Ae. Willner et W. Shieh, OPTIMAL SPECTRAL AND POWER PARAMETERS FOR ALL-OPTICAL WAVELENGTH SHIFTING - SINGLE-STAGE, FANOUT, AND CASCADABILITY, Journal of lightwave technology, 13(5), 1995, pp. 771-781
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.