Wide band erbium-doped fiber amplifier with gain enhancement

1. A wide band erbium-doped fiber amplifier with a gain enhancement comprising:

a first fiber amplifier adapted to amplify C-band components of an input optical signal;

a second fiber amplifier connected to the first fiber amplifier in series while being disposed downstream from the first fiber amplifier, and adapted to amplify L-band components of the input optical signal;

a C/L splitter disposed between the first and second fiber amplifiers, and adapted to split the amplified C and L-band optical signals to flow along different paths;

a fiber reflector disposed downstream from the second fiber amplifier, and adapted to reflect the amplified L-band optical signal to flow backwards toward the second fiber amplifier;

a circulator disposed between the C/L splitter and the second fiber amplifier, and adapted to guide the amplified L-band optical signal, reflected to flow backwards by the fiber reflector, so that the amplified L-band optical signal flows along a path different from that of optical signals applied to the circulator; and

a C/L combiner adapted to combine the amplified C-band optical signal split by the C/L splitter with the amplified L-band optical signal guided by the circulator, and to apply the resultant optical signal to an output stage.

2. The wide band erbium-doped fiber amplifier according to claim 1 , wherein the first fiber amplifier comprises a first erbium-doped fiber connected to a 980 nm pumping laser diode via a first wavelength selective coupler, thereby receiving a pumping light from the 980 nm pumping laser diode.

3. The wide band erbium-doped fiber amplifier according to claim 1 , wherein the second fiber amplifier comprises a second erbium-doped fiber connected to a 1,480 nm pumping laser diode via a second wavelength selective coupler, thereby receiving a pumping light from the 1,480 nm pumping laser diode.

4. The wide band erbium-doped fiber amplifier according to claim 1 , wherein the circulator is configured to cut off backward flowing of an amplified spontaneous emission generated during an amplification operation of the second fiber amplifier.

5. The wide band erbium-doped fiber amplifier according to claim 1 , further comprising an isolator disposed between the C/L splitter and the C/L combiner.

6. A wide band erbium-doped fiber amplifier with a gain enhancement comprising:

a first fiber amplifier adapted to amplify C-band components of an input optical signal;

a second fiber amplifier connected to the first fiber amplifier in series while being disposed downstream from the first fiber amplifier, and adapted to amplify L-band components of the input optical signal;

a C/L splitter disposed between the first and second fiber amplifiers, and adapted to split the amplified C and L-band optical signals to flow along different paths;

a fiber reflector disposed downstream from the second fiber amplifier, and adapted to reflect the amplified L-band optical signal to flow backwards toward the second fiber amplifier;

a circulator disposed between the C/L splitter and the second fiber amplifier, and adapted to guide the amplified L-band optical signal, reflected to flow backwards by the fiber reflector, so that the amplified L-band optical signal flows along a path different from that of optical signals applied to the circulator;

a C/L combiner adapted to combine the amplified C-band optical signal split by the C/L splitter with the amplified L-band optical signal guided by the circulator, and to apply the resultant optical signal to an output stage; and

re-using means for supplying the amplified C-band optical signal split by the C/L splitter, as a seed beam for the second fiber amplifier.

7. The wide band erbium-doped fiber amplifier according to claim 6 , wherein the re-using means comprises:

a first coupler disposed between the C/L splitter and the C/L combiner, and adapted to partially couple the amplified C-band optical signal applied thereto; and

a second coupler disposed between the circulator and the second fiber amplifier, and adapted to connect, to the second fiber amplifier, the amplified C-band optical signal partially coupled by the first coupler,

whereby the amplified C-band optical signal is partially used as a seed beam for the second fiber amplifier.

8. The wide band erbium-doped fiber amplifier according to claim 7 , wherein each of the first and second coupler uses 10% of the amplified C-band optical signal applied thereto.

9. The wide band erbium-doped fiber amplifier according to claim 6 , wherein the re-using means comprises a reflection filter disposed between the C/L splitter and the second fiber amplifier, and adapted to reflect C-band components of an amplified spontaneous emission generated during an amplification of the second fiber amplifier.

10. The wide band erbium-doped fiber amplifier according to claim 9 , wherein the reflection filter comprises a fiber grating having a variation in refractive index along a longitudinal fiber direction.

11. The wide band erbium-doped fiber amplifier according to claim 10 , wherein the fiber grating is a short period fiber grating.