Optical: systems and elements – Single channel simultaneously to or from plural channels
Patent
1997-12-04
1999-05-11
Ben, Loha
Optical: systems and elements
Single channel simultaneously to or from plural channels
359122, 359189, 359192, 359629, 372 92, 385 49, G02B27/10
Patent
active
059033932
ABSTRACT:
Simultaneaous phase- and polarization-diversity in a coherent receiver are provided from a single-unit 90.degree.-hybrid (as shown in the upper section of FIG. 2) by combining the polarization angle and the phase angle of the input lightwave signal into an effective phase angle in the hybrid output. Thus, the number of components in the receiver is reduced as compared to conventional systems, thereby simplifying the processing network operations in the coherent detection system. The hybrid is implemented by the use of a quarter-waveplate (QWP)/etalon 30 in conjunction with an input QWP 32. The linearly polarized signal beam transmitting through the QWP 32 (of variable polarization angle) is incident to the 2-face 14 of the QWP/etalon 30. The linearly-polarized local-oscillator beam 18 is incident on the 1-face 12, and is aligned co-directionally to the reflected beamlets 20 of the signal beam 28. The proper orientation of the waveplates 30 and 32 and the proper selection of the etalon phase angle are key elements in providing simultaneous phase- and polarization-diversity in the single-unit 90.degree.-hybrid. A detector processing network module converts the four output beams P.sub.1, 1/2P.sub.2, 1/2P.sub.2x, and 1/2P.sub.2y into balanced electrical signals and combines the signals into quadrature outputs that are squared and summed, thereby producing an electrical output signal that is independent of both phase and polarization fluctuations of the input signal beam 16.
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