Abstract: The optical fibre lattice signal processor comprises at least two coupling devices through which two optical fibres pass in a manner permitting optical coupling therebetween. The optical coupling devices are arranged in parallel with respect to each other and each fibre experiences a 180.degree. turn between the couplers. Recursive and non-recursive arrangements are provided for, together with equal and arbitrary delays.

Abstract: An optical resonant assembly which comprises a plurality of partially light-transmitting mirrors, a layer of photochromic material disposed between the mirrors, a light source providing a light beam of variable intensity incident on the layer of photochromic material and detecting means for determining transmittance values of said incident beam at different intensity levels, said photochromic material having a low quantum yield for bleaching with light of a wavelength corresponding to said light beam and being selected from pyran compounds of the general formula (I) below: ##STR1## wherein X and Y together represent a spiro-adamantylidene group or a spiro-carbocyclic or heterocyclic group or X and Y independently represent hydrogen, alkyl (preferably lower alkyl having 1 to 5 carbon atoms) or phenyl and R.sub.3 and R.sub.4 each independently represent hydrogen, alkyl, aralkyl, aryl, halogen or a heterocyclic group and R.sup.