Simple and compact optical half-subtractor based on photonic crystal resonant cavities in silicon rods

We propose a very simple and compact structure to realize the subtracting operation using resonant cavities in a photonic crystal structure. The cross section of the structure is ${103}\;\unicode{x00B5}{\rm m}^2$103µm² and is desirable for integration based on popular planar technology. In the designed subtractor, the cavity was responsible for selecting the wavelength. By changing the boundary rods' cavity condition, the mode could resonate at the desired frequencies. To have resonant cavities, we introduce four defect rods between the input and the output waveguides. The results exhibit the true performance of the device. We used only silicon rods in the proposed device, and hence it is very simple to be fabricated. The finite-difference time-domain method was used for analyzing the proposed structure. The simulation results show that the contrast ratio of the device is 5 dB. The maximum rise and fall times are 1.5 and 0.5 ps, respectively.