On linearity of all optical asynchronous binary delta–sigma modulator

Since the role of optical signal processing is rapidly increasing within the communication systems, the opportunity to convert the analog signal to digital pulses directly in the optical domain will result in a systems simplification. Following our previous work, this paper describes a simple highly linear all-optical delta–sigma modulator, using the gain modulation in optically coupled single mode ring lasers. The key building blocks are an optical leaky integrator and a switching device, leading to meet the requirements of high-speed dynamic response, input/averaged-output linearity, and functioning without external clock. Linearity of the modulator and the corresponding parameters are discussed in theory, simulation, and experiment.