A wavelength-division-multiplexing (WDM) free-space optical (FSO) communication system of a high-speed hybrid signal is proposed and demonstrated in this study. This study is the first to transmit a high-speed hybrid signal mixed with four wavelengths that are modulated with different signals, namely 10, 25, 28, and 32 Gb/s, using a single beam. Favourable bit error rate (BER) and clear eye maps are achieved by adopting parameters after investigating the bandwidth of tuneable optical bandpass filter, channel spacing, and number of mixed light channel effects on system performance. The WDM-FSO communication system of a high-speed hybrid signal has a simple configuration, low cost, and low BER.
A wavelength-division-multiplexing (WDM) fourlevel pulse amplitude modulation (PAM4) free-space optical (FSO)-underwater wireless optical communication (UWOC) integrated system with a channel capacity of 100 Gb/s is proposed and attainably demonstrated. Analytic results reveal that 1.8-GHz 405-nm blue-violet-light and 1.7-GHz 450-nm blue-light laser diodes (LDs) with two-stage light injection and optoelectronic feedback techniques are competently adopted for 100 Gb/s PAM4 signal transmission through a 500-m free-space transmission with 5-m clear ocean underwater link. Combining dual-wavelength WDM scenario with PAM4 modulation, the channel capacity of FSO-UWOC integrated systems is significantly enhanced with an aggregate transmission rate of 100 Gb/s (25 Gbaud PAM4/wavelength × 2 wavelengths). With doublet lenses in FSO, laser beam reducer and transmissive spatial light modulator in UWOC, a sufficiently low bit error rate of 10 −9 and acceptable PAM4 eye diagrams are acquired. This demonstrated 100 Gb/s PAM4 FSO-UWOC integrated system with a WDM scenario is advantageous for the enhancement of a high-speed optical wireless link with long-reach transmission.
A high-speed 84 Gb/s vestigial sideband (VSB)-eight-level pulse amplitude modulation (PAM8) fiber-invisible laser light communication (IVLLC) integration based on vertical-cavity surface-emitting laser (VCSEL) transmitter with injection locking scheme is proposed. To the authors' knowledge, this study is the first to realize a high-speed 84 Gb/s VSB-PAM8 VCSEL transmitter-based fiber-IVLLC integration. It is effectual to adopt an optical VSB-PAM8 signal in fiber-IVLLC integrations to suppress the linewidth of an optical signal so as to reduce the fiber dispersion. An injection locking scheme and a linear equalizer possess enhancements in frequency response, and thereby provide good transmission performances in a high-speed VSB-PAM8 fiber-IVLLC integration. Impressive bit error rate performance and clear eye diagrams are acquired in real time at a 25-km single-mode fiber operation with a 10-m free-space link. Such proposed 84 Gb/s VSB-PAM8 VCSEL transmitter-based fiber-IVLLC integration is a notable option for providing high transmission rates at optical fiber and optical wireless communications.
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