A tunable laser device (1) comprises integrally formed first and second ridge waveguides (5, 6). A longitudinally extending ridge (12) defines first and second light guiding regions (19, 20) of the first and second waveguides (5, 6) which communicate with each other. A plurality of first slots (27) extending laterally in the ridge (12) adjacent the first waveguide (5), and a plurality of second slots (28) extending laterally in the ridge (12) adjacent the second waveguide (6) produce first and second mirror loss spectra of the respective first and second waveguides (5, 6) with minimum peak values at respective first and second wavelength values. The first slots are equi-spaced apart to produce the first mirror loss spectrum, and the second slots (28) are also equi-spaced apart, but the spacing between the second slots (28) is different to the spacing between the first slots (27) so that the minimum peak values of the second mirror loss spectrum occur at different wavelength values to the wavelength values at which the minimum peak values of the first mirror loss spectrum occur, with the exception of one minimum peak value of each of the first and second mirror loss spectra, which coincide at a common wavelength value. The tunable laser device (1) produces light of that common wavelength value. In order to vary the wavelength value at which the minimum peak value of each of the first and second mirror loss spectra occur, currents with which the first and second waveguides (5, 6) are pumped are independently varied for varying the wavelengths at which the minimum peak values of the respective first and second mirror loss spectra occur, thereby providing Vernier tuning of the tunable laser device for producing light of selectable wavelengths.