We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

The propagation of electromagnetic radiation in periodically stratified media is considered. Media of finite, semi-infinite, and infinite extent are treated. A diagonalization of the unit cell translation operator is used to obtain exact solutions for the Bloch waves, the dispersion relations, and the band structure of the medium. Some new phenomena with applications to integrated optics and laser technology are presented.

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Electromagnetic propagation in periodic stratified media. I. General theory

Integrated optics is a far-reaching attempt to apply thin-film technology to optical circuits and devices, and, by using methods of integrated circuitry, to achieve a better and more economical optical system. The specific topics discussed here are physics of light waves in thin films, materials and losses involved, methods of couplings light beam into and out of a thin film, and nonlinear interactions in waveguide structures. The purpose of this paper is to review in some detail the important development of this new and fascinating field, and to caution the reader that the technology involved is difficult because of the smallness and perfection demanded by thin-film optical devices.

Light waves in thin films and integrated optics.

We report the fabrication and accurate measurement of propagation and bending losses in single-mode silicon waveguides with submicron dimensions fabricated on silicon-on-insulator wafers. Owing to the small sidewall surface roughness achieved by processing on a standard 200mm CMOS fabrication line, minimal propagation losses of 3.6+/-0.1dB/cm for the TE polarization were measured at the telecommunications wavelength of 1.5microm. Losses per 90 masculine bend are measured to be 0.086+/-0.005dB for a bending radius of 1microm and as low as 0.013+/-0.005dB for a bend radius of 2microm. These record low numbers can be used as a benchmark for further development of silicon microphotonic components and circuits.

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Losses in single-mode silicon-on-insulator strip waveguides and bends.

The prism coupler, known from experiments on integrated optics, can be used to determine the refractive index and the thickness of a light-guiding thin film. Both parameters are obtained simultaneously and with good accuracy by measuring the coupling angles at the prism and fitting them by a theoretical dispersion curve. The fundamentals and limitations. of this method are discussed, its practical use, and mathematical procedures for the evaluation.

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Measurement of Thin Film Parameters with a Prism Coupler

The continued development of integrated optics is heavily dependent upon the availability of materials that are suitable for the construction of thin-film optical circuitry and devices We report here an investigation of new films made by an rf discharge polymerization process of organic chemical monomers We concentrate our discussion on films prepared from vinyltrimethylsilane and hexamethyldisiloxane These films are smooth, tough, pinhole-free, transparent from 04 μm to 075 μm, and exhibit very low loss (<004 dB/cm) for light-wave propagation More importantly, experiments demonstrate the possibility of controlling the refractive index of the films either by the mixing of the two monomers before deposition or by chemical treatment after the film is deposited The use of the prism–film coupler for studying the refractive index of each material is discussed in detail

Thin Organosilicon Films for Integrated Optics

We demonstrate a new and simple method of forming light-guiding interconnections in an integrated optical circuit. This involves bridging the devices with a thin film having tapered ends that form naturally during the deposition process. Experiments show that there is no specific requirement for the thickness, refractive index, or relative position of the bridging film. A theory of composite waveguides provides an understanding of these interconnections.

Formation of light-guiding interconnections in an integrated optical circuit by composite tapered-film coupling.

Attention is drawn to the properties of Ta2O5 film which make it attractive as a new dielectric medium for use in integrated optical circuitry. The Ta2O5 film discussed was formed by thermally oxidizing sputtered β-tantalum films in an oxygen atmosphere. Measurements showed that these films will support propagation of coherent red (6328-A.) light with a loss of 0.9 dB cm−1 and coherent blue (4880-A) light with a somewhat higher loss of 4.1 dB cm−1. From measurements of the coupling angle at which propagation of the various modes takes place, refractive indices for the TE and TM modes at 6328 A, 5145 A, and 4880 A were obtained. The loss mechanisms are discussed, and it is shown that most of the loss is due to scattering during the internal reflections at the air–oxide and oxide–substrate film surfaces. A small fraction of the loss appears to occur in the interior of the film. With Ta2O5 it is demonstrated for the first time that optical circuit components can be formed for use in integrated optics by employing existing thin-film technology. The basic process steps include the pattern generation of the β-Ta followed by thermal oxidation of the pattern. Experimental studies of propagation in straight and curved waveguides are described. It was found that the losses in pattern generated waveguides are of the order of 5 dB cm−1 to 7 dB cm−1, with the excess loss due to scattering from the waveguide edges. It is concluded that improvements in the smoothness of the boundaries of circuit elements are desirable to reduce transmission losses in pattern generated film.

Optical propagation in sheet and pattern generated films of ta(2)o(5).

A report of the first Topical Meeting on Integrated Optics—Guided Waves, Materials, and Devices has been prepared by four members of the Technical Program Committee. The meeting was held 7–10 February 1972 and was sponsored by the Lasers Technical Group of the Optical Society of America, the International Commission for Optics, and the International Union of Pure and Applied Physics.

P. K. Tien

Papers

Light waves in thin films and integrated optics.

Thin Organosilicon Films for Integrated Optics

Formation of light-guiding interconnections in an integrated optical circuit by composite tapered-film coupling.

Optical propagation in sheet and pattern generated films of ta(2)o(5).

Integrated Optics and Guided Waves-a Report of the Topical Meeting.