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nanotimes News in Brief

11-08 :: August 2011

Optics // An Octave Spanning Chip-based Optical Ruler

© Text: MPQ

der of the Max Planck Research Group “Laboratory of Photonics and Quantum Measurements” at MPQ, who has since then become Associate Professor at the Ecole Polytechnique Fédérale de Lausanne (EPFL), succeeded for the first time in generating op- tical frequency combs using chip-based quartz glass toroids with diameters on the micrometer scale. Now the scientists made a big step further: their new mi- croresonators produce light over a range of more than an octave and are at the same time precisely tunable.

A

A frequency comb is a light source containing – simi- lar to a rainbow – a large spectrum of colours. Howe- ver, the frequencies are not continuously distributed. Instead, up to a million spectral lines are spaced in exactly the same distance. The superposition of this “comb” with another laser beam results in a pattern from which the unknown laser frequency can be determined with very high accuracy. The frequency comb developed by Prof. Hänsch is based on a mo- de-locking process in short-pulse lasers. This set-up consists of many optical components, even though it is made today relatively compact and commercially available. Indeed, Menlo System a spin-off company established by MPQ which is meanwhile marketing the frequency comb technology worldwide.

lready a couple of years ago, a team of scientists around Dr. Tobias Kippenberg, formerly Lea-

Octave spanning frequency comb generation in a microresonator. Panel (a) shows the experiment with a glass nano-fiber and a silicon chip with optical re- sonators. A scanning electron microscope picture of a resonator is shown in panel (b). Panel (c) shows the optical spectrum of the frequency comb generated in such a microresonator seeded by a single frequency laser. © MPQ

A couple of years ago, the group “Laboratory of Photonics and Quantum Measurements”, which was associated with the Laser Spectroscopy Division of Professor Hänsch, has succeeded in generating a frequency comb by means of a tiny microstructure, a toroidal glass resonator with a diameter of less than 100µm. This was done in cooperation with Dr.