Design of a Broadband Fiber Optic Mode Coupler for Multimode Optical Coherence Tomography

In this paper, we propose an optical fiber-based broadband mode coupler for multimode coherence tomography (OCT) in the O-band (1.26–1.36 μm). The proposed device uses a tapered few-mode fiber (FMF) to lower effective index of selected higher-order mode, which can be phase matched fundamental single-mode (SMF). FMF and SMF are side polished reduce core-to-core separation achieve efficient coupling. Key design parameters such as tapering ratio FMF, core separation, length, coupling studied thoroughly. Higher-order modes will effectively coupled from sample arm OCT system. reflected signals separated into several using same before interfering with reference light, was not possible before. key component efficiently operation better signal collection efficiency improved penetration depth deep tissue imaging.