John D. O'Brien

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 (/spl lambda//2n)/sup 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 (/spl ap/500 /spl mu/W absorbed).

Modal reflectivity in finite-depth two-dimensional photonic-crystal microcavities

We present finite-difference time-domain calculations of the Q factor for an optical microcavity defined by a slab waveguide and two-dimensional photonic-crystal end mirrors. The effect of the finite depth of the photonic crystal on the cavity s optical modes is examined. From these calculations, we can optimize the performance of the photonic-crystal mirrors and determine the loss mechanisms within optical cavities defined by these structures. The Q of the cavity modes is shown to be strongly dependent on the depth of the holes defining the photonic crystal, as well as the refractive index of the material surrounding the waveguide core.

Lithographic tuning of a two-dimensional photonic crystal laser array

One attraction of photonic crystals is the ability to control optical device characteristics by lithographically varying the geometry. In this letter, we demonstrate a 10/spl times/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-InGaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method.

Grating-assisted coupling of optical fibers and photonic crystal waveguides

We propose and analyze a highly efficient method of coupling light from optical fibers to two-dimensional photonic crystal waveguides. Efficient coupling is achieved by positioning of a tapered fiber parallel to the linear defect, where the photonic crystal’s cladding functions as a grating coupler and provides field confinement as well. Numerical simulations indicate that better than 90% transmission is possible with a full width at half-magnitude bandwidth of 12 nm. It is shown that one can increase the bandwidth by increasing the field overlap between the two waveguides.

Sapphire-bonded photonic Crystal microcavity lasers and their far-field radiation patterns

Room-temperature continuous-wave lasing was demonstrated in photonic crystal microcavities with diameters of approximately 3.2 /spl mu/m. Far-field radiation patterns of these lasers were experimentally measured and compared with numerical simulation predictions.

Tailoring of the Resonant Mode Properties of Optical Nanocavities in Two-Dimensional Photonic Crystal Slab Waveguides

Optically thin dielectric slabs, in which a fully etched-through two-dimensional patterning is applied, are used to form high-Q optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength. Resonant cavities are formed from local defect regions within the photonic lattice. Simple group theoretical techniques are developed to design cavities which support resonant modes with a particular polarization and radiation pattern. Numerical simulations using the finite-difference time-domain method are then used to study the detailed emission and loss properties of these modes. The cavities are probed spectroscopically through photoluminescence measurements, which when compared with numerical results show the presence of both donor and acceptor type modes. These experimental results show the predictive power of the modest symmetry analysis presented here in describing highly localized defect states within photonic crystals.

Reducing the out-of-plane radiation loss of photonic crystal waveguides on high-index substrates

Two-dimensional photonic crystal linear defect waveguides on semiconductor substrates are studied. It is predicted that the out-of-plane radiation loss can be reduced by shifting one side of the photonic crystal cladding by one-half period with respect to the other along the propagation direction.

Optimization of a two-dimensional photonic-crystal waveguide branch by simulated annealing and the finite-element method

The finite-element method including simulated annealing algorithm is adopted for the analysis and optimization of photonic-crystal waveguiding structures. The dispersion relations of the photonic-crystal waveguides are found by solution of an eigenvalue equation. The waveguide structures including bends and branches are analyzed by use of a scattering formulation. The symmetry of the structure is exploited to classify the modes as well as to reduce the computations. Based on the transmission spectra of a waveguide’s bends and branches, a branch is optimized by use of the simulated annealing algorithm.

Room-temperature operation of VCSEL-pumped photonic crystal lasers

Room-temperature operation of two-dimensional photonic crystal lasers optically pumped by a vertical-cavity surface-emitting laser emitting at 860 nm is reported. The photonic crystal membrane is surrounded by air on both sides and consists of four compressively strained quantum wells as the active region. The incident threshold pump power of an approximately 2.6-/spl mu/m-diameter hexagonal defect cavity laser operating at 1.6 /spl mu/m is 2.4 mW.

Finite-Difference Time Domain Method for Nonorthogonal Unit-Cell Two-Dimensional Photonic Crystals

A finite-difference time-domain (FDTD) method based on a regular Cartesian Yees lattice is developed for calculating the dispersion band diagram of a 2-D photonic crystal. Unlike methods that require auxiliary difference equations or nonorthogonal grid schemes, our method uses the standard central-difference equations and can be easily implemented in a parallel computing environment. The application of the periodic boundary condition on an angled boundary involves a split-field formulation of Maxwells equations. We show that the method can be applied for photonic crystals of both orthogonal and nonorthogonal unit cells. Complete and accurate bandgap information is obtained by using this FDTD approach. Numerical results for 2-D TE/TM modes in triangular lattice photonic crystals are in excellent agreement with the results from 2-D plane wave expansion method. For a triangular lattice photonic crystal slab, the dispersion relation is calculated by a 3-D FDTD method similarly formulated. The result agrees well with the 3-D finite-element method solution. The calculations also show that the 2-D simulation using an effective index approximation can result in considerable error for higher bands.