Light transmitting/receiving module

Details Light transmitting/receiving module Light transmitting/receiving module

2000-02-04

2001-11-20

Ngo, Hung N. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S092000

Reexamination Certificate

active

06318908

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light transmitting/receiving module, eg., to PD/LD(or LED) module having a light signal receiving part and a light signal transmitting part. This invention, in particular, proposes an improvement of an inexpensive resin-molded package for a PD/LD module for simultaneous bidirectional optical communication by light signals of different wavelengths. This invention aims at the protection of the PD port against the noise generated by the LD port in the simultaneous, bidirectional PD/LD module.
2. Description of Related Art
This application claims the priority of Japanese Patent Application No. 11-30855 (30855/1999) filed on Feb. 9, 1999 which is incorporated herein by reference.
A prior PD/LD module has an independent laser diode (LD) module (e.g., shown in
FIG. 1
) and an independent photodiode (PD) module (e.g., shown in FIG.
2
). The PD module is sealed in a metal package. The LD module is also sealed in another metal package. The PD module and the LD module are independently shielded from noise by their own metal-can package.
A prior typical LD module is explained by referring to FIG.
1
. The LD module
1
has a round metal stem
2
. A pole
3
stands on the stem
2
. An LD chip
4
is mounted on a submount fixed on the side wall of the pole
3
. A PD chip
5
is fitted at the center of the stem
2
just beneath the LD chip
4
. The stem
2
holds a metallic cylindrical lens holder
6
welded on the upper surface. The lens holder
6
sustains a lens
7
at a top opening. A conical ferrule holder
8
is welded upon the lens holder
6
. A ferrule
10
holds an end of an optical fiber
9
. The ferrule holder
8
supports the ferrule
10
at a top opening. A cap
14
having a top hole covers the central part of the stem
2
.
Edges of the ferrule
10
and the fiber
9
are slantingly ground for preventing the reflecting light from going back to the LD
4
. The LD
4
yields transmitting light signals. The rear PD
5
is equipped for monitoring the output light power of the LD
4
. The transmitting signals are converted from electric signals to light signals by modulating the driving current of the LD
4
. The driving current of the LD
4
and the photocurrent of the PD
5
are supplied from or replenished to external electric circuits through lead pins
11
,
12
and
13
on the stem
2
. The stem
2
, the lens holder
6
and the ferrule holder
8
are made from metals. These members form a metal package of the LD module. Since the package is made from metals, the package shields and protects the LD module from external electromagnetic noise. The transmitting part generates large electromagnetic waves (inner noise) due to the big driving current flowing in the LD. The inner noise is shielded by the LD metal package. The PD module was doubly protected from the noise by the metal-can package.
A prior PD module is explained by referring to FIG.
2
. The PD module
15
has a circular metallic stem
16
including a central protuberance. A PD chip
17
is mounted upon the protuberance. A metal cap
18
with a top opening is welded upon the stem
16
for protecting the PD chip
17
and other members. A metallic cylindrical lens holder
19
is welded upon the stem
16
. The lens holder
19
maintains a lens
26
at a top opening. A conical ferrule holder
20
is welded upon the lens holder
19
. A tubular ferrule
22
keeps an end of an optical fiber
21
. The ferrule
22
is inserted and fixed in a top hole of the ferrule holder
20
. Ends of the fiber
21
and the ferrule
22
are ground slantingly for inhibiting the end surface from reflecting the light back to the laser. The PD module
15
is protected in a metallic case comprising the metal stem
16
, the metal lens holder
19
and the metal ferrule holder
20
. The receiving part has a high impedance which is subject to external noise. The metallic case connected to the ground level shields the PD module from the external noise.
A driving circuit accompanies the LD module for supplying the driving current modulated by the transmitting signals. The driving circuit contains a modulating circuit, a power amplifier or so. The driving circuit is enclosed by a metal package which forbids noise to go out of the driving circuit. Thus, the prior driving circuit does not emit noise. An amplification circuit follows the PD module for amplifying the photocurrent. The amplification circuit is also resistant against external noise since it is protected by a metallic case.
The prior PD/LD module has an independent PD module, a free amplification circuit, an isolated LD module and a separated driving circuit. Each of the parts is stored in an independent metallic package. The metallic packages kill mutual interference between the LD and the PD. Simultaneous signal reception and signal transmission does not induce a problem that the strong transmitting signals from the LD would mix with the weak received signals on the PD in the prior PD/LD module. The simultaneous transmission and reception is an important precondition of the present invention. The LD generates strong electromagnetic waves since the LD is applied by strong, rapid-changing modulating current. The reception port is subject to noise due to the weak photocurrent and the high amplification rate. The simultaneous transmission and reception has a tendency of bringing the transmission signals to the reception port as noise. If the transmitting part and the receiving part are stored in two different metal cases, the packages doubly shield and protect the PD port from the noise of the LD.
The noise (crosstalk) transference from the LD to the PD is an important criterion of the PD/LD module which makes use of a single fiber for transmitting and receiving signals, as shown in FIG.
3
.
FIG. 3
shows a bidirectional system between the central base station and the subscriber (ONU: optical network unit). Although there are a plenty of subscribers for a single station,
FIG. 3
shows only a single subscriber (ONU). The base station is equipped with an LD
1
for transmitting optical signals to the ONU and a PD
1
for receiving signals from the ONU. The LD
1
and the PD
1
are connected by fibers
27
and
33
to a WDM (wavelength division multiplexer)
28
. The WDM
28
joins with an optical fiber
29
. The ONU has an LD
2
for transmitting signals to the station and a PD
2
for receiving signals from the station. The PD
2
and the LD
2
are connected by fibers
31
and
32
to another WDM
30
. The ONU side WDM
30
communicates with the station side WDM
28
by the fiber
29
. In
FIG. 3
, the signals propagating from the station to the subscriber are called “down-flow”. The signals spreading from the ONU to the station are called “up-flow”. The single fiber
29
allows simultaneous bidirectional transmission of information between the ONU and the station.
The transmission/reception system has a simultaneous communication type and an alternate communication type concerning the timing of signal transmission, and has a single fiber type and a double fiber type with regard to the number of fibers. The alternate type is also called a ping-pong communication. There are thus four types of communication systems. The system of
FIG. 3
can be applied also to the alternate type. The alternate (ping-pong) type allocates different timing for the transmission and the reception on the subscriber site (ONU). The alternate type allows both the single-fiber medium and the double-fiber medium. The ping-pong type system can make use of the same wavelength of light for both the up-flow and the down-flow transmissions. In the case of using the same wavelength, the light division devices
28
and
30
are beam-splitters. The ping-pong type is free from the crosstalk or the internal noise between the transmitting signals and the receiving signals, since the timing of the reception is different from the timing of the transmission on the subscriber site. There is no need for shielding the receiving part from the transmitting part in th

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