A tunable external cavity laser equipped with an optical path length compensator for adjusting an optical path length of the cavity, a wavelength selector for selecting an operating wavelength of the light in a single longitudinal mode and a dispersion compensator for compensating a dispersion of the light. In order to achieve mode-hop-free tuning the laser has a synchronizer for synchronizing the optical path length compensator, the wavelength selector and the dispersion compensator to maintain the light in the selected single longitudinal mode while the wavelength selector tunes the operating wavelength. The laser employs a pair of prisms and a wedge filter or a gap filter to perform the functions of the optical path length compensator, the wavelength selector and the dispersion compensator.