A surface plasmon polariton (SPP) is composed of collective electron oscillations that confine optical energies in nanoscale
beyond the diffraction limit. This advantage of SPPs has promoted the development of high-density optoelectronic
integrated circuits (OEICs) using SPPs. Schottky-type plasmonic detectors have attracted particular attention, because
these devices show sensitivity in the telecommunications wavelength range and can be integrated into Si-based
electronic circuits with a simple fabrication process. We have developed an Au/Si Schottky-type plasmonic detector with
nano slits that excites SPPs at the Au/Si interface. In this report, we demonstrate a novel nano-slit arrangement that
provides a sensitivity improvement for the detector. Using the finite-difference time-domain method, we have shown that
the highest electric field intensity in the SPP mode on the Au/Si interface is generated by positioning slits with twice the
pitch of the SPP wavelength at the Au/Si interface. Using this slit pitch, a weaker SPP mode intensity on the air/Au
interface and a stronger SPP mode intensity at the Au/Si interface have also been confirmed. Nano slits with different slit
pitches were formed in the Au film of the detector, and the slit pitch dependence of the photocurrent was measured. The
experimental results showed similar tendencies to the simulation results. This novel nano-slit arrangement can provide an
efficient plasmonic detector for future high-speed data processing applications.
The operation of a metal-oxide-semiconductor field-effect transistor (MOSFET) by a surface plasmon (SP) signal was
demonstrated. The SP detector, composed of a gold/silicon Schottky diode with a nano-slit grating, was monolithically
integrated with the MOSFETs on a silicon substrate. SP generation by the nano-slit gating (slit width of 100 nm, slit
pitch of 440 nm, and slit depth of 300 nm) was confirmed by analytical calculations based on the finite-difference timedomain
method. The SP detector operated at a photon energy (0.80 eV) that was below the bandgap energy of silicon
(1.1 eV), with responsivity of 24 nA/mW and a dark current of 1.7 nA under reverse bias of 5.0 V. The photocurrent
generated by the SP detector controlled the drain current of a monolithically integrated MOSFET.
Grating inscription in azo-dye doped polymers is an interesting phenomenon because of its high diffraction performance and applicability to real-time 3D displays. Although some of these materials were investigated under no external electric field with symmetric optical alignments in preceding studies, they often showed a phase shift of periodic modulation of refractive index from the interference fringe formed by irradiation beams, resulting in asymmetric energy exchange between two coupled beams. The mechanism of the behavior has been usually attributed to the molecular motions triggered by trans-cis isomerization, but their details are still unknown. Therefore, studies on temporal evolution of the process and their translation into physical meaning are necessary. In order to investigate the evolution of grating inscription and phase shift, several methods have been developed. In this study, we analyzed the coupled wave equations proposed by Kogelnik, and derived general solution applicable to the system with both phase and amplitude gratings with arbitrary phase relationship. We showed that the analysis based on the equation can give a direct evidence of the phase shift between the phase and amplitude gratings if it exists. This method was applied to the fringe pattern inscribed in thick films of PMMA doped with an azo-carbazole dye, showing that observed signals indicated the phase deviation between two types of gratings.
In this study, we present an analysis of optical frequency signal transmission through the whispering gallery mode
(WGM) generated in a silica microsphere for the application of optical frequency signal transmission to integrated
circuits. The behavior of the WGM within a microsphere was analyzed in detail using the finite-difference time-domain
method. The electric field distribution in the silica microsphere led to the WGM, and the electric field was amplified
within the microsphere. The interval between the peaks of the WGM (free spectral range of the microcavity) was clearly
observed in the wavelength spectrum. When two light beams having slightly different wavelengths were guided into the
microsphere, a beat frequency corresponding to the difference frequency of the two light beams was also obtained in the
simulation. The simulation results were experimentally confirmed by observing the WGM and the beat signal generated
in a silica microsphere. From these results, we have theoretically and experimentally clarified the feasibility of optical
frequency signal transmission through the WGM.