Researchers at the Chinese University of Hong Kong (Shatin, N.T., Hong Kong SAR, PRC) say they have overcome two of the primary efficiency limitations of conventional single-pump four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for wavelength conversion. Conversion efficiency tends to suffer with wavelength detuning and with variations in input signal polarization.
The Chinese research team has addressed these problems in a 10-Gbit/s system with a single SOA by using broadband orthogonal pumps (BOPs) to broaden the bandwidth and a polarization diversity scheme to provide polarization independence. A nearly constant conversion efficiency (about -25 dB) was obtained, with less than 3-dB variation over a 36-nm wavelength range, by using three input BOPs (two pumps and one signal). The polarization diversity scheme was implemented using a single SOA with a distributed-feedback laser in an optical loop configuration that kept polarization sensitivity below 0.34 dB. With a 10-Gbit/s input signal and a 10-9 bit error rate (BER), the system power penalty was less than 0.9 dB.
System performance could be further improved in terms of bandwidth, according to the researchers, by using an SOA with a wider material gain spectrum or by increasing pump power to operate the FWM in the SOA at saturated gain. Conversion efficiency could be further improved by increasing pump power and decreasing wavelength detuning. For more details, contact Hon Ki Tsang at firstname.lastname@example.org.