Single-defect Cavity Research Articles

Propertities of Modes of Compound Cavity in Quasicrystal Under Low Index-Contrast

Comparing with periodic photonic crystal structures, quasicrystals have more interesting and complex defect modes, so that they are expected to be applied in novel defect-based photoelectronic devices. Modes of compound cavity in octagonal and dodecahedral quasicrystal investigated under the low index contrast. The results show that in the quasicrystal structure with double and several nine-air-hole-missing microcavities, it is observed not only the mode splitting, but also a new mode generation supported by a compound resonator, which covers two microcavities and the scatterers between. The field distribution of the new mode is studied. It is found that the field intensity and transmission of the new mode are much stronger than those of the modes in single defect cavity. These results will lay a theoretical foundation for the research of photonic crystal laser arrays and sensors.

Large mode-volume, large beta, photonic crystal laser resonator

We propose an optical resonator formed from the coupling of 13, L2 defects in a triangular-lattice photonic crystal slab. Using a tight-binding formalism, we optimized the coupled-defect cavity design to obtain a resonator with predicted single-mode operation, a mode volume five times that of an L2-cavity mode and a beta factor of 0.39. The results are confirmed using finite-difference time domain simulations. This resonator is very promising for use as a single mode photonic crystal vertical-cavity surface-emitting laser with high saturation output power compared to a laser consisting of one of the single-defect cavities.

Square lattice photonic crystal point-shifted nanocavity with lowest-order whispering-gallery mode

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 approximately 14,000) in point-shifted nanocavity can be with smaller mode volume (approximately 5.5(lambda/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 microW 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.

Design of high polarization and single-mode photonic crystal laser

The dipole mode in triangular photonic crystal single defect cavity is degenerate. By deforming the lattice in photonic crystal we can obtain non-degenerate dipole modes. Lattice deforming in the whole photonic crystal destroys the characteristic of symmetry, so the distribution of the electromagnetic field is affected and the polarization of the electromagnetic field is also changed. Lattice deforming divides the degenerate dipole mode into the x-dipole mode and the y-dipole mode. It is found that the non-degenerate modes have better properties of polarization. So the high polarization and single dipole mode photonic crystal laser can be achieved by deforming the lattice of photonic crystal. In this paper, we simulated the cavity in photonic crystal slab and mainly calculated the quality factor of x-dipole mode under different deforming conditions and with different filling factors. The properties of polarization of x-dipole and y-dipole modes are also calculated. It is found that the ratio of intensities of Ex to Ey in x-dipole mode and that of Ey to Ex in y-dipole mode are 44 and 27, respectively.

Photonic crystal defect mode cavity modelling: a phenomenological dimensional reduction approach

A phenomenological dimensional reduction approach (PDRA) for the cavity characteristics in defect mode based photonic crystal (PC) lasers is presented. Based on the fully vectorial three-dimensional finite-difference time-domain (3D FDTD) technique, simultaneous enhancement and suppression in spontaneous emission and absorption were obtained in an absorptive photonic crystal slab (PCS) cavity. Effective index perturbation (EIP) was proposed for fast and accurate determination of the effective index and the dominant resonant cavity frequency in a 3D PCS structure, with two-dimensional (2D) FDTD simulation. Further dimensional reduction from 2D to one-dimensional planar cavity enables phenomenological modelling of lasing characteristics via the effective reflectivity calculation and rate equation analysis. Very fast and accurate results have been achieved with this PDRA approach. A high spontaneous emission factor and cavity quality factor Q were obtained in a single defect cavity, which led to over an order reduction in lasing gain threshold. The model offers a fast and accurate tool for the design and modelling of PC defect mode cavity based devices and aids the research in the proposed novel defect mode based devices such as ultra-compact light sources on Si and spectrally resolved PC infrared photodetectors.

Photonic band gaps in nanowire superlattices

This paper examines how a complete photonic band gap in a semiconductor nanowire superlattice can be achieved. By choosing the nanowire superlattice periodicity and its radius, a photonic band gap can be localized below the single optical mode cut-off frequency of the nanowire waveguide. We show that Bragg mirrors with near-unity reflectivity as well as high quality factor single defect cavities can be designed in a nanowire even by using dielectric stack materials with a low index contrast.

Controlling the Spontaneous Emission Rate of Single Quantum Dots in a Two-Dimensional Photonic Crystal

We observe large spontaneous emission rate modification of individual InAs quantum dots (QDs) in a 2D photonic crystal with a modified, high-Q single-defect cavity. Compared to QDs in a bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase of up to a factor of 8. In contrast, off-resonant QDs indicate up to fivefold rate quenching as the local density of optical states is diminished in the photonic crystal. In both cases, we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with a pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using finite difference time domain simulations and find good agreement with experiment.

Coupled optical and electronic simulations of electrically pumped photonic-crystal-based light-emitting diodes

We use coupled optical and electronic simulations to investigate design trade-offs in electrically pumped photonic-crystal-based light-emitting diodes. A finite-difference frequency-domain electromagnetic solver is used to calculate the spontaneous emission enhancement factor and the extraction efficiency as a function of frequency and of position of the emitting source. The calculated enhancement factor is fed into an electronic simulator, which solves the coupled continuity equations for electrons and holes and Poisson’s equation. We simulate a two-dimensional structure consisting of a photonic-crystal slab with a single-defect cavity and investigate different electrical pumping geometries for such a cavity.

Enhancement of spontaneous emission from the resonant modes of a photonic crystal slab single-defect cavity.

Modification of the spontaneous-emission lifetime in photonic crystal single-defect resonant modes is studied with the finite-difference time domain method. We investigate spontaneous-emission enhancement from the monopole and the dipole modes of a hexagonal lattice cavity, considering the effects of the finite emitter linewidth and spectral detuning. Large spontaneous-emission enhancement of > 50 is achieved numerically from the high-quality-factor monopole mode when the emitter linewidth is comparable with the resonant-mode linewidth. However, if broad-linewidth material is used and a detuning effect is included, the dipole mode with a low quality factor and a smaller mode volume could be more advantageous for spontaneous-emission enhancement.

High-quality-factor and small-mode-volume hexapole modes in photonic-crystal-slab nanocavities

Using finite-difference time-domain calculations, we investigate the hexapole mode of photonic-crystal-slab modified triangular single-defect cavity structures as a good candidate for a high-quality factor (Q) and small-mode volume (V) resonant mode. Structural parameters are optimized to obtain very large Q of even higher than 2×106 with small effective V of the order of cubic wavelength in material, the record value of theoretical Q/V. It is found, by the Fourier-space investigation of resonant modes, that such a high Q from the hexapole mode is achieved due both to the cancellation mechanism related to hexagonally symmetric whispering-gallery-mode distribution and to the mode delocalization mechanism.

Coupling of point-defect microcavities in two-dimensional photonic-crystal slabs

We investigate the coupling of two single point-defect microcavities formed in a two-dimensional photonic-crystal slab. The mode structure is probed using photoluminescence spectroscopy of self-assembled InGaAs quantum dots embedded in GaAs/AlGaAs membrane-based, photonic-crystal microcavities. As a baseline, we start from single defect cavities: We observe defect states originating from both the ground and the first-excited slab waveguide mode, depending on the photonic-crystal lattice period. This is explained using three-dimensional, plane-wave-expansion calculations. In the case of coupling between two such single defects, a splitting of the mode energies into binding and antibinding states controlled by the coupling strength is observed. These photonic-defect–molecule states are identified by a comparison of their expected far-field distributions with polarization-dependent measurements.

The smallest possible whispering-gallery-like mode in the square lattice photonic-crystal slab single-defect cavity

The smallest possible whispering-gallery-like mode (WGM) formed in a free-standing square-lattice photonic-crystal slab single-defect cavity is studied by using the three-dimensional finite-difference time-domain method. The WGM is nondegenerate and the only existing resonant mode in the transverse electric mode bandgap of the square lattice. High-quality factors are achieved from this mode by suppressing both the in-plane and the out-of-plane optical losses. By optimizing the structural parameters, a total quality factor of 18 000 and a vertical quality factor of 40 000 are obtained from the WGM. The quality factor does not decrease significantly in the presence of a current flow path at the center of the cavity due to the null of electromagnetic energy at the cavity center, which means this mode is advantageous to achieve electrically pumped photonic-crystal lasers. In addition, by combining the high-quality factor with wavelength-size small-mode volume, very high Purcell factors >8000 are achieved, the largest value ever reported. The WGM of the square-lattice single-defect cavity is promising for both cavity quantum electrodynamics research and the low-threshold microcavity laser.

Separation of radiation and absorption losses in two-dimensional photonic crystal single defect cavities

We have characterized the optical modes present in a two-dimensional photonic crystal single defect cavity fabricated in an InP/In0.53Ga0.47As/InP double heterostructure thin film on a glass slide. The cavity resonance was tuned to different frequencies in the 1.55 μm spectral region. Radiation losses and material absorption influence the measured value of cavity quality factor Q. We separated these two loss mechanisms by performing a curve fit of the loss rate 1/Q versus the wavelength-dependent absorption coefficient of In0.53Ga0.47As. By extrapolating this curve to zero absorption, the radiation loss rate 1/Qrad is obtained.

Analysis and design of single-defect cavities in a three-dimensional photonic crystal

We theoretically investigate the properties of a single-defect cavity, which is created by adding dielectric material to a three-dimensional (3D) photonic crystal, by utilizing the plane-wave expansion method and the 3D finite-difference time-domain method. We show that the resonant frequency can be controlled well by changing the defect size, and a large frequency separation of the defect modes can be achieved by adjusting the defect shape and position appropriately. We calculate the time response of each defect mode in order to examine the dependence of the quality factor on the number of stacked stripes and on the resonant frequency. The quality factor increases exponentially with the number of stacked stripes. Furthermore, a large quality factor can be obtained with relatively small number of stacked stripes and can be kept very large over a wide frequency range. These results provide significant design rules for developing a single-mode high-Q cavity in a 3D photonic crystal.

Semiconductor three-dimensional and two-dimensional photonic crystals and devices

Semiconductor three-dimensional (3-D) and two-dimensional (2-D) photonic crystals and their effects on the control of photons are investigated for possible applications to optical chip and functional devices. First we review our approaches creating full 3-D photonic bandgap crystals at near-infrared wavelengths, and also functional devices based on 2-D photonic crystals where the focus is on surface-emitting-type channel-drop filtering devices utilizing single defects in 2-D photonic crystal slabs. Then, we describe the recent progress on 3- and 2-D crystals. On 3-D crystals, the effect of the introduction of a light emitter into the 3-D photonic crystal is investigated, and the design of a single defect cavity is performed. On the 2-D photonic crystals, the photonic states are investigated from the perspective of their polarization properties.

High quality two-dimensional photonic crystal slab cavities

We have fabricated and characterized donor-mode nanocavities formed by a single defect cavity defined within a two-dimensional photonic crystal slab. Quantum dots emitting in the 1.1–1.3 micron range were used as luminescence sources, and a design using fractional edge dislocations was used to demonstrate well-confined dipole modes with high quality factors. By applying the fractional dislocation geometry, the measured quality factor could be increased to values as high as 2800. This compares with typical quality factors of around 1500 measured from more conventional shallow donor mode cavities with larger mode volumes.