Laterally coupled InGaAsP/InP distributed feedback lasers at 1.5 /spl mu/m for chemical sensing applications

Summary form only given. Single frequency semiconductor lasers with emission wavelength at /spl sim/1.5 /spl mu/m are finding applications as chemical sensors because a large number of molecules have strong absorption bands at this wavelength region including ammonia. Tunable diode laser (TDL) spectroscopy employing tunable single longitudinal mode lasers provides a means in which, trace gases can be accurately monitored using systems that are relatively small in size and low in power consumption. Conventional distributed feedback (DFB) lasers can achieve wavelength selectivity through feedback from a periodic change in index or gain along the laser cavity and this usually requires regrowth, over the corrugation, greatly complicating the fabrication process and making the completed lasers susceptible to unreliability due to the defects at grating/regrowth interface. One way to eliminate this regrowth problem is to introduce the gratings after the lasing cavity is formed and to rely on the coupling of the evanescent optical fields. This has been demonstrated by etching the ridge first and then defining the gratings on both sides of the ridge to fabricate a laterally-coupled (LC) ridge waveguide (RW) DFB laser. In this paper, we report on the lasing characteristics of InGaAsP/InP LC-RW-DFB lasers realized by a greatly simplified fabrication process.