Depressed cladding fiber design for reducing coupling to cladding modes in fiber gratings

A waveguide, such as an optical fiber waveguide for guiding light waves, which can provide a strongly reflective grating (e.g., a Bragg grating) at a specified wavelength while maintaining very low losses at adjacent wavelengths. The waveguide includes a core, an inner cladding laterally surrounding the core, an outer cladding laterally surrounding the inner cladding, and a grating pattern. The core has a refractive index nco and a first transverse dimension 2A. The inner cladding has a width W and a refractive index nic. The outer cladding has a refractive index noc. The relation between the refractive indexes, nco> noc > nic and 0.5