Skip to main content

Transverse Optical Patterns

Objective

The TOPP Action aimed to solve the following problems:
-information encoding into transverse field structures emitted by lasers
-utilisation of lasers for the execution of complex logic functions, such as pattern recognition and image processing.
A theoretical and experimental study of pattern formation in lasers and other non-linear optical resonators was made. Non-linear optical systems of large Fresnel number were applied in complex logic functions such as pattern recognition. Lasers were examined (as typical example of non-linear resonators) for possible use in parallel optical processing, similar to optical neural networks but with substantially higher speeds. Lasers can emit radiation patterns containing phase singularities of order minus to plus infinity. These singularities tend to be arranged in a crystalline manner. For problems involving expansions in models of indices up to a sum of 4, stable laser emission patterns have been derived from a variational principle. These patterns can contain phase singularities of order up to 4. Radiation patterns exhibit multistability, which already permits the simpler kinds of pattern recognition and image processing. Theoretical predictions have been confirmed using helium-neon and sodium (Na2) (laser-pumped) lasers, showing optically induced switching between coexisting radiation patterns. Theoretical work shows the mathematical correspondence of lasers with compressible fluids(and of phase singularities with vortices). The existence of free optical vortices shows that lasers are capable of high numbers of coexisting states (images). One way of coding information into the transverse structure of laser fields is to use dislocated optical vortex crystals, or the pixellization of images by using arrangements of phase singularities of different charge.
APPROACH AND METHODS
The research started from noting that non-linear systems usually show coexistence of solutions or states between which switching is possible (eg for an optical system by optical means), so that decision-making and pattern recognition by lasers are conceivable.
Work focused on the role of defects or optical singularities and their geometric arrangement in laser fields as a method for coding information into the laser fields themselves, and took into account the similarity between the temporal evolution and finalstates of certain cellular automata and lasers.
Theoretical studies addressed the laser equations, including transverse effects. The optical pattern formation cases which can be treated by mode expansions were studied. The possible and stable optical patterns were found from a variational principle. The experiments used, among others, optically pumped lasers to test the predictions made.
PROGRESS AND RESULTS
-Lasers can emit radiation patterns containing phase singularities of order minus to plus infinity. These singularities tend to be arranged in a crystal-like manner.
-For problems involving expansions in modes of indices up to a sum of 4, stable laser emission patterns have been derived from a variational principle. These patterns can contain phase singularities of order up to 4.
-Radiation patterns exhibit multistability, which already permits the simpler kinds of pattern recognition and image processing. Theoretical predictions have been confirmed using He-Ne and Na2 (laser-pumped) lasers, showing optically induced switching be tween coexisting radiation patterns.
-Theoretical work shows the mathematical correspondence of lasers with compressible fluids (and of phase singularities with vortices).
-The existence of free optical vortices shows that lasers are capable of high numbers of coexisting states (images). One way of coding information into the transverse structure of laser fields is to use dislocated optical vortex crystals, or the pixellis ation of images by using arrangements of phase singularities of different orders.
-In addition to stationary transverse patterns, the laser is able to give rise to dynamical structures, for example rotating patterns or structures which display creation and annihilation of pairs of vortices (phase singularities) with opposite topologic al charge.
-An optical associative memory might be realised by combining a multistable laser with a linear optical system composed of lenses, holograms and pinholes. The memory consists in a set of images stored in one of the holograms; the number of images is equa l to the number of coexisting stationary states of the laser.
POTENTIAL
Non-linear optical resonators (possibly semiconductors) could be used for parallel optical processing in the same way as the "optical neural networks" but with substantially higher speeds. This would enable complex tasks like image processing and pattern recognition to be executed much faster than with current technology.
Systems which perform gating and routing operations can be conceived. Rotating patterns could be utilised, for example, to realise optical tweezers or to perform scanning operations.

Coordinator

Physikalisch-Technische Bundesanstalt
Address
Bundesallee 100
38116 Braunschweig
Germany

Participants (1)

Università degli Studi di Genova
Italy
Address
Via Dodecaneso 35
16146 Genova