Single-photon Counting

A single-photon counting sensor for imaging trace chemical cloud. It involves a device called Single-photon Avalanche Diode (SPAD), shown below, capable of creating an avalanche of electrons by a single incident photon. A 2-d Focal Plane Array (FPA) of this SPAD is capable of imaging a large field of view of a chemical cloud.

Slide1Single-photon Avalanche Diode (SPAD) FPA for chemical sensing.

 

 

PhotonPicSingle-photon Avalanche Diode (SPAD) FPA for chemical sensing.

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Toxic Industrial Chemical Sensing (TICS)

A toxic industrial chemical sensor (TICS). It's designed to sense common toxic industrial chemicals such as ammonia, chlorine, hydrochloric acid, acetic acid, hydrogen sulphide, and hydrogen fluoride, The chart below is showing their IR absorption bands, not considered particularly lethal, but can easily be acquired, concentrated, and planted in public food, water, and urban environments to pose a significant threat to the general public.

ToxicPic1IR absorption bands of TICS within the atmospheric windows

 

 

A sensor on a micro-chip using an array of the MFPTF cavities, each tuned to a specific wavelength to sense a specific chemical. It's capable of detecting of a wide range of chemicals simultaneously.

ToxicPic2TICS array of MFPTF for sensing industrial toxic and pollution chemicals.

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Large-format Imaging (LFI)

A large-format imaging sensor with multi-mega pixels forming the Focal Plane Array (FPA), made for smart phones and digital cameras, such as the FPA with 30,000x5,000 (150 mega) pixels made by Gpixel. Target detection from a 35k km orbit is shown below using step staring of a single 150-mega FPA to cover the whole earth to achieve a linear resolution (or Instantaneous Field of View -IFOV,) of less than 1 km –suitable for search of distressed ships, aircraft and other targets at sea.

LargePic150-mega sensor for search and rescue from a geosynchronous orbit.

 

The figure of merit for assessing this sensor performance is the NEP (Noise Equivalent Power – the target's emitted power in watt). This analysis shown in the figure below depicts that aircraft bodies can be easily detected with optics no larger than 5 cm in diameter and a detectivity D* no higher than 1010 cm-Hz1/2/W, which is readily available in the Si photodiodes of the 150-mega sensor.

Slide1Figure of merit (NEP) of the 150-mega sensor for search and rescue missions.

 

 

 

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Un-Cooled Ultra-High Sensitivity Imaging

In the annals of infrared detection and imaging, heightened sensitivity and noise reduction is usually accompanied by cooling and/or purifying the sensing elements. Both the photonic (such as HgCdTe and superlattices) and microbolometer (such as semiconductors) detectors need the required cooling and material purity which incurs high cost and structural complexity, both are undesirable for portable military systems and even more so for commercial systems.

However, our Micro Fabry-Perot Interferometry (MFPI) based detectors are capable of extraordinarily high sensitivity either in the uncooled or cooled state, as illustrated in the graph below on detectivity vs. temperature. This graph shows that the sensitivity of our MFPI detector is superior to all other detectors, except at extremely low temperatures. This is due primarily to the exploitation of interferometry as the sensing mechanism which, unlike conventional detectors, is independent of material purity.

Detectivity of our MFPI detector compared to other common detector types

Detectivity of our MFPI detector compared to other common detector types (click to enlarge)

 

For un-cooled sensors or FPAs, such as bolometers and our MFPI sensor, employed for thermal imaging, the conventional Figure of Merit describing the sensor's ability to image the minute temperature changes in a thermal scene or target is the so-called Noise Equivalent Delta Temperature (or NEDT). This NEDT is usually plotted against the thermal conductance of the support that isolates the sensors thermally from its surroundings as shown in the figure below. The graph highlights the high NEDT performance of our MFPI sensor compared to the conventional bolometer sensors.

uncooled2

Comparison of NEDT performance. (click to enlarge)

 

 

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Sub-mm-wave Imaging

We have developed Focal Plane Arrays (FPAs) using micro antenna structures as sensing elements responding to waves with wavelengths greater than 100 micron in the sub-millimeter wave (or teraHZ) domain for imaging objects behind walls, embedded in debris or under human skin. This technology leads to advanced imaging sensors for through-wall surveillance in fighting terrorists, through-skin imaging of foreign objects embedded in human tissue or through clothing to detect hidden narcotics, weapons or alcohol.

submmwave1

 Frequency vs. Relative Radiance. (click to enlarge)

 

Covering sub-mmw spectral ranges

  • Spectral coverage: from 100 to 300 micron (TeraHz)
  • Technology: Micro Antenna Array
  • Frame rate: 30 Hz- 1,00 Hz
  • Array size: 128x128 – 256x1256
  • Operating temperature: 300 K
  • Applications: Thru-clothe, thru-wall imaging for law enforcement
 

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Hyper-Spectral & Multi-Spectral Imaging

Hyper-Spectral Imaging Focal Plane Arrays (HSI-FPA) have been developed for imaging in the ultra-violet (UV), 0.200 - 0.320 micron in wavelength, to the very long wave infrared (VLWIR), 8-16 micron in wavelength. The true potential of this newly developed and innovative technology is yet to be fully realized.
A diagram of the HSI-FPA is shown below.

hyperspectral1

An array of MFPI (click to enlarge)

It's most innovative aspects are (1) high sensitivity, (2) hyper-spectral tunability, (3) small pixel size, (4) high spatial resolution, and (5) compactness. It accomplishes this by using three separate arrays: a tuner Micro Fabry-Perot Inteferometer (MFPI) array for hyper-spectral tuning, a sensor MFPI array for sensing tuned bands, and a silicon detector array for detecting the visible beam.

The next figure is an example of an array of Micro Fabry-Perot Inteferometers (MFPIs) fabricated entirely on silicon by micromachining.

hyperspectral2b

An example of a micromachined MFPI structures.
(click to enlarge)

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