Seita Iwahashi

Higher-order vector beams produced by photonic-crystal lasers

We have successfully generated vector beams with higher-order polarization states using photonic-crystal lasers. We have analyzed and designed lattice structures that provide cavity modes with different symmetries. Fabricated devices based on these lattice structures produced doughnut-shaped vector beams, with symmetries corresponding to the cavity modes. Our study enables the systematic analysis of vector beams, which we expect will lead to applications such as high-resolution microscopy, laser processing, and optical trapping.

Three-dimensional coupled-wave model for square-lattice photonic crystal lasers with transverse electric polarization: A general approach

A general coupled-wave model is presented for square-lattice photonic crystal (PC) lasers with transverse-electric polarization. This model presents a realistic treatment of the full three-dimensional structure of typical laser devices by incorporating the surface emission and high-order coupling effects. Numerical examples based on our model are presented for various PC structures with different air-hole shapes. The accuracy of the results is verified using three-dimensional finite-difference time-domain simulations. Using this model, we demonstrate that the PC lattice with asymmetric air holes can give rise to a high-output power, efficient device.

Three-dimensional coupled-wave analysis for square-lattice photonic crystal surface emitting lasers with transverse-electric polarization: finite-size effects

We develop a coupled-wave model that is capable of treating finite-size square-lattice photonic crystal surface emitting lasers with transverse-electric polarization. Various properties of interest including threshold gain, mode frequency, field intensity envelope within the device, far-field pattern, as well as polarization and divergence angle of the output beam for the band-edge modes are calculated. Theoretical predictions of the lowest threshold mode and the output beam profile are in good agreement with our experimental findings. In particular, we show that, contrary to the infinite periodic case, the finite length of the device significantly affects surface emission and mode selection properties of the laser device.

Three-dimensional coupled-wave analysis for triangular-lattice photonic-crystal surface-emitting lasers with transverse-electric polarization

Three-dimensional coupled-wave theory is extended to model triangular-lattice photonic-crystal surface-emitting lasers with transverse-electric polarization. A generalized coupled-wave equation is derived to describe the sixfold symmetry of the eigenmodes in a triangular lattice. The extended theory includes the effects of both surface radiation and in-plane losses in a finite-size laser structure. Modal properties of interest including the band structure, radiation constant, threshold gain, field intensity profile, and far-field pattern (FFP) are calculated. The calculated band structure and FFP, as well as the predicted lasing mode, agree well with experimental observations. The effect of air-hole size on mode selection is also studied and confirmed by experiment.

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.

Air-hole design in a vertical direction for high-power two-dimensional photonic-crystal surface-emitting lasers

We investigate the air-hole shape of photonic-crystal lasers in the vertical direction to increase the radiation constant for the surface emission. Numerical analysis indicates a maximum radiation constant when the air-hole depth is half the wavelength and a minimum when it is about the same as the wavelength, due to the interference of light waves diffracted in the vertical direction. We propose an air-hole design using two photonic-crystal layers offset by a half-period; the design more than doubles the radiation constant over that of a conventional design, leading to higher-power operation.

Comprehensive investigation of composite photonic-crystal cavities emitting arbitrary-angled laser beams

We perform comprehensive investigations of various composite photonic crystal cavities, which produce a laser emission in arbitrary directions. We then demonstrate a maximum beam angle of 45 degrees with low-lasing threshold values.

Three-dimensional coupled-wave theory for triangular-lattice photonic-crystal lasers

We develop a three-dimensional coupled-wave theory to model triangular-lattice photonic-crystal surface-emitting lasers. Unlike previous theories, our presented theory is able to treat non-Γ-point modes. We compare our theoretical results with experiments and find good agreement.

Two-dimensional photonic-crystal lasers with centered-rectangular lattice structure

We propose and investigate two-dimensional photonic-crystal lasers with a centered-rectangular lattice, which spans the lattice structure between the conventional square and triangular lattices.