Polarization mode dispersion compensation

A method of compensating for polarisation mode dispersion in an optical signal transmitted via an optical waveguide of an optical communications system, the method comprising the steps of;

• separating the optical signal into first and second components having a dispersion delay therebetween;
• delaying the first and second components by respective delays differing by a delay increment;
• recombining the delayed first and second components to form an output signal;
• and
• controlling the delay increment such that in the output signal the dispersion delay is substantially compensated by the delay increment;
• wherein the delaying step comprises delaying at least one component by transmission via a delay line having a chirped Bragg reflector extending longitudinally of the delay line, wherein said respective delay results from a time taken for said respective component to traverse the delay line to and from a reflection position at which Bragg reflection occurs, and wherein the controlling step variably regulates at least one parameter determining the conditions under which Bragg reflection occurs to variably define the reflection position relative to the Bragg reflector.

Delay apparatus for compensating for an unwanted delay between first and second components of an optical signal, the apparatus comprising;

• first and second delay lines operable to delay the first and second components by respective delays differing by a delay increment;
• recombining means operable to recombine the delayed first and second components to form an optical output signal;
• and
• control means operable to control the delay increment such that in the output signal the dispersion delay is substantially compensated by the delay increment;
• wherein at least one delay line comprises a chirped Bragg reflector extending longitudinally of the delay line, wherein said respective delay results from a time taken for said respective component to traverse the delay line to and from a reflection position at which Bragg reflection occurs, and wherein the control means is operable to variably regulate a characteristic of spatial periodicity as a function of position of a chirped refractive index grating formed in an optical medium of the Bragg reflector to thereby variably define the reflection position relative to the Bragg reflector.