Gianni Portela

Compact optical switch based on 2D photonic crystal and magneto-optical cavity

A compact optical switch based on a 2D photonic crystal (PhC) and a magneto-optical cavity is suggested and analyzed. The cavity is coupled to two parallel and misaligned PC waveguides and operates with dipole mode. When the cavity is nonmagnetized, the dipole mode excited by a signal in the input waveguide has a node in the output waveguide. Therefore, the input signal is reflected from the cavity. This corresponds to the state off of the switch. Normal to the plane of the PhC magnetization by a dc magnetic field produces a rotation of the dipole pattern in the cavity providing equal amplitudes of the electromagnetic fields in the input and the output waveguides. This corresponds to the state on with high transmission of the input signal. Numerical calculations show that at the 1.55 μm wavelength the device has the insertion loss -0.42 dB in the on state, the isolation -19 dB in the off state and the switch off and on ratio P(on)/P(off) about 72. The frequency band at the level of -15 dB of the resonance curve in off state is about 160 GHz.

Possible mechanisms of switching in symmetrical two-ports based on 2D photonic crystals with magneto-optical resonators

We analyze possible mechanisms of switching in two-ports based on 2D photonic crystals (PhCs) with a magneto-optical resonator. The input and output waveguides can be side or front coupled with the resonator. The resonator operates with a dipole mode. In the switch with front coupling in the nonmagnetic state the standing dipole mode provides equal nonzero wave amplitudes in the input and output waveguides and therefore transmission of the signal from the input to output waveguides. This is the state on. The applied magnetic field normal to the plane of the PhC rotates the standing dipole mode by 90° setting the nodes in the input and output waveguides. This corresponds to the state off. On the contrary, in the switch with side coupling and nonmagnetized resonator, the standing dipole mode excited by a wave in the input waveguide has its node in the output waveguide. Therefore, the signal is reflected from the input port. This corresponds to the state off of the switch. Magnetization by a DC magnetic field produces a rotating dipole pattern in the cavity. Due to this rotating, the mode signal passes from the input port to the output one and this is the state on.

Three-port circulators with low symmetry based on photonic crystals and magneto-optical resonators

Three-port circulators based on magneto-optical resonators in 2D photonic crystals with low symmetry are investigated. We consider different geometries of the circulators in photonic crystals with triangular and square unit cells. All of the three-ports possess only one specific element of symmetry named antiplane of symmetry. The theoretical part of our paper concerns scattering matrix analysis for different regimes of circulation. In particular, we define the scattering matrices of ideal circulator and a special type of conditions which allow one to transform the non-reciprocal three-port in ideal circulator. One case of non-ideal circulators is considered as well. We also discuss some peculiarities of a special regime of the circulators when they are used as isolators. Finally, one example of the circulator simulations with calculated frequency responses in photonic crystals based on triangular unit cells is presented.

Photonic crystal-based circulators with three and four ports for sub-terahertz region

Three- and four-port circulators based on resonators in 2D photonic crystals with square unit cell possessing a low symmetry are investigated. The three-ports are described by only one specific element named antiplane of symmetry. On the other hand, the four-port circulators formed by cascading these two three-ports can have one of the two symmetries. One of them is described by the antiplane of symmetry, and the other symmetry corresponds to a twofold rotational axis. The theoretical part of our paper concerns scattering matrix analysis of the devices with different symmetries and also the operation of the four-port circulator as a single-pole triple-throw switch. Finally, the calculated frequency responses of two circulators are presented.

Multifunctional two-dimensional photonic crystal optical component based on magneto-optical resonator: nonreciprocal two-way divider-switch, nonreciprocal 120 deg bending-switch, and three-way divider

Abstract. We suggest and analyze a compact nonreciprocal optical four-port based on a magneto-optical resonator in two-dimensional photonic crystal, which can fulfill many functions. This component can be used in three regimes: first, with magnetization by a direct current (DC) magnetic field +H0, second, with magnetization by the DC magnetic field −H0, and finally, with magnetization by the DC magnetic field +H1. In the first regime, the four-port ensures equal division of the input signal between two output ones simultaneously providing protection of the generator in the input port from harmful reflected signals in the output ports; this can also be used as a switch by reversing +H0 to −H0. In the second regime, the same four-port fulfills 120-deg bending and it provides protection of the generator in the input port from reflected signals; it can also be used as a switch by reversing −H0 to +H0. In the third regime, with DC magnetic field +H1, the device can be used as a three-way divider with equal division to the output ports. We analyze the scattering matrix of this component and discuss the physical mechanisms of its functioning. In addition, computational simulations were performed and their results confirm our theoretical predictions.

Magneto-optical resonator switches in two-dimensional photonic crystals: geometry, symmetry, scattering matrices, and two examples

We discuss different geometrical structures of optical switches based on two-dimensional photonic crystals with hexagonal geometry of the unit cell and a magneto-optical resonator. Transition between the states on and off in these switches is achieved by an external DC magnetic field. The input and output waveguides can be front-front, side-side, or front-side coupled to the resonator and these different types of coupling can lead to different mechanisms of switching. Analysis of symmetry and scattering matrices of the switches is based on magnetic group theory. Two examples of switches with 60° and 120° bends and their characteristics are also presented.

Optical component: nonreciprocal three-way divider based on magneto-optical resonator.

We suggest and analyze a new compact nonreciprocal optical component based on a magneto-optical resonator. This component fulfills simultaneously two functions, namely, equal division of the input signal between three output ports and isolation of the input port from output ones. Using group theory, we analyze the scattering matrix of this symmetrical component. Our numerical results for one of the possible schemes of the divider based on 2D photonic crystal with magneto-optical material demonstrate that at the central frequency, the division of the signal between the three output ports is about -5.4 dB. The variation of the division levels in the output ports in this band is (-5.4 ± 0.4) dB. For the level -20 dB of the isolation, the calculated bandwidth is around 190 GHz at the wavelength 1.55 μm.

A new optical component: Nonreciprocal three-way divider based on magneto-optical resonator

We suggest and analyze a new compact nonreciprocal optical component based on a magneto-optical resonator. This component fulfills simultaneously two functions, namely, equal division of the input signal between three output ports and isolation of the input port from output ones. Using group theory, we analyze the scattering matrix of this symmetrical component. Our numerical results for one of the possible schemes of the divider based on 2D photonic crystal with magneto-optical material demonstrate that at the central frequency, the division of the signal between the three output ports is about -5.4 dB. The variation of the division levels in the output ports in this band is (-5.4 ± 0.4) dB. For the level -20 dB of the isolation, the calculated bandwidth is around 190 GHz at the wavelength 1.55 μm.

Temporal Coupled-Mode Theory of Electromagnetic Components Described by Magnetic Groups of Symmetry

We consider peculiarities of application of the temporal coupled-mode theory to the electromagnetic components with magnetic symmetry. The coupled-mode theory is widely used for analysis of reciprocal devices described by symmetrical scattering matrices and by unitary elements of symmetry, such as for example, a plane of symmetry. However, nonreciprocity and low symmetry of components described by antiunitary elements lead to a necessity of modification of the method. Using as an example a photonic crystal-based W-circulator described by an antiplane of symmetry, we show applicability of the method to the components with antiunitary elements. The circulator characteristics are calculated and compared with those obtained by a numerical method, demonstrating good agreement between the two methods.

Vortex-based ferromagnetic resonance isolator in 2D photonic crystal waveguide

We suggest and numerically analyze a new type of THz isolator possessing a very compact structure. It is based on a 2D photonic crystal with square unit cell. The forward incident wave in the photonic crystal waveguide with a magnetized ferrite rod is transmitted while the backward wave is blocked due to ferromagnetic resonance losses in the rod. The necessary structure of the AC magnetic field in the ferrite rod with circular rotation in the plane normal to the DC magnetic field is provided by two stubs in the waveguide. The electromagnetic field in the rod has a vortex-like profile. Numerical simulations show that, at the central frequency 0.1066 THz, the proposed isolator has insertion losses lower than −0.8 dB and isolation level better than −15 dB in the operating bandwidth of 0.8 GHz.