Three-dimensional woodpile photonic crystals with a variety of crystal orientations and surfaces, including (110), (001),
(100) and (010) planes, are fabricated in GaAs and silicon with the multi-directional etching method. The optical
properties of the fabricated woodpile photonic crystals are characterized via reflectance spectra measurement. High
reflectivity is observed in 1200 nm to 1550 nm wavelength, exhibiting a photonic bandgap. The ultra-high-Q
microcavities designed by unit cells size modulation consist of straight dielectric rods only; therefore, they could be
fabricated by the directional etching methods. A high quality factor is expected in the microcavity fabricated by the one-top,
one-side etching approach.
Transparent conductive oxide (TCO) films are proposed as electrode materials for direct current injection optical
microcavity devices. Four types of planar indium-tin-oxide (ITO) clad optical microcavities -1-D photonic crystal
nanobeam, 2-D photonic crystal slab, 3-D photonic crystal and microdisk are designed and analyzed both by perturbation
theory and 3D finite difference time domain (FDTD) analysis. The quality (Q) factors of cavities obtained by
perturbation theory in which imaginary part of the dielectric constant of ITO is introduced as a perturbation agree with
those obtained from FDTD method. Microcavities analyzed in this work still preserve high Q-factor in the presence of
metal clad and would provide an excellent heat sink and efficient carrier injection for electrically-driven continuous-wave,
A complete photonic band gap inhibits light propagation in all directions regardless of the polarization. This likely
provides a means of molding light at the level of physical limits. For example, a complete PBG can be applied to
construct nanocavities with ultra-high quality (Q) factor while maintaining a small mode volume, and low-loss
waveguide. These are useful for the applications, such as thresholdless lasers, nonlinear optics and 3D optics. Only
three-dimensional (3D) photonic crystals can possess a complete band gap. However, the application of 3D photonic
crystal is restricted because of the difficulties in precisely fabricating the structures in optical wavelength. Here, we
report the fabrication of large-area woodpile photonic crystal in GaAs at 1.55 μm wavelength by two-directional etching
method without wafer bonding technique. A woodpile with 40×55×2.25 unit cells is fabricated in a two-patterning
process, in which high-resolution electron beam lithography (EBL) defines 2D patterns, and then chemically assisted ion
beam etching (CAIBE) provides high-aspect-ratio, anisotropic and deep GaAs etching at an angle of 45 degree relative
to the wafer surface. The two-directional etching is a simple method to fabricate high-precision woodpile photonic
crystals. The only alignment required in this process is performed by EBL overlay, which has a resolution of less than 30
nm. With our designs of ultra-high-Q nanocavities by unit cell size modulation, we can construct woodpile nanocavities
with active materials, such as epitaxially-grown quantum well (QW) and quantum dot (QD) layers, using the same
fabrication method without wafer bonding process.
The Cu-based interconnect is a major bottleneck for sustaining technological advances in semiconductor integrated
circuits. Matured optics technology may be able to resolve this challenge. Optics can provide high-speed, wavelengthdivision-
multiplexing signals with the capability of interfacing optics with electronics through EO and OE conversion-
directly-modulated laser, external modulator, and photodiode. An optical waveguide is a major building block for optical
interconnects technology. A three-dimensional photonic crystal may provide single-mode, low-loss, group-velocitydispersionless,
and compact waveguides. We report designs of double-heterojunction optical waveguides in a threedimensional
photonic crystal. Compact optical waveguide modes are induced by modulating unit cells onedimensionally
or two-dimensionally. One way to do this is to modulate the unit cell size. A well-type waveguide
structure is formed by modulating the lattice constant of woodpile in one direction. For some 1D double-heterojunction
geometries, light propagation becomes non-dispersive in the space domain, i.e. light is self-collimated along certain
directions within the well plane. Next, two-dimensional unit-cell-modulation is applied to a 3D photonic crystal for
exciting wire-type waveguide modes, for which light propagates along the horizontal or vertical wire. As a result, light
may be guided in the same level or into different levels. The propagation properties, such as group velocity, and
waveguide group velocity dispersion, are also analyzed in this work.
We have investigated the miniaturization of photonic devices for ultimate photon localization, and have demonstrated two-dimensional photonic crystal nanolasers with two important quantum nanostructures-quantum wells (QWs) and quantum dots (QDs). Photonic crystal cavities with QW active material, are simple, but powerful nanolasers to produce intense laser output for signal processing. On the other hand, when located in a high-quality factor (Q) nanocavity, because QD(s) strongly couple with the intense optical field, QD photonic crystal cavities are expected to be good experimental setups to study cavity quantum electrodynamics, in addition to high speed and compact laser sources. Our photonic crystal nanolasers have shown as small thresholds as 0.12mW and 0.22mW for QD-photonic crystal lasers and QW-photonic crystal lasers, respectively, by proper cavity designs and nanofabrication. For QD-photonic crystal lasers, whispering gallery modes in square lattice were used together with coupled cavity designs and, for QW-photonic crystal lasers, quadrapole modes in triangular lattice with fractional edge dislocations were used to produce high-<i>Q</i> modes with small mode volume.
Quantum dot photonic crystal lasers are demonstrated at room temperature by optical pulse pumping. Coupled cavities were designed based on square lattice PC slabs. Optimized two-dimensional photonic crystal cavities were defined in 200nm slabs with five-stacked InAS QDs layers. The two- and four-coupled cavities showed as incident pump power threshold as 120μW and 370μW, respectively, both from QD ground state emission range. Both clear threshold in pump power-output resonance power and resonance line width narrowing were observed from our membrane samples. The measured wavelengths matched very well with wavelengths predicted by 3D-Finite Difference Time Domain modelling.
We have fabricated planar photonic crystal nanocavity lasers, based on our new high-quality factor design that incorporates fractional edge dislocations in triangular lattice photonic crystal cavities. Lasers with InGaAsP quantum well active material emitting at 1550nm were optically pumped with 10ns pulses, and lase at room temperature at threshold pumping powers below 220 microWatt. We have attributed this to the small mode volume and the high Q factors inherent to our device design. We have performed detailed numerical analysis of our structures, and have found an excellent agreement between theoretical predictions and experimental results. The optical field of the lasing mode in our nano-laser is localized in the air-hole region and therefore the laser can be used to investigate interaction between light and matter introduced in the cavity and nanospectroscopy.
Planar photonic crystals are constructed by combining two-dimensional periodic structures with high refractive index contrast slabs. By suppressing the loss in these structures due to imperfect confinement in the third dimension, one can fully take advantage of their relatively simple fabrication, and achieve the functionality of three-dimensional photonic crystals. One of the greatest challenges in photonic crystal research is a construction of optical nanocavities with small mode volumes and large quality factors, for efficient localization of light. Beside standard applications of these structures (such as lasers or filters), they can potentially be used for cavity QED experiments, or as building blocks for quantum networks. This paper will address our theoretical and experimental results on optical nanocavities based on planar photonic crystals, with mode volumes as small as one half of cubic wavelength of light in material, and with Q factors even larger than 1x10<SUP>4</SUP>.