Thin Film Technology Based Micro-fourier Spectrometer

A novel Fourier spectrometer using thin film technology was developed. The spectrometer based on a semi transparent thin film detector in combination with a tunable micro machined mirror. The semi transparent detector is introduced into a standing wave created in front of the mirror to sample the profile of the standing wave. Varying the position of the mirror results in a shift of the phase of the standing waves and thus in a change of the optical generation profile within the semi transparent detector. The active region of the sensor (thickness ⋅ absorption) is thinner than the wavelength of the incoming light, so that the modulation of the intensity results in a modulation of the overall photocurrent. The spectral information of the incoming light can be determined by the Fourier transformation of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of 1D and 2D arrays of spectrometers combining medium range spectral resolution with medium range spatial resolution. The novel device is filling the gap between solid-state camera technology with only three-color channels (red, green and blue) but high spatial resolution on one hand and precision spectrometers with high spectral resolution but no spatial resolution on the other hand. An analytical optical model of the spectrometer was applied to evaluate different detector concepts. The model was used to study the performance of different device designs regarding the spectral resolution of the spectrometer, the spectral range and the linearity of the response. The calculations will be compared with experimental results of semi transparent amorphous silicon detectors.