<p>Frequency shift keying demodulators are used to generate binary codes from the frequencies of the input signal. In this paper, authors propose all-optical single-bit frequency shift keying demodulator in Photonic crystal which can generate different single-bit binary outputs for different input frequencies. The system is designed in a small wafer of footprint area 130.275 µm² which is constructed by inserting cylindrical silicon rods in air substrate. The operating frequencies are 204.22 THz and 181.69 THz respectively. The proposed system is simulated by finite difference time domain (FDTD) method. Response time and extinction ratio of the system are found to be 100&#xa0;fs and 19.18 dB respectively with this design. Photonic crystal-based ring resonators are used to manipulate the path of optical signals for this purpose. The compactness of the structure and small wafer area provide an excellent response time and very high extinction ratio which make the proposed system a potential candidate to be a part of optical integrated circuits (ICs) for optical communication networks.</p>