JP2817898B2 - Branch and multiplex optical waveguide circuit - Google Patents

Description

The present invention relates to a branch having one main waveguide and two or more branch waveguides formed on a substrate and performing light branching and multiplexing. The present invention relates to a multiplexed optical waveguide circuit.

(Prior Art) In an optical integrated circuit, an optical branch circuit and an optical multiplexing circuit are:
It is indispensable as its basic component. As such a branch multiplexed optical waveguide circuit, a Y-branch optical waveguide circuit having two or more branch optical waveguides is conventionally known.

This Y-branch optical waveguide circuit has the advantages of being less wavelength-dependent and having a smaller branching ratio deviation than a branch optical waveguide circuit using a directional coupler. The application of is expected.

2A and 2B are configuration diagrams showing a conventional Y-branch optical waveguide circuit, in which FIG. 2A is a top view, and FIG. 2B is a cross-sectional view taken along line AA of FIG. FIG. In FIG. 2, 1
Is a substrate, 2 is a clad, 31 is a main waveguide, 32 is a main waveguide 31
The extended waveguides whose outer diameters gradually increase from, and 33 and 34 are branch waveguides.

In this Y-branch optical waveguide circuit, the waveguides 31, 32, 33, and 34 are formed so as to be embedded in the cladding 2 on the substrate 1. The radius of curvature of the branch waveguides 33, 34 is R, the main waveguide is 31 width W
Ideally, the widths W ₃₃ and W _{34 of 31} and the branch waveguides 33 and ₃₄ are all equal, and the wedge-shaped tip width surrounded by the branch waveguides 33 and 34 near the branch point 4 is zero. It has a shape.

The fabrication of such a Y-branch optical waveguide circuit is described in, for example,
This is performed by a method as disclosed in JP-A-58-105111.

That is, a chloride of SiCl ₄ , GeCl ₄ , TiCl ₄ , PCl ₃ , BCl ₃ is used as a starting material. For example, first, as shown in FIGS. Next, a cladding layer 2a and a core layer 3 are sequentially deposited.

Then, as shown in FIG. 2D, the core layer 3 corresponding to each of the waveguides 31, 32, 33, and 34 shown in FIG. By depositing the layer 2a and embedding a Y-shaped waveguide, a Y-branch optical waveguide circuit as a branched multiplexed optical waveguide circuit is manufactured.

(Problems to be Solved by the Invention) In the above-described branched multiplexed optical waveguide circuit, the shape of the branch point 4 is formed so as to be close to an ideal sharp shape in order to reduce the loss.

However, with the current manufacturing technology, it has been difficult to accurately process the vicinity of the branch point 4 where the waveguide is close or to embed the portion with the cladding layer 2a.

That is, as shown in FIG. 4 (a), a shape deformation occurs near the branch point 4, or as shown in FIG. 4 (b), the cladding glass is moved to the branch waveguides 33 and 34 near the branch point 4. And the gap 5 is formed in the cladding layer 2a, or the branch waveguides 33 and 34 near the branch point 4 as shown in FIG.
Since the supply of the clad glass is not sufficient between these two cases, there have been various inconveniences such as waveguide deformation such as inclination of the branch waveguides 33 and 34.

For this reason, conventionally, it has been difficult to manufacture a branched multiplexed optical waveguide circuit with good reproducibility as designed.

In the conventional Y-branch optical waveguide circuit, the branch point 4
Because of the imperfections in the vicinity, the polarization dependence of the branch loss has been observed in that the TM-polarized light has a higher scattering loss than the TE-polarized light.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a low-loss branching and multiplexing optical circuit that is easy to manufacture and has excellent reproducibility without causing pattern deformation or waveguide embedding failure near a branch point. .

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, there is provided a main waveguide formed in a cladding on a substrate and an enlarged waveguide whose outer diameter gradually increases from the waveguide. In a branch multiplexed optical waveguide circuit including two or more branch waveguides connected to the enlarged waveguide, in a state where both waveguide axes are aligned at a connection portion between the enlarged waveguide and the branch waveguide, Each end face of both waveguides was opposed to each other in parallel with a gap of 3 to 10 μm, and each branch waveguide was separated from each other at a predetermined interval to form a branched multiplexed optical waveguide circuit.

(Function) According to the present invention, in the step of embedding the main waveguide, the enlarged waveguide, and the branch waveguide in the clad during circuit fabrication, the clad material is sufficiently supplied between the waveguides, especially also in the vicinity of the branch point. Further, since the waveguide gap is not less than 3 μm, easiness of manufacturing the waveguide is secured, and since the waveguide gap is not larger than 10 μm, low loss property is secured.

(Embodiment) FIG. 1 is a configuration diagram showing a first embodiment of a branching and multiplexing optical waveguide circuit according to the present invention, and the same components as those in FIG. 2 showing a conventional example are denoted by the same reference numerals. That is, 2 is a clad, 31 is a main waveguide, 32a is an enlarged waveguide continuous from the main waveguide 31, and 33a and 34a are branch waveguides.

The branch waveguides 33a and 34a are straight waveguides having no curvature, and the branch angle is set to 1 degree. Each of the branch waveguides 33a and 34a has the end faces 320a and 330a in a state where the enlarged waveguide 32a and the waveguide axis are aligned.
And 320a and 340a to each other are formed separately with a predetermined gap L _GAP. Further, the branch waveguides 33a and 34a are also formed such that their closest distances are separated by a predetermined distance _WGAP .

The value of the waveguide gap L _GAP between the enlarged waveguide 32a and the branch waveguides 33a and 34a is desirably 3 μm or more from the current state of the waveguide fabrication technology, and desirably 10 μm or less from the viewpoint of an increase in loss and the like.

The branched multiplexed optical waveguide circuit having such a configuration is manufactured through the same steps as the steps shown in FIG.

That is, for example, a porous glass film having a composition of SiO ₂ —P ₂ O ₅ —B ₂ O ₃ is deposited as a cladding layer 2a on a silicon substrate 1 having a diameter of 3 inches and a thickness of 700 μm by a flame deposition method.

Next, the composition of the core layer 3 is SiO ₂ —GeO ₂ —P ₂ O ₅ —B ₂ O ₃
He and O _{2 at} a temperature of 1390 ° C.
2 hours in a mixed atmosphere of

Next, an optical waveguide pattern as described above is formed by reactive ion etching. Then, this core layer 3
Is formed by depositing the same cladding layer 2a as described above so as to embed the above.

Actually, a branched combined optical waveguide circuit having a core size of 8 × 8 μm and a relative refractive index difference of 0.25% was manufactured by this method.

FIGS. 5 and 6 are graphs showing the relationship between the waveguide gap L _GAP and the branch waveguide interval W _GAP and the waveguide circuit loss. The horizontal axis of FIG. 5 represents the length of the waveguide gap L _GAP , the vertical axis represents the excess loss when the branch waveguide spacing W _GAP is 3 μm, 4 μm, and 5 μm, and the horizontal axis of FIG. Wave path spacing W _GAP ,
The vertical axis represents excess loss when the waveguide gap L _GAP is 4 μm.

As can be seen from FIG. 5, when the waveguide gap L _GAP is about 10 μm, the excess loss can be almost ignored. Also, as can be seen from FIG. 6, the excess loss can be suppressed to 0.3 dB or less when the branch waveguide interval W _GAP is also about 4 μm.

As described above, according to the first embodiment, since the waveguide gap L _{GAP is set} to 3 to 10 μm, it is possible to prevent the deformation of the waveguide pattern in the etching step in the conventional manufacturing.

Further, the main waveguide 31, the enlarged waveguide 32a, the branch waveguides 33a, 3
The cladding 2 burying 4a is easily inserted between the waveguides, thereby preventing a gap between the branch waveguides 33a and 34a and preventing the two branch waveguides 33a and 34a from being inclined to each other.

Therefore, the branched multiplexed optical waveguide circuit shown in FIG. 1 can be manufactured with high reproducibility as designed. Further, since the imperfections near the branch point of the Y-branch do not occur, the polarization dependence of the branch loss, that is, the scattering loss of the TM-polarized light becomes larger than that of the TE-polarized light, can be suppressed.

FIG. 7 is a configuration diagram showing a second embodiment of the branched multiplexed optical waveguide circuit according to the present invention.

The difference of the second embodiment from the first embodiment is that the branch waveguides 33b and 34b are formed of curved waveguides having a radius of curvature of 40 mm or more, instead of straight waveguides having no curvature. . The spread angle of the enlarged waveguide 32b is 1 degree.

Also in the second embodiment, the same effect as in the first embodiment can be obtained.

(Effects of the Invention) As described above, according to the present invention, each end face of both waveguides is 3 to 10 μm in a state where both waveguide axes are aligned at the connection portion between the enlarged waveguide and the branch waveguide. All of them are opposed to each other in parallel with a gap, and each branch waveguide is separated from each other at a predetermined interval, so that pattern deformation and waveguide embedding failure near the branch point can be reliably prevented, and easy and reproducible. There is an advantage that it can be manufactured well, and therefore the polarization dependence of the branch loss can be suppressed, and a very low loss branch multiplexed optical waveguide circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a branching and multiplexing optical waveguide circuit according to the present invention, FIG. 2 is a block diagram of a conventional example, and FIG. FIG. 4, FIG. 4 is an explanatory view of a conventional problem, FIG. 5 is a graph showing the relationship between the waveguide gap length and excess loss, FIG. 6 is a graph showing the relationship between the branch waveguide spacing and excess loss, FIG. 7 is a configuration diagram showing a second embodiment of the branching and multiplexing optical waveguide circuit according to the present invention. In the figure, 1... Substrate, 2... Clad, 2a... Clad layer, 3... Core layer, 31. Waveguide, L _GAP … waveguide gap, W _GAP … branch waveguide spacing.

Continuation of the front page (72) Inventor Masao Kawachi 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-62-118308 (JP, A) JP-A-57-157207 (JP, A)

Claims (1)

(57) [Claims] 1. A main waveguide formed in a cladding on a substrate, an expanded waveguide whose outer diameter gradually increases from the waveguide, and two or more branch waveguides connected to the expanded waveguide. Wherein each end face of each of the two waveguides is 3 to 10 in a state where both waveguide axes are aligned at a connection portion between the enlarged waveguide and the branch waveguide.
A branching and multiplexing optical waveguide circuit, wherein all of the branching waveguides are opposed to each other in parallel with a gap of μm, and each branching waveguide is separated from each other at a predetermined interval.