The influences of plasma parameters on the deposition of a-Si:H film and particle growth have been studied with silane discharge using amplitude-modulated RF methods. Plasma parameters have been measured with the Langmuir probe system and optical emission spectrometer. Behaviors and generation processes of particles have been observed by the laser scattering method. The deposited thin film has been characterized by various techniques such as Fourier-transform infrared (FT-IR) spectrometry, ESR and the constant photocurrent method (CPM). High deposition rate with low particle density as well as high film quality has been realized for a-Si:H film by amplitude-modulated RF methods.

Propagation and filtering characteristics of two dimensional pillar-type photonic crystal waveguide with triangular lattice were measured and improved experimentally. Measurement was done by using a scale model in microwave frequency with lattice period P=26.5 mm, diameter of pillar .=7.5mm and its dielectric constant ε _r =36.0 around 4 GHz. First, symmetric Y-branch waveguide was set up by using line-defect in array of pillars. After confirming symmetric branching operation in frequency range between 3.6 and 4.2 GHz, a pair of pillars which have length of 3.0P and 2.5P respectively, were situated in each output waveguide as cavities. These cavities showed resonant characteristics at frequencies corresponding to λ _g /2 in the waveguide. Also, good extinction ratios of over 20 dB between output ports were observed at these resonant frequencies. Next, cascading the Y-branch by two stages and situating four cavities with different lengths at each output port, filtering characteristics were observed at each output in frequency range of 3.6 to 4.2 GHz. The extinction ratios at each resonance frequency were over 17 dB. Though the structure showed good filtering characteristics, unnecessary resonances in frequency domain were observed near main peaks of filtered frequency. To suppress these unwanted peaks, stabs with length of λ _g /4 were inserted after the cavities, where λ _g is wavelength of the unnecessary frequency. Due to the stabs, peaks of the unnecessary resonances were suppressed over 20 dB compared with simple cavities. This structure is applicable as a basic filter component in wavelength division multiplexing (WDM) systems in photonic crystal optical circuits.

A Bragg-mirror-assisted terahertz (THz) high-contrast and broadband plasmonic interferometer is proposed and theoretically investigated for potential sensing applications. The central microslit couples the incident THz wave into unidirectional surface plasmon polaritons (SPPs) waves travelling to the bilateral Bragg gratings, where they are totally reflected over a wide wavelength range back towards the microslit. The properties of interference between the SPPs waves and transmitted THz wave are highly dependent on the surrounding material, offering a flexible approach for the realization of refractive index (RI) detection. The systematic study reveals that the proposed interferometric sensor possesses wavelength sensitivity as high as 167 μm RIU⁻¹ (RIU: RI unit). More importantly, based on the intensity interrogation method, an ultrahigh Figure-of-Merit (FoM) of 18,750% RIU⁻¹, surpassing that of previous plasmonic sensors, is obtained due to the high-contrast of interference pattern. The results also demonstrated that the proposed sensors are also quite robust against the oblique illumination. It is foreseen the proposed configuration may open up new horizons in developing THz plasmonic sensing platforms and next-generation integrated THz circuits.

Graphene, a two-dimensional monatomic layer of carbon material, has demonstrated as a good candidate for applications of ultrafast photodetectors, transistors, transparent electrodes, and biosensing. Recently, many studies have shown that using metallic deep gratings could enhance the absorptance of graphene of 2.3% up to 80% in the near infrared region for applications in photon detection. This paper presents utilizing a nanograting structure, namely, a compound metallic grating could greatly enhance the absorptance of graphene to 100% and widen its spectral bandwidth to 600 nm, which are greater than those of previous work. The study also showed that the absorptance spectrum is insensitive to angles of incidence. Furthermore, the proposed graphene-covered compound grating might bring a lot of benefits for graphene designs-based optical and optoelectronic devices.