JP3309877B2 - Optical waveguide circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide circuit comprising a combination of a planar waveguide and a rectangular waveguide formed on a substrate.

[0002]

2. Description of the Related Art In an integrated optical waveguide circuit, a planar waveguide and a rectangular waveguide are basic structures of a waveguide, and an optical branching circuit for dividing optical power and a light splitting device for separating light for each wavelength are provided by combining them. Wave circuits are made.

FIG. 6 is a diagram showing a conventional optical branch circuit composed of a combination of a planar waveguide and a plurality of rectangular waveguides. FIG. 6A is a top view, and FIG. Is AB
It is sectional drawing of a line direction. In FIG. 6, 1 is a rectangular waveguide for input, 2 is a rectangular waveguide for output, 3 is a tapered waveguide connected to the rectangular waveguide for input, 4 is a tapered waveguide connected to the rectangular waveguide for output, 5 is a planar waveguide, 6 is a substrate, and 7 is a clad. Reference numeral 31 denotes hatching indicating light propagating in the waveguide, and reference numeral 32 denotes a thin line indicating an equal phase plane of light spread by diffraction, which is also used in the drawings described later.

The light guided from the input rectangular waveguide 1 spreads in the horizontal direction due to the diffraction effect in the planar waveguide 5, and then the tapered light is arranged in an array on the circumference of the phase plane of the diffracted wave. The light is received by the waveguide 4 and guided to the rectangular waveguide 2 for output. At this time, in order to efficiently distribute the optical power to the output rectangular waveguide 2, the wedge-shaped tip width surrounded by the tapered waveguides 4 has an ideal shape such that the width is zero. The input rectangular waveguide 1, the output rectangular waveguide 2, the tapered waveguides 3, 4, and the planar waveguide 5 are formed by cladding on a substrate 6 as shown in FIG. 7.

FIG. 7 is a view showing a second example of the prior art, which has a structure in which a rectangular waveguide 8 for input and a rectangular waveguide 11 for output are connected to a planar waveguide 14. An optical star coupler for equally distributing the optical signal from the input rectangular waveguide 8 to all the output rectangular waveguides 11 is illustrated.
The dummy waveguides 10 and 13 are provided for equalizing the structural conditions of the rectangular waveguide located at the center and the rectangular waveguide located at the end. The planar waveguide 14, the input rectangular waveguide 8, and the output rectangular waveguide 11 are connected via the tapered waveguides 9 and 12 for the above-mentioned reason.

FIG. 8 is a diagram showing a third example of the prior art, in which two planar waveguides to which a plurality of rectangular waveguides are connected are connected by a plurality of rectangular waveguide arrays having different optical path lengths. An optical multiplexing / demultiplexing circuit having the above structure is illustrated.

The light guided through the input rectangular waveguide 15 spreads by diffraction in the first planar waveguide 17,
Light is received by the tapered waveguide 18 arranged perpendicular to the diffracted wavefront. The light immediately after being received by each tapered waveguide has the same phase relationship, but reaches the second planar waveguide 21 by guiding the rectangular waveguide array 19 having a predetermined optical path length difference. At this point, a phase difference corresponding to the optical path length difference is generated. Since this phase difference varies depending on the wavelength, when the light is focused on the output rectangular waveguide 23, the light is focused on the output rectangular waveguide which differs for each wavelength.
It operates as an optical demultiplexing circuit. If this operation is performed in reverse, light having different wavelengths can be converged on one waveguide, so that it operates as an optical multiplexing circuit. At the connection point between the planar waveguide and the rectangular waveguide, the tapered waveguides 16, 18, 20, and 22 are provided for the reason described above.

The fabrication of such an optical branching circuit may be performed, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-105111. That is, SiCl ₄ , GeCl ₄ , TiCl ₄ , POC
Using a chloride of l ₃ and BCl ₃ as a starting material, a clad 7 and a core glass layer 24 are sequentially deposited on a substrate 6 such as silicon as shown in FIGS. As shown in FIG. 9D, core portions 24-1 and 24-2 corresponding to the above-described waveguides are formed by etching, and finally, as shown in FIG. And bury the waveguide.

[0009]

In the above-described optical circuit, the portion surrounded by the rectangular waveguides is made closer to an ideal sharp shape in order to reduce the loss. However, in an actual manufacturing technique, it is difficult to sharply and accurately process a portion where a rectangular waveguide is close or to embed the portion with a clad. The etching mask is formed by irradiating the photosensitive resist with ultraviolet rays. However, in the portion where the pattern width is small, the diffraction of the ultraviolet rays and the aberration of the condensing lens cause the etching of FIG.
There is a problem that shape deformations 25 and 26 as shown in FIG. When the waveguide interval is small and the structure is like a dead end sandwiched by a plurality of waveguides, when the waveguide is embedded, as shown in FIG. Gap 2 in clad 7 without filling
7 also occurs. That is, in the related art, an optical waveguide circuit including a planar waveguide and a rectangular waveguide cannot be manufactured with high reproducibility as designed, and it has been difficult to distribute optical power to a branch waveguide at a desired ratio. Therefore, at the expense of some loss, a method of setting a large space 28 between the rectangular waveguides as shown in FIG. 12 to prevent shape deformation at the time of manufacturing has been adopted. Since is small and has a structure of a blind alley of about several μm, it was difficult to prevent the generation of the voids 27 in the clad 7 as described in FIG.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical waveguide circuit composed of a planar waveguide and a rectangular waveguide which is easy to manufacture and has excellent reproducibility.

[0011]

Means for Solving the Problems The configuration of the present invention for achieving the above object, the plane was produced in the cladding on a substrate
Connect only one waveguide to one end face of the planar waveguide
Input rectangular waveguide, and another rectangular waveguide facing the end face.
And a plurality of output rectangular waveguides connected to one end face.
In the optical branch circuit manufactured by the flame deposition method.
A connecting portion between the planar waveguide and the output rectangular waveguide.
A distance between the planar waveguide and each of the output rectangular waveguides.
Separated by a gap, and each of the output rectangular waveguides
Are separated by an interval, and the planar waveguide and the input are separated.
The connection portion with the force rectangular waveguide is the planar waveguide and the
The input rectangular waveguide is separated by a gap .

[0012]

In the above configuration, since there is a gap between the rectangular waveguides or between the planar waveguide and the rectangular waveguide, the waveguide processing is facilitated and the clad glass is easily supplied to the waveguide gap. As a result, the waveguide can be uniformly embedded, so that the manufacturability and reproducibility of the optical waveguide circuit are improved.

[0013]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. FIG. 1 shows an optical branch circuit according to a first embodiment of the present invention. In the drawing, 1 is a rectangular waveguide for input, 2 is a rectangular waveguide for output, 5 is a planar waveguide that spreads light from the rectangular waveguide for input by a diffraction effect, and 29 is a plane which is a feature of the present invention. A gap between the waveguide 5 and the input rectangular waveguide 1;
Numeral 0 is a gap between the planar waveguide 5 and the plurality of output rectangular waveguides 2 which is a feature of the present invention. Reference numeral 33 denotes a line that is necessary for design but is not actually manufactured.
The output rectangular waveguide 2 is arranged so as to be perpendicular to the equal phase plane of the light diffracted and spread in the planar waveguide 5.

The maximum value of the gap size of the waveguide is determined by excess loss due to diffraction, and the minimum value is determined by an etching mask manufacturing technique. FIG. 2 is a graph showing the relationship between the waveguide gap and excess loss due to diffraction. It can be seen that the excess loss due to the provision of the waveguide gap is as small as 0.1 dB at the maximum when the gap size is 10 μm or less, which is sufficiently negligible. The excess loss is smaller as the gap is smaller, but it is difficult to form a gap of 1 μm or less with an etching mask when using a normal ultraviolet exposure apparatus, and conversely, the risk of deforming the waveguide pattern increases. . Furthermore, since the clad glass is less likely to enter the gap, the risk of the above-described void (see 27 in FIG. 11) is increased. Therefore, it can be said that the waveguide gap is optimal for optical coupling of about 1 to 10 μm.

In this embodiment, a porous glass film having a composition of SiO ₂ —P ₂ O ₅ —B ₂ O ₃ is firstly formed as a cladding layer on a silicon substrate having a diameter of 3 inches and a thickness of 700 μm by a fire deposition method. Is deposited, and then has a composition of SiO ₂ --GeO _2-
P ₂ O ₅ -B ₂ O ₃ porous glass was deposited,
Heat treatment was performed at 90 ° C. in a mixed atmosphere of He and O ₂ for 2 hours. Next, an optical waveguide pattern as described above was formed by reactive ion etching, and then a clad layer similar to that described above was formed so as to embed the core layer. The core size is 6.5 × 6.5 μm, and the relative refractive index difference between the core glass and the clad glass is 0.75%.

Thus, the gaps 29, 3 between the waveguides
With 0, the steep shape and the fine shape are eliminated, so that the deformation of the waveguide pattern in the above-described etching step is prevented. Further, since the clad glass for embedding the waveguides easily enters the waveguide gaps, the generation of voids between the waveguides is also prevented. Further, the reflected return light is not a problem because the difference in the refractive index between the core glass and the clad glass is small.
As a result, according to the present invention, an optical waveguide circuit can be manufactured as designed with good reproducibility. Similar effects can be obtained in the embodiments described below.

FIG. 3 is a view showing a second embodiment of the present invention. In the optical branch circuit according to the first embodiment, a tapered waveguide is used for a connection portion between a rectangular waveguide and a planar waveguide. Things. In the drawing, 1 is a rectangular waveguide for input, 2 is a rectangular waveguide for output, 3 is a tapered waveguide connected to the rectangular waveguide 1 for input, and 4 is a tapered waveguide connected to the rectangular waveguide 2 for output. Reference numeral 5 denotes a planar waveguide for expanding the light from the input rectangular waveguide 1 by a diffraction effect. Reference numeral 29 denotes a gap between the planar waveguide 5 and the input rectangular waveguides 1 and 3, which is a feature of the present invention.
Reference numeral 0 denotes a gap between the planar waveguide 5 and a plurality of output rectangular waveguides 2 and 4, which is a feature of the present invention. The tapered waveguide 4 is
The light is arranged so as to be perpendicular to the equal phase plane of light that spreads by diffracting in the planar waveguide 5.

FIG. 4 shows an optical star coupler according to a third embodiment of the present invention. The input tapered waveguide 10 and the output tapered waveguide 13 are opposed to each other with the plane waveguide 15 as a center.
Are arranged, and the tapered waveguide is a rectangular waveguide 9 for input,
It is connected to the output rectangular waveguide 12, and has a function of distributing an optical signal from an arbitrary input rectangular waveguide to all output rectangular waveguides. The tapered waveguide 1
A gap 30 between the planar waveguide and the plurality of rectangular waveguides, which is a feature of the present invention, is provided at the connection between the planar waveguide 15 and the plane waveguides 0 and 13.

FIG. 5 shows an optical multiplexing / demultiplexing circuit according to a fourth embodiment of the present invention. An optical multiplexing / demultiplexing circuit having a structure in which two planar waveguides to which a plurality of input rectangular and output rectangular waveguides are connected are connected by a plurality of rectangular waveguide arrays having different optical path lengths. Tapered waveguides 17 and 2 connected to rectangular waveguide 16 for input and rectangular waveguide 24 for output
The connecting portions of the tapered waveguides 19 and 21 connected to the arrayed waveguide 20 having the optical path length difference 3 and the predetermined optical path length difference and the planar waveguides 18 and 22 having the function of two lenses are provided with the waveguide which is a feature of the present invention. A gap 30 between them is provided.

[0020]

As described above, according to the present invention, the connecting portion between the planar waveguide and the rectangular waveguide is separated from the planar waveguide and each rectangular waveguide by a gap, and each rectangular waveguide is connected to each other. Are separated from each other at intervals, so that an optical waveguide circuit composed of a planar waveguide and a plurality of rectangular waveguides, which is easy to manufacture and excellent in reproducibility, can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an optical branch circuit according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a waveguide gap and excess loss due to diffraction.

FIG. 3 is an explanatory diagram showing an optical branch circuit according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an optical star coupler according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an optical multiplexing / demultiplexing circuit according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an optical branch circuit according to a conventional technique.

FIG. 7 is an explanatory diagram showing an optical star coupler according to a conventional technique.

FIG. 8 is an explanatory diagram showing an optical multiplexing / demultiplexing circuit according to a conventional technique.

FIG. 9 is an explanatory diagram illustrating a method for manufacturing an optical waveguide.

FIG. 10 is an explanatory diagram showing a first problem of the related art.

FIG. 11 is an explanatory diagram showing a second problem of the related art.

FIG. 12 is an explanatory view showing a waveguide structure in a conventional solution.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Rectangular waveguide for input 2 Rectangular waveguide for output 3 Tapered waveguide connected from rectangular waveguide for input 4 Tapered waveguide connected from rectangular waveguide for output 5 Planar waveguide 6 Substrate 7 Cladding 8 Optical star coupler Rectangular waveguide for input 9 Tapered waveguide connected from rectangular waveguide for input 10 Dummy waveguide on input side 11 Rectangular waveguide for output of optical star coupler 12 Tapered waveguide connected to output rectangular waveguide 13 Output dummy waveguide 14 Planar waveguide of optical star coupler 15 Rectangular waveguide for input of optical multiplexing / demultiplexing circuit 16 Tapered waveguide connected from rectangular waveguide for input 17 First planar waveguide for distributing light to rectangular waveguide array 18 Rectangular Tapered waveguide connected to waveguide array 19 Rectangular waveguide array having optical path length difference 20 Tapered waveguide connected from rectangular waveguide array Reference Signs List 21 second planar waveguide having condensing action 22 tapered waveguide connected from output rectangular waveguide 23 rectangular waveguide for output of optical multiplexing / demultiplexing circuit 24 core glass layer 24-1 and 24-2 core after etching Part 25, 26 Deformed portion of tapered waveguide 27 Gap created between claddings 28 Conventional structure for preventing deformation 29 Gap between planar waveguide and rectangular waveguide connection point 30 Between planar waveguide and a plurality of rectangular waveguide connection points Gap 31 Shading indicating light propagating in the waveguide 32 Thin wire indicating equal phase plane of light spreading by diffraction 33 A line that is necessary for design but is not actually produced

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Claims (1)

(57) [Claims] 1. A planar waveguide formed in a clad on a substrate, and only one planar waveguide connected to one end face of the planar waveguide.
Input rectangular waveguide and the other end facing the end face.
Consisting of a plurality of output rectangular waveguides connected to the end face,
In the optical branching circuit manufactured by flame hydrolysis deposition, the connection portion between the planar waveguide and the rectangular waveguide the output, and said planar waveguide and the rectangular waveguide each said output is separated with a gap, and, The output rectangular waveguides are separated from each other with an interval, and a connection portion between the planar waveguide and the input rectangular waveguide is formed.
Has a gap between the planar waveguide and the input rectangular waveguide.
An optical branching circuit characterized in that the optical branching circuit is separated.