Photonic Systems Brown Bag Seminar Series

Thursday, October 27, 2005, at 12 noon                        RLE Haus  Conf. room 36-428

"Modal Decomposition for Photonic Bandgap Fibers and Fiber-Web Detectors"

Ofer Shapira

"Decomposing the optical field emerging from a multimode waveguide
explicitly in terms of its constituent modes is a problem that has not been
satisfactorily solved heretofore. The main obstacle is lack of access to
the phase of the emerging complex field. Here I introduce an approach to
achieve modal decomposition of the fields at the output of a general
waveguiding structure.  The technique utilizes a mapping of the
two-dimensional field distribution onto the one-dimensional space of
waveguide eigenmodes, together with a phase retrieval algorithm to extract
the amplitudes and phases of all the guided vectorial modes. Experimental
validation is provided by using this approach to examine the interactions
of modes in a hollow-core photonic bandgap fiber.

I next discuss the use of two dimensional photodetecting arrays that
utilize our recently demonstrated metal-insulator-semiconductor
photodetecting fibers. In particular I demonstrate  that two such arrays
can provide a full characterization of a large-area complex optical wave
front, enabling one to readily reconstruct the object from which the field
originally emanated and, hence, demonstrate lensless imaging of the object
using this arrangement. This new geometric approach to optical detection
lifts some of the fundamental limitations associated with conventional
detection and imaging systems. The underlying computational algorithm is,
interestingly, the same phase retrieval algorithm used above in a different
context."