of a microcavity (e.g. two mirrors, at least one formed using nonabsorbing dielectric layers), encapsulation (E.G. a substantially transparent dielectric such as silicon nitride (Si3N4) or silicon dioxide, or e.g. an epoxy or other material to protect various materials from environmental oxygen or humidity), or optical filtering (e.g. to allow one radiation 1000 band to pass and a second radiation