Reconfigurable or tunable metasurfaces are of great interest for adaptive multi-modal sensing and imaging. Phase change materials (PCMs) have been recently explored for reconfigurable optical devices such as spatial light modulators and metasurfaces. In this talk, we will present large-scale reconfigurable infrared metasurfaces consisting of greater than 30 million pixelated optical antennas integrated with PCM mesa structures over a 1cm x 1cm area.
Phase change materials (PCM) provide unique optical characteristics such as a dramatic change in optical refractive index greater than 1, not obtainable from conventional semiconductor optical materials such as Si and InP. Thus, the PCM is being explored to program and reconfigure optical devices to adapt to the sensing needs per environment. Also, the non-volatile nature of PCM devices offers its system integration without disturbing the sensing. Here, we report on a new solid-state optical modulator device with SbTe PCM operating in the infrared range and at cryogenic temperatures with excellent switching cycle reliability for the programming of PCM-based optical devices.
Phase change materials (PCM) provide unique optical characteristics, such as a dramatic change in optical refractive index <1, not obtainable from conventional semiconductor optical materials such as Si and InP. Thus, PCMs are being explored to program and reconfigure optical devices to adapt to the sensing needs per the environment. Also, the nonvolatile nature of PCM devices offers system integration without disturbing the sensing. An example of a PCM-based optical device can be a spatial light modulator (SLM) that enables a coded aperture imaging technique to extract spectral signature for remote detection and identification without platform motion. SLMs offer a way to carry out spectral imaging with reconfigurability, which allows signature detection against a spectrally cluttered background. Here, we report on a new solid-state optical modulator device with a SbTe PCM operating in the infrared range and at cryogenic temperatures with excellent switching cycle reliability for the programming of PCM-based optical devices.
A spatial light modulator (SLM) is a key device that enables a coded aperture imaging technique to extract spectral signature for remote detection and identification without platform motion. The SLMs offer a way to carry out spectral imaging with reconfigurability, which allows signature detection against a spectrally cluttered background. Liquidcrystal display (LCD) arrays and digital micro-mirror devices (DMDs) are used to implement the spatial light modulators, and there are shortcomings in infrared (IR) applications. Here, we report on a new solid-state SLM modulator device operating in the infrared range with SbTe-based phase change material. The SLM leverages a dramatic change (<2) in refractive index of SbTe phase change material within most of the IR bands, depending on their phase (amorphous versus crystalline).
We report GeTe-based phase change material RF switches with on-state resistance of 0.07 ohm*mm and off-state capacitance of 20 fF/mm. The RF switch figure-of-merit, Ron*Coff is comparable to RF MEMS ohmic switches. The PCM RF shunt and series switches were fabricated for the first time in a lateral FET configuration to reduce parasitics, different from the vertical via switches. In a shunt switch configuration, isolation of 30 dB was achieved up to 67 GHz with return loss of 15 dB. RF power handling was tested with ~10 W for series and 3 W for shunt configurations. Harmonic powers were suppressed more than 100 dBc at fundamental power of 1 W, for future tunable and reconfigurable RF technology.
Antennas collect radio waves and channel them into radio frequency (RF) transmission lines which direct the signals to circuits from which information can be demodulated and decoded. Glass, the most common portal between outside and inside environments, is clear at the visible part of the electromagnetic spectrum, and it is also relatively transparent to a large portion of the electromagnetic spectrum useful for radio wave communications. Since glass as a building material is used everywhere, it could be a readily accessible substrate upon which to mount or fabricate the antennas and RF electronics, but only if these circuit components are also transparent. In this paper, we present our development to date of glass RF circuits along two tracks: 1) transparent antennas and 2) graphene based active and passive circuit elements. Along the first track we have demonstrated antennas made from nanowire films capable of an optical transparency of 72% and sheet resistance of 4-5Ω/sq. Along the second track, we have in so far demonstrated graphene on glass field effect transistors with an fmax of 7 GHz, varactors with 1.4:1 tuning range, resistors with 3-70 kΩ, and capacitors from 13-860 pF. This is just the start; our plans are to increase the frequency and tuning ranges of the active and passive devices. Since graphene is inherently transparent at visible wavelengths, we ultimately would like to merge these two tracks to integrate active and passive RF circuitry with the antenna either directly on glass or as an applique put on glass, circuits which we’ve termed RF Glass®.
We are developing micro chemical sensor nodes that can be used for real time, remote detection and early warning of
chemical agent threats. The chemical sensors in our sensor nodes utilize GaN HEMTs (High Electron Mobility
Transistors) fabricated with catalytically active transition metal gate electrodes. The GaN HEMT chemical sensors
exhibit high sensitivity and selectivity toward chemical agent simulants such as DECNP (Diethyl cyano phosphonate),
and this is the first time that chemical agent simulants have been detected with GaN micro sensors. Response time of the
GaN HEMT sensor to a chemical species is within a second, and the maximum electronic response speed of the sensor is
~3 GHz. A prototype micro chemical sensor node has been constructed with the GaN sensor, a micro controller, and an
RF link. The RF sensor node is operated with a single 3V Li battery, dissipating 15 mW during the RF transmission with
5 dBm output power. The microcontroller allows the operation of the RF sensor nodes with a duty cycle down to 1 %,
extending lifetime of the RF sensor nodes over 47 days. Designed to transmit RF signals only at the exposures to
chemical agents and produce collective responses to a chemical agent via a sensorweb, the GaN micro chemical sensor
nodes seem to be promising for chemical agent beacons.
We present a prototype photodetector in which the built-in "tunneling structure" serves as an internal gain
mechanism for photon detection. Initial feasibility studies demonstrated that the new photon detector offers an optical
responsivity as high as 3000 A/W peaked at λ=1.3 μm at less than 1 V bias applied. The measurements were carried out
using a photospectrometer setup in a continuous mode at room-temperature. Very strong (> 1000) responsivity is also
measured from visible to SWIR even with a simple optical coupling scheme that utilizes very thin absorber layers in the
prototype devices. The dark current density is ~ 5×10-10 A/μm2 at the operating bias. Room-temperature NEP was calculated based on a shot noise measurement, yielding NEP of 4~ 5×10-15 W/Hz1/2 and D* of 2~3×1012 cmHz1/2/W,
peaked at a bias of 0.3 V at a fixed wavelength of λ=1.3 μm.
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