Fiber-optic asynchronous delta-sigma modulator

A novel photonic analog-to-digital convertor (ADC) based on an asynchronous delta-sigma modulator (ADSM) has been investigated and demonstrated in this paper. Because of the non-negative signal in the optical domain, a pseudo-positive feedback loop requires the design of an inverted bistable quantizer, promising non-interferometric optical implementation. The principles of the proposed optical 1^st-order and 2^nd-order ADSM are modeled and analyzed. Two main components of the new optical ADSM; the leaky integrator and the inverted bistable quantizer have been analyzed, simulated mathematically, constructed, and characterized. Finally, a prototype fiber-optic ADSM is constructed. The prototype operates at 25 MS/s and corresponding binary output have ENOB of 4. The operation characteristics, such as signal-to-noise ratio, dynamic range of this fiber-optic ADSM will be reported.