MODELING OF MISIM/MIS NANO-PHOTONIC SWITCHES AND SENSOR FOR IR-BAND

Abstract

Nano-photonic IR-band switches employing metal-insulator-semiconductor-insulator-metal (MISIM)/metal-insulator-semiconductor (MIS) hybrid plasmonic waveguides (HPWG) and sensors have been investigated within the scope of the present work. The scope of the work is two-fold. In brief, the first part of the thesis deals with modelling and numerical simulations of HPWG based nano-photonic switching components whereas in the second part we discuss HPWG sensor, in specific for detection of volatile alcohols. From the switching aspect, various 1×1 and 1×2 switches have been modelled and simulated. In the beginning, through numerical simulations we have demonstrated all optical switching within the MISIM waveguide working in the 1.473 μm-1.502 μm band (achieved ER = 5.5 dB at λC = 1.488 μm) and 1.512 μm-1.5306 μm band (ER = 3.079 dB at λC = 1.52 μm). However, because of the direct coupling of the pump beam to the main waveguide via control port, we found ER to be degraded for the first scheme of switching. In this regard, light leakage from the main waveguide core was resolved through tuning absorption co-efficient of the control port material (Si0.15Ge0.85) via Franz–Keldysh effect (FKE). In the next, a threedimensional frequency selective 1×1 vertical hybrid plasmonic switch based on metalinsulator- semiconductor (MIS) structure having vanadium oxide (VO2) fin Bragg grating is studied. To achieve frequency selective switching, effective index theory is employed in order to design Bragg grating and, narrow band switching (ER = 11.14 dB) is demonstrated thereof in the IR-band. We furthermore studied impact of various dimension tolerances on the ER and figure of merit (FoM) of the switch. Switching speed due to time taken by the VO2 phase transition was also assessed. Following that, 1×2 MISIM nano-photonic switches with thermo-optic switching elements (VO2 and GST) were numerically simulated for different switches having 1×2 planar splitter and micro-ring resonator architectures. Employing thermo-optic tuning 1×2 switch response is tailored in the IR-band. For 900 bend splitter, we have obtained 14.36 (10.08) dB extinction with VO2 (GST) whereas for the ring resonator 2.72 dB extinction ratio is obtained, in 1.505-1.584 μm and 1.54-1.553 μm band, respectively. Both splitter and micro-ring version of switches with thermo-optic switching element have been investigated in detail from the various design perspectives, especially impedance mismatch due to the insertion of VO2 on the bifurcated section of the splitter and coupling loss arises due to aperture coupling from the bus waveguide to the ring. ii In the second part of the thesis, we have demonstrated a methanol sensor in a hybrid plasmonic aperture waveguide, with gold nano-rings on the coupling plane. From mathematical modelling, we have designed the waveguide aperture for excitation of LSPR on the gold nanorings, whereas due to incorporation of methanol LSPR is shown to be tuned. The latter has been employed for methanol sensing in the IR band, which we have studied in detail against waveguide clad porosity and various other structural parameter variations.