Examples include a tunable laser, in particular, an external cavity type laser. Examples also include a method of operating the tunable laser. The tunable laser is designed for fast and repeatable wavelength tuning over a wide wavelength range. The tunable laser includes a cavity and a gain medium arranged in the cavity. The gain medium is configured to generate light by stimulated emission and to emit the light into the cavity. The tunable laser also includes a laser output configured to output a portion of the light in the cavity as a laser beam. The cavity includes a first resonator and a second resonator that are optically coupled to each other. A resonance frequency of the first resonator is tunable. A free spectral range (FSR) of the second resonator is an integer multiple of an FSR of the cavity.