Switching is a principle process in digital computers and signal processing systems. The growth of optical signal processing systems, draws particular attention to design of ultra-fast optical switches. In this paper to investigate the operation of the photonic crystal switches, several methods are described. Among different methods, FDTD is a preferable method and is used. We have studied the application of photonic crystal lattices, the physics of optical switching and different types of all optical photonic crystal switches. In this paper, an all optical switch based on photonic crystal directional coupler has been simulated and analyzed by the finite difference time domain (FDTD) method. In this paper, a different structures with changes in central row rods (0.12a) in all optical directional coupler switch have been proposed then electric field intensity and the power output that are two factors to improve the switching performance and the device efficiency, have been  investigated and simulated by using COMSOL software. Manuscript profile

To the best of our knowledge, it is for the first time that
TERS system in near-infrared (NIR) spectrum is
reporting. The current study proposed a most favorable
atomic force microscopy (AFM) tip based on an
incorporated optimal grating structure close to the tip
apex. The optimized M2 factor and the best spatial
resolution are obtained as 5.9× 109 and 8.5 nm
respectively in the NIR range of radiation light. The
results show that the optimized grating can effectively
increase the amount of intensity of electric field and
improve spatial resolution within the nanoslit between the
AFM tip and substrate. The detection sensitivity of
materials can be done by our proposed AFM-TERS
system. The difference between the maximum
enhancement factors that are correlated to several under
test sample molecules show the selectivity potential of
the proposed AFM-TERS system in material detection
topic. Manuscript profile