Publications

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Epsilon-near-zero (ENZ) modes provide a new path for tailoring light-matter interactions at the nanoscale. In this paper, we analyze a strongly coupled system at near-infrared frequencies comprising plasmonic metamaterial resonators and ENZ modes supported by degenerately doped semiconductor nanolayers. In strongly coupled systems that combine optical cavities and intersubband transitions, the polariton splitting (i.e., the ratio of Rabi frequency to bare cavity frequency) scales with the square root of the wavelength, thus favoring the long-wavelength regime. In contrast, we observe that the polariton splitting in ENZ/metamaterial resonator systems increases linearly with the thickness of the nanolayer supporting the ENZ modes. In this work, we employ an indium-tin-oxide nanolayer and observe a large experimental polariton splitting of approximately 30% in the near-infrared. This approach opens up many promising applications, including nonlinear optical components and tunable optical filters based on controlling the polariton splitting by adjusting the frequency of the ENZ mode.

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We report on the development of single-frequency VCSELs (vertical-cavity surface-emitting lasers) for sensing the position of a moving MEMS (micro-electro-mechanical system) object with resolution much less than 1nm. Position measurement is the basis of many different types of MEMS sensors, including accelerometers, gyroscopes, and pressure sensors. Typically, by switching from a traditional capacitive electronic readout to an interferometric optical readout, the resolution can be improved by an order of magnitude with a corresponding improvement in MEMS sensor performance. Because the VCSEL wavelength determines the scale of the position measurement, laser wavelength (frequency) stability is desirable. This paper discusses the impact of VCSEL amplitude and frequency noise on the position measurement.

We present all-dielectric 2D and 3D metamaterials that are monolithically fabricated from III-V semiconductor nanostructures. The active/gain and high optical nonlinearity properties of the metamaterials can lead to new classes of active devices.

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We experimentally demonstrate efficient third harmonic generation from an indium tin oxide nanofilm (λ/42 thick) on a glass substrate for a pump wavelength of 1.4 μm. A conversion efficiency of 3.3 × 10-6 is achieved by exploiting the field enhancement properties of the epsilon-near-zero mode with an enhancement factor of 200. This nanoscale frequency conversion method is applicable to other plasmonic materials and reststrahlen materials in proximity of the longitudinal optical phonon frequencies.

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InPSb and InAsPSb have been investigated for use as absorber materials in GaSb-based n-type/barrier/n-type (nBn) detectors with cutoff wavelengths shorter than 4.2 μm. The growth temperature window for high-quality InPSb lattice-matched to GaSb by molecular beam epitaxy is approximately 440-460 °C. InPSb films with thicknesses greater than approximately 1 μm or films grown outside this temperature window have high densities of large defects, with films grown at lower temperatures exhibiting evidence of significant phase separation. In contrast, InAsPSb films can be grown with excellent surface morphologies and no apparent phase separation over a wide temperature range. InAsPSb samples with low-temperature photoluminescence between 3.0 and 3.4 μm and lattice mismatch of less than 1 × 10-3 have been grown, although both photoluminescence and x-ray diffraction data exhibit peak splitting indicative of compositional nonuniformity. AlAsSb-barrier nBn detectors with InPSb and InAsPSb absorbers have been fabricated. At 160 K, InPSb-absorber devices have a photocurrent responsivity edge at approximately 2.8 μm and a dark current of approximately 1.4 × 10-7 A/cm2, and InAsPSb devices with responsivity edges of 3.1-3.2 μm have a dark current of 2.3 × 10-8 A/cm2. Both InPSb and InAsPSb devices require significant reverse bias for full photocurrent collection at low temperature, suggesting the existence of an undesirable valence band energy discontinuity. The temperature dependence of dark current indicates that it is dominated by a mechanism other than generation in the undepleted absorber region. © 2013 American Vacuum Society.

We report on the development of 850-nm high-speed VCSELs optimized for low-power data transmission at cryogenic temperatures near 100 K. These VCSELs operate on the n=1 quantum well transition at cryogenic temperatures (near 100 K) and on the n=2 transition at room temperature (near 300 K) such that cryogenic cooling is not required for initial testing of the optical interconnects at room temperature. Relative to previous work at 950 nm, the shorter 850-nm wavelength of these VCSELs makes them compatible with high-speed receivers that employ GaAs photodiodes. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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We report the demonstration of a fully micro-fabricated vertical-external-cavity surface-emitting laser (VECSEL) operating at wavelengths near 850 nm. The external-cavity length is on the order of 25 microns, and the external mirror is a dielectric distributed Bragg reflector with a radius of curvature of 130 microns that is micro-fabricated on top of the active semiconductor portion of the device. The additional cavity length, relative to a VCSEL, enables higher output power and narrower laser linewidth, and micro-fabrication of the external mirror preserves the manufacturing cost advantages of parallel lithographic alignment. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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