B.S.T.J. Briefs: A New Optical Fiber

B. S. T. J. BRIEF A New Optical F i b e r B y P . KAISER, E . A . J . MARCATILI, a n d S . E . MILLER (Manuscript received November 20, 1972) C u r r e n t l y t h e r e is s t r o n g interest in optical fibers for use as a t r a n s mission m e d i u m , analogous to t h e use of coaxial or wire pairs in t h e low-frequency region. M o s t work is d e v o t e d to a fiber s t r u c t u r e consisting of a c e n t r a l glass core s u r r o u n d e d by a cylindrical glass cladding h a v i n g a slightly lower index of r e f r a c t i o n . T h i s in t u r n requires t h a t t h e chemical composition of t h e core glass differs f r o m t h a t of t h e cladding glass, leading to undesired effects at t h e core-cladding i n t e r f a c e a n d p e r h a p s limiting t h e m i n i m u m fiber losses achievable. T h e N i p p o n Sheet Glass C o m p a n y a n d t h e N i p p o n Electric C o m p a n y t o g e t h e r h a v e developed a fiber (which t h e y call S E L F O C ) w i t h an index of r e f r a c t i o n decreasing parabolically f r o m t h e fiber axis to its o u t e r b o u n d a r y . T h i s fiber requires a c o n t i n u o u s v a r i a t i o n in chemical composition f r o m t h e fiber axis o u t w a r d , w i t h a t t e n d a n t complicat i o n s in t h e f a b r i c a t i o n process. A related guide requiring a film v e r y t h i n c o m p a r e d t o t h e w a v e l e n g t h has j u s t been r e p o r t e d . 1 T h e u n i q u e p r o p e r t y of t h e new fiber is t h a t a viable, h a n d l e a b l e t r a n s m i s s i o n m e d i u m is created by a s t r u c t u r a l f o r m t h a t uses only a single low-loss m a t e r i a l .