Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1999-12-09
2003-04-15
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S089000, C385S092000, C359S199200
Reexamination Certificate
active
06547451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical communications module for use in an optical transfer system for bidirectionally transferring a light signal through an optical fiber, the optical communications module having a light signal transmission capability or a light signal transmission/reaction capability; and a method for mounting an optical communications module. More particularly, the present invention relates to an optical communications module capable of utilizing a portion of light which is emitted from a front facet of a semiconductor laser device and is coupled to an optical fiber as monitor light so as to generate an optical output control signal; and a method for mounting such an optical communications module.
2. Description of the Related Art
In recent years, there have been proposed various optical subscriber network systems for transferring multi-channel video information and/or data from a central station to households, and ways for putting such systems to practical use have been studied. Such a system requires each household to install a plurality of optical reception modules as well as an optical transmission module having a light emission capability or a light emission/reception capability. A plurality of optical reception modules are necessary for simultaneously receiving different types of light signals which are transmitted across a wavelength division multiplexing optical network system. Therefore, there is always desired a cheaper and higher-performance optical reception module. On the other hand, an optical transmission module is necessary for transmitting requests and/or data from each household to the central station. Therefore, there is always desired a cheaper, smaller, and yet higher-performance optical transmission module.
Furthermore, an optical communications module for use in such systems, having a light signal transmission capability or a light signal transmission/reception capability, needs to be designed so as to be installable in any desired place. Specifically, an optical communications module to required to have excellent temperature characteristics for greater flexibility in the selection of installation locations. In particular, the tracking error characteristics with respect to optical output are very important to the stable transmission of signals.
An example of an optical transmission/reception apparatus for the aforementioned purposes is disclosed in the proceedings of the Institute of Electronics, Information and Communication Engineers Spring Conference in Japan, 1997, SC-3—3.
FIG. 13
is a plan view showing an optical transmission/reception apparatus
800
.
First, the structure of the optical transmission/reception apparatus
800
is described. At a common port
88
and an output port
89
on a PLC (Planar Lightwave Circuit) substrate
81
, external transfer paths (optical fibers)
90
a
and
90
b
are coupled to PLC waveguides
91
a
and
91
b
, respectively. The external transfer paths
90
a
and
90
b
are disposed in a fiber connection block
87
. At a WDM (wavelength division multiplexing) filter
85
, the PLC waveguides
91
a
and
91
b
are combined into a PLC waveguide
91
c
, which is again split into PLC waveguides
91
d
and
91
e
at a Y-juncture
86
. The PLC waveguides
91
d
and
91
e
are coupled to, respectively, a photodiode element
83
for a 1.3 &mgr;m wavelength band and a semiconductor laser device
52
for a 1.3 &mgr;m wavelength band. According to this technique, the semiconductor laser device
82
is equivalent to an optical communications module having a transmission capability, and the photodiode device
83
is equivalent to an optical reception module. Behind the semiconductor laser device
82
, a waveguide-type photodiode
84
for optical output monitoring purposes is provided on the PLC substrate
81
. The conventional optical transmission/reception apparatus
800
is thus constructed.
The optical transmission/reception apparatus
800
receives light in the following manner: First, multiplexed light including a 1.3 &mgr;m wavelength component and a 1.55 &mgr;m wavelength component is input from the external transfer path
90
a
to the common port
88
. Among the two light components, the light component of the 1.55 &mgr;m wavelength band is reflected by the WDM filter
85
so as to be output to the external transfer path
90
b
via the output port
89
. The other light component of the 1.3 &mgr;m wavelength band is transmitted through the WDM filter.
85
and split at the Y-juncture
86
so as to be received by the photodiode device
83
for the 1.3 &mgr;m wavelength band.
The optical transmission/reception apparatus
800
transmits light in the following manner: The light which is emitted from the front facet of the semiconductor laser device
82
for the 1.3 &mgr;m wavelength band (which is a transmission light source) is optically coupled, without using any lens system, into the PLC waveguide
91
e
and propagated therethrough. This light undergoes an attenuation at the Y-juncture
86
in accordance with its branching ratio, and thereafter is propagated through the PLC waveguide
91
a
. Next, this light is transmitted through the WDM filter
85
and output to the external transfer path
90
a
via the common port
88
.
Herein, the “front facet” of the semiconductor laser device
82
refers to a face which is optically coupled to the waveguide
91
e
. A “rear facet” refers to the opposite facet of the semiconductor laser device
82
.
The above-described configuration of the conventional optical transmission/reception apparatus
800
is suitable for surface mounting, utilizing passive alignment, except for the junction portions between the external transfer paths (optic fibers)
90
a
and
90
b
and the common port
88
and the output port
89
on the PLC substrate
81
.
In accordance with the conventional optical transmission/reception apparatus
800
shown in
FIG. 13
, a signal which is utilized for optical output control is obtained by the use of the optical output-monitoring waveguide-type photodiode
84
. Specifically, the light which is emitted from the rear facet of the semiconductor laser device
82
is received by the optical output-monitoring waveguide-type photodiode
84
, and a photocurrent which is generated responsive to the received light is utilized as a signal for optical output control.
In accordance with the conventional optical transmission/reception apparatus
800
, it may be difficult to equalize the temperature characteristics (front facet temperature characteristics) of the coupling efficiency between the semiconductor laser device
82
and the PLC waveguide
91
e
with the temperature characteristics (rear facet temperature characteristics) of the light-current conversion efficiency of the optical output-monitoring waveguide-type photodiode
84
receiving the light which is emitted from the rear facet of the semiconductor laser device
82
. This may lead to deterioration in the tracking error characteristics.
Examples of semiconductor laser devices for use in the above-described class of optical communications modules include spot size conversion laser devices and narrow divergence angle laser devices. In general, the radiation angle of laser light which is provided by a semiconductor laser device is known to have some dependency on the temperature of the semiconductor laser device. Furthermore, the radiation angle-temperature characteristics of the laser light which is emitted from the front facet of a semiconductor laser device (hereinafter referred to as the “radiation angle-temperature characteristics on the front facet”) may have discrepancies with the radiation angle-temperature characteristics of the laser light which is emitted from the rear facet of the semiconductor laser device (hereinafter referred to as the “radiation angle-temperature characteristics on the rear facet”). In particular, semiconductor laser devices such as narrow divergence angle laser devices, which provide an enlarged spot size by employi
Kobayashi Yasuhiro
Mitsuda Masahiro
Nishikawa Tohru
Uno Tomoaki
Matsushita Electric - Industrial Co., Ltd.
Sanghavi Hemang
Snell & Wilmer LLP
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