarization beam apparatus and first, second polarization beam combiner adopt birefringece crystal.

Technique effect of the present invention:

The present invention adopts discrete optical element package technique, has avoided using fiber coupling technique in technology [1] and the array waveguide grating technology in technology [3] earlier earlier, has reduced the influence of problems such as polarization, temperature; Avoid the coating process that uses pinpoint accuracy to require in the ring cavity structure that is adopted, be better than technology [4] formerly; This structure also adopts the extra ring cavity in the second level to be used for dispersion compensation, thereby dispersion characteristics are better than technology [2] formerly.To sum up, odd-even signal separator of the present invention has that equipment is simple, technology is reliable, production cost is low and excellent performance, reliability advantages of higher.The present invention mainly is used in parity signal two channel separation that are used for wavelength-division multiplex signals in the wavelength division multiplexing communications systems needs the wave filter of planarization spectral-transmission favtor function with all.

Description of drawings:

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

Fig. 2 index path that to be light propagate in to 5 at the cascade ring cavity of Fig. 1.

Fig. 3 is the structural representation of cascade ring cavity to the ring cavity in 5, and wherein l is the optical length of light in ring cavity.

Fig. 4 is the channel isolation curve map of 25GHz odd-even signal separator of the present invention.

Fig. 5 is the passband width curve map at the 0.5dB place of 25GHz odd-even signal separator of the present invention.

Fig. 6 is the resistance band curve map at the 30dB place of 25GHz odd-even signal separator of the present invention.

Fig. 7 is for the dispersion compensator of 25GHz odd-even signal separator of the present invention and before carrying out dispersion compensation with the dispersion characteristic curve figure after the compensation.

Embodiment:

Details are as follows in conjunction with the accompanying drawings for a preferred embodiment of the present invention:

Referring to Fig. 1, this comprises input optical fibre 1 based on the cascade ring cavity to the odd-even signal separator of structure, be equipped with collimation lens 2 successively on the direction that the emission light beam advances, polarization beam apparatus 3, be input half-wave plate 4 subsequently, the cascade ring cavity to 5 place the input half-wave plate 4 after, then be provided with the first output half-wave plate 6 and first polarization and bundle device 7 successively along this light path horizontal direction, vertical direction along this light path is provided with the second output half-wave plate 10 and second polarization and bundle device 11 successively, the light beam of exporting from first polarization and bundle device 7 end faces is connected with first condenser lens 8 and first output optical fibre 9 that places on first condenser lens, 8 focuses, is connected with second condenser lens 12 and second output optical fibre 13 that places on second condenser lens, 12 focuses from second polarization and the light beam of restrainting the output of device 11 end faces.

The cascade ring cavity is formed 14,15 cascades by the ring cavity of two same structures successively to 5, as shown in Figure 2, wherein each ring cavity is identical to two ring cavity structures in 14,15, each ring cavity is formed by a prism 16 and two catoptrons 17,18, two catoptrons 17,18 and prism 16 symmetries are placed, and promptly prism 16 equates with two catoptrons, 17,18 angulations.Each ring cavity is to identical, the equal and opposite in direction of two prisms 16 structures in 14,15, the planar structure of prism 16 is a pentagon, is the base angle to be equaled 45 ° isosceles trapezoid cut away go to the bottom for this is trapezoidal pentagon of isosceles right triangle (dash area among Fig. 3) of a part of a hypotenuse at a base angle; In addition, each ring cavity is coated with semi-transparent semi-reflecting film to two prisms 16 cross surfaces in 14,15.Because two catoptrons 17,18 are placed with respect to prism 16 symmetries in each ring cavity, then the light beam of glancing incidence ring cavity is with vertical outgoing ring cavity.The light path of light in ring cavity as shown in Figure 3.

Collimation lens 2 is used for random polarized wave division multiplex signal light beam to input optical fibre 1 emission and collimates and expand bundle, the parallel light pencil x of collimation lens 2 outputs, it incides the parallel beam that is broken down into the two bundle polarized orthogonals that separate about equicohesive behind the polarization beam apparatus 3 in the horizontal direction, 4 unusual light beams for the vertical polarization on the left side of input half-wave plate work, and 90 ° in rotatory polarization direction, thereby be the parallel beam that two bundles are all the horizontal direction polarization behind the input half-wave plate 4, enter the cascade ring cavity subsequently again to 5.

From the cascade ring cavity 5 right side is exported at horizontal in-plane polarization two parallel beams parallel to each other, from the cascade medium polarization state two parallel beams parallel to each other in perpendicular are exported in 5 lower surface, the first output half-wave plate 6 produces additional 90 ° polarization direction rotation for left side light beam parallel to each other in horizontal plane, 10 pairs of left side light beams parallel to each other in perpendicular of the second output half-wave plate produce additional 90 ° polarization direction rotation, therefore by behind the first output half-wave plate 6, two-beam polarization direction in the same horizontal plane is orthogonal, behind the second output half-wave plate 10, two-beam polarization direction in the same perpendicular is also orthogonal, first polarization beam combiner 7 is combined light beam in the horizontal direction, it makes the interior two parallel light beams of horizontal plane of two bundle polarization direction quadratures merge into output beam y, second polarization beam combiner, 11 in the vertical direction combined light beams, it makes the interior two parallel light beams of perpendicular of two bundle polarization direction quadratures merge into output beam z.First condenser lens 8 focuses on and is coupled into for y road output beam among first output optical fibre 9, and second condenser lens 12 focuses on and is coupled among second output optical fibre 13 for z road output beam.

In the system, polarization beam apparatus 3 and input half-wave plate 4 are used to decompose the input beam of random polarization, the first output half-wave plate 6 and first polarization beam combiner 7 are used for the light beam on the filtered horizontal direction is synthesized again the output beam of random polarization, the second output half-wave plate 10 and second polarization beam combiner 11 are used for the light beam on the filtered vertical direction is synthesized again the output beam of random polarization, and fundamental purpose is the operating characteristic of realization and input beam polarization irrelevant.

Cascade ring cavity between the input half-wave plate 4 and the first output half-wave plate 6 (or second output half-wave plate 10) is cores of total system to 5, as accompanying drawing 2, beam level incident first order ring cavity is on 14 the cross surface, the light of half energy is reflected, the light of second half energy is by transmission, this two-beam transmission generation delay in two prisms 16 respectively afterwards, then respectively incident left side ring cavity (being designated as ring cavity 1) carries out the position with right side ring cavity (being designated as ring cavity 2) and modulates mutually, the vertical incidence ring cavity is to 15 subsequently, and on its cross surface, interfere, second level ring cavity to the left side ring cavity (being designated as ring cavity 3) in 15 and right side ring cavity (being designated as ring cavity 4) respectively to two light beams of 15 cross surface outgoing being carried out dispersion compensation from ring cavity, one road light is directly exported 5 lower surface from the cascade ring cavity subsequently, form even road output beam, another Lu Guangcong cascade medium is exported 5 right side, forms strange road output beam.By the refractive index of suitable each prism of selection, can obtain having big smooth passband (and stopband) width, the spectral-transmission favtor of high isolation and low dispersion characteristics.

One. the generation of planarization spectral-transmission favtor

When the incident light glancing incidence ring cavity with s polarization state to 5 the time, the reflectivity of the prism-air interface of ring cavity can be expressed as:

Here, n is the refractive index of prism, and θ is the refraction angle.

The normalization transmissivity at arbitrary output port place can be expressed as:

$I={\cos }^2[\frac{\mathrm{\π}}{\mathrm{\λ}}(n_2-n_1)L+({\mathrm{\φ}}_2-{\mathrm{\φ}}_1)/2],---\left(2\right)$

Here, λ is an optical wavelength, L by light from the 1st grade of ring cavity of incident to cross surface to the 2nd grade of ring cavity of incident to the cross surface process in prism the distance of process, n ₁, n ₂Be respectively the refractive index of ring cavity, φ to two prisms 16 in 14 ₁, φ ₂Be respectively the catoptrical position phase translation of light in two ring cavitys 1,2, be expressed as:

${\mathrm{\&phi;}}_2-{\mathrm{\&phi;}}_1=-{2\tan }^{-1}\left(\frac{1-\sqrt{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}}{1+\sqrt{R_2}}\tan (\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\&CenterDot;\frac{{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">l</figure-callout>}}_2}{2})\right)+{2\tan }^{-1}\left(\frac{1-\sqrt{R_1}}{1+\sqrt{R_1}}\tan (\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}\&CenterDot;\frac{l_1}{2})\right),---\left(3\right)$

Here, R ₁, R ₂Be respectively the reflectivity of the prism-air interface of two ring cavitys 1,2, l ₁, l ₂Be respectively the optical length of light in two ring cavitys 1,2.In order to obtain required planarization spectral-transmission favtor, light in ring cavity optical length and light from the 1st grade of ring cavity of incident to cross surface to the 2nd grade of ring cavity of incident to the cross surface process in prism satisfy certain relation the distance of process, can be expressed as:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="l\; i"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">l</figure-callout>}}_i}{2}=(n_2-n_1)L,---\left(4\right)$

Here i=1,2.The spectral period of odd-even signal separator is:

$\mathrm{\&Delta;f}=\frac{C}{(n_2-n_1)L}---\left(5\right)$

Here C is the light velocity.

Two. dispersion characteristics and compensation

The group delay of odd-even signal separator is:

$\mathrm{\&tau;}\left(\mathrm{\&omega;}\right)=-\frac{1}{2}\&CenterDot;\frac{\&PartialD;}{\&PartialD;\mathrm{\&omega;}}({\mathrm{\&phi;}}_1+{\mathrm{\&phi;}}_2),---\left(6\right)$

Here, ω=2 π C/ λ, it is the optics angular frequency.According to chromatic dispersion definition D (λ)= τ/ λ, the chromatic dispersion of this odd-even signal separator can be expressed as:

$D\left(\mathrm{\&lambda;}\right)=\frac{{2r}_1(1-{r_1}^2)\&CenterDot;{\left(\frac{{\mathrm{\&pi;l}}_1}{\mathrm{\&lambda;}}\right)}^2\&CenterDot;\sin \left(\frac{{2\mathrm{\&pi;l}}_1}{\mathrm{\&lambda;}}\right)}{\mathrm{\&pi;c}{[1+{r_1}^2+{2r}_1\cos \left(\frac{{2\mathrm{\&pi;l}}_1}{\mathrm{\&lambda;}}\right)]}^2}+\frac{{2r}_2(1-{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2)\&CenterDot;{\left(\frac{{\mathrm{\&pi;<figure-callout\; id="2"\; label="l"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">l</figure-callout>}}_2}{\mathrm{\&lambda;}}\right)}^2\&CenterDot;\sin \left(\frac{{2\mathrm{\&pi;<figure-callout\; id="2"\; label="l"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">l</figure-callout>}}_2}{\mathrm{\&lambda;}}\right)}{\mathrm{\&pi;c}{[1+{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}^2+{2\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">r</figure-callout>}}_2\cos \left(\frac{{2\mathrm{\&pi;<figure-callout\; id="2"\; label="l"\; filenames="A20071003873300101.png"\; state="\{\{state\}\}">l</figure-callout>}}_2}{\mathrm{\&lambda;}}\right)]}^2},---\left(7\right)$

Here, $r_1(=\sqrt{R_1}),$ $r_1(=\sqrt{R_2})$ Be respectively the amplitude reflectance of the prism-air interface of ring cavity 1 and 2.

Three. the separation of parity signal

The core parts of this device for the cascade ring cavity that cascade constituted by two ring cavitys to 5, first order ring cavity is made the usefulness of beam splitting to 14 cross surface film, two ring cavitys carry out the position to the two-beam after the beam splitting respectively to be modulated mutually, and this two-beam interferes 15 cross surface film place at second level ring cavity subsequently.The equal refractive index that depends on two prisms 16 wherein of moving in position that light takes place in two ring cavitys, therefore the refractive index by two prisms 16 of suitable selection can produce the planarization spectral-transmission favtor with smooth passband and smooth stopband, keeping maximum transmission rate simultaneously is 1, minimum transmittance is 0, thereby the strange signal that is in passband is separated with the even signal that is in stopband.

Four. other

In above-mentioned said input half-wave plate 4 and first, second output half- wave plate 6,10, the fast axle (or slow axis) of half-wave plate is 45 ° with the angle of input polarisation of light direction, above-mentioned said polarization beam apparatus 3 and first and second polarization beam combiner 7,11 adopt the birefringece crystal sheet, and above-mentioned said cascade ring cavity adopts isotropic material such as glass to each prism in 5.

Fig. 1 is the optical system structure synoptic diagram of the embodiment of the invention.

Present embodiment is mainly used in the odd even of 25GHz wavelength-division multiplex signals to be separated.One-piece construction is seen accompanying drawing 1.The reflectivity of the optimization prism-air interface of ring cavity is respectively R ₁=0.5560, R ₂=0.0710.According to formula (1) and refraction law, the reflectivity that can calculate prism 16 is respectively n ₁=1.399, n ₂=1.224.By formula (5) can calculate light from the 1st grade of ring cavity of incident to cross surface to the 2nd grade of ring cavity of incident to the cross surface process in prism the distance of process be L=0.343m.Can calculate the optical length of light in two ring cavitys by formula (4) and be respectively l ₁=l ₂=0.012m.Fig. 4 is the channel isolation of this embodiment.Isolation is greater than 32dB as can be seen.Fig. 5 is the passband width at 0.5dB place.The passband width at 0.5dB place is 24GHz as can be seen from Figure 5, and it is 96% of this frequency interval.Fig. 6 is the resistance band at 30dB place.The resistance band at 30dB place is 21.2GHz as can be seen from Figure 6, and it is 84.8% of this frequency interval.

The prismatic refraction rate that is used for two ring cavitys of compensation of dispersion is 1.413, and the optical length of light in this ring cavity is 11991.7 μ m.Fig. 7 is the dispersion characteristics of the odd-even signal separator after this compensator and compensation length and the compensation.As can be seen from Figure 7, before the compensation, in the free transmission range internal dispersion of centre frequency 193,400 ± 2GHz be ± 90ps/nm, the compensation back in identical free transmission range internal dispersion is ± 50ps/nm.When free transmission range was centre frequency 193,400 ± 1GHz, chromatic dispersion can be ± 10ps/nm.

Claims (5)

1. one kind based on the odd-even signal separator of cascade ring cavity to structure, comprises an input optical fibre (1), first output optical fibre (9) and one second output optical fibre (13), it is characterized in that:

1) direction of advancing along described input optical fibre (1) output beam is provided with a collimation lens (2), a polarization beam apparatus (3), an input half-wave plate (4) and a cascade ring cavity successively to (5); Along the cascade ring cavity (5) output horizontal light beam working direction is provided with one first described first output optical fibre (9) of exporting half-wave plate (6), first polarization beam combiner (7), first condenser lens (8) and being positioned at this first condenser lens (8) focus successively;

2) along the cascade ring cavity (5) output normal beam working direction is provided with one second described second output optical fibre (13) of exporting half-wave plate (10), second polarization beam combiner (11), second condenser lens (12) and being positioned at this second condenser lens (12) focus successively.

2. according to claim 1 based on the odd-even signal separator of cascade ring cavity to structure, it is characterized in that described cascade ring cavity is that ring cavity by two same structures constitutes (14,15) cascade to (5), wherein each ring cavity is identical to two ring cavity structures in (14,15), each ring cavity is formed by a prism (16) and two catoptrons (17,18), and two catoptrons (17,18) are placed with prism (16) symmetry, and promptly prism (16) equates with two catoptrons (17,18) angulation.

3. according to claim 2 based on the odd-even signal separator of cascade ring cavity to structure, it is characterized in that described each ring cavity is identical to two prisms (16) equal and opposite in direction, structure in (14,15), the planar structure of prism (16) is a pentagon, is the base angle to be equaled 45 ° isosceles trapezoid cut away go to the bottom for this is trapezoidal pentagon of isosceles right triangle of a part of a hypotenuse at a base angle; In addition, each ring cavity is coated with semi-transparent semi-reflecting film to two prisms (16) cross surface in (14,15).

4. according to claim 2 based on the odd-even signal separator of cascade ring cavity to structure, it is characterized in that described ring cavity adopts isotropic material to two prisms (16) in (14,15) or the glass of different refractivity is arranged; First order ring cavity is to two prisms (16) the material difference in (14), and second level ring cavity is identical to two prism materials (16) in (15).

5. according to claim 1 based on the odd-even signal separator of cascade ring cavity to structure, it is characterized in that described polarization beam apparatus (3) and first, second polarization beam combiner (7,11) adopt birefringece crystal.

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