Tuning wavelength and linewidth of an external cavity diode laser using an active control scheme based on polarization spectroscopy

We present a novel technique for external cavity diode lasers (ECDL) in Littrow configuration which guarantees large mode-hop free tuning ranges combined with the ability to adjust and control the linewidth. These features are favorable in many applications. For tuning an ECDL it is required that the internal, i.e. the diode itself, and the external cavities, i.e. the resonator formed by the facet of the diode and the grating, are simultaneously in resonance. Our method implements a closed loop control in order to sustain the resonance condition of the ECDL. The error signal for the control loop is given by the state of polarization (SOP) of the laser light. By placing a quarter-wave-plate into the external cavity, cf. Fig. 1a, the information about the resonance of the ECDL is transferred to the SOP.