Stuart D. Elby

WDMA/subcarrier-FDMA lightwave networks: limitations due to optical beat interference

The authors present a general model of optical beat interference, and its contribution of channel outage in a WD-SFDMA (wavelength division-subcarrier frequency division multiple access) network. The probability of channel outage due to optical beat interference is determined from analysis and computer simulation for externally and directly modulated single-mode lasers. These results are used to calculate the ultimate limitation on the throughput and capacity of the network due to beat note interference, for a simple retransmission protocol. It is shown that, as more subcarrier channels are added, network capacity increases sublinearly and eventually saturates. >

Low-loss, high-impedance integrated fiber-optic tap

A passive optical tap that uses cladding modes in a single-mode fiber to provide continuous adjustability of tapped power, large tapping ratios, low excess loss, and structural compatibility with integrated circuit technology has been fabricated and demonstrated. This prototype suffers excess loss of less than 0.07 dB and yields tapping ratios as large as 36 dB. System performance analysis of an optical bus incorporating the integrated fiber-optic tap is discussed, and comparison to conventional singlemode fiber-optic taps, such as fused couplers, is made.

All-optical distributed packet-switched networks: limitations and potential

It is shown that to take advantage of photonic switching in distributed packet-switched networks, a routing scheme suitable for optical implementation, e.g., the so-called hot-potato scheme, must be employed, and the optoelectronic bottleneck, associated with injecting packets onto and off of the network must be overcome. In hot-potato routing schemes, packets arriving at a node, but not destined for it, are immediately placed on an outgoing link. Since no buffering is required at the switching nodes, such routing algorithms are ideal for photonic switching. It is further shown that hot-potato routing is less efficient than store-and-forward routing, but when it is used in conjunction with time-compressed optical packets it provides a greater throughput.<<ETX>>

Optical transmitter for fiber-optic interconnects

An optical transmitter for fiber optic interconnects that consists of an off-chip centralized laser in conjunction with on-chip multiple quantum well electroabsorption modulators is proposed and demonstrated, and its performance is discussed.

WDM-subcarrier FDMA lightwave networks: optical beat note interference

It is shown that the introduction of subcarrier frequency-division multiaccess (SFDMA) into a wavelength-division multiplexing (WDM) network provides an increase in throughput which is limited significantly by beat-note-interference-induced channel outage. The reduction of throughput prevents the network capacity from growing unabated as more subcarrier channels are added. The analysis is useful for studying the tradeoffs associated with adding subcarrier channels to a WDM network, specifically in terms of key parameters such as laser modulation format and optical and subcarrier channel bandwidths. It is found that for a WD/SFDMA network with N optical channels each having M subcarrier channel, i.e., NM concurrently accessible channels, using a slotted-Aloha-like protocol, there is a maximum throughput corresponding to an optimum offered load, and these values decrease as more subcarrier channels are offered.<<ETX>>