| 摘要 |
An optical filter eliminates most optical noise (e.g., solar noise) in underwater LIDAR, imaging, bathymetry or communication systems. A reflected backscattered or emitted laser beam is split 102 into two beams of different polarizations filtered by identical FADOF filters 10, 10', and recombined 124 before being detected 128. Substantially all other wavelengths not corresponding to the transmitted wavelength are rejected by the FADOFs (Faraday anomalous dispersion optical filters) since the laser source is tuned to the FADOF pass-frequency. Each FADOF (Fig. 1) comprises a ceasium vapour (18) in a variable magnetic field which is heated to smooth out the hyperfine structure by means of the Doppler effect, preceded and succeeded by a polarizer (14, 34). Since the FADOFs are polarization-dependent, use of two in separately polarized channels reduces losses. <IMAGE>
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