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We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.

We propose an approach for the design of resonant cavities employed in magnetophotonic crystal (MPC) circulators and isolators. Starting from the analysis of a model circularly symmetric cavity, we show how to obtain a significant splitting of the eigenfrequencies of the two counterrotating cavity modes without introducing subdomains magnetized in opposite directions. Using the multiple-scattering method extended to handle uniaxial gyrotropic materials, we demonstrate numerically an MPC circulator working in a uniform external magnetic field.

The design, fabrication, and characterization of an amplifying transverse magnetic ͑TM͒-mode optical waveguide isolator operating at a wavelength of 1300 nm are presented. The magneto-optical Kerr effect induces nonreciprocal modal absorption in a semiconductor optical amplifier with a laterally magnetized ferromagnetic metal contact. Current injection in the active structure compensates for the loss in the forward propagation direction. Monolithic integration of this optical isolator configuration with active InP-based photonic devices is straightforward. An optical isolator allows to avoid one of the main noise sources in an optical communication system by blocking optical feedback in the laser source. Current commercial isolators are bulk components requiring collimating lenses and expensive alignment techniques when applied in a laser diode package. Development of an integrated laser-isolator system is highly desirable as it would reduce cost and size and enhance mechanical and thermal stability. The cost reduction of a laser diode package would be the largest with directly modulated lasers, operating at 1300 nm. Traditional research focuses on applying ferrimagnetic garnets to induce nonreciprocity. 1 The interest in this class of materials comes from their unique combination of low optical loss at telecom wavelengths and a considerably strong magneto-optical ͑MO͒ effect, the source of the nonreciprocity. Stand-alone devices with good isolation performance have been reported. The integration with III-V host material however remains an issue. The best reported result demonstrated isolation not higher than 5 dB in a device several millimeters in length. 2A different research approach is based on the requirement that for monolithic integration, the isolator structure should be very similar to that of the laser it is to be integrated with. If, in a standard semiconductor optical amplifier ͑SOA͒, an adequately magnetized ferromagnetic metal is placed very close to the guiding region, the MO Kerr effect induces a nonreciprocal complex shift of the complex effective index of the guided mode. In other words, the modal absorption is different in both propagation directions. The remaining loss in the forward direction can be compensated for by current injection in the active material. The result is a component which-being transparent or amplifying in one direction, while providing loss in the opposite direction-is isolating and can be monolithically integrated with InP-based active photonic devices. A configuration for transverse magnetic ͑TM͒-polarized light was theoretically proposed in 1999 ͑Ref. 3͒ and demonstrated in 2004. 4 Recently, a variant for transverse electric-mode operation has been demonstrated. 5 In spite of the high levels of nonreciprocal absorption that have been reported, all results so far suffer from a large level of insertion loss with consequently an impractically large injection current. In this letter, we present the design, fabrication, and characterization of a TM-mode device demonstratin...

Magneto-optical permittivity tensor spectra of undoped InSb, n-doped and p-doped InSb crystals were determined using the terahertz time-domain spectroscopy (THz-TDS) and the Fourier transform far-infrared spectroscopy (far-FTIR). A Huge polar magneto-optical (MO) Kerr-effect (up to 20 degrees in rotation) and a simultaneous plasmonic behavior observed at low magnetic field (0.4 T) and room temperature are promising for terahertz nonreciprocal applications. We demonstrate the possibility of adjusting the the spectral rage with huge MO by increase in n-doping of InSb. Spectral response is modeled using generalized magneto-optical Drude-Lorentz theory, giving us precise values of free carrier mobility, density and effective mass consistent with electric Hall effect measurement.

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We show that the enhancement of the transverse magneto-optical Kerr effect of a smooth magnetic dielectric film covered by a noble metal grating, is strongly dependent on the precise geometry of this grating. Up till now this magnetoplasmonic enhancement was solely attributed to a nonreciprocal shift of the dispersion of the surface plasmon polariton resonances at the interface with the magnetized substrate. It is demonstrated that by hybridization of surface and cavity resonances in this 1D plasmonic grating, the transverse Kerr effect can be further enhanced, extinguished or even switched in sign and that without inverting or modifying the film's magnetization. This strong geometrical dispersion and the accompanying anomalous sign change of the magneto-plasmonic effects in such systems has never been considered before, and might find interesting applications in sensing and nanophotonics.

The optimization design of the layer structure for a novel type of a 1.3 m monolithically integrated InP-based optical waveguide isolator is presented. The concept of this component is based on introducing a nonreciprocal loss-gain behavior in a standard semiconductor optical amplifier (SOA) structure by contacting the SOA with a transversely magnetized ferromagnetic metal contact, sufficiently close to the guiding and amplifying core of the SOA. The thus induced nonreciprocal complex transverse Kerr shift on the effective index of the guided TM modes, combined with a proper current injection, allows for forward transparency and backward optical extinction. We introduce two different optimization criteria for finding the optimal SOA layer structure, using two different figure-of-merit functions (FoM) for the device performance. The device performance is also compared for three different compositions of the Co x Fe 1−x ͑x =0,50,90͒ ferromagnetic transition metal alloy system. It is found that equiatomic (or quasi-equiatomic) CoFe alloys are the most suitable for this application. Depending on the used FoM, two technologically practical designs are proposed for a truly monolithically integrated optical waveguide isolator. It is also shown that these designs are robust with respect to variations in layer thicknesses and wavelength. Finally, we have derived an analytical expression that gives a better insight in the limit performance of a ferromagnetic metal-clad SOA-isolator in terms of metal parameters.