Uncooled Terahertz (THz) focal plane array (FPA), 320x240 format-23.5 μm pitch, and THz imager were
developed. There are two types of THz-FPAs, i.e., broad-band type and narrow-band type. Since broad-band
type THz-FPA was developed, a couple of modifications have been made to improve Noise Equivalent Power.
The narrow-band type THz-FPA has such a new structure that Si cover is put above thermal isolation structure
of broad-band type THz-FPA at a distance of half of wavelength of interest. Measurements on responsivities
of narrow-band type FPAs show enhancement by a factor of ca. 3. Lock-in imaging technique has been
developed, which increases signal-to-noise ratio as a function of square root of the number of frames of
integration. Both passive and active THz imaging experiments were finally described.
For high-density recording at a wavelength of 690 nm, we developed a phase-change optical disk with a Si reflective layer. We estimated the effect of interference layer by calculating optical properties. The absorption control required for mark edge recording and a 2 dB C/N improvement was obtained by forming a ZnS-SiO<SUB>2</SUB> interference layer on the Si layer. Under recording conditions with a minimum bit length of 0.335 micrometers and a track pitch of 1.2 micrometers , a sufficient C/N and a BER less than 10<SUP>-4</SUP> were confirmed. This result indicates that the recording capacity of the new disk is more than 4 GB.
Overwrite characteristics have been studied for Ge-Sb-Te phase change media under high linear velocity conditions, ranging from 11.3 m/s to 22.6 m/s, with mark-edge-recording (MER). The Ge<SUB>1</SUB>Sb<SUB>4</SUB>Te<SUB>7</SUB> recording layer composition was chosen for the rapid cooling structure to obtain a sufficient erase ratio under high linear velocity conditions. The optical optimization for the disk structure and the narrow-grooved substrate have been applied to improve erase characteristics with MER. The optical phase-difference-reproduction (PDR) has been studied to realize a high carrier to noise ratio (C/N). The pulse-width-reduction (PWR) recording compensation has been developed for high recording density. A 44.8 dB C/N was obtained for 0.68 micrometers minimum recording mark length. A -26.8 dB erase ratio was obtained at 22.6 m/s linear velocity.