Daniel Hofstetter

Quantum-well intermixing for fabrication of lasers and photonic integrated circuits

Various applications of quantum-well intermixing, ranging from multiwavelength lasers to complex photonic integrated circuits, are described. The fabrication of these GaAs-AlGaAs-based devices relies on the postgrowth definition of regions with varying bandgap, enabling the manufacture of wavelength shifted modulators and lasers, as well as the integration of transparent waveguides with absorbing lasers and detectors. The impurity-free vacancy-enhanced disordering technique employed, and its integration with existing process technologies, will be presented, and examples of multicolor lasers, wavelength shifted modulators and integrated optical interferometers are shown. These applications yield high-optical functionality using relatively simple process and integration technology.

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.

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.

Quantum well engineering for semiconductor integrated optical sensors

Semiconductor technology, when applied to the design and fabrication of integrated optical sensors, will yield structures of improved performance and reduced cost. Key advances in this area employ two quantum well-based effects, the quantum confined Stark effect and selective quantum well intermixing, the use of which enable the monolithic integration and enhanced functionality of semiconductor-based optical sensor circuits. In this paper, we discuss the application of these effects to the fabrication of semiconductor devices useful for integrated optical sensors based on waveguide interferometry. The quantum confined Stark effect allows us to electrically define the absorption edge of detectors and permits the fabrication of high- efficiency phase modulators. By the use of different surface dielectrics, quantum well intermixing is employed to generate transparent and absorbing regions on a single substrate. Current and future applications are discussed.

Semiconductor Integrated Photonic Transducer Chip for High-Resolution Displacement Measurement

Optical displacement measurement using interferometric techniques is a well established and technologically advanced discipline. Two of the limitations which may be encountered in applying an optical approach to high-resolution determination of distances or movements, however, are optical system size and robustness. The use of semiconductor integrated optics for optical interferometry can circumvent these restrictions: photonic integrated circuits1 (PICs) are typically quite small and monolithic integration of the various components can result in a microsystem of considerable physical ruggedness.

Optical displacement measurement using a monolithic Michelson interferometer

Contactless optical displacement measurement has the potential for a variety of industrial and scientific applications. For highly accurate displacement measurements at distances below 1 m, interferometric methods are preferred over most other methods. This is mainly because of the good resolution and the possibility of doing the measurements in real-time. Furthermore, the use of direct bandgap semiconductor materials also enables the fabrication of a compact interferometer-based device which unites all necessary components, including the light emitter, on a single chip. In this paper, a monolithically integrated optical displacement sensor fabricated in the GaAs/AlGaAs material system is reported. This single chip microsystem is configured as a double Michelson interferometer and comprises a distributed Bragg reflector laser, photodetectors, phase shifters and waveguide couplers. In the course of this paper, we will also briefly discuss possible scientific and industrial applications of such devices.

Photonic integrated circuits for optical displacement sensing

We discuss a III-V-based monolithically integrated measurement microsystem for optical displacement sensing. The sensor, consisting of a Michelson interferometer with an integrated DBR laser and waveguide photodetector, has been fabricated on a single GaAs substrate. Alignment requirements are reduced to that of a lens for beam collimation; displacement measurements with sub-1 O0 nm resolution have been performed. The same technology may also be employed for integrated optical refractometric chemical sensors.

Monolithically integrated interferometer for optical displacement measurement

We discuss the fabrication of a monolithically integrated optical displacement sensors using III-V semiconductor technology. The device is configured as a Michelson interferometer and consists of a distributed Bragg reflector laser, a photodetector and waveguides forming a directional coupler. Using this interferometer, displacements in the 100 nm range could be measured at distances of up to 45 cm. We present fabrication, device results and characterization of the completed interferometer, problems, limitations and future applications will also be discussed.