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# PT-symmetry in photonics, metamaterials and plasmonic systems II

## 14:00 Invited talk : Parity-Time Symmetry Breaking beyond One Dimension: the Role of Degeneracy

### Li Ge (1),A. Stone (2)

#### (1)The Graduate Center City University of New York (USA) , (2)Yale University (USA)

We consider the role of degeneracy in Parity-Time (PT) and Rotation-Time symmetry breaking for non-hermitian wave equations beyond one dimension. We show that the non-hermicity of the system eigenmodes can either onset abruptly as in typical PT-symmetric systems or be a linear function of the gain/loss parameter. These results are illustrated by using different T-breaking perturbations of a uniform dielectric disk and sphere, and a group theoretical analysis is given in the disk case.

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## 14:20 Invited talk : Surprises in systems with oscillating gain and loss: infinite ladder of PT transitions and the PT Rabi problem

### Yogesh N. Joglekar

#### Indiana University Purdue University Indianapolis (USA)

I will discuss a PT system in the presence of oscillatory gain and loss. I will show that the PT symmetry breaking occurs at arbitrarily small gain if the frequency of its modulation is at resonance with the coupling. I will also show that in the neighborhood of the static PT-transition point, PT symmetry is repeatedly broken and restored in the low frequency regime, this result is a significant departure from the standard adiabatic theorem or Berry-phase considerations.

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## 14:40 Invited talk : Spatially nonreciprocal Bragg gratings based on surface plasmons

### Elham Keshmarzi (1),Niall Tait (1),Pierre Berini (2)

#### (1)Carleton University (Canada) , (2)University of Ottawa (Canada)

The concept of spatial non-reciprocity in surface plasmon based Bragg gratings is introduced. It is shown that balanced modulation of index and gain/loss with quarter pitch spatial shift cause a nearly perfect unidirectional coupling between contra-propagating modes in a long range surface plasmon polariton Bragg grating. Such a Bragg grating operates at the breaking threshold of parity-time symmetry.

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## 15:00 Invited talk : Optical properties of PT-symmetric periodic stacks of the layers

### Oksana V. Shramkova, Giorgos P. Tsironis

#### University of Crete (Greece)

The scattering properties of PT-symmetric periodic stack of binary dielectric layers characterised by balances loss and gain are explored. It is shown that resonant phenomena are connected with surface mode excitation at internal boundaries of the stack. The effects of structure parameters and direction of incidence on resonant phenomena and spontaneous symmetry breaking transition are determined. It is shown that structure periodicity significantly increase the number of resonant phenomena, especially in stacks with high dielectric permittivity of layers.

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## 15:20 : Matched Quarter Stacks with Balanced Loss/Gain

### Josue Ramirez-Hernandez, Felix Izrailev, Nykolay Makarov

#### Benemerita Universidad Autonoma de Puebla (Mexico)

With the transfer matrix approach, we study the spectral and transport properties for an array of PT-symmetric bilayers. The number of spectral bands turns out finite and depends on the loss/gain parameter. The transmittance T exhibits the Fabry-Perrot resonances with T=1, however, between them T can be either larger or less than unity. We have found a new kind of specific frequencies inside every spectral band, which separate the regions with T>1 from those with T.

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## 15:35 Invited talk : Parity-Time Symmetric Optics in Compound Microtoroid Cavities

### Jianming Wen (1),Liang Jiang (1),Xiaoshun Jiang (2),Yanhong Xiao (3),Min Xiao (4)

#### (1)Yale University (USA) , (2)Nanjing University (China) , (3)Fudan University (China) , (4)University of Arkansas (USA)

Parity-time (PT) symmetric optics has recently attracted great attention, partly due to the theoretical discovery that non-Hermitian Hamiltonians may possess entirely real spectra by satisfying PT symmetry. Another major driving force comes from the facts that synthesized PT-symmetric materials allow observing novel optical phenomena which would be difficult in conventional media. Here, we report our recent experimental realizations of on-chip PT-symmetric optics using two directly active-passive-coupled microtoroid cavities at the telecom band.

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