A low-latency, small-form-factor optical link for the high-luminosity LHC experiments

We present a low-latency, small-form-factor optical link designed for the high-luminosity LHC experiments in which the latency and form factor are critical. The optical link on the transmitter side is composed of a transmitter ASIC and a custom-made optical transmitter module. The transmitter ASIC includes an encoder and a serializer. Two serializer ASIC prototypes, operating at 5 and 8 Gbps per channel respectively, have been designed and tested. A low-latency, low-overhead encoder has been verified in FPGAs and is being integrated into a two-channel, 8∶1 transmitter ASIC with each channel operating at 5.12 Gbps. A prototype of the custom-made optical transmitter module (called MTx) with separate transmitter optical sub-assemblies (TOSAs) has been demonstrated. A Vertical-Cavity Surface-Emitting Laser (VCSEL) driver ASIC has been developed and will replace the commercial VCSEL laser driver used in the current MTx prototypes. The latency of the whole link, including the transmitter latency and the receiver latency but not including the latency of the fiber, is estimated to be less than 80 ns. The size of the MTx is 42 mm × 15 mm × 6 mm.