  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.
