The characteristics of a tunable wavelength filter in a-SiC:H multilayered stack p-i'i-n graded cells are studied both theoretically and experimentally. Three different architectures are tested for proper fine tuning of the spectral sensitivity. The simplest configuration is a two terminal p-i-n photodiode where the active intrinsic layer is a double layered a-SiC:H/a-Si:H thin film. In the others the active device consists of a p-i'(a-SiC:H)-n / p-i(a-Si:H)-n heterostructures where the doped layers can have high or low conductivities. The spectral analysis of the device is performed under different optical and electrical applied bias and frequencies. Results show that, depending on the architecture and time window used, the device acts as an optical filter, an amplifier or a multiplexer /demultiplexer for optical signal processing, wavelength conversion, signal demultiplexing, and pattern recognition. A theoretical analysis supported by numerical and electrical simulations is presented. The analysis uses simple phototransistor and photodiode equations to explain the response of the device under different optical signals, and to compare the generated photocurrent with the experimental data.