Lukasz Chorchos

Effective 100 Gb/s IM/DD 850-nm Multi- and Single-Mode VCSEL Transmission Through OM4 MMF

To cope with the ever increasing data traffic demands in modern data centers, new approaches and technologies must be explored. Short range optical data links play a key role in this scenario, enabling very high speed data rate links. Recently, great research efforts are being made to improve the performance of vertical-cavity surface-emitting lasers (VCSELs) based transmission links, which constitute a cost-effective solution desirable for massive deployments. In this paper, we experimentally demonstrate intensity-modulation direct-detection transmissions with a data rate of 107.5 Gb/s over 10 m of OM4 multimode fiber (MMF) using a multimode VCSEL at 850 nm, and up to 100 m of OM4 MMF using a single-mode VCSEL at 850 nm. Measured bit error rates were below 7% overhead forward error correction limit of 3.8e−03, thus, achieving an effective bit rate of 100.5 Gb/s. These successful transmissions were achieved by means of the multiband approach of carrierless amplitude phase modulation.

Outdoor

This letter proposes a W-band hybrid photonic wireless link based on a commercial small form-factor pluggable (SFP+) module and experimentally demonstrates its performance. Using a free running laser as local oscillator and heterodyne photonic upconversion, good frequency stability is achieved. Outdoor wireless transmission over 225 m with a bit error rate below 10-6 is demonstrated, and the maximum reach of the system with typical RF components is calculated, finding wireless distances above 2 km to be feasible. Being based on a commercial SFP+, the proposed hybrid photonic wireless link offers seamless integration with existing distribution networks and passive optical networks, and thus paves the way for future mobile frontand backhaul architectures.

W

We report for the first time on wafer-fused InGaAs-InP/AlGaAs-GaAs 1550 nm vertical-cavity surface-emitting lasers (VCSELs) incorporating a InAlGaAs/InP MQW active region with re-grown tunnel junction sandwiched between top and bottom undoped AlGaAs/GaAs distributed Bragg reflectors (DBRs) all grown by molecular beam epitaxy. InP-based active region includes seven compressively strained quantum wells (2.8 nm) optimized to provide high differential gain. Devices with this active region demonstrate lasing threshold current < 2.5 mA and output optical power > 2 mW in the temperature range of 10-70°C. The wall-plug efficiency (WPE) value-reaches 20 %. Lasing spectra show single mode CW operation with a longitudinal side mode suppression ratio (SMSR) up to 45 dB at > 2 mW output power. Small signal modulation response measurements show a 3-dB modulation bandwidth of ~ 9 GHz at pump current of 10 mA and a D-factor value of 3 GHz/(mA)1/2. Open-eye diagram at 30 Gb/s of standard NRZ is demonstrated. Achieved CW and modulation performance is quite sufficient for fiber to the home (FTTH) applications where very large volumes of low-cost lasers are required.

-Band Hybrid Photonic Wireless Link Based on an Optical SFP+ Module

The results of studies on fabrication of vertical-cavity surface-emitting 1.55-μm lasers by fusing AlGaAs/GaAs distributed-Bragg-reflector wafers and an active region based on thin In0.74Ga0.26 As quantum wells grown by molecular-beam epitaxy are presented. Lasers with a current aperture diameter of 8 μm exhibit continuous lasing with a threshold current below 1.5 mA, an output optical power of 6 mW, and an efficiency of approximately 22%. Single-mode lasing with a side-mode suppression ratio of 40–45 dB is observed in the entire operating current range. The effective modulation frequency of these lasers is as high as 9 GHz and is limited by the low parasitic cutoff frequency and self-heating.

Continuous wave and modulation performance of 1550nm band wafer-fused VCSELs with MBE-grown InP-based active region and GaAs-based DBRs

In this letter a reconfigurable remote access unit (RAU) is proposed and demonstrated, interfacing dense wavelength division multiplexed (DWDM) optical and W-band wireless links. The RAU is composed of a tunable local oscillator, a narrow optical filter, and a control unit, making it reconfigurable via software. The RAU allows selection of a DWDM channel and tuning of the radio carrier frequency. Real-time transmission results at 2.5 Gbit/s and performance measurements with offline data processing at 4 and 5 Gbit/s are presented. Error free real-time transmission was achieved after 15 km of standard single mode fiber and 50 m of wireless transmission with carriers between 75 and 95 GHz.

Vertical-Cavity Surface-Emitting 1.55-μm Lasers Fabricated by Fusion

In this article, we propose and test a reconfigurable Remote Access Unit (RAU) to interface optical and W-band wireless communication links (75–110 GHz), utilizing optical heterodyne signal upconversion. The RAU is composed of a tunable local oscillator, narrow optical filter and a control unit. The RAU can be software-reconfigured to select a specific dense wavelength division multiplexed (DWDM) channel. Real-time tests with 100 GHz spaced DWDM signals have been performed. Real-time 2.5 Gbit/s error free radio transmission in the 75 GHz to 95 GHz range of the W-band was achieved after 15 km of standard single mode fiber and 50 m of wireless link.

Reconfigurable Radio Access Unit for DWDM to W-Band Wireless Conversion

The ever growing data volumes in the IT infrastructure can only by carried by the optical transmission technologies. The key requirements for such transmission systems are the small footprint, high energy efficiency and the low cost of ownership. One of the most promising candidates to realize the energy efficient high speed transmission over the short distance is transmission with the multi-mode fibre and the 850 nm VCSELs. In this paper the transmission performance of the two types of the 850 nm VCSEL, namely single mode and multimode one is compared. Several key VCSEL transmission characteristics, like bandwidth of both VCSEL types were measured and evaluated. The transmission experiments in the various system configurations were performed at the bit rates up to 56 Gbit/s. The results demonstrate that the SM VCSEL outperforms MM VCSEL for longer distances and higher data rates.

W-band real-time transmission utilizing a reconfigurable RAU for NG-PON networks

Design of the oxide-confined vertical cavity surface emitting laser (VCSEL) with anti-guiding AlAs-rich core has recently attracted a lot of attention. Lack of the waveguiding core increases the oscillator strength of the VCSEL mode, allows the ultimate optical confinement (“λ/2 design”) and reduces dramatically the optical power accumulated in the VCSEL mesa in the regions outside of the oxide aperture. We consider basic differences of conventional and antiwaveguiding VCSEL and address optical modes in the device. Both Joule heat and heat generated by the free carrier absorption of the optical mode in the doped semiconductor layers and their impact on the refractive index profile are considered. We show that for typical regimes of the VCSEL design and operation absorption-induced heat exceeds by several times the Joule heat while the shape of the generated heated domains strongly differ. Modeling shows that current increase results in an increase in spectral separation of the fundamental and high-order transverse optical modes. Selection of the fundamental mode persists upon increase in injection current up to 10 mA at 5 µm aperture diameter. We report on data transmission experiments up to 160 Gb/s using single mode antiwaveguiding VCSELs.

High speed transmission with 850 nm SM and MM VCSELs

Global data traffic is increasing at an unprecedented rate. This increase is due in large part to the rise of cloud computing services, multimedia web applications, and Internet-of-Things technologies. Indeed, the bandwidth requirements imposed by these applications are expected to double network traffic in data centers within five years.1 To cope with these demands, the viability of using new photonics technologies and approaches to improve the performance (i.e., to increase the capacity and reduce the latency) of data-center interconnects must be explored. Furthermore, these new approaches must ensure a reduced carbon footprint and lower operating costs.2 A large amount of research has recently been carried out on vertical-cavity surface-emitting lasers (VCSELs) with the aim of meeting these requirements. VCSELs represent one of the most appealing technologies for application to optical interconnects because of the advantages that they provide (e.g., low power consumption, reduced fabrication cost, the feasibility of on-wafer testing, and high coupling efficiencies).3 Additionally, the rapid development of electronics has led to the increased efficacy of advanced modulation techniques over larger bandwidths, thereby significantly increasing the spectral efficiency of communications systems. Combining these new photonics technologies with advanced modulation formats has enabled the development of single-polarization and single-wavelength intensity modulation/direct detection (IM/DD) high-speed links. A number of recent research efforts have achieved effective bitrates of close to 100Gb/s using VCSELs. Specifically, effective bitrates Figure 1. Chip wafer of single-mode vertical-cavity surface-emitting lasers (VCSELs), shown together with a fiber-optic pigtail test probe.7

Progress in design and development of anti-guiding vertical cavity surface emitting laser at 850 nm: Above 50 Gb/s and single mode

To reach >50 Gb/s bit data rates using 850nm vertical cavity surface emitting laser (VCSEL) at distances up to a few hundred meters, narrow spectrum single mode VCSELs are used to avoid negative influence of the chromatic dispersion that can significantly limit performance beside the mode dispersion. Currently available single-mode VCSELs suffer from small oxide aperture diameter, and thus from higher resistances and lower powers. Oxide–confined apertures in VCSELs can be engineered such that the design promotes leakage of the high order transverse optical modes from the non–oxidized core region into the selectively oxidized periphery of the device. This novel leaky VCSEL approach may allow fabrication of single-mode VCSELs with significantly larger oxide apertures, improving the performance of the single-mode VCSELs. In this paper, we investigate the high speed transmission over long distance multimode fiber using single mode 850nm leaky VCSELs.