Multiplex optical communication system

Details Multiplex optical communication system Multiplex optical communication system

1998-06-03

2002-02-19

Chan, Jason (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200, C359S341410, C359S341420

Reexamination Certificate

active

06348987

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a multiplex optical communication system for transmitting multiplex optical signals under a signal transmission technology of Wavelength Division Multiplexing (WDM) or Optical Time Division Multiplexing (OTDM).
In particular, the present invention relates to optical amplifiers for amplifying power of the multiplex optical signals transmitted through the system.
FIG. 1A
is a block diagram for illustrating the multiplex optical communication system of the related art, operating under the WDM or OTDM technology. The multiplex optical communication system is composed of optical signal terminating equipment (TERM EQUIP) (
1
and
1
′) placed at both terminals of the OPT-TRANS LINE
3
, for transmitting and receiving the multiplex optical signals, an optical transmission line (OPT-TRANS LINE) (
3
) made of an optical fiber depicted by a thick line, for transmitting the multiplex optical signal, and optical amplifier repeater equipment (OAMP REP EQUIP) (
2
) placed along the OPT-TRANS LINE
3
, for amplifying and repeating the multiplex optical signals transmitting between the TERM EQUIP
1
and
1
′.
The TERM EQUIP
1
includes a transmitting unit (TX-UNIT) (
1001
) for transmitting a multiplex optical signal to the TERM EQUIP
1
′ and a receiving unit (RX-UNIT) (
1002
) for receiving a multiplex optical signal transmitted from TERM EQUIP
1
′. The same as TERM EQUIP
1
, the TERM EQUIP
1
′ includes TX-UNIT
1001
′ and RX-UNIT
1002
′. The TERM EQUIP
1
and TERM EQUIP
1
′ have the same constitution and function, so that the TERM EQUIP
1
will be representatively described hereinafter. The OAMP REP EQUIP
2
includes two repeater optical amplifiers (REP OPT-AMPs) (
8
and
8
′). The REP OPT-AMP
8
is to amplify the multiplex optical signal transmitted from the TX-UNIT
1001
in the TERM EQUIP
1
, for repeating the multiplex optical signal to RX-UNIT
1002
′ in the TERM EQUIP
1
′, and the REP OPT-AMP
8
′ is to amplify the multiplex optical signal transmitted from the TX-UNIT
1001
′ in the TERM EQUIP
1
′, for repeating the multiplex optical signal to RX-UNIT
1002
in TERM EQUIP
1
. When a distance between TERM EQUIP
1
and
1
′ is long, a plurality of the OAMP REP EQUIP
2
are placed. However, one OAMP REP EQUIP
2
is representatively depicted in FIG.
1
A.
FIG. 1B
shows a block diagram of the TX-UNIT
1001
of the related art. The TX-UNIT
1001
consists of electro-optical signal converter (ELEC-OPT CONV) (
4
) connected with electrical signal channel lines (ELEC-SIG CHANNEL LINEs) (
9
) through which a plurality of electrical signals formed to channels are sent to the ELEC-OPT CONV
4
, an optical signal combiner (OPT-SIG COMB) (
5
) connected with the ELEC-OPT CONV
4
through optical fibers depicted by thick lines, and a transmitting unit optical amplifier (TX-UNIT OPT-AMP) (
6
) connected with the OPT-SIG COMB
5
through an optical fiber depicted by a thick line. The ELEC-OPT CONV
4
is for converting the electrical signals to optical signals at every channel. The ELEC-OPT CONV
4
consists of converters
4
-
1
,
4
-
2
, - - - and
4
-n in correspondence with the ELEC-SIG CHANNEL LINEs
9
. When the electrical signals are fed to the ELEC-OPT CONV
4
through the ELEC-SIG CHANNEL LINEs
9
, the converters
4
-
1
,
4
-
2
, - - - and
4
-n convert the electrical signals to optical signals and send the optical signals to the OPT-SIG COMB
5
, respectively. The OPT-SIG COMB
5
is for combining the optical signals sent from the ELEC-OPT CONV
4
, adopting the WDM technology or the OTDM technology, so as to produce a multiplex optical signal. The TX-UNIT OPT-AMP
6
is for amplifying the power of the multiplex optical signal sent from the OPT-SIG COMB
5
. The amplified multiplex optical signal is sent out from the TX-UNIT
1001
to the REP OPT-AMP
8
in OAMP REP EQUIP
2
through the OPT-TRANS LINE
3
.
FIG. 1C
shows a block diagram of the RX-UNIT
1002
. The RX-UNIT
1002
consists of an optical signal branching unit (OPT-SIG BRANCH) (
5
′) and optical-electro signal converters (OPT-ELEC CONVs) (
4
′). The OPT-SIG BRANCH
5
′ is connected with the OPT-TRANS LINE
3
depicted by a thick line, for optically demultiplexing the received multiplex optical signal to a plurality of received optical signals which are called “received demultiplexed optical signals” hereinafter. The received demultiplexed optical signals produced at the OPT-SIG BRANCH
5
′are sent to the OPT-ELEC CONV
4
′ through optical fibers depicted by thick lines. The OPT-ELEC CONV
4
′ consists of converters
4
′-
1
,
4
′-
2
, - - - ,
4
′-n at which the received demultiplexed optical signals are converted to received electrical signals and sent out from RX-UNIT
1002
to the ELEC-SIG CHANNEL LINEs
9
, respectively.
In
FIG. 1A
, the OAMP REP EQUIP
2
includes two optical amplifiers (
8
and
8
′) which will be called REP OPT-AMPs
8
and
8
? hereinafter. The REP OPT-AMP
8
and
8
′ are for amplifying the power of multiplex optical signals received from TERM EQUIP
1
and
1
′,respectively. By virtue of the REP OPT-AMPs
8
and
8
′, power loss, caused by the OPT-TRANS LINE
3
, of the multiplex optical signals transmitting between TERM EQUIP
1
and
1
′ are recovered. Therefore, when a length of the OPT-TRANS LINE
3
between TERM EQUIP
1
and
1
? is long, a plurality of the OAMP REP EQUIP
2
are placed along the OPT-TRANS LINE
3
, and the number of the OAMP REP EQUIP
2
is determined by considering both the power loss due to the OPT-TRANS, LINE
3
and the power amplification factors of REP OPT-AMPs
8
and
8
′ in GAMP REP EQUIP
2
, so that the multiplex optical signals can be transmitted between the TERM EQUIP
1
and
1
′ in high fidelity and a high signal to noise ratio (SNR).
Generally, there are two kinds of optical amplifiers, a semiconductor amplifier and an optical fiber amplifier. The both kinds of optical amplifiers can be applied to the TX-UNIT OPT-AMP
6
in FIG.
1
B and the REP OPT-AMPs
8
and
8
′ in FIG.
1
A.
For example, in case the TX-UNIT OPT-AMP
6
is the semiconductor amplifier, the multiplex optical signal fed to the TX-UNIT OPT-AMP
6
is amplified by a semiconductor device operating under DC supply current, and in case the TX-UNIT OPT-AMP
6
is the optical fiber amplifier, the multiplex optical signal fed to the TX-UNIT OPT-AMP
6
is amplified in an optically amplifying technology using an induced emission.
Recently, the optical fiber amplifier is used to the TX-UNIT OPT-AMP
6
and the REP OPT-AMP
8
mostly. Because, the optical fiber amplifier has features such as a low Noise Figure, a little non-linearity in amplification, a low connection loss with the OPT-TRANS LINE
3
, high capability of a power amplification and a high stability against a temperature change.
The optical fiber amplifier is composed of a rare earth metal-doped optical fiber such as Erbium (Er)-doped optical fiber and a pump light source such as a semiconductor laser.
In the multiplex optical communication system of the related art, the output power of the multiplex optical signal from the TX-UNIT OPT AMP
6
or the REP OPT-AMP
8
is controlled so as to be always constant in level under constant output level control performed in the TX-UNIT OPT AMP
6
and the REP OPT-AMP
8
respectively. In case of the REP OPT-AMP
8
, by virtue of the constant output level control, the OAMP REP EQUIP
2
can be placed independently on a length of the OPT-TRANS LINE
3
connected with the OAMP REP EQUIP
2
. In other words, the power level of each section between REP OPT-AMPs or between TERM EQUIP and REP OPT-AMPs is independent. The change of power level and different of OPT-TRANS LINE
3
loss at one section don't affect the power level at next section.
If a multiplex optical signal includes “n” channels a

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