Gradient Filters

Graduated filters are used to achieve a defined stepless change in transmission wavelength over a given area.

Fig.1:Gradient filter, 8 x 10 mm

LAYERTEC manufactures dielectric graduated filters from single pieces to small series. The lateral characteristics, the spectral properties and the geometric dimensions can be adapted to the customer’s specifications. Complex systems with small geometric dimensions are developed and produced.

The example shows a graduated line filter from 450 – 800 nm with a linear displacement of approx. 9 mm. This makes it possible to build miniaturized spectrometers in combination with inexpensive CCD chips, for example.

Fig.2:

a)Transmittance of a multiple line filter

b)Transmittance of a gradient filter

For spectral calibration of the sensor (consisting of a graduated filter and the CCD chip), we produce multiple line filters on request. Depending on the task, line spacing and line width can be varied. If necessary, a spectral range that is too wide must be covered with two multiple line filters. The spectral position of the transmission maxima is determined to <1 nm accuracy.