Aniwat Tandaechanurat

Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap

Researchers demonstrate the first laser confined in all three spatial dimensions by a three-dimensional photonic crystal. The device, in this case driven by quantum dots, represents the long-standing goal of achieving lasing in a cavity formed entirely by a complete-photonic-bandgap medium.

Demonstration of high-Q (>8600) three-dimensional photonic crystal nanocavity embedding quantum dots

The authors report on an experimental demonstration of coupling of quantum dots with a point-defect nanocavity in woodpile three-dimensional (3D) photonic crystal (PhC) with the highest quality (Q) factor among those for 3D PhC cavities. The Q factor of more than 8600 was achieved by stacking 25 layers using a micromanipulation technique. The size of the square-shaped defect cavity was optimized to tune the cavity mode to the midgap frequency of the complete photonic bandgap to achieve high Q.

Increase of Q-factor in photonic crystal H1-defect nanocavities after closing of photonic bandgap with optimal slab thickness

We investigate the dependence of quality factor Q of dipole modes in photonic crystal H1-defect nanocavity on the slab thickness and observe an increase of Q even after closing of the photonic bandgap both in numerical simulation and experimentation. This counter intuitive behavior results from the weak coupling between the cavity mode and the 2nd-guided mode in the photonic crystal slab. This is confirmed by computing the overlap between them in the momentum space.

Cavity Quantum Electrodynamics and Lasing Oscillation in Single Quantum Dot-Photonic Crystal Nanocavity Coupled Systems

Our recent advances in solid-state cavity quantum electrodynamics and lasing oscillation in single quantum dot (QD)photonic crystal (PhC) nanocavity coupled systems are discussed. These include the fabrication of high-quality 2-D PhC nanocavities (Q >; 50 000), which enabled the generation of spontaneous two-photon emission from a single QD, and the realization of lasing oscillation with single QD gain in the strong coupling regime. Moreover, we have fabricated high-quality 3-D PhC nanocavities (Q ~ 38 500), which have facilitated the realization of both lasing oscillation and the Purcell effect. Lasing oscillation in a 1-D PhC nanobeam cavity with gain produced by a few QDs has also been demonstrated.

Photonic band-edge micro lasers with quantum dot gain

We demonstrate optically pumped continuous-wave photonic band-edge microlasers on a two-dimensional photonic crystal slab. Lasing was observed at a photonic band-edge, where the group velocity was significantly small near the K point of the band structure having a triangular lattice. Lasing was achieved by using a quantum dot gain material, which resulted in a significant decrease in the laser threshold, compared with photonic band-edge lasers using quantum well gain material. Extremely low laser thresholds of approximately 80 nW at 6 K was achieved. Lasing was observed in a defect-free photonic crystal as small as approximately 7 microm square.

Design of high-Q photonic crystal microcavities with a graded square lattice for application to quantum cascade lasers

A high-Q photonic crystal (PC) microcavity for TM-like modes, which can be applied to quantum cascade lasers (QCLs), was successfully designed in an air-hole based PC slab with semiconductor cladding layers. In spite of no photonic badgaps for TM-like modes in air-hole based PC slabs, cavity Q reached up to 2,200 by utilizing a graded square lattice PC structure. This is approximately 18 times higher than those previously reported for PC defect-mode microcavities for QCLs. This large improvement is attributed to a suppression of the coupling between the cavity mode and the leaky modes thanks to the dielectric perturbation in the graded structure. We also predicted a dramatic reduction of the threshold current in the designed cavity down to one-fifteenth of that of a conventional QCL, due to a decreased optical volume.

Giant optical rotation in a three-dimensional semiconductor chiral photonic crystal.

Optical rotation is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC) at a telecommunication wavelength. We design a rotationally-stacked woodpile PhC structure, where neighboring layers are rotated by 45° and four layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. The linearly polarized light incident on the structure undergoes optical rotation during transmission. The obtained results show good agreement with numerical simulations. The measurement demonstrates the largest optical rotation angle as large as ∼ 23° at 1.3 μm wavelength for a single helical unit.

Silicon-based three-dimensional photonic crystal nanocavity laser with InAs quantum-dot gain

We report on the demonstration of lasing oscillation in a silicon-based three-dimensional photonic crystal nanocavity using InAs quantum dots as gain material by pulsed optical pumping at 11 K. An active layer embedding InAs quantum dots was inserted in the cavity using micromanipulation technique. The highest quality factor for silicon-based three-dimensional photonic crystal cavities (∼22 000) was achieved. We also evaluated the spontaneous emission coupling factor of the laser to be ∼0.78 by fitting the experimental light-in light-out curve with coupled rate equations. This result would pave the way to the realization of CMOS-compatible high-density three-dimensional photonic integrated circuits.

A three-dimensional silicon photonic crystal nanocavity with enhanced emission from embedded germanium islands

We report the realization of a silicon three-dimensional photonic crystal nanocavity containing self-assembled germanium-island emitters. The three-dimensional woodpile photonic crystal was assembled layer by layer by micromanipulation using silicon plates grown by molecular beam epitaxy. An optical nanocavity was formed in the center of the photonic crystal by introducing a point defect into one of the plates. Measurements of the filtered spontaneous emission from the Ge islands in the active plate through the localized modes of the structure directly reveal information on the evolution

Design of large-bandwidth single-mode operation waveguides in silicon three-dimensional photonic crystals using two guided modes

We report on the design of silicon three-dimensional (3D) photonic crystal (PC) waveguides with a combination of acceptor-type and donor-type line defects. Tuning the width of the acceptor-type line defect allows the waveguide to support two guided modes, which enable single-mode propagation over 98.7% of the complete photonic bandgap (cPBG). In addition, we demonstrate that the frequency ranges for single-mode propagation can be extended to the entire range of the cPBG by further tuning the thickness of the layers in which the donor-type line defects are located. The wide ranges of available frequencies for single mode propagation enable flexible design of 3D PC components and will provide a route towards future 3D photonic circuits.