Ent tools

A registration device, comprising:

• a wand having a distal tip;
• a light guide passing through the wand and having a distal end at the distal tip of the wand and a proximal end extending proximally from the wand;
• a position sensor fixed to the wand and configured to output a first signal indicative of a location of the distal tip in a sensor frame of reference;
• a light source, which is coupled to output a beam of light, having an intensity that is modulated temporally at a predefined carrier frequency, into the proximal end of the light guide, whereby the light is emitted from the distal end of the light guide toward a surface in proximity to the distal tip of the wand;
• a detector, configured to receive, from the proximal end of the light guide, the light that has been reflected from the surface into the distal end of the light guide, and to output a second signal that is indicative of the intensity of the reflected light;
• and
• a processor, configured to compute a distance from the distal tip of the wand to the surface by extracting a phase difference between the output beam and the reflected light from the second signal, and to compute a position of the surface in the sensor frame of reference responsively to the computed distance and the location of the distal tip that is indicated by the first signal.