Recent advances on all-optical photonic crystal analog-to-digital converter (ADC)

Today, one of the most important objectives concerned with integrated optical circuits is to realize all-optical networks. High transmission speed and efficiency and no interference between optical and electronic signals encourage us to manufacture all-optical devices. In the present paper, photonic analog-to-digital converters that are one of the key structures required in integrated optical circuits have been investigated. One of the advantages of these converters is the generation of binary codes, which leads to faster data transfer. In all the proposed designs, a power and wavelength discretizer and a coder have been used to find the optimal structure with the best specifications. The optical discretizer located at the input and designed as a combination of rods and ring resonators is strongly influenced by the input power due to nonlinear effects. The coder structure that consists of input and output ports can be controlled by controlling such elements as radius and refractive index and sometimes creating cavities in the structure. Reviewing the relevant literature can make it clear that a delay time of 5 ps and a footprint of 1520 μm can be achieved by controlling the resonance modes. By creating a cavity in the proposed design, an operation speed of 1 Ts and a footprint of 42 µm2 can be achieved, causing significant improvements compared to previous designs. For better transmission, additional GaN ring resonators can be placed in the structure so that it can support the sampling rate of 220 GS/s with a resolution of 880KS. By adjusting the coupling coefficients in the structures, the threshold level can also be adjusted. These coefficients depend on the radius and refractive index. The improved optical ADC operation and switching speed and the reduced power consumption can be realized by adjusting them. In structures where the binary code “11” is generated, a sampling time of 1.5 ps can be achieved using a number of optical switches. Such converters are designed with a square and triangular topology using dielectric rods in the air (or air rods in dielectric) with a certain lattice constant and filling ratio. The Finite-difference time-domain (FDTD) method is used to simulate these structures.