CN1472553A - Plane waveguide and optical fiber low-loss connecting method - Google Patents

Abstract

In the method the waveguide with bisect structure is connected to optical fibre at tail end of single-mode waveguide. The light mode spot is gradually changed to match with optical fibre intrinsic mode spot to decrease couple losses for butt-joint of optical waveguide with optical fibre when the light is transmitted from single-mode waveguide to branch waveguide and then transmitted along with the branch waveguide structure.

Description

The low-loss method of attachment of planar optical waveguide and optical fiber

Technical field

The present invention relates to the method for attachment of optical waveguide and optical fiber.

Background technology

Optical integrated device has important use in information processings such as optical communication.In the material and waveguiding structure of numerous formation optical integrated devices, be that the optical waveguide of representative has a wide range of applications with the SiO 2 waveguide material.In the device of simple structure, waveguide core layer and coating refringence are very little, belong to weak restriction waveguide, so waveguide cross-sectional dimensions are bigger, and the loss that is connected with optical fiber is less.And increasingly sophisticated along with optical integrated device, because the restriction of factors such as chip size has generally improved the sandwich layer refractive index and the coating refringence of waveguide, in order to keep single mode waveguide, need to reduce the sectional dimension of waveguide simultaneously, this just causes the coupling loss of waveguide and fiber alignment to increase.

Summary of the invention

The object of the invention provides the low-loss method of attachment of a kind of planar optical waveguide and optical fiber, to reduce the coupling loss of optical waveguide and fiber alignment.

For reaching above-mentioned purpose, technical solution of the present invention is: adopt the end that is connected with optical fiber with single mode waveguide to separate the branch-waveguide that is y-type structure, the Waveguide branching place is a wedge angle, and the branch length L of this y-branch waveguide is at 500 μ m～1000 μ m, the width h of branch-waveguide _xAs follows with definite process of the interval S of branch end:

By formula calculate at different branch-waveguide width h (1) _xWith the coupling loss under the interval S, $L_s=-10\log 10\[\frac{{|\∫\∫E(x,y)F(x,y)\mathrm{dxdy}|}^2}{\∫\∫{\left|E(x,y)\right|}^2\mathrm{dxdy}\∫\∫{\left|F(x,y)\right|}^2\mathrm{dxdy}}\]---\left(1\right)$ E in the formula (x, y) and F (x is respectively the mould field distribution of waveguide and optical fiber y), obtains different h _xWith the coupling loss isogram under the S numerical value, select hour corresponding branch-waveguide width h of coupling loss from isogram _xInterval S with branch end.

When the wedge angle that causes the Waveguide branching place because of manufacture craft can't be realized, can adopt another technical solution: go into a multiple-mode interfence wave guide zone (A) with branch in the termination that single mode waveguide is connected with optical fiber, the length of multiple-mode interfence wave guide zone is Lm, single mode waveguide link to each other with the multiple-mode interfence wave guide zone end width be W _t, the multiple-mode interfence duct width is W _m, the branch-waveguide top width is W _i, each parameter deterministic process is as follows:

The length of multiple-mode interfence wave guide zone by formula (2) is definite, $L_m=\frac{\mathrm{\λ}}{2(n_e^{\left(0\right)}-n_e^{\left(2\right)})}---\left(2\right)$ λ is an input wavelength in the formula, n _e ⁽⁰⁾And n _e ⁽²⁾Be the basic mode in multiple-mode interfence district and the equivalent refractive index of second order mode;

Parameter W _t, W _mAnd W _iDefinite employing optimized Algorithm, the scope of selection of parameter is as follows,

W _mScope choose by formula (3): $\frac{\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-{\mathrm{<figure-callout\; id="2"\; label="n\; cl"\; filenames="A0312956500091.png"\; state="\{\{state\}\}">n</figure-callout>}}_{\mathrm{cl}}^{}}}\&le;W_m<\frac{2\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-n_{\mathrm{cl}}^2}}---\left(3\right)$ N in the formula _ClAnd n _CoIt is respectively the refractive index of the coating and the sandwich layer of waveguide;

If W _mSpan is [W ₁, W ₂], W then _tScope be [h _X0, W ₂], W _iScope be [h _X0, W ₂/ 2], right back-pushed-type (4) objective definition function, $P=-10\log 10\&lsqb;\frac{{|\&Integral;\&Integral;e_1(x,y)e_2(x,y)\mathrm{dx}|}^2}{\&Integral;\&Integral;{\left|e_1(x,y)\right|}^2\mathrm{dx}\&Integral;\&Integral;{\left|e_2(x,y)\right|}^2\mathrm{dx}}\&rsqb;---\left(4\right)$ E in the formula (4) ₁(x) be the optical field distribution of light field when being transferred to multiple-mode interfence district end face, e ₂(x) be that symmetrical super model under the different branch-waveguide top width distributes, calculate P and reach minimum pairing single mode waveguide and link to each other with the multiple-mode interfence wave guide zone and hold width W _t, multiple-mode interfence duct width W _mWith branch-waveguide top width W _i

The present invention is owing to adopt the branched structure waveguide to be connected with optical fiber, and when light passes to branch-waveguide from single mode waveguide, and during along the branch-waveguide structural transmission, its mould spot changes into gradually and optical fiber eigenmode spot mates, and reaches the purpose of reduction coupling loss.

The invention has the advantages that: under the situation that does not increase the additional technique processing, can effectively reduce the coupling loss of slab guide and optical fiber, and polarization dependent loss is low, and technology is had tolerance characteristic preferably; Can be widely used in being connected of all kinds light integrated waveguide device and optical fiber.

Description of drawings

Fig. 1 is a kind of connection diagram of planar optical waveguide and optical fiber, and wherein scheming a) is connection diagram, figure b) xsect of single mode waveguide, figure C) be the end face of two branch-waveguides;

Fig. 2 is the another kind of connection diagram of planar optical waveguide and optical fiber;

Fig. 3 is the coupling loss isogram under different branch-waveguide width and the waveguide distance values, wherein schemes a) waveguide index difference Δ=0.75%, figure b) waveguide index difference Δ=1.5%.

Embodiment

Be example to bury the type waveguide below, specify embodiment.Concrete method of attachment shown in Figure 1 at the end that is connected with optical fiber of single mode waveguide, is adopted single mode waveguide is separately become the waveguide of two at regular intervals and width gradually and is the y-type structure branch-waveguide, and the Waveguide branching place is wedge angle α.Suppose the width of former single mode waveguide and highly be respectively h _X0And h _Yo, the parameter of branched structure waveguide has so: branch-waveguide length L, branch-waveguide width h _xDistance s with branch end.

For the branch-waveguide length L, as long as guarantee that light field is gradual in transmission course, generally at 500 μ m～1000 μ m.And branch-waveguide width h _xWith the coupling loss of rationally choosing with waveguide and optical fiber of the distance s of branch end direct relation is arranged.Its deterministic process is as follows: by formula (1) calculates optical waveguide and optical fiber coupling loss, $L_s=-10\log 10\&lsqb;\frac{{|\&Integral;\&Integral;E(x,y)F(x,y)\mathrm{dxdy}|}^2}{\&Integral;\&Integral;{\left|E(x,y)\right|}^2\mathrm{dxdy}\&Integral;\&Integral;{\left|F(x,y)\right|}^2\mathrm{dxdy}}\&rsqb;---\left(1\right)$ E in the formula (x, y) and F (x y) is the mould field distribution of waveguide and optical fiber respectively.This mould field distribution can be tried to achieve by method of finite difference.Therefore, we can be the width h by branch-waveguide _xWith the scanning of the parameter space of the formation of distance s, promptly calculate the coupling loss under different branch-waveguide width and distance s.h _xThe calculating span duct width that can reach in minimum technology and the single mode waveguide width h of half _X0(be h _X0/ 2) between, waveguide end distance and single mode waveguide width h that the calculating span of S can reach in minimum technology _X0(h _X0Get final product) between.In this scope, can calculate the coupling loss under the different numerical value of two parameters so and obtain coupling loss isogram (as Fig. 3 a and 3b).Can select hour corresponding branch-waveguide spacing and branch-waveguide width of coupling loss from isogram, thereby finish definite process of branch-waveguide structural parameters.

When the wedge angle α that causes the Waveguide branching place because of manufacture craft can't realize, can adopt method of attachment as shown in Figure 2, go into a multiple-mode interfence wave guide zone (A) in the termination that single mode waveguide is connected with optical fiber with branch.The length of multiple-mode interfence wave guide zone is Lm, single mode waveguide link to each other with the multiple-mode interfence wave guide zone end width be W _t, the multiple-mode interfence duct width is W _m, the branch-waveguide top width is W _t, for multiple-mode interfence district Lm, W _t, W _mAnd W _iDefinite process of 4 parameters is as follows: the length L m in multiple-mode interfence district by by formula (2) determine, $L_m=\frac{\mathrm{\&lambda;}}{2(n_e^{\left(0\right)}-n_e^{\left(2\right)})}---\left(2\right)$

λ is an input wavelength in the formula, n _e ⁽⁰⁾And n _e ⁽²⁾Be the basic mode in multiple-mode interfence district and the equivalent refractive index of second order mode.As for other three parameters, single mode waveguide links to each other with the multiple-mode interfence wave guide zone and holds width W _t, multiple-mode interfence duct width W _mAnd branch-waveguide top width W _i, its deterministic process adopts optimized Algorithm (as genetic algorithm) to determine.With the genetic algorithm is example, in the parameter deterministic process, at first needs the scope of given selection of parameter.The width W in multiple-mode interfence district _m, there are 2 in this district of card of going bail for to 4 eigenmodes, so its width range is: $\frac{\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-{\mathrm{<figure-callout\; id="2"\; label="n\; cl"\; filenames="A0312956500091.png"\; state="\{\{state\}\}">n</figure-callout>}}_{\mathrm{cl}}^{}}}\&le;W_m<\frac{2\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-n_{\mathrm{cl}}^2}}---\left(3\right)$ N in the formula _ClAnd n _CoIt is respectively the refractive index of the coating and the sandwich layer of waveguide.Therefore the width span according to formula (3) multiple-mode interfence district is made as [W ₁, W ₂], so single mode waveguide link to each other with the multiple-mode interfence wave guide zone end width W _tScope be [h _X0, W ₂], branch-waveguide top width W _iScope be [h _X0, W ₂/ 2], after parameter area is determined, need the objective definition function, its objective function is defined as follows, $P=-10\log 10\&lsqb;\frac{{|\&Integral;\&Integral;e_1(x,y)e_2(x,y)\mathrm{dx}|}^2}{\&Integral;\&Integral;{\left|e_1(x,y)\right|}^2\mathrm{dx}\&Integral;\&Integral;{\left|e_2(x,y)\right|}^2\mathrm{dx}}\&rsqb;---\left(4\right)$ E in the formula ₁(x) be the optical field distribution of light field when being transferred to multiple-mode interfence district end face, e ₂(x) be that symmetrical super model under the different branch-waveguide top width distributes.In computation process, consider the problem of calculated amount, so used the equivalent refractive index method that two-dimensional structure is arrived in original three-dimensional structure equivalence.The optimization aim of genetic algorithm promptly is that P reaches minimum in the formula (4) so.And, be a general algorithm in the optimal design field, so set forth in this expansion of not doing computation process as for genetic algorithm.And three parameter W _t, W _m, W _iConcrete numerical value, promptly when genetic algorithm provide P a hour corresponding parameters promptly be.

Testing surface adopts the method for Y-type branch-waveguide structure of the present invention, and the coupling loss of planar optical waveguide and optical fiber can effectively reduce.Referring to Fig. 3, with waveguide coating refractive index 1.455 is example, the waveguide index difference is respectively Δ=0.75% (single mode waveguide sectional dimension 4.4 μ m * 4.4 μ m) and Δ=1.5% (single mode waveguide sectional dimension 3.1 μ m * 3.1 μ m), if directly use single mode waveguide and fiber alignment, then Xiang Ying coupling loss is respectively 0.74dB and 2.1dB.If adopt the method for Y-type branch-waveguide, then for Δ=0.75%, work as h _x=1.5 μ m, coupling loss is 0.09dB during s=2.0 μ m; For Δ=1.5%, work as h _x=0.8 μ m, coupling loss is 0.14dB during s=2.8 μ m.Be connected with the direct of optical fiber with respect to single mode waveguide, coupling loss has had tangible reduction.

And if consider the waveguide minimum spacing, so for Δ=1.5%, getting the waveguide minimum spacing is 1.7 μ m (actual process is determined), the optimal design result of multimode interference region is W so _t=6.2 μ m, W _m=11.5 μ m, W _i=5.2 μ m, L _m=97.2 μ m, whole junction loss (comprise branch's top loss and with the junction loss of optical fiber) 0.33dB.For Δ=0.75%, the waveguide minimum spacing is 2.0 μ m, so the structural parameters W of multimode interference region _t=10 μ m, W _m=17.7 μ m, W _i=8.5 μ m, L _m=220.4 μ m, the minimal losses that obtains is 0.17dB.Dock with the direct of optical fiber with single mode waveguide relatively equally, coupling loss has had tangible reduction.

Claims (3)

1. the low-loss method of attachment of planar optical waveguide and optical fiber is characterized in that the end that is connected with optical fiber of single mode waveguide being separated the branch-waveguide that is y-type structure, the width h of branch-waveguide _xAs follows with definite process of the interval S of branch end:

By formula calculate at different branch-waveguide width h (1) _xWith the coupling loss under the interval S, $L_s=-10\log 10\&lsqb;\frac{{|\&Integral;\&Integral;E(x,y)F(x,y)\mathrm{dxdy}|}^2}{\&Integral;\&Integral;{\left|E(x,y)\right|}^2\mathrm{dxdy}\&Integral;\&Integral;{\left|F(x,y)\right|}^2\mathrm{dxdy}}\&rsqb;---\left(1\right)$ E in the formula (x, y) and F (x is respectively the mould field distribution of waveguide and optical fiber y), obtains different h _xWith the coupling loss isogram under the S numerical value, select hour corresponding branch-waveguide width h of coupling loss from isogram _xInterval S with branch end.

2. the low-loss method of attachment of planar optical waveguide according to claim 1 and optical fiber is characterized in that h _xThe calculating span duct width that can reach in minimum technology and the single mode waveguide width h of half _X0Between, waveguide end distance and single mode waveguide width h that the calculating span of S can reach in minimum technology _X0Between.

3. the low-loss method of attachment of planar optical waveguide and optical fiber, it is characterized in that going into a multiple-mode interfence wave guide zone (A) with branch in the termination that single mode waveguide is connected with optical fiber, the length of multiple-mode interfence wave guide zone is Lm, single mode waveguide link to each other with the multiple-mode interfence wave guide zone end width be W _t, the multiple-mode interfence duct width is W _m, the branch-waveguide top width is W _i, each parameter deterministic process is as follows:

The length of multiple-mode interfence wave guide zone by formula (2) is definite, $L_m=\frac{\mathrm{\&lambda;}}{2(n_e^{\left(0\right)}-n_e^{\left(2\right)})}---\left(2\right)$ λ is an input wavelength in the formula, n _e ⁽⁰⁾And n _e ⁽²⁾Be the basic mode in multiple-mode interfence district and the equivalent refractive index of second order mode;

Parameter W _t, W _mAnd W _tDefinite employing optimized Algorithm, the scope of selection of parameter is as follows, W _mScope choose by formula (3): $\frac{\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-n_{\mathrm{cl}}^2}}\&le;W_m<\frac{2\mathrm{\&lambda;}}{\sqrt{n_{\mathrm{co}}^2-n_{\mathrm{cl}}^2}}---\left(3\right)$ N in the formula _ClAnd n _CoIt is respectively the refractive index of the coating and the sandwich layer of waveguide;

If W _mSpan is [W ₁, W ₂], W then _tScope be [h _X0, W ₂], W _iScope be [h _X0, W ₂/ 2], right back-pushed-type (4) objective definition function, $P=-10\log 10\&lsqb;\frac{{\left|{\&Integral;\&Integral;e}_1(x,y)e_2(x,y)\mathrm{dx}\right|}^2}{\&Integral;\&Integral;{\left|e_1(x,y)\right|}^2\mathrm{dx}\&Integral;\&Integral;{\left|e_2(x,y)\right|}^2\mathrm{dx}}\&rsqb;---\left(4\right)$ E in the formula (4) ₁(x) be the optical field distribution of light field when being transferred to multiple-mode interfence district end face, e ₂(x) be that symmetrical super model under the different branch-waveguide top width distributes, calculate P and reach minimum pairing single mode waveguide and link to each other with the multiple-mode interfence wave guide zone and hold width W _t, multiple-mode interfence duct width W _mWith branch-waveguide top width W _i

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