Design of VCSEL´s for feedback insensitive data transmission and external cavity active mode-locking

We present a detailed study of feedback effects in the regime of -60 to -2 dB feedback of top surface-emitting vertical-cavity laser diodes (VCSEL). Feedback dependent properties such as threshold current reduction, mode-locking, relative intensity noise and power penalty in high data rate transmission are shown to be strongly dependent on the output mirror reflectivity. A two-resonator model is applied to derive design equations and to explain feedback properties. In 1 Gbit/s single-mode fiber transmission VCSEL´s with top Bragg mirror reflectivity of 99.8% require a power penalty of 1.5 dB at -10 dB feedback level while similar VCSEL´s with 99.0% top mirror reflectivity run into a noise floor of 10^-4 bit-error rate for the same feedback conditions. Strong feedback is used to generate nearly transform limited mode-locked 22 ps pulses with timing jitter below 1 ps in a single-mode fiber VCSEL module of 1.7-mA threshold current