Optical comparators have the potential to improve the operational speed and power consumption of optical communication systems, as they directly perform the required operations in the optical domain to avoid any optic-electro conversions. Various comparators are optically implemented; however, most studies have been confined to an ON-OFF keying modulation. Although there is a comparator available for the phase-shift keying (PSK) modulation, the device has a limitation that requires integration into an actual system. In this paper, the author provides an optical comparator based on a silicon waveguide for a quadrature PSK (QPSK) signal. The proposed comparator is a simple 2.0 × 0.1 mm 2 rectangle, which is approximately 1/7500 the size of comparators from previous studies, and the device mainly comprises a delay line interferometer, a variable splitting ratio optical coupler, and a phase shifter. The performance of the comparator designed for 00 00 and 11 00 codewords was experimentally evaluated. The comparator generates the coupled symbol with the comparison result between the target code and the input signal. The paper demonstrates the feasibility of the ultracompact optical comparator for a 4-bit QPSK-modulated signal at 10 Gbaud.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.