Vibration measurement with a micromachined mirror in a very-short external cavity laser

We have fabricated, modeled and tested a displacement sensor based on an external cavity laser with a micro-mirror integrated with a positioning actuator. We have developed an improved model for simulating the intensity change in the external cavity laser when the feedback from the external mirror exceed 20% of the feedback from the laser facet. A special surface-micromachined mirror has been developed to obtain a very short external cavity laser ( ≈10 μ m) that allow removing all coupling optical elements in the external cavity. During testing, we could verify the theoretical prediction and achieve a large relative feedback providing a strong intensity modulation. We observed a good angular tolerance suggesting a good manufacturability of the device. The tested device has a noise floor at 5 pm/ Hz above 500 Hz. This sensor could be used as a high sensitivity acceleration sensor.