Compact optical circulator based on a uniformly magnetized ring cavity

Abstract

We propose a new class of compact integrated optical circulators providing a large isolation level while maintaining a straightforward technological feasibility. Their layout is based on a nonreciprocal radial Bragg cavity composed of concentric magneto-optical rings. The circulator ports are standard rib waveguides, butt-coupled to the cavity by cutting through its outer rings. The device is specifically designed for operation in a uniform external magnetic field. Using a coupled-mode description of the complete cavity/waveguide-port system, we explore the rich behaviour of cavity circulators in presence of varying levels of direct port-to-port coupling. We demonstrate numerically a strongly miniaturized two-dimensional cavity circulator, with a total footprint of less than (10λ) 2 , achieving a 20-dB isolation level at telecom frequencies over a bandwidth of 130 GHz. The device is found to be very tolerant with respect to fabrication imperfections. We finish with an outlook on three-dimensional versions of the proposed nonreciprocal cavities.

Preparation of Bi₂Gd₁Fe₅O₁₂ magnetic garnet films showing Faraday rotation of 36.3 deg./µm on glass substrates by metal organic decomposition method

“…It was reported that with increasing the amount of Bi substitution for rare-earth element, FR of Bi:RIG becomes large [2]. Bi:RIG have been used for magneto-optical device elements in such as magnetoplasmonic structure [3,4], optical isolators [5], circulators [6], and magnet photonic crystals (MPCs) used in magneto-optic spatial light modulators (MOSLMs) [7]. Among them, bismuth substituted gadolinium iron garnet (Bi:GdIG) is one of the ferrimagnetic rate-earth iron garnets showing perpendicular magnetic anisotropy [8,9].…”

Preparation and Characterization of Bi substituted gadolinium iron garnet Films by Metal Organic Decomposition and their Dependence on Annealing Gases

“…Bi-substituted rare-earth iron garnets have long been known and received much attention because of their high magneto optical effects (high transparency and large Faraday rotation in near infrared region 1) which made these materials very attractive among all semi-transparent dielectrics for various fundamental investigations as well as practically usable materials for magneto-optical device elements such as optical isolators 2) , circulators 3,4) , printers 5) and MPC which is used in magneto-optic spatial light modulators (MOSLM) 6,7,8,9) . A single crystal garnet with perpendicular magnetic anisotropy and two polarizers have been used as a pixel element to switch the optical output depending on the up and down magnetization owing to Faraday effect in MOSLMs.…”

Optical three-port circulators made with ring resonators

“…A further reduction in size can be achieved by a resonance enhancement of the interaction between light wave and the magneto-optical active medium. There are concepts for four-port circulators using ring resonators coupled to two waveguides [4,5] and there are concepts for three-port circulators using photonic-crystal resonators [6][7][8][9]. For both concepts the footprint is comparable and is in the 10 μm range.…”

“…But there are no realistic 3D concepts proposed for photonic-crystal isolators so far. The vertical confinement in the photonic-crystal slab will in most cases not be achieved with the two-dimensional (2D) structures discussed in [6][7][8][9]. Magneto-optical ring resonators, on the other hand, have already been shown experimentally by bonding a garnet to a silicon-ring resonator [10] and by deposition of a garnet on a silicon ring with pulsed laser deposition [11].…”

“…Except for some details, which we explain below, the working principle for this device is now very similar to the photonic-crystal circulators described in [6][7][8][9]. The magneto-optical active material causes the resonance frequencies of the cw and the ccw traveling wave to split.…”