We present the fabrication of 3D adiabatically tapered structures, for efficient coupling from an optical fiber, or free-space, to a chip. These structures are fabricated integrally with optical waveguides in a silicon-on-insulator wafer. Fabrication involves writing a single grayscale mask in HEBS glass with a high-energy electron beam, ultra-violet grayscale lithography, and inductively coupled plasma etching. We also present the experimentally determined coupling efficiencies of the fabricated tapers using end-fire coupling. The design parameters of the tapered structures are based on electromagnetic simulations and are discussed in this paper.

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While recent advances in optical integrated circuits and photonic crystal devices have been impressive, there presently exists an unsatisfied need for an efficient means of coupling into these systems from the outside world. To this end, we have developed writing techniques for continuous-tone grayscale masks in highenergy beam sensitive (HEBS) glass, which we subsequently employ in the fabrication of tapered coupling devices. These devices demonstrate efficient coupling of free-space and fiber signals into waveguides fabricated on silicon-on-insulator substrates. This approach significantly reduces losses as compared to standard butt-coupling and end-fire coupling methods, in addition to being inherently broadband. In this paper, we discuss grayscale mask process development, fabrication techniques for the coupling devices, and characterization of device performance.

The 2-2.5 µm region of the electromagnetic spectrum is of particular importance for the noninvasive monitoring of blood glucose using absorption spectroscopy, since it can provide the strongest signature as compared to other water transmission windows. Currently available spectroscopy systems for this application require high-gain and low-noise detectors in order to achieve sufficient signal-to-noise ratio measurements. In this context, we are investigating the integration of micro-optics along with InGaAsSb/AlGaAsSb avalanche photodetectors in order to demonstrate high-fill factor, high quantum efficiency and eventually the ability to evaluate the blood glucose concentration with high accuracy. Also, using the bandgap engineering options afforded by the quaternary antimonide structures, the spectral response of the detector can be tuned over this wavelength range. In this paper, we present the design, fabrication and integration of the multi-chip modules, the constituent technologies required to realize them and experimental results from their characterization.