  We characterize a semiconductor external cavity diode laser whose optical
feedback is provided by a guided mode resonance filter (GMRF). We focus on the
spectral properties. The wavelength of operation falls in the telecom range
(1506 nm). The GMRF acting both as a wavelength intracavity filter and feedback
mirror allows for a compact laser design. The single-mode operation is verified
in a wide range of driving currents. We finely tune the cavity length to adjust
the frequency by 14 GHz without mode-hops in agreement with the expected
free-spectral range of the resonator $\sim$20 GHz. The compactness of the
cavity allows fast frequency sweeps when modulating the current (90 MHz/mA at
100 kHz, the modulation bandwidth). The frequency noise (366 kHz white-noise
contribution) is also analysed to evaluate the potential of our design for
high-resolution applications.
