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Classical nonlinear or quantum all-optical transistors are dependent on the value of input signal intensity or need extra co-propagating beams. In this paper, we present a kind of all-optical transistors constructed with parity-time (PT)-symmetric Y-junctions, which perform independently on the value of signal intensity in an unsaturated gain case and can also work after introducing saturated gain. Further, we show that control signal can switch the device from amplification of peaks in time to transformation of peaks to amplified troughs. By using these PT-symmetric Y-junctions with currently available materials and technologies, we can implement interesting logic functions such as NOT and XOR (exclusive OR) gates, implying potential applications of such structures in designing optical logic gates, optical switches, and signal transformations or amplifications.

In this paper, we present a kind of periodical ternary parity-time (PT) -symmetric multilayers to realize nearly 100% reflectance and transmittance simultaneously when light is incident from a certain direction. This extraordinary reflection and transmission is original from unidirectional Bragg reflection of PT-symmetric systems as the symmetry spontaneous breaking happens at PT thresholds. The extra energy involved in reflection and transmission lights is obtained from pumping light to the gain regions of the structure. Moreover, we find that our PT-symmetric structure shows direction dependent wavelength selectivity. When the illumination light is incident from two opposite directions into the multilayer structure, such extraordinary reflection and transmission appear at visible and near-infrared wavelengths, respectively. Such distinguishing properties may provide these structures with attractive applications as beam splitters, laser mirrors, narrow band filters, and multiband PT-symmetric optical devices.

We demonstrate a kind of ternary parity-time (PT)-symmetric complex waveguide arrays to observe nonreciprocal optical Bloch-Zener oscillations (OBZOs) at the PT thresholds. The waveguide arrays are periodically constructed with a unit of a dielectric waveguide sandwiched by a loss and a gain waveguides. The nonreciprocal optical Bloch-Zener oscillations are attributed to the unidirectional Bragg scattering behaviors of light in the systems, which can be controlled by the propagation constant mismatch between dielectric waveguides and loss or gain waveguides through independently tuning the propagation constants of the dielectric waveguides of the units.