Investigation of optical circular propagation in microfiber-based asymmetric Sagnac interferometer

Abstract

In this paper, we investigate and analyze the optical unidirectional transmission based on a tapered fiber-based asymmetric Sagnac interferometer. By carefully designing the asymmetric structure, there are the different coupling conditions and different intensities of multi-mode interferences in the Sagnac loop when the light enters from the different input ports. The maximal difference of the transmission spectra between the forward propagation and the backward propagation is up to 40.4 dB. Furthermore, by using as an extensible topological structure, two fiber Sagnac loops are arranged to realize the three-port circular propagation, showing the strict transmitting order in the three ports, along with the blocked propagation in the reverse order. Meanwhile, three fiber Sagnac elements are also arranged to achieve the four-port circular propagation, also along with the strict pass order. With ultra-compact size, wideband, and great extensibility, this proposed fiber device is competitive to be the attractive building blocks for the integrated photonic circuits.