Review of VCSELs for Complex Data-Format Transmission Beyond 100-Gbit/s

Abstract

The developing progress on the structural design and data algorithms to enable the vertical-cavity surface-emitting lasers (VCSELs) for transmitting multiple complex data formats beyond 100-Gbit/s has been reviewed in this paper. Up to now, academic and industrial institutions still keep their research pace on studying how to improve the allowable data rate of various data formats carried by the VCSEL device. Persistent efforts are endeavored not only to achieve the IEEE802.3 standards for data center applications but also to initiate the new era of wired and wireless network coverage. To date, the highest allowable data rates of the single-VCSEL-based optical link for transmitting the NRZ-OOK format at 80 Gbit/s in the BtB case, the PAM-4 format at 168 Gbit/s over 150-m OM5 MMF, and the QAM-OFDM format at 224 Gbit/s in the BtB case have been achieved in 2021. For the high-level complex data-format transmission with rigorous demand of the signal-to-noise ratio (SNR), this work demonstrates the most up-to-date 32-ray quadrature amplitude modulation generalized frequency division multiplexing (32-QAM GFDM) data algorithm with optimized amplitude and K value for encoding the multimode (MM) VCSEL. To achieve the higher spectral-usage efficiency based on the SNR spectrum for maximal transmission data rate, the bit-loading discrete multi-tone (DMT) technique is implemented by rearranging each subcarrier to the appropriate QAM levels. By utilizing 32-QAM GFDM and bit-loading DMT, the maximal data rate in the back-to-back case could respectively achieve 119.5 Gbit/s and 130 Gbit/s when operating the MM VCSEL at 55 o C. After propagating through OM5 MM fiber (MMF), the transmission capacity of the VCSEL operated at 55 o C would decrease to 93.8 Gbit/s for 32-QAM GFDM and 83 Gbit/s for bit-loading DMT owing to the modal dispersion in OM5 MMF.

Backscattering Effects on High-Speed Modulation of Strongly Injection-Locked Whistle-Geometry Semiconductor Ring Lasers

“…Further improvement of modulation bandwidth in injectionlocked VCSELs can come solely from increasing the power of master lasers used for optical injection. The data rate of the NRZ transmission can hardly achieve 100 Gbit/s, so setting several VCSEL chips as the VCSEL array to aggregate the whole data rate was mentioned in [19] as the only method to achieve the data rates of the NRZ transmission beyond that level. Special complex data formats, such as 4-level pulse amplitude modulation (PAM-4) or quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM), are necessary to maximize the encoding data rate under the same modulation bandwidth of solitary VCSELs [19].…”