Here, we present a solution to this issue by realizing low-loss (0. 81 dB), broadband (at least 50 GHz bandwidth) and high-extinction (up to 27 dB) circulators, based on Mach-Zehnder interferometers including so-called fiber null-couplers. The ABSTRACT optical circulator is one of the key devices in the optical add-drop modules (OADMs) used in wavelength-division multiplexing (WDM) technology, which finds applications in large-capacity long-haul telecommunications systems. The latter are directional couplers, whose splitting-ratio. generate a nonreciprocal phase shift (NRPS). An alternate design is to utilize a microring which significantly reduces the. Polarization-dependent Loss (PDL): The variation in insertion loss with respect to the polarization state of the input light. To minimize insertion loss and maximize isolation, circulator designers employ various materials and technologies, such as: Ferrite materials: These materials exhibit. Fiber optic circulators act as signal routers, transmitting light from an input fiber to an output fiber, but directing light that returns along that output fiber to a third port.
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