Higher speed VCSELs are being developed to minimize the number of parallel lanes as the aggregate interconnect capacity increases from 200 to 400 and 800 Gbps. In this talk we will discuss VCSEL dynamics and speed limitations and what improvements we expect with further developments.

We experimentally demonstrate 90Gbps error-free PAM-2 transmission and 102Gbps PAM-2 transmission below the KP4 FEC threshold over 50m OM5 multimode fiber at 850nm The link includes unpackaged 850nm VCSELs with 26GHz bandwidth and implements limited linear equalization and raised cosine pulse shaping.

We demonstrate a 6.5 mW single transverse and polarization mode GaAs-based oxide-confined VCSEL at 850 nm.High power is enabled by a relatively large oxide aperture and an epitaxial design for low resistance, low optical loss, and high slope efficiency VCSELs.With the oxide aperture supporting multiple polarization unrestrained transverse modes, single transverse and polarization mode operation is achieved by a transverse and polarization mode filter etched into the surface of the VCSEL.While the VCSEL is specifically designed for light source integration on a silicon photonic integrated circuit, its performance in terms of power, spectral purity, polarization, and beam properties are of great interest for a large range of applications.

We demonstrate effective transmitter equalization for 850nm, 980nm, and 1060nm VCSELs and 100m OM5 links enabling 78Gbps PAM-2 and >100Gbps PAM-4 100m error free links. Extracted link penalties reveal net fibre dispersion and RIN enhancement create small to negligible power penalties for all wavelengths.

Cross-correlations of VCSEL transverse mode groups with different apertures are used to predict dispersion dependent RIN. Experiments with wideband multimode fiber confirm the noise enhancement dependence on aperture, which increases with fewer mode VCSELs.

We determine the most efficient modulation format for deployable 25Gbps, 50Gbps, and 100Gbps links. Error-free performance was tested and compared for PAM-2, PAM-4, and duobinary until maximum data rates were achieved. The link includes unpackaged 850nm VCSELs and transmitter equalization.

The vertical-cavity surface-emitting laser (VCSEL) is a well-established light source for sensing and short-reach optical links. The surface emission allows wafer-scale testing enabling low-cost manufacturing, while the VCSELs’ small modal volume leads to low power consumption, high-speed modulation at small currents, and small footprint [1]. Conventional VCSELs consist of an active region sandwiched between two distributed Bragg reflectors (DBRs). Replacing the top DBR with a high-contrast grating reflector offers unique possibilities to engineer and control VCSEL emission wavelength and modal properties [2,3]. A high-contrast grating (HCG) is typically formed by bars of high refractive index suspended in air. HCGs with certain grating parameters (duty cycle, period, and thickness) can function as ultra-thin reflectors with close to 100% reflectivity [4]. Besides the reflectivity, the grating parameters also influence the reflection phase. This enables fabrication of multi-wavelength VCSEL arrays by fabricating HCG-VCSELs with different grating parameters. In order to utilize the extraordinary properties of the HCG, the VCSEL mode must be sensitive to the HCG, which leads to complicated cavity configurations with coupled cavity effects and low optical confinement. This talk will summarize experimental work performed at Chalmers University of Technology in collaboration with Hewlett Packard Enterprise. The design of HCGs and HCG-VCSELs will be presented as well as experimental results from 980 nm HCG-VCSELs and demonstration of post-growth wavelength setting for wavelength-division multiplexing (WDM) VCSEL arrays [5]. References [1] Larsson, “Advances in VCSELs for communication and sensing,” IEEE J. Sel. Top. Quantum Electron. 17(6), 1552-1567 (2011). [2] V. Karagodsky, et al., ”Monolithically integrated multi-wavelength VCSEL arrays using high-contrast gratings”, Opt. Express 18(2), 694-699 (2010). [3] S. Inoue, et al., “Highly angular dependent high-contrast grating mirrors and its application for transverse-mode control of VCSELs”, Jpn. J. Appl. Phys. 53, 090306 (2014). [4] C. J. Chang-Hasnain et al., “High-contrast gratings for integrated optoelectronics”, Adv. Opt. Photon. 4, 379-, (2012). [5] E. Haglund, et al., “Demonstration of post-growth wavelength-setting of VCSELs using high-contrast gratings”, Opt, Express 24(3), 1999-2005 (2016). Acknowledgement This work was been supported by Hewlett Packard Enterprise (HPE), the Swedish Foundation for Strategic Research (SSF) and the Swedish Research Council (VR). The epitaxial material was provided by IQE Europe.

Vertical-cavity surface-emitting lasers and multi-mode fibers is the dominating technology for short-reach optical interconnects in datacenters and high performance computing systems at current serial rates of up to 25-28 Gbit/s. This is likely to continue at 50-56 Gbit/s. The technology shows potential for 100 Gbit/s.

We demonstrate and analyze polybinary signaling as a low complexity alternative to PAM-4 for achieving higher bitrates in VCSEL-MMF links. Experimental results demonstrate that duobinary and polybinary-3 achieves similar performance as PAM-4 through 105m of wideband fiber at 10 −12 BER.

GaAs-based hybrid-cavity VCSELs integrated onto silicon by ultra-thin DVS-BCB adhesive bonding are presented. The hybrid-cavity implies that the optical field extends over both the GaAs- and the Si-based parts, which could allow a fraction of the light in the vertical-cavity to be coupled into an in-plane waveguide. Surface-emitting devices are demonstrated at ~860 nm with up to 2.3 mW optical output power and 12 GHz modulation bandwidth, providing error-free large signal data transmission up to 25 Gb/s.

The impact of bonding interface thickness on the performance of 850-nm silicon-integrated hybrid-cavity vertical-cavity surface-emitting lasers (HC-VCSELs) is investigated. The HC-VCSEL is constructed by attaching a III-V “half-VCSEL” to a dielectric distributed Bragg reflector on a Si substrate using ultrathin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding. The thickness of the bonding interface, defined by the DVS-BCB layer together with a thin SiO 2 layer on the “half-VCSEL,” can be used to tailor the performance, for e.g., maximum output power or modulation speed at a certain temperature, or temperature-stable performance. Here, we demonstrate an optical output power of 2.3 and 0.9 mW, a modulation bandwidth of 10.0 and 6.4 GHz, and error-free data transmission up to 25 and 10 Gb/s at an ambient temperature of 25 and 85 °C, respectively. The thermal impedance is found to be unaffected by the bonding interface thickness.

The hybrid vertical-cavity laser is a potential low current, high-efficiency, and small footprint light source for silicon photonics integration. As part of the development of such light sources we demonstrate hybrid-cavity VCSELs (HC-VCSELs) on silicon where a GaAs-based half-VCSEL is attached to a dielectric distributed Bragg reflector on silicon by adhesive bonding. HC-VCSELs at 850 nm with sub-mA threshold current, >2 mW output power, and 25 Gbit/s modulation speed are demonstrated. Integration of short-wavelength lasers will enable fully integrated photonic circuits on a silicon-nitride waveguide platform on silicon for applications in life science, bio-photonics, and short-reach optical interconnects.

We experimentally demonstrate error-free rates beyond 100Gbps over 100m WBMMF. Power penalties and maximum data rates of PAM-2 and PAM-4 using shaped and unshaped pulses were studied. The link includes unpackaged 850nm VCSELs with different apertures and only transmitter equalization.

The use of a high-contrast grating (HCG) as the top mirror in a vertical-cavity surface-emitting laser (VCSEL) allows for setting the resonance wavelength by the grating parameters in a post-epitaxial growth fabrication process. Using this technique, we demonstrate electrically driven multi-wavelength VCSEL arrays at ~980 nm wavelength. The VCSELs are GaAs-based and the suspended GaAs HCGs were fabricated using electron-beam lithography, dry etching and selective removal of an InGaP sacrificial layer. The air-coupled cavity design enabled 4-channel arrays with 5 nm wavelength spacing and sub-mA threshold currents thanks to the high HCG reflectance.

The realization of 850 rim hybrid III-V/dielectric VCSELs is reported in order to realize low power consumption integrated light sources for SiN waveguide circuits, which find applications both in short-reach optical communication and optical sensors.

In this Letter a fully vectorial numerical model is used to search for the construction parameters of monolithic high-contrast grating (MHCG) mirrors providing maximal power reflectance. We determine the design parameters of highly reflecting MHCG mirrors where the etching depth of the stripes is less than two wavelengths in free space. We analyze MHCGs in a broad range of real refractive index values corresponding to most of the common optoelectronic materials in use today. Our results comprise a complete image of possible highly reflecting MHCG mirror constructions for potential use in optoelectronic devices and systems. We support the numerical analysis by experimental verification of the high reflectance via a GaAs MHCG designed for a wavelength of 980 nm.

We report on highly reflective suspended GaAs high-contrast gratings (HCGs) using an InGaP sacrificial layer. A high reflectivity approaching 100% was observed both in direct reflectivity measurement and by low threshold currents in fabricated multi-wavelength HCG-VCSEL arrays.