Parity-time symmetry optics for modal selection in transverse and longitudinal waves (Conference Presentation)

Abstract

The evolving field of optics for information and communication is currently seeking directions to expand the data rates in all concerned devices, fiber-based or on chips. We describe here two possibilities where the new concept of PT-symmetry in optics [1,2] can be exploited to help high data rate operation, considering either transverse or longitudinal aspects of modal selection, and assuming that data are carried using precise modes. The first aspect is transverse multimode transport. In this case, a fiber or a waveguide carries a few modes, say 4 to 16, and at nodes, they have to undergo a demux/mux operation to add or drop a subset of them, as much as possible without affecting the others. We shall consider to this end the operation as described in ref. [3] : if a PT-symmetric “potential”, which essentially consists of a transverse gain-loss profile with antisymmetry, is applied to a waveguide, it has a very different impact on the different modes and mode families in the waveguide. One can in particular find situations where only two modes of the passive waveguide to be analyzed may enter into a gain regime, and not the other ones. From this scheme and others [4], we will discuss what is the road left towards an actual device, either in dielectrics or in case plasmonics is envisioned [5], i.e. with rather constant losses, but the possible advantage of miniaturization. The second aspect is longitudinal mode selection. The special transport properties of PT-symmetric Bragg gratings are now well established. In order to be used within a data management system, attention has to be paid to the rejection rate of Bragg gratings, and to the flatness of their response in the targeted window. To this end, a slow modulation of both real and imaginary parts of the periodic pattern of the basically PT-symmetric waveguide can help, in the general spirit of “apodization”, but now with more parameters. We will detail some aspects of the designs introduced in [6] , notably their ease of implementation in established optoelectronic fabrication platforms. To conclude these considerations, the perspectives offered by the combination of transverse multimode systems and PT-symmetric type of periodicity will be discussed. [1] C. M. Bender and S. Boettcher, “Real spectra in non-Hermitian Hamiltonians having PT-symmetry,” Phys. Rev. Lett. 80, 5243 (1998). [2] J. Ctyroký, V. Kuzmiak, and S. Eyderman, “Waveguide structures with antisymmetric gain/loss profile,” Opt. Express 18, 21585-21593 (2010). [3] H. Benisty, A. Lupu, A. Degiron, “Transverse periodic PT symmetry for modal demultiplexing in optical waveguides,” Phys. Rev. A 91, 053825 (2015). [4] N. Rivolta, B. Maes, Symmetry recovery for coupled photonic modes with transversal PT symmetry, Opt. Letters, 40, 16, 3922-3925, (2015) [5] A. Lupu, H. Benisty, A. Degiron, “Switching using PT symmetry in plasmonic systems: positive role of the losses,” Opt. Express 21, 21651-21668 (2013). [6] A. Lupu, H. Benisty, A. Lavrinenko, “Tailoring spectral properties of binary PT-symmetric gratings by using duty cycle methods,” JSTQE 22, 35-41 (2016).