Metasurfaces and metalenses have shown remarkable progress and performance in laboratory results in the past years. For metasurfaces to make the transition from laboratory to large scale adaptation, several challenges need to be overcome: high manufacturing yields must be shown to reach cost-effective fabrication, the robustness of metalenses to various imperfections should be demonstrated and integrated systems with metalenses need to be made with higher performance than conventional systems. Controlling the various types of unavoidable fabrication imperfections is critical for achieving these. In this paper we present Monte-Carlo simulations of metalenses with random fabrication defects as a tool to quantify the performance loss associated with different types of errors. We model changes in sidewall steepness, feature size and missing structures. We study these effects in a reference metalens consisting of SiliconNitride pillars on a glass substrate. The methods presented in this paper can be readily applied to other metalens and metasurface designs and are implemented in the PlanOpSim software package. We find that when the deviations in sidewall steepness are within a distribution with root mean square of 1.5° and changes in pillar shape have a root mean square no larger than 10nm the focusing efficiency of the metalens remains within 90% of its nominal value.
A technological platform for a vertical cavity surface emitting laser (VCSEL) with tunable polarization is presented. It is realized by integrating an 850nm VCSEL chip in a liquid crystal (LC) cell that uses photo-alignment (PA) to orient the LC. Two kinds of LC are filled in and form a thin layer over the emitter of the VCSEL: nematic LC or chiral nematic LC (cLC). The VCSEL and the nematic LC layer can be electrically driven with separate electrodes. The polarization state of the laser emission can be controlled by applying an appropriate voltage over the nematic LC layer. The chiral nematic LC has a reflection band that contains the VCSEL emission wavelength, so that one circular polarized mode of the laser emission is reflected as a feedback into the VCSEL. We found that the emission from the VCSEL with cLC overlay is circularly polarized.
In this paper we investigate the performance of a transparent photoconductive sensor based on a double layer of organic materials (m-MTDAB / PTCBI) which are deposited on two interdigitated transparent ITO electrodes. The performance of the sensor is demonstrated with electro-optical measurements: the I(V) curves consist of two linear sections meeting at a knee voltage V<sub>t</sub>. Linear regression performed on the I(V) curves below V<sub>t</sub> show that the conductance is a power law of the luminance incident on the device. We present a model to describe the behaviour of the sensor below V<sub>t</sub>. We present measurements of I(t) for a transient illumination of the sensor. Plotting the inverse of the current as a function of time we find that the transient is consistent with the model for voltages below V<sub>t</sub>. For voltages above V<sub>t</sub> we find that the sensor behaves like a resistor in series with a space charge (SC) region. We present a local illumination experiment that confirms the existence of a SC region between the electrodes of the photoconductive sensor for V<V<sub>t</sub>. The space charge region is located near the cathode of the sensor.