Thermally induced birefringence tuning of 37 GHz in VCSELs

Vertical-cavity surface-emitting lasers (VCSELs) are the transmitters of choice in high-speed optical interconnects. Further progress beyond present 25 Gb/s devices is hampered by the limited modulation bandwidth of not more than 30 GHz. For higher data rates one thus has to resort to higher-order modulation formats [1] with substantially increased system complexity. Polarization modulation of VCSELs is a potential alternative to intensity modulation. In this technique the birefringence splitting B, namely the frequency difference between the two fundamental polarization modes, is a key parameter. By optical spin injection a birefringent VCSEL can be excited to oscillations in the degree of circular polarization, where the oscillation frequency is close to B [2]. In this work we show a large tuning range of B in a VCSEL achieved via anisotropic strain caused by an integrated heater.