Optical communications – Optical transceiver
Reexamination Certificate
2000-11-30
2004-05-04
Pascal, Leslie (Department: 2633)
Optical communications
Optical transceiver
C398S139000, C398S140000, C398S137000, C398S041000, C398S042000, C398S102000, C398S182000, C398S192000, C398S194000, C398S195000, C398S202000, C398S208000, C398S209000, C398S213000, C385S088000, C385S089000, C385S092000, C385S093000
Reexamination Certificate
active
06731881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an asynchronous transfer mode-passive optical network (ATM-PON) system, more particularly to a device for transmitting and receiving optical signals used in an ATM-PON system, and most particularly to removal of a coherent light in such a device.
2. Description of the Related Art
FIG. 1
illustrates an ATM-PON system. In the ATM-PON system, optical signals are interactively transmitted between a station
201
and subscribers
202
to
206
. The station
201
is connected to each of the subscribers
202
to
206
through one-core optical fibers
400
.
Herein, optical signals successively transmitted from the station
201
to the subscribers
202
to
206
are called down signals, and burst signals transmitted from each of the subscribers
202
to
206
to the station
201
is called up signals. The up and down signals are designed to have different wavelengths from each other.
Devices
301
to
306
equipped in the station
201
and each of the subscribers
202
to
206
are designed to be able to not only transmit an optical signal, but also receive an optical signal.
Each of the devices
301
to
306
is designed to include a laser diode (LD) from which an optical signal is transmitted.
FIG. 2
is a circuit diagram of a circuit included in each of the devices
301
to
306
for receiving optical signals. The illustrated circuit is comprised of a photodiode
101
, a trans-impedance amplifier
102
electrically connected in series to the photodiode
101
, and a feedback resistor
103
electrically connected in parallel to the trans-impedance amplifier
102
.
The photodiode
101
converts a received optical signal into an electric signal. The trans-impedance amplifier
102
amplifies and converts the electric signal transmitted from the photodiode
101
, into a voltage signal. The feedback resistor
103
defines a gain of the trans-impedance amplifier
102
.
The above-mentioned devices
301
to
306
are accompanied with a problem that when the laser diode transmits an optical signal, the optical signal to be transmitted strays in the devices
301
to
306
, and enters the circuit illustrated in
FIG. 2
as a coherent light, resulting in deterioration in photosensitivity in the devices
301
to
306
.
When the devices
301
to
306
are of an optical waveguide, in particular, the above-mentioned coherent light exerts much harmful influence on the circuit illustrated in
FIG. 2
, resulting in more remarkable deterioration in photosensitivity in the devices
301
to
306
.
In order to minimize deterioration in photosensitivity in the devices
301
to
306
in their operation, it is necessary to remove a coherent light component from a received optical signal.
In order to remove a coherent light component from a received optical signal, optical countermeasure has been conventionally applied to an optical waveguide. For instance, Japanese Unexamined Patent Publication No. 10-54917 has suggested the formation of a slit in an optical waveguide for interrupting a coherent light from reaching the optical waveguide.
However, it was quite difficult or almost impossible to sufficiently remove a coherent light only by means of optical countermeasures.
Japanese Unexamined Patent Publication No. 5-289120 has suggested an optical waveguide device including a device for combining optical signals to one another and separating optical signals into respective optical signals, an optical directional coupler, and an optical circuit substrate on which the device and the optical directional coupler are formed in monolithic.
Japanese Patent No. 2923884 (Japanese Unexamined Patent Publication No. 10-311875) has suggested a device including a semiconductor laser emitting a laser beam, a laser receiver receiving the laser beam emitted from the semiconductor laser, a filter positioned between the laser receiver and the semiconductor laser and allowing the laser beam to pass therethrough, the filter removing background noises, an angle adjuster adjusting an inclination angle of the filter to change an incident angle of the laser beam into the filter, and a controller controlling the angle adjuster such that the laser beam passes through the filter at a maximum, in accordance with an output signal transmitted from the laser receiver. The controller includes an oscillator, a multiplier multiplying an output of the oscillator by an output of the laser receiver, a differential amplifier amplifying a difference between an output of the multiplier and a reference voltage, and a manipulator overlapping an output of the differential amplifier with an output of the oscillator, and providing a command to the angle adjuster.
Japanese Unexamined Patent Publication No. 11-27215 has suggested an optical communication module to be used in a parent station radially connected to a plurality of child stations through optical devices and making interactive communication with each of the child stations in time division multiplex by switching a mode between a receipt mode and a transmission mode. The parent station includes first output means for transmitting a first reset signal in accordance with a difference in a signal receiving level in the receipt mode, second output means for transmitting a second reset signal when the transmission mode is switched to the receipt mode, and ATC means for automatically setting a threshold level when the first or second reset signal is received.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem in the prior art, it is an object of the present invention to provide a device for interactively transmitting optical signals and receiving optical, which is capable of removing a coherent light by which photosensitivity in the device would be deteriorated.
In one aspect of the present invention, there is provided a device for interactively transmitting optical signals in a first wavelength and receiving optical signals in a second wavelength both through a one-core optical fiber, including (a) a first light-electricity signal converter which converts a received optical signal into a first electric signal, (b) a second light-electricity signal converter which converts an optical signal to be transmitted, into a second electric signal, and (c) a coherent light remover which subtracts a level of the second electric signal from a level of the first electric signal to remove a coherent light included in the received optical signal.
There is further provided a device for interactively transmitting optical signals in a first wavelength and receiving optical signals in a second wavelength both through a one-core optical fiber, including (a) a first light-electricity signal converter which converts a received optical signal into a first electric signal, (b) a second light-electricity signal converter which converts an optical signal to be transmitted, into a second electric signal, (c) a delay line which adjusts a phase difference between the first and second electric signals such that the first and second electric signals are in phase with each other, and (d) a coherent light remover which subtracts a level of the second electric signal from a level of the first electric signal to remove a coherent light included in the received optical signal.
For instance, the delay line is positioned between the first light-electricity signal converter and the coherent light remover when the first electric signal reaches the coherent light remover earlier than the second electric signal.
As an alternative, the delay line is positioned between the second light-electricity signal converter and the coherent light remover when the second electric signal reaches the coherent light remover earlier than the first electric signal.
It is preferable that the device further includes a first variable gain amplifier electrically connected in series between the first light-electricity signal converter and the coherent light remover.
For instance, the first variable gain amplifier is comprised of a first impedance amplifier electrically connec
McGinn & Gibb PLLC
NEC Corporation
Pascal Leslie
Phan Hanh
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