Abstract
For high-speed optical OFDM transmission applications, a comprehensive comparison of the homemade multi-/few-/single-transverse mode (MM/FM/SM) vertical cavity surface emitting laser (VCSEL) chips is performed. With microwave probe, the direct encoding of pre-leveled 16-QAM OFDM data and transmission over 100-m-long OM4 multi-mode-fiber (MMF) are demonstrated for intra-datacenter applications. The MM VCSEL chip with the largest emission aperture of 11 μm reveals the highest differential quantum efficiency which provides the highest optical power of 8.67 mW but exhibits the lowest encodable bandwidth of 21 GHz. In contrast, the SM VCSEL chip fabricated with the smallest emission aperture of only 3 μm provides the highest 3-dB encoding bandwidth up to 23 GHz at a cost of slight heat accumulation. After optimization, with the trade-off set between the receiving signal-to-noise ratio (SNR) and bandwidth, the FM VCSEL chip guarantees the highest optical OFDM transmission bit rate of 96 Gbit/s under back-to-back case with its strongest throughput. Among three VCSEL chips, the SM VCSEL chip with nearly modal-dispersion free feature is treated as the best candidate for carrying the pre-leveled 16-QAM OFDM data over 100-m OM4-MMF with same material structure but exhibits different oxide-layer confined gain cross-sections with one another at 80-Gbit/s with the smallest receiving power penalty of 1.77 dB.
Highlights
High-speed data centers and optical interconnects [1] rely strictly on developing ultrafast optical transmitters to solve the heavy data traffic induced from data switching/routing in central offices, and add/drop among remote nodes, and so on
To fulfill such demands standardized by IEEE P802.bs [2], the transmission capacity of laser diode modules have been up-scaled from 100 Gbit/s/module to 400Gbit/s/module for constructing cloud data centers based on the use of 8-channel vertical cavity surface emitting laser (VCSEL) array transmitter with 50 Gbit/s/channel [3]
Note that the MM VCSEL chip exhibits more than 15 transverse modes at wavelengths ranging from 856 nm to 863 nm
Summary
High-speed data centers and optical interconnects [1] rely strictly on developing ultrafast optical transmitters to solve the heavy data traffic induced from data switching/routing in central offices, and add/drop among remote nodes, and so on. To fulfill such demands standardized by IEEE P802.bs [2], the transmission capacity of laser diode modules have been up-scaled from 100 Gbit/s/module to 400Gbit/s/module for constructing cloud data centers based on the use of 8-channel vertical cavity surface emitting laser (VCSEL) array transmitter with 50 Gbit/s/channel [3]. In view of previous works, the shrinkage of the emission aperture confined via oxidation has emerged as the simplest approach for obtaining quasi-single-mode or single-mode (SM) VCSEL transmitter [11,12,13,14,15,16]
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