8-Channel CWDM TOSA for CPO External Laser Sources

This paper describes the design and characteristics of an 8-channel (4-λ x 2) CWDM TOSA which can be built in external laser source (ELS) modules for a Co-Packaged Optics (CPO)-based network switch server. The TOSA achieves a fiber-coupled power of >20 dBm for all channels over the case temperature ranging from 25°C to 55 °C. All channels obtain a polarization extinction ratio of >20 dB. The mechanical size of the TOSA as small as 23.5 mm x 13.0 mm x 4.0 mm enables to be bult in a standard QSFP housing. We also design and fabricate a pigtailed QSFP ELS using the TOSA. Based on the thermal simulation, the bottom surface of the TOSA should be thermally connected to the top housing to realize a small temperature difference of 0.7 °C between the case temperature of TOSA and the housing temperature of QSFP ELS. The QSFP ELS achieves the fiber-coupled power of >20 dBm at a housing temperature of 55°C, PER of>20 dB, and RIN of <−150 dB/Hz for all channels.