Gaussian bandpass filter with tunable bandwidth and center wavelength based on diffraction grating and spatial mode coupling.

We propose a tunable Gaussian bandpass filter based on a diffraction grating and spatial mode coupling, of which the bandwidth and center wavelength can be easily and independently adjusted by the location and angle of the grating, respectively. In an experimental demonstration for proof of principle, the center wavelength was tuned from 775 to 805 nm according to the bandwidth of the light source used, but note that there is no particular limitation of the tuning range. In addition, the bandwidth was tuned in this work from 0.79 to 4.65 nm, but this can be changed as well by modifying the grating and experimental settings. The particular advantage of this method is that it involves no significant change in peak transmittance depending on the center wavelength and bandwidth.