We investigate experimentally metal-insulator-silicon-insulator-metal (MISIM) waveguides that are fabricated by using fully standard CMOS technology. They are hybrid plasmonic waveguides, and they have a feature that their insulator is replaceable with functional material. We explain a fabrication process for them and discuss fabrication results based on 8-inch silicon-on-insulator wafers. We measured the propagation characteristics of the MISIM waveguides that were actually fabricated to be connected to Si photonic waveguides through symmetric and asymmetric couplers. When incident light from an optical source has transverse electric (TE) polarization and its wavelength is 1318 or 1554 nm, their propagation losses are between 0.2 and 0.3 dB/μm. Excess losses due to the symmetric couplers are around 0.5 dB, which are smaller than those due to the asymmetric couplers. Additional measurement results indicate that the MISIM waveguide supports a TE-polarized hybrid plasmonic mode. Finally, we explain a process of removing the insulator without affecting the remaining MISIM structure to fabricate ~30-nm-wide nanochannels which may be filled with functional material.

Metal-insulator-silicon-insulator-metal (MISIM) waveguides are proposed and investigated theoretically. They are hybrid plasmonic waveguides, and light is highly confined to the insulator between the metal and silicon. As compared to previous ones, they are advantageous since they may be realized in a simple way by using current standard CMOS technology and their insulator is easily replaceable without affecting the metal and silicon. First, their structure and fabrication process are explained, both of which are compatible with standard CMOS technology. Then, the characteristics of the single MISIM waveguide whose insulator has its original or an adjusted refractive index are analyzed. The analysis demonstrates that its characteristics are comparable to those of previous hybrid plasmonic waveguides and that they are very effectively tuned by changing the refractive index of the insulator. Finally, the characteristics of the two coupled MISIM waveguides are analyzed. Through the analysis, it is obtained how close or far apart they are for efficient power transfer or low crosstalk. MISIM-waveguide-based devices may play an important role in connecting Si-based photonic and electronic circuits.

Horizontal slot waveguides based on graphene have been considered an attractive structure for optical waveguide modulators for transverse magnetic (TM) modes. Graphene is embedded in the slot region of a horizontal slot waveguide. If graphene were treated as an isotropic material and its dielectric constant were made close to zero by adjusting its Fermi level, the surface-normal electric field component of the fundamental TM mode of a horizontal slot waveguide might be highly enhanced in graphene. This could cause a large increase in the attenuation coefficient of the mode. This is called the epsilon-near-zero (ENZ) effect. This paper discusses that graphene needs to be treated as an anisotropic material that has an almost real surface-normal dielectric constant component. Then, the ENZ effect does not exist. Approximate analytic expressions and numerical simulation are used for the discussion, and they demonstrate that horizontal slot waveguides are not appropriate for graphene-based modulators for TM modes.

We propose and investigate experimentally a micro-ring-resonator-based sensor with which we can measure both the concentration and temperature of glucose solution. It consists of two micro-ring resonators consecutively coupled to a bus waveguide by the overlap between them. The resonance wavelengths of the two resonators change similarly with the temperature but differently with the concentration. For that purpose, the core of just one micro-ring resonator is exposed directly to the solution. Using polymers, conventional processes, and a polymer lift-off process, we implement the sensor. Through the measurement of the fabricated sensor, we obtain its characteristics of measuring the temperature and concentration.

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