Distributed feedback (DFB) InGaAsP/InP lasers with a window region formed at an end of the corrugated DFB region were made in order to overcome the problems inherent in the previous structures of DFB lasers with cleaved, sawed, etched, or AR-coated facets, or with an unexcited corrugation region. The window structure DFB lasers showed linear current versus output J-L) curves, in contrast to those with a hysteresis or a kink appearing in a DFB laser with an unexcited region. Suppression of Fabry-Perot (F-P) resonances due to the two facets were sufficient enough to keep a single longitudinal mode property by DFB up to high excitation level. CW operation up to 65°C was achieved at the 1.5 μm wavelength range. Axial modes concerning the corrugated resonator were measured at about the threshold current. A stop band of a DFB laser was clearly observed with two dominant modes and much smaller submodes, which almost agreed with the axial modes predicted from a basic DFB theory.
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