M. Kuznetsov

A next-generation optical regional access network

We describe an optical regional access network which combines electronic IP routing with intelligent networking functionality of the optical WDM layer. The optical WDM layer provides such networking functions as network logical topology reconfiguration, optical flow switching to offload traffic and bypass IP routers, wavelength routing of signals, protection switching and restoration in the optical domain, and flexible network service provisioning by reconfigurable wavelength connectivity. We discuss key enabling technologies for the WDM layer and describe their limitations. The symbiosis of electronic and optical WDM networking functions also allows support for heterogeneous format traffic and will enable efficient gigabit-per-second user access in next-generation Internet networks.

The NGI ONRAMP test bed: reconfigurable WDM technology for next generation regional access networks

Next generation internet optical network for regional access using multi-wavelength protocols (NGI ONRAMP) is a pre-competitive consortium sponsored by DARPA. Its mission is to develop architectures, protocols, and algorithms for wavelength division multiplexing (WDM)-based regional access networks that will effectively support the NGI. A reconfigurable WDM test bed is being built to demonstrate some of the key thrusts of the consortium, including dynamic service provisioning and optical flow switching, service protection in the optical domain, medium access control protocols, and network control and management geared for the efficient transport of Internet traffic over WDM networks. The ONRAMP test bed will consist of a feeder network connecting via access nodes to distribution networks on which the end users reside. ONRAMP network reconfiguration is enabled by access nodes that contain both optical and electronic switching components, allowing data traffic to be routed all-optically through the network or to be switched and aggregated by electronic Internet protocol (IP) routers. This paper describes the goals and basic architecture of the ONRAMP test bed, as well as the design, construction, and characterization of the network access nodes. To illustrate test bed operation, we demonstrate optical flow switching over the test bed that achieves Gb/s throughput of TCP data between end user workstations.

Radiation loss in dielectric waveguide Y-branch structures

Volume current method is used to calculate the radiation loss of dielectric waveguide Y-branch structures. Radiation loss of a Y-branch in the power-dividing mode of operation is calculated accurately for the first time, obtaining proper zero loss in the limit of the zero branching angle. Radiation loss of a Y-branch with parallel output guides is calculated and compared to the loss of a three guide coupler-divider; the Y-branch has smaller loss. Simple analytical formulas are given for approximate loss calculation in these structures.

Dispersion-induced power penalty in fiber-Bragg-grating WDM filter cascades using optically preamplified and nonpreamplified receivers

In wavelength-division-multiplexed optical networks, signals pass through cascades of multiplexing/demultiplexing channel filters present in the network access nodes. We describe experimental measurements and numerical simulations of the signal power penalty at 10 Gbps due to dispersion slope in such a cascade of fiber-Bragg-grating filters. The dispersion penalty of the cascade limits the allowed frequency detunings of the signal laser and channel filters. We observe that optically-preamplified receivers show a significantly larger dispersion penalty than nonpreamplified receivers, with a simple relation between the two penalties. This penalty difference should exist for any signal impairment that degrades optical signal extinction such as dispersive filter or fiber transmission and optical channel bandwidth narrowing.

Expressions for the coupling coefficient of a rectangular- waveguide directional coupler

More-accurate expressions are obtained for the coupling coefficient of the dielectric rectangular-waveguide directional coupler. The previous expressions may overestimate the coupling coefficient by as much as a factor of 2 in some cases of interest.

Theory of bistability in two-segment diode lasers.

Optical bistability in two-segment diode lasers with inhomogeneous injection is considered. Analytical solution of the rate-equation model gives a simple bistability condition. Slower carrier recombination in the absorber relative to the gain region is required for bistability when the gain and the absorber optical cross sections are equal. Carrier lifetimes, switch-on and switch-off powers, and currents are investigated for these bistable lasers.

Design of widely tunable semiconductor three-branch lasers

We describe the design and operating principles of the new, widely tunable, three-branch semiconductor Y3-lasers, which we have demonstrated recently. This multibranch tunable laser structure is formed by a cascade of Y-junctions and uses a geometrical tuning leverage to achieve wide-range discrete frequency tuning. Y3-lasers have demonstrated experimentally a tuning range of 45 nm (5.6 THz) and access to 50 frequency channels, with potential access to more than a 100 channels. Among the important issues discussed in this paper are the Y3-laser structure, mode selection of the Y3-laser filter, laser side-mode suppression, number of accessible channels, tuning range, and the tuning mechanism of the Y3-laser. A specific design example is also presented. The simplicity of Y3-laser fabrication and the powerful digital channel-access control make these lasers important electronically-tunable sources for multichannel wavelength-division-multiplexed (WDM) optical communication networks. >

Modeling short optical pulse generation using electroabsorption modulators

Model short optical pulse generation in sinusoidally-driven lumped-electrode electroabsorption modulators, describes pulse width scaling with device and applied modulation parameters, and defines a new device figure of merit.

Optical networking with reconfigurable access nodes in the NGI ONRAMP test bed

We have built reconfigurable access nodes for the next generation Internet (NGI) ONRAMP test bed and used them to demonstrate basic optical networking functionality, including over a 100 km installed fiber link.

Dispersion-induced power penalty in fiber-Bragg-grating WDM filter cascades

In wavelength-division-multiplexed optical networks signals pass through cascades of multiplexing/demultiplexing filters. We present experimental measurements and theoretical modeling of transmission power penalty at 10 Gbps due to dispersion slope of fiber-Bragg-grating and thin-film cascades.