Double-heterostructure Cavities Research Articles

Mode selection in InGaAs/InGaAsP quantum well photonic crystal lasers based on coupled double-heterostructure cavities.

Photonic crystal lasers with a high-Q factor and small mode volume are ideal light sources for on-chip nano-photonic integration. Due to the submicron size of their active region, it is usually difficult to achieve high output power and single-mode lasing at the same time. In this work, we demonstrate well-selected single-mode lasing in a line-defect photonic crystal cavity by coupling it to the high-Q modes of a short double-heterostructure photonic crystal cavity. One of the FP-like modes of the line-defect cavity can be selected to lase by thermo-optically tuning the high-Q mode of the short cavity into resonance. Six FP-like modes are successively tuned into lasing with side mode suppression ratios all exceeding 15 dB. Furthermore, we show a continuous wavelength tunability of about 10 nm from all the selected modes. The coupled cavity system provides a remarkable platform to explore the rich laser physics through the spatial modulation of vacuum electromagnetic field at submicron scale.

A Tunable Photonic Double Heterostructure Cavity on Ferroelectric Barium Titanate

We designed a photonic double heterostructure cavity on rectangular lattice with an incorporated slot waveguide, which shows high quality factor for both TE and TM modes despite an absence of complete bandgap. The confinement capability of the cavity has been studied using the finite difference time domain method. The ferroelectric barium titanate (BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is used as the base material of the proposed cavity. The dispersive and absorptive natures of the material have been incorporated in the calculations. The presence of the slot waveguide improved the quality factor of the cavity, confirming the existing results. Despite the absorptive nature of BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , the finite extent of the photonic crystal and absence of complete bandgap, the calculated quality factor compares favorably with values reported previously in the literature.

Double-heterostructure cavities: From theory to design

We derive a frequency-domain-based approach for radiation (FAR) from double-heterostructure cavity (DHC) modes. We use this to compute the quality factors and radiation patterns of DHC modes. The semi-analytic nature of our method enables us to provide a general relationship between the radiation pattern of the cavity and its geometry. We use this to provide general designs for ultrahigh quality factor DHCs with radiation patterns that are engineered to emit vertically.

Liquid crystal dynamics in a photonic crystal cavity created by selective microfluidic infiltration

A microfluidic double heterostructure cavity is created in a silicon planar photonic crystal waveguide by selective infiltration of a liquid crystal. The spectral evolution of the cavity resonances probed by evanescent coupling reveals that the liquid crystal evaporates, even at room temperature, despite its relatively low vapor pressure of 5 × 10(-3) Pa. We explore the infiltration and evaporation dynamics of the liquid crystal within the cavity using a Fabry-Perot model that accounts for the joint effects of liquid volume reduction and cavity length variation due to liquid evaporation. While discussing how the pattern of the infiltrated liquid can be optimized to restrict evaporation, we find that the experimental behavior is consistent with basic microfluidic relations considering the small volumes of liquids and large surface areas present in our structure.

Paired modes of heterostructure cavities in photonic crystal waveguides with split band edges

We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate.

Strategies for Reducing the Out-of-Plane Radiation in Photonic Crystal Heterostructure Microcavities for Continuous Wave Laser Applications

The directional optical loss properties of photonic crystal double heterostructure cavities are analyzed using the three-dimensional finite-difference time-domain method. It is found that these high quality factor cavities are dominated by vertical radiation loss, and the addition of heat-sinking lower substrates exacerbates the vertical loss problem. An alternative heterostructure geometry based on introducing a glide-plane is proposed and is shown to significantly reduce out-of-plane radiation. This new geometry is a promising candidate for building chip-scale edge-emitting photonic crystal lasers operating under continuous wave conditions. Alternative vertical slab structures are investigated, and the plausibility of forming electrically injected photonic crystal lasers is discussed.

Controlled coupling of a single-diamond nanocrystal to a photonic crystal cavity

We demonstrate the controlled coupling of a single diamond nanocrystal to a planar photonic crystal double-heterostructure cavity. A dip-pen deposition method and subsequent manipulation with an atomic force microscope was used to precisely position the nanocrystal on top of the cavity. The optical properties of this combined system are investigated with regard to changes in the quality factor and resonance wavelength of the cavity mode as a function of the size and relative position of the diamond nanocrystal. These studies represent an important step toward well-controlled cavity-QED experiments with single-defect centers in diamond.

Room temperature spontaneous emission enhancement from quantum dots in photonic crystal slab cavities in the telecommunications C band

We report on the control of the spontaneous emission dynamics from InAsP self-assembled quantum dots emitting in the telecommunications C band and weakly coupled to the mode of a double heterostructure cavity etched on a suspended InP membrane at room temperature. The quality factor of the cavity mode is 44×103 with an ultralow modal volume of the order of 1.2(λ/n)3, inducing an enhancement in the spontaneous emission rate of up a factor of 2.8 at 300 K.

Direct extraction of large quality factors and resonant frequencies from Padé interpolated resonance spectra

Extracting the quality factor and resonant frequency of photonic crystal resonators simulated using the finite-difference time-domain algorithm is investigated. The Pade interpolation method is applied to the resonance spectra, and closed form expressions for the quality factor and center frequency in terms of the coefficients in the Pade function are presented. The method is applied to simulations of the photonic crystal double heterostructure cavity.

High-Q microfluidic cavities in silicon-based two-dimensional photonic crystal structures

We demonstrate postprocessed microfluidic double-heterostructure cavities in silicon-based photonic crystal slab waveguides. The cavity structure is realized by selective fluid infiltration of air holes using a glass microtip, resulting in a local change of the average refractive index of the photonic crystal. The microcavities are probed by evanescent coupling from a silica nanowire. An intrinsic quality factor of 57,000 has been derived from our measurements, representing what we believe to be the largest value observed in microfluidic photonic crystal cavities to date.

Reconfigurable microfluidic photonic crystal slab cavities

We demonstrate the spectral and spatial reconfigurability of photonic crystal double-heterostructure cavities in silicon by microfluidic infiltration of selected air holes. The lengths of the microfluidic cavities are changed by adjusting the region of infiltrated holes in steps of several microns. We systematically investigate the spectral signature of these cavities, showing high Q-factor resonances for a broad range of cavity lengths. The fluid can be removed by immersing the device in toluene, offering complete reconfigurability. Our cavity writing technique allows for tolerances in the infiltration process and provides flexibility as it can be employed at any time after photonic crystal fabrication.

Emission properties of high-Q silicon nitride photonic crystal heterostructure cavities

We report on the fabrication and optical characterization of photonic crystal (PC) double-heterostructure cavities made from silicon nitride (SiN). The intrinsic luminescence of the SiN membranes was used as an internal light source in the visible wavelength range (600–700nm) to study the quality factor and polarization properties of the cavity modes. Quality factors of up to 3400 were found experimentally, which represents the highest value reported so far in low-index PCs. These results highlight the role of SiN as a promising material system for PC devices in the visible.

Microfluidic photonic crystal double heterostructures

We demonstrate postprocessed and reconfigurable photonic crystal double-heterostructure cavities via selective fluid infiltration. We experimentally investigate the microfluidic cavities via evanescent probing from a tapered fiber at telecommunication wavelengths. Fabry-Pérot fringes associated with modes of the induced cavity are in good agreement with the theory. We also demonstrate a cavity with quality factor Q=4300. Our defect-writing technique does not require nanometer-scale alterations in lattice geometry and may be undertaken at any time after photonic crystal waveguide fabrication.

Design of high-Q Cavities in Photosensitive Material-based Photonic Crystal Slab Heterostructures

We propose a novel concept for creating high-Q cavities in photonic crystal slabs (PCS). We show that photonic crystal slab-based double heterostructure cavities, formed by variations in the refractive index, can have large a Q-factor (up to Q = 1 £ 10 6 ), and that such cavities can be implemented in chalcogenide glasses using their photosensitive properties. In the last few years the study of optical microcavities based on photonic crystal slabs has attracted much attention (1{10). Almost all of these studies consider a PCS composed of a hexagonal array of cylindrical air holes in a high-index semiconductor slab. There are many possible device applications of compact and e-cient PCS nanocavities, such as channel drop fllters (1), low-treshold laser (5), and cavity QED experiments (6,7). The principal design aim for all these applications is to obtain a high quality factor within a small modal volume. A cavity is usually formed in either of two ways: forming a point cavity or forming a \hetero- Microcavities with the highest Q values achieved to date, have been realised through the use of photonic crystal double-heterostructures (9,10), where regions of slightly difierent lattice constant are combined in a single slab to create a cavity. Song etal., constructed double hetero- structure PCS, in which a short length of crystal (PC2) with a lattice constant stretched in one direction, interrupts the main crystal (PC1) (9,10) (see Fig. 1 ). (a) (b) Figure 1: (a) Schematic of PCS with a W1 waveguide in the i-K direction and (b) refractive index distri- bution in the plane of the structure considered. The central darker region indicates the increased index. It is possible to form heterostructures exploiting material properties, rather than the geometry of the structure. In this paper we consider a chalcogenide glass-based PCS. It has been already shown that high quality PCS can be fabricated in this material (11). The key property here is that chalcogenide glasses are photosensitive. This means that the refractive index of the material can change by 1 to 8%, depending on the type of glass, when it is illuminated by light, typically in the visible part of the spectrum (12). The concept of the cavity design in hetero-structures relies on the mode-gap efiect, a narrow frequency range for which PC2 supports a mode, but not PC1. Therefore, flrst we determine if there is a su-cient mode-gap to support a localized state between the structures having difierent refractive indices. We introduce a W1 waveguide in these structures: W11 for PC1 with n = 2:7, and W12 for PC2 with n = 2:75. Using the Plane Wave Expansion method, we obtain the dispersion curves. The results are shown in Fig. 2(a). The size of the mode-gap is comparable to those of the hetero-structures formed by geometric variation (10). This suggests that hetero-structures formed by photosensitive index enhancement should also be capable of supporting localized states.

InGaAsP(1.3 μm)/InP vertical-cavity surface-emitting laser grown by metalorganic vapor phase epitaxy

We report InGaAsP/InP vertical-cavity surface-emitting lasers (VCSELs) with an emission wavelength near 1.3 μm grown by metalorganic vapor phase epitaxy. The VCSEL structure contains a double-heterostructure cavity, a metal mirror, and a SiO2/Si dielectric stack (three pairs) mirror with a measured reflectivity of 98%. A threshold current as low as 5 mA for 15-μm-diam devices with a 1-μm-thick active layer at 77 K was achieved, which is close to the best reported value (6 mA) within the accuracy of the pulse measurement. The highest operating temperature was 220 K.