$290fs$ switching time of Fe-doped quantum well saturable absorbers in a microcavity in $1.55μm$ range

Ultrafast all-optical switch has been demonstrated by inserting Fe-doped multiple quantum wells (MQWs) in asymmetric Fabry-Perot microcavities. Heavy Fe doping during the $InGaAs∕InP$ MQW epitaxial growth is a well-controlled technique to reach subpicosecond optical time constants. An asymmetric Fabry-Perot microcavity using gold metal as a back mirror and air/InP interface as a front mirror is realized. Pump-probe experiments using a conventional scheme on such switching devices are investigated. The device reveals an ultrafast response time, as low as $290fs$⁠, for an iron concentration of $2×1019cm−3$⁠, a contrast ratio of $8dB$⁠, a threshold switching fluence of $3.5μJ∕cm−2$⁠, and a $37-nm$ $3-dB$ bandwidth in the $1.55-μm$ telecommunication spectral range.