| 摘要 |
<p>A method and apparatus for locking the frequencies of a number of first beams of coherent radiation from respective sources (17). Typically, the sources (17) will form local oscillators in respective transmitters (1). The apparatus comprises a reference beam generator (10) such as a HeNe laser which generates a primary reference beam fed to an interferometer (12) which generates a second, reference beam composed of a number of reference frequencies. This second reference beam is caused to interfere with each of the beams from the local sources (17) in an optical coupler (16) and the resultant beam is detected with a photodiode (22). The electrical output signal of the photodiode (22) is filtered and fed to a discriminator (25) which controls the frequency of the local laser (17). The discriminator (25) controls the laser (17) to maintain the relationship between the frequencies of the laser (17) and the reference laser (10) substantially constant.</p> |
