Modeling and simulation of next-generation multimode fiber links

This paper describes an advanced multimode-fiber-link model that was used to aid the development of Telecommunication Industry Association standard specifications for a next-generation 50-/spl mu/m-core laser-optimized multimode fiber. The multimode-link model takes into account the interactions of the laser, the transmitter optical subassembly, and the fiber, as well as effects of connections and the receiver preamplifier. We present models for each of these components. Based on these models, we also develop an efficient and simple formalism for the calculation of the fiber transfer function and the signal at the link output in any link configuration. We demonstrate how the model may be used to develop specifications on transmitters and fibers that guarantee any desired level of performance.     

120-Gb/s VCSEL-based parallel-optical interconnect and custom 120-Gb/s testing station

A 120-Gb/s optical link (12 channels at 10 Gb/s/ch for both a transmitter and a receiver) has been demonstrated. The link operated at a bit-error rate of less than 10/sup -12/ with all channels operating and with a total fiber length of 316 m, which comprises 300 m of next-generation (OM-3) multimode fiber (MMF) plus 16 m of standard-grade MMF. This is the first time that a parallel link with this bandwidth at this per-channel rate has ever been demonstrated. For the transmitter, an SiGe laser driver was combined with a GaAs vertical-cavity surface-emitting laser (VCSEL) array. For the receiver, the signal from a GaAs photodiode array was amplified by a 12-channel SiGe receiver integrated circuit. Key to the demonstration were several custom testing tools, most notably a 12-channel pattern generator. The package is very similar to the commercial parallel modules that are available today, but the per-channel bit rate is three times higher than that for the commercial modules. The new modules demonstrate the possibility of extending the parallel-optical module technology that is available today into a distance-bandwidth product regime that is unattainable for copper cables.     

Computer modeling and simulation of the Optoelectronic TechnologyConsortium (OETC) optical bus

The Optoelectronic Technology Consortium (OETC) 16 Gbit/s, 32-channel parallel fiber optic bus introduces new requirements for modeling and simulation of an optical bus which were not present for previous single-channel optical link systems. These requirements include the simulation of the statistical variation in component parameters, timing skew, and crosstalk. Due to the required simulation of statistical variation in component parameters, a time efficient simulation approach such as the quasi-analytical simulation methodology is vital. In addition, the adoption of a block-oriented simulation environment facilitates mixed-level simulation which minimizes the computational requirements of the bus simulation while achieving the required accuracy in the simulation of all bus components. Simulation results indicate that while noise is not a limiting factor in the performance of the optical bus, timing skew, and device uniformity across the channels of the bus are the most important factors for satisfactory performance. Experimental measurements confirm these simulation results     

Development of system specification for laser-optimized 50-/spl mu/m multimode fiber for multigigabit short-wavelength LANs

This paper presents the scientific arguments used in the specification development process by the Telecommunications Industry Association (TIA) Working Group FO-2.2.1 to develop the new multimode fiber and vertical-cavity surface-emitting laser specifications for high-speed application in data communications. Numerous engineering and commercial tradeoffs are described. The specification minimizes the link failure rate and overall link cost through utilization of communication-theory-based modeling and experimental verification. This was balanced against the reality of manufacturing costs attempting to maximize the yield of individual link components. The specific application used as an example has 50-/spl mu/m graded-index multimode fiber operating at 10 Gb/s (e.g., 10 Gb/s Ethernet and fiber channel). The link performance is determined by the interaction of the fiber intermodal dispersion measured by the differential modal delay, and the transceiver launch distribution into the multimode fiber measured by encircled flux. A theoretically based model and the simulation approach that were used to simulate 40 000 links are described. The information from these simulations was used to determine the specification limits. In addition, sensitivity to the specification limits was evaluated. The experimental results of a round robin conducted by the TIA are presented, which confirm that the modeled performance would yield the expected results in actual practice.     

Measurements for enhanced bandwidth performance over 62.5-/spl mu/m multimode fiber in short-wavelength local area networks

The Telecommunications Industry Association (TIA) FO-2.2.1 Working Group on the modal dependence of bandwidth has conducted industrywide interlaboratory comparisons on measurements aimed at improving the bandwidth performance of short-wavelength, laser-based, multimode-fiber local area networks (LANs). Measurements of both transceiver encircled flux and fiber restricted-mode-launch bandwidth can together successfully predict an enhanced system performance, provided that the proper limiting criteria are selected. System performance is determined by a measurement of effective bandwidth and/or intersymbol interference. Recommendations for source and fiber selection criteria come from a risk analysis based on an extensive multilaboratory comparison involving 95 fibers and 69 laser transceivers. For this paper, enhanced system performance is defined as a performance that allows operation at a data rate of at least one gigabit per second over a 500-m length of 62.5/125-/spl mu/m graded-index glass fiber.     

Criteria for optimizing laser launch conditions in 10 Gb/s links using OM3 fibers

In this paper we present the dependence of the ISI penalty and ISI failure rate on various transmitter and fiber parameters characterizing 10 Gb/s Ethernet links with 300 m long OM3 multimode fibers operated at 850 nm. Statistical optimization of the launch conditions results in optimal values for the laser encircled flux (13–17 μm) and lateral offset of the source (10–18 μm). The analysis of the ISI failure rate and ISI correlation coefficients showed that without additional optimization, the axial offset between the laser and the fiber axes has detrimental effects on the performance of the TIA-compliant links and it should be less than 60 μm. The optimization of the launch conditions with additional criteria going beyond TIA requirements may reduce the ISI penalty by as much as 0.7 dB leading to ISI penalty well below its allocation limit of 2.5 dB. This gives an opportunity to increased link lengths beyond standardized 300 m.     

Integrated transversal equalizers in high-speed fiber-optic systems

Intersymbol interference (ISI) caused by intermodal dispersion in multimode fibers is the major limiting factor in the achievable data rate or transmission distance in high-speed multimode fiber-optic links for local area networks applications. Compared with optical-domain and other electrical-domain dispersion compensation methods, equalization with transversal filters based on distributed circuit techniques presents a cost-effective and low-power solution. The design of integrated distributed transversal equalizers is described in detail with focus on delay lines and gain stages. This seven-tap distributed transversal equalizer prototype has been implemented in a commercial 0.18-/spl mu/m SiGe BiCMOS process for 10-Gb/s multimode fiber-optic links. A seven-tap distributed transversal equalizer reduces the ISI of a 10-Gb/s signal after 800 m of 50-/spl mu/m multimode fiber from 5 to 1.38 dB, and improves the bit-error rate from about 10/sup -5/ to less than 10/sup -12/.     

Interferometric noise reduction in fiber-optic links bysuperposition of high frequency modulation

The reduction of interferometric noise by superposition of high frequency modulation is analyzed. It is shown that the nature of this reduction is due to a redistribution of noise energy from baseband to higher frequencies where it can be discarded by low-pass filtering. Detailed analysis revealed the dependence of the noise reduction factor on the product f_0τ, and the modulation index of the high frequency superimposed modulation. The proper choice of parameters can lead to complete elimination of the converted phase noise from the system