Spectral measurement using IC-compatible linear variable optical filter

Abstract

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 mm 2 . 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.

An UV linear variable optical filter-based micro-spectrometer

“…Figure 3b shows a 4 pixels shift at each 1 nm wavelength shift, which is equivalent to a 0.5 nm spectral resolution. Spectral measurement using the LVOF, involves the design of collimator optics based on the equations mentioned earlier, capturing the raw data of pixels on the CMOS camera and using a signal processing algorithm to extract the spectrum of the light [6]. The spectrum of a Mercury lamp is to be measured with the current LVOF and is the subject of future work.…”

Mid- infrared uncooled sensor for the identification of pure fuel, additives and adulterants in gasoline

“…Blend octane (1) [4,6,11]. The fuel industry is constantly on the lookout for sensors to be used for insitu monitoring of fuel quality and adulteration detection.…”

“…These have huge potential in systems for chemical analysis by optical absorption, fluorescence and emission line characterization [1]. Such micro spectrometers offer significant advantages over existing instruments, including size reduction, small sample size, and fast data acquisition [2].…”

“…Another kind of adulteration practice is frequent in countries where bioethanol is currently used as a common biofuel, mixed with gasoline in its dehydrated form (Hydrated Ethyl Alcohol Fuel, usually known as HEAF). HEAF is commonly adulterated with methanol, as methanol and ethanol present similar physical and chemical properties, and the price of methanol is lower 1 Corresponding author. E-mail address: pilar.barreiro@upm.es (P. Barreiro).…”

Design and implementation of a sub-nm resolution microspectrometer based on a Linear-Variable Optical Filter

“…This paper covers different aspects for realization of such microspectrometers. Parts of this work, such as the initial idea [6,7] and the fabrication technique [8], have been published before. This paper covers all the design issues in detail, whereas the fabrication is summarized.…”