Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-06-02
2002-11-12
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Plural
C385S042000, C385S045000, C385S047000
Reexamination Certificate
active
06480647
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical communications and more particularly to a waveguide-type wavelength mul-tiplexing optical transmitter/receiver module used for wavelength multiplexing transmission.
2. Description of the Related Art
In recent years, the need for bidirectional optical communications has increased and the adaptation of this system to home use has long been desired as well. To establish bidirectional optical communications, an optical transmitter and an optical receiver are required. However, the, separate or discrete construction of these two devices inevitably causes upsizing of an optical transmitting and receiving system, hindering the widespread use thereof. Furthermore, it is not economical to lay two optical fibers for sending and receiving for home use; and therefore, it is essential to establish bidirectional communications by employing only one optical fiber.
To do communications with one optical fiber, a device such as an optical transmitter and receiver intended for the home which can be connected to one optical fiber is required.
At this point, it is necessary to isolate an upward signal light from individual households from a downward signal light from a station.
For isolating the upward signal light from the downward signal light, there is a method in which two types of light each having a different wavelength are used. Accordingly, an optical demultiplexer is required which is able to differentiate a wavelength of light signal outputted from a light transmitter from that inputted to a light receiver. In addition, the device having such functions must be small-sized and low-priced for individual households. To meet these requirements, the integration of an optical transmitter, receiver and de-multiplexer into one device is essential. With this in mind, for the purpose of making the device small-sized, highly-integrated and low-priced, the use of an optical waveguide has been investigated. A silica glass waveguide in particular has been generally employed owing to its small propagation loss and excellent coupling efficiency to an optical fiber. Though the silica glass waveguide itself has no property of sending or receiving light, as a method for highly efficient coupling to a laser diode (LD) being an optical transmitter or a photodiode (PD) being an optical receiver has been recently developed; its importance as an optically packaged substrate is increasingly recognized. In the past, the coupling of the LD to the optical waveguide was impossible due to a very big coupling loss caused by a difference in spot size. However, the LD allowing changes in its spot size has been recently developed, providing a high efficiency in coupling to the optical waveguide.
In the case of a PD, owing to its relatively large light-receiving area of about 80-100 &mgr;m, the coupling to an optical waveguide can be easily implemented.
An optical transmitter/receiver module having an optical demultiplexer composed of an optical waveguide disclosed in Japanese Laid-open Patent Application No. Hei 9-105824 has been known in the art.
FIG. 11
shows the conventional waveguide-type wave-length multiplexing optical transmitter/receiver module described in the above Japanese Provisional Publication.
As depicted in
FIG. 11
, if there is light with two types of wavelengths, for example, &lgr;1 and &lgr;2, a dielectric multilayer filter
108
is so configured as to allow the light with one wavelength to pass therethrough and reflect the light with the other wavelength. The demultiplexing function of this module has been achieved by providing, using:a dicing process, a groove
107
in optical waveguides
110
,
111
and
112
formed on a substrate
109
and by inserting the dielectric multilayer filter
108
into the groove
107
.
The light with a wavelength of &lgr;2 from a port
101
passes through the dielectric multilayer filter
108
and is outputted from a port
103
while the light with a wavelength of &lgr;1 from a port
102
reflects off of the dielectric multilayer filter
108
and is outputted from the port
101
.
Thus, the wavelength multiplexing optical transmitter/receiver module has been implemented by connecting an optical fiber
104
to the port
101
of the optical demultiplexer and by connecting each of the LD
105
and PD
106
to a port
102
and
103
respectively.
An optical transmitter/receiver module having an optical demultiplexer composed of an optical waveguide disclosed in Japanese Laid-Open Patent Application No. Hei 09-159851 has been known in the art as another example.
FIG. 12
shows the conventional waveguide-type wavelength multiplexing optical transmitter/receiver module described in the above Japanese Provisional Publication.
Referring to
FIG. 12
, a dielectric multilayer filter
208
has properties of reflecting light of a wavelength of &lgr;1 and allowing light of a wavelength of &lgr;2 to pass therethrough.
Two optical waveguides
210
and
211
are formed on a substrate
209
, and one end of the optical waveguide
211
is connected to an optical fiber
204
on a port
201
while one end of the optical waveguide
210
is connected to a LD
5
at a port
202
.
The other end of each of the optical waveguides
210
and
211
are positioned so that they converge at an end of the substrate
209
to constitute a directional coupler
212
.
The directional coupler
212
is adapted to provide one-half coupling length of a perfect coupling length to light with a wavelength of &lgr;1 outputted from a LD
205
connected to one end of the optical waveguide
210
.
The demultiplexing function of this module has been thus achieved by affixing the dielectric multilayer filter
208
through a transparent substrate
213
to an end face of the side of the substrate
209
where the directional coupler
212
is formed thereon.
The light with a wavelength of &lgr;1 outputted from the LD
205
propagates through the optical waveguide
210
and, after entering the directional coupler
212
, reflects off this dielectric multilayer filter
208
and is outputted to the optical waveguide
211
and then eventually enters the optical fiber
204
. On the other hand, the light with a wavelength of &lgr;2 from the optical fiber
204
propagates through the optical waveguide
211
and, after entering the directional coupler
212
, passes through the dielectric multilayer filter
208
and enters the PD
206
positioned in a backward position and then eventually is received.
However, there are problems to be solved in the conventional module. In the conventional wavelength multiplexing optical transmitter/receiver module having an optical demultiplexer wherein the dielectric multilayer filter as described above is positioned on the optical waveguide, the module has a high function to prevent light with a wavelength of &lgr;1 from the LD
105
from entering the PD
106
(
206
) by reflecting the light off the dielectric multilayer filter
108
(
208
). However, the light with a wavelength of &lgr;2 or so from the LD
105
, though being generally weak, passes through the dielectric multilayer filter
108
(
208
), causing all the light to be received by the PD
106
(
206
).
According to experiments, for example, in the case of a level of an output with a wavelength of &lgr;1 from the LD
105
being 0 dBm (i.e., 1 mW), even if a dielectric multilayer filter is used which is capable of isolating light with a wavelength of &lgr;1 at a level of −50 dB or so, the output level of −40 dBm has been detected at the PD
106
(
206
).
Generally, light receiving characteristics of a photodiode in an optical transmitter/receiver module are determined depending on how low the level of signal light from an optical fiber can be received.
For example, if the level of to-be-received signal light transmitted from an optical fiber is −40 dBm, the level is almost the same as that of to-be-sent signal light transmitted from a LD, making it impossible to differentiate to-be-received light from to-be-sent light.
The level o
Dickstein Shapiro Morin & Oshinsky LLP.
Font Frank G.
Mooney Michael P.
LandOfFree
Waveguide-type wavelength multiplexing optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waveguide-type wavelength multiplexing optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waveguide-type wavelength multiplexing optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2960560