An electrically-tunable liquid crystal lens coupler for the fiber communication systems

Abstract

In this study, we demonstrated an electrically tunable lens coupler for both variable optical attenuation (VOA) and polarization selection. This coupler consists of a liquid crystal (LC) lens sandwiched between two GRIN lens. A GRIN lens is used to couple the light into the single mode fiber, and a LC lens is used to electrically manipulate the beam size of light. It is known that the lens power of a LC lens is tunable with high polarization sensitivity. Then, as the applied voltage on the LC lens is zero, the incident light is focused due to GRIN lens and coupled into the fiber. On the other hand, the beam size of the transformed e-ray becomes larger because the lens power of a LC lens for the e-ray decreases with the increase of the applied voltage. This results in the decrease of the coupling efficiency, and the optical power coupled into the fiber is smaller. This lens coupler for the e-ray functions as a VOA due to a continuous optical attenuation. On the contrary, the lens power of this LC lens for the o-ray does not vary because of optical anisotropy of the LC layer, and then the coupling efficiency for the o-ray remains high. For an arbitrary polarized incidence, this tunable lens coupler acts as a broadband polarizer for the fiber systems. The polarization dependent loss is larger than 30 dB and the switching time is around 1 second.