Suspended guided mode resonator in germanium for photothermal detection

Herein, we present the first demonstration of a near-IR photosensor exploiting the opto-thermo-mechanical property of a germanium-guided mode resonator. The work exploits the resonant coupling of IR radiation-induced thermal energy to the mechanical-vibrational mode of a free-standing GMR membrane to realise an on-chip IR sensor. The resonantly coupled light confined in the GMR structure results in absorption, leading to a frequency shift in the membrane vibration. A 6-fold electric field enhancement is estimated for the GMR-embedded germanium membrane compared to an unpatterned germanium slab. An average frequency shift of -0.9 kHz / mW is measured for the germanium-GMR membrane. This confirms that a suitably designed GMR-patterned membrane can be used as a photothermal conversion platform for the detection of infrared radiation. This demonstration paves the way forward for the realisation of miniature on-chip near-IR and mid-IR photodetectors for integrated photonics applications.