High Output Power SOA Assisted Extended Reach EADFB Laser (AXEL) TOSA for 400-Gbit/s 40-km Fiber-Amplifier-Less Transmission

An AXEL sub-assembly and a 4-channel AXEL TOSA were designed and fabricated. The sub-assembly with a width of less than 0.65 mm was needed to make the width of TOSA applicable to QSFP-DD transceiver. On the other hand, the wire that connects between the terminator and the DC block capacitor must be 0.5 mm or longer to obtain 3-dB bandwidth of over 40 GHz which is enough for 50-Gbaud operation. To become that wire length 0.5 mm or more on the narrow sub-assembly, the AXEL chip was placed between the RF circuit board integrated with the terminator and the DC block capacitor. As a result, the AXEL sub-assembly with a width of only 0.65 mm and with a 3-dB bandwidth of more than 40 GHz was realized. Based on the designed sub-assembly, the 4-channel AXEL TOSA was fabricated. Size of the TOSA is only 18.2 × 6.2 × 5.4 mm (which is suitable for a QSFP-DD transceiver). Optical-modulation amplitudes (OMAs) of the fabricated TOSA exceed +4.7 dBm for all channels. 40-km SMF fiber-amplifier-less transmission of 4-channel × 100-Gbit/s/λ signals was successfully demonstrated by using the fabricated 4-channel AXEL TOSA, 4-channel APD ROSA, and a commercially available DSP. Loss budgets exceed 18 dB for all channels.