JP3228233B2 - Optical waveguide device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention, an optical waveguide device
The involvement relates <br/> Suitable optical waveguide device used in optical communications or the like.

[0002]

2. Description of the Related Art With the rapid spread of the Internet, the commercialization of optical communication systems is proceeding at an extremely rapid pace. 1. More than 30,000 lines can be transmitted over normal telephone lines.
5 Gb / s systems and the like have been introduced in many areas, and a system for increasing the number of multiplexes multiple times by a wavelength multiplexing system has already been put into practical use in accordance with an increase in information transmission capacity. From the initial wavelength multiplexing at several wave levels to the high-density wavelength multiplexing method up to 80 wave levels, commercialization has been started. In such a wavelength division multiplexing optical communication system, a multiplexer for introducing a plurality of signal lights having different wavelengths into one optical fiber, and a multiplexer for separating a wavelength multiplexed optical signal into signals of different wavelengths. Demultiplexers have become important, and an array waveguide grating (hereinafter, referred to as AWG) has attracted attention as an example. The AWG is formed by forming an array of optical waveguides having the same optical path length difference between the input and output two star couplers. It shows. AWGs in which a quartz-based optical waveguide is formed on a Si substrate or a quartz substrate have already been commercialized and used in actual optical communication systems. AWGs currently commercially available generally have a size of about 3 cm × 4 cm and require a temperature control function. Therefore, the AWG is attached to a Paltier element and housed in a package. Is about 5 cm × 6 cm, which occupies a considerable amount of space in the board of the transmission device, and miniaturization of the device is one of the important issues.

[0003] In addition to those used in trunk systems, there is a strong demand for small optical waveguide devices in access systems requiring two-way communication. Multiplexing, demultiplexing,
The element size of an optical waveguide device having a function such as branching is generally limited by a radius of a curved portion of a curved waveguide portion. In order to form a low-loss curved waveguide even with a smaller radius of curvature, the refractive index difference Δ between the core layer and the cladding layer may be set to a large value. In the case of a waveguide having a refractive index difference Δ of about 4%, the radius of curvature needs to be 40 mm or more in order to keep the bending loss within 0.1 dB.
By doing so, the radius of curvature can be reduced to 10 mm or less. However, simply increasing the refractive index difference Δ increases the coupling loss with the optical fiber,
Even if the element size can be reduced, the loss as an optical module will increase. Therefore, in order to manufacture a small and low-loss optical module, the curved region may have a high refractive index difference and the optical coupling portion with a fiber or the like may have a low refractive index difference. As an example, Ishii et al. Disclosed a quartz optical waveguide with a partially changed refractive index difference in Electronics 1, Paper # C-3-148, Proceedings of the IEICE General Conference, 1998, published in 1998. are doing. Ishii et al. Formed a rectangular waveguide core by RIE after forming an under clad and a core, and then provided a shadow mask for preventing film formation above the curved region, thereby forming an FHD (Frame Hydrosys Depo).
An upper clad layer having a refractive index difference Δ of 0.3% was formed by a method (flame deposition method), and after removing the mask, an upper clad layer having a refractive index difference Δ of 0.6% was formed. A film was formed. By this method, an optical waveguide having a partially different refractive index difference Δ was successfully formed along the optical waveguide.

However, in such a conventional method, the distance between the shadow mask and the core layer cannot be reduced (for example, on the order of several μm), and therefore, the difference between the high refractive index difference region and the low refractive index difference region cannot be reduced. It is difficult to set the boundary precisely. Therefore, a waveguide having a high refractive index difference and a low refractive index difference cannot be formed in a desired region with precise positional accuracy, and a small-sized and low-loss optical waveguide device can be realized with a high yield. Did not. Furthermore, since a high-temperature process of about 1400 ° C., which is called the FHD method, is used, the shadow mask to be used deteriorates quickly and there is a problem that productivity is insufficient.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art, and in particular, to provide a small and low-loss optical waveguide device and to provide an optimum refractive index difference according to the shape. it is to provide a novel optical waveguide device which makes it possible to produce a high yield of small and low-loss optical waveguide device integrated optical waveguide having.

[0006]

SUMMARY OF THE INVENTION The present invention basically employs the following technical configuration to achieve the above object. That is, the aspect of the optical waveguide device according to the present invention includes an optical waveguide portion in which the refractive index difference between the core and the clad is the first refractive index difference, and a second refractive index difference different from the first refractive index difference. In the optical waveguide device provided with the optical waveguide portion, the waveguide width of the connecting portion between the optical waveguide portion having the first refractive index difference and the optical waveguide portion having the second refractive index difference is tapered. It is characterized by being formed by.

[0007]

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for manufacturing an optical waveguide device according to the present invention, a quartz core layer and a clad layer are provided on a substrate, and the refractive index difference between the core layer and the clad layer is the first. In a method for manufacturing an optical waveguide device comprising a first optical waveguide portion having a refractive index difference and a second optical waveguide portion having a second refractive index difference different from the first refractive index difference,
A first step of forming a mask material on the upper surface of the core layer, and forming the first optical waveguide portion selectively leaving the mask material on the upper surface of the core layer; A second step of forming the second optical waveguide portion without providing a mask material, a third step of depositing a first upper clad layer having a composition different from that of the core layer over the entire surface, A fourth step of selectively removing only the first upper clad layer in the waveguide portion, and a fifth step of depositing a second upper clad layer having a composition different from that of the first upper clad layer over the entire surface Therefore, instead of using a shadow mask as in the conventional example, a mask is formed directly on the upper surface of the core layer, and the temperature is low enough to hold the mask material thereon. Formed a quartz film A means of adopting. Since the mask can be formed directly on the upper surface of the core layer, the uncertainty of the boundary position between the portion where the mask is formed and the portion where it is not, which is a problem in the conventional example, is greatly reduced. For this reason, it is possible to manufacture an optical waveguide device having excellent characteristics with a small size and low loss with a high yield.

[0009]

EXAMPLES Hereinafter, the <br/> specific example of an optical waveguide device according to the present invention with reference to the drawings will be described in detail. FIG.
FIG. 2 is a view showing a structure of a specific example of an optical waveguide device according to the present invention, FIG. 2 is a cross-sectional view in the middle of manufacturing, and FIG. 3 is a cross-sectional view in a final manufacturing stage. A first optical waveguide portion 2 in which a silica-based core layer and a clad layer are provided, and a refractive index difference between the core layer and the clad layer is a first refractive index difference; In a method for manufacturing an optical waveguide device including a second optical waveguide portion 1 having a different second refractive index difference, a first step of forming a mask material 6 on an upper surface of the core layer 5; The first optical waveguide portion 2 with the mask material 6 selectively left thereon is formed on the upper surface of the core layer 5 and the second optical waveguide portion 1 without the mask material is formed on the upper surface of the core layer 5. A second step, and a first upper clad having a composition different from that of the core layer 5 on the entire surface. A third step of depositing a de layer 7,
A fourth step of selectively removing only the first upper cladding layer 7 of the first optical waveguide portion 2, and a second upper cladding layer having a composition different from that of the first upper cladding layer 7 over the entire surface. A method of manufacturing an optical waveguide device including: a fifth step of depositing an 8; and a fourth step of removing the mask material 6 together with the first upper cladding layer 7 in the fourth step. Is shown.

Hereinafter, the first embodiment of the present invention will be described in more detail. FIG. 1 is a plan view of an optical waveguide device manufactured according to the present invention. Linear waveguides (second waveguide portions) 1 are formed in the regions at both ends, and curved waveguides (first waveguide portions) 2 are formed in the central portion. This first
In the specific example, the refractive index difference Δ
= 0.4%, refractive index difference Δ = 1.0% at central curve
It was set to be. The radius of curvature of the curved waveguide 2 is 10
mm. In order to manufacture such an optical waveguide device, the following may be performed. The cross section of the AA ′ part which is a straight line part in FIG. 1 and the BB ′ which is a curved part
As shown in FIGS. 2A and 2B, the under cladding layer 4 made of a quartz (GPSG) film doped with Ge and P on a Si substrate 3 and a different amount of Ge And P-doped quartz (GPSG)
A core layer 5 made of a film is continuously formed. The under cladding layer 4 and the core layer 5 were 15 μm and 4 μm in thickness, respectively. At this time, the refractive index difference Δ between the core layer 5 and the under cladding layer 4 was set to about 0.5%. Thereafter, a mask material 6 (in this specific example, a WSi material is used) is formed on the entire surface of the core layer 5, and only the region of the curved waveguide 2 in FIG. 1 is patterned. Further, a photoresist is formed thereon, and etching is performed to form a waveguide having a radiation of 4 μm. At this time, the RIE method was used for the etching. In this step, a mask material 6 is formed on the upper surface of the curved waveguide 2,
At the same time, it is possible to adopt a structure in which the mask material 6 does not exist in the linear waveguide 1. A first upper clad layer 1 of GPSG having a thickness of 1 was formed on the entire surface of the substrate thus fabricated.
0 μm was formed. The cross-sectional structure at this stage is shown in FIG.
(B). The composition of the first upper cladding layer 7 is such that the refractive index difference Δ = 0.4% in the portion of the linear waveguide 1.
It was set to be. Subsequently, only the region including the curved waveguide 2 is etched by RIE to remove the first upper cladding layer 7. At this time, since the mask material 6 is formed only on the curved optical waveguide 2, only the first upper clad layer 7 is removed, and the core layer 5 is kept as it is. After that, the mask material 6 is selectively removed, and the second upper clad layer 8 is formed on the entire surface including the portion of the linear waveguide 1.
Is formed by a normal pressure CVD method. The refractive index of the second upper cladding layer 8 was set lower than that of the first upper cladding layer 7 so that Δ = 1.0% in the curved waveguide 2 portion. As described above, in the manufacturing method according to the present invention, the boundaries between the high-refractive index difference and the low-refractive index difference waveguides can be determined accurately, and the uncertainty of the boundary portion, which is a problem in the conventional example, For example, it is possible to solve a problem such as an increase in loss due to a low refractive index difference waveguide up to the portion of the curved waveguide 2, which results in an extreme increase in bending loss. With respect to the optical waveguide manufactured as described above, the following values were obtained as a result of evaluating the loss with the linear portion having both sides of 10 mm, the curved portion having a radius of curvature of 10 mm, and a total length of 43 mm.

A: The present invention (linear refractive index difference = 0.4%, curve refractive index difference =
1.0%) Total insertion loss = 0.75 dB B: When all refractive index differences are 0.4% Total insertion loss> 10 dB C: When all refractive index differences are 1.0% Total insertion loss = 1.25 dB The breakdown of each loss is shown in the table below. (unit:
dB)

[0012]

[Table 1]

Here, an optical waveguide having a uniform refractive index difference is shown for comparison. In the case of the conventional example, it is considered that if the boundary portion of the shadow mask is formed in the same manner as in the present invention, substantially the same low loss characteristics can be obtained, but the manufacturing variation may be large. It is a problem. The manufacturing yield was about 40% in the conventional example in the case of the simple configuration as shown in the above specific example, but in the present invention, a yield of about 100% was obtained.

FIG. 4 shows a planar structure of an optical waveguide according to a second embodiment of the present invention. In this case, the waveguide width W is gradually changed in accordance with the change in the refractive index difference at the boundary between the regions having different refractive index differences in order to reduce the excess loss shown in the first specific example. The configuration was adopted. Specifically, the width is 4 μm in the high refractive index difference (1.0%) region, and the low refractive index difference (0.
4%) region, the width was 6 μm, and the tapered region 10 in which the core width was gradually changed in the range of the boundary portion length of 100 μm was formed, thereby forming a tapered waveguide. As a result, the excess loss of about 0.1 dB generated in the first specific example can be reduced to a level that can be ignored.

It is easy to manufacture a small-sized and low-loss AWG or an optical transmission / reception waveguide module for an optical access system by the same method. In the specific example of the present invention, a quartz film doped with Ge and P is used as the quartz film, but the material to be used is not limited to this, and a quartz film doped with B or the like or a system containing N is used. There is no problem with using materials. The substrate is not limited to Si, and any material such as quartz or ceramic may be used. Further, although WSi was used as the mask material, it is needless to say that the present invention is not limited to this, and other metal materials, dielectric materials, semiconductor materials, or the like may be used. Furthermore, although a TEOS ozone-based APCVD method was used as a film forming method,
Other film forming methods such as a CVD method using plasma or a low pressure CVD method may be used.

[0016]

The optical waveguide device according to the present invention, since the structure described above, a small and with integrated optical waveguide having an optimum refractive index difference according to the shape, and, low-loss optical waveguide device Can be manufactured with a high yield.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical waveguide device according to a first specific example of the present invention.

FIGS. 2A and 2B are cross-sectional views in the middle of manufacturing, and FIG.
FIG. 7A is a cross-sectional view, and FIG.

FIGS. 3A and 3B are cross-sectional views at the final stage of manufacturing, and FIG.
FIG. 7A is a cross-sectional view, and FIG.

FIG. 4 is a plan view of an optical waveguide device according to a second specific example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 linear optical waveguide (second optical waveguide portion) 2 curved optical waveguide (first optical waveguide portion) 3 Si substrate 4 under cladding layer 5 core layer 6 mask material 7 first upper cladding layer 8 second upper cladding Layer 10 Tapered region

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-110405 (JP, A) JP-A-11-344630 (JP, A) JP-A-11-125726 (JP, A) JP-A-11- 38253 (JP, A) JP-A-3-243904 (JP, A) JP-A-3-200904 (JP, A) JP-A-1-321408 (JP, A) Proceedings of the 1998 IEICE General Conference Electronics 1 C-3-148 (p. 314) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (1)

(57) [Claims] 1. An optical waveguide having a refractive index difference between a core and a clad having a first refractive index difference, and an optical waveguide having a second refractive index difference different from the first refractive index difference. In the optical waveguide device, the waveguide width of a connecting portion between the optical waveguide portion having the first refractive index difference and the optical waveguide portion having the second refractive index difference is tapered. Optical waveguide device.