Abstract-The main bandwidth bottleneck in today's networks is in the access segment. To address that bottleneck, broadband fiber access technologies such as passive optical networks (PONs) are an indispensable solution. The industry has selected timedivision multiplexing (TDM) for current PON deployments. To satisfy future bandwidth demands, however, next-generation PON systems are being investigated to provide even higher performance. In this paper, we first review current TDM-PONs; we designate them as generation C. Next, we review next-generation PON systems, which we categorize into C+1 and C+2 generations. We expect C+1 systems to provide economic near-term bandwidth upgrade by overlaying new services on current TDM-PONs. For the long term, C+2 systems will provide more dramatic system improvement using wavelength division multiplexing technologies. Some C+2 architectures require new infrastructures and/or equipment, whereas others employ a more evolutionary approach. We also review key enabling components and technologies for C+1 and C+2 generations and point out important topics for future research.Index Terms-Access networks, passive optical network (PON), time division multiplexing (TDM), wavelength division multiplexing (WDM).

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A flexible TWDM PON system is proposed which allows pay-as-you-grow in capacity, supports load balancing among different ODNs, and achieves significant power saving at OLT. Integrated OLT transceiver in enhanced CFP module and low-cost tunable ONU transceiver in SFP+ module are developed, for the first time, for cost effective deployment of TWDM PONs. System experiments demonstrate error free performance with 36 dB power budget in a flexible TWDM PON test bed.

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Experimental observations on the capacity of a spudcan footing model on loose sand subjected to combined vertical, horizontal and moment loads at stresses relevant for modern jack-up drilling units are presented. The observations are developed from drum centrifuge experiments using an apparatus capable of independently translating and rotating the footing. The results are interpreted within the framework of strain-hardening plasticity theory previously used to develop force-resultant models from flat circular footing experiments conducted at 1g. The complete combined loading yield surface for spudcan foundations on loose sand has been successfully derived through seven specially designed swipe tests. An empirical equation previously derived to describe the yield surface of flat footing is recalibrated for spudcans. A three-dimensional sliding surface that intersects the traditional yield surface has been experimentally recorded and an analytical expression derived. With model parameters being refined and the sliding surface added, the theoretical yield surface describing circular spudcan footing on loose sand is complete.

We present a review of research performed in the area of coherent access technologies employing vertical cavity surface emitting lasers (VCSELs). Experimental demonstrations of optical transmission over a passive fiber link with coherent detection using VCSEL local oscillators and directly modulated VCSEL transmitters at bit rates up to 10 Gbps in the C-band as well as in the O-band are presented. The broad linewidth and frequency chirp associated with directly modulated VCSELs are utilized in an envelope detection receiver scheme which is demonstrated digitally (off-line) as well as analog (real-time). Additionally, it is shown that in the optical front-end of a coherent receiver for access networks, the 90 • hybrid can be replaced by a 3-dB coupler. The achieved results show that VCSELs are attractive light source candidates for transmitter as well as local oscillator for coherent detection PONs

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