Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1998-08-06
2001-12-25
Henry, Jon (Department: 2872)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C356S401000
Reexamination Certificate
active
06332719
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmitter/receiver apparatus with integrated hybrid functions of optical reception and transmission for use in optical fiber communication for transmitting an optical signal, which has been output from a semiconductor laser device, through an optical fiber, and also relates to a method for fabricating the same. The present invention further relates to an optical semiconductor module formed by optically coupling a semiconductor laser device to an optical fiber.
In recent years, a fiber-to-the-user system for transmitting data and multi-channel image information from a center station to a home user by using an optical fiber has been proposed and the implementation of such a system is now under consideration. Such a fiber-to-the-user system requires a plurality of optical receiver apparatuses for simultaneously receiving dissimilar optical signals transmitted by wavelength division multiplexing to the terminal device of a home user and an optical transmitter apparatus for transmitting requests, data and the like from the user's terminal device to the center station.
In an optical transmitter apparatus or optical receiver apparatus used for a fiber-to-the-user system, various types of passive alignment mounting techniques are often employed for the purposes of coupling the apparatus to an optical fiber without operating a light-emitting device or a light-receiving device and thereby reducing the costs thereof.
In order to further reduce the size of such an apparatus and further enhance the performance thereof, technology for integrating optical receiver apparatus and optical transmitter apparatus in a compact package is now in great demand.
In response to such demand, an optical transmitter/receiver apparatus, in which an optical receiver apparatus and an optical transmitter apparatus are integrated in a compact package as shown in FIGS.
37
(
a
) and
37
(
b
), has been suggested (see, for example, 1996 Annual Convention of Institute of Electronics, Information and Communication Engineers in Japan, SC-2-5).
Hereinafter, the conventional optical transmitter/receiver apparatus will be described with reference to FIGS.
37
(
a
) and
37
(
b
).
FIG.
37
(
a
) shows a planar structure of the conventional optical transmitter/receiver apparatus, while FIG.
37
(
b
) shows the cross-sectional structure thereof taken along the line A—A of FIG.
37
(
a
). The conventional optical transmitter/receiver apparatus includes a fiber block
10
and a PLC (planar lightwave circuit) substrate
20
that are joined with each other. The fiber block
10
supports one end of a first optical fiber
11
for transmitting/receiving an optical signal therethrough and one end of a second optical fiber
12
for receiving an optical signal therethrough. On the other hand, the PLC substrate
20
supports: a semiconductor laser device
21
for outputting light on a wavelength band of 1.3 &mgr;m; a monitoring light-receiving device
22
for monitoring the output of the semiconductor laser device
21
; a first light-receiving device
23
for signal reception for receiving light on the wavelength band of 1.3 &mgr;m; and a WDM (wavelength division multiplexed) filter
24
for transmitting light on the wavelength band of 1.55 &mgr;m and reflecting light on the wavelength band of 1.3 &mgr;m. An optical waveguide
25
is formed inside the PLC substrate
20
. A second light-receiving device
13
for signal reception for receiving light on the wavelength band of 1.55 &mgr;m and outputting image information is connected to the other end of the second optical fiber
12
for reception.
The fiber block
10
and the PLC substrate
20
are optically coupled to each other at an output port
26
and a common port
27
. The light to be transmitted on the wavelength band of 1.3 &mgr;m, which has been output from the semiconductor laser device
21
, is passed through a Y-shaped branch
25
a
of the optical waveguide
25
, the WDM filter
24
and the common port
27
so as to be output through the other end of the first optical fiber
11
. Light on the wavelength band of 1.3 &mgr;m and light on the wavelength band of 1.55 &mgr;m are input to be received through the other end of the first optical fiber
11
. The former light, i.e., light on the wavelength band of 1.3 &mgr;m, is passed through the common port
27
, the WDM filter
24
and the Y-shaped branch
25
a
of the optical waveguide
25
so as to be received by the first light-receiving device
23
. The latter light, i.e., light on the wavelength band of 1.55 &mgr;m, is reflected by the WDM filter
24
and passed through the output port
26
so as to be received by the second light-receiving device
13
.
In the conventional optical transmitter/receiver apparatus, the entire coupling, except for the coupling between the first and second optical fibers
11
and
12
(which are external transmission lines) and the PLC substrate
20
, is realized by passive alignment.
The conventional optical transmitter/receiver apparatus shown in FIGS.
37
(
a
) and
37
(
b
) uses the PLC substrate
20
as an optical platform. However, if a PLC substrate
20
made of silica material is used, shortening of the length of the PLC substrate
20
is restricted by the minimum bend radius of the waveguide
25
. Thus, since the PLC substrate
20
becomes rather long in the direction in which light travels, downsizing of such an optical transmitter/receiver apparatus is hard to realize. That is to say, the waveguide
25
of the PLC substrate
20
has a minimum bend radius, over which loss is caused because of difference in refractive indices between a waveguide layer and a cladding layer. If the difference between the refractive indices is increased, then the minimum bend radius can be decreased. However, in actuality, even when the difference between the refractive indices is increased up to 0.75% (which is the maximum value considering the internal loss of the waveguide and the loss resulting from the coupling with the optical fiber), the minimum bend radius cannot be decreased less than about 5 mm. Thus, in the optical transmitter/receiver apparatus shown in FIGS.
37
(
a
) and
37
(
b
), the required minimum length of the PLC substrate
20
in the optical axis direction is as long as about 15 mm. Since the optical transmitter/receiver apparatus further requires the fiber coupling portion, the resulting length of the apparatus in the optical axis direction becomes 20 mm or more.
Also, in the conventional optical transmitter/receiver apparatus, the light to be received on the wavelength band of 1.55 &mgr;m, which has been input into the waveguide
25
of the PLC substrate
20
, is output through the output port
26
of the PLC substrate
20
into the second optical fiber
12
and then received by the second light-receiving device
13
. Accordingly, cost reduction and downsizing of the optical transmitter/receiver apparatus are adversely restricted.
During the assembly process of this apparatus, a cut recess is provided for the PLC substrate
20
by using a dicing saw, the WDM filter
24
is inserted into the recess, and position and angle of the WDM filter
24
are adjusted. However, since it is difficult to mount the WDM filter
24
with high accuracy, the loss of the light, which is incident through the common port
27
and then travels toward the output port
26
, disadvantageously increases.
In addition, when the fiber block
10
is joined with the PLC substrate
20
, the first optical fiber
11
and the second optical fiber
12
need to be simultaneously connected to the common port
27
and the output port
26
with high efficiency. Thus, since these parts should be aligned through active alignment, the assembly process is adversely complicated.
Furthermore, mounting process steps requiring high accuracy should be performed when the semiconductor laser device
21
is mounted onto the PLC substrate
20
, when the first light-receiving device
23
is mounted onto the PLC substrate
20
, when the monitoring light-receiving
Mitsuda Masahiro
Nishikawa Tohru
Tohmon Genji
Uno Tomoaki
Henry Jon
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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