40-GHz electro-optic polarization modulator for fiber optic communications systems

TLDR

The paper introduces a novel ultrahigh‑speed electro‑optic polarization modulator. The modulator employs a mode converter built from an AlGaAs ridge waveguide with slow‑wave traveling‑wave electrodes and a static polarization controller to steer the output polarization along a great‑circle path on the Poincaré sphere, with electrodes velocity‑matched to the electrical and optical signals over a wide bandwidth. The device can connect any two polarization states, achieves a 3‑dB bandwidth exceeding 40 GHz, and operates with only a few tens of femtoseconds differential group delay and a drive voltage around 5 V.

Abstract

A novel ultrahigh-speed electro-optic polarization modulator is introduced. The modulator uses a mode converter and a static polarization controller to change the output polarization state in a circular path, following a great circle, around the Poincaré sphere. Any two states on the Poincaré sphere can be connected. The mode converter is constructed using an AlGaAs ridge waveguide combined with slow-wave travelling wave electrodes. The travelling wave electrodes are designed to match the velocity of the electrical modulating signal, the data signal, to the optical carrier signal over a broad frequency range. This modulator demonstrates a 3 dB bandwidth in excess of 40 GHz. The polarization modulator exhibits extremely low differential group delay, on the order of a few 10s of femto-seconds, and low drive voltage, on the order of 5 V.