Micromechanical Photonics: Microresonator Displacement Measurement by an Extremely-Short-Length External Cavity Laser Diode

A composite cavity laser diode was used to monitor the displacement of the external cavity microresonator from the phase difference in the near field. The carrier-to-noise ratio was very high (more than 45 dB) because of the lack of mode hopping noise due to the extremely short (less than 3 μm) external cavity length and strong optical feedback. The small distance (near field) allows a lensless system, making it easier to integrate on a gallium arsenide (GaAs) substrate.