A tunable optical source comprises a laser diode and an external optical feedback
device. The feedback device has a waveguiding portion fabricated at least in part
out of a glass material having both organic and inorganic components. A control
device is provided for controlling the refractive index of the glass material so
as to change the wavelength of feedback to the laser diode. The glass material
may for example have thermo-optic properties and the control device might then
be a heating device for heating the glass material. The feedback device can have
more than one portion, a second portion for example having controllable coupling
characteristics for coupling optical radiation into or out of the feedback device.
It also preferably has a portion for controlling optical path length in the feedback device.
