Which technology allows 100G transponders to accept multiple wavelengths at their input, without requiring demultiplexing of the composite signal?

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1. 10G systems typically use direct detection, whereas 100G systems use coherent detection.

   Coherent detection means that an optical receiver can track the phase of an optical transmitter so as to extract any phase and frequency information carried by a transmitted signal. It has many benefits to increasing bandwidth over a link, such as enabling higher throughput over shorter distances (200G) using 16-QAM modulation, normal bandwidth (100G) over normal distances using QPSK modulation, or lower throughput over much farther distances (50G) using dual polarization modulation, as well as Local Oscillator (LO) tuning without the use of an optical filter or demultiplexer. (That last benefit is what the question is asking about.)

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