Optical preamplifier with one amplification unit

Details Optical preamplifier with one amplification unit Optical preamplifier with one amplification unit

2002-08-08

2004-10-26

Moskowitz, Nelson (Department: 3663)

Optical: systems and elements

Optical amplifier

Dispersion compensation

Reexamination Certificate

active

06809857

ABSTRACT:

CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application entitled OPTICAL PREAMPLIFIER HAVING ONE STAGE CONFIGURATION earlier filed with the Korean Industrial Property Office on 28, Nov. 2001 and there duly assigned Serial No. 74699/2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmission system for a long distance, and more particularly, to an optical preamplifier including one amplification unit for outputting an optimum level of an optical signal to an optical receiver.
2. Description of the Related Art
Generally, as shown in
FIG. 1
, an optical transmission system includes an optical transmitter for generating an optical signal, an optical power amplifier OPA for amplifying powers of the optical signal, multiple optical line amplifiers OLAs according to an optical signal damping, an optical preamplifier OPRA for compensating damping amounts of the optical signal, and an optical receiver. The optical signal from the optical transmitter is transmitted to the optical receiver through OPA, OLAs, and OPRA.
The wavelength of the optical signal differs according to the optical transmission system. For the optical transmission system for a long distance, the wavelength of 1550 nm (nanometers) is typically used because it belongs to a bandwidth of a gain wavelength of the optical amplifier and the loss of the wavelength is small during a transmission. On the contrary, for the optical transmission system for a short or medium distance, the wavelength such as 1300 nm is used because the dispersion value of the wavelength is nearly zero even though the wavelength loss is large.
In other words, the wavelength of the optical channel belongs to a bandwidth of 1550 nm in an optical transmission system of high speed such as more than 10 Gbps (gigabits per second). As described in the above statements, such an optical channel of a bandwidth of 1550 nm has a dispersion value making some troubles in a long distance transmission of the optical signal. Therefore, to compensate the dispersion value of the optical fiber, a dispersion compensation fiber module DCFM is normally used in the OLA and the OPRA.
The DCFM compensates dispersions of the wavelength while transmitting an optical signal. However, when the optical intensity of the inputted optical signal is more than 0 dBm (decibels) because the damping amount, such as 8 dBm, is large and the diameter of the core is too small, a signal distortion can happen due to a non-linear phenomena. To solve such problems, the conventional optical transmission system for a high speed and a long distance includes an optical preamplifier with two amplification units and a DCFM between the two amplification units. The amplification unit is normally an erbium doped fiber EDF.
The conventional optical preamplifier including two amplification units, EDFs, is illustrated in FIG.
2
. Generally, the conventional optical preamplifier applies two optical pumping methods to get gains. One method is that both ends of the DCFM respectively include a laser diode LD and a gain media such as an EDF to get gains in both ends of the DCFM independently. The other method is to use a wavelength division multiplexor WDM to get gains, a first gain and a second gain. The first gain is acquired by the way of dividing the output of a pumping LD by a first gain media EDF, and sequentially, the second gain is acquired by the way of dividing the output of a pumping LD by a second gain media EDF. The conventional optical preamplifier of
FIG. 2
illustrates the latter pumping method.
Referring to
FIG. 2
, the conventional optical preamplifier includes a first erbium doped fiber EDF
1
21
, a DCFM, and a second erbium doped fiber EDF
2
22
. The EDF
1
21
amplifies an input level of the optical signal, such as −10~−20 dBm, to an out level of about −3~−6 dBm. The EDF
2
22
compensates the losses of the optical signal generated while the optical signal from the EDF
1
21
is passing through the DCFM, and amplifies the optical signal to maintain the entire optical outputs in −3 dBm. The amplification procedures are illustrated as follows.
The EDF
1
21
transmits the optical signal input from the input terminal IN to a first wavelength division multiplexor WDM
1
while the first wavelength division multiplexor WDM
1
inverse-multiplexes the optical signal to a management channel of 1510 nm and a signal channel of 1550 nm. Parts of the optical signal of 1550 nm inverse-multiplexed in the WDM
1
are divided through a first tap coupler TAP
1
, and a photo detector LOS monitors optical losses during this process. The optical signal output from the TAP
1
sequentially passes through a first optical isolator ISO
1
, and is received to one input terminal of a second wavelength division multiplexor WDM
2
. The other input terminal of the WDM
2
receives a pumping light of 980 nm to multiplex the optical signal.
The optical signal multiplexed in the WDM
2
is amplified through the EDF
1
21
, and a third wavelength division multiplexor WDM
3
inverse-multiplexes the optical signal of 1550 nm and the pumping light of 980 nm. The optical signal of 1550 nm passes through an optical isolator band pass filter ISOF, and is received to the DCFM. The DCFM compensates the dispersion value included in the optical signal.
The EDF
2
22
transmits the optical signal of 1550 nm compensated in the DCFM to a second optical isolator ISO
2
and then to one input terminal of a fourth wavelength division multiplexor WDM
4
. The other input terminal of the WDM
4
receives a pumping light of 980 nm inverse-multiplexed in the WDM
3
, and the WDM
4
multiplexes the optical signal of 1550 nm and the pumping light of 980 nm. The multiplexed optical signal passes through the EDF
2
, and the EDF
2
amplifies the optical signal of 1550 nm. The amplified optical signal of 1550 nm passes through a third optical isolator ISO
3
, and is transmitted into a manual turnable filter MTF. The MTF eliminates maximum amounts of an amplified spontaneous emission ASE generated during the process of amplifying the optical signal. Finally, the optical signal is transmitted into a second tap coupler TAP
2
. The TAP
2
divides a portion of the optical signal for use in an auto power control APC circuit and outputs the other optical signal to the optical receiver through the output terminal OUT. The APC circuit adjusts an optical intensity outputted from the pumping LD to maintain the entire optical output regularly even though the optical intensity of the inputted optical signal is variable.
The input terminal of the above described conventional optical preamplifier receives an optical signal of −10~−26 dBm, and the output terminal outputs an optical signal of −3 dBm to the optical receiver. However, the optimum intensity of the optical signal input to the optical receiver is −6~−8 dBm. Therefore, an additional variable or fixed damper is necessary between the optical preamplifier and the optical receiver to adjust the output level of the optical signal from −3 dBm to −6~−8 dBm.
In other words, because the conventional optical preamplifier includes two amplification units, the configuration is complex and the production cost is increased. Furthermore, because the optical intensity of the optical signal from the optical preamplifier is higher than the optimum intensity of the optical signal to the optical receiver, an additional device is necessary.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide an optical preamplifier with one amplification unit for amplifying an optical signal, compensating dispersion of the optical signal after receiving the optical signal from an optical transmitter and supplying the optical signal to an optical receiver.
It is another object to provide an optical preamplifier that is simpler to manufacture in order to reduce production costs withou

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