Mansour I. Irshid

Bit error probability for coherent M-ary PSK systems

A simple technique for evaluating the bit-error probability of coherent M-ary phase-shift keying (PSK) with any bit-mapping is proposed. Closed-form expressions are given in terms of error functions for half- and quadrant-plane probabilities in the decision space, avoiding the numerical evaluation of complicated integrals that occurs in the direct method. Bit error probability expressions for M-ary PSK with Gray, natural binary, and folded binary bit-mappings are derived. >

A full transparent fiber-optic ring architecture for WDM networks

A fully transparent fiber-optic ring architecture for wavelength division multiplexed (WDM) networks is proposed. The physical topology of the proposed network is based on a single or multifiber ring. The nodes at the periphery of the network are connected onto the ring via a polarization-independent acoustically tunable optical filter (PIATOF). This device is used for injecting the transmission from each node at a predefined wavelength onto the ring and at the same time for accessing the transmission of the other nodes. Expressions are derived for the throughput of different network configurations. >

Coherence and intersymbol interference in digital fiber optic communication systems

Because of the quadratic relation between optical power and optical field, the transmission of optical power through an optical fiber is, in principle, nonlinear. Under usual conditions, random fluctuations of the incoherent source field and mode mixing tend to linearize the system. Previous assessments of the effect of intersymbol interference (ISI) on the performance of digital fiber optical communication systems are based on the assumption of linearity. This paper examines the effect of ISI on error rates in the other limit of complete coherence where fields are additive but powers are not. It is found that in this nonlinear regime and for weak dispersion, ISI may reduce the error rates slightly, whereas strong dispersion augments it considerably.

An efficient bitwise Huffman coding technique based on source mapping

Abstract In this paper, we propose an efficient source encoding technique based on mapping a non-binary information source with a large alphabet onto an equivalent binary source using weighted fixed-length code assignments. The weighted codes are chosen such that the entropy of the resulting binary source multiplied by the code length is made as close as possible to that of the original non-binary source. It is found that a large saving in complexity, execution time, and memory size is achieved when the commonly used source encoding algorithms are applied to the n th-order extension of the resulting binary source. This saving is due to the large reduction in the number of symbols in the alphabet of the new extended binary source. As an example to validate the effectiveness of this approach, text compression using Huffman encoder applied to the n th-order extended binary source is studied. It is found that the bitwise Huffman encoder of the fourth-order extended binary source (16 symbols) achieves a compression efficiency close to that of the conventional Huffman encoder (256 symbols).

A WDM cross-connected star topology for multihop lightwave networks

The authors propose a star topology for multihop lightwave networks in which the conventional N*N passive star coupler is replaced by fixed wavelength division multiplexed (WDM) cross connects. The proposed topology overcomes three major limitations of the conventional star topology. First, it reduces the number of wavelengths needed in a (p,k) ShuffleNet from kp/sup k+1/ wavelengths in the conventional topology to p wavelengths in the proposed one. Second, the signal power loss due to the 1/N power splitting at the star coupler no longer exists in the WDM cross connects and, therefore, the restriction on the supported number of users by the star network is alleviated. Third, it completely eliminates the need for wavelength filtering at the input to the receivers as is the case in the conventional star topology. >

Collett-Wolf equivalence theorem and propagation of a pulse in a single-mode optical fiber.

It is shown that the propagation of a temporal pulse in a single-mode optical fiber is mathematically equivalent to Fresnel diffraction of a spatial beam. A time-domain Collett-Wolf equivalence theorem applies to pulse propagation in fibers.

Wavelength-division demultiplexing using graded-index planar structures

In this paper, the authors propose a novel technique for wavelength-division demultiplexing using a graded-index planar structure. The device consists of three layers of the same bulk material: The two outer layers are homogeneous media with refractive indices n/sub 1/ and n/sub 2/, while the inner layer is an inhomogeneous medium where its refractive index is graded according to a certain profile. The proposed technique exploits the spatial shift that results from the material dispersion found in dispersive media such as silicon dioxide (silica). It is found that the graded-index structure produces a spatial shift that is much higher than that encountered in conventional prisms, provided a certain refractive index profile is chosen. Unlike graded-index fibers, it is found that the value of /spl alpha/ of the refractive index profile (/spl alpha/-profile) for the proposed device must be < 1 to get large spatial dispersion. A mathematical expression for the spatial shift between adjacent wavelengths is found by determining the path profiles followed by the different wavelengths as they propagate through the graded-index layer. Theoretically, it is found that any spatial shift can be obtained by either reducing the value of /spl alpha/ far below 1 for a fixed size of the structure or increasing the size of the structure for a fixed value of /spl alpha/.

A WDM cross-connected star multihop optical network

The authors propose a star topology for multihop lightwave networks in which the conventional N*N passive star coupler is replaced by fixed wavelength division multiplexing (WDM) cross-connects. The proposed topology overcomes three major limitations of the conventional star topology. First, it reduces the number of wavelengths needed in a (p,k) ShuffleNet from kp/sup k+1/ wavelengths in the conventional topology to p wavelengths in the proposed one. Second, the signal power loss due to the 1/N power splitting at the star coupler no longer exists in the WDM cross-connects and, therefore, the restriction on the supported number of users by the star network is alleviated. Third, it completely eliminates the need for wavelength filtering at the input to the receivers, as is the case in the conventional star topology. The use of 2*2 WDM lapped couplers as a cheap WDM cross-connect for a (2,k) ShuffleNet is investigated. A p*p star coupler followed by p fiber Fabry-Perot filters can be used as a p*p WDM cross-connect for a (p,k) ShuffleNet at the expense of using p/sup 2/ rather than p wavelengths.<<ETX>>

A simple programmable frequency meter for low frequencies with known nominal values

A meter which can be used to measure instantaneously the frequencies of various signals, such as power line frequencies, heart rates, and motor speeds, by only choosing the proper clock and nominal frequencies is described. The technique is based on using an up/down counter operating in the down mode only, resulting in minimum timing signals. Thus the meter is designed with a minimum number of digital integrated circuits. Two frequency meters for heart rate and power line frequency measurements are discussed. A prototype of the proposed meter is built and tested for various frequencies. >

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.<<ETX>>