G. Allen Vawter

Useful design relationships for the engineering of thermodynamically stable strained‐layer structures

Recent studies have provided sufficient knowledge about the dominant failure mechanisms for lattice‐mismatched strained‐layer heterostuctures to permit the design of thermodynamically stable strained‐layer systems for device applications. We have developed procedures that summarize this knowledge for the working device designer, and apply these relationships to the design of ion‐implanted, strained‐layer, quantum‐well lasers.

Femtosecond laser-pulse-induced birefringence in optically isotropic glass

We used a regeneratively amplified Ti:sapphire femtosecond laser to create optical birefringence in an isotropic glass medium. Between two crossed polarizers, regions modified by the femtosecond laser show bright transmission with respect to the dark background of the isotropic glass. This observation immediately suggests that these regions possess optical birefringence. The angular dependence of transmission through the laser-modified region is consistent with that of an optically birefringent material. Laser-induced birefringence is demonstrated in different glasses, including fused silica and borosilicate glass. Experimental results indicate that the optical axes of laser-induced birefringence can be controlled by the polarization direction of the femtosecond laser. The amount of laser-induced birefringence depends on the pulse energy level and number of accumulated pulses.

Improved epitaxial layer design for real‐time monitoring of dry etching in III–V compound heterostructures with depth accuracy of ±8 nm

Etching structures for state‐of‐the‐art electronic and optoelectronic devices such as heterojunction bipolar transistors, optical waveguide modulators, gratings, and vertical‐cavity surface‐emitting lasers often requires nonselective etching with depth accuracy on the order of ±8 nm. We disclose the application of in situ optical reflectance monitoring during chlorine reactive‐ion‐beam etching of III‐V compound heterostructure devices for real‐time determination of etch depth to ±8 nm independent of total etch depth. High‐vertical‐resolution etching of thick, layered structures is achieved through use of a resonant periodic set of reflective interfaces, greatly enhancing the reflected amplitude oscillations without detrimental effects on device performance. This method demonstrates that slight modifications of material structure to optimize monitor response greatly enhance the accuracy of nonselective dry etching.

Reactive‐ion‐beam etching of InP in a chlorine–hydrogen mixture

We present the first application of Cl2+H2 reactive‐ion‐beam etching of InP. Specularly smooth etching is achieved using an ion beam of 53%–73% Cl2 in H2 at a 300 eV extraction potential with the substrate held at 250 °C. InP etch morphology and rate are examined as functions of Cl2+H2 mixture, sample temperature, and chamber pressure. Significant deviation from the optimum smooth‐etch conditions are seen to result in rough surfaces.

Characterization of Si3N4/SiO2 planar lightwave circuits and ring resonators

The large refractive index contrast between silicon nitride and silicon dioxide allows silicon nitride/dioxide planar waveguides to have a small mode size and low radiation bending loss compared with doped silicon dioxide waveguides. Small waveguide bend with low radiation loss can help make small integrated planar lightwave circuits (PLCs), and also high-Q waveguide ring resonators. This presentation will talk about the design, fabrication and characterization of low loss silicon nitride/dioxide planar waveguide devices including waveguide bend, waveguide cross, and leaky mode waveguide polarizer. The key contribution of this work is the use of the lateral mode interference (LMI) 3dB splitter to accurately measure the loss of the planar lightwave circuit devices. We will also talk about the waveguide ring resonators with silicon nitride/dioxide materials. The application for photonic biochemical sensors will also be discussed.

Low threshold current implanted-planar buried-heterostructure graded-index separate confinement heterostructure laser in GaAs/AlGaAs

We report dramatic improvements to the implanted‐planar buried‐heterostructure graded‐index separate confinement heterostructure (IPBH‐GRINSCH) laser in (AlGa)As/GaAs which produces low threshold current, continuous‐wave operation. Our process features significantly reduced fabrication complexity of high quality, index‐guided laser diodes compared to regrowth techniques and, in contrast to diffusion‐induced disordering, allows creation of self‐aligned, buried, blocking junctions by ion implantation. The improved single‐stripe IPBH‐GRINSCH lasers exhibit 39 mA threshold current, cw operation.

High-Q integrated on-chip micro-ring resonator

We report a fully integrated high-Q factor micro-ring resonator using silicon nitride/dioxide on a silicon wafer. The micro-ring resonator is critically coupled to a low loss straight waveguide. An intrinsic quality factor of 2.4/spl times/10/sup 5/ has been measured.

Chlorine reactive ion beam etching of InSb and InAs0.15Sb0.85/InSb strained‐layer superlattices

We report the first successful application of Cl2 reactive ion beam etching (RIBE) to the dry etching of bulk InSb and InAs0.15Sb0.85/InSb strained‐layer superlattices (SLSs). Etching was performed in a load‐locked ultrahigh vacuum chamber using an electron cyclotron resonance ion source. Etching rates for InSb and InAs0.15Sb0.85/InSb SLS with a 500 eV Cl2 beam at 0.6 mA/cm2 are 280 and 240 nm/min, respectively, compared to 310 nm/min for GaAs. The sputter yield for Cl2 RIBE in this antimonide system is double that obtained by Ar ion milling under identical conditions.

Optical AND and NOT gates at 40 Gbps using electro-absorption modulator/photodiode Pairs

We demonstrate an optical gate architecture using electro-absorption modulator/photodiode pairs to perform AND and NOT functions. Optical bandwidth for both gates reach 40 GHz. Also shown are AND gate waveforms at 40 Gbps.

Integrated Guided-Wave Photodiode Using Through-Absorber Quantum-Well-Intermixing

A high-speed, high-saturation power photodiode compatible with a relatively simple monolithic integration process is described. The detector is comprised of an intrinsic bulk absorption layer, an electron drift region, and a field termination layer, and is grown above a main waveguide core comprised of a number of quantum wells, which are used as the active region of a phase modulator. Through-absorber quantum-well-intermixing is used to blue-shift the bandedge of the underlying quantum wells, reducing the optical losses of that material. The detectors demonstrate quantum efficiency, input saturation power, and 3-dB bandwidth of 50 GHz.