Characterization of two-sided output vertical-cavity laser diodes by external optical feedback modulation

We have fabricated 5.6 nm wavelength tunable vertical-cavity laser diodes with record low CW threshold currents of 650 μA. Laser output power depends on mirror reflectivities as well as intrinsic loss and effective internal efficiency which gives the conversion of carriers into photons of the lasing mode. To optimize laser mirror design for maximum output power it is important to know the loss and efficiency values. With in-plane lasers these intrinsic device parameters are commonly determined by measuring the threshold currents of equally processed devices of different cavity lengths. Obviously, this is impossible for vertical-cavity lasers even if in-plane lasers are made of epitaxial multilayers grown for vertical-cavity lasers due to different waveguiding mechanism. Therefore we have modulated the effective reflectivity of the vertical-cavity laser Bragg mirrors by external reflection to obtain the intrinsic parameters. We applied the technique for the first time to vertical-cavity laser diodes with two-sided light output but it can be applied to devices with one-sided output as well