Abstract
By enhancing the differential gain and reducing the capacitance of the 850-nm multi-mode vertical cavity surface emitting laser (VCSEL) with an analog bandwidth beyond 25 GHz via the use of InGaAs/AlGaAs quantum wells and multiple oxide confinement layers, the transmission of directly encoded 4-level pulse amplitude modulation (PAM-4) data at 42 GBaud and 16-quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM OFDM) data at 35 GBaud are demonstrated. After passing through 100-m OM5 multimode fiber (MMF), the detailed comparison between the VCSELs designed with different aperture sizes of 5.5/7.5 μm is performed. The 7.5-μm-aperture VCSEL provides the higher power with larger quantum efficiency but exhibits the narrower 3-dB bandwidth and higher noise level than those of the 5.5-μm-aperture VCSEL. Shrinking the oxide-confined aperture to 5.5 μm assists the VCSEL to expand its 3-dB bandwidth to 25.2 GHz and suppresses its relative intensity noise to -135 dBc/Hz, which contributes to support the highest data rate up to 84 and 140 Gbit/s, respectively, for PAM-4 and 16-QAM OFDM data under forward error correction criterion at optical back-to-back condition. Even after transmitting through 100-m-long OM5-MMF, the allowable data transmission rate still remains at 80 Gbit/s for PAM-4 and 120 Gbit/s for 16-QAM OFDM with their receiving power penalty of 3.24 and 3.1 dB, respectively, when the data is carried by the 5.5-μm-aperture VCSEL. Such a newly designed VCSEL structure promotes its allowable bandwidth to manifest the feasibility toward 50-GBaud per channel capacity for future data center applications.
Highlights
Nowadays, more and more data-center has been constructed to confront a tremendous change of cyber city in recent years due to the incredible requirement from several applications such as cloud data computing, streaming, and mining
The 25 Gbit/s non-return-to-zero on-off keying (NRZ-OOK) data carried by vertical cavity surface emitting laser (VCSEL) through 100-m OM4-multimode fiber (MMF) has already emerged [2], which benefits from plenty of advantages including wide analog bandwidth, cost-effective package, low threshold current, and low power consumption [3]–[5]
By fabricating the multi-mode VCSELs with different mesa/aperture sizes through employing the multi-layered oxidation and adding 5 pairs of In0.07Ga0.93As quantum well (QW) for reducing parasitic capacitance, their allowable encoding bandwidths can be significantly improved to enforce the digital broadband data transmission in data centers
Summary
More and more data-center has been constructed to confront a tremendous change of cyber city in recent years due to the incredible requirement from several applications such as cloud data computing, streaming, and mining. The 400GBASE-SR16 standard was established for 400 Gbit/s Ethernet with 25 Gbit/s per channel to fulfill the immediate demand on high-speed data transmission at current stage [1]. Huang et al.: Multimode VCSEL Enables 42-GBaud PAM-4 and 35-GBaud 16-QAM OFDM the 25 Gbit/s non-return-to-zero on-off keying (NRZ-OOK) data carried by vertical cavity surface emitting laser (VCSEL) through 100-m OM4-MMF has already emerged [2], which benefits from plenty of advantages including wide analog bandwidth, cost-effective package, low threshold current, and low power consumption [3]–[5]. The VCSEL linked with graded-index multimode fiber (MMF) has met its limitation on the effective modal bandwidth (EMB), which can only satisfy the short-reach communication in high-speed intra-data-center [6]
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