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The free-space optical communication of high-speed 120 Gbit/s wavelength-division multiplexing (WDM) QPSK signals is demonstrated in an outdoor atmospheric channel with a distance of about 1 km. A pair of optical terminal systems with the capture and tracking functions is used to establish the atmospheric channel. The power fluctuation through the atmospheric turbulence agrees well with the exponentiated Weibull distribution. At the BER of 3.8 × 10 −3 , the required receiving powers for the three WDM channels are similar, which are all <−15.4 dBm.

An on-chip quadplexer is proposed and demonstrated with four wavelength-channels of 1270, 1310, 1490, and 1577 nm. The present quadplexer consists of four cascaded filters based on multimode waveguide grating (MWG), which are composed of a two-mode (de)multiplexer and an MWG. For the fabricated quadplexer on silicon, all four wavelength channels have flat-top responses with low excess losses of < 0.5    dB as well as the desired bandwidths, which are about 16, 38, 19, and 6 nm, respectively. The cross-talk for both upstream channels and downstream channels is less than − 24    dB . Moreover, the data transmission of 10    Gb / s of the present silicon quadplexer is also successfully demonstrated.

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