How is a Thin Film filter fabricated?（）

A.The glass core is doped with an Erbium in periodic segments of the fiber.

B.Layers of high index ?and low index ?material are deposited on a glass substrate.

C.Thin layers of silica glass are placed onto wafers to produce a prism-like effect.

D.Fiber is etched with an ultraviolet laser that is precisely spaced for specific wavelength filtering.