Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-02-05
2001-04-17
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S199200
Reexamination Certificate
active
06219177
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical amplifying apparatus, an optical output controlling method by the optical amplifying apparatus, and an optical transmitting apparatus suitable for use to control an optical amplifier in an optical communication system.
(2) Description of Related Art
An optical fiber amplifier using an optical fiber doped with mainly a rare earth element such as erbium (Er) or the like has features of high gain, low noise, etc., which plays an important role in an optical transmission system as an optical amplifier amplifying an optical signal without converting the optical signal into an electric signal.
In the optical transmitting system, the optical amplifier is required an optical output constant control to keep an optical output level constant in order to absorb a difference in level of optical inputs to the optical amplifier due to a difference in transmission path length.
An optical amplifying apparatus performing the optical output constant control will be now described with reference to FIG.
9
.
FIG. 9
is a diagram schematically showing a structure of the above optical amplifying apparatus.
The optical amplifying apparatus has, as shown in
FIG. 9
, optical/electric converting units
101
and
108
, an input disconnection detecting unit
102
, an operation sequence unit
103
, a pumping source
104
, a pumping source driving unit
105
, an operation change-over switch
106
, an optical output constant control unit
107
, a first demultiplexer
109
, isolators
110
and
113
, an erbium-doped optical fiber
111
(hereinafter referred as EDF
111
), a multiplexer
112
, and a second demultiplexer
114
.
The first demultiplexer
109
is configured with an optical fiber coupler, which sends an optical signal inputted to the optical amplifying apparatus to the isolator
110
, while demultiplexing a part of the optical signal and sending the optical signal to the optical/electric converting unit
101
. The optical/electric converting unit
101
converts the optical signal sent from the first demultiplexer
109
into an electric signal (voltage signal). In other words, the optical/electric converting unit
101
converts the optical signal demultiplexed by the first demultiplexer
109
into a voltage signal proportional to an optical input level of the optical signal, and sends the voltage signal as an input monitor signal to the input disconnection detecting unit
102
.
The input disconnection detecting unit
102
compares the input monitor signal sent from the optical/electric converting unit
101
with a reference value set in advance in the input disconnection detecting unit
102
, determines that input light is disconnected when the input monitor signal drops below the reference value, and notifies the operation sequence unit
103
that the input light is disconnected.
The operation sequence unit
103
controls an operation of the operation change-over switch
106
. The operation sequence unit
103
controls the operation change-over switch
106
to stop the optical output constant control when notified of disconnection of the input light from the input disconnection detecting unit
102
.
A power-on/recovery detecting unit not shown detecting that power is on or that the input light signal is recovered is connected to the operation sequence unit
103
. When the power-on/recovery detecting unit detects that power is on or that the input optical signal is recovered, the operation sequence unit
103
is notified of that.
Namely, the operation sequence unit
103
controls the operation change-over switch
106
to perform the optical output constant control when the power-on/recovery detecting unit detects that power is on or that the input light is recovered.
An end of the operation change-over switch
106
is connected to the pumping source driving unit
105
. The other end of the operation change-over switch
106
is switchabley connected to either the optical output constant control unit
107
or ground, so that the operation change-over switch
106
is selectively switched under a control of the above operation sequence unit
103
. The other end of the operation change-over switch
106
is connected to the optical output constant control unit
107
when the inputted optical signal is in a steady state condition, while being grounded when the inputted optical signal is disconnected.
The pumping source driving unit
105
drives the pumping source
104
to generate pump light, which is controlled by the optical output constant control unit
107
. The pumping source
104
is configured with a light emitting element such as a semiconductor laser diode or the like, which supplies an energy of the pumping source
104
to the EDF
111
to amplify inputted optical signal.
The multiplexer
112
is configured with an optical fiber coupler or the like, which outputs pump light outputted from the pumping source
104
to the EDF
111
, while outputting optical signal amplified by the EDF
111
to the isolator
113
. The isolators
110
and
113
are connected to the both ends of the EDF
111
, which are served to prevent resonance of the optical amplifier caused by that amplified light amplified by the EDF
111
is fed back to the EDF
111
.
The second demultiplexer
114
is configured with an optical fiber coupler or the like, which is demultiplexes a part of the optical signal amplified by the EDF
111
to use a part of the demultiplexed optical signal as an output optical signal, while sending the other part of the demultiplexed optical signal as monitor light to the optical/electric converting unit
108
. The optical/electric converting unit
108
converts the optical signal sent from the second demultiplexer
114
into an electric signal (voltage signal), similarly to the optical/electric converting unit
101
. Namely, the optical/electric converting unit
108
converts the optical signal demultiplexed by the second demultiplexer
114
into a voltage signal proportional to an optical output level of the optical signal, and sends the voltage signal as an output monitor signal to the optical output constant control unit
107
.
The optical output constant control unit
107
controls the pumping source driving unit
105
on the basis of the output monitor signal from the optical/electric converting unit
108
such that a level (optical output level) of the output optical signal is stable. In concrete, the optical output constant control unit
107
compares the output monitor signal (voltage signal) inputted from the optical/electric converting unit
108
with a reference voltage value corresponding to a desired optical output set in advance, and controls the pumping source driving unit
105
such that pump light corresponding to a difference in voltage between the reference voltage value and the output monitor signal is outputted from the pumping source
104
.
In the above structure, a part of an optical signal inputted to the apparatus through the optical fiber is demultiplexed by the first demultiplexer
109
, sent to the EDF
111
through the isolator
110
, and amplified with pump light inputted from the multiplexer
112
in the EDF
111
. The amplified optical signal is sent to the second demultiplexer
114
through the isolator
113
, and a part of the amplified optical signal is demultiplexed by the second demultiplexer
114
, then outputted as an amplified optical signal (output light signal).
On the other hand, the part of the input light demultiplexed by the first demultiplexer
109
is sent to the optical/electric converting unit
101
, and converted into a voltage signal proportional to an optical level of the input light in the optical/electric converting unit
101
. The optical signal converted into the voltage signal is sent as an input monitor signal to the input disconnection detecting unit
102
. The input disconnection detecting unit
102
compares a level of the input monitor signal with a reference value set in advance to detect whether the input light is disconnected or not.
In
Fujitsu Limited
Hellner Mark
Staas & Halsey , LLP
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