Abstract

Photonic couplers and switches, used in communication systems, are based on integrated optic devices. These devices are actually miniature interferometers and have a polarization sensitivity. To eliminate these limitation factors and insertion losses, it has been natural to examine the possible uses of the fiber links for coupling and switching of the optical signals. Coupling between adjacent fibers can be controlled by replacing the cladding with an active material and applying an external field to this modified region. The principle of using an active modified cladding to control the propagation characteristics within the fiber core has been discussed in previous work.¹,² In this paper, we present a novel structure of an all-fiber tunable coupler and switch. This is accomplished by twisting two uncladded sections of adjacent fibers together and using an electro-optic material as an active modified cladding. When the structure is exposed to an electromagnetic field, the index of refraction of the active material varies. This change in the boundary conditions of the fibers results in a change in the coupling coefficient between the twisted fibers. A device has been fabricated in which a nematic liquid crystal is employed as the electro-optic cladding. The response of the device to the external fields shows precise control of the coupling coefficient. Ferroelectric liquid crystals and solid electro-optic materials can be used for high-speed switching. This structure presents a new class of all-fiber devices and can be used in modulation and sensor applications.

© 1990 Optical Society of America