An overview of key materials for optical communications, including semiconductors, dielectrics, glasses, and organics, is presented in this issue of MRS Bulletin. Materials quality is in all cases crucial for advanced device and system performance. Materials properties and important problems are reviewed, and their impact on the performance of state-of-the-art optical devices is assessed and demonstrated by means of selected examples.

We describe how the material properties of III–V semiconductors, including bandgap, band structure, band offset, refractive index, absorption, and ionization coefficient, are exploited for lasers and photodetectors for fiber-optic communications. The material systems discussed for 1.3 μm and 1.55 μm light emission include the more traditional GaInAsP and AlGaInAs on InP, the more recently investigated GaInAs quantum dots and low-bandgap GaInNAs on GaAs as well as GaAsSb/GaAs Type II structures, and the potentially viable GaN/AlGaN from intersubband transitions (i.e., between quantized conduction-band energy levels). As an example of photodetector applications, GaInAsP/InP and wafer-fused GaInAs/Si are discussed in terms of gain and noise factor for use in avalanche photodiodes with separate absorption and multiplication regions.

With the advent of bright-blue light-emitting diodes in 1994, violet laser diodes in 1996, and vertical-cavity surface-emitting lasers at telecommunications wavelengths in 2000, all based on nitride-containing III–V compounds, a new age for optoelectronics began. Despite their technological success, III-nitride materials still hold some mysteries. Compared with conventional III–V semiconductors, even commercial nitride devices are of poor material quality. Due to their heteroepitaxial origin, their crystals are full of dislocations. Electrical properties, particularly in the case of p-type material, are fairly unsatisfactory. Still, light-emitting diodes with extremely high brightness and lasers with high power and good lifetime can be produced with III–V nitride compounds. In this review, we will give an overview of the essential properties of nitride materials for optoelectronic devices, their current development status, open questions, and recent device achievements.

Current issues in the development of organic materials for photonic applications are reviewed. Organic light-emitting diodes, which are a main focus of industrial research at the moment, are given special emphasis. Other applications in optical communications technology, including organic solid-state lasers, optical switching devices, and data storage, are also covered.

This article reviews loss components of standard transmission silica optical fibers and their connections to glass structure and manufacturing parameters. Loss-reduction possibilities are described. In particular, the Rayleigh scattering component, which is the main contributor to fiber losses within the transmission window, can be significantly reduced by lowering the fictive temperature (the temperature at which the liquid structure is “frozen” during cooling) and tuning the glass composition. The issue of a compromise between manufacturing productivity and minimization of excess loss is also addressed.

This article reviews the fabrication technologies and optical characteristics of silica-based planar lightwave circuits (PLCs) on Si developed for photonic networks based on wavelength-division multiplexing (WDM). While there have been various planar optical waveguides made with different materials, silica-based PLCs are the most suitable for constructing practical devices because of their excellent design flexibility, stability, and reproducibility. These advantages mainly result from their material characteristics, that is, silica glass is chemically and physically stable. The article also describes the basic characteristics and recent development of arrayed waveguide grating (AWG) multiplexers/demultiplexers as a device application. Since AWGs offer the advantages of low-loss, high-output port counts and mass producibility, they have played a pivotal role in the construction of flexible, large-capacity WDM networks.

Explosive growth in the fiber-optic telecommunications infrastructure during the past decade has driven noteworthy advances in thin-film-based optical interference filter technology. In particular, the widespread deployment of wavelength-division multiplexing (WDM), a means of increasing the communication capacity of an optical fiber by utilizing more than one wavelength of light, has motivated significant improvements in bandpass filter performance. A common requirement is for filters that combine or separate wavelengths spaced 100 GHz (0.8 nm) apart. The foundation for these recent breakthroughs has been laid by the development of optical coating technology over the past century. This article reviews the materials and processes used in the production of thin-film-based optical communications filters.