Continuous frequency tuning of an external cavity diode laser significantly beyond the free spectral range by sweeping the injection current

In this study, the frequency of an external cavity diode laser with an antireflection-coated laser diode was continuously tuned over a range of 14.8 GHz, which was 4.5 times larger than the free spectral range, by only sweeping the injection current to the laser diode. Without the antireflection coating, the tuning range was reduced to one-fifth of the free spectral range, and mode hops occurred with hysteresis. The theoretical analysis starting from the hysteresis indicated that an unexpectedly wide tuning is possible if the longitudinal modes of the solitary laser diode vanish owing to antireflection coating.