An improved frequency locking circuit suitable for indirectly locking an optical frequency f.sub.0 to a radio frequency f.sub.1 or of locking the radio frequency to the optical frequency. A beam of optical frequency f.sub.0 is modulated by a compound signal which is the sum of a signal at frequency f.sub.2...http://www.google.de/patents/US4925302?utm_source=gb-gplus-sharePatent US4925302 - Frequency locking device
