The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 15, 1990
Filed:
Apr. 13, 1988
Gregory M Cutler, Cupertino, CA (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
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 and an FM subcarrier at frequency f.sub.1 that is phase modulated at frequency f.sub.3 to produce a phase modulated beam. The phase modulated beam is filtered by a filter having a transfer function having a characteristic frequency f.sub.f. A pair of control signals are generated that are proportional respectively to the amplitudes of two components of the filtered signal at frequencies f.sub.2, f.sub.3. These control signals are separately used in a pair of servo loops to separately establish fixed values of f.sub.0 /f.sub.f and f.sub.1 /f.sub.f. By using an optical cavity of the filter, the frequency locking circuit may be used for measuring the refractive index of a gas. The circuit may also be used for calibrating a multi-mode filter.