This paper presents a novel optical leaky integrator for an all-optical A/D converter based-on sigma-delta modulation.
The device consists of two main components: a fiber ring resonator (FRR) and a wavelength converter. The FRR
comprises a SOA and an optical filter that defines the resonance wavelength λ<sub>2</sub>. The modulated input signal, at
wavelength λ<sub>1</sub>, changes the gain of the loop through cross-gain modulation (XGM) and thus modifies the loop
accumulation. A theoretical model for the system is developed that accounts for critical design parameters such as the
loop coupling ratio, length, and XGM in the SOA. The system is characterized for square input signals ranging 0.5-
5MHz. The integrator time constant is adjusted between 5% and 25% of the input signal period through modifications in
the loop coupling ratio and the SOA driving-current. Experimental results show excellent agreements with the numerical
simulations. Due to the length of the fiber-loop, the operation frequency of the integrator is limited to the MHz range.
However, the operating frequency can be increased up to hundreds of MHz by shrinking the components' optical fibers,
or up to GHz range, by using current photonic integration technologies.
A novel optical inverted bistable switch based on a nonlinear fiber ring resonator (FRR), which contains a
semiconductor optical amplifier (SOA) in the loop, have been analyzed and experimentally demonstrated. The optical
bistability phenomenon is obtained due to the combined nonlinear effects of the transmission characteristics of the
resonator and the SOA's gain property. A complete theoretical analysis and supporting simulations are presented. A
working prototype is build using commercial optical components. Experimental results show switching speed in tens of
MHz with rising and falling times lower than 10 ns. Limitations in switching speed are caused by the length of the fiber
loop. Therefore, improvements in operating frequencies can be increased up to GHz range if the length of the loop is
reduced to the order of centimeters.