Optical diode activity in an axially asymmetric nonlinear medium incorporated with phenothiazine and silver nanoparticles

In order to overcome the limitations posed by electronic devices, and to fulfill the need for optical elements in integrated photonic circuits, it is crucial to develop an optical analogue of an electronic diode which is one of the most basic elements of electronic circuits. Asymmetric light transmission is essential for fabricating such an all optics based system. Different structures and configurations have been proposed for exhibiting asymmetric photonic signal transmission but found ineffective due to their complex structure and/or relatively large size. Here we discuss the results of theoretical investigation and consequent experimental realization of a nonlinear thin-film multilayer device that exhibits passive anisotropic optical transmission an optical analogue of electronic diode. This optical diode requires neither a magnetic field nor strong input fields for the diode action, whereas many conventional optical diode systems fail to work under ambient conditions and are unsuitable for integration into optical circuits. The system proposed here is based on axially asymmetric nonlinear absorption in an orderly arranged thin saturable absorber and a thin reverse saturable absorber. The variation of optical diode action on changing the parameters such as linear transmittance, nonlinear absorption coefficients and saturation intensity are theoretically simulated to understand how the forward and reverse transmittances change with the parameters. The experimental demonstration of the diode activity has been accomplished using single beam open aperture z-scan technique at an on-axis input intensity of similar to 0.27 GW/cm(2), where the saturable absorber was Ag nanoparticles prepared by liquid phase laser ablation technique and the reverse saturable absorber was Phenothiazine-Ag composite. The system exhibited good non-reciprocity in this range 0.14-0.42 GW/cm(2) and the observed non-reciprocity factor at 0.27 GW/cm(2) on-axis input intensity is around 3. Due to a large bandwidth, good chemical and thermal stability, cost-effectiveness and large-scale integration with existing fabrication technologies, this optical diode based on axial asymmetry in nonlinear absorption is a good candidate for future all optical communications and computing.