Hans P. Zappe

A GaAs/AlGaAs-based refractometer platform for integrated optical sensing applications

Abstract We present a new type of integrated optical refractometer, based on a Mach-Zehnder interferometer using III–V semiconductor and TiO2 on SiO2 waveguides. We report on the design, optimized for high sensitivity in immunoassay sensing applications, and the fabrication of this sensor chip. Using a test liquid system of ethanol in water, we demonstrate a refractive-index resolution of 1× 10−5 for this refractometer. This device is a basic building block of a novel, monolithically integrated optical sensing circuit, which can be used for example in chemical or immunological sensing applications.

Multiple wavelength Fabry–Pérot lasers fabricated by vacancy‐enhanced quantum well disordering

Wavelength‐shifted GaAs/AlGaAs Fabry–Perot ridge waveguide lasers were fabricated by vacancy‐enhanced quantum well disordering using dielectric cap annealing. 500 μm long and 4 μm wide Fabry–Perot lasers with emission wavelengths selectively shifted by 20 nm were integrated with unshifted lasers on the same chip, characterized and further compared with lasers fabricated from as‐grown material. These investigations showed that the absorption edge of a single‐quantum well double heterostructure can be selectively blueshifted after epitaxial growth without compromising diode laser performance.

Polymer and III-V transducer platforms for integrated optical sensors

Integrated optical transducer platforms for the measurement of small changes in the refractive index or thickness of a sensing layer are of considerable interest for the fabrication of a wide variety of sensors. Progress toward the development of two types of such platform is described. A replicated polymer platform fabricated by the embossing or molding of a surface relief microstructure followed by the evaporation of a dielectric waveguide layer forms the basis of a low-cost disposable device for applications such as medical diagnostics. A fully integrated, monolithic III-V platform with laser, interferometer, modulator, sensor pad, and detector is also being developed for compact, rugged sensors required in applications such as environmental sensing and process control. Both transducer platforms are suitable for many different types of sensors and can be extended to multichannel sensor structures for the simultaneous measurement of a number of analytes.

Monolithically integrated DBR laser, detector, and transparent waveguide fabricated in a single growth step

The monolithic integration of a GaAs-AlGaAs distributed Bragg reflector (DBR) laser with a nonabsorbing grating section, a transparent waveguide, and an absorbing photodetector is reported. Transparent and absorbing segments were defined after growth by vacancy-enhanced quantum-well disordering (VED). Laser output power was 5 mW with a threshold current of 22 mA. Detector current was linearly dependent on the laser output power and the emission from the grating side of the laser could be directly coupled into the detector. The conversion efficiency, defined as the ratio between detector current and laser output power, was 0.47 A/W. Using a comparison with as-grown, SiO/sub 2/-capped and SrF/sub 2/-capped devices, both lasers and detectors were not seen to be adversely affected by the anneal required for the VED.<<ETX>>

Optical displacement measurement with GaAs/AlGaAs-based monolithically integrated Michelson interferometers

Two monolithically integrated optical displacement sensors fabricated in the GaAs/AlGaAs material system are reported. These single-chip microsystems are configured as Michelson interferometers and comprise a distributed Bragg reflector (DBR) laser, photodetectors, phase shifters, and waveguide couplers. While the use of a single Michelson interferometer allows measurement of displacement magnitude only, a double Michelson interferometer with two interferometer signals in phase quadrature also permits determination of movement direction. In addition, through the use of two 90/spl deg/ phase-shifted interferometer signals in the latter device, a phase interpolation of 2/spl pi//20 is possible, leading to a displacement resolution in the range of 20 nm. The integration of these complex optical functions could be realized with a relatively simple fabrication process.

Polarization switching and modulation dynamics in gain- and index-guided VCSELs

In this contribution, we bring forward and compare the polarization switching (PS) dynamics and the polarization modulation characteristics of gain- and index-guided VCSELs. We then discuss the steady-state and dynamic characteristics of both types of VCSELs. Finally we focus on the polarization modulation limit and the average mode hopping frequency, which both scale over 8 orders of magnitude when the switching current is varied from just above threshold up to 2 times the threshold current.

A monolithically integrated double Michelson interferometer for optical displacement measurement with direction determination

A monolithically integrated optical displacement sensor fabricated in the GaAs-AlGaAs material system is reported. The single-chip device consists of a distributed Bragg reflector laser, two photodetectors, two phase modulators, two Y-couplers, and two directional couplers. It is configured as a double Michelson interferometer and allows the determination of both magnitude and direction of a displacement. The detection of two 90/spl deg/ phase-shifted interferometer signals also resulted in on improved phase interpolation of o/20. Despite the relatively simple fabrication process, the integration of rather complex optical functions could be realized.

Investigation of optical losses in photoelastic and ridge waveguides in GaAs-AlGaAs heterostructures

Two approaches have been used to fabricate stable photoelastic waveguides with planarized surfaces on GaAs-AlGaAs heterostructures. The first approach uses tensile Ni/sub 3/GaAs stressors formed by metal-semiconductor reactions. The second approach uses inert, refractory and compressive stressors, such as RF sputtered W and RF co-sputtered WNi films. For comparison purposes, ridge waveguides have also been fabricated using the same heterostructure by a dry etching technique. Optical losses of photoelastic waveguides, measured by Fabry-Perot (FP) method at a wavelength of 1.53 /spl mu/m, are comparable to or better than those of the ridge waveguides. Material loss appears to be the primary loss mechanism in both photoelastic and ridge waveguides. These results indicate that the photoelastic waveguide processing technique reported in this study is a promising alternative to commonly used dry etching techniques for planarization.

Technology and devices for hybrid and monolithically integrated optical sensors

Abstract Many types of optical sensors stand to benefit from monolithic integration through the use of semiconductor technology; improvements in performance, size, flexibility and price are expected. The application of III-V optoelectronic devices and processing technology to the fabrication of both monolithically and hybridly integrated optical sensors have been discussed. The fabrication of lasers, waveguides, modulators and detectors in the GaAs/ AlGaAs material system is outlined. The monolithic integration of these optoelectronic components into a passive Mach-Zehnder interferometer sensor platform are presented as well as the issues of sensor layer design, integration and sensitivity.

Optical refractometry using a monolithically integrated Mach-Zehnder interferometer

Integrated optical sensors, based on evanescent wave sensing, are useful for numerous applications, including medical, environmental and food analysis. System miniaturization is a key issue in their further development. We present the design and fabrication of a novel refractometric transducer, where all optoelectronic components (laser, waveguide, modulators, detectors and sensor pads) are and report on its performance as a refractometer in a flow-through system.