Phase-shifted chirped volume Bragg gratings.

A new, to the best of our knowledge, type of tunable narrowband optical filter is demonstrated. The design utilizes a phase-shifted volume Bragg grating (VBG) with a chirped Bragg period encoded monolithically in photo-thermo-refractive (PTR) glass. The grating output is tunable in wavelength through both angular and spatial translation. The relationships between chirp rate, diffraction efficiency, and bandwidth are discussed. The fabricated gratings have transmission peak bandwidths ranging from 30 to 146 pm in the 1 μm spectral region, peak transmission up to 91%, tuning ranges of several nanometers, and resonant group delay associated with the phase-shift transmission.