Optical surface edge Bloch modes: low-loss subwavelength-scale two-dimensional light localization.

An optical surface edge Bloch mode is an optical state evanescently bound at an edge on a finite-size three-dimensional photonic crystal; the edge is the intersection of two termination planes on the crystal. Low-loss subwavelength-scale edge modes can appear on an <010> edge of a dielectric woodpile within a complete photonic bandgap. The mode area is as small as 0.066 squared half-in-vacuum-wavelengths. The edge mode has field maxima in vacuum near the termination surface, like surface plasmon modes. This edge mode would provide new opportunities of low-loss light localization in a sub-diffraction-limit space without the use of metal.

Design of subwavelength-size, indium tin oxide (ITO)-clad optical disk cavities with quality-factors exceeding 104.

Indium tin oxide is used as a top cladding electrode of optical disk resonators with subwavelength size in all dimensions. Calculated quality (Q)-factors exceed 104 in visible wavelengths (650-670nm). The disk aspect ratio is an important parameter to optimize the resonator properties. The Q-factor and threshold material gain based on finite-difference time-domain method are optimized for eight different disk resonator optical modes. Proposed cavity designs are promising for building electrically-pumped, low-threshold nano-lasers at room temperature.

Optical surface Bloch modes of complete photonic bandgap materials as a basis of optical sensing.

Surface Bloch modes induced on three-dimensional dielectric photonic crystals with a complete photonic bandgap are evanescently decaying states at surfaces and have large field overlap with low-index media, resulting in narrow spectrum linewidth and simultaneously a large resonance shift due to a perturbation of the refractive index in the background media. Surface Bloch resonance states are analyzed for (001), (100), and (110) woodpile surface planes. Low-loss, high-sensitivity surface Bloch modes are also analyzed on a flat-top (001) woodpile planar surface. These analyzed surface Bloch modes are confined in a subwavelength scale and are expected to form a basis set used for optical resonance sensing.

Optical microcavity: sensing down to single molecules and atoms.

This review article discusses fundamentals of dielectric, low-loss, optical micro-resonator sensing, including figures of merit and a variety of microcavity designs, and future perspectives in microcavity-based optical sensing. Resonance frequency and quality (Q) factor are altered as a means of detecting a small system perturbation, resulting in realization of optical sensing of a small amount of sample materials, down to even single molecules. Sensitivity, Q factor, minimum detectable index change, noises (in sensor system components and microcavity system including environments), microcavity size, and mode volume are essential parameters to be considered for optical sensing applications. Whispering gallery mode, photonic crystal, and slot-type microcavities typically provide compact, high-quality optical resonance modes for optical sensing applications. Surface Bloch modes induced on photonic crystals are shown to be a promising candidate thanks to large field overlap with a sample and ultra-high-Q resonances. Quantum optics effects based on microcavity quantum electrodynamics (QED) would provide novel single-photo-level detection of even single atoms and molecules via detection of doublet vacuum Rabi splitting peaks in strong coupling.

High-Q hybrid 3D-2D slab-3D photonic crystal microcavity.

The radiation loss in the escaping light cone with a two-dimensional (2D) photonic crystal slab microcavity can be suppressed by means of cladding the low-Q slab microcavity by three-dimensional woodpile photonic crystals with the complete bandgap when the resonance frequency is located inside the complete bandgap. It is confirmed that the hybrid microcavity based on a low-Q, single-defect photonic crystal slab microcavity shows improvement of the Q factor without affecting the mode volume and modal frequency. Whereas 2D slab microcavities exhibit Q saturation with an increase in the number of layers, for the analyzed hybrid microcavities with a small gap between the slab and woodpiles, the Q factor does not saturate.

On-chip waveguide isolator based on bismuth iron garnet operating via nonreciprocal single-mode cutoff.

We analyze an on-chip optical isolator based on direction dependent single-mode cutoff, which is described in 1D and 2D momentum space. Isolation is shown using 3D finite difference time domain (FDTD) where the magnetization is represented by imaginary off-diagonal permittivity tensor elements. The isolator designs are optimized using perturbation theory, which successfully predicts increased isolation for rib waveguides and structures with non-magnetic dielectric layers. Our isolators are based on bismuth iron garnet and its compatible substrates; an isolation ratio of 10.7 dB/mm is achieved for TM modes.

Monopole woodpile photonic crystal modes for light-matter interaction and optical trapping.

Two types of ultra-high-Q monopole modes are designed in a woodpile three-dimensional photonic crystal. The unit cell size modulation is applied to a woodpile photonic crystal waveguide in a complete photonic band gap. A monopole mode overlapping with a dielectric rod is designed for solid-state sub-wavelength-scale light-matter interaction devices such as nanolasers, cavity-QED and optical switches, whereas another type of monopole mode overlapping with vacuum is designed for optical trapping experiments. For the mode overlapping with vacuum, the mode volume is as small as 0.4 cubic half-wavelengths.

Single-mode waveguide optical isolator based on direction-dependent cutoff frequency.

A single-mode-waveguide optical isolator based on propagation direction dependent cut-off frequency is proposed. The isolation bandwidth is the difference between the cut-off frequencies of the lowest forward and backward propagating modes. Perturbation theory is used for analyzing the correlation between the material distribution and the bandwidth. The mode profile determines an appropriate distribution of non-reciprocal materials.

Ultra-high-Q three-dimensional photonic crystal nano-resonators.

Two nano-resonator modes are designed in a woodpile three-dimensional photonic crystal by the modulation of unit cell size along a low-loss optical waveguide. One is a dipole mode with 2.88 cubic half-wavelengths mode volume. The other is a quadrupole mode with 8.3 cubic half-wavelengths mode volume. Light is three-dimensionally confined by a complete photonic band gap so that, in the analyzed range, the quality factor exponentially increases as the increase in the number of unit cells used for confinement of light.