Exciting progress in our optical research journey! Two years ago, our Fiber-optic and Quantum Technologies and Systems team, led by Prof. Ryszard Buczynski embarked on a ground-breaking project focused on dual-core fibers for all-optical switching.
Inspired by the PT-symmetric breaking phenomenon,we aimed together with the research team of Prof. Marek Trippenbach (Faculty of Physics, Uniwersytet Warszawski), to merge gain and loss systems into one with no net energy flux. This concept from 1982, has shown promise in various optical systems, from periodic structures to high-power lasers. It is based on the possibility of combining two physical systems, one called GAIN (with positive flux of energy) and one called LOSS (with negative flux of energy), into a single system with no total flux of energy.
Theoretical works predicted such scenario in several optical systems, and also experimental were achieved in periodic structures, photonics lattices, semiconductor-based dual microring laser resonators, plasmonic systems, and-recently-in high-power large-area lasers.
Our approach involved dual-core fibers with parallel GAIN core and LOSS core channels. The motivation stemmed from leveraging Mattia Longobucco’s findings to create a robust switching device.
Drawing inspiration from Dr. Stępień’s study on phosphate glass photonic crystal fiber lasers, we designed the fiber with Yb-doped and Cu-doped cores.
Furthermore, the development of the fiber design -particularly the implementation of the GAIN core – drew inspiration from a related study conducted by our group at Łukasiewicz – Institute of Microelectronics and Photonics. This study focused on phosphate glass photonic crystal fiber lasers. The base material of the fiber is, in fact, a phosphate glass in a P2O5-Al2O3-Yb2O3-BaO-ZnO-MgO-Na2O oxide system.
The separated gain and loss cores are realized with two cores with Yb and Cu doping of the base phosphate glass. The Yb-doped core supports a laser (gain) activity under excitation with a pump at 1000 nm wavelength, while the CuO-doped is responsible for strong attenuation at the same wavelength.
The manuscript delves into simulation results of ultrafast optical pulses at 1000 nm in the PT-symmetry dual-core fiber. We predict two states:
Linear oscillation of pulse energy between gain and loss core with strong power attenuation
Retention of the pulse in the excited gain core (broken PT-symmetry), with very modest attenuation. Optimal pulse energy levels: 100 pJ (first state) and 430 pJ (second state), which are easy to achieve. Moreover, the fiber length is just below 30cm, which also helps to achieve a very compact device.
The plan is to fabricate the fiber at IMiF and demonstrate PT-symmetric breaking experimentally. This could pave the way for robust all-optical switches, high-power fiber lasers, and applications in optical communication and networks.