This article reviews the current knowledge on the main properties and applications of hydrogen in LiNbO₃. The review is divided into three parts. The first is devoted to general properties such as methods of defect production and control, techniques used for their detection and characterization, as well as interactions with other lattice defects. The second part considers the central role played by OH^- defects in the fabrication of optical waveguides by the protonexchange method. Conditions for the exchange process, the structure of exchanged layers, optical properties of exchanged waveguides and connection with relevant practical devices are examined. Finally, the third part discusses the production of permanent volume photorefractive gratings by the fixing process, where OH^- ions are also considered to be the main responsible defects. In particular, the physics of the fixing process, current mathematical models and two major applications are discussed.

The study and applications of ferroelectric materials in the biomedical and biotechnological fields is a novel and very promising scientific area that spans roughly one decade. However, some groups have already provided experimental proof of very interesting biological modulation when living systems are exposed to different ferroelectrics and excitation mechanisms. These materials should offer several advantages in the field of bioelectricity, such as no need of an external electric power source or circuits, scalable size of the electroactive regions, flexible and reconfigurable “virtual electrodes,” or fully proved biocompatibility. In this focused review, we provide the underlying physics of ferroelectric activity and a recount of the research reports already published, along with some tentative biophysical mechanisms that can explain the observed results. More specifically, we focus on the biological actions of domain ferroelectrics and ferroelectrics excited by the bulk photovoltaic effect or the pyroelectric effect. It is our goal to provide a comprehensive account of the published material so far and to set the stage for a vigorous expansion of the field, with envisioned applications that span from cell biology and signaling to cell and tissue regeneration, antitumoral action, or cell bioengineering to name a few.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

Optical and optoelectronic techniques for micro- and nano-object manipulation are becoming essential tools in nano- and biotechnology. The use of photovoltaic optoelectronic tweezers is a remarkable optoelectronic technique that has undergone rapid development in recent years, with excellent results and widespread potential applications. It is based on light-induced electric fields generated by the bulk photovoltaic effect in certain ferroelectrics, such as ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$. The technique is simple and versatile, enabling the successful manipulation of a large variety of micro- and nano-objects with only optical control, without the need for electrodes or power supplies. However, the handling of objects in aqueous solutions remains a challenge for this tool, due to the electric-screening effects of polar liquids. This has hindered their application in biotechnology and biomedicine, where most processes occur in aqueous solution. Here, an efficient route to overcome this problem is proposed and demonstrated. It uses photovoltaic optoelectronic tweezers to manipulate aqueous droplets, immersed in a nonpolar oil liquid, but hanging at the air-oil interface. In this singular configuration, the high electric fields generated by the bulk photovoltaic effect in the ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ substrate allow simple and flexible manipulation of aqueous droplets controlled by the light. Droplet guiding, trapping, merging, and splitting are achieved and efficient operation with water and a variety of biodroplets (DNA, sperm, and phosphate-buffered saline solutions) is demonstrated. A discussion on the physical mechanisms responsible for the manipulation processes is also provided. The reported results overcome the main limitation of these tweezers to handle biomaterials and promise high potential for biotechnological and biochemistry applications, including their implementation in optofluidic devices.

This review presents an up-dated summary of the fundamentals and applications of optoelectronic photovoltaic tweezers for trapping and manipulation of nano-objects on the surface of lithium niobate crystals. It extends the contents of previous reviews to cover new topics and developments which have emerged in recent years and are marking the trends for future research. Regarding the theoretical description of photovoltaic tweezers, detailed simulations of the electrophoretic and dielectrophoretic forces acting on different crystal configurations are discussed in relation to the structure of the obtained trapping patterns. As for the experimental work, we will pay attention to the manipulation and patterning of micro-and nanoparticles that has experimented an outstanding progress and relevant applications have been reported. An additional focus is now laid on recent work about micro-droplets, which is a central topic in microfluidics and optofluidics. New developments in biology and biomedicine also constitute a relevant part of the review. Finally, some topics partially related with photovoltaic tweezers and a discussion on future prospects and challenges are included.