Optical grating and method of fabricating an optical grating

An optical grating including a sequence of grating lines, the sequence being characterized in that:

• a) the position of each grating line in said sequence is centered at an integer multiple of a predetermined line spacing distance from a fixed point;
• b) said sequence of grating lines being non-periodic;
• and
• c) the sequence of grating lines being formed from a multiplicity of N concatenated subsequences of grating line, each subsequence comprising a series of one or more instances of a predetermined pattern of grating lines;
• in which N=p. 2.sup.M, where p is a prime number and M is a whole number.

A method of fabricating an optical grating, said method comprising the steps of:

• c) calculating a grating response of a grating comprising an optical grating including a sequence of grating lines, the grating being such that:
• the position of each grating line is centered at an integer multiple of a predetermined line spacing distance from a fixed point;
• the sequence of grating lines being non-periodic and being formed from N concatenated subsequences, each subsequence comprising a series of one or more instances of a respective grating line pattern;
• and
• (d) subsequence repeatedly altering a subsequence of the grating whose response is being calculated and determining whether to accept the alteration of the subsequence until a predetermined criterion is achieved;
• and
• e) forming the resultant optical grating sequence on a substrate;
• in which the decision whether to accept an alteration to one of the subsequences is determined by an annealing algorithm.