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:
Feb. 02, 1988
Filed:
Jun. 24, 1986
William B Wetherell, Stoneham, MA (US);
Itek Corporation, Lexington, MA (US);
Abstract
A method of mixing light from a signal source with light from a local oscillator for heterodyne or homodyne detection using differential detection techniques is described. In the method and apparatus of the invention, incoming light is matched to the polarization of the local oscillator no matter what the polarization of the incoming light is. A sequence of three polarization beamsplitters is utilized to achieve this match. The local oscillator signal and the incoming signal are incident on separate faces of a first polarization beamsplitter. Each is divided into two beams by that beamsplitter and paired with the orthogonally polarized component of the other, each signal/local oscillator pair exiting from one exit face of the first polarization beamsplitter. The second polarization beamsplitter resolves one of these pairs into sum and difference pairs of matched polarization which interfere and are detected by square law detectors, forming currents which are subtracted in a differential amplifier. The third polarization beamsplitter repeats this process with the other pair of beams from the first polarization beamsplitter. The result is two net output currents which between them contain all the phase and amplitude information needed to define and control the polarization of the incoming signal. In addition to reducing sensitivity to the polarization state of the incoming signal, the use of polarization beamsplitters substantially improves optical efficiency, in comparison to prior art using amplitude beamsplitters.