Dynamic optical reflector and interrogation system
A retro-reflective identification tag capable of modulating an optical signal whereby to support bi-directional communication with an associated remote optical interrogation device. The tag comprises a MOEMS modulating layer over a retro-reflective substrate, giving the tag a wide angle of effective operation. The tag modulator may optionally be switched on only responsive to detection of a precursor beam from the interrogation system in order to save power. The interrogation device may make use of multiple optical wavelengths for communicating with the tag.
1. A reflective tag comprising at least one modulator for modulating an optical signal, the modulator comprising:
a spacing-controllable etalon; and
a retro-reflector arranged to retro-reflect light received directly via the etalon back through the etalon.
2. A reflective tag according to claim 1 in which the etalon comprises a coherent planar MOEMS structure.
3. A reflective tag according to claim 1 in which the retro-reflector comprises an array of one or more corner-cube reflectors.
4. A reflective tag according to claim 1 arranged to be modulated at a fixed frequency.
5. A reflective tag according to claim 1 in which the cavities in the etalon are vacuum cavities.
6. A reflective tag according to claim 1 comprising a self-contained electrical power supply.
7. A reflective tag according to claim 1 comprising a detector arrangement coupled to the modulator.
8. A reflective tag according to claim 1 in which detection of a precursor signal causes the modulator to be activated.
9. A reflective tag according to claim 1 comprising attachment means.
10. A reflective tag according to claim 1 comprising an input or output port for local communication.
11. A reflective tag according to claim 1 wherein the etalon is located adjacent said retro-reflector.