Capacitive Humidity Sensor Based on Carbon Black/Polyimide Composites.

A novel capacitive humidity sensor based on carbon black/polyimide composites is presented in this paper. The details of the fabrication, sensor characteristics, and effect of the carbon black additive are described. It was confirmed that the polyimide composite filled with a tiny amount of carbon black was suitable for a humidity sensing dielectric. The humidity sensors with three different dielectrics, which were pure polyimide, 0.01 wt% carbon black/polyimide, and 0.05 wt% carbon black/polyimide, were fabricated by a micro-electro-mechanical-system (MEMS) process. As the amount of the carbon black additive increased, the sensitivity of the humidity sensor increased. The humidity sensor with 0.05 wt% of carbon black had a much higher sensitivity of 15.21% (20-80% RH, 0.2535%/% RH) than that of the sensor with pure polyimide, which was 9.73% (0.1622%/% RH). The addition of carbon black also led to an enhancement in the hysteresis and response speed. The hysteresis of the humidity sensor decreased from 2.17 to 1.80% when increasing the amount of the carbon black additive. The response speed of the humidity sensor with 0.05 wt% of carbon black was measured to be ~10% faster than that of the sensor with pure polyimide. The long-term stability of the humidity sensors was demonstrated as well.

Birefringent waveguide sensor using a polarizer rotating technique.

A birefringence measurement system is introduced to get high phase resolution for detection of low contents of biochemicals. By using a fixed quarter-wave plate and a rotating polarizer, the phase difference between two orthogonal polarizations is transformed into phase delay of output sinusoidal signal. Analyzing the output phase, birefringence change could be detected with a phase noise of 0.14 degrees. As well as the birefringence measurement system, an optical evanescent waveguide sensor was developed. A rib-type silica waveguide overlaid with TiO2 film was fabricated, and a developed birefringence measurement technique was employed in evaluating a refractive index change on waveguide surface. For the fabricated waveguide with a 40-nm-thick TiO2 film, experiment results showed that the minimum detectable index change was 5.9x10(-7).

Integrated optical modulator for signal up-conversion over radio-on-fiber link.

An integrated optical modulator, which consists of a dual-sideband suppressed carrier (DSB-SC) modulator cascaded with a single-sideband (SSB) modulator, is proposed for signal up-conversion over Radio-on-Fiber. Utilizing a single-drive domain inverted structure in both modulators, balanced modulations were obtained without complicated radio frequency (RF) driving circuits and delicate RF phase adjustments. Intermediate frequency (IF) band signal was up-conversed to 60GHz band by using the fabricated device and was transmitted over optical fiber. Experiment results show that the proposed device enables millimeter wave generation and signal transmission without any power penalty caused by chromatic dispersion.

Leaky modes of curved long-range surface plasmon-polariton waveguide.

A three-dimensional method for obtaining the bending losses and field distributions of bent surface plamon-polariton waveguides is presented. The method is based on a so called 'method of line', which discretises potential in the direction of the metal-widths, and leads to Airy-equations in the radial direction. From the results obtained. It is confirmed that thiner metal waveguide enable longer-ranging propagation of surface plasmon-polariton mode, but the weakened confinement requires larger bending radii on order to keep radiation loss.