ORC Seminar Series

"Non-Zero-Order Light: Beams that can do what a Gaussian cannot"

Speaker: Siddharth Ramachandran, DTU-Fotonik; Danish Technical University

Date: 10 June 2009

Time: 2pm

Venue: Building 2, 1039 (L/T K)


When we think of laser light, we think of a beam that looks like a spot, or more precisely, like a Gaussian. This ground state solution, in free space, resonators, waveguides, etc., has several well-known properties – for instance they diffract, carry energy (or momentum) in the direction of the beam, are blocked by opaque obstructions, etc. However, many of these properties are dramatically altered if one were able to generate and stably propagate beams that are higher-order, spatially variant solutions of an optical system. For instance, certain non-uniform polarisation distributions of light, when focussed, result in beams that carry no energy along the optic axis. Alternatively, beams with special Bessel-functional profiles can be shown to be strictly diffraction-free, and can even navigate around dark objects.

This talk will introduce the physics of such interesting beam shapes. In particular, we will describe how an optical fiber is an attractive, and perhaps in many cases the only, means to realise these solutions. We will illustrate the utility of such fiber devices, both from the standpoint of studying fundamental physical phenomena and quantum systems, and from the standpoint of realising novel devices with applications in emerging areas such as sensing, high-power lasers and biology.


Dr Siddharth Ramachandran obtained his Ph.D. in Electrical Engineering from the University of Illinois, Urbana-Champaign, in 1998. Thereafter, he joined Bell Laboratories, Lucent Technologies, as a Member of Technical Staff, and subsequently continued with its spin-off, OFS Laboratories. In 2003, he was promoted to the position of Distinguished Member of Technical Staff. After a decade in industry, Dr. Ramachandran has moved to academics, and is currently a Professor at the Danish Technical University.

Dr. Ramachandran’s research focuses on the optical physics of guided waves, with applications to quantum and atom optics, biomedical imaging, lasers, sensors, as well as telecom. He has authored over 125 refereed journal and conference publications, more than 20 invited talks and papers, 2 book-chapters, over 30 patent applications, and is the editor of a Springer-Verlag book on “Fiber-based dispersion compensation.” His work on higher order mode fibers has been highlighted several times in popular or trade magazines such as Laser Focus World and Photonics Spectra. Dr. Ramachandran is a topical editor for Optics Letters and has served on numerous conference and grant-review committees.

Dr. Ramachandran is a member of OSA and IEEE-LEOS.


Copyright University of Southampton 2006