Simultaneous C+L-band nano-ITLA based on co-packaged multi-channel interference lasers for 400G coherent communication

To meet the growing bandwidth demand in coherent optical communications, compact light sources with C+L-band tuning and narrow linewidth are essential for expanding transmission capacity. This work presents, for the first time, a novel C+L-band nano-integrable tunable laser assembly (nano-ITLA) based on multi-channel interference lasers. An innovative co-packaging scheme integrates two separate laser chips covering the full C++ and L++ bands, a Z-block, two thermoelectric coolers, and a wavelength locker into a single transmitter optical subassembly (TOSA). The laser structure is folded with the semiconductor optical amplifier section, reducing chip length by 37.5%, while the 16 phase sections of the two lasers are connected in parallel, saving 40% of pins. A compact printed circuit board integrated with a fast frequency characterization system is designed and assembled with the TOSA, achieving a nano-ITLA sized 25.0 mm (L) × 15.6 mm (W) × 6.5 mm (H). This device supports 240 ITU grids with 50 GHz spacing in the C+L band, achieving a side mode suppression ratio >45 dB, output power >16.5 dBm, and Lorentzian linewidth <180 kHz. It is integrated into a CFP-2 coherent optical module and maintains a pre-forward-error-correction bit-error rate below 4 × 10−3 under 400 Gbit/s transmission. This C+L-band tunable nano-ITLA demonstrates excellent potential for next-generation coherent optical communication.