Yoshitaka Kurosaka

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.

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.

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.

High-Power Surface-Emitting Photonic Crystal Laser

We report on a record CW surface-emitting output-power operation of 2D photonic-crystal lasers at RT. We also propose new cavity design for further increase of output power.

Effects of non-lasing band in two-dimensional photonic-crystal lasers clarified using omnidirectional band structure

We investigated the effects of non-lasing bands on the beam patterns in photonic-crystal lasers by evaluating the omnidirectional band structure both experimentally and theoretically. We found that a new, weak dual-streak pattern is occasionally generated around the main lobe of the output beam because of scattering of the lasing beam in the non-lasing bands despite a wavenumber mismatch. This result indicates that we can design the high-quality devices without such a noise pattern. In addition, this evaluation method is expected to be useful for developing various high-functionality PC lasers.

High power photonic-crystal surface-emitting lasers

We demonstrate the highest output power of 780 mW in single photonic crystal surface emitting lasers under continuous wave operation at room temperature. We also report the beam quality M2 = 1.1.

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.

Phase-modulating lasers toward on-chip integration

Controlling laser-beam patterns is indispensable in modern technology, where lasers are typically combined with phase-modulating elements such as diffractive optical elements or spatial light modulators. However, the combination of separate elements is not only a challenge for on-chip miniaturisation but also hinders their integration permitting the switchable control of individual modules. Here, we demonstrate the operation of phase-modulating lasers that emit arbitrarily configurable beam patterns without requiring any optical elements or scanning devices. We introduce a phase-modulating resonator in a semiconductor laser, which allows the concurrent realisation of lasing and phase modulation. The fabricated devices are on-chip-sized, making them suitable for integration. We believe this work will provide a breakthrough in various laser applications such as switchable illumination patterns for bio-medical applications, structured illuminations, and even real three-dimensional or highly realistic displays, which cannot be realised with simple combinations of conventional devices or elements.

Realization of high-power narrow beam divergence in photonic-crystal surface-emitting laser

The photonic-crystal surface-emitting laser (PCSEL) is an attractive semiconductor laser in which a thin two-dimensional photonic-crystal (2D-PC) layer is incorporated into the ordinary broad area edge-emitting laser structure to control the longitudinal-transverse mode owing to diffraction. In principle, the zero group velocity effect at the band edge of the 2D-PC is utilized as a resonator and can be used for the unique properties including large-area coherent oscillation as well as arbitrary beam controlling, which includes the polarization, beam patterns, directions, and generation of vector beams. We investigated the PCSEL toward realizing a practical device that has high power and high beam quality. Here, we show our recent progress. The device structure, which consists of an InGaAs/AlGaAs material system on n-GaAs substrates, is based on an ordinary broad area edge-emitting laser structure except it has a thin 2D-PC layer. The 2D-PC layer is placed near the active layer, and both are embedded between the p and n cladding layers. It is fabricated by using EB lithography, dry etching, and regrowth or MOCVD. The square emitting area has side of 200 micrometers, and transverse modes are well controlled in the entire region. The output power is more than 0.75 W with a single wavelength of 966 nm, and the narrow beam divergence is as narrow as 1° under continuous wave (CW) operation at room temperature. The beam quality is superior with an M2 of 1.1, which is almost the same as that of the ideal Gaussian beam.