Gain equalization in C+L erbium-doped fiber amplifiers
Techniques for improving gain equalization in C- and L-band (“C+L”) erbium-doped fiber amplifier (EDFAs) are provided. For example, the C- and L-band amplification sections of a C+L EDFA may be separated and configured in a parallel arrangement or a serial arrangement. For both the parallel and serial arrangements, the C- and L-band amplification sections may share a common gain flattening filter (GFF) or each amplification section may include and employ a separate GFF. Moreover, in some examples, an “interstage” L-band GFF may be located before or upstream of the L-band amplification section such that the L-band optical signal is gain-equalized or flattened prior to the L-band amplification section amplifying the L-band.
1 . An apparatus comprising:
a C-band amplification section;
an L-band amplification section;
a first gain flattening filter (GFF) for performing C-band gain equalization, the first GFF coupled to the C-band amplification section; and
a second GFF, different from the first GFF, for performing L-band gain equalization, the second GFF coupled to the L-band amplification section,
wherein the C-band amplification section includes at least a first erbium doped fiber (EDF) for amplifying a C-band optical signal,
wherein the L-band amplification section includes at least a second EDF for amplifying an L-band optical signal, and
wherein the C-band amplification section and the L-band amplification section are configured in a serial arrangement.
2 . The apparatus of claim 1 , further comprising:
a splitter for splitting an input signal to the C-band and L-band optical signals;
a first optical isolator, wherein the first optical isolator and the splitter arranged or coupled between the first EDF of the C-band amplification section and the first GFF; and
a second optical isolator arranged or coupled between the second EDF of the L-band amplification section and the second GFF.
3 . The apparatus of claim 2 , further comprising:
a third optical isolator for receiving the input signal, and
wherein the third optical isolator is arranged or coupled before or upstream of the splitter.
4 . The apparatus of claim 2 , wherein the serial arrangement comprises the C-band amplification section arranged or coupled before or upstream of the L-band amplification section and wherein the first and second GFFs are coupled to and arranged after or downstream of the first and second EDFs, respectively, such that the first and second GFFs perform gain equalization of the amplified C-band and L-band signals.
5 . The apparatus of claim 2 , wherein at least the first and second optical isolators and the first and second GFFs form a hybrid component.
6 . The apparatus of claim 5 , further comprising:
a combiner for combining the amplified C-band and L-band optical signals, wherein the combiner is arranged or coupled downstream between the first and second GFFs and an output node.
7 . The apparatus of claim 6 , wherein the second GFF is arranged or coupled between the first optical isolator and the second EDF of the L-band amplification section, the second GFF being located before or upstream of the second EDF, such that the L-band gain equalization is performed on the L-band optical signal prior to the second EDF amplifying the L-band optical signal.
8 . The apparatus of claim 1 , wherein the second GFF is arranged or coupled before or upstream of the second EDF such that the L-band gain equalization is performed on the L-band optical signal prior to the second EDF amplifying the L-band optical signal.
9 . The apparatus of claim 1 , further comprising:
a first blocking filter; and
a second blocking filter,
wherein a guard band corresponding to the amplified C-band optical signal is narrowed or reduced by the first blocking filter, and
wherein a guard band corresponding to the amplified L-band optical signal is narrowed or reduced by the second blocking filter.
10 . The apparatus of claim 8 , the second GFF is an interstage GFF and is configured to provide gain tilt correction.
11 . The apparatus of claim 1 , wherein the first and second EDFs perform amplification using a 980 nm pump light provided by a laser diode and wherein the apparatus is a C+L EDFA arranged or implemented in a long-haul optical communication system.
12 . The apparatus of claim 6 , wherein the hybrid component includes the combiner.
13 . The apparatus of claim 12 , wherein the hybrid components includes an optical tap.
14 . A method for transmitting an optical signal, comprising:
receiving an input optical signal;
amplifying a C-band portion of the input optical signal;
splitting the input optical signal into an amplified C-band portion of the input optical signal and an L-band portion of the input optical signal;
amplifying the L-band portion of the input optical signal;
performing gain flattening of the amplified C-band portion of the input optical signal and the amplified L-band portion of the optical signal;
combining gain-flattened amplified C-band and L-band portions of the input optical signal into an output optical signal; and
transmitting the output optical signal.