Modulator-Based, High Bandwidth Optical Links for HEP Experiments

As a concern with the reliability, bandwidth and mass of future optical links in large High Energy Physics experiments, we are investigating CW lasers and separate light modulators as an alternative to modulated lasers called VCSELs. These links will be particularly useful if they can utilize light modulators which are very small, low power, high bandwidth, and are very radiation hard. We have constructed a test system with 3 such links, each operating at 10 Gb/s. We present the quality of these links (jitter, rise and fall time, and bit error rate (BER)) and eye mask margins (10 GbE) for 3 different types of modulators: LiNbO3-based, InP-based, and Si-based. We present the results of radiation hardness measurements with up to
$\sim 10^{12}\ {\rm protons/cm}^{2}$
and
$\sim$
64 krad total ionizing dose (TID), confirming no single event effects (SEE) at 10 Gb/s with any of the 3 types of modulators. We have used a Si-based photonic transceiver to build a complete 40 Gb/s bi-directional link (10 Gb/s in each of four fibers) for a 100 m run and have characterized it to compare with standard VCSEL-based optical links. Some future developments of optical modulator-based high bandwidth optical readout systems, and applications based on both fiber and free space data links, such as local triggering and data readout and trigger-clock distribution, are also discussed.