A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

WDM optical network with passive pass-through at each node

A communication network has a flexible bi-directional bus architecture (FBDNA) and is arranged as a ring structure. Each node of the network has at least one on/off node switch, i.e., a switch that permits or blocks transmission around what would otherwise be a ring. If the network has one node switch per node, one node switch is set initially off to avoid problems with circulating amplified spontaneous emission (ASE) normally associated with a ring structure. If a fiber break occurs, the node switch (or node switches) in the node (or nodes) next to the break and on the same side of the node as the break switches off, and the node switch that was off before the break switches on, permitting the network to operate largely as before. If the network has two node switches per node, two node switches next to each other in neighboring nodes are initially set off, and if a cable break occurs, both node switches around a break switch off, and the node switches that were initially off switch on. The network provides protective switching of traffic and solves the problem of circulating ASE in a simple and economical way. The network also permits wavelength reconfiguration to reduce the number of required wavelengths.

Optical multichannel system

The strengths and limitations of the photonic technology are reviewed, beginning with the temporal bandwidth limitations of photonic devices and then focusing on spatial bandwidth, commonly referred to as the parallelism of optics, and how it can be used in photonic fabrics. Some of the proposed photonic switching fabrics that are based on guided-wave devices are discussed, comprising switching fabrics based on space channels, using directional couplers and optical amplifiers, and those based on time channels. The latter include active reconfigurable fabrics based on TDM, time-slot interchangers, and universal time slots, in addition to passive shared media fabrics. Some of the switching fabrics that have been proposed using wavelength channels are outlined, and multidimensional fabrics are briefly reviewed. Photonic switching fabrics based on free-space devices are described, covering free-space relational switching fabrics, the basic hardware required for digital free-space optical fabrics, and digital free-space switching fabrics. >

Photonic switching fabrics

Using the wavelength selectivity and low loss characteristics of optical couplers, in which index of refraction gratings in a non-evanescent waveguide merged region reflect only a selected wavelength band, signal switching and control systems of novel characteristics are provided for multi-wavelength optical communication systems. In a router, for example, selected wavelengths or wavelength bands on an add/drop line can be added to or dropped from a main fiber, by cross switching between wavelength selective loops disposed sequentially in the lines. In a collector box, as another example, selected wavelength bundles can be routed from one fiber onto multiple fibers. In a bandpass filter a selected wavelength band is transmitted with low loss while those wavelengths outside the selected wavelength band are rejected with very high loss.

Wavelength selective optical routers

Methods and apparatus to sense both discrete and continuous magnetic reference systems installed in the roadway, and provide information to support lateral and, to some extent, longitudinal and vertical vehicle control and/or driver assistance. The position of an object, such as a vehicle, relative to a magnetic reference infrastructure, such as that representing a dividing line on a roadway, is determined by sensing, with a sensor associated with the object, at least one axial field strength component of the magnetic field emitted from the magnetic reference, computing a ratio of the sensed axial field strength components, and then determining the positional offset of the object as a function of the ratio. The lateral offset is independent of the magnetic field strength due to the use of the ratio which cancels out the magnetic field strength. The invention is also capable of providing three-dimensional positioning relative to a magnetic reference.

Intelligent ultra high speed distributed sensing system and method for sensing roadway markers for intelligent vehicle guidance and control

Mach-Zehnder interferometers with fiber Bragg gratings (MZ-FG) are investigated as promising devices for wavelength-selectable optical add-and-drop multiplexers (OADM). A wavelength reused OADM performance is demonstrated for the first time to our knowledge in a six-channel, 10 Gb/s WDM experiment using a single-stage MZ-FG. We discuss both theoretically and experimentally the interferometric crosstalk induced by imperfect Bragg-reflectivity. Two methods are proposed to solve the interferometric crosstalk issues. The first one is wavelength offset scheme. It is experimentally confirmed that there is no interference when the wavelength of crosstalk is away from that of the signal at least two times of bit-rate. In order to separate each wavelength, the master-slave wavelength control method is proposed with Fabry-Perot interferometer made of a set of fiber gratings. The second one is a cascaded MZ-FG scheme eliminating the crosstalk itself. The calculation indicates that a Bragg-reflectivity of only 93% can suppress the crosstalk to be -35 dB. Cascaded MZ-FG's have been fabricated to show that the interferometric crosstalk can be successfully reduced to -50 dB for the add signal, and -71 dB for the drop signal, respectively. The eight-wavelength 10 Gb/s OADM experiment is carried out to demonstrate the low interferometric crosstalk performance.

Interferometric crosstalk-free optical add/drop multiplexer using Mach-Zehnder-based fiber gratings

A basic bidirectional fibre optic loop-structured network configuration which provides an automatic recovery mechanism against a line failure and employs WDM-TDMA techniques for signal multiplexing is presented. Experimental results of a prototype of such a network are also described.

Bidirectional fibre optic loop-structured network

Automatic Gain Control of Erbium-Doped Fiber Amplifiers for WDM Transmission Systems

A fiber-optic loop-configured passive network using burst TDMA scheme which features high reliability and efficient communication capability is presented. The basic analysis for the passive network design including the level diagram, dynamic range, and TDMA burst synchronization are discussed. It is calculated that about 20 stations can be installed if the output peak power of laser diode is +20 dBm and the connector pair loss of optical access coupler is 1 dB. Efficient data transmission of nearly 80 percent with a frame length of 1 ms can be obtained in the TDMA system for 20 stations. The station equipment designs concerning to the burst-mode optical transmission and the unique word detection are also described. An experimental system model with three stations using 51.2-Mbit/s bit rate is constructed, and the feasibility of this passive loop-configured network has been confirmed.

Fiber-optic local area passive network using burst TDMA scheme

PURPOSE:To make the level of an optical signal, which arrives at an optical receiver, constant, by permitting data stations, which use a looped trunk line optical fiber as a common transmission line, to communicate with one another through an optical repeating device. CONSTITUTION:Optical signals with wavelength lambda1 transmitted from data stations 13-17 are coupled with a trunk line optical fiber 1 by T-shaped optical couplers 12a-12e, and transmitted in both the ways of the optical fiber. The optical signals propagating through the fiber 1 are received by an optical repeating device 18 theough the T-shaped optical couplers 12a-12e. The received optical signals are repeated and amplified by the device 18 to be converted into light signals with wavelength lambda2, which are sent out. Those optical signals are distributed to the stations 13-17 through the coupler 11, fiber 1, and couplers 12a- 12e respectively. If the breaking of the fiber 1 occurs, a trunk line controller 9 detects that and operates its optical switch from an open-circuit state to a closed-circuit state, so that both ends of the fiber are connected by the optical transmission line of the optical switch.

Katsuyoshi Ito

Papers

Interferometric crosstalk-free optical add/drop multiplexer using Mach-Zehnder-based fiber gratings

Bidirectional fibre optic loop-structured network

Automatic Gain Control of Erbium-Doped Fiber Amplifiers for WDM Transmission Systems

Fiber-optic local area passive network using burst TDMA scheme

Optical fiber multiple access communication device