Fiber-lattice accumulator design considerations for optical Sigma Delta analog-to-digital converters

Integrated optical sigma-delta (Sigma Delta) analog-to-digital converters ( ADCs) use a pulsed laser to oversample an input signal at two Mach-Zehnder interferometers. A fiber-lattice accumulator is embedded within a feedback loop around a single-bit quantizer to spectrally shape the quantization noi se to fall outside the signal band of interest. Decimation filtering is app lied to the quantizer output to construct the input signal with high resolu tion. Applications of integrated optical Sigma Delta ADCs include digitizin g wideband radio-frequency signals directly at an antenna (digital antenna) . In this paper, a novel fiber-lattice accumulator design is presented, and a coherent simulation of an integrated optical first-order, single-bit Sig ma Delta ADC is reported. The accumulator leakage resulting from a mismatch in the optical circuit parameters is quantified. A time-domain analysis is presented, and the simulation results from an all-electronic Sigma Delta A DC are presented for comparison. A frequency-domain analysis of a ten times oversampling (n=4 bits) simulation is used to compare the dynamic performa nce parameters, including the spurious-free dynamic range, signal-to-noise- plus-distortion ratio, and effective number of bits. The formation of image frequencies when the accumulator is overloaded (i.e., the optical amplifie r gain is too large) is also investigated. (C) 2000 Society of Photo-Optica l Instrumentation Engineers.