Abstract

Up to about a decade or more ago Circular Variable Filters (CVF) were a commercial optical component useful in the visible and infrared wavelength ranges and were being produced and sold by the US company Optical Coating Laboratory, Inc. The CVF was used as a monochromator and its advantage was in its ease of use for spectroscopy especially in remote sensing applications. Based on the idea of multilayer interference coating with linearly varying thickness on the circumference of a rotating wheel, it worked as a continuously variable center-wavelength narrowbandpass filter with 1-2% spectral resolution. One spin of the wheel placed on the optical path of a light beam provided a full scan in the wavelength range and allowed a detector to record a full spectrum in that range. Since then this component was discontinued and companies used old remaining stocks from previous production batches. CI is now reconstructing the technology to be able to produce the CVF again and is building new radiometers for new applications based on it. In this paper we review the history of the CVF and its use by CI and we provide some details on the characteristics of the CVF as planned and as preliminarily tested.

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