An apparatus that features an optical fiber with a core surrounded by a cladding, wherein at least one of the core and the cladding has a reduced thickness along an interval of the fiber to enlarge a modal field diameter of the guided mode in the fiber. A control layer is disposed on an external surface...http://www.google.de/patents/US6208798?utm_source=gb-gplus-sharePatent US6208798 - Variable optical attenuator with thermo-optic control
