What is FBG? An in-fibre Bragg grating is constructed by varying the refractive index of the core lengthwise along the fibre. Light of the specified wavelength traveling along the fibre is reflected from the grating back in the direction from which it came. Wavelengths which are not selected are passed through with little or no attenuation
What is GRIN lenses GRIN lenses are short cylindrical lengths of glass with a graded refractive index: the index decreases with the square of the distance from the axis of the lens. GRIN lenses are very similar to graded index fibre and are sometimes called SELFOC lenses