OPTIMAL SPECTRAL AND POWER PARAMETERS FOR ALL-OPTICAL WAVELENGTH SHIFTING - SINGLE-STAGE, FANOUT, AND CASCADABILITY

We analyze a gain-saturated semiconductor-optical-amplifier (SOA) all- optical wavelength shifter with respect to its spectral and power char acteristics as well as its capability for high fanout and cascadabilit y. The extinction and signal-to-noise ratios, the two main figures-of- merit for a wavelength-shifted signal, are determined by accounting fo r gain saturation and spectral shifting which occur due to the depleti on of the injected carrier density. We find that the optimal pump (i.e . original) and probe (i.e. shifted) wavelengths are red-shifted by 15 mm and blue-shifted by 20 nm, respectively, relative to the initial u nsaturated SOA gain peak, with the optimal wavelength separation being similar to 35 nm for an SOA gain bandwidth of 50 mm; optimal conditio ns maximize the signal-to-noise ratio of the wavelength-shifted output signal when considerations include the output extinction ratio and th e SOA noise figure. We determine that a pump and probe can be chosen a t any wavelength within a 20 nm range centered rat the original gain p eak and still produce <3 dB decrease in SNR. Extinction ratios exceedi ng 10 dB result when a pump power of -3 dBm and a probe power of -15 d Bm are coupled into the SOA. Additionally, the wavelength shifter can broadcast the data residing on the pump wavelength to as many as 50 pr obe wavelengths, with each pump and probe coupling a power of 0 dBm an d -25 dBm into the SOA; this fanout results in an extinction ratio exc eeding 8 dB for each probe. Finally, greater than 10 stages of wavelen gth shifters can be cascaded if the SOA's at each stage are optimized for the incoming and outgoing wavelengths given that appropriate pump and probe powers are chosen. If the spectral location of the gain peak of each SOA in a cascade is not optimized but is fixed, only similar to 3-4 stages can be cascaded successfully. Higher pump powers will re sult in more possible cascaded stages.