![]() ![]() In order to overcome such limitations of the circulator designs reported in the literature, we suggest in this paper a compact PhC-based three-port circulator that can operate at the 1550 nm wavelength and, most importantly, whose operation does not require an external DC magnetic field. Numerical calculations of the suggested circulator show that its operating bandwidth around the 620 nm wavelength is about 170 GHz for the 20 dB isolation level. A moderate static external magnetic field (<0.5 T) is required for the BIG saturation and the off-diagonal element g of the BIG permittivity tensor in the order of 0.1 is not feasible at the 1550 nm wavelength, but only at shorter ones (around 620 nm). The presented design is based on a PhC made of a triangular lattice of holes drilled in a BIG film in which three waveguides and a multi-ring resonator are inserted. Since the electromagnet demands an electric current for its operation, additional issues beyond the size of the magnetizing element, such as current supply and Joule heating, can hinder the utilization of the circulator in integrated optical circuits.Īnother optical circulator design is suggested in. The external DC magnetic field required for the magnetization of the Ce:YIG film is provided by an electromagnet based on a gold microstrip coil. The operating bandwidth of the device around the 1550 nm wavelength calculated from computational simulations is about 5 GHz (taking into consideration the 9 dB isolation level). The waveguides and the ring resonator are fabricated on a conventional silicon on insulator (SOI) wafer and a MO film made of a cerium-substituted yttrium iron garnet (Ce:YIG) is bonded on the silicon ring resonator. In, a four-port circulator comprising a ring resonator coupled to two waveguides for operation at the 1550 nm wavelength is suggested. The BIG thin film requires an external magnet to keep its magnetic domains saturated and the suggested design is feasible only at the 633 nm wavelength, with an estimated 213 GHz bandwidth for the 30 dB isolation level. In this case, three waveguides and one resonator are inserted in a photonic crystal made of a triangular lattice of holes etched in a bismuth iron garnet (BIG) film. For example, a three-port circulator based on a photonic crystal (PhC) structure is presented in. These magnetizing elements are bulky and their utilization does not favor the design of circulators with a reduced footprint for optical communication systems with high integration density. Otherwise, the magnetic domains are randomly oriented and the MO effect is weakened. In order to provide an useful magneto-optical activity, the material must have its magnetic domains aligned by an external magnetizing element, like a permanent magnet or an electromagnet. Ĭonventional optical circulator designs referred to in the literature are based on the reciprocity breaking caused by the application of a static magnetic field to a material with magneto-optical (MO) properties. ![]() ![]() Nonreciprocal devices, like circulators and isolators, can be used to mitigate the effect of such reflections by absorbing or routing them to a matched load. ![]() The operation of signal sources, like LASERs or LEDs, in an optical communication system is subject to instabilities caused by parasitic reflections arising from unmatched loads connected to the system. Since its operation does not require an electromagnet or a permanent magnet, the suggested circulator is much more compact, being able to reach footprints in the range of three orders of magnitude smaller, when compared to other circulator designs referred to in the literature and the presented results can be useful for the design of other nonreciprocal devices with reduced dimensions for optical communication systems. Two- and three-dimensional simulations of the device performed with full-wave electromagnetic solvers based on the finite element method demonstrate that, at the 1550 nm wavelength, the insertion loss, isolation, and reflection levels are equal to or better than −1 dB, −14 dB, and −20 dB, respectively. By maximizing the incorporation of europium to its molecular formula, the magneto-optical material can remain in the saturated magnetic state even in the absence of an external DC magnetic field. A three-port circulator for optical communication systems comprising a photonic crystal slab made of a magneto-optical material in which an magnetizing element is not required to keep its magnetic domains aligned is suggested for the first time. ![]()
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