CN1310044C - Single fiber three-way depolarizing cut off filter - Google Patents

Abstract

The present invention discloses a single-fiber three-way depolarizing cut-off filter which relates to the field of filters in the field of optical fiber communication. The present invention aims to overcome the defects in the prior art, and design a single-fiber three-way depolarizing cut-off filter which is steep in the transmittance curve and low in insertion loss and can eliminate polarization influences. The present invention comprises a base sheet and a plated film layer, wherein the plated film layer has the film system structure of G|2H{0.5L (HL) <^3>0.13H (LH) <^3> 0.5L}<^4>(2.38H) <^1>(1.41L) <1>|A, the central wavelength is 1590 nm, the low-refractivity material is SiO2, the high-refractivity material is Ta2O5, G stands for the base sheet, A stands for the air, ^3 or ^4 stands for the number of cycles, 0.13 stands for the disorder factor, and 0.5 stands for the optical thickness which is one half of one quarter of the central wavelength.

Description

A kind of single fiber three-way depolarizing cut off filter

Technical field

The present invention relates to the optical filter field in the optical-fibre communications field, a kind of single fiber three-way depolarizing cut off filter of saying so more specifically.

Technical background

Along with the rise of user terminal video program request, ecommerce, novel business such as end-to-end, then inevitable requirement is carried out integrated audio frequency, video, data transmission at user side.The single fiber three-way technology is one of major technique that realizes at the optical access network of EPON (PON) (OAN) audio frequency, video, data integration transmission, is the optical communication technology focus of developing in the world at present.Emphasis is that the three-dimensional partial wave of an optical access network single fiber closes ripple, light signal is sent to ONT Optical Network Terminal (ONT) from optical line terminal (OLT) in the prior art, 1490nm wave band carry data signals wherein, 1550nm carries cable TV signal, 1310nm carries up feedback signal, requires in ONT Optical Network Terminal (ONT) these three wave bands to be realized that partial wave closes ripple.

General technology is to realize the wavelength-division multiplex of EPON with optical thin film.Realize that by three optical filters it is 45 degree that the separation of the light of different wave length, the receiver module of optical access network system require the angle of incidence of light degree of these three optical filters.And the oblique incidence meeting causes the characteristic generation of S polarized light and P polarized light to separate, and causes natural light unsmooth, not precipitous to this section of rest position curve from the passband position.Particularly to the 1st three partial wave optical filters, the 1500nm at the 1540nm at rest position edge and edge, passband position is only at a distance of 40nm when 45 ° of wide-angle incident, the spectral characteristic of optical filter is except satisfying optical access network system to the requirements such as Insertion Loss, isolation, also want the special requirement transmittance curve very steep, so the preparation difficulty of this piece optical filter will be far above the 2nd and the 3rd traditional optical filter.At present have only the optical filter supplier of only a few can produce this three partial waves optical filter both at home and abroad, but the polarization that generally also exists S component and P component rest position not to overlap end separation problem, has influenced the stability of optical filter Polarization Dependent Loss.

Summary of the invention

The objective of the invention is to overcome the shortcoming of prior art, design and a kind ofly can satisfy that transmittance curve is very precipitous, Insertion Loss is low, eliminate the single fiber three-way depolarizing cut off filter of polarization influence.

The present invention is achieved through the following technical solutions its goal of the invention.

The invention provides a kind of single fiber three-way depolarizing cut off filter, comprise substrate and coatings, the film structure of coatings is: G|{0.5L (HL) ^ ³0.13H (LH) ^ ³0.5L}^ ⁴| A, wherein low refractive material is SiO ₂, high-index material is Ta ₂O ₅, G represents substrate, A represents air, ^3 or ^4 represent periodicity, 0.13 for the imbalance factor, 0.5 to have represented optical thickness be 0.5 1/4th centre wavelength, centre wavelength is 1590nm.

Adopt the most wavestrip pass filters of rectangle can prepare narrow bandwidth, high-transmission rate and the dark optical filter that suppresses, its basic structure is:

G|[(HL) ^S1H2mLH(LH) ^S1L] ^S2|G (1)

G represents substrate in the formula, S ₂Be periodicity, S ₁Be that main film is the number of plies, m is an order of interference.

(1) formula basic structure is modified as:

G|[0.5L(HL) ^S1ρH(LH) ^S10.5L] ^S2|G (2)

During imbalance factor ρ=2m is exactly general cutoff filter, and their P components when the light oblique incidence separate with the S component, the formation polarization.When ρ ≠ 2m, just can obtain the cutoff filter of depolarization.The ρ value is the key parameter of depolarization cutoff filter design, can calculate S by setting ρ=2m earlier ₁, S ₂, and then go out ρ by the calculation of parameter of boundary condition, the high-index material of selecting for use and low-index material.

For improving the transmitance of light 1490 ± 10nm, by computer optimization, add plating coupling film in main film system, caudacoria binds fruit and is:

G|2H{0.5L(HL)^ ³0.13H(LH)^ ³0.5L}^ ⁴(2.38H)^ ¹(1.41L)^ ¹|A

The film structure of coupling film is that the outside adds plating (2.38H) ^ for add plating 2H between substrate and main film system at main film ¹(1.41L) ^ ¹

The present invention has following outstanding substantive distinguishing features and obvious improvement with respect to prior art:

1. the characteristics that adopt the optical filter of this film structure can possess narrow bandwidth, high-transmission rate simultaneously, suppress and can depolarization end deeply;

2. film structure of the present invention has overcome S component and P component rest position do not overlap under wide-angle incident polarization by separation problem, has eliminated the polarization separation influence.

3. be a kind of optical filter that ends at 45 depolarizations of spending polarized component rest position coincidence under the incidents, transmittance curve is precipitous, Insertion Loss is low, eliminates the polarization separation influence, has satisfied the requirement of optical access network single fiber three-way system;

4. the present invention adds the cooperation of other two optical filters, make device that these three optical filters constitute can be well at the optical information of this section of Access Network fiber-to-the-home realization uplink 1490nm, 1550nm wave band, and downlink transfer 1310nm wave band light wave is as feedback information, in the optical line terminal that can be widely used in spreading out in the optical access network construction, the ONT Optical Network Terminal.

Description of drawings

Fig. 1 closes the ripple synoptic diagram for the present invention is incorporated in optical access network system single fiber three-way partial wave;

Fig. 2 is the Insertion Loss curve map of Theoretical Calculation of the present invention;

The actual Insertion Loss curve map that records of Fig. 3 the present invention.

Embodiment

The present invention is described further below in conjunction with accompanying drawing.

Optical access network (OAN) single fiber three-way technology is to realize one of fiber-to-the-home major technique, is the optical communication technology focus of developing in the world at present.In the optical access network single fiber three-way system, it is the key factor that restricting channel separates that wide-angle incident causes the polarized light division.As shown in Figure 1, two transmission window 1550nm of the descending employing of passive optical access network and 1490nm carry analog catv signal and data-signal respectively, up employing 1310nm window wavelength.Therefore EPON needs wavelength division multiplexer that the wavelength of these three transmission windows is carried out wave splitting/composing at optical line terminal (OLT), ONT Optical Network Terminal (ONT).General system all adopts optical filter to realize the wavelength-division multiplex of EPON: the light of optical filter 1 high saturating 1490nm wavelength, and the light of high anti-1310,1550nm wavelength; The light of optical filter 2 high saturating 1550nm wavelength, and the light of high anti-1310nm wavelength; The light of optical filter 3 high anti-1550nm wavelength.It is 45 degree that the receiver module of optical access network system requires the angle of incidence of light degree of these three optical filters.

The present invention uses the optical thin film depolarization by principle, design has also been developed a kind of single fiber three-way depolarizing cut off filter as optical filter 1, overcome and under wide-angle incident, to have ended separation problem with the polarization that P component rest position does not overlap by the S component, eliminated the polarization separation influence.The principle of the present invention's design is as follows:

During imbalance factor ρ in above-mentioned formula (2)=2m is exactly general cutoff filter, and the P component separates with the S component when the light oblique incidence, the formation polarization.When ρ ≠ 2m, just can obtain the cutoff filter of depolarization.Therefore the ρ value is the key parameter of depolarization cutoff filter design, below the derivation of equation is carried out in the calculating of ρ value.

The structure of formula (2) also can be write as

G|[(0.5LH0.5L) ^S1(0.5LρH?0.5L)(0.5LH?0.5L) ^S1] ^S2|G (3)

The periodicity film system that formula (3) is made up of three seriess of symmetrical film is because series of symmetrical film a ₁A ₁a ₂A ₂... a _nA _n... a ₂A ₂a ₁A ₁Eigenmatrix and the eigenmatrix of monofilm have same nature, on mathematics, can equivalence be monofilm ^[8], according to the interference matrix of formula (3) film system be:

$M={\left(\left[\begin{array}{cc}\cos \left(S_1{\mathrm{\&delta;}}_1\right)& j\sin \left(S_1{\mathrm{\&delta;}}_2\right)/{\mathrm{\&eta;}}_1\\ j{\mathrm{\&eta;}}_1\sin \left(S_1{\mathrm{\&delta;}}_1\right)& \cos \left(S_1{\mathrm{\&delta;}}_1\right)\end{array}\right]\left[\begin{array}{cc}\cos \left({\mathrm{\&delta;}}_2\right)& j\sin \left({\mathrm{\&delta;}}_2\right)/{\mathrm{\&eta;}}_2\\ j{\mathrm{\&eta;}}_2\sin \left({\mathrm{\&delta;}}_2\right)& \begin{array}{}\end{array}\cos \left({\mathrm{\&delta;}}_2\right)\end{array}\right]\left[\begin{array}{cc}\cos \left(S_1{\mathrm{\&delta;}}_1\right)& j\sin \left(S_1{\mathrm{\&delta;}}_2\right)/{\mathrm{\&eta;}}_1\\ j{\mathrm{\&eta;}}_1\sin \left(S_1{\mathrm{\&delta;}}_1\right)& \cos \left(S_1{\mathrm{\&delta;}}_1\right)\end{array}\right]\right)}^{S_2}$

$=\left[\begin{array}{cc}{M}_{11}& M_{12}\\ M_{12}& M_{22}\end{array}\right]---\left(4\right)$

Wherein

${\mathrm{\&delta;}}_1=\arccos [{\cos }^2\mathrm{\&delta;}-\frac{1}{2}(\frac{{\mathrm{\&eta;}}_L}{{\mathrm{\&eta;}}_H}+\frac{{\mathrm{\&eta;}}_H}{{\mathrm{\&eta;}}_L})\sin \left(2\mathrm{\&delta;}\right)]---\left(5a\right)$

${\mathrm{\&eta;}}_1=\sqrt{\frac{\frac{1}{2}{\mathrm{\&eta;}}_L\sin \left(2\mathrm{\&delta;}\right)+{\mathrm{\&eta;}}_H{\cos }^2\frac{\mathrm{\&delta;}}{2}\cos \mathrm{\&delta;}-\frac{{\mathrm{\&eta;}}_L^2}{{\mathrm{\&eta;}}_H}{\sin }^2\frac{\mathrm{\&delta;}}{2}\sin \mathrm{\&delta;}}{\frac{1}{2{\mathrm{\&eta;}}_L}\sin \left(2\mathrm{\&delta;}\right)+\frac{1}{{\mathrm{\&eta;}}_H}{\cos }^2\frac{\mathrm{\&delta;}}{2}\sin \mathrm{\&delta;}-\frac{{\mathrm{\&eta;}}_H}{{\mathrm{\&eta;}}_L^2}{\sin }^2\frac{\mathrm{\&delta;}}{2}\cos \mathrm{\&delta;}}}---\left(5b\right)$

${\mathrm{\&delta;}}_2=\arccos [\cos \frac{\mathrm{\&delta;}}{2}\cos \left(\mathrm{\&rho;\&delta;}\right)-\frac{1}{2}(\frac{{\mathrm{\&eta;}}_L}{{\mathrm{\&eta;}}_H}+\frac{{\mathrm{\&eta;}}_H}{{\mathrm{\&eta;}}_L})\sin \frac{\mathrm{\&delta;}}{2}\cos \left(\mathrm{\&rho;\&delta;}\right)]]---\left(5c\right)$

${\mathrm{\&eta;}}_2=\sqrt{\frac{{\mathrm{\&eta;}}_L\sin \mathrm{\&delta;}\cos \left(\mathrm{\&rho;}\mathrm{\&delta;}\right)+{\mathrm{\&eta;}}_H{\cos }^2\frac{\mathrm{\&delta;}}{2}\cos \left(\mathrm{\&rho;\&delta;}\right)-\frac{{\mathrm{\&eta;}}_L^2}{{\mathrm{\&eta;}}_H}{\sin }^2\frac{\mathrm{\&delta;}}{2}\sin \left(\mathrm{\&rho;\&delta;}\right)}{\frac{1}{{\mathrm{\&eta;}}_L}\sin \mathrm{\&delta;}\cos \left(\mathrm{\&rho;\&delta;}\right)+\frac{1}{{\mathrm{\&eta;}}_H}{\cos }^2\frac{\mathrm{\&delta;}}{2}\sin \left(\mathrm{\&rho;\&delta;}\right)-\frac{{\mathrm{\&eta;}}_H}{{\mathrm{\&eta;}}_L^2}{\sin }^2\frac{\mathrm{\&delta;}}{2}\cos \left(\mathrm{\&rho;\&delta;}\right)}}---\left(5d\right)$

Equivalence position phase thickness d=pg/2 in the formula, wave number g=λ/λ ₀, λ ₀Be centre wavelength, η _HAnd η _LThe equivalent refractive index of representing H, L material respectively.

Abbreviation formula (4) can get

$M_{11}=\cos \left\{S_2\arccos \right[\cos \left(2S_1{\mathrm{\&delta;}}_1\right)\cos {\mathrm{\&delta;}}_2-\frac{1}{2}(\frac{{\mathrm{\&eta;}}_2}{{\mathrm{\&eta;}}_1}+\frac{{\mathrm{\&eta;}}_1}{{\mathrm{\&eta;}}_2})\sin \left(2S_1{\mathrm{\&delta;}}_1\right)\sin {\mathrm{\&delta;}}_2\left]\right\}---\left(6\right)$

When | M ₁₁|＞1 o'clock, equivalent optical admittance was an imaginary number, and an equivalence position phase thickness is a plural number, expression be the Gao Fanqu of film system; When | M ₁₁|＜1 o'clock, equivalent optical admittance and equivalence position phase thickness all were real numbers, corresponding to the transmission band of film system; | M ₁₁|=1 corresponding film is a rest position, and two films are that depolarization point must corresponding two films be that rest position overlaps.

Therefore according to formula (6), as selected S ₁, S ₂After the value, M ₁₁It only is the function of ρ and g.When oblique incidence,, have respectively in rest position to S, P component:

$\left\{\begin{array}{c}\left|M_{11s}\right|=1\\ \left|M_{11p}\right|=1\end{array}\right.---\left(7\right)$

Eliminate polarization, even two polarized component rest position overlap, at this moment

g _s＝g _p (8)

Can obtain separating of ρ value to (8) formula substitution system of equations (7), this ρ value is the value of gained when satisfying the coincidence of two polarized component rest position (one-sided).

For first ripple optical filter, see Fig. 1, make separating of 1490nm light wave and 1550nm and 1310nm two light waves, can realize with the depolarization cutoff filter of periodic symmetry film system imbalance Center Gap layer.The present invention adopts Ta2O5 as high-index material, and SiO2 as low refractive material is, require 1490 ± 10nm transmissivity greater than the reflectivity of 95%, 1310 ± 50nm and 1550 ± 10nm greater than 99% (20db), according to passband width with by the definite S of degree ₁Be 3 and S ₂After being 4, it is 0.13 that the utilization depolarization solves the ρ value by principle.

For improving the transmitance of light 1490 ± 10nm, by computer optimization, add plating coupling film in main film system, caudacoria binds fruit and is:

G|2H{0.5L (HL) ^ ³0.13H (LH) ^ ³0.5L}^ ⁴(2.38H) ^ ¹(1.41L) ^ ¹| A, n _H=2.065, n _L=1.465, centre wavelength is 1590nm, and the theoretical spectral characteristic under 45 degree incidents as shown in Figure 2.

Adopt this film structure to carry out plated film on the plated film machine of the precious APS1104 of Lay, high low-index material is chosen Ta ₂O ₅And SiO ₂, substrate uses K9 glass, and supervisory wavelength is 1590nm.With institute's plating sample Lamda900 spectrophotometer measurement, test angle is 45 degree, measures the spectrum of S, P light respectively, as shown in Figure 3.As seen, the S component of the sample that plates overlaps substantially with the rest position of P component between 1490～1550nm, reaches depolarization by effect.

This rest position polarization is by fractional dose

Δ λ=| λ _ES-λ _EP|=3.6nm, and polarization by the Theoretical Calculation result of fractional dose is:

Δλ＝|λ _ES-λ _EP|＝3.8nm。Experimental result and notional result are approaching.

Therefore, the sample that is coated with has proved that the depolarization of this paper is remarkable by design effect, can be applied in the passive optical access network.This piece optical filter adds the cooperation of other two optical filters, make device that these three optical filters constitute can be well at the optical information of this section of Access Network fiber-to-the-home realization uplink 1490nm, 1550nm wave band, and downlink transfer 1310nm wave band light wave is as feedback information.

Claims (1)

1. a single fiber three-way depolarizing cut off filter comprises substrate and coatings, it is characterized in that the film structure of coatings is:

G|2H{0.5L(HL)^ ³0.13H(LH)^ ³0.5L}^ ⁴(2.38H)^ ¹(1.41L)^ ¹|A

Wherein low refractive material L is SiO ₂, high-index material H is Ta ₂O ₅, G represents substrate, and A represents air, { 0.5L (HL) ^ ³0.13H (LH) ^ ³0.5L}^ ⁴Be that main film is, centre wavelength is 1590nm, and main film is fastened the coupling film that also is coated with passband ripple cancellation, and the film structure of coupling film is that the outside adds plating (2.38H) ^ for add plating 2H between substrate and main film system at main film ¹(1.41L) ^ ¹