Spectral measurement using IC-compatible linear variable optical filter

This paper reports on the functional and spectral characterization of a microspectrometer based on a CMOS detector array covered by an IC-Compatible Linear Variable Optical Filter (LVOF). The Fabry-Perot LVOF is composed of 15 dielectric layers with a tapered middle cavity layer, which has been fabricated in an IC-Compatible process using resist reflow. A pattern of trenches is made in a resist layer by lithography and followed by a reflow step result in a smooth tapered resist layer. The lithography mask with the required pattern is designed by a simple geometrical model and FEM simulation of reflow process. The topography of the tapered resist layer is transferred into silicon dioxide layer by an optimized RIE process. The IC-compatible fabrication technique of such a LVOF, makes fabrication directly on a CMOS or CCD detector possible and would allow for high volume production of chip-size micro-spectrometers. The LVOF is designed to cover the 580 nm to 720 spectral range. The dimensions of the fabricated LVOF are 5×5 mm2. The LVOF is placed in front of detector chip of a commercial camera to enable characterization. An initial calibration is performed by projecting monochromatic light in the wavelength range of 580 nm to 720 nm on the LVOF and the camera. The wavelength of the monochromatic light is swept in 1 nm steps. The Illuminated stripe region on the camera detector moves as the wavelength is swept. Afterwards, a Neon lamp is used to validate the possibility of spectral measurement. The light from a Neon lamp is collimated and projected on the LVOF on the camera chip. After data acquisition a special algorithm is used to extract the spectrum of the Neon lamp

Compact Hyperspectrals

Numerous Hyperspectral Imagers have been launched or are being built for resource management, monitoring anthropogenic effects on the troposphere gases, and for defense applications. Payloads such as Hyperion, EnMAP, HyspIRI, and SCHYAMACHY are instruments with mass in excess of 100 Kg. Technologies recently developed in precision manufacturing of aspherical mirrors, detectors, and spectral filters allow to shrink a hyperspectral instrument in an envelope that will fit on a small satellite, or even in a CubeSat. The reduction of mass, volume, and power is not the only problems to be solved to successfully use a hyperspectral on board of a small satellite. The amount of data acquired over one orbit can be as high as 1 TB (terabyte). To store and download the data can be unmanageable tasks for the resources of a small satellite. The reduced mass and volume of a compact hyperspectral comes at the expenses of a decreased signal to noise ratio. Can digital image processing and the knowledge acquired with the hyperspectral already in orbit help to compress the data to a manageable size? What type of information can be extracted from a compact hyperspectral? The paper describes the results obtained with the PhytoMapper, a technology demonstrator of a Compact Hyperspectral Instrument recently developed. The instrument fits in a volume of approximately 15 cm^3 (6 cubic inches) and has a mass of approximately 2 Kg. The instrument has a spectral resolution of 10nm, a field of view 34 degrees, and 2400 spectral bands. If flown on a 600km polar orbit, it will provide 100m spatial resolution and 3 days revisit time. The work presents the performance measured in the lab and the analyses performed to assess what type of mission objectives are achievable with this instrument. Further work has been done to push the envelope of a Hyperspectral within a CubeSat. A micro-telescope with a very aggressive optical design has been built and tested. The paper gives an overview of the performance that can be achieved with this extreme downscaled hyperspectral instrument and what, in the view of the Authors, can be the possible applications. A roadmap from the current technology status to the in-flight demonstration is finally presented