Optical Transmitter Equalization With Mismatched Terminations In A Mach-Zehnder Modulator

Electro-optic modulators, critical components in optical communication systems, transmit data by altering the frequency, phase, or amplitude of an optical carrier wave based on input electrical signals. Traveling-wave Mach-Zehnder modulators (TW-MZMs) are generally favored over other types of modulators due to their temperature insensitivity. However, optical transmission components, including TW-MZMs, are typically the bandwidth bottleneck in optical communication links. There is an inherent challenge in reaching high data rates while simultaneously maintaining low power consumption and a low bit error rate. Optical equalization methods are a promising solution to improve link performance.

Researchers at the University of California, Santa Barbara have invented a new technique for optical equalization that enables optical links to operate at significantly higher data rates while also benefiting from the inherent broadband optical response and temperature insensitivity of TW-MZMs. This technology employs a termination circuit that introduces a tunable mismatch where the termination resistance is less than the driver side impedance of the transmission line electrodes. Consequently, the termination has a tunable negative real reflection coefficient, and incident electrical waves are reflected in inverted form. As the leading edge of a forward-traveling electrical pulse (FTEP) arrives at the end of the electrode, an inverted backwards-traveling electrical pulse (BTEP) starts to propagate. The BTEP produces an opposite phase change in the forward-traveling optical pulse (FTOP) compared to the FTEP. The accumulated phase change produced by the BTEP is largest at its trailing edge, resulting in a modulated optical signal with emphasis at the bit transitions. This invention also circumvents any alterations to the driver circuit and leverages monolithic electronic-photonic fabrication processes.

• Enhances bandwidth
• Can reduce bit error rate
• Can be implemented monolithically
• Variable termination resistance allows reflection coefficient to be tuned for optimal performance