Wavelength stability of DFB lasers for non-hermetic applications

As the opto-electronics telecommunication components industry moves toward higher speed, lower cost packages, with higher and higher levels of integration, the need for non-hermetic distributed feedback (DFB) laser diodes has arrived. As an example, we have integrated these laser diodes into non-hermetic 2.5 Gbit/s transponder samples, which have demonstrated 20-kilometer link distances. We consider here DFB lasers for non-hermetic telecommunication applications. One of the critical issues facing non-hermetic laser diodes involves proper passivation of the laser facet region to prevent electro-chemical corrosion of the InP semiconductor material. One approach involves the use of a polymer encapsulent to protect the laser diode from electrochemical corrosion induced by moisture. However, polymer encapsulent does not inhibit moisture penetration, and may only passivate the laser diode at the junction region. Our approach involves the use of an Al_xTa_yO_z facet coating that inhibits the absorption of moisture and serves as both a back (highly reflective) and front (antireflective) coating. For the non-hermetic DFB laser, we are concerned with not only moisture penetration and facet coating delamination, but also wavelength stability which is highly sensitive to changes in facet coating refractive index. We have examined the power aging and wavelength stability of non-hermetic DFB lasers with two different Al_xTa _yD_z facet coatings under temperature/humidity/bias (THB) conditions. Small populations of lasers have been subjected to 85 C/85% RH conditions under low bias (~10 mA) conditions. It is extremely important to accelerate the effects of moisture and humidity in these laser diodes to ensure that they remain robust for 15-20 years in non-hermetic environments. Low bias prevents the laser junction region from heating up with respect to the local ambient, yet still provides ample potential (~1V) to promote any electro-chemical corrosion effects. The use of low current effectively prevents the laser from drying out (which will drastically lower the relative humidity at the junction region) and generating false negative results. Data is provided on wavelength and power stability of nonhermetic DFB lasers subjected to accelerated THB conditions. To our knowledge this is the first reported data on wavelength stability of non-hermetic DFB lasers in hot humid ambients