A method that significantly increases the detection efficiency of filter array-based spectral sensors is proposed. The basic concept involves a wavelength-dependent redistribution of incident light before it reaches the filter elements located in front of the detector. Due to this redistribution, each filter element of the array receives a spatially concentrated amount of a pre-selected and adjusted spectral partition of the entire incident light. This approach can be employed to significantly reduce the reflection and absorption losses of each filter element. The proof-of-concept is demonstrated by a setup that combines a series of consecutively arranged dichroic filters with Fabry–Perot filter arrays. Experimentally, an efficiency increase by a factor larger than 4 compared to a reference system is demonstrated. The optical system is a non-imaging spectrometer, which combines the efficiency enhancement module with the filter arrays, is compact ( 17.5 m m × 17.5 m m × 7.8 m m ), and integrated completely inside the CCD camera mount.

This contribution presents the design and implementation of a compact and robust Echelle-inspired cross-grating spectrometer which is arranged as a double pass setup. This allows use of the employed refractive elements for collimation of the incoming light and, after diffraction at the reflective crossed diffraction grating, for imaging the diffracted light onto the detector. The crossed diffraction grating combines the two dispersive functionalities of a classical Echelle spectrometer in a single element and is therefore formed by a superposition of two blazed linear gratings which are oriented perpendicularly. The refractive elements and the plane grating are arranged in a rigid objective group which is beneficial in terms of stability and robustness. The experimental tests prove that the designed resolving power of more than 300 is achieved for the addressed spectrum ranging from 400 nm to 1100 nm by using an entrance pinhole diameter of 105 µm. The utilization of a single mode fiber increases the resolving power to more than 1000, but leads to longer acquisition times.