Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1986-05-08
1988-02-02
Orsino, Jr., Joseph A.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
H04B 900
Patent
active
047233176
ABSTRACT:
The present invention relates to an optical heterodyne mixer providing image-frequency rejection which (a) detects a desired signal at frequency f.sub.L.O. .+-.f.sub.IF while rejecting interference from any signal at the image frequency f.sub.L.O. .-+.f.sub.IF, and (b) provides performance which is insensitive to fluctuations in the optical dimensions of the circuit. More particularly, the mixer receives both a local oscillator input signal and a received input signal comprising one or more optical signals, one of the input signals being linearly polarized and the other being circularly polarized. The two signals are merged by an optical device and transmitted to a polarizing beam splitter which has its polarization axes oriented at 45 degrees to the polarization direction of the linearly polarized signal. Each of the two beams from the polarizing beam splitter is detected by a separate photodetector and the resulting two currents from the two photodetectors are added by means of a 3 dB 90 degree IF coupler. One of the coupler outputs provides the IF signal and the other coupler output provides the IF signal of the image frequency.
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American Telephone and Telegraph Company AT&T Bell Laboratories
Orsino Jr. Joseph A.
Pfeifle Erwin W.
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