Low insertion-loss, high extinction ratio optical amplitude modulation using two beam interference into single-mode fibers

Abstract

Optical modulation components are widely used in optical telecommunications. These devices allow signals to be coded using an optical field prior to being transmitted through fiberoptic networks [1]. In a previous publication, we have shown that by launching the central fringe of an interference pattern of two Gaussian beams into a single-mode fiber (SMF), it is possible to spatially redistribute the optical intensity to achieve better mode matching between the input light and the SMF and obtain optical coupling efficiencies close to 97% [2]. In this paper, we show theoretically and experimentally that the two-beam optical interference approach when used to modulate continuous wave optical signals can yield insertion-losses much lower than the 9 dB commonly attained by other Mach-Zenhder modulators [3] or the 3.6 dB obtained with electro-absorption modulation modules [4]. Our approach consists of spatially shifting an optical interference fringe across the input cross section of a SMF and taking advantage of the high (resp., low) coupling efficiency of the central (resp. first dark) fringe into the SMF.