Scientists at the University of Bonn have built optical fibre filters in a very simple way. They are not only extremely compact and stable, but also colour-tuneable, which means they can be used in quantum technology and as sensors for temperature or for detecting atmospheric gases.
Optical resonators or filters are important components cutting out very narrow spectral lines from white light sources. In the simplest case, they are built from two opposing mirrors reflecting light back and forth. The wavelength of the filtered light is set by the mirror separation. Suitable mirrors have been integrated with the end of optical fibres for some time. Recently, researchers from the University of Bonn have built such optical fibre resonators in a simple way. They are not only extremely compact and stable, but also allow the wavelength to be tuned. The fibre ends carrying the mirrors are glued into a common ferrule which can be stretched by means of a piezo crystal and hence the mirror separation controlled.
“The miniaturised optical filter makes a further contribution to making photonics and quantum technologies the decisive technology of the 21st century”, says Prof. Dr Dieter Meschede from the Institute of Applied Physics at University of Bonn. He is a member of the “Matter and light for quantum computing” (ML4Q) Cluster of Excellence of the Universities of Bonn and Cologne and RWTH Aachen University and is also a member of the Transdisciplinary Research Area “Building Blocks of Matter and Fundamental Interactions” at the University of Bonn.
Miniaturised, highly stable optical precision filters have promise in multiple applications: they can store light energy within such a small volume that already single photons can be efficiently stored and manipulated. Their high sensitivity indicates that it may be possible to build extremely compact and selective sensors, e.g. for detecting atmospheric gases. Using even more stable materials for the ferrule, it miniature optical clocks with extremely high frequency stability may be built.
