Two-dimensional Photonic Crystal Membranes Research Articles

Polarization- and angle-dependent characteristics in two dimensional photonic crystal membrane reflectors

We report here measured angle- and polarization-dependent reflection properties in two-dimensional photonic crystal broadband membrane reflectors. Polarization independent reflection was obtained at surface normal direction. High reflection can also be obtained for one transverse electric (TE) polarization state over a wide range of incident angles. With the target of 1550 nm spectral band, the measured spectral bandwidths for TE polarization with reflectivity greater than 90% are 180 nm and 56 nm at surface normal and oblique incidence of 45°, respectively. The experimental spectrum approximates the theoretical spectral response of this membrane reflector.

Highly anisotropic decay rates of single quantum dots in photonic crystal membranes

We have measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes. We observe a maximum anisotropy factor of 6 between the decay rates of the two bright exciton states. This large anisotropy is attributed to the substantially different projected local density of optical states for differently oriented dipoles in the photonic crystal.

Resonant coupling of quantum dot intersublevel transitions with midinfrared photonic crystal modes

We show that quantum dot intersublevel transitions can be coupled to midinfrared photonic crystal modes. The coupling is observed under optical pumping with S-P intersublevel transitions of InGaAs self-assembled quantum dots resonant around 20 μm wavelength. An enhancement in the intersublevel absorption and a spectral tuning are evidenced when the optical modes of two-dimensional photonic crystals enter in resonance with the photoinduced intersublevel absorption. This effect is illustrated in the case of GaAs two-dimensional photonic crystal membranes with lattice periodicities of 10.5, 9.5, and 8.5 μm containing multilayers of self-assembled quantum dots.

Design and fabrication of a midinfrared photonic crystal defect cavity in indium antimonide

Simulation results and fabrication details are presented for a two-dimensional photonic crystal membrane defect cavity for use as a laser in gas sensing and communications applications in the 3–4 µm wavelength range. The design is based on a modified L3 cavity in an aluminium–indium–gallium–antimonide membrane structure which contains two strained quantum wells. Peak emission is predicted at λ = 3.372 µm with a Q factor of 26 233 for an optimized membrane thickness of 1000 nm. A focused ion beam procedure is described for creating the membrane directly in a Fabry–Perot laser structure. A 400 nm thick membrane is fabricated and the photonic crystal pattern is etched into the membrane.

Decay dynamics of quantum dots influenced by the local density of optical states of two-dimensional photonic crystal membranes

We have performed time-resolved spectroscopy on InAs quantum dot ensembles in photonic crystal membranes. The influence of the photonic crystal is investigated by varying the lattice constant systematically. We observe a strong slow down of the quantum dots’ spontaneous emission rates as the two-dimensional bandgap is tuned through their emission frequencies. The measured band edges are in full agreement with theoretical predictions. We characterize the multiexponential decay curves by their mean decay time and find enhancement of the spontaneous emission at the bandgap edges and strong inhibition inside the bandgap in good agreement with local density of states calculations.

Germanium-based nanophotonic devices: Two-dimensional photonic crystals and cavities

Two-dimensional photonic crystals are promising structures for photonic applications. Here, we show that the optical properties of two-dimensional photonic crystal membranes fabricated from silicon-on-insulator substrates can be probed at room temperature by the internal continuous wave photoluminescence of Ge/Si self-assembled islands. Quality factors up to 15 000, limited by the spectrometer resolution, are measured. We also show that two-dimensional photonic crystals can be fabricated as well with germanium-on-insulator substrates by using the same processing techniques. The optical properties of these two-dimensional photonic crystals can be probed by the room-temperature photoluminescence associated with the direct band gap of the bulk Ge layer. Enhanced resonant extraction efficiency can be obtained for wavelengths longer than 1.55 μm. The quality factors of H1 hexagonal cavities are found in good agreement with those obtained by finite-difference time domain calculations.

Double-layer fabrication scheme for large-area polymeric photonic crystal membrane on silicon surface by multibeam interference lithography

We report on the fabrication of two-dimensional polymeric photonic crystal membranes on the surface of silicon using visible-light multibeam interference lithography. The structures are created by the interference of three beams of a green laser. A polymer buffer layer doped with a Rhodamine B laser dye, interlaid between the lithography layer and the silicon substrate, suppresses the effects of strong reflection and nonradiative absorption of silicon on the interference pattern. Large-area defect-free photonic crystal membranes are experimentally realized on silicon surface.

Surface-emitting microlaser combining two-dimensional photonic crystal membrane and vertical Bragg mirror

We report on the design and fabrication of heterogeneous and compact surface-emitting microlasers, optically pumped and operating at 1.5μm at room-temperature. A very low threshold, below 15μW, is achieved. The devices consists of a top two-dimensional InP photonic crystal slab, including four InAsP quantum wells, a SiO2 bonding layer, and a bottom high index contrast Si∕SiO2 Bragg mirror deposited on a Si wafer. The graphitelike photonic crystal lattice is tailored for vertical emission. We theoretically and experimentally demonstrate that the Bragg reflector can strongly enhance the quality factor of the photonic crystal resonant mode, leading to a drastic decrease of the lasing threshold.

Controlling the Resonance of a Photonic Crystal Microcavity by a Near-Field Probe

We demonstrate theoretically that the resonance frequencies of high-Q microcavities in two-dimensional photonic crystal membranes can be tuned over a wide range by introducing a subwavelength dielectric tip into the cavity mode. Three-dimensional finite-difference time-domain simulations show that by varying the lateral and vertical positions of the tip, it is possible to tune the resonator frequency without lowering the quality factor. Excellent agreement with a perturbative theory is obtained, showing that the tuning range is limited by the ratio of the cavity mode volume to the effective polarizability of the nanoperturber.

Fabrication of planar photonic crystals in a chalcogenide glass using a focused ion beam

Free-standing "AMTIR-1" (Ge33As12Se55) chalcogenide glass films have been patterned using a focused ion beam (FIB) to create two-dimensional photonic crystal membranes. The triangular lattices were selected for a photonic bandgap relevant to fiber telecommunications. Optical measurements of transmission spectra as a function of incident angle showed clear signs of Fano resonances, indicating that the structures had strongly modified guided modes.

Calculation of losses in 2-D photonic Crystal membrane waveguides using the 3-D FDTD method

The three-dimensional finite-difference time-domain method is used to obtain loss per unit length in a two-dimensional photonic crystal membrane waveguide by simulating three different length guides. Results are shown for propagation both above and below the light line. The results are compared with a Fourier expansion method and good agreement is obtained above and below the light line.

Removal of thick (>100nm) InGaN layers for optical devices using band-gap-selective photoelectrochemical etching

We report on band-gap-selective photoelectrochemical (PEC) etching of thick InGaN layers for use in optical devices, such as GaN microdisks, distributed Bragg reflectors, and two-dimensional photonic crystal membranes. Three InGaN sacrificial layer structures are studied: a 300nm InGaN layer, an InGaN∕GaN superlattice, and an InGaN∕InGaN superlattice. Calculated equilibrium band diagrams of the epitaxial structures are used to explain the observed etching behavior. The strong piezoelectric-induced fields within the InGaN sacrificial layers are found to greatly affect carrier confinement and etching behavior. As a demonstration of the etching technique, a free-standing GaN microdisk on an InGaN post is fabricated.

InP photonic crystal membrane structures: Fabrication accuracy and optical performance

Two-dimensional photonic crystal membranes with coupled ridge waveguides were fabricated in InP∕InGaAsP by using e-beam lithography and reactive ion etching. The optical transmission characteristics were measured and a photonic band gap with better than 20dB extinction ratio was observed. The band-gap dependence on radius-to-lattice constant ratio (r∕a) was numerically and experimentally investigated. Predictable, accurate placement of the band edge by varying r∕a is demonstrated.

Fabrication of InP-based two-dimensional photonic crystal membrane

The fabrication process of a InP-based two-dimensional photonic crystal membrane structure is developed. The process includes a well-calibrated electron-beam (e-beam) lithography and InGaAsP/InP etching using methane–hydrogen–argon reactive ion etching. The photonic crystal blocks with ten rows of a hexagonal array of holes with various lattice constants and filling factors are successfully fabricated and characterized by optical transmission measurement. The sensitivity of the band gap to the systematic fabrication error is determined.