Two fundamental requirements for realization of continuously tuning external cavity semiconductor lasers

Two fundamental requirements on the simultaneous adjustments of the grating reflection wavelength and cavity length,antireflection coating stacked on the rear facet of the semiconductor laser(LD) have been discussed quantitatively in order to realize a continuous tuning in an external semiconductor lasers.Studies indicate that the reported adjustable range of the cavity length is not a precondition for achieving the maximum tuning range,but rather a condition for practically achieving a continuous tuning.For certain antireflection coating stacked on the rear facet of the diode,the achievable continuous tuning range has been investigated.