A tuneable laser including a light creating section to generate light and a tuneable section formed of a semiconductor material which utilises the electro-optic effect to achieve a change in the refractive index of the material, W n, under the influence of an applied field, F, in accordance with the equation:; where n0 is the refractive index at zero field and W nL and W nQ are the linear and quadratic contributions to the change in refractive index respectively, r is the linear electro-optic coefficient of the material and s is the quadratic electro-optic coefficient of the material, the tuning section including a waveguide and the material of the waveguide incorporating a plurality of quantum dots and operating in a wavelength region where the value of rF is sufficiently greater than the value of sF<2>, so as to operate with the dominant effect on W n being contributed by the linear effect.; The bandgap wavelength, g g of the quantum dots ( g g may be less than 1400 nm) incorporated into the tuning section may be less than that of photons emitted by the light creating section (whose wavelengths range between g 1 and g 2), and the change in refractive index at g 1 and g 2 in operation may be substantially the same. The tuneable section may incorporate a DBR and the laser may include a phase change section that is also tuneable. The laser can be made from a III-V semiconductor material.
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