  New optical sensors called the "D-Egg" have been developed for cost-effective
instrumentation for the IceCube Upgrade. With two 8-inch high quantum efficient
photomultiplier tubes (PMTs), they offer increased effective photocathode area
while retaining as much of the successful IceCube Digital Optical Module design
as possible. Mass production of D-Eggs has started in 2020. By the end of 2021,
there will be 310 D-Eggs produced with 288 deployed in the IceCube Upgrade. The
D-Egg readout system uses advanced technologies in electronics and computing
power. Each of the two PMT signals is digitised using ultra-low-power 14-bit
ADCs with a sampling frequency of 240 megaSPS, enabling seamless and lossless
event recording from single-photon signals to signals exceeding 200 PE within
10 nanosecond, as well as flexible event triggering. In this paper, we report
the single photon detection performance as well as the multiple photon
recording capability of D-Eggs from the mass production line which have been
evaluated with the built-in data acquisition system.
