A dual wavelength optical fiber distributed feedback laser comprises a pump laser
coupled to a birefringent fiber in which a first grating device (two co-located
single phase-shift fiber Bragg gratings (FBGs)) is provided. The grating device
gives the laser two potential lasing modes in each of two orthogonal polarization
states. A polarization mode coupling FBG selects two orthogonally polarized modes
on which the laser oscillates. In a photonic data carrying signal source, the laser
is coupled to a polarization dependent, optical modulator operable to apply a modulation,
at a data signal frequency, to one polarization mode of the laser output. In an
optical waveguide based electronic signal transmission system the modulated and
un-modulated polarization modes output from the source are transmitted across a
fiber transmission line to a polarizing optical fiber in which the two modes heterodyne
to generate an electronic carrier signal in the optical domain.