Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1998-09-30
2001-07-03
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Particular coupling structure
C385S147000
Reexamination Certificate
active
06256437
ABSTRACT:
SPECIFICATION
An optical device and its production method.
1. Field of the Invention
The present invention relates to a substrate for optical device, wherein an optical waveguide such as optical fiber and an optical element such as light-emitting device or photo detector are aligned on a substrate to optically couple these optical parts with higher accuracy, an optical module using said substrate, and a method for producing said device and module. In the following, the substrate for optical device and the optical module are simply called optical devices.
2. Prior Art
In recent years, optical communication systems have been required to have a larger capacity and a greater variety of functions, and with these trends, optical devices such as optical transmitters and optical receivers have been required to be smaller in size, greater in integration, and lower in cost. In particular, to reduce the assembling costs of optical devices, special attention has been given to a technique for mounting optical parts such as an optical fiber and a semiconductor optical element on the same substrate, so-called optical hybrid assembly technique and silicon platform.
When the above-mentioned technique is used, an optical fiber and an optical element can be positioned on a substrate, without alignment, by just assembling the optical fiber in a V-groove formed on the substrate and assembling the optical element on a conductor pattern formed on the same substrate. To achieve this assembly of optical parts on the substrate without alignment, for example, both the V-groove for assembling the optical fiber that is formed in the substrate and the electrode for assembling the optical element that is formed on the substrate, or both the V-groove and an alignment marker for mounting the optical element must be formed with higher accuracy, and the positional relation between the two optical parts must be determined with an accuracy of submicron-order.
With reference to
FIG. 6
, a method of producing such a silicon platform will be described. FIG.
6
(
a
) through (
h
) are plan views illustrating production steps of a conventional substrate for optical hybrid assembly.
First, as shown in FIG.
6
(
a
), on a single crystal substrate
71
having a principal plane set in a certain direction, a film that is resistant to an etchant of silicon, such as silicon oxide film or silicon nitride film, is formed. Next, a photo mask for forming a V-groove is used to pattern the above-mentioned film by photo-lithography, then a pattern
72
for forming a V-groove having an area of exposed silicon substrate
71
is obtained.
Next, as shown in FIG.
6
(
b
), the pattern
72
for forming a V-groove is used as a mask and the exposed area
71
a
of FIG.
6
(
a
) is subjected to anisotropic etching with an etchant such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) to form a V-groove
73
.
Next, as shown in FIG.
6
(
c
), the pattern
72
for forming a V-groove of FIG.
6
(
b
) is removed, then a protective layer
74
such as a silicon oxide film or a silicon nitride film is formed entirely over one principal plane, including the V-groove
73
, of the silicon substrate
71
by, for example, thermal oxidation, sputtering or plasma CVD.
Next, as shown in FIG.
6
(
d
), a photo mask for forming electrodes and markers for assembling an optical element is used to form a photoresist
77
over a region excluding electrode formation regions
75
and regions for a marker
76
for an optical element.
Next, as shown in FIG.
6
(
c
), a metal film
78
of an electrode material such as gold (Au) is formed entirely, by vapor deposition or the like, over one principal plane of the silicon substrate
71
.
Next, as shown in FIG.
6
(
f
), the photoresist
77
of the region except the electrode formation regions
75
and regions for marker for optical element
76
in FIG.
6
(
d
) is removed by liftoff to form an electrode pattern
79
including the optical element mounting part and markers for markers for assembling optical element
80
.
Next, as shown in FIG.
6
(
g
), solder layers are formed on the optical element mounting parts
81
of the electrode pattern
79
. After that, as shown in FIG.
6
(
h
), a fiber stopper groove
82
is formed by slicing, and the silicon substrate
81
is cut off at an end facing
81
a
. As a result, a substrate J for an optical device, wherein a V-groove
83
for assembling an optical fiber not illustrated and optical element mounting parts
81
for assembling an optical element not illustrated are formed on the same silicon substrate
71
m
is completed.
According to the above method, alignment is effected with alignment markers that are formed near the edges of the silicon substrate when the V-groove for mounting an optical fiber is formed and with markers of the photo mask that is used when the electrodes and markers for assembling the optical element are formed.
However, it has been impossible for aligners of the contact type, etc. to make alignment of submicron-order in many cases, and even if such an alignment is possible, it has been hard to distinguish markers formed on a substrate because a distribution of film thickness is generated in the photoresist around a V-groove when the photoresist is applied to the silicon substrate in which the V-groove has been formed.
Even when such problems are cleared, as the alignment markers on the silicon substrate side have to undergo various production processes, the silicon substrate may warp due to heat history of these production processes. This warp may cause displacement of the alignment markers.
Accordingly, in the past, it has been very difficult to align the V-groove and the markers for mounting optical element, and in turn, it has been hard to assemble an optical fiber and an optical element with high accuracy without making an alignment operation. Hence it has been hard to provide excellent optical devices of good performance.
To solve this problem, the present inventors proposed a method for producing an electrode and/or an alignment marker concurrently with the formation of a V-groove (Japanese Provisional Patent Hei8-334303), however, its production process is more complicated in comparison with the above conventional method. Moreover, the stack structure itself of the electrode and/or the alignment marker formed by the more complicated production process is more complicated, and the fluctuation of edges of the marker is greater. This, in turn, deteriorates the accuracy of detection of the edges of the marker by image analysis. Hence, even if a platform is formed with high accuracy, it is hard to expect an improvement in the accuracy of assembly of an optical element. As a result, the positioning accuracy between the optical waveguide and the optical element such as a light-emitting device or a photo detector deteriorates, and it is hard to provide an optical device of excellent performance.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-mentioned conditions. One object of the present invention is to provide an optical device wherein a groove for mounting an optical fiber or an optical waveguide and an alignment marker for an optical element are aligned with a high accuracy, said optical device having an alignment marker enabling accurate detection of a pattern, and a method of producing the optical device.
The optical device according to the present invention comprises a substrate, a resist film provided on one principal plane thereof, an opening for forming an optical waveguide provided in said resist film, a marker being a recess being formed concurrently with said opening and having a predetermined positional relationship with said opening and having a flat bottom, an alignment groove for optical waveguide being formed by etching said substrate through said opening, and an electrode pattern for fixing an optical element on said substrate.
Said resist film may be a single layer, and in that case, when the alignment groove is formed, the marker is masked to prevent it from being etched. Preferably, said resis
Hiraoka Michiaki
Kyomasu Mikio
Sakushima Shiro
Takemura Koji
Font Frank G.
Hogan & Hartson L.L.P.
Kyocera Corporation
Lauchman L.
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