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:
Mar. 05, 1985
Filed:
Nov. 12, 1982
Keith D Anderson, Ottawa, CA;
Northern Telecom Limited, Montreal, CA;
Abstract
In dual wavelength equipment such as a combined read/write unit for an optical disc system, read light of wavelength .lambda..sub.1 is directed through an isolator and a combiner, is reflected from a target back through the combiner and, at the isolator is directed out of the incident beam path to photodetectors. Write light of wavelength .lambda..sub.2 is directed from a position off the read beam path to the combiner where it is re-directed into the read beam path and onto the target. The isolator has a linear polarizer, a polarizing beam splitter, and a retarder functioning together to ensure that at the polarizing beam splitter reflected light is linearly polarized in a direction perpendicular to the incident light. The combiner is typically an interference filter inclined both to the read and write beam path, which transmits .lambda..sub.1 and reflects .lambda..sub.2. Since the filter strongly alters the polarization state of obliquely incident light, a second interference filter located between the polarizing beam splitter and the first filter is used to compensate for the change in polarization state caused by the first filter and by other elements of the optical system.