Optical evenescent field sensing
Optical evenescent field is a solution of the electric field whose amplitude is exponentially decaying outside of some physical domain. However, the perturbation of such field will have a significant effect on the propogation of light pulses inside the waveguide. Using this effect, sound wave can be translated as optical phase variations. It will further be converted to intensity variations at the photodetector. Here we employ mid-ir wavelength photonics circuit on a silicon chip to realize ultra sensitive, high-bandwidth microphone.
Figure 1. A picture of the photonics cavity intersection, the waveguide is suspended to achieve a high sensitivity to acoustics pressure
Figure2. A picture of the MID-infrared optical microphone in a gel-pak looking from the side