LT-GaAs detector with 451 fs response at 1.55 µmvia two-photon absorption

The impulse photoresponse from low temperature (LT) grown GaAs coplanar stripline switches was measured at 1.55 µm using double sliding-contact sampling. The response was attributed to two-photon absorption as confirmed by the observed quadratic dependence of the photocurrent on average incident illumination. The devices exhibited a response full width at half maximum of 451 fs and a 3 dB bandwidth of 190 GHz, which is, to date, the fastest response measured from LT-GaAs switches at this wavelength. The response peak was linearly dependent on the applied bias and showed a strong dependence on incident field polarisation. These devices could find applications in high temporal resolution sampling at 1.55 µm.