A micro Fabry-Perot interferometer (MFPI) cavity, formed by two parallel mirrors sandwiching a dielectric medium, which senses an incident IR by detecting the intensity change of a near IR (NIR) inserted into the cavity medium.This cavity creates several innovative MFPI devices with many applications:
- MFPI Focal Plane Array (FPA) for IR Imaging: designed with a 2-dimensional (2-d) array of MFPI cavities to image IR, as shown in Fig.1(a). Its sensitivity vs. temperature is shown in Fig.1(b).
- MFPTF (Micro Tunable Filter) Array: designed with a 2-d array of cavities each made tunable to filter a broad IR beam into a desired narrower band, as shown in Fig.2(a) and Fig.2(b).
- MFPI FPA for Hyperspectral Imaging: designed with a 2-d array of cavities shown in Fig.3, each tuned to a specific waveband for detection.
- MFPTF Array for Hardware-in-the-loop simulation (HWILS): designed to produce dynamic visible to long wave IR (LWIR) scenes for testing complex IR sensors, as shown in Fig.4.
- MFPI FPA for Space:
MFPI Focal Plan Array (FPA) for IR Imaging
Our first product is a MFPI FPA, shown in Fig.1, designed to image IR by allowing the incident IR power to change the intensity of a secondary NIR beam deliberately injected into the FPA cavity. This change is then easily detected by an ordinary Si photodiode, whose readout circuit is shown in Fig.1(a). The FPA is fabricated on a Si substrate, making each cavity into a thermal bolometer that's thermally isolated from its surroundings, giving it's high sensitivity to detect IR without cooling, as shown in Fig.1(b) – showing its sensitivity vs. temperature, contrasting with other conventional FPAs.
MFPTF (Micro Tunable Filter) Array
Our second product is a micro Fabry-Perot tunable filter (MFPTF) array, made so that each cavity can be tuned independently to transmit a specific waveband, as shown conceptually in Fig.2(a) and Fig.2(b), showing the IR transmitted intensity (I) is highly dependent on the reflectivity (R) of the mirrors.
MFPI FPA for Hyperspectral Imaging
Our third product is a hyperspectral MFPI FPA shown in Fig.3. Each pixel of this FPA contains two MFPI cavities, one on top of the other, made to be thermally isolated. The top cavity is a tuner, like the pixel of the MFPTF shown in Fig.2, while the bottom one is an IR sensor, like the pixel shown in Fig.1. Its operation is such that each pixel will sense a different wavelength determined by the spectral tuning of that pixel.
MFPTF Array for Hardware-in-the-loop simulation (HWILS)
Our fourth product is a scene-generator array using a MFPTF array, shown in Fig.4, to generate an IR scene. This product is a set of four MFPTF arrays forming a HWILS (hardware-in-the-loop simulation) system to project four dynamic scenes, each in a different spectral region, for testing complex IR sensors. Each array will project to the sensor under test a specific scene at a certain waveband by illuminating that array with a suitable laser source.
MFPI FPA for Space
High sensitivity without cooling is the MFPI FPA's most attractive feature for target detection from space. A simple analysis of a figure of merit for assessing its ability to detect targets from a geosynchronous orbit is NET (Noise Equivalent Target intensity).
Plotting NET vs DO for different D*, we can see the size DO needed to detect high intensity targets when our MFPI sensor has a D* of about 109 cm-Hz1/2/watt. And to detect cold-body targets we need a higher D* and larger optics, as depicted in Fig.5's violet-shaded region.
