Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2001-09-13
2004-01-27
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S015000, C385S039000, C385S050000
Reexamination Certificate
active
06684012
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical communication module for optical signal transmission, and more particularly to an optical communication module having a structure adopting folding at a filter and a process for producing the same.
BACKGROUND OF THE INVENTION
A conventional optical communication module having a structure adopting folding at a filter is disclosed, for example, in Japanese Patent Laid-Open No. 068705/1999. This module is shown in FIG.
1
.
Japanese Patent Laid-Open No. 068705/1999 proposes that, in the optical communication module utilizing two-way WDM (wavelength division multiplexing), a groove is provided in a silicon substrate and a dielectric multilayer film filter is inserted into the groove with a view to reducing crosstalk light, which has leaked from LD (laser diode) light into PD (photodiode) light, to a level such that poses no practical problem.
FIG. 2
shows another prior art technique disclosed in Japanese Patent Laid-Open No. 352341/1999.
This Japanese Patent Laid-Open No. 352341/1999 proposes that, in a wavelength multiplexing optical communication module, in order to realize good receive characteristics, a cross portion, which crosses a first optical waveguide and a second optical waveguide each other at the end face of an optical waveguide substrate is provided and, in addition, a filter, which reflects light with wavelength &lgr;
1
and permits transmission of light with wavelength &lgr;
2
, is provided at the end face of the optical waveguide substrate.
In these optical communication modules, the structure utilizing folding at a filter can reduce crosstalk light, i.e., light that has leaked from LD light into PD light, to a level which poses no practical problem.
In assembling the above optical communication modules, however, the optical axis of the optical fiber and the optical waveguide should be regulated while monitoring output light, and the troublesome assembling work disadvantageously incurs high assembly cost.
In order to solve this problem of the prior art, a method has been proposed wherein a V groove for a fiber guide is provided in an optical waveguide substrate to facilitate the regulation of the optical axis of the optical fiber and the optical waveguide.
The use of the V groove in the regulation of the optical axis of the optical fiber and the optical waveguide can realize the registration of the optical fiber without the regulation of the optical axis which in turn realizes a reduced assembly cost.
The V groove is generally prepared by removing the (100) crystal face of a wafer by anisotropic etching to form a V-shaped groove of (
111
) crystal face. Therefore, the direction of the V groove is determined by the axial direction of the wafer crystal.
FIG. 3
is an example of crystal axial direction (<110>axial direction) and mask direction of a wafer
90
g
in the preparation of a conventional optical waveguide substrate
10
.
A V groove
13
in the optical waveguide substrate
10
is formed by removing the (100) crystal face of the wafer
90
by anisotropic etching to form a V-shaped groove having (111) crystal face.
In the conventional production method of a V groove, as shown in
FIG. 3
, positioning is carried out so that the direction of a mask for preparing a pattern of the optical waveguide substrate
10
is parallel to the crystal axial direction of the wafer
90
.
In the same manner as described in the conventional optical communication modules shown in
FIGS. 1 and 2
, a bent waveguide is used to apply, in the inside of the optical waveguide substrate, an optical signal diagonally to the filter provide perpendicularly to the V groove to perform reflection or transmission of the optical signal.
As described above, the conventional optical communication modules had the following problems.
First, in assembling an optical communication module having a structure adopting folding at a filter, the optical axis of the optical fiber and the optical waveguide should be regulated while monitoring output light, and this work disadvantageously incurs high assembly cost.
Second, in the inside of the optical waveguide substrate, an optical signal is applied diagonally to a filter. This necessitates a bent waveguide.
In the conventional production process of an optical communication module, as shown in
FIG. 3
, the optical waveguide substrate
10
is masked parallel to the crystal axial direction of the wafer, and, in addition, a filter is provided perpendicularly to the center line of the optical waveguide substrate
10
. For this reason, the direction of the V groove
13
formed by anisotropic etching becomes perpendicular to the filter, and a bent waveguide is necessary for diagonally applying the optical signal.
When the waveguide is not straight but has a bend, the optical signal loss occurs. In order to reduce this loss, the radius of curvature of the bent waveguide should be larger than a given dimension. For this reason, a certain length is necessary for the optical waveguide. This makes it impossible to reduce the size of the optical waveguide substrate.
Since the size of the optical waveguide substrate cannot be reduced, the size of the optical communication module cannot also be reduced. For this reason, the production cost of optical communication modules has hitherto been high.
SUMMARY OF THE INVENTION
Accordingly, it is a first object of the invention to solve the above problems of the prior art and to provide an optical communication module, which has a small size and a low production cost and is suitable for mass production, and a process for producing the same.
It is a second object of the invention to solve the above problems of the prior art and to provide an optical communication module, which, through the realization of the formation of a V groove for fiber guide diagonally to a filter, can render a bent waveguide unnecessary and can construct the waveguide by a straight waveguide only to realize a reduction in size of the optical waveguide substrate, and a process for producing the same.
According to the first feature of the invention, an optical communication module for optical signal communication, comprises:
a filter for transmission and reflection of the optical signal;
an optical fiber; and
a straight waveguide provided, between the filter and the optical fiber, as a waveguide for communication of the optical signal.
Preferably, a groove for installing the optical fiber is linearly provided, from the end of the waveguide, in the same direction as and parallel to the direction of the optical fiber.
Preferably, a first optical waveguide and a second optical waveguide are provided as the straight waveguide for optical signal communication, the first optical waveguide and the second optical waveguide are provided at respective angles such that an optical signal introduced from the first optical waveguide is reflected from the filter and transmitted to the second optical waveguide and one end of each of the first and second optical waveguides is disposed at a position close to the optical signal reflection point in the filter, and a groove for installing the optical fiber is disposed straightly relative to and in the same direction as the second optical waveguide so as to extend from the end of the second optical waveguide remote from the filter toward the opposite direction of the second optical waveguide.
Preferably, the optical communication module further comprises a receive photodetector for receiving a receive optical signal, and a light-emitting device for sending a send optical signal. In this case, preferably, the first optical waveguide receives the send optical signal sent from the light-emitting device and then sends the optical signal to the filter, the second optical waveguide receives the send optical signal sent through the first optical waveguide and reflected from the filter and sends the optical signal to the optical fiber provided in the groove, and, further, receives the receive optical signal sent through the optical fiber and sends the optical signal to the f
Lee John D.
NEC Corporation
Valencia Daniel
LandOfFree
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