Gale S. Petrich

Enhanced coupling to vertical radiation using a two-dimensional photonic crystal in a semiconductor light-emitting diode

Enhanced coupling to vertical radiation is obtained from a light-emitting diode using a two-dimensional photonic crystal that lies entirely inside the upper cladding layer of an asymmetric quantum well structure. A sixfold enhancement in light extraction in the vertical direction is obtained without the photonic crystal penetrating the active material. The photonic crystal is also used to couple pump light at normal incidence into the structure, providing strong optical excitation.

Air‐bridge microcavities

We introduce and analyze a new type of high‐Q microcavity consisting of a channel waveguide and a one‐dimensional photonic crystal. A band gap for the guided modes is opened and a sharp resonant state is created by adding a single defect in the periodic system. An analysis of the eigenstates shows that strong field confinement of the defect state can be achieved with a modal volume less than half of a cubic half‐wavelength. We also present a feasibility study for the fabrication of suspended structures with micron‐sized features using semiconductor materials.

Low-cost, single-mode diode-pumped Cr:Colquiriite lasers

We present three Cr3+:Colquiriite lasers as low-cost alternatives to Ti:Sapphire laser technology. Single-mode laser diodes, which cost only

Large-area broadband saturable Bragg reflectors by use of oxidized AlAs

150 each, were used as pump sources. In cw operation, with approximately 520 mW of absorbed pump power, up to 257, 269 and 266 mW of output power and slope efficiencies of 53%, 62% and 54% were demonstrated for Cr:LiSAF, Cr:LiSGaF and Cr:LiCAF, respectively. Record cw tuning ranges from 782 to 1042 nm for Cr:LiSAF, 777 to 977 nm for Cr:LiSGaF, and 754 to 871 nm for Cr:LiCAF were demonstrated. In cw mode-locking experiments using semiconductor saturable absorber mirrors at 800 and 850 nm, Cr:Colquiriite lasers produced approximately 50-100 fs pulses with approximately 1-2.5 nJ pulse energies at approximately 100 MHz repetition rate. Electrical-to-optical conversion efficiencies of 8% in mode-locked operation and 12% in cw operation were achieved.

Photonic band-gap waveguide microcavities: Monorails and air bridges

Broadband saturable Bragg reflectors (SBRs) are designed and fabricated by monolithic integration of semiconductor saturable absorbers with broadband Bragg mirrors. The wet oxidation of AlAs creates low-index AlxOy layers for broadband, high-index-contrast AlGaAs/AlxOy or InGaAlP/AlxOy mirrors. SBR mirror designs indicate greater than 99% reflectivity over bandwidths of 294, 466, and 563 nm for center wavelengths of 800, 1300, and 1550 nm, respectively. Highly strained and unstrained absorbers are stably integrated with the oxidized mirrors. Large-scale lateral oxidation techniques permit the fabrication of SBRs with diameters of 500 microm. Large-area, broadband SBRs are used to self-start and mode lock a variety of laser systems at wavelengths from 800 to 1550 nm.

Supercollimation in photonic crystals composed of silicon rods

Photonic band-gap monorail and air-bridge waveguide microcavities, operating at the wavelength regime of 1550 nm, are fabricated using GaAs-based compound semiconductors. The fabrication process involves gas-source molecular beam epitaxy, electron-beam lithography, reactive ion etching, and thermal wet oxidation of Al0.93Ga0.07As. The fabrication of the air-bridge microcavity, in particular, also entails the sacrificial wet etch of AlxOy to suspend the micromechanical structure. The monorail and air-bridge microcavities have been optically characterized and the transmission spectra exhibit resonances in the 1550 nm wavelength regime. Tunability of the resonant wavelength is demonstrated through changing the defect size in the one-dimensional photonic crystal. The quality factors (Q) of the microcavities are about 140 for the monorail and 230 for the air bridge, respectively.

The Role of the Thermal Oxide in GaAs‐Based Photonic Bandgap Waveguide Microcavities

Supercollimation is the propagation of light without diffraction using the properties of photonic crystals. We present the first experimental demonstration of supercollimation in a planar photonic crystal composed of nanoscale rods. Supercollimation was observed over distances of up to 1000 lattice periods.

Fabrication of photonic crystal waveguides composed of a square lattice of dielectric rods

Recent work on optical microcavities is concisely reviewed in this article. Optical microcavities can be fabricated using III–V compound semiconductors by introducing a large periodic refractive-index variation along the axis of GaAs waveguides. Strong optical confinement in the microcavities is achieved by oxidizing the underlying III–V material and further optimized by preferentially etching away the oxide to form an air-bridge structure. The III–V thermal oxide is obtained from the wet thermal oxidation of high Al-content AlxGa1–xAs material. The critical role of the thermal oxide in the design and fabrication of the waveguide microcavities is outlined and the characterization of the properties of the thermal oxide salient to the fabrication of the devices is described. Finally, preliminary transmission data demonstrating the successful realization of these microcavities are presented.

Large scale oxidation of AlAs layers for broadband saturable Bragg reflectors

The use of a negative resist, hydrogen silsesquioxane (HSQ), combined with electron-beam lithography, was found to greatly simplify the fabrication of photonic crystal structures having submicron-sized features. Two methods of fabrication were compared for the creation of photonic crystals; in this example, the structures were composed of a square lattice of dielectric rods. One method utilized positive resist PMMA, whereas another method used a negative resist HSQ. The process sequence using PMMA required a lift-off step and a hard mask in order to convert the hole-patterned PMMA into high-aspect-ratio dielectric rods through reactive ion etching. Alternatively, the electron-beam exposure and development of HSQ resist resulted in the formation of SiO2-like posts which then served as a hard mask for subsequent etches. The use of HSQ eliminated the need for the SiO2 deposition and nickel lift-off, thereby reducing the required number of steps in the process sequence and greatly simplified the fabrication.

Automatic feedback control of an Er-doped fiber laser with an intracavity loss modulator

Summary form only given. Describes oxidation of AlAs to Al/sub x/O/sub y/ for use as a broadband saturable Bragg reflector (SBR) where an Al/sub x/O/sub y//GaAs mirror with lateral dimensions >300 /spl mu/m is required. For the SBR structure described, the simulated bandwidth extends from 1200 nm to 1800 nm with greater than 99.5% reflectivity. The layers within the SBR are grown using gas-source molecular beam epitaxy. The SBR structure contains an 8 period GaAs/AlAs quarter-wave stack grown on a GaAs substrate. The Al/sub x/O/sub y/ layer is initially grown as AlAs and later oxidized. The AlAs layer is relatively thick (240 nm) to correspond to a quarter wavelength in Al/sub x/O/sub y/ (n = 1.66) minus a 10% shrinkage upon oxidation. The active region consists of an InP/InGaAs quantum well emitting near /spl lambda/ = 1550 nm. The effects of the SBR for self-starting the laser cavity are detailed.