Optical waveguides – Integrated optical circuit
Reexamination Certificate
1999-04-26
2001-04-10
Kim, Robert (Department: 2877)
Optical waveguides
Integrated optical circuit
C385S008000, C359S199200
Reexamination Certificate
active
06215917
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical signal transmitter-receiver module of the class wherein there are arranged on an identical substrate, a light emitting element and a light receiving element.
Regarding the optical signal transmitter-receiver system, especially for connecting its central office with subscribers, it has been pointed out that to more popularize the system, the optical signal transmitter-receiver module to be installed on the subscriber side should be preferably more compact and be available at a lower cost. A technical report entitled “Present State and Future of Hybrid Optical Integration Technology Using PLC Platform,” published by the Institute of Electronics, Information and Communication Engineers of Japan, EMD96-24, discusses an optical signal transmitter-receiver module that could respond to such pointing out. This optical signal transmitter-receiver module includes at least one light emitting element, at least one light receiving element, and an optical waveguide, all of which are mounted on an identical substrate.
At present, such optical signal transmitter-receiver module is still discussed as to whether it is applicable or not, to the synchronous transfer mode passive double star (STM-PDS) system and to the asynchronous transfer mode passive double star (ATM-PDS) system. The STM-PDS system is such a system that operates the optical signal transmitter-receiver module such that it transmits and receives the optical signal in the time sharing mode. On one hand, the ATM-PDS system is such a system that operates the optical signal transmitter-receiver module such that it transmits and receives the optical signal asynchronously.
A prior art optical signal transmitter-receiver module
200
will now be explained in the following with reference to
FIGS. 37 through 39
of the accompanying drawings. In these figures,
FIG. 37
is a perspective view of the prior art optical signal transmitter-receiver module
200
.
FIG. 38
is a plan view of the optical signal transmitter-receiver module
200
.
FIG. 39
is a circuit diagram of an optical signal transmission-reception circuit
205
of the optical signal transmitter-receiver module
200
.
As shown in
FIG. 37
, the optical signal transmitter-receiver module
200
transmits and receives the optical signal having a wavelength of lambda
1
in the time sharing mode. However, it makes the optical signal having a wavelength of lambda
2
transfer to the outside, this optical signal being inputted asynchronously with the transmission-reception of the optical signal having a wavelength of lambda
1
.
In the following description and the accompanying drawings, the transmitting optical signal having a wavelength of lambda
1
will be referred to and indicated as “optical signal Pt” while the receiving optical signal with the wavelength of lambda
1
will be referred to and indicated as “optical signal Pr.” Furthermore, in this specification and the accompanying drawing, the optical signal having a wavelength of lambda
2
that is indifferent to transmission-reception will be referred to and indicated as “optical signal Pu.”
As shown in
FIG. 38
, the optical signal transmitter-receiver module
200
includes a planar lightwave circuit (PLC)
201
, and a signal transmission-reception circuit
205
. PLC
201
is composed of a Si substrate
2
, a quartz layer
3
formed on the Si substrate
2
, an optical waveguide passage
204
formed on the quartz layer
3
, a branch passage
204
d
that is formed in the optical waveguide passage
204
for use in separating the wavelength, a dielectric interference filter
5
arranged on the branch passage
204
d,
a laser diode (referred to as LD hereinafter)
206
mounted on the surface of the Si substrate
2
and for transmitting the optical signal, a photodiode for monitoring the transmitting optical signal (referred to as m-PD hereinafter)
202
that is mounted on the surface of the Si substrate
2
, and a photodiode for receiving the optical signal (referred to as r-PD hereinafter)
203
that is mounted on the surface of the Si substrate
2
.
The optical waveguide passage
204
includes an input/output port
204
a,
an output port
204
b,
a Y-shaped branch passage
204
c
, a branch passage
204
d
, a signal transmitting port
204
e
, and a signal receiving port
204
f.
An optical fiber (not shown) for transmitting the optical signal is arranged in the vicinity of the input/output port
204
a.
Optical signals Pr and Pu transmitted through the above-mentioned optical fiber are inputted to the input/output port
204
a.
The optical signal Pt generated from the LD
206
is emitted from the input/output port
204
directing to the above-mentioned optical fiber. An optical module (not shown) is arranged in the vicinity of the output port
204
b
in order to receive the optical signal Pu.
The dielectric interference filter
5
is provided at the branch passage
204
d
of the optical waveguide passage
204
such that it is buried in a slot formed in the quartz layer
3
. This dielectric interference filter
5
allows the optical signal having a wavelength of lambda
1
to pass therethrough, but it reflects the optical signal having a wavelength of lambda
2
inputted through the input/output port
204
a,
directing to the output port
204
b.
The LD
206
is arranged such that its front face is located in the vicinity of the signal transmitting port
204
e
and emits the optical signal Pt. This optical signal Pt emitted from the LD
206
is inputted to the signal transmitting port
204
e.
The m-PD
202
is arranged such that its front face is located in the vicinity of the backside face of the LD
206
and receives the optical signal Pm emitted therefrom. The r-PD
203
is arranged such that its front face is located in the vicinity of the signal receiving port
204
f
and receives the optical signal Pr outputted therefrom.
The signal transmission-reception circuit
205
is composed of a signal transmitting circuit
11
and a signal receiving circuit
12
. The signal transmitting circuit
11
drives the LD
206
responding to the transmitting electric signal, keeping the light emission power of the LD
206
constant. As shown in
FIG. 39
, this signal transmission-reception circuit
205
includes a flip-flop (referred to as F/F hereinafter) circuit
13
, an LD driving circuit
14
, and an automatic power control (referred to as APC hereinafter) circuit
15
. The F/F circuit
13
latches the transmitting electric signal directed to the LD driving circuit
14
. The LD driving circuit
14
supplies the LD
206
with a driving current corresponding to the transmitting electric signal given by the F/F
13
, and drives the LD
206
. The APC circuit
15
controls the driving current supplied from the LD driving circuit
14
to the LD
206
depending on the quantity of the optical signal Pt (emitted from the backside of LD
206
) received by the m-PD
202
, thereby keeping the light emission power of the LD
206
constant.
The m-PD
202
and the APC circuit
15
are provided just for the purpose of keeping the light emission power of the LD
206
constant. Therefore, should it be enough to consider only the function of transmitting and receiving the optical signal having a wavelength of lambda
1
, there might be no need for the m-PD and the APC circuit to be prepared. However, the light emission power of the LD
206
is considerably varied by the ambient temperature even though the driving current is kept constant, so that in order to keep the light emission power of the LD
206
, it is needed to adjust the driving current in response to variation of the ambient temperature. For this, it is required that the signal transmission-reception circuit
205
monitors the light emission power of the LD
206
by means of the m-PD
202
and controls the driving current by means of the APC circuit
15
such that difference between the monitored current coming from the m-PD
202
and a reference current value becomes as small as possible, thereby keeping the light emis
Kobayashi Yoshihiko
Takahashi Atsushi
Takasaki Sigeru
Frank Robert J.
Kim Robert
Kunitz Norman N.
Oki Electric Industry Co. Inc.
Stafira Michael P.
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