The present invention provides a continuously tunable
external cavity laser (ECL) with a
compact form factor and precise tuning to a selected center
wavelength of a selected
wavelength grid. The ECL may thus be utilized in telecom applications to generate the center wavelengths for any channel on the ITU or other optical grid. The ECL does not require a
closed loop feedback. A novel tuning mechanism is disclosed which provides for electrical or mechanical tuning to a known position or electrical parameter, e.g.,
voltage, current or
capacitance, with the required precision in the selected center
wavelength arising as a result of a novel arrangement of a
grid generator and a channel selector. The
grid generator exhibits
first pass bands which correspond to the spacing between individual channels of the selected wavelength grid and a
finesse which suppresses
side band modes of the
laser. The channel selector exhibits second pass bands that are wider than the
first pass bands. In an embodiment of the invention the second pass bands have a periodicity substantially corresponding with the separation between the shortest wavelength channel and the longest wavelength channel of the selected wavelength grid and a
finesse which suppresses channels adjacent to the selected channel. The broad second pass bands of the channel selector reduce the sensitivity of the ECL to tuning variations about the selected channel, thus avoiding the requirement of a
closed loop feedback
system to control the channel selector.