Patent ID: 8797540

Claim:
An optical device comprising: a fiber Bragg grating comprising a substantially periodic refractive index modulation along a length of the fiber Bragg grating, wherein the fiber Bragg grating has a power transmission spectrum as a function of wavelength comprising a plurality of local transmission maxima, the local transmission maxima each having a maximum power at a transmission peak wavelength, the fiber Bragg grating having a group index spectrum as a function of wavelength; and a narrowband optical source in optical communication with a first optical path and a second optical path, the narrowband optical source configured to generate light, the device configured to split the light into a first portion and a second portion, the first portion transmitted along the first optical path extending along and through the length of the fiber Bragg grating at a group velocity, wherein the light has a wavelength at or in the vicinity of a wavelength at which one or more of the following quantities is at a maximum value: (a) the product of the group index spectrum and a square root of the power transmission spectrum, (b) the slope of a product of the group index spectrum and one minus the power transmission spectrum, and (c) the slope of a product of the group index spectrum and the power transmission spectrum.