Development of 850 nm VCSEL for optical interconnects continues with advances in modeling and device fabrication. The nonlinear large-signal response of a directly modulated laser is derived from rate equations. The resulting analytical expression exhibits the unequal rise and fall time in square wave response, and eye skew observed in PAM4 modulation. Demand for higher data rates and reduced power consumption will persist as long as the buildout of AI/ML networks lasts. The performance of VCSEL- based links at 212.5 Gb/s and feasibility of low power linear links at 106.25 Gb/s per lane is discussed.

The connectivity demands of high-performance computing (HPC), artificial intelligence (AI) and data centers are driving the development of a new generation of multimode optical components. This paper discusses the vertical cavity surface emitting laser (VCSEL) bandwidth and noise performance needed to support 106 Gbd line rates with PAM4 modulation for 200 Gbps per lane multimode optical links. A −3 dB bandwidth greater than 35 GHz and a RIN of less than −152 dB/Hz are demonstrated. No uncorrectable errors were observed over 50 m of OM4 fiber, demonstrating good link stability. VCSEL device performance and the associated wear-out life are presented. Leveraging good device reliability and low power consumption of VCSEL-based links, a novel VCSEL near-packaged optics (NPO) concept is proposed for optical interconnects in AI scale-up network applications. Optical interconnects allow for longer reaches, compared to copper interconnects, which facilitate larger AI clusters with network disaggregation. The proposed VCSEL NPO can achieve an energy efficiency of ~1 pJ/bit, which is the highest among optical interconnects.

The market for 100Gb/s per lane multimode (MM) vertical-cavity surface-emitting lasers (VCSELs) continues to be driven by the growing demand from data centers, cloud storage, and enterprise networks. Low cost and energy efficient VCSEL-based multimode links are especially suited for the high speed interconnections (HSI) that facilitate generative artificial intelligence ( AI). The VCSEL technologies are largely shaped by the Fibre-channel and the Ethernet standards, and more recently by the Terabit Bidi MSA and InfiniBand requirements. In this paper, we present the development and performance of a 940nm multimode VCSEL with 3-dB small-signal modulation bandwidth exceeding 25GHz over temperature and relative intensity noise (RIN) below -145dB/Hz, suitable for 100Gb/s per lane data transmission. The VCSEL's 940nm center wavelength is within the wavelength range directed by IEEE 802.3 VR4 and offers the advantages of higher differential gain and lower thermal impedance. Large-signal performance at 100 Gb/s as well as device reliability will also be presented.

Direct modulation at 212.5 Gb/s PAM4 and low power 106.25 Gb/s links are being enabled by advances in 850 nm VCSELs. Open eyes are demonstrated after 30 m OM4 transmission at 212.5 Gb/s. Half-retimed links at 106.25 Gb/s show pre-FEC BER below 1E-8 for trace loss up to 16 dB.

Progress in the development of multimode 850 nm VCSELs is demonstrated at 100 GBd PAM4 operation, and at 53.125 GBd PAM4 with transmission over 100 m of OM3 fiber. Continued advances will help introduce the next generation of multimode links.

The entry of 100G 850 nm VCSELs enables the replacement of copper by multimode fiber in switch-to-server links, and facilitates the upgrade of switch-to-switch links in enterprise networks and data centers. This paper will present the key features and characteristics of multimode VCSELs that enable direct modulation at 100 Gb/s suitable for multimode Ethernet and Fibre Channel standards. Beyond 100G, a bidirectional link using VCSELs of two wavelengths is one potential solution to double the aggregate data rate on duplex fiber links. Elements of both 850 and 910 nm VCSELs that would enable the next generation data links are described.

This paper reviews the VCSEL technology used to enable 100 Gb/s multi-mode optical links. Link performance, device characterization over temperature and wear-out lifetime will be presented. The manufacturability of these high performance and reliable VCSELs will be discussed.

Multi-mode vertical-cavity surface-emitting lasers (VCSELs) with improved bandwidth and noise performance have been developed for 100 Gb/s data communication links over multi-mode fiber. The VCSELs are designed for the peak multi-mode fiber bandwidth at 850 nm to maximize reach. The small-signal modulation 3dB bandwidth exceeds 25 GHz over temperature and relative intensity noise is below -145 dB/Hz. Transmission of 53.125 GBd PAM-4 signals over a 100m OM4 fiber is demonstrated by using equalization on both transmit and receive side. The transmitter and dispersion eye closure quaternary (TDECQ) penalty is below 4 dB for VCSEL operating up to 75°C.

This paper reviews the advancement in VCSEL technology at Broadcom to support the next generation of 850nm multi-mode data communication links at channel bit rates beyond 100Gb/s.

This paper will review the VCSEL performance requirements and link length limitations to support next generation 53Gbaud line rates with PAM-4 modulation for 100G per lane multi-mode optical links for both active optical cables and transceivers. VCSEL performance with bandwidth in excess of 25GHz and relative intensity noise lower than -145dB/Hz will be needed to enable this next generation of multi-mode links. VCSEL device performance and associated wear out life data will be included.

The development of robust next generation multi-mode VCSEL-based optical links requires an accounting of all penalties in the link. While limitations from fiber bandwidth can be overcome to a significant extent using equalization and forward error correction, noise in the link cannot be equalized. Measurements show that mode partition noise depends on launch condition, and the noise penalty can be decreased using devices with small k factor. Time and frequency domain characterization of mode power fluctuations shows that they occur primarily at frequencies below 5 GHz. These findings guide the development of VCSELs for 25GBaud PAM4 and higher bit rate applications.

This paper will review the device design and performance of Broadcom’s 50Gb/s PAM-4 VCSEL to enable the next generation of transceivers using a PAM-4 advanced modulation scheme at 25-28 GBd. The VCSEL has been optimized to minimize noise and improve dynamic performance for cleaner eyes. Preliminary wear out lifetime studies indicate that the time to 1% failure exceeds 10 years, making the VCSELs suitable for data communication applications.

This paper reviews the technology used to enable commercial deployment of VCSELs at 25-28G and some of the device challenges that need to be addressed to enable the next generation of data rates.

Mode partition noise (MPN) can become the dominant limitation in 850 nm VCSEL-based multi-mode fiber (MMF) links at high data rates. Fluctuations in the partition of energy between the transverse modes of the VCSEL combined with the chromatic dispersion in the fiber leads to intensity noise at the receiver. The impact of MPN on non-equalized and equalized links has been studied with a numerical model of the VCSEL and MMF. The MPN in 25 Gb/s VCSELs has been investigated by examining noise in individual mode groups isolated using a thin film Fabry-Perot filter. The measured k factor below 0.15 should enable links significantly longer than 100 m at 25 Gb/s and higher data rates.

Applications of 850 nm VCSELs have bloomed in recent years arising from their low cost, and the ease of forming one- and two-dimensional arrays. In addition to the traditional measures of device lifetime, operation over a wide temperature range and link length, the figures of merit increasingly include power consumption (pJ/bit), footprint (bits/mm2) and cost ($/Gb/s). As 1 × 12 arrays of 10G VCSELs are widely adopted, there is a clear need for improvement along all these fronts. This is achieved through development of VCSELs operating at higher data rates, and modifications to the oxide VCSEL structure. In this paper, we discuss the development of VCSELs with electrostatic discharge protection, and high bandwidth for operation at 10 – 25 Gb/s.

X-ray scattering is used to investigate the surface dynamics on Au(111) during Ar + ion irradiation. During 500 eV Ar + ion irradiation, we observe the three regimes of step retraction, quasi-layer-by-layer removal and three dimensional rough erosion, analagous to molecular beam epitaxy. The quasi-layer-by-layer sputtering regime has been studied to identify similarities and differences in surface evolution during ion irradiation and molecular beam epitaxy. X-ray measurements suggest that 500 eV Ar + ion irradiation does not lead to stable adatom island formation. Also, in contrast to molecular beam epitaxy, adatom detachment and diffusion seems important in describing the surface kinetics during ion irradiation.

Pulsed laser deposition of Si on dihydride-terminated (l×1) Si (001) at low temperatures yields epitaxial layers, unlike molecular beam epitaxy. Si films were grown by ultrahigh vacuum pulsed laser deposition on the dihydride surface at substrate temperatures from 40 °C to 350 ° C. Epitaxial thickness and interface roughness were measured by high-resolution cross-sectional transmission electron microscopy and found to be comparable to known data for Si films grown by molecular beam epitaxy on monohydride-terminated (2×l) Si (001). Si films were grown at 200 °C by pulsed laser deposition on the dihydride surface at argon background pressures between 10− torr and 10−1 torr. Ion probe time of flight data was collected over the same pressure range. Comparison of the results suggests that loss of epitaxy is correlated with low incident energy. This, in conjunction with information on surface reconstruction obtained from reflection high-energy electron diffraction, suggests that the mechanism enabling epitaxy on the dihydride surface is Si subplantation, a mechanism only possible in growth with an energetic beam.

Frequently quoted advantages of VCSELs over other optical sources include wafer scale fabrication and testing, low cost, ease of fabricating arrays and ease of fiber coupling. To benefit from these advantages a robust manufacturing process and product demand are needed. Avago Technologies produces a range of single channel and parallel optical link products incorporating 850nm band VCSEL sources operating at up to 10Gb/s per channel. This paper will explore some important factors which need to be controlled for manufacturability of VCSEL devices.

An 850 nm VCSEL with a lithographically defined aperture and a dielectric index guide has been fabricated with low threshold current and bandwidth for operation at 10 Gb/s and beyond. The device structure and characteristics are described.