Photonic crystals represent a viable option for the creation of small and high-speed optical devices because of their special ability to manipulate light. The progress in photonic crystal-based comparators, encoders, and logic gates is examined in this review of the literature. The review addresses the structural parameters, functional parameters, approaches, and applications related to combinational device (comparators, encoders, and logic gates) based on photonic crystals. For improving the functionality of the device, various techniques were reviewed. By compiling research studies and experimental demonstrations to summarize the state-of-the-art at this time, the review offers valuable insights into the advancements and potential of photonic crystals for optical device development.