Tight control of blood glucose levels has been shown to dramatically reduce the long-term complications of diabetes. Current invasive technology for monitoring glucose levels is effective but underutilized by people with diabetes because of the pain of repeated finger-sticks, the inconvenience of handling samples of blood, and the cost of reagent strips. A continuous glucose sensor coupled with an insulin delivery system could provide closed-loop glucose control without the need for discrete sampling or user intervention. We describe an optical glucose microsensor based on absorption spectroscopy in interstitial fluid that can potentially be implanted to provide continuous glucose readings. Light from a GaInAsSb LED in the 2.2-2.4 µm wavelength range is passed through a sample of interstitial fluid and a linear variable filter before being detected by an uncooled, 32-element GaInAsSb detector array. Spectral resolution is provided by the linear variable filter, which has a 10 nm band pass and a center wavelength that varies from 2.18-2.38 µm (4600-4200 cm −1 ) over the length of the detector array. The sensor assembly is a monolithic design requiring no coupling optics. In the present system, the LED running with 100 mA of drive current delivers 20 nW of power to each of the detector pixels, which have a noise-equivalent-power of 3 pW/Hz 1/2 . This is sufficient to provide a signal-to-noise ratio of 4500 Hz 1/2 under detector-noise limited conditions. This signal-to-noise ratio corresponds to a spectral noise level less than 10 µAU for a five minute integration, which should be sufficient for sub-millimolar glucose detection.

An optical parametric oscillator is tuned to the resonance wavelength of the etalon in an optical pumping injection cavity (OPIC) laser with a type-II "W" active region, thereby minimizing the threshold pump intensity and maximizing the output slope efficiency. Previous OPIC experiments employed fixed-wavelength sources with only limited tuning available by adjusting the incident angle. Low threshold pump intensities of 330 W / cm 2 at 100 K and 14 kW/ cm 2 at 300 K (where the output wavelength is 3200 nm) were achieved. The energy conversion efficiency is found to decrease by over a factor of 100 when the pump wavelength is tuned from the resonance condition (1822 nm at 300 K) to only slightly off resonance (e.g., 1808 nm).

A focal plane array detector sensitive from 2.0-2.5 µm and consisting of 32, 1.0 mm x 50 µm pixels, all functional, is demonstrated. Mean room-temperature R 0 A is found to be 1.0 Ω-cm 2 , limited by sidewall leakage. The focal plane array is fabricated from an MBE-grown homojunction p-i-n GaInAsSb grown on an n-type GaSb substrate. Backillumination geometry is compared to front-illumination geometry and is found to be favorable, particularly the improved responsivity (1.3 A/W at 2.35 µm corresponding to 68% quantum efficiency) due to reflection of light off the metal contact. Further, back-illumination is the most convenient geometry for mounting the array onto a compact blood glucose sensor because both contacts can be mounted on one side, while detector illumination occurs on the other.

Recent efforts to improve the performance of mid-infrared antimonide-based semiconductor lasers have focused on enhancing the absorption of the pump beam to maximize power conversion efficiencies and minimize threshold intensities. One successful approach has been the optical pumping injection cavity (OPIC) laser, in which a type-II W active region is enclosed between distributed Bragg reflector (DBR) mirrors in order to achieve multiple passes of the pump beam and thereby to enhance absorption.Previously, fixed wavelength sources have been used for optical pumping of OPIC laser structures, with limited tuning available by adjusting the incident angle. By tuning the pump wavelength using an optical parametric oscillator, we demonstrate minimum threshold intensities and maximum slope efficiencies at the resonance of the DBR cavity surrounding the active region, further demonstrating the potential of OPIC lasers. A 3.2 µm OPIC laser operated at 350 K in pulsed mode (at the highest operating temperature of the dewar), with a characteristic temperature of 50 K. The power conversion efficiency for a single facet at 300 K was the highest ever observed in the mid-IR, at approximately 4%.Results are presented for two OPIC samples (emitting at ~3.2 µm and 4.3 µm at high temperature), one of which was designed with a broadened cavity resonance, suitable for pumping with a multi-mode source. Threshold intensities and slope efficiencies measured as a function of pump wavelength demonstrate the strong resonance effect, and that the "broadened OPIC" does in fact manifest a much wider resonance than the non-broadened resonance cavity design.

The performances of a pin versus a pn structure from GaInAsSb materials operating at room temperature are compared both from a theoretical point of view and experimentally. Theoretically, it is found in materials limited by generationrecombination currents, pn junctions have a higher D* than pin junctions. The thinner depletion region of pn junctions results in a lower responsivity but a higher dynamic resistance, giving an overall higher D* compared to a pin structure. A series of five p+pn+ Ga 0.80 In 0.20 As 0.18 Sb 0.82 detector structures latticed matched to GaSb substrates and with 2.37 µm cut off wavelength were grown by molecular beam epitaxy and processed into variable size mesa photodiodes. Only the doping of the absorbing (p) region was varied from sample to sample, starting with nominally undoped (~1x10 16 cm -3 pbackground doping due to native defects) and increasing the doping until a p+n+ structure was attained. Room temperature dynamic resistance-area product R 0 A was measured for each sample. A simple method is presented and used to disentangle perimeter from areal leakage currents. All five samples had comparable R 0 A's. Maximum measured R 0 A was 30 Ω-cm 2 in the largest mesas. Extracted R 0 A's in the zero perimeter/area limit were about ~50 Ω-cm 2 (20-100 Ω-cm 2 ) for all samples. Within uncertainty, no clear trend was seen. Tentative explanations are proposed.