We demonstrate novel all-fiber and magnetic-field-free circulators based on Mach-Zehnder interferometers including so-called fiber null-couplers. Their low insertion loss makes them ideal tools for the transmission and processing of optically encoded quantum information. ©. Here, we present a solution to this issue by realizing low-loss (0. © 2024 The Author (s) View. 📦 For purchasing, use the RP Photonics Buyer's Guide for Faraday circulators. It provides an expert-curated supplier directory, buyer-focused technical background information, and structured selection criteria to support professional procurement decisions. The latter are directional couplers, whose splitting-ratio. An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next.