Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding

Abstract

Optical isolators and circulators are fundamental building block in photonic integrated circuits to block undesired reflections and routing light according to a prescribed direction. In silicon photonics, heterogeneous integration of magneto-optic garnet bonded on a pre-patterned silicon layer has been demonstrated to be an effective solution for manufacturing optical isolators and circulators for TM polarized light. However, most integrated semiconductor lasers emit TE polarized light, which indicates the need to find a reliable solution for this polarization. In this work, we demonstrated broadband optical isolators and circulators for TE polarized light based on heterogeneous bonding on the silicon photonics platform. To achieve this goal, an integrated adiabatic coupler and a broadband polarization rotator are designed and optimized. The nonreciprocal behavior is induced through an energy-efficient integrated electromagnet with a minimum power consumption of 3 mW. Two isolators/circulators are fabricated with small and large free spectral range, respectively. In the former case, an optical isolation ratio as large as 30 dB is measured at 1555 nm with an insertion loss of 18 dB, while for the broadband circulator an optical isolation larger than 15 dB is guaranteed over more than 14 nm (1.75 THz) for all port-combinations with an insertion loss between 14 dB and 18dB at 1560 nm. Finally, it has been theoretically shown that the insertion loss can be reduced below 6 dB with design and fabrication improvements. To the best of the authors' knowledge, the proposed integrated TE optical circulator is the first experimental demonstration of this device in silicon photonics.

Resonantly enhanced nonreciprocal silicon Brillouin amplifier

“…Moreover, though narrowband in comparison, the level of nonreciprocity demonstrated here (∼ 30 dB) is competitive with that achievable using integrated magneto-optic [43][44][45][46] or acousto-optic strategies [47,48]. While magneto-optic-based siliconphotonic isolator and circulator technologies are advancing steadily, they require complex fabrication techniques [43][44][45][46]. Acousto-optic strategies are also very promising; however, they have yet to achieve efficiencies necessary to produce optical isolation with low insertion losses [47,48].…”

Polarization-independent optical isolator in a Sagnac-type configuration

“…The major drawback of Rayleigh's optical isolators is to work in an optimum way only for one specific input light polarization that should be known in advance. The same is true also for most recent magneto-optics-based isolators developed in integrated photonics, where either the TM or the TE polarization is generally being addressed (see [2][3][4][5][6] and references therein).…”

Multi-channel swept source optical coherence tomography concept based on photonic integrated circuits

“…In fiber optical systems, low-loss optical circulators can be used to separate the forward and backward optical path. However, integrated optical circulators require complex fabrication steps, and even then they exhibit a limited operational wavelength bandwidth in current implementations [15,16]. Broadband PIC-based polarization beam splitters can be implemented without intricate fabrication steps in various waveguide materials [17].…”