US Patent 7415049 Laser with tilted multi spatial mode resonator tuning element

An external cavity laser has a mirror-based resonant tunable filter, such as a Fabry Perot tunable filter or Gires-Tournois interferometer tuning element, with the tunable filter being preferably used as a laser cavity mirror. A mirror-based resonant tunable filter is selected in which the spectral response in reflection has an angular dependence. A tilt scheme is used whereby by selecting an appropriate angle between the filter's nominal optical axis and the cavity optical axis, a narrowband peak spectral reflection is provided to the laser cavity. This tunable narrowband spectral reflection from the filter is used to lock and tune the laser output wavelength.