Two-dimensional Photonic Crystal Mirrors Research Articles

Enlarging the bandwidth of a two-dimensional photonic crystal mirror in the visible range

Enlarging the bandwidth of a two-dimensional photonic crystal mirror in the visible range

High-Reflectivity Broadband Photonic Crystal Mirror MEMS Scanner With Low Dependence on Incident Angle and Polarization

In this paper, we introduce a single-axis resonant comb drive highly reflective broadband photonic crystal (PC) mirror microelectromechanical systems (MEMS) scanner with low dependence of reflectivity on incident angle and polarization. Two-dimensional PC mirrors have several advantages over metal coatings and dielectric stacks (1-D PCs) as mirrors. They can tolerate much higher processing temperatures and higher incident powers, as well as operate in more corrosive environments than metals. Compared to multilayer dielectric stacks, 2-D PC mirrors are compact and allow for simpler process integration, making them highly compatible with CMOS and MEMS processing. Our PC mirrors show broadband high reflectivity of > 90% in the wavelength range from 1345 to 1490 nm (> 95% for 1380 to 1450 nm) and very low angular and polarization dependence over this same range. The single-axis MEMS scanners are fabricated on silicon-on-insulator wafers with the PC mirrors fabricated in polysilicon films on oxide. Although the scanner presented in this paper is single axis, the low angular and polarization dependence properties of the 2-D-PC mirror also make it useful for dual-axis scanners. The scanners are actuated by in-chip plane electrostatic combdrives on resonance. Dynamic deflection measurements show that the scanners can achieve 20deg total scan angle with an input square wave of 40 V and up to 120deg total scan angle with 190 V at a resonance frequency of 2.03 kHz. Although the achievable scan ranges are very large, the useful scan angles will be limited by the angular and polarization dependence properties of the PC reflector and its application. For the 2-D PC scanner presented in this paper, applications that can tolerate 10% decrease in reflectivity will have a scan range of 20deg.

GaSb-based lasers with two-dimensional photonic crystal mirrors

We present the realization of two-dimensional (2D) photonic crystals (PhCs) on the GaSbmaterial system. An electron cyclotron resonance reactive ion etch process usingCl2/Ar allows the fabrication of PhCs covering air fill factors off = 20%–50%, latticeperiods of a = 400–500 nm and aspect ratios of 5:1. Quality and reflectivity of these structuresare evaluated by incorporating the PhCs as high reflective back mirrors inGaSb-based ridge waveguide lasers with cavity lengths between 200 and1100 µm with thefront facet as cleaved. The shortest devices show remarkable threshold currents below 12 mA and efficienciesof 0.23 W A−1, yielding a maximum output power of almost 19 mW, proving the applicability of thechosen approach to numerous further concepts based on 2D PhCs on the GaSb materialsystem.

Digital resolution enhancement in surface plasmon microscopy

The use of photonic crystal and negative refractive index materials is known to improve resolution of optical microscopy and lithography devices down to 80 nm level. Here we demonstrate that utilization of well-known digital image recovery techniques allows us to further improve resolution of optical microscope down to 30 nm level. Our microscope is based on a flat dielectric mirror deposited onto an array of nanoholes in thin gold film. This two-dimensional photonic crystal mirror may have either positive or negative effective refractive index as perceived by surface plasmon polartions in the visible frequency range. The optical images formed by the mirror are enhanced using simple digital filters.

Design of two-dimensional photonic-crystal mirrors for InGaAs QW laser applications

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Tunable photonic crystals fabricated in III-V semiconductor slab waveguides using infiltrated liquid crystals

Microcavity structures formed by two-dimensional photonic crystal mirrors with triangular lattice and a crystal period of 280 nm suitable for transmission experiments at about 1 μm were fabricated in III-V semiconductor planar waveguides. The photonic crystals were filled with a liquid crystal of type E7. The wavelength of the resonance peak can be shifted by the temperature-dependent refractive index of the liquid crystal. The temperature shift follows the typical refractive index behavior of liquid crystals, with a jump in wavelength at the clearing point (about 60 °C) and a continuous shift below. The wavelength jump is about 4 nm within a few Kelvin, while the total shift amounts to 9 nm between 20 and 70 °C. The experimental results agree well with the calculated temperature dependent photonic band structure by assuming a preferential alignment of the liquid-crystal molecules parallel to the holes.

Deeply etched two-dimensional photonic crystals fabricated on GaAs/AlGaAs slab waveguides by using chemically assisted ion beam etching

High quality two-dimensional photonic crystals were fabricated by electron-beam lithography and a combination of reactive ion etching (RIE) and chemically assisted ion beam etching (CAIBE) in GaAs/AlGaAs slab waveguides. With optimized parameters, etch depths of more than 2 μm were achieved. This technique was used to fabricate three-dimensionally confined optical microcavities defined by a slab waveguide and a two-dimensional photonic crystal mirror structure. The optical quality of the deeply etched structures were tested by optical spectroscopy. The Q-factor of the cavity mode is dependent on the structural quality and depth of the holes in the photonic crystals. Due to the large etch depth and smooth surfaces, high quality planar microcavities could be realized with Q-factors of about 1000.

Single-mode operation of coupled-cavity lasers based on two-dimensional photonic crystals

We report the fabrication of short-cavity lasers with highly reflective two-dimensional photonic crystal mirrors on an InGaAsP/InP laser structure emitting at 1.57 μm. An intracavity photonic crystal mirror creates two coupled cavities, which provide additional longitudinal mode selection for stable single-mode operation with side-mode suppression ratios exceeding 35 dB. The shortest lasers with l=100 μm overall length have a threshold current of 13 mA and provide more than 4 mW power under continuous wave operation. Longer devices with l=200 μm deliver up to 9 mW. A maximum modulation bandwidth of 7.9 GHz was determined by relative intensity noise measurements.

Nanofabrication of two-dimensional photonic crystal mirrors for 1.5 μm short cavity lasers

We have developed a fabrication scheme for two-dimensional (2D) triangular photonic crystals (PCs) on InP-based material systems involving high resolution electron beam lithography, pattern transfer to a SiO2 etch mask, and a Cl2/Ar electron cyclotron resonance reactive ion etch step yielding PCs with periods of a=300–450 nm and air fill factors of f=18%–63%. These PCs are employed as high reflectivity mirrors for 1.5 μm short cavity lasers, which are key components in future highly integrated PC based photonic circuits. We have fabricated lasers with 2 PC mirrors and cavity lengths down to 100 μm. Threshold currents as low as 7.6 mA were achieved for the shortest lasers with 2 PC mirrors. The short laser cavity results in a large Fabry–Pérot mode spacing and mode competition leads to single mode lasing over a reasonably large current range up to 4.5× threshold. Lasers with one PC back mirror and a cleaved output facet show a higher threshold current of 13 mA and a maximum output power of more than 4 mW. The variation of laser performance with different cavity lengths is presented and discussed.

Nanofabrication techniques for lasers with two-dimensional photonic crystal mirrors

The fabrication of photonic crystals (PC) involves a periodic modulation of the refractive index on nanometer scales thus requiring state-of-the-art patterning and dry etch technologies. In this article, we compare three different mask techniques for the fabrication of ridge waveguide lasers with two-dimensional triangular PC mirrors. After defining the hole pattern in 500 nm polymethylmetacrylate by 100 kV e-beam lithography the structure is transferred to the mask layer. The first mask layer is a metal mask consisting of Ti/Cr/Ti. The second one is formed by wet chemical oxidation of a buried 60 nm AlAs layer and the third one uses a single SiO2 layer in order to transfer the hole pattern into the semiconductor. The periods of the PC, with an average air filling factor of 45%, were chosen in the range of 160–400 nm in order to probe the region where high reflectivity of the PC is expected. The observed laser performance is used to deduce information about the quality of the fabricated PCs. The advantages of each technique are discussed, leading to conclusions for future techniques for the fabrication process of photonic crystals.

Two-dimensional photonic band-Gap defect mode laser

A laser cavity formed from a single defect in a two-dimensional photonic crystal is demonstrated. The optical microcavity consists of a half wavelength-thick waveguide for vertical confinement and a two-dimensional photonic crystal mirror for lateral localization. A defect in the photonic crystal is introduced to trap photons inside a volume of 2.5 cubic half-wavelengths, approximately 0.03 cubic micrometers. The laser is fabricated in the indium gallium arsenic phosphide material system, and optical gain is provided by strained quantum wells designed for a peak emission wavelength of 1.55 micrometers at room temperature. Pulsed lasing action has been observed at a wavelength of 1.5 micrometers from optically pumped devices with a substrate temperature of 143 kelvin.

Demonstration of cavity mode between two-dimensional photonic-crystal mirrors

The authors report the observation of a cavity mode, at λ = 0.94 µm, which is tightly confined between two slabs of two-dimensional photonic crystals deeply etched into a laser-like heterostructure waveguide. Guided photoluminescence of this heterostructure is used as an internal point source to probe the horizontal cavity.