Highly efficient fiber Bragg grating spectrometer fabricated with violet and near-infrared femtosecond laser pulses and the phase mask technique

All-fiber visible spectrometers with a sub-nanometer resolution and record-high light outcoupling (70%) are fabricated using violet (400 nm) and near-infrared (800 nm) femtosecond laser pulses and the phase mask technique. The spectrometers are based on highly localized uniform Bragg gratings produced by tightly focusing the femtosecond pulses into the core of visible single-mode fibers. The unique nanoscale morphology of the resultant Bragg gratings ensures very strong outcoupling of light from the fiber, while bending of the fiber provides the focusing capability to define an efficient all-fiber spectrometer.