We developed a nano-photodiode that confines and absorbs the sub-wavelength-size optical near field in small-scale
silicon. A surface plasmon resonance antenna is used to enhance the near field in silicon. The response time of the nanophotodiodes
is shorter than that of conventional photodiodes because the separation between anode and cathode and the
size of the electrodes can be as small as one thousandth of that for conventional photodiodes. The full-width at halfmaximum
of the impulse response of the silicon nano-photodiode was as fast as ~20 ps even when the bias voltage was
less than 1 V. This nano-photodiode technology can be applied to other semiconductor materials such as germanium and
ternary compound semiconductors.
We developed a Fabry-Perot (FP) optical modulator with electro-optic (EO) films fabricated by aerosol deposition (AD). We found the ferroelectric Pb(Zr,Ti)O<sub>3</sub> film by AD produced a fairly high EO coefficient (>150 pm/V), approximately 10 times larger than that of LiNbO<sub>3</sub>. Since thick EO films greater than 5 μm can be deposited on a transparent electrode layer or a metallic mirror layer of the FP optical modulator by AD, the FP optical modulator can achieve low capacitance, resulting in high modulation speed. Transmittance spectra of the FP optical modulator coincided with the optical simulation spectra, which indicated that optical scattering in AD films and at the surface/boundary were very small. We demonstrated an optical intensity modulation with applied electric field to EO film of ferroelectric Pb (Zr, Ti)O<sub>3</sub>. We obtained a 4-dB modulation with 50 V for the 10-μm-thick modulator with dielectric multilayer mirror on a glass substrate.