Access Couplers Research Articles

Numerical study on Kerr frequency comb generation in Si3N4 microresonators with frequency-dependent access coupler properties

Within the framework of vertically coupled silicon nitride (Si 3 N 4) resonators characterized by 220 GHz free spectral range driven by a continuous wave laser at 1.55 µm for Kerr comb generation, severe issues may arise in the design of achromatic critically coupled resonators because of the difficulty in designing dispersion-free access couplers with controlled coupling factor over a large spectral bandwidth. As a consequence, numerical simulations of Kerr frequency comb in these structures may drastically differ from reality if frequency dependence of the access coupler's properties is not taken into account in the simulated model. In order to address this issue, we have developed a numerical model that takes into account the frequency dependence of the access coupler coefficients and remains valid even for the simulation of low Q factor resonators. Field propagation within the ring is described by nonlinear Schrodinger equation. The novelty of this model lies in the computation of a complex-valued, frequency-dependent coupling transfer function between a resonant ring and underlying access waveguide that models frequency-dependent dispersion and losses in the access-coupling region of the resonator. Based on simulation results, we discuss the differences observed in Kerr comb generation in resonators with three different coupler designs initially intended to yield critical coupling over the largest achievable bandwidth.

Passive fiber optic bus using bidirectional integrated optic bus access couplers

The feasibility of a passive fiber optic bus that uses bidirectional integrated optics bus access couplers is studied. The number of bus nodes can be increased when an optimized asymmetric bus access coupler is used instead of a symmetric one. A modified Ag-Na ion exchange process provides the possibility of manufacturing integrated optics asymmetric couplers for the bus. The process is suitable for the processing of integrated optics components that combine deep multimode waveguides with different core sizes on a single substrate. An access coupler is designed, modeled, and processed. The coupler is optimized for seven nodes; the asymmetry of the coupler is 5 dB.

Fiber-optic interconnection of local area networks: physical limitations of topologies

This paper examines and quantifies the physical limitations imposed by basic topologies and access couplers in fiber-optic interconnection of local area networks (LAN's). To that end a detailed comparison of the basic topologies and access couplers is provided. The comparison is in terms of amount of fiber required, average propagation delay, fault tol- erance, maintainability, number of access couplers required, and maximum bit rate. These results lead to simple guidelines for the choice of topology and the type of access couplers that may be used in practical LAN interconnection. Our results indicate that for 100 node LAN interconnection, the star topology requires 3.8 times as much fiber as a dual ring, which may be of significant concern if the interconnection network is in an urban business area. The average propagation delay of a dual ring for a 100 node interconnection, on the other hand, is 3.3 times that of the star. This may be a significant disadvantage in LAN interconnection networks where the distance between nodes is large. The maximum bit rate, by assuming simple direct detection, is calculated for a fiber network based on the topology and type of access coupler. Our results show that the more fault tolerant an access coupler is, the lower is the maximum bit rate it can support.

Lithium niobate devices in switching and multiplexing

Integrated-optics devices in lithium niobate have reached a significant maturity in recent years, and several complex devices have been demonstrated. In addition to performing modulation of light in fibre-optic transmission systems, lithium niobate devices currently offer the only components for photonic switching. Thus lithium niobate devices can be used as spatial, temporal and wavelength switches in high-speed and low-speed systems. In these systems electronic signals control the lithium niobate switches, which process the optical information and which are optically interfaced to optical fibres. Hence I am not concerned with all-optical switching. Examples of applications are multiplexing and demultiplexing of high-speed data streams, bit-by-bit or word-by-word switching in, for example, time-space-time stages or in access couplers in high-speed bus systems. Switch arrays, generally operating at lower speeds (below 1 GHz), can be used for network rearrangement, digital crossconnect, protection switching and generally in situations where the frequency and code transparency of the devices can be used to advantage. The status of lithium niobate devices for switching is reviewed, and performance limitations (including those imposed by polarization properties) and trade-offs are discussed, emphasizing time- and space-switching devices and applications.

A robust fiber optic active star coupler for the SAE linear token-passing multiplex data bus

The Society of Automotive Engineers (SAE) linear token-passing multiplex data bus draft standard (AS4074.1, version 2.0) calls for two sets of fiber-optic medium characteristics which support a generous power loss budget of about 30 dB. Since there are applications for this bus needing an even greater loss budget one solution is to make the access coupler (the star) an active (powered) network component. A description is given of a simple, low-power, high-reliability active star coupler design meeting the overall requirements of the SAE high-speed data bus (HSDB) standard without changes to the fiber-optic implementation characteristics. The basic active star network is introduced and important quantities defined. Technical issues which influence the active star design are discussed. These include the properties of the protocol which have the greatest effect on the design of the active star, such as the initialization procedure, the system monitoring and control times, the preamble, and the intertransmission gap time. Component options are introduced and a completed design presented. Its performance in a high-speed data-bus environment is characterized and modifications to the standard for best active star performance are suggested.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fiber-optic local area passive network using burst TDMA scheme

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.

Modal-noise generation in biconical-taper couplers

The modal noise resulting from the dividing of coherent light in fused biconical-taper star and access couplers is measured. The theoretical explanation of the results is presented. It is found that modal-noise generation is not severe even in those cases in which the light is strongly subdivided by a biconical-taper star coupler with a large number of ports. The performance of most digital fiber systems using such couplers is not expected to be significantly degraded by the measured levels of modal noise.

Tapped tee single-mode data distribution system

An eight-terminal tapped tee fiber distribution system was constructed using six single-mode fiber access couplers. Data transmission at a 500 Mbit/s rate was demonstrated with a maximum thruput loss of -27 dB. Transmission and coupling fraction data for the couplers is given as well as throughput loss measurements for the data bus. Predicted bus capacity with this type of coupler is up to 15 terminals at 500 Mbits/s with a bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> .

Fused single mode fibre access couplers

Single mode fibre access couplers have been fabricated by chemically etching most of the glass cladding material surrounding the fibre core, and thermally fusing the fibres together in the etched region. The resulting couplers have low loss and are both durable and insensitive to ambient temperature variations.

Liquid-crystal fiber-optic switch

An adjustable access coupler for multimode fiber-optic networks has been constructed, based on the voltage-tunable total-internal-reflection effect in nematic liquid crystals. Fibers are coupled via graded-index rod lenses at normal incidence to flint-glass prisms in contact with a 6-microm liquid-crystal layer. The achromatic four-port switch has a 1.6-dB optical insertion loss, a tap ratio controllable from -4.6 to -48 dB, a directionality of 44 dB, and an operating voltage of 5 to 20 V rms.

Improved planar optical branching elements for multimode fibre transmission systems

The optical tapping and fan-out elements which we had previously fabricated for multimode fibre transmission systems all suffered from the serious drawback that the aging of the light-sensitive foil used in our simple planar technology resulted in a deterioration in the performance of structures using such foil as a planar waveguide. This paper introduces improved optical structures in which this drawback has been avoided while stil retaining the simple technique by which high fibre positioning accuracy is assured. In addition the overall insertion loss of the structures has been reduced to about 2 dB for the fan-out structure and 1.2 dB–1.5 dB for the access coupler.

Optimized layout for a data bus system based on a new planar access coupler

The optimum layout of a single-fiber data bus T-system based on a planar access coupler has been calculated. In this layout the tapping ratio of each individual access coupler is optimized permitting a considerably higher number (typically twice as many) of terminals than in a nonoptimized system.

Star and access couplers for multichannel fiber cables

Star and access couplers for multichannel fiber cables

New planar optical coupler for a data bus system with single multimode fibers

We report an optical coupler suitable for use as an access coupler in a data bus T-system with single multimode fibers as transmission lines. The in- and out-coupling factors are determined by a lateral displacement of the main trunk-fibers which are butt joined. The fabrication of the coupler takes advantage of a simple, sufficiently reproducible, and cheap planar photolithographic process. Using fibers with 100-microm o.d. and 90-microm core diam a total insertion loss of about 1.5 dB and an out-coupling of about -14 dB was measured with a lateral displacement of 20 microm.

Low-loss access coupler for multimode optical fiber distribution networks

Low-loss access coupler for multimode optical fiber distribution networks

Fabrication of an access coupler with single-strand multimode fiber waveguides

Fabrication of an access coupler with single-strand multimode fiber waveguides

Optical access couplers and a comparison of multiterminal fiber communication systems

Optical T and multiple T access couplers designed for tapped trunk line multiterminal communication systems that use bundles of multimode fibers as the transmission media have been investigated. The particular coupler designs tested used bent Pyrex rods for bifurcation and scrambling. Coupler throughput losses (not counting packing fraction losses) are 1.5-2.5 dB. The bent rod optical T and multiple T access couplers must be used with high N.A., low packing fraction loss fibers. To avoid the use of a repeater a multiple T or star configuration must be used in a system comprising ten or more terminals.