Application Note: Filter Bandwidth Definition

The WaveShaper family of Programmable Optical Processors allow creation of user-customized filter profiles over the C- or L- band, providing a flexible tool for industrial or research laboratories. Bandpass filter profiles can be created with a bandwidth ranging from 10 GHz to 5 THz,  in 1 GHz steps. However, upon measuring the spectral response of the filter, users can be confused by the bandwidth definition, which conforms to neither a full-width half-maximum (FWHM) nor a 1/e measurement. Furthermore, an inspection of the shape of a nominally flat-top filter shows that there is a finite slope to the roll-off edge of the filter. This can limit the adjacent channel extinction, particularly for very narrow filter bandwidths. What does the specified bandwidth refer to – and is it constant for all devices and channels?

This application note aims to provide the reader with an understanding of how the Finisar WaveShaper Programmable Optical Processor can generate spectral filters that are defined as having a bandwidth, B. First, a theoretical treatment of the filter shape is presented, with a prediction of how the filter bandwidth should be specified. Second, experimental results are shown which confirm the theoretical analysis. Finally, these findings are summarized and clearly stated for the reader.

To download a copy of the Filter Bandwidth Definition Application Note, please click on the thumbnail image below.

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