Monolithically integrated 4 ch × 25.8 Gbps lens-integrated surface-emitting DFB laser array directly coupled to SMF

Direct optical coupling and a 4 × 25.8-Gbps 2-km optical link were demonstrated simultaneously by using a lens-integrated surface-emitting DFB laser (LISEL) array for a low-cost multi-lane optical module. The integrated lens was optimized so that the LISEL had a focused beam, resulting in high-efficiency (−3.5 dB) direct optical coupling to a SMF. Thanks to its short DFB cavity with high-gain InGaAlAs active layer, the LISEL array demonstrated 4 × 25.8-Gbps 2-km error-free transmission. Moreover, it achieved error-free transmission up to 70 °C.