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Recent years have witnessed an inflow of ideas from quantum field theory and condensed matter physics into the field of optics. In this talk, we describe how notions from topological physics and supersymmetry can be used in designing novel laser arrays with properties that are of interest in some applications. Likewise, such lasing arrangements can be used to emulate a variety of topological and supersymmetric phenomena, beyond what is possible in their respective original platforms.

A non-Hermitian He-Ne ring laser gyroscope (RLG) that operates at an exceptional point is proposed and experimentally realized. Compared to a standard RLG, the device exhibits more than an order of magnitude enhancement in sensitivity.

Gyroscopes play a crucial role in many and diverse applications associated with navigation, positioning, and inertial sensing [1]. In general, most optical gyroscopes rely on the Sagnac effect -- a relativistically induced phase shift that scales linearly with the rotational velocity [2,3]. In ring laser gyroscopes (RLGs), this shift manifests itself as a resonance splitting in the emission spectrum that can be detected as a beat frequency [4]. The need for ever-more precise RLGs has fueled research activities towards devising new approaches aimed to boost the sensitivity beyond what is dictated by geometrical constraints. In this respect, attempts have been made in the past to use either dispersive or nonlinear effects [5-8]. Here, we experimentally demonstrate an altogether new route based on non-Hermitian singularities or exceptional points in order to enhance the Sagnac scale factor [9-13]. Our results not only can pave the way towards a new generation of ultrasensitive and compact ring laser gyroscopes, but they may also provide practical approaches for developing other classes of integrated sensors., 15 pages

Non-Hermitian exceptional points (EPs) represent a special type of degeneracy where not only the eigenvalues coalesce, but also the eigenstates tend to collapse on each other. Recent studies have shown that in the presence of an EP, light-matter interactions are profoundly modified, leading to a host of novel optical phenomena ranging from enhanced sensitivity to chiral light transport. As of now, however, in order to stabilize a system at the vicinity of an exceptional point, its related parameters must be carefully tuned and/or continuously controlled. To overcome this limitation, here we introduce a new family of broadband exceptional points based on unidirectional coupling, implemented by incorporating an Sshaped waveguide in a microring cavity. In active settings, the resulting unidirectionality exhibits unprecedented resilience to perturbations, thus providing a robust and tunable approach for directly generating beams with distinct orbital angular momentum (OAM). This work could open up new possibilities for manipulating OAM degrees of freedom in applications pertaining to telecommunications and quantum computing, while at the same time may expand the notions of non-Hermiticity in the orbital angular momentum space.

Supersymmetric transformations aim to relate boson and fermions, two different species of particles, and their interactions. In quantum mechanics, the mathematical framework of SUSY can be used to design isospectral potentials. By virtue of the isomorphism between Schrodinger and wave equations, one can use such transformations for designing novel optical systems. In this talk, we review the recent developments in the general area of supersymmetric optics and photonics. We will also discuss the possibility of generating high brightness coherent light in supersymmetric laser arrays.

Stability through symmetry A common route to get more light out of a laser system is to couple multiple lasers to form an array. However, instabilities owing to cross-talk and interference between different modes of individual cavities is generally detrimental to performance and could ultimately be damaging to the laser cavities. Hokmabadi et al. applied notions derived from supersymmetry, a theory developed in high-energy physics to describe the make-up and properties of particles, to design a stable array of semiconductor lasers (see the Perspective by Kottos). Based on symmetry arguments, the method is scalable and could provide a practical platform to design and develop complex photonic systems. Science , this issue p. 623 ; see also p. 586

The synergetic use of gain and loss in parity-time symmetric coupled resonators has been shown to lead to single-mode lasing operation. However, at the corresponding resonance frequency, an ideal ring resonator tends to support two degenerate eigenmodes, traveling along the cavity in opposite directions. Here, we show a unidirectional single-moded parity-time symmetric laser by incorporating active S-bend structures with opposite chirality in the respective ring resonators. Such chiral elements break the rotation symmetry of the ring cavities by providing an asymmetric coupling between the clockwise (CW) and the counterclockwise (CCW) traveling modes, hence creating a new type of exceptional point. This property, consequently, leads to the suppression of one of the counter-propagating modes. In this paper, we first measure the extinction ratio between the CW and CCW modes in a single ring resonator in the presence of an S-bend waveguide. We then experimentally investigate the unidirectional emission in PT-symmetric systems below and above the exceptional point. Finally, unidirectional emission will be shown in systems of two S-bend ring resonators coupled through a link structure.

A multimode, chaotic, and broadband emission is an undesired characteristic of laser arrays which is an adverse effect of supermodes in coupled waveguides. Employing optical supersymmetry, we experimentally demonstrate single mode lasing in arrays of supersymmetric lasers where a superpatner array eliminates undesired lasing modes.

A new scheme for ultrasensitive micro-ring laser gyroscopes based on the physics of exceptional points is proposed. In such systems, the sensitivity to low rotation rates can be enhanced by several orders of magnitude.

Multimode emission adversely affects phased-locked laser arrays resulting in chaotic behaviors. Utilizing optical supersymmetry, we experimentally demonstrate a single mode laser array where a superpartner array eliminates undesired higher order transverse modes.

At resonance, mircoring resonators tend to support two counter-propagating degenerate modes. By incorporating S-bend chiral elements in each resonator, unidirectional single mode lasing below and above PT-symmetry breaking point is experimentally demonstrated.