Optical materials

Optical materials not only stands as a basic science but also as a key technology that impacts our daily lives. Indeed, this research field is crucial to many areas of the economy with recent major advances in telecommunications, healthcare, energy production and environmental monitoring. For example, optical materials contributed to the advent of ultra-low loss telecommunication optical fibers, which enabled the Internet revolution.

Although optical materials are supporting the development of many high-impact technological areas, the evolution of optical and photonic applications has particularly benefited from the contribution of this core technology, which is expected to become more and more ubiquitous in the coming decades. This field of science studies the interactions of light in its wave-photon duality with optical materials and aims at developing techniques to structure and engineer optical materials so that they can reach the capability to alter, control, and manipulate light. If originally, optical materials were primarily used to passively transmit visible light, today, thanks to recent advances in molecular design and synthesis of new compounds, in material processing, in methodologies and instrumentation for the characterisation of materials, we are beginning to witness the emergence of new materials with novel properties capable of acting on light in a controlled manner.

The mastery of matter comes with the abundance of research focused on exploring and compiling the chemical, physical and optical properties of newly synthesized materials. Basic optical properties, such as extended transparency from the UV to the far infrared or nonlinear optical properties and photosensitivity, have been studied extensively. A wide range of materials with improved optical properties such as glasses, polymers and ceramics are actually ready for integration in the next generation of displays, optical fibers, sensors, laser materials and optical devices. Composite, hybrid and nanostructured materials are emerging on the market as prospects for large volume applications (telecom, imaging, etc.) as well as in niche applications (medical, robotics, adaptive vision, etc.). Some of these materials also exhibit biocompatibility, which is particularly attractive for healthcare applications. Organic optical materials have also raised strong interest due to their relatively strong nonlinear optical properties and large volume applications. They are being integrated in optical devices in display, lighting and information processing.

It may improve a property that the lubricant already possesses or give it properties that it does not naturally possess. In addition to the emergence of these new core materials, there is actually a strong trend towards tailoring existing materials in novel ways to produce innovative outcome. These so-called meta- or nano-materials, are materials that can be structured and engineered to show new optical properties that the bulk original materials themselves would not naturally possess. Structuring materials with features less than or close to one wavelength of light can lead to these novel properties and allow the control of optical properties such as spectral and polarization dependence in transmission, refraction, reflection, absorption, and nonlinear emission of light. Photonic crystals are two-dimensional (2D) or three-dimensional (3D) periodic sub-wavelength structures that affect the motion of photons. Since the first publications by Eli Yablonovitch and Sajeev John, co-founders of the field of photonic crystals in 1987, rapid progress has been made on this topic. Photonic crystal devices are being actively deployed in biosensors, semiconductor lasers and hollow-core fibers. One may add metal patterns to such periodic structures to produce negative refractive indices and superlens effects; a properly designed pattern can, for example, focus light below the conventional diffraction limit.

Recently, important new fabrication technologies have begun to emerge, challenging once again the current limits. They have been put to use in the design of innovative multimaterial or multifunctional materials. As a result, innovative solutions and technologies are now coming to the market. On the one hand, multimaterial and multifunctional components have demonstrated their potential to concurrently offer multiple functionalities like electrical conductivity, piezoelectricity, physical/chemical sensing in addition to light transmission. Complex associations of materials with specific properties in the form of fibers that can be easily integrated or interconnected provide novel solutions to specific problems where the collection and integration of data of different nature is required. On the other hand, ultrafast laser processing of materials, including 3D laser writing, has evolved very rapidly and is currently revealing its technological and industrial potential. Laser writing via two-photon or multiple-photon absorption is becoming a mature technology and its ease of application for 3D printing at a micro-/nano-meter scale is just revolutionary. All these advances allow designing and producing complex structures by taking inspiration directly from nature as, for example, bio-inspired photonic materials.

This special issue could simply not address the entire broad field of science and applications of optical materials. For such reason, this issue will be divided into two parts. In the current issue, we will have one tutorial, one review and five research articles. The tutorial of Nicholson-Smith about the Parametric Analysis of Thin Multifunctional Elastomeric Optical Sheets illustrates the concept and key design parameters of the controlled light propagation in flexible polymeric sheets. These flexible optical sheets are considered as a new generation of innovative materials that can be used for passive light harvesting and illumination systems.

The review of Doris Ehrt on Exploring Materials for Deep UV provides a large series of materials such as fluoride single crystals, fluoride glasses, fluorophosphate multicomponents, silica and organic materials. The author explains the role of the intrinsic absorption that affects the optical properties of different materials.

Martin Rochette’s paper demonstrates All-Fiber Far Detuned and Tunable Mid-IR Wavelength Conversion using chalcogenide microwires. He provides new solutions for the next generation of integrated optical devices operating in the mid-IR.

The Anatoliy paper entitled Frequency-Dependent Electro-Optics of Liquid Crystal Devices Utilizing Nematics and Weakly Conducting Polymers covers the process control and design of optical materials based on liquid crystals.

A paper on the Design of a 1D Phase-Mask Translational Scanner for Large-Size Spatially Coherent Grating Printing by Yves Jourlin explains the process of producing spatially highly coherent gratings on long sheets of large width substrates produced in a continuous way.

Two papers are presented regarding the interaction of light with matter. The paper from Marowsky presents a Comparative Study between Experiment and Simulation of Single Pulse Femtosecond Laser Ablation of Silicon. The second paper by Sandra Messaddeq deals with the Formation of Superposed Structure in As₂S₃ Based Glasses Using fs-Laser. In both papers, original structure is observed at the surface of those materials.

Warm thanks are extended to the authors and reviewers for their time and input as well as to the Advanced Optical Technologies team for their valuable support in building this collection of papers.