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The present work describes the development of an organic photodiode (OPD) receiver for high-speed optical wireless communication. To determine the optimal communication design, two different types of photoelectric conversion layers, bulk heterojunction (BHJ) and planar heterojunction (PHJ), are compared. The BHJ-OPD device has a -3 dB bandwidth of 0.65 MHz (at zero bias) and a maximum of 1.4 MHz (at -4 V bias). A 150 Mbps single-channel visible light communication (VLC) data rate using this device by combining preequalization and machine learning (ML)-based digital signal processing (DSP) is demonstrated. To the best of the authors' knowledge, this is the highest data rate ever achieved on an OPD-based VLC system by a factor of 40 over the previous fastest reported. Additionally, the proposed OPD receiver achieves orders of magnitude higher spectral efficiency than the previously reported organic photovoltaic (OPV)-based receivers.

tuning in the whole visible regime through large changes in the particle-particle separation originating from the electrophoretic movement of the charged particles while maintaining the ordered crystal structure under the external fields.[10] In spite of these merits, there is no report that considered these systems applicable for reversible switching for practical application. Although de-ionized water is the most suitable dispersion medium for producing high quality periodic crystalline structures with enhanced reflectance in these systems, the electrolysis of water molecules at the indium tin oxide (ITO) surface produces significant amounts of H+ and OH− ions as by-products at the cathode and anode, respectively. Therefore, the diffusion of those ions into colloidal arrays substantially limits the tuning stability and range because this phenomena induces decreased thickness of electrical double layer on the surface of the colloidal nanoparticles. To solve this problem, ITO surface was modified by various dielectric insulator passivation layers, including SiO2, SiN, polyimide, and parylene that can block electrochemical reactions at the electrodes (unpublished results). However, this methodology resulted in a substantial reduction of the color tuning range due to decreases in voltage applied to the colloidal dispersion because of the large amount of additional impedance introduced by the passivation layer. Considering the volume resistivity of these commonly used passivation materials (∼1016 Ω m), required thickness of the passivation layer should be at the sub-nm scale in order not to decrease the voltage applied significantly in colloidal dispersion. Preparation of such a thin and uniform film without any defected area is extremely difficult to achieve. Here we report our effort for achieving enhanced tuning stability of the colloidal photonic crystal composed of long-range ordered crystalline colloidal arrays through modifying the ITO electrode with ion exchange resins. The thin layer of over-coating on the ITO surface allowed increased number of cycles of stable color-tuning switching from red to green over 800 times, which is the best result ever reported for a tunable photo nic crystal whose Δλ can be manipulated more than 100 nm. Figure 1(a) depicts the device structure of a unit pixel and the concept of improving the stability of photonic structural color tuning through blocking ion diffusion from both electrodes by coating the electrode surface with a layer of ion-exchange resin. A colloidal dispersion composed of monodisperse 138 nm-diameter polystyrene (PS) nanoparticles dispersed in deionized water was injected between two electrodes. The strong negative charge of the nanoparticles and their thick electrical double layer induce the self-assembly of the long-range ordered colloids through electrostatic repulsion, which dominates the Structural Color Manipulation Using Tunable Photonic Crystals with Enhanced Switching Reliability

An electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of high refractive index particles. Through modulation of the refractive index of the particle, and the applied electric field, both the bandwidth and position of the photonic bandgap could be tuned. Full color modulation with high optical quality is achieved, which paves a way to develop a novel reflective display.

Thin-film color reflectors inspired by Morpho butterflies are fabricated. Using a combination of directional deposition, silica microspheres with a wide size distribution, and a PDMS (polydimethylsiloxane) encasing, a large, flexible reflector is created that actually provides better angle-independent color characteristics than Morpho butterflies and which can even be bent and folded freely without losing its Morpho-mimetic photonic properties.

This work was supported a grant from the Creative Research Initiative Program of the Ministry of Science and Technology for ‘‘Complementary Hybridization of Optical and Fluidic Devices for Integrated Optofluidic Systems.’’ The authors also appreciated partial support from the Brain Korea 21 Program. Supporting Information is available online from Wiley InterScience or from the author.

The spontaneous crystallization of colloidal particlesprovides a simple and cheap alternative to nanolithographyfor creating three-dimensional periodic structures. Colloidalcrystals with long-range order diffract light and displayphotonic bandgaps, which is of practical significance forphotonic and phononic crystal devices