An ultra-fast optical analog-to-digital converter using nonlinear X-shaped photonic crystal ring resonators

This paper reports a new optical analog-to-digital converter (OADC) design based on nonlinear X-shaped photonic crystal ring resonators (X-PCRRs). The dielectric rods made of silicon and nonlinear rods composed of doped glass are used to form X-PCRRs. The proposed structure consists of a nonlinear three-channel demultiplexer and an optical encoder. The nonlinear demultiplexer converts the continuous input signal into three quantized discrete levels, and the optical encoder generates two-bit binary codes depending on the output channel number of the demultiplexer. Two well-known plane wave expansion and finite difference time domain methods are applied to study and analyze the photonic band structure and light propagation inside the PhC-based structure, respectively. The wide TM photonic band gap of the fundamental PhC covers the second window of telecommunication in the C-band. Our calculations reveal that the proposed OADC has a maximum response time of about 4 ps and a sampling rate of 125 GS/s that is much faster than the designed ADC in previous studies. The proposed ADC also has a total footprint of 1785 μm2 with a minimum leakage loss.