Integrated GaInAsP laser diodes with monitoring photodiodes through semiconductor/air Bragg reflector (SABAR)

A 1.3-μm GaInAsP laser diode (LD) is integrated with a monitoring photodiode (M-PD) through a semiconductor/air Bragg reflector (SABAR). Instead of conventional cleavage, the SABAR can provide not only Fabry-Perot resonance with high reflectivity, but also possibility of integration of laser with other functional devices. The design, fabrication, and some characteristics including threshold current, monitoring photocurrent, SABAR reflectivity as a function of the number of semiconductor/air pairs N are reported. The threshold current of ridge waveguide laser with SABAR (cavity length L=160 μm, ridge width W=7 μm, SABAR pairs N=3) is 20 mA. The threshold current is reduced by improving butt-coupled interface between active and passive waveguides employed in this laser and is expected 2 mA/μm. The monitoring photocurrent responds linearly with output power from the laser and 0.024 mA at laser output power of 5 mW. From the threshold characteristics, SABAR reflectivity is determined to >80%. The increase of photocurrent can be achieved by optimizing the number of SABAR pairs to N=1. We have obtained threshold current of 22 mA in the followed laser structure (L=270 μm, W=7 μm, N=1), and detector photocurrent of 1.13 mA (@5 mW). The experimental SABAR reflectivity is ~50%, which is estimated by threshold characteristics and efficiency of light output power. The laser has a mode field converter section, resulting in narrow beam divergence 11° along vertical axis. This integrated laser is very promising candidate for coming optical module in low-power consumption and low-cost access network systems