Spatially nonreciprocal Bragg gratings based on surface plasmons

Abstract

Using the concept of parity-time symmetry in optics, we propose a spatially non-reciprocal Bragg grating at near infrared wavelengths, operating with long-range surface plasmon polaritons, by employing balanced modulation of index and gain/loss in a step-in-width configuration. The index perturbation is created by stepping the width of an Ag stripe supporting long-range plasmons. Gain/loss modulation is generated by periodically doping the top polymer cladding of the structure with IR-140 dye molecules and pumping the grating optically from top. Loss exists inherently in the undoped regions due to plasmonic propagation loss. The transmission matrix method was employed as an accurate modeling technique to compute the reflectance and transmittance spectra of the proposed structures. Simulation results exhibit a strong reflectance from one end of the grating at about 880 nm as opposed to nearly no reflectance from the other end at the same wavelength.