Attometer resolution of wavelength shifts by use of fiber modal interferometers.

A method for on-line, real-time detection of wavelength drifts in laser diodes is proposed. This technique uses the wavelength dependence of the differential propagation constant between the LP(01)/LP(even)(11) or LP(01)/LP(02) modes in two-mode fibers to measure wavelength changes that manifest themselves as intensity modulation in the output far field. Theoretical calculations show that wavelength drifts of the order of 10(-18) m can be resolved by this technique.