Kazuyoshi Hirose

Demonstration of a photonic crystal surface-emitting laser pumped Yb:YAG laser

We developed a cryogenically cooled Yb:YAG continuous wave oscillator directly pumped with a photonic crystal surface-emitting laser (PCSEL). A high slope efficiency of 65.7% was obtained at an output power of 208 mW. The beam quality was close to the diffraction limit, with M2<1.2 in both directions. To the best of our knowledge, this is the first PCSEL pumped solid state laser to be developed.

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.

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.

Evaluation of Laguerre-Gaussian beam generated with integrable phase-modulating surface-emitting lasers

We demonstrated direct surface-emitting of Laguerre–Gaussian beams with wavefront modulated lasers. This integrable phase-modulating surface-emitting lasers has potential to emit arbitrarily configured beam patterns without requiring any optical elements or scanning devices. The fabricated devices are on-chip-sized, making them suitable for integration. We introduce a phase-modulating resonator in a semiconductor laser, which analogically behaves as phaseonly holograms, kinoform, to allow the concurrent realization of lasing and phase modulation. Particularly, this is promising in the use for free-space optical communications due to the fact that coaxial propagation of orbital angular momentum (OAM) properties with different OAM mode states are mutually orthogonal.

Fabrication and characterization of photonic-crystal surface-emitting lasers with triangular double-hole lattice points

Recently, W-class photonic-crystal surface-emitting lasers (PCSELs) with both a single spectrum and narrow spot beam pattern are reported. These highly coherent PCSEL properties cause a highly bright laser light that is useful for various applications. To improve the PCSEL output power, it is important to enlarge the emitting area to reduce the heat generation effect. However, multi-mode oscillation occurs in a broad emitting area because the difference in the threshold gain between the fundamental and higher modes becomes narrower as the emitting area is broadened. In this work, we fabricate PCSELs with double-hole lattice points that decrease the optical confinement to prevent multi-mode oscillation. The fabricated device, consisting of an AlGaAs/InGaAs material system designed to be oscillated at a wavelength of 940nm, has an emitting area of 300 × 300 μm2. In a square lattice photonic crystal whose lattice period equals the lasing wavelength embedded in PCSELs, the distance between the centers of the double hole is set to one quarter of the lasing wavelength to decrease in-plane coupling caused by interference. We confirm that this device is oscillated at the Γ point of band edge A in the photonic band structure. The peak power is more than 5 W under pulse operation at 10 A. The device has a narrow beam divergence of less than 1° and single lobe spectrum in spite of the broad emitting area, so these double-hole lattice points are an effective structure to improve the PCSEL output power.

Demonstration of watt-class high-power photonic-crystal lasers

We demonstrate watt-class high output power (1.5 W) operation in single-chip photonic-crystal surface-emitting lasers under room-temperature continuous-wave condition. The beam quality factor M2 has been found to be kept at 1.0 up to 0.5 W.

Single mode operation of edge-emitting semiconductor lasers with 2D photonic crystal

Single transverse and longitudinal mode operation of a broad gain stripe edge-emitting laser are realized with 2D photonic crystals. Despite an emitting width of 350 μm, we obtain narrow horizontal FFP and a single spectrum.

Effects of non-lasing band in 2D photonic crystal lasers

We investigate the effects of a non-lasing band in photonic-crystal lasers. We found that the non-lasing band may scatter the laser beam despite wavenumber mismatch, which leads to the generation of weak dual-veined beam patterns.