Optical Star Coupler Research Articles

The receiver collision avoidance (RCA) protocol for a single-hop WDM lightwave network

We propose a multiple access protocol for a single-hop wavelength division multiplexing (WDM)-based multichannel local lightwave network. The protocol can support a large number of high-speed bursty traffic nodes interconnected via a passive optical star coupler. Each node is equipped with only one transmitter and one receiver, both of which are tunable over all the channels. A single control channel is established to arbitrate access to the other channels, called data channels. Access to the control channel is provided via a variation of slotted ALOHA so that the system is scalable. Unlike other protocols proposed in [11], [18], [23], our protocol contains a simple mechanism which can dynamically detect and avoid receiver collisions (hence it is called the receiver collision avoidance (RCA) protocol)

Distributed Transmissive Optical Star Couplers Using Erbium-Doped Fiber Amplifiers

Distributed Transmissive Optical Star Couplers Using Erbium-Doped Fiber Amplifiers

Analysis of N*N passive optical star coupler based on the normal modes of N input waveguides

An integrated passive N*N optical star coupler on silicon wafer is described. Antiresonant reflecting optical waveguides (ARROWs) are analyzed and utilized as the input and output waveguides of the N*N coupler. Combining the exact solutions of the slab ARROW waveguide with the effective index method, a 5*5 coupler is analyzed. In the slab waveguide analysis, the input waveguides are coupled to their neighbors. The interaction of the waveguides is described in terms of the normal modes of propagation. The resultant field distribution is then diffracted into the free space region which separates the input and output sections. The radiation illuminates the receiving aperture from which the receiving N waveguides branch out, each output element obtaining equal power levels. Different types of loss such as spillover loss and mismatch loss were analyzed and estimated for N=5. A 5*5 star coupler with a transmission efficiency of 56% at a wavelength of 1.3 mu m is achievable. >

A wavelength division multiple access protocol for high-speed local area networks with a passive star topology

In this paper a multiple access protocol is proposed for a system consisting of many high-speed bursty traffic stations interconnected via an optical passive star coupler. Each station has access over a range of wavelengths. Time is divided intp fixed-sized slots. A station must reserve a wavelength first, then transmits the data on that wavelength. New stations can join the system anytime without any system reconfiguration. Broadcast and multicast traffic can also be easily supported. The performance of both the infinite and finite population cases has been modeled and analyzed. Numerical results show that low delay and high throughput (larger than the electronic speed of a single station) can be achieved. The analysis also shows that the best performance is obtained when the capacities of the reservation channels and the data channels are balanced.

N*N passive fiber star coupler using grating degeneration and sandwich structures

Designs for an efficient N*N passive integrated optical star coupler are proposed. The concepts of grating degeneration and sandwich structures are presented as solutions to the dynamic range limitation problem encountered by holographic fiber star couplers. The techniques and their combinations can significantly reduce the number of gratings required by the coupler. For instance, the number of superimposed gratings is decreased from 120 to no more than 4 for a 16*16 coupler. This reduction makes it possible to build holographic N*N star couplers with recording materials of a moderate modulation index.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amplified distributed reflective optical star couplers

A practical configuration for an amplified distributed reflective N-star coupler using 2*2 3-dB fiber couplers and minimum numbers of erbium-doped fibers, pump lasers, and standard fibers is presented. The constitution and characteristics of this coupler are investigated. Besides a tremendous amount of saving of the required standard fibers, this distributed coupler is more efficient, more reliable, more flexible for future expansion, and more cost-effective for application in optical networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Passive optical fiber star coupler

A fused polymer optical fiber star coupler utilizing a new fabrication technology has been developed. The uncladded fibers over the coupling region are fused together by a heat shrink sleeve. Low-cost star couplers with large port numbers, low excess losses, and high-uniformity variation are realized.

Grating degeneration technique and sandwich structures for holographic N*N passive star couplers

Design for an efficient N*N passive integrated optical star coupler are proposed. The concepts of grating degeneration and sandwich structures are presented. The techniques and their combinations can significantly reduce the number of gratings required by the coupler and thus make it possible to build holographic N*N star couplers with recording materials of a moderate dynamic range. >

Selective-broadcast optical passive star comer design for dense WDM networks

A technique is described for design and implementation of an integrated selective-broadcast passive optical star couplers that uses a space-varying refractive index slab. The coupler offers the potential for inexpensive implementation of various routing schemes. It is possible to incorporate a network traffic routing matrix in the design fabric of this bandwidth-selective coupler. The matrix may resemble any desired physical cross connection for routing user traffic. As an example, a shuffle-exchange cross-connect implementation is described. It is shown how this specific routing matrix can be built into the coupler fabric. Such a coupler has application in dense wavelength division multiplexed optical passive star networks where a selective or limited-broadcast coupling capability is desirable. >

Theory of an efficient N*N passive optical star coupler

A method for configuring an efficient N*N optical passive star coupler is introduced. It makes the construction of a one-piece coupler possible and thus eliminates the excess loss problem associated with cascade couplers and reduces the structural complexity. The authors show that a 100% efficiency figure can be achieved through the entire array by using a properly designed space-varying refractive-index slab. The authors give a mathematical analysis of the space-varying refractive-index slab and examine spatial frequencies of the required refractive-index pattern. The authors demonstrate how the wave-mixing method can be utilized as one possible method of configuring such a slab, using a constant temporal optical frequency involving nonlinear media such as photorefractive crystals.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and performance of a repeater for CSMA/CD passive optical star network connection

One method to expand a network is to employ repeaters operating at layer 1. When networks using the optical passive star coupler are connected through repeaters with only a relaying function, there arises the problem of “self-collision.” This problem occurs when the packet returned from the optical star coupler connected to the destination network is relayed unconditionally by the repeater to the originating network. As a means to avoid the self-collision, the authors have proposed a repeater with wavelength-division multiplex technique and gate control [1]. Through the design of the wavelength filter, it is shown that a satisfactory performance is obtained [3]. This paper shows further the results of studies, from the functional viewpoint, for the transmission design of the repeater, the control method for the gate, and the relaying method for the code rule violation. The repeater is built into a system constructed experimentally for the star configured optical transmission system with the transmission rate of 32 Mbit/s. The result of measurement of the transmission performance and the functional operation are described. The design for the repeater, which is applicable to the connection of the passive star network, is now described clearly.

Distributed optical passive star couplers

A technique is presented by which a single centralized passive star coupler in an optical star network is replaced by a distributed one. This is done by partitioning the star coupler into numerous pieces and placing them at the network nodes. Such a placement results in a great saving in the number of fibers required to build the star network. In addition to this saving, the problems associated with constructing a large single N*N star coupler are bypassed. >

A large ATM switch based on memory switches and optical star couplers

The authors propose a large asynchronous transfer mode (ATM) switch architecture based on memory switches of the type being developed by several research groups and on optical star couplers. Fast contention resolution makes it possible to combine a number of these modules, memory switches, and optical stars in order to attain a capacity of 2.5 Tb/s. This switch architecture has a relatively small failure group size of 128 STS-3 lines out of a total of 16384. The scaling of the switch to smaller capacities is discussed, showing how tradeoffs in the various parameters can be used to overcome particular technological limitations. Fault tolerance and recovery schemes are presented, showing that with minimal increase to the switch complexity and cost, a very reasonable fault recovery scheme is available for almost every sort of failure. >

Computer-controlled multichannel heterodyne optical communication system

The described system consists of eight frequency-shift-keying (FSK) modulated channels multiplexed by a 16*16 optical star coupler. Six of these channels are generated by individual digitally tuned optical frequency synthesizers. The frequency of these six channels can be randomly selected from a set of equispaced frequencies (2.2 GHz). Two of the 16 multichannel signals coming out of the star coupler are demultiplexed by their individual digitally tuned heterodyne receivers. Each receiver can randomly select, from the computer keyboard, a desired channel. The computer can identify missing channels. More importantly, the digital tuning of the frequency synthesizers and of the receivers is insensitive to variations of the frequency-tuning current relationship of the lasers. These results show that the digital tuning capability of today's radio systems can be transposed to the optical domain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A selective-broadcast passive star coupler for self-routing dense wavelength division multiplexed optical networks

The authors describe a technique for design and implementation of a selective-broadcast passive optical star coupler, that uses a space-varying refractive-index slab. A network traffic routing matrix can be incorporated in the design fabric of this bandwidth-selective coupler. The matrix may resemble any desired physical cross connection for routing user traffic. As an example, the authors show how a perfect shuffle network connectivity can be built into the fabric of a passive star coupler. A wave-mixing method is proposed to configure such a coupler. With this implementation, the authors have realized the physical connectivity appropriate for any desired routing matrix in dense wavelength division multiplexed optical star network applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flow control and deadlock avoidance on the partial optical hypergraph

The optical hypergraph is a distributed network in which each edge of the hypergraph is a multiple-access broadcast medium constructed as a passive optical star coupler. The partial optical hypergraph can be also viewed as a centralized switching network. The nodes with two ports (switch nodes) are centered in one location, and the nodes with one port (external nodes) are distributed within an area of 0–20 km around the switching nodes. The main result of this work is a flow control protocol for an arbitrary traffic pattern, which includes algorithms for preventing overflows, while maintaining the maximum switching capability of the switch nodes. Overflow prevention may cause deadlocks, so an algorithm for avoiding deadlocks is shown. These algorithms are realized at the network interface and, therefore, can operate in realtime at a traffic rate of over 1 Gbit/s per link. This network architecture demonstrates a close relationship between centralized and distributed systems. Potential applications of the partial optical hypergraph are varied and include large distributed databases, metropolitan area networks, factory automation, fault tolerant and realtime networks.

Broad-band high-silica optical waveguide star coupler with asymmetric directional couplers

A broadband optical waveguide star coupler with asymmetric directional couplers is proposed. A coupling or splitting ratio of the coupler is flattened with respect to wavelength by choosing appropriate values for Delta beta and complete power transfer length. The wavelength characteristics of uniform and alternating Delta theta b directional couplers are investigated, and their broadband operation is shown theoretically. To demonstrate the feasibility of the new proposal, 8*8 star couplers composed of such asymmetric directional couplers are fabricated by using high-silica waveguides on a silicon chip. A star coupler composed of asymmetric directional couplers exhibited 2-dB loss variation in the wavelength range of 1.3-1.55 mu m, and this value was almost one fourth of that of a star coupler composed of symmetric directional couplers. >

Development of a substation digital protection and control system using fiber-optic local area network

A substation protection and control system was developed and has been under trial use at a 50 kV substation. The system's digital protection and control equipment are located close to the outdoor power apparatus, and they are linked by an optical local area network (LAN). An IEEE 802.4 token-passing bus was used as the protocol of the LAN system. Optical star couplers were used for the physical layer. A specially designed synchronous sampling mechanism is also applied to the token bus to make the system more effective. Three manufacturers fabricated terminal equipment, which was linked by the optical LAN. Their interoperability was verified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of a Substation Digital Protection and Control System Using a Fiber-Optic Local Area Network

This article discusses a newly developed protection and control system for which substation digital protection and control equipment are separately located around the outdoor power apparatus and are linked by an optical LAN. Fig. 1 shows a basic system configuration. The monitoring control, bus protection, and transformer protection subsystems are located independently of each other, and are linked by an optical LAN. An IEEE 802.4 complied token bus is used as the protocol of the optical LAN. An optical fiber data transmission system consisting of optical star couplers is applied for the physical layer. The token bus is provided with a unique synchronous sampling function to make the digital protection and control system more efficient. This function attains synchronous data sampling by maintaining the circulating cycle of the token constant. Fig. 2 shows the principle of this synchronization system. Three related manufacturers each made a prototype of the terminal equipment following a unified standard. These units are linked with each other by an optical LAN. The interoperability of the transmission protocol and protection/control function was successfully confirmed. Following an integral function test, this system has been under a trail use test at TOKYO ELECTRIC POWER COMPANY's 500 kV capacity SHIN-HATANO SUBSTATION. In the test, practicability of the system, such as weatherability and surge withstand capability etc., has been checked.

Channel switching between receivers of FDM coherent optical star network

We present channel switching results obtained between receivers of an FDM optical coherent fibre star network. The system consists of six optical channels FSK-modulated at 200 Mbit/s and spaced by 2.2GHz. The channels are multiplexed by a 16 × 16 optical star coupler. Two of the multichannel signals exiting this device are demultiplexed by their respective random access digitally tuned heterodyne receivers. Simultaneous switching between pairs of channels is obtained by command of a personal computer controlling both receivers