Eiji Miyai

Lasing band-edge identification for a surface-emitting photonic crystal laser

The possibility of single-mode oscillation over a large cavity area for photonic crystal lasers emitting at the photonic band edge has resulted in much interest in such materials for new forms of solid-state laser. In this paper, we measure the photonic bandstructure in our sample and identify the lasing band edge. By mapping out the bandstructure at the /spl Gamma/-point, we have observed fine structure at the band edge. The experimental results are in good agreement with the theoretically predicted bandstructure. Above threshold, we observe a lasing peak at 965 nm at one of the band edges. The far-field distribution of the laser is measured, showing an annular profile and azimuthal polarization. Calculations on the far-field distribution at the lasing band edge suggest the annular profile is due to an anti-symmetric resonant mode.

Two-dimensional coupled wave theory for square-lattice photonic-crystal lasers with TM-polarization

We present a useful framework based on the coupled-wave theory, through which we can survey the resonant modes of TM polarization in 2D photonic-crystal lasers and understand their properties in detail. Through numerical calculations, we clarify their threshold gains, deviations from the Bragg frequency and field distributions. We find that the lasing mode can be selected by manipulating the hole-filling factor or the boundary reflection.

Coupled-Wave Theory for Square-Lattice Photonic Crystal Lasers With TE Polarization

We present a coupled-wave analysis for square-lattice photonic crystal lasers with transverse electric polarization. A model consisting of eight plane waves coupled by Bragg diffraction is used to describe two-dimensional optical coupling. The resonant frequencies and threshold criteria for the modes of oscillation have been determined for the case of index periodicity with a lattice of circular holes. The spatial intensity distributions of these resonant modes have also been calculated. For the fundamental modes, we have investigated how the intensity distribution varies as a function of coupling strength. The dependence of the threshold gain of these modes on hole size has also been elucidated. This semianalytical approach provides a comprehensive understanding of square-lattice photonic crystal lasers and allows more effective optimization of their cavity design.

Coupled-wave model for square-lattice two-dimensional photonic crystal with transverse-electric-like mode

We propose a coupled-wave model for a square-lattice two-dimensional (2D) photonic crystal (PC) with a transverse electric mode. A set of coupled-wave equations is obtained from this model and it is shown that 2D optical coupling occurs between four light waves propagating in the Γ-X direction via higher-order waves propagating in the Γ-M direction. The expressions for the resonant mode frequencies derived from the coupled-wave equations describe the characteristics of experimental results for the band-edge frequencies of the 2D PC laser.

Analysis of coupling between two-dimensional photonic crystal waveguide and external waveguide

Coupling between conventional wire waveguide and two-dimensional photonic crystal waveguide was analyzed by means of a three-dimensional finite difference time domain method. We evaluated the transmittance corresponding to the coupling efficiency between two waveguides. By using SiO2 clad below the wire and setting the width of the wire to be an appropriate value, we obtained single mode guiding and a coupling efficiency over 80% for the wave length around 1.55 μm.

Structural dependence of coupling between a two-dimensional photonic crystal waveguide and a wire waveguide

The coupling dependence between a wire waveguide and a two-dimensional photonic crystal waveguide on a shared connection structure was analyzed theoretically. By calculating the transmittance at the connecting point for various sample geometries, we found the structure to have high coupling efficiency and fabrication tolerance. The maximum transmittance can be as high as 95% for a wavelength near 1.55 μm within our investigation when the structure of the connecting point is well designed.

Controlling vertical optical confinement in two-dimensional surface-emitting photonic-crystal lasers by shape of air holes

We use the finite-difference time domain method to calculate the vertical optical confinement, which corresponds to the quality factor in the vertical direction, of two-dimensional photonic-crystal (PC) lasers as a function of the asymmetry of the shape of the air holes that form the PC. The vertical optical confinement for triangular air holes, which give the highest output power measured thus far, is decreased by two thirds when V-shaped air holes are used. In contrast, the vertical optical confinement becomes infinite for rhomboid air holes. The vertical optical confinement decreases when the air holes are deformed such that areas of opposing electric fields exist in regions of the PC with different dielectric constants. In this way, the vertical optical confinement can be controlled by changing the shape of the air holes.

Phase-shift effect on a two-dimensional surface-emitting photonic-crystal laser

Theoretical analysis was performed by means of the finite-difference time-domain method to examine the mode properties of two-dimensional surface-emitting photonic-crystal lasers with elliptical air holes. It was found that a single-lobed beam pattern could be obtained from the device surface by introducing a phase shift to the center of the crystal. The effects of the shift on the polarization mode and on two-dimensional optical coupling (which is needed for single-mode lasing over a large area) were also investigated. It was shown that the phase shift emphasized the linear polarization of the emitted beam due to symmetry reversal. On the other hand, it was also found that the shift did not spoil the two-dimensional optical coupling.

High-power single-lobed surface-emitting photonic-crystal laser

High-power (46 mW), single-lobed, surface-emitting operation is successfully achieved in a 2D photonic-crystal laser by optimizing the structure of the lattice points, under room temperature, continuous-wave conditions.

Band structure observation of 2D photonic crystal with various V-shaped air-hole arrangements

The band structure of three types of photonic crystals is studied. In these photonic crystals, the rotationally asymmetric V-shaped air holes are combined while changing their orientation. We find that the band structure is very sensitive to the method of combination. From this result, we can say that the periodical perturbation produced only by change of the air-hole orientation can change the band structure largely. This idea can be applied to many apprications such as lasers which have unique beam patterns.