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.