Optics and photonics

Light, through our vision, gives us the most information of any of our senses. In spite of this fact many applications of light are relatively “invisible”. When we speak in a mobile phone, for instance, the information is carried by radio waves only a few hundred meters to the nearest base station. There, the radio waves are detected and re-transmitted as light in an optical fiber. Only a few hundred meters from the receiver the light waves are converted into radio waves again as to become “wire-less”. The bulk of the transmission in our “wire-less networks” are hence transmitted by light in optical fibers!

In a similar manner light and optics are used for information transmission and storage in CD- and DVD-discs, in fax machines, in printers, and in copiers. Light is also used to check the insulation in buildings, to weld car bodies and chassis, to sterilize food and water, and to check the oxygenation of blood. Light has thousands of diverse applications.

Stockholm harbors Sweden’s largest research cluster in Optics and Photonics

Photonics is the common label for a large number of applications of light in laser technology, material-science and –technology, information technology, biotechnology, and medicine. The Linné Center in Advanced Optics and Photonics aims to strengthen the competence and knowledge-base at KTH and at Stockholm University in fundamental optics. In particular we have chosen to direct the research toward four rapidly evolving fields that we judge have a substantial potential for future applications. For decades, optics and photonics have been internationally competitive and visible research fields at KTH. As we possess excellent facilities for computation, experiments, and fabrication and employ good people with both a broad and deep knowledge base, we aim to continue to let photonics and optics flourish in our center.

Functional optical materials

The first of the four research fields is functional materials. When light propagates through matter, e.g., glass, semiconductors, or crystals, it interacts with the matter. The interaction results in the light being refracted, absorbed, or frequency converted. Almost any application of optics, even ordinary glasses, requires a thorough knowledge of the material’s optical characteristics. These days, advanced material fabrication technology lets us “artificially” combine materials to form compounds that Nature has not provided for us. The result is multi-functional materials, e.g., materials simultaneously having strong magnetic and optical properties. The development of novel optical materials and materials with novel optical properties, and the simultaneous development of fabrication technology are bound to provide numerous novel, interesting, and useful applications.

Near-field optics

Another of these research fields is near-field optics. In a crude model, light can be seen as a bundle of rays. Lenses bend the rays and mirrors reflect them. However, if one wants to describe interference effects, a better description is to model light as propagating waves. A wave has both an amplitude and a phase and hence two or more waves can either add constructively or destructively. Such a model accounts for phenomena like diffraction from a grating or a hologram very well. If one wants to model the light very close to the light-source one needs to use an even more complex model. Field components that do not propagate, but seems “glued” to the source must be added. These components exist only locally, in the so-called near-field, and these components can be used to study objects smaller than the optical wavelength. This gives a resolution advantage over ordinary microscopy which is limited to wavelength resolution.

Quantum information and quantum communication

The third research field we focus on is quantum information and quantum communication. In this field one is looking at extremely weak light-fields, so weak that the “graininess” of light, the photons, will matter. In addition, the laws of quantum mechanics, such as the uncertainly relations, will influence what we can measure, how well we can make the measurement, and what back-action the measurement will have on the measured system. The uncertainty relation will, e.g., enable us to determine if someone has attempted to measure the state of a weak optical pulse since every measurement will leave a “fingerprint” in terms of measurement back-action. If we want to transmit a secret coding key to someone, this will protect the integrity of the secret key, because any eavesdropping attempt can be detected by looking at the “fingerprints”. Quantum mechanics thus allow us to keep secrets from leaking out. The technology is called quantum key distribution and is a rapidly developing technology.

Nanooptical devices and nanofabrication

The fourth and last area we will focus on is nanooptical devices and nanofabrication. Modern fabrication technology allows reliable fabrication of wavelength-size devices that generate, guide, filter and amplify light. In some cases the components can be smaller than the optical wavelength in vacuum. Some of these components utilize quantum-mechanical properties. Others can do optical signal-processing in an efficient manner. It is of course desirable to be able to fabricate some of the components on a silicon substrate and using silicon fabrication technology to enable both electronics and integrated optics on the very same chip. This would lead to significantly cheaper, simpler and more versatile optical components.