Double-mode operation and fast piezo fi ne tuning properties of a gain chip on a thermoelectric cooler in
an external cavity are investigated. A widely course double-mode tuning range of 120 nm for the spectral
range between 1470 and 1590 nm is achieved by rotating the diffraction gratings forming a double
Littrow-type confi guration. A fast piezo fi ne tuning range over −7 cm 1 (1.5 nm, 210 GHz) in a single-mode
operation is obtained by scanning the external cavity length with scan rates up to 0.5 kHz.