Photonic Crystal Cavities and Waveguides

Recently, it has also become possible to microfabricate high reflectivity mirrors by creating two- and three-dimensional periodic structures. These periodic "photonic crystals" can be designed to open up frequency bands within which the propagation of electromagnetic waves is forbidden irrespective of the propagation direction in space and define photonic bandgaps. When combined with high index contrast slabs in which light can be efficiently guided, microfabricated two-dimensional photonic bandgap mirrors provide us with the geometries needed to confine and concentrate light into extremely small volumes and to obtain very high field intensities. Here we show the use of these "artificially" microfabricated crystals in functional nonlinear optical devices, such as lasers, modulators, and waveguides

Room temperature photonic crystal defect lasers at near-infrared wavelengths in InGaAsP

Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (lambda/2n)(3). Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (approximate to 500 μW absorbed)

Photonic Bandgap Defect Laser

In this work we form a microcavity laser using two-dimensional photonic crystals embedded in a half wavelength thick waveguide. Modes localized to a single defect in the photonic crystal can be theoretically shown to have mode volumes as small 2(λ/2n)^3 and near unity spontaneous emission coupling factors. The flexibility in design of the photonic crystal enables one to tailor the device for vertical emission or for coupling into an in-plane waveguide. These type of devices may be useful for high density, low threshold optical sources in compact optical systems. The added versatility in being able to etch the laser cavity may also help develop low threshold laser sources in material systems in which high index contrast epitaxial mirrors do not exist

Lithographic tuning of a two-dimensional photonic crystal laser array

One attraction of photonic crystals is the ability to control optical device characterstics by lithographically varying the geometry. In this letter we demonstrate a 10 x 10 array of optically pumped two-dimensional (2-D) photonic crystal defect lasers with varying lattice parameters. By adjusting the photonic crystal interhole spacing as well as the hole diameter we are able to tune the laser wavelength from 1500 to 1625 nm on a monolithic InP-In-GaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method

Inhibited Spontaneous Emission in Solid-State Physics and Electronics

Abstract: In this report, we present the design principles to achieve a highly sensitive optical stress sensor. The structure we use is a double-layered (DL) photonic molecule with optical bonding and anti-bonding states based on whispering-gallery mode in photonic crystal microcavity. By applying finite-difference time-domain and finite-element methods, we simulate the change of optical properties (including wavelength and quality (Q) factor) of bonding mode caused by the DL structural variation due to the applied stress in two DL geometries. In the end, we summarize an optical stress sensor design with high Q factor, large structural response due to the applied stress, and large optical spectrum change due to the DL structural variation. The minimum detectable stress variation is estimated to be as small as 0.95 nN

OCIS codes: (230.5298) Photonic crystals; (140.3945) Nanocavities; (140.5960) Semiconductor lasers

Abstract: We propose a point-shifted nanocavity based on square lattice photonic crystal, which sustains a lowest-order whispering-gallery (WG) mode. In simulation, the optimized WG mode (quality (Q) factor ~14,000) in point-shifted nanocavity can be with smaller mode volume (~5.5(λ/2n) 3 ) but larger nano-post tolerance than those in single-defect cavity design. From well-fabricated device, single WG mode lasing with measured Q factor of 4,100 and low threshold of 160 µW is obtained. Besides, we also observe the changed polarization of WG mode due to modal symmetry breaking caused by the presence of a nearby dielectric nano-particle, which would be useful in sensing molecule binding or attaching for bio-chemical applications. (C ©2010 Optical Society of Americ

Copy Number Variation and Transposable Elements Feature in Recent, Ongoing Adaptation at the Cyp6g1 Locus

The increased transcription of the Cyp6g1 gene of Drosophila melanogaster, and consequent resistance to insecticides such as DDT, is a widely cited example of adaptation mediated by cis-regulatory change. A fragment of an Accord transposable element inserted upstream of the Cyp6g1 gene is causally associated with resistance and has spread to high frequencies in populations around the world since the 1940s. Here we report the existence of a natural allelic series at this locus of D. melanogaster, involving copy number variation of Cyp6g1, and two additional transposable element insertions (a P and an HMS-Beagle). We provide evidence that this genetic variation underpins phenotypic variation, as the more derived the allele, the greater the level of DDT resistance. Tracking the spatial and temporal patterns of allele frequency changes indicates that the multiple steps of the allelic series are adaptive. Further, a DDT association study shows that the most resistant allele, Cyp6g1-[BP], is greatly enriched in the top 5% of the phenotypic distribution and accounts for ∼16% of the underlying phenotypic variation in resistance to DDT. In contrast, copy number variation for another candidate resistance gene, Cyp12d1, is not associated with resistance. Thus the Cyp6g1 locus is a major contributor to DDT resistance in field populations, and evolution at this locus features multiple adaptive steps occurring in rapid succession