Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2003-04-15
2004-06-08
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S088000, C385S089000, C385S093000, C385S094000
Reexamination Certificate
active
06748143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transceiver module whose submodule is accommodated in a metal package and which can intercept noise, having a highly reliable long life, and an optical communications system using the same.
2. Description of the Related Art
FIG. 1
shows a general structure of a single-fiber bi-directional optical communications system, in which a central station and a subscriber are connected together by one optical fiber. At the central station, optical signals having a wavelength of &lgr;
2
(1.55 &mgr;m) are generated by an LD
1
for providing to the subscriber. The optical signals are transmitted through a wavelength division multiplexer (WDM)
1
and is sent to an optical fiber OF. The optical signals transmitted through the optical fiber OF are subjected to wavelength division by a WDM
2
at the subscriber side, and the resulting signals enter and are received by a PD
2
at the subscriber sides. These signals are a “downward signals” which are directed towards the subscribers from the central station and have a wavelength of &lgr;
2
.
On the other hand, at the subscriber side, signals for the central station are converted into optical signals having a wavelength of &lgr;
1
(1.31 &mgr;m) by an LD
2
, and the converted signals are sent to the optical fiber OF through the WDM
2
. The WDM
1
demultiplexes the optical signals having a wavelength of &lgr;
1
and the resulting signals are directed to a PD
1
, by which the signals are converted to electrical signals. These signals are “upward signals” directed towards the central station from the subscribers, and have a wavelength of &lgr;
1
. Since the wavelengths are different, it is possible to perform simultaneous bi-directional transmission. Obviously, ping-pong transmission can also be carried out. A WDM is provided at a branching portion of an optical transmission line (optical fiber, optical waveguide) and carries out wavelength selection.
An optical receiver module having a structure in which a light receiver device (photodiode (PD)), a lens, an optical fiber, etc., are disposed on an optical axis receives optical signals. In
FIG. 1
, the optical receiver modules are simply indicated as PD
1
(central station side) and PD
2
(subscriber side). An optical transmitting module having a structure in which a light emitting device (semiconductor laser, laser diode (LD)), a lens, and an optical fiber are disposed at the same optical axis generates optical signals.
The following types are actually and currently used as optical receiver modules. In one type, a PD chip is mounted to the top surface of a disk-shaped metal stem having lead pins protruding from the bottom surface, a cap holding a lens is secured to the stem, and a ferrule holding an end of an optical fiber is secured to the stem by a circular conical ferrule holder. In another type, a PD is attached to a metal stem, a cap having an opening is mounted to the stem, a circular cylindrical lens holder holding a lens is aligned with and secured at the outer side of the cap at the stem, a ferrule holding an end of an optical fiber is passed through a circular conical ferrule holder, and the ferrule holder is aligned with and secured on top of the lens holder.
Here, the lens is disposed at an axial line of the optical fiber, and the PD is disposed vertically on a line extending therefrom. Light exiting from the optical fiber propagates through space and is focused by the lens. The focused light enters the PD. Each type of optical receiver module is entirely enclosed by a metal package (stem, lens holder, and ferrule holder) by hermetic sealing, so it is highly airtight. Because moisture and oxygen do not enter the package, the PD chip, wiring, etc., do not deteriorate. Each type of optical receiver module is stringently enclosed by the metal package, so electromagnetic waves and light do not enter it, and therefore crosstalk is low. Each type of optical receiver module has been actually used for a long time, so it is highly reliable.
The optical transmitting module which is currently used is a metal-can-type package module which is accommodated in a similar metal package. In one type of optical transmitting module, a protrusion (called a “pole”) is formed at a disk-shaped metal stem, a semiconductor laser is vertically attached to a side surface of the pole, a monitor photodiode (monitor PD) is mounted to a stem surface that is disposed directly below the semiconductor laser, a circular cylindrical cap having a lens is secured on top of the photodiode, a ferrule holding an end of an optical fiber is supported by a ferrule holder, and the ferrule holder is aligned with and secured to the stem.
In another type of optical transmitting module, a cap only having an opening is mounted to a surface of a stem, a circular cylindrical lens holder holding a lens is mounted to the top surface of the stem disposed at the outer side of the cap, a ferrule holding an end of an optical fiber is supported by a ferrule holder, and the ferrule holder is aligned with and secured on top of the lens holder. These types of optical transmitting modules each accommodated in a metal package are enclosed by hermetic sealing, so they are highly reliable, have a long life, and prevent the occurrence of crosstalk because they do not allow the flow of electromagnetic waves and light to and from the metal package. A metal-can-type optical transmitting module and an optical receiver module are provided, being branched out by optical fibers from the associated WDM shown in FIG.
1
. Therefore, there are an optical fiber which connects each metal-can-type optical transmitting module and its associated WDM, and an optical fiber which connects each optical receiver module and its associated WDM. The transmitting device and the receiver device of each module are independent devices, and are connected to their respective WDMs through optical fibers.
These modules having three-dimensional shapes and being entirely enclosed by metal packages have been used, are highly reliable, and will be subsequently used in the future.
Although, in the aforementioned description, an optical transmitting module and an optical receiver module are connected to a WDM by optical fibers, respectively, there are those integrally connected, such as disclosed in Japanese Patent No. 3167650, for example. A general structure thereof is shown in
FIG. 2. A
transmitting device
29
comprises an LD
32
and a monitor PD
33
mounted to a pole
31
inside a box metal package, and a condenser lens
34
provided in a front opening of the box package. A transmitting section is enclosed in the metal package by hermetic sealing and shielded from the outside. A receiver device
35
comprises a box metal package
36
, a submount
37
, a circular cylindrical cap
38
, a condenser lens
39
, and a PD chip
40
.
These modules are independent modules, but are integrally formed by an integration metallic housing
41
. The transmitting device
29
is welded and secured to an opening on an extension line from an axial line of the integration housing
41
. The receiver device
35
is welded to the integration housing
41
so as to face a side opening of the integration housing
41
. Light emitted from the LD
32
of the transmitting device
29
is focused by the condenser lens
34
, and the focused light is transmitted through a WDM
42
and enters an optical fiber
43
. The light that has propagated through the optical fiber
43
is reflected by the WDM
42
, and the reflected light is transmitted through a condenser lens
39
from the side opening, and is incident upon and received by the PD chip
40
.
In this manner, the independent transmitting device (optical transmitting module) and receiver device (optical receiver module), which are enclosed in metal packages, are integrally formed by the housing. However, these modules are still independent, separate modules. Therefore, these modules are nearly the same as a transmitting device and a receiver device that are
Kuhara Yoshiki
Yamaguchi Akira
Doan Jennifer
Fish & Richardson P.C.
Sumitomo Electric Industries Ltd.
Ullah Akm Enayet
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