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If we can make wavelength-sized detectors, we approach the limit at which smaller detectors have no further advantage for imaging focal plane arrays with practical (f/1-2) optics. Of course, this must be accomplished without compromising performance-a challenge for 5-lm devices for which the perimeter, the currents of which depend on passivation quality, is very large compared with the area of the device. This paper describes the development of small LWIR HgCdTe detectors and compares dark current performance with that of larger basic devices, as described by ''Rule 07'', a well-known rule of thumb which gives the HgCdTe dark-current density characteristics of the best reported diodes as a function of device cutoff wavelength and operating temperature. Low cross-talk requires a fully-depleted absorber layer sufficiently thick to provide adequate quantum efficiency (QE). Preliminary results show dark-current densities are more than a factor of ten below the Rule 07 trend line. With these dark-current densities, the measured $40% non-antireflection-coated QE in the 8-10 lm region is more than adequate to achieve background-limited performance with the margin under tactical backgrounds for the fast (f/1), diffraction-limited optics required for the small pixels.

No abstract

We present the first integration of fluidically tunable filters with a separate particle detection channel on a single planar, optofluidic chip. Two optically connected, but fluidically isolated liquid-core antiresonant reflecting optical waveguide (ARROW) segments serve as analyte and spectral filter sections, respectively. Ultrasensitive detection of fluorescent nanobeads with high signal-to-noise ratio provided by a fluidically tuned excitation notch filter is demonstrated. In addition, reconfigurable filter response is demonstrated using both core index tuning and bulk liquid tuning. Notch filters with 43 dB rejection ratio and a record 90 nm tuning range are implemented by using different mixtures of ethylene glycol and water in the filter section. Moreover, absorber dyes and liquids with pH-dependent transmission in the filter channel provide additional spectral control independent of the waveguide response. Using both core index and pH control, independent filter tuning at multiple wavelengths is demonstrated for the first time. This extensive on-chip control over spectral filtering as one of the fundamental components of optical particle detection techniques offers significant advantages in terms of compactness, cost, and simplicity, and opens new opportunities for waveguide-based optofluidic analysis systems.