12 December 2008 ICFO on OPN\'s cover

OPN's cover

A new source of entangled light, designed at ICFO, highlighted in the December issue of OPN Optics of
the Year.
A device for generating pairs of entangled photons with an ultra-broad frequency spectrum is on the cover of the current issue of Optics and Photonics News, as one of the outstanding scientific results achieved in Optics during 2008. The work was published in Physical Review Letters by an international collaboration effort between Boston University, Stanford University and ICFO. Profs. Juan P. Torres and Lluís Torner participated in the work, as well as Dr. Silvia Carrasco, who at that time was affiliated with the Quantum Imaging Lab of the Boston University.

Light containing huge numbers of frequencies is useful in many fields, as for example in metrology applications, allowing for high precision measurements, or in Optical Coherence Tomography, where images in great detail of the retina are obtained non-invasively. A large bandwidth is also a requisite for generating light with very short duration in time. In this work, pairs of entangled photons with a large bandwidth are obtained through the use of a nonlinear crystal which changes its property along the direction of propagation of the light beam, namely, it changes the sign of the nonlinear coefficient. While a fixed period is usually used, in the work highlighted in OPN, the period is made to change. As the cover shows, the researchers were able to achieve a record ultra-broad bandwidth, which translates in optical coherence tomography images with resolution as high as 1 micron. The generation of such ultra-broadband non-classical light opens the door to the generation of pairs of photons with a time separation of just a few femtoseconds, a race where several groups around the world are involved.