Masayuki Fujita

Inhibiting spontaneous light emission and redistributing the energy into useful forms are desirable objectives for advances in various fields, including photonics, illuminations, displays, solar cells, and even quantum-information systems. We demonstrate both the "inhibition" and "redistribution" of spontaneous light emission by using two-dimensional (2D) photonic crystals, in which the refractive index is changed two-dimensionally. The overall spontaneous emission rate is found to be reduced by

Abstract We have been developing a system for detecting seafloor crustal movement by combining kinematic GPS and acoustic ranging techniques. A linear inversion method is adopted to determine the position of seafloor stations from coordinates of a moving survey vessel and measured travel times of acoustic waves in seawater. The positioning accuracy is substantially improved by estimating the temporal variation of the acoustic velocity structure. We apply our method to the ranging data acquired a

We have calculated lasing characteristics of current injection microdisk lasers of several microns in diameter, taking account of the scattering loss at center posts and the carrier diffusion effect. We found that the optimum width of the disk wing exposed to the air is 0.6-0.7 /spl mu/m and the minimum threshold current is nearly 10 /spl mu/A for the disk diameter of 2 /spl mu/m. The internal differential quantum efficiency can be 95% if the transparent carrier density is reduced to 7.5/spl tim

A threshold current of 40 µA, nearly 1/4 of the previous lowest record, has been obtained in a GaInAsP-InP microdisk injection laser. This decrease was thought to be mainly due to the reduction of disk diameter and symmetric post-claddings by Cl2/Xe inductively coupled plasma etching.

Abstract The terahertz frequency range locates between 0.1 and 10 THz. This range accommodates atmospheric windows with staggering absolute bandwidth. It holds a potential for point‐to‐point wireless communications with an aggregate capacity reaching terabit per second in a range up to a kilometer. This unique capability is envisaged for backhauls between base stations and for local area networks. To this end, efficiency and compactness of the transceivers are crucial for successful large‐scale

A microlaser, microgear, composed of a microdisk and a rotationally symmetric Bragg grating is described. A GaInAsP–InP device with μm radius was fabricated and the room-temperature continuous-wave operation was obtained by photopumping with a low threshold of 17 μW. The experiment clearly demonstrated that the Q factor in a microdisk was enhanced by the microgear due to the minimization of the radiation field. Resonant spectra showed some unique mode characteristics influenced by an elliptical

Efficient light extraction is a critical issue for improving the overall efficiency of organic light-emitting diodes (OLEDs). Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) layers, which are expected to enable versatile control of photons. We fabricate two-dimensional PC structures in organic and electrode layers, in which most light is confined, to extract the light in the waveguide mode. Improvements in OLED efficiency of 20 and 130% are observed in s

A reduction of the operating voltage is achieved for an organic light-emitting diode containing a corrugated photonic crystal structure fabricated by the etching of an indium-tin-oxide anode layer. This is due to a partial reduction in the thickness of the organic layer. The light extraction efficiency can be also improved due to the diffraction of confined light by the photonic crystal effect. The voltage reduction is demonstrated in combination with an improvement in the luminance efficiency a

The possible three-pulse echoes in two-level systems of solids and gases are discussed with particular emphasis on backward-wave echoes. One example of the backward echoes was realized with the atomic sodium $D$ line. The detection of this echo requires neither optical shutters nor magnetic field. The decay rate of the echo due to Na-Ar collisions was measured. It is shown that the effect of velocity changing collisions is negligible compared with that of phase interrupting ones.

We have introduced a photonic crystal into a single-crystal silicon slab in order to manipulate the light emission. When the lattice constant of a defect-free photonic crystal matches the wavelength of light in the medium, the light emitted from the silicon is resonantly extracted at the photonic band edge within the escape light cone. When the lattice constant is larger than the wavelength, Brillouin zone folding of the photonic band also allows the light to be extracted; we achieved an intensi

Conventional photonic-crystal waveguides make use of an equilateral triangular lattice of through holes, here we develop an isosceles triangular lattice photonic-crystal waveguide based on a silicon slab at 0.3 terahertz (THz) band, for THz high-speed communications. The propagation loss of the proposed waveguide is as small as ∼1/10, compared with that of a conventional waveguide under the conditions of broadband bandwidth (>20 GHz) for both the loss and dispersion, due to the broadband low-dis

The existence of many high Q whispering gallery modes in microdisk and microcylinder lasers seriously affects the internal efficiency in lasing operation and disturbs the enhancement of the spontaneous emission factor. To suppress these modes except for one lasing mode, we propose the microgear cavity having a grating with the same period as that of the mode standing wave. A finite-difference time-domain simulation theoretically demonstrates that the microgear selects one resonant mode that sati