Miniaturized optical fiber couplers based on direct–jointing architecture: Loss improvement by a new space–sharing technique

Abstract

AbstractA miniaturized optical fiber directional coupler based on a new space‐sharing technique has been investigated. To obtain a miniaturized size, we propose a direct‐jointing technique, in which the optical fibers to be coupled are directly jointed without an intermediate of any other optical component. Moreover, an intrinsic excess loss of ‐0.0015 dB in the direct‐jointing architecture is theoretically possible for graded‐index multimode optical fiber systems.Instead of the conventional power‐sharing technique with a half‐mirror, we use a space‐sharing technique, in which the optical power is divided in space with a distributed digital reflectance (R = 1 or 0) mirror. The present method is advantageous in that it improves the loss characteristics, particularly at a 1:1 division ratio. The excess loss of the conventional half mirror coupler may be more than 2 dB, but the new technique produced a loss lower than 0.5 dB (at λ = 1.55 μm) in a test sample.