Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-05-28
2004-09-14
Healy, Brian M. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S036000, C385S092000, C398S079000, C398S086000, C398S087000
Reexamination Certificate
active
06792181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module in the field of optical communication and particularly relates to an optical coupling geometry for bidirectional optical transmission of wavelength-multiplexed signals and a mounting method of such an optical geometry.
Wavelength-multiplexing communication systems are widely applied to communication networks such as a trunk system to deal with increasing network traffic due to rapid growth of the Internet.
In a wavelength-division multiplexing (WDM) system, a plurality of optical signals of different wavelengths are simultaneously transmitted on a single optical fiber. In other words, there are a plurality of channels on a single optical fiber. Therefore, an optical transmission module requires a multiplexing or demultiplexing function (WDM function) for allotting optical signals of different wavelengths and a bidirectional transmission function (send/receive function).
Wavelength multiplexing of optical transmissions is not only applied for trunk communication systems but is also applied for subscriber optical communication systems that extend to office and home environments.
FIG. 1
is a diagram showing an example of an optical subscriber communication system that is presently used in practical applications. The system shown in
FIG. 1
is a so-called ATM-PON (Passive Optical Network) system with an up-stream transmission of a 1.3 &mgr;m band (1260-1360 nm) and a down-stream transmission of a 1.55 &mgr;m band (1480-1580 nm). In such a system, transmission is established with one channel for upstream transmission and another channel for downstream transmission.
However, as has been stated above, due to the rapid growth of the Internet, there is a need for providing services at an increased speed and with wider bands in optical subscriber communications.
FIG. 2
shows a system in which the number of wavelengths that are multiplexed is increased to satisfy the need described above. In this system, the 1.55 &mgr;m down-stream band is divided to increase number of services to be offered.
On the other hand, a major requirement for optical modules (optical devices) used in such an optical subscriber system is to reduce cost and size.
In order to provide a module that can be applied in the system shown in
FIG. 2
, a transmitter LD (laser diode), a receiver PD (photo diode), a multiplexing/demultiplexing coupler between the 1.3 &mgr;m band and the 1.55 &mgr;m band, and a WDM function for dividing the 1.55 &mgr;m band are necessary. For the system to become widely used, such functions should be provided with reduced size and cost.
Based on the above, there is an effort of reducing the size and number of components of an optical transmission module and simplifying the assembly process thereof so as to perform mass production at a low cost.
In order to satisfy the above needs, the object of the present invention is to provide a wavelength multiplexing bidirectional optical transmission module of reduced cost and size that can be applied to the optical subscriber communication system of the next generation as shown in FIG.
2
.
2. Description of the Related Art
The following description relates to an example of a wavelength multiplexing bidirectional optical transmission module.
FIG. 3
is a diagram showing a structure of a module disclosed in Japanese laid-open patent No. 61-226713 entitled “OPTICAL WAVELENGTH-TRANSMISSION OPTICAL MODULE” (Example 1 of the related art).
The optical module includes a refractive index distribution type rod lens
235
, an optical fiber
212
.
2
for transmission, which is provided on one end of the rod lens
235
, and spacer glasses
216
-
218
provided on the other end of the rod lens
235
, each spacer glass having an interference film filter.
A solid-state light-receiving element (for receiving an optical signal of wavelength &lgr;
3
)
224
having a lens
223
-
1
is provided at a position along an extension of the central axis of the rod lens
235
. Further, a solid-state light-emitting element (for emitting an optical signal of wavelength &lgr;
2
)
225
having a lens
223
-
3
and a solid-state light-emitting element (for emitting an optical signal of wavelength &lgr;
1
)
226
having a lens
223
-
2
are provided in radial directions of the rod lens
235
.
The interference film filter is made of a short-wavelength pass filter or a long-wavelength pass filter.
With the optical module of the above structure, an optical signal of wavelength &lgr;
3
propagates through the transmission optical fiber
212
.
2
, and is transmitted through the interference film filters
219
,
221
and then received at the solid-state light-receiving element
224
.
A light beam of wavelength &lgr;
2
from the solid-state light-emitting element
225
is incident on the interference film filter
220
at an angle &thgr;
1
. The interference film filter
220
is transparent to a light beam of wavelength &lgr;
2
. Then the light beam of wavelength &lgr;
2
is reflected by the interference film filter
219
and is directed to the transmission optical fiber
212
.
2
.
Similarly, a light beam of wavelength &lgr;
1
from the solid-state light-emitting element
226
is incident on the interference film filter
222
at an angle &thgr;
2
. Then the light beam of wavelength &lgr;
1
is reflected by the interference film filter
221
and is directed to the transmission optical fiber
212
.
2
.
Accordingly, a three-wave multiplexed bidirectional transmission is achieved.
A more detailed structure of a hybrid-integrated module is known from Japanese laid-open patent application NO. 2000-180671 entitled “structure of an optical send/receive module and a fabrication method thereof” (Example 2 of the related art).
FIG. 4
is a diagram showing the structure of such a hybrid integrated module.
An optical fiber
342
is placed inside a ferrule
341
. On an end surface of the ferrule
341
, a prism-shaped wavelength multiplexing/demultiplexing coupler
343
is fixed that has an interference film filter
344
. The interference film filter
344
transmits a light beam of wavelength &lgr;
31
along the optical axis of the optical beam and reflects a light beam of wavelength &lgr;
32
in a direction perpendicular to the optical axis of the light ray.
An LD package having a light-emitting element
322
for emitting a light beam of wavelength &lgr;
3
l and a PD package having a light-receiving element
331
for receiving a light beam of wavelength &lgr;
32
are provided along the optical axis and in a direction perpendicular to the optical axis, respectively. Both the LD package and the PD package are fixedly supported by a single housing member
311
.
With such a structure, a two-way bidirection transmission is achieved. When the above-described example is applied, a three-wave multiplexing transmission can be achieved using a similar technique.
In the field of optical transmission, there is a need for reducing cost and size of optical transmission devices. However, optical transmission devices include expensive optical modules having an optical multiplexing/demultiplexing function and a photoelectric transfer function. Therefore, there is a requirement for improving functions of optical modules with compact integrated structures and with a simplified assembly process at a low cost.
However, in the above-mentioned related art, there are problems as described below.
The interference film filters used in Examples 1 and 2 of the related art are formed of multiple layers of dielectric materials such as SiO
2
and TiO
2
. In order to achieve a wavelength characteristic in which proximate wavelengths are separated at a high extinction ratio, the number of stacked layers of the dielectric film should be increased while accurately controlling the thickness of each layer.
Therefore, conventionally manufacturing a film for separating proximate wavelengths is feasible but will be extremely expensive.
The number of interference film filters required for Examples 1 and 2 of the related art is greater than
Healy Brian M.
Staas & Halsey , LLP
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