In contrast to academic research, commercial developments, which have mostly
adopted the Littman configuration to achieve better side-mode suppression, have
incorporated two or more degrees of freedom in the actuator design so that both
initial alignment and compensation for cavity dispersion can be controlled by the
MEMS structure [153, 154]. These types of lasers have excellent stability and
optical characteristics. The complexity of the optical hardware and the control
circuitry lead to costs that are significantly higher than for fixed-wavelength
semiconductor lasers. Systems solutions that use single fixed-wavelength lasers
are therefore still preferred, even in application that would benefit from wave-
length tuning. One solution with intermediate ...