Short-distance Optical Links Research Articles

SC-FDE for MMF short reach optical interconnects using directly modulated 850 nm VCSELs

We propose the use of single-carrier frequency-domain equalization (SC-FDE) for the compensation of modal dispersion in short distance optical links using multimode fibers and 850 nm VCSELs. By post-processing of experimental data, we demonstrate, at 7.9% overhead, the error-free transmission (over a 4 Mbit sequence) of OOK-modulated 5 Gbps over 2443 meters of OM3 fiber (with a nominal 3300 MHz×km bandwidth). The proposed solution may be applied as a low cost alternative for data center and supercomputer interconnects.

A Modulator Design Methodology Minimizing Power Dissipation in a Quantum Well Modulator-Based Optical Interconnect

There is a strong need for a methodology that minimizes total power, which inherently includes device design, for short-distance optical link applications (chip-to-chip or board-to-board communications). We present such a power optimization methodology for a modulator-based optical link, where we do a full 3-D modulator parameter optimization, keeping the power of the entire link in mind. We find for low bit rates (10 Gb/s) that the optimum operational voltage for the modulator was within the supply voltage at the 65-nm technology node. At higher bit rates, the optimum voltage is found to increase and go beyond the stipulated supply voltage. In such a case, a suboptimum operation at the supply voltage incurs a 46% power penalty at 25 Gb/s. Having obtained the optimum modulator design and operation parameters and the corresponding total link power dissipation, we examine the impact of device and system parameters on the optimization. We find that a smaller device capacitance is an efficient solution to push the optimum swing voltage to be within the supply voltage. This is feasible using monolithically integrated Ge-based complementary-metal-oxide-semiconductor-compatible modulator and metal-semiconductor-metal photodetectors.

A Modulator Design Methodology Minimizing Power Dissipation in a Quantum Well Modulator-Based Optical Interconnect

There is a strong need for a methodology that minimizes total power, which inherently includes device design, for short-distance optical link applications (chip-to-chip or board-to-board communications). We present such a power optimization methodology for a modulator-based optical link, where we do a full 3-D modulator parameter optimization, keeping the power of the entire link in mind. We find for low bit rates (10 Gb/s) that the optimum operational voltage for the modulator was within the supply voltage at the 65-nm technology node. At higher bit rates, the optimum voltage is found to increase and go beyond the stipulated supply voltage. In such a case, a suboptimum operation at the supply voltage incurs a 46% power penalty at 25 Gb/s. Having obtained the optimum modulator design and operation parameters and the corresponding total link power dissipation, we examine the impact of device and system parameters on the optimization. We find that a smaller device capacitance is an efficient solution to push the optimum swing voltage to be within the supply voltage. This is feasible using monolithically integrated Ge-based complementary-metal-oxide-semiconductor-compatible modulator and metal-semiconductor-metal photodetectors.

Optimization of VCSEL spatiotemporal operation in MMF links for 10-gb ethernet

A complete model of the spatiotemporal behavior of multimode vertical-cavity surface-emitting lasers (VCSELs), through static and dynamic response, noise, thermal effects, and its coupling to multimode fibers (MMF) has been investigated in low-cost 10-Gb Ethernet (10-Gb E) prototype optoelectronic packages using GaAs VCSEL arrays coupled to MMF ribbons for short-distance optical links. Eye diagram simulations compared to measurements allow the analysis of critical parameters, such as launching conditions, in order to maximize the MMF bandwidth as well as VCSEL static and dynamic conditions. A new bit error rate (BER) estimation method is proposed by taking into account not only the Q-factor but random and deterministic jitter and digital pattern effects. Global system optimization is discussed for a BER less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> for an aggregate link speed of 120 Gb/s over 300 m of a 12-fiber MMF ribbon

Spatiotemporal and Thermal Analysis of VCSEL for Short-range Gigabit Optical Links

High-speed Optoelectronic Modules using Vertical Cavity Surface Emitting Lasers (VCSEL) coupled to Multi Mode Fibers (MMF) are a performing and low-cost solution for 10 Gigabit Ethernet (10 GbE) in short-distance optical links. A complete model of the spatiotemporal behavior of multimode VCSELs, through static and dynamic response, noise, thermal effects, and its coupling to MMF has been investigated. Relative Intensity Noise shows modal dependence and can be affected by spatial filtering due to coupling and fiber propagation. Simulations permit to evaluate critical parameters, such as modulation formats, launching conditions, and operating temperature for global bandwidth and eye diagram optimization up to 10 Gb/s. Simulation results are compared to measurements on prototype optoelectronic modules.

Performance comparison between vertical-cavity surface-emitting laser and quantum-well modulator for short-distance optical links

We quantify and compare two competing transmitter technologies: vertical-cavity surface-emitting laser (VCSEL) and quantum-well modulator (QWM) for the interchip communication using high-speed optical links. VCSEL-based links are power favorable compared to QWM-based links at higher bandwidths (20 Gb/s) and larger distances. However, the QWM is better for lower detector capacitances. We also extend the comparison to high-speed electrical links and quantify the critical length beyond which optical links are power favorable compared to electrical links for both VCSEL and QWM transmitters

Tradeoffs of vertical-cavity surface emitting lasers for the development of driver circuits in short distance optical links

Tradeoffs of vertical-cavity surface emitting lasers for the development of driver circuits in short distance optical links

Tradeoffs of vertical-cavity surface emitting lasers modeling for the development of driver circuits in short distance optical links

In short-distance optical links, the development of driving circuits for vertical-cavity surface-emitting lasers (VCSELs) requires precise and computationally efficient VCSEL models. A small-signal model of a VCSEL is computationally efficient and simple to implement; however, it does not take into account the nonlinear output behavior of the VCSEL. In contrast, VCSEL models that are highly based on first principles cannot be implemented in standard circuit device simulators, because the simulation of eye diagrams becomes too time consuming. We present another approach using VCSEL models, which are based on the 1-D rate equations. Our analysis shows that they combine efficient extraction and short simulation time with an accurate calculation of eye diagrams over a wide range of ambient temperatures. As different implementations of the rate equations exist, tradeoffs between three different versions are presented and compared with measured GaAs oxide-confined VCSELs. The first model has a linear and the second a logarithmic function of the gain versus the carrier density. The third model considers the additional transport time for carriers to reach the active region with quantum wells. For parameter extraction, a minimum set of parameters is identified, which can be determined from fundamental measurements.