Contact FiberFinHard Clad Silica Fiber Hard Clad Silica Fiber POF Specifications Graded Index Fiber PMMA Fiber Perflourinated Fiber Step Index Fiber Mitsubishi SI Fiber Ashi Sojitz SI Fiber Toray SI Fiber Hard Clad Silica Fiber OFS Fiber Specialty Fiber Holey Fiber Hard Clad Silica Fiber HCS POF Plastic Optical Fiber that has a silica core covered with a hard polymer to help protect the fiber from damage that can occur in harsh environments. Hard clad silica is also known commercial in fiber optics as its abbreviation, HCS.