Optical Code Division Multiple Access

A novel approach for an optical direct-sequence spread spectrum is presented. It is based on the complementary processes of broad-band parametric down-conversion and up-conversion. With parametric down-conversion, a narrow-band continuous-wave (CW) optical field is transformed into two CW broad-band white-noise fields that are complex conjugates of each other. These noise fields are exploited as the key and conjugate key in optical direct-sequence spread spectrum. The inverse process of parametric up-conversion is then used for multiplying the key by the conjugate key at the receiver in order to extract the transmitted data. A complete scheme for optical code-division multiple access (OCDMA) based on this approach is presented. The salient feature of the approach presented in this paper is that an ideal white-noise key is automatically generated, leading to high-capacity versatile code-division multiple-access configurations.

In this paper, we investigate the performance of Spectral Amplitude Coding Optical Code Division Multiple Access technique based on Free Space Optical channel. SAC OCDMA is one of the most popular multiplexing techniques since many years and FSO is gaining popularity and is very useful especially in point to point communication. The system presented in this paper utilizes Walsh Hadamard code as signature code. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). This system focuses on the performance analysis of FSO based systems for subtropical regions. This paper demonstrates the error rate performance in the form of eye diagrams/BER under varying channel gain and link distances. Five cases have been taken which shows that SAC OCDMA FSO system is reliable even for distances sufficient to overcome the last mile problem.  

A media access control protocol for optical codedivision multiple-access packet networks with variable length data traffic is proposed. This protocol exhibits a sliding window with variable size. A model for interference-level fluctuation and an accurate analysis for channel usage are presented. Both multipleaccess interference (MAI) and photodetector's shot noise are considered. Both chip-level and correlation receivers are adopted. The system performance is evaluated using a traditional average system throughput and average delay. Finally, in order to enhance the overall performance, error control codes (ECCs) are applied. The results indicate that the performance can be enhanced to reach its peak using the ECC with an optimum number of correctable errors. Furthermore, chip-level receivers are shown to give much higher performance than that of correlation receivers. Also, it has been shown that MAI is the main source of signal degradation.

We present the transmission of four users with 5 WDM × 4 TDM × 4 CODE channel at variable data rate for 3D OCDMA system based on Model A using GF (5) with varying receiver attenuation at the front end on OPTSIM simulation software using optical orthogonal codes and cubic congruent operator from algebraic coding theory. The performance of these coding sequences is judged in terms of BER, Signal Strength and Eye Diagrams.

Developing Java Clients 1 Java Client Installation and JRE Requirements 2 Client Installation 2 JRE Requirements 2 Java Client Security 3 Using the IOM Server 3 Overview of Using the IOM Server 3 Using a Metadata Server with the Connection Service 4 Connecting a Java Client to an IOM Server 4 Developing Java Clients The application programming interfaces that are provided with SAS Integration Technologies enable you to develop Java-based distributed applications that are integrated with the SAS platform. SAS Integration Technologies includes the following features for developing Java clients: 3 The Connection Factory interface, which enables Java programs to communicate with Integrated Object Model (IOM) servers through an IOM Bridge connection. The connection factory allows you to obtain server attributes from a SAS Metadata Server, from the Information Service (which is part of SAS Foundation Services), or directly from an application program. When it is used with the SAS Open Metadata Architecture, the Java Connection Factory interface provides the following: 3 connections to new types of IOM servers (SAS Metadata Servers, SAS Stored Process Servers, and SAS OLAP Servers) in addition to SAS Workspace Servers 3 the ability to use load balancing for workspace and stored process servers and spawners 3 SAS Foundation Services, which extends Java application development beyond access to IOM servers. The following core infrastructure services are provided: 3 client connections to application servers (including the Java Connection Factory interface previously mentioned) 3 dynamic service discovery 3 user authentication and profile management 3 session context management 3 metadata and content repository access 2 Java Client Installation and JRE Requirements 4 Chapter 1 3 activity logging SAS Foundation Services also includes extension services for event management, information publishing, and stored process execution. 3 The SAS Foundation Services Facade, which includes convenience services that Web application developers can use to easily access the most commonly used SAS Foundation Services methods and objects. Use of this software requires some knowledge of distributed programming. However, the software rigorously conforms to Java distributed programming standards such as CORBA and JDBC. Whether you are developing an applet, a stand-alone application, a servlet, or an enterprise JavaBean, you can focus your attention on exploiting the features of the SAS platform rather than determining how to communicate with it. SAS Integration Technologies supports any Java integrated development environment (IDE), including Eclipse, JBuilder, and SAS AppDev Studio. Java Client Installation and JRE Requirements Client Installation To install the Java client software, you must install SAS Foundation Services.

In this paper, we investigate the performance of Spectral Amplitude Coding Optical Code Division Multiple Access technique based on Free Space Optical channel. SAC OCDMA is one of the most popular multiplexing techniques since many years and FSO is gaining popularity and is very useful especially in point to point communication. The system presented in this paper utilizes Walsh Hadamard code as signature code. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). This system focuses on the performance analysis of FSO based systems for subtropical regions. This paper demonstrates the error rate performance in the form of eye diagrams/BER under varying channel gain and link distances. Five cases have been taken which shows that SAC OCDMA FSO system is reliable even for distances sufficient to overcome the last mile problem.  

This paper describes the InP platforms for photonic integration and the development on these platforms of an optical code division multiple access (O-CDMA) system for local area networks. We demonstrate three building blocks of this system: an optical pulse source, an encoder/decoder pair, and a threshold detector. The optical pulse source consists of an integrated colliding pulse-mode laser with nearly transform-limited 10 Gb/s pulses and optical injection locking to an external clock for synchronization. The encoder/decoder pair is based on arrayed waveguide gratings. Bit-error-rate measurements involving six users at 10 Gb/s showed error-free transmission, while O-CDMA codes were calibrated using frequency resolved optical gating. For threshold detection after the decoder, we compared two Mach-Zehnder interferometer (MZI)-based optical thresholding schemes and present results on a new type of electroabsorber-based MZI. Index Terms-Arrayed-waveguide gratings (AWG), crosscorrelation frequency-resolved optical gating (XFROG), InP platform, Mach-Zehnder interferometer (MZI), optical code division multiple access (O-CDMA), optical thresholding, photonic integrated circuit. I. INTRODUCTION P HOTONIC integration has been maturing to a level where system scale functionality can be integrated on a single substrate. Most suitable for advanced photonic integration is the InGaAsP/InP material system, because of its tunable bandgap across the 1.3-and 1.5-µm wavelength communication windows of optical fiber and, therefore, the ability to integrate active and passive waveguides. An InP platform supporting active-passive integration provides three key functionalities on a single substrate: passive optical waveguiding (with bend radii down to 50-500 µm for compact design), phase shifting, and amplification/detection of light. Platforms usually add one or more functionalities like electroabsorption modulators, polarization converters, spot-size converters, on-chip mirrors, or/and electrical high-frequency (HF) phase and HF amplitude modulators. Several InP platforms, using different techniques, have been reported: quantum well (QW) intermixing [1] enables activepassive integration without regrowth, but often at the expense Manuscript

We demonstrate optical code-division multiple access (OCDMA) code conversion in the wavelength domain using periodically poled LiNbO 3 for enhanced transmission security. The number of possible OCDMA codes in the channel is greatly increased and randomized dynamic code conversion is feasible, thus making it more difficult for an eavesdropper to intercept and decode the code. A 2.5-dB power penalty is reported at a bit-error rate of 10 9 after two back-to-back wavelength conversions. Index Terms-Code conversion, optical code-division multiple access (OCDMA), periodically poled lithium niobate (PPLN).

We present the modification of decoder for 2-D Wavelength/Time (W/T) Optical Code Division Multiple Access (0-CDMA) system by optical hardlimiters. The performance improvement of the system using proposed decoder modification is shown by numerical simulation of the average Signal to interference difference and Bit error probability as a function of active user number and weight of codeword for the different topology of the decoder. The influence of non-ideal properties of the used optical hardlimiters upon the bit error probability in system is studied.

Performance analysis of an incoherent time spread on-off keying optical Code Division Multiple Access (O-CDMA) system with non-ideal optical hard-limiters is reported in this paper. For the first time we made an approximation of the properties of an implemented passive optical hard-limiter. It was named as a non-ideal optical hard-limiter and its nonideal parameter was defined. Shortened optical orthogonal codes generated by an extended set technique achieved multiple accesses in the investigated O-CDMA system. Performance improvement of O-CDMA system for the cases of O-CDMA receiver without any, with one and with two optical hard-limiters is shown by simulation of the signal-tointerference ratio and the bit error probability. The influence of non-ideal properties of the optical hard-limiter upon the performance of O-CDMA system is studied.

This investigation proposes and experimentally demonstrates an optical code-division multiple-access (OCDMA) light source using a directly modulated Fabry-Pérot laser diode in an external injection scheme. This light source has an optical sidemode suppression ratio of over 27.5 dB and a pulsewidth of around 55 ps. Such a narrow pulsewidth has great potential for a two-dimensional OCDMA system. Additionally, the bit-error-rate performance with a 2 31 1 pseudorandom bit sequence indicates the feasibility of this light source in a 2.488-Gb/s system application.

A new detection technique named AND subtraction which is based on subtraction technique is proposed for a hybrid system of subcarrier multiplexed (SCM) spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) of a point-to-point link. Spectral-amplitudecoding OCDMA is used because of its ability to cancel the multiple access interference (MAI) when code sequences with fixed in-phase cross correlation are used. On the other hand, the SCM scheme is able to enhance the channel data rate of OCDMA systems. This hybrid system is proposed for the purpose of combining the advantages of both techniques. As a result, the hybrid system is robust against interference and is much more spectrally efficient. A new code structure for spectral-amplitudecoding OCDMA system based on double weight (DW) code family is employed. The experimental simulation results of the hybrid system using the new proposed AND subtraction detection technique are compared to the hybrid system using complementary subtraction detection technique. The results show that the hybrid system using the proposed new AND subtraction detection technique improve the system performance significantly.

This paper presents the comparative performance of different detection and coding schemes for spectral-amplitude-coded optical code division multiple access (SAC-OCDMA) system. SAC-OCDMA systems are receiving more attention because of their ability to completely eliminate multiple access interference (MAI). Fiber Bragg grating (FBGs) are used as encoder/decoder. Experimental simulation was carried out using OptiSystem version 5.0 and performance of OCDMA network is characterized through bit error rate (BER) received power and no of filters required for a particular code.

The design of a new family of two-dimensional single pulse per column codes for optical code division multiple access (OCDMA) networks is reported. The 1-D modified pseudo-noise codes have been known to be orthogonal and their generation and system design based on these codes is rather simple. But their performance is limited due to the bandwidth constraints if the code length increases. Hence, using these 1-D modified pseudo-noise codes, modified 2-D pseudo-noise matrix codes (MPMCs) are generated. The system performance is evaluated for two, three and four simultaneous users using the link with all the sources responsible for degradation included: attenuation, chromatic dispersion, non-linear refractive effects, non-linear scattering and four-wave mixing. The effect of the non-linear and lossy dispersive medium over the system performance is shown by plotting the BER with respect to the link length for the systems designed using encoders/decoders base on 1-D modified pseudo-noise codes and our MPMCs. The performance is compared for the two types of codes by finding the crosstalk due to interfering users simultaneously operating in the network.

First of all I want to thank my parents, they're guidance and unconditional love have been the fuel to my achievements. My mother Rosalia, who made me the man that I am today, whose wisdom and teaching far transcends any college education. The lifelong dedication and sacrifice to her sons is an astonishing, and I feel blessed beyond comprehension to have a mother like her. My father Raphael, the smartest man I have ever known. Because of him, I have a thirst for knowledge that drove me to begin this thesis. My brother Rene, whose incredible discipline, intelligence, and support helped me make the right decisions in life, without his guidance I would not be writing these acknowledgements. My appreciation to all at the UTEP Electrical and Computer Engineering Department is immeasurable. My advisor Dr. Virgilio Gonzalez, whose only concern was my education and growth; whose only question was "what do you need?" and was an inspiration for continuing education and the desire to educate others. All the professors that answered questions about course work, engineering, or otherwise, thank you for your collective knowledge and wisdom; whether it be on fundamentals of electromagnetism and Fourier transforms, or the current state of property taxes in the state of California. The staff: Suki Quezada and Ralph Loya undoubtedly the mother and father figure for all the students in the department. Thanks to Gabby Gandara for all his help and guidance in becoming a successful student and above all a professional. To all my friends and relatives, who showed me how to have fun and not take myself too seriously, or anyone else for that matter. All my best memories include them. My fiancé Marcy vi whose love and support make me feel as there's no problem I can't solve. I feel honored that you will have me be your husband. Thank you all!! vii

Due to the large bandwidth offered by the optical fiber, its implementation in local area network (LAN) where the traffic is typically bursty could be considered as the strongest candidates for the future high speed optical networks if coding technique is used. This paper presents a new code family named, diagonal permutation shifting (DPS) for spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems with fixed in-phase cross correlation (CC) and short code length. DPS code derived from well-known prime codes and some matrix operations. The results reveal that the DPS code acts effectively in removing multiple access interface (MAI) and mitigate phase induced intensity noise (PUN) impact with an adequate signal to interference plus-noise ratio (SINR) and low bit error rate (BER). It has been shown that the DPS code family can suppress intensity noise effectively and improve the system performance significantly.

We demonstrate that direct sequence optical code-division multiple-access (DS-OCDMA) encoders and decoders using sampled fiber Bragg gratings (S-FBGs) behave as multipath interferometers. In that case, chip pulses of the prime sequence codes generated by spreading in time-coherent data pulses can result from multiple reflections in the interferometers that can superimpose within a chip time duration. We show that the autocorrelation function has to be considered as the sum of complex amplitudes of the combined chip as the laser source coherence time is much greater than the integration time of the photodetector. To reduce the sensitivity of the DS-OCDMA system to the coherence time of the laser source, we analyze the use of sparse and nonperiodic quadratic congruence and extended quadratic congruence codes.

Optical Code Division Multiple Access (OCDMA) is considered as the strongest candidates for the future high speed optical networks due to the large bandwidth offered by the system, Based on the vast amount of bandwidth, OCDMA systems have received much attention in fiber optic Local Area Networks where the traffic is typically bursty. However, Multiple Access Interference (MAI), which is originated from other simultaneous users, severely limits the capacity of the system. Optical Parallel Interference Cancellation (OPIC) has been used to reduce the effect of MAI. However, the usage of OPIC in OCDMA systems will increase the demand for hardware complexity which results in higher processing time and cost. The hardware complexity increases in the receiver side of OPIC when the number of transmitter (users) increases. To overcome these difficulties, an efficient method is presented in this paper called, One Stage Optical Parallel Interference Cancellation (OS-OPIC) which is based mainly on the OPIC. Optical Orthogonal Code (OOC) is adopted as a signature sequence for the performance analysis and a new expression for the error probability is derived. It is shown that, the proposed method is effective to reduce the hardware complexity, processing time and cost while maintaining the same bit error probability at the cost of increasing threshold value.

One dimensional (1D) spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems are generally known by a strict limitation in the number of users that can simultaneously connect. A main solution to overcome this drawback consists of constructing a two-dimensional (2D) structure using a new hybrid spectral/spatial code through combining a one dimensional new zero cross correlation code (NZCC) to a one dimensional multi-diagonal code (1D MD) to easily provide null cross-correlation properties and totally remove the multiple access interferences. Accordingly, this research paper describes an easy and fast technique to construct a hybrid two-dimensional NZCC-MD code based on a non diagonal matrix for SAC-OCDMA systems with direct spectral/spatial dimension (SDD) detection technique and water-filling (WF) optimization. The novel code presents many advantages such as less complex structure, acceptable code length as well as the possibility to construct it for any weight value. The proposed code demonstrates a very good performance for systems with high debit and high simultaneous user number keeps a less complex structure.

One dimensional (1D) spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems are generally known by a strict limitation in the number of users that can simultaneously connect. A main solution to overcome this drawback consists of constructing a two-dimensional (2D) structure using a new hybrid spectral/spatial code through combining a one dimensional new zero cross correlation code (NZCC) to a one dimensional multi-diagonal code (1D MD) to easily provide null cross-correlation properties and totally remove the multiple access interferences. Accordingly, this research paper describes an easy and fast technique to construct a hybrid two-dimensional NZCC-MD code based on a non diagonal matrix for SAC-OCDMA systems with direct spectral/spatial dimension (SDD) detection technique and water-filling (WF) optimization. The novel code presents many advantages such as less complex structure, acceptable code length as well as the possibility to construct it for any weight value. The proposed code demonstrates a very good performance for systems with high debit and high simultaneous user number keeps a less complex structure.

Direct-sequence optical code-division multiple-access (DS-OCDMA) encoder/decoder based on sampled fiber Bragg gratings (S-FBGs) is characterized using phase-sensitive optical low-coherence reflectometry (OLCR). The OLCR technique allows localized measurements of FBG wavelength and physical length inside one S-FBG. This paper shows how the discrepancies between specifications and measurements of the different FBGs have some impact on spectral and temporal pulse responses of the OCDMA encoder/decoder. The FBG physical lengths lower than the specified ones are shown to affect the mean optical power reflected by the OCDMA encoder/decoder. The FBG wavelengths that are detuned from each other induce some modulations of S-FBG reflectivity resulting in encoder/decoder sensitivity to laser wavelength drift of the OCDMA system. Finally, highlighted by this OLCR study, some solutions to overcome limitations in performance with the S-FBG technology are suggested.

Direct-sequence optical code-division multiple-access (DS-OCDMA) encoder/decoder based on sampled fiber Bragg gratings (S-FBGs) is characterized using phase-sensitive optical low-coherence reflectometry (OLCR). The OLCR technique allows localized measurements of FBG wavelength and physical length inside one S-FBG. This paper shows how the discrepancies between specifications and measurements of the different FBGs have some impact on spectral and temporal pulse responses of the OCDMA encoder/decoder. The FBG physical lengths lower than the specified ones are shown to affect the mean optical power reflected by the OCDMA encoder/decoder. The FBG wavelengths that are detuned from each other induce some modulations of S-FBG reflectivity resulting in encoder/decoder sensitivity to laser wavelength drift of the OCDMA system. Finally, highlighted by this OLCR study, some solutions to overcome limitations in performance with the S-FBG technology are suggested.

Optical short pulse processors enable several systems including optical code division multiple access networks, optical secure communications, and optical pulse shapers. For instance, compact and low cost integrated solutions for optical short pulse en/de-coders with large code length and capable of processing large optical bandwidth may enable realization of Tbps communication networks. Here, we report an integrated 128-bit short pulse processor capable of signal processing on large amount of optical bandwidth, demonstrated ≈ 25 nm, using sub-ps optical short pulse signal. The chip fabricated in a commercial foundry SOI CMOS process and includes more than 500 distinct optical components and over 150,000 distinct electrical components.

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, ON-OFF keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is shown that under certain conditions, the system performance can be dramatically degraded due to the jamming signals; also, systems using 2CK modulation show a better resistance and performance when compared to systems using OOK modulation.

In this work, we investigate the performance of a distributed power control algorithm (DPCA) for signalto-interference (SIR) optimization in wavelength-hopping time spreading code routed networks. These networks are based on 2D codes (time/wavelength) to establish end-to-end optical code paths (OCPs). The SIR model considers multiple access interference (MAI) between OCPs and amplified spontaneous emission (ASE) at cascaded amplified spans. The utilization of power control has a significant impact on both performance and capacity of practical optical networks. The DPCA can be effectively implemented in each node because uses only local parameters or measurements.

This paper investigates the Parallel Interference Cancellation technique in Direct Sequence Optical Code Division Multiple Access (DS-OCDMA) system. In the proposed system, the estimated interference is removed from the received signal. We have developped a new approach to obtain the analytical expression of error probability in chip synchronous case, for Optical Orthogonal Codes (ooc). We have shown that under specific conditions between codes parameters and users' number, the interference can be completely neutralized. Simulation results have validated the theoretical analysis. It is shown that the proposed receiver is effective in reducing significantly the effects of Multiple Access Interference (MAt) compared to other interference cancellation systems.

This paper demonstrates the construction of unipolar Modified Walsh Code (MWC) in Optical CDMA system. Present work attempts to analyze the performance of MWC and compare with several other existing OCDMA codes like Modified Frequency Hopping (MFH) code and Hadamard (HD) code and Modified Quadratic Congruence (MQC) Code. It has been observed that the weight of the designed MWC is fixed and in-phase cross correlation value is zero which in turn will increase signal to noise ratio(SNR) and reduce the bit error rate (BER) of the system.

The performance of a two-dimensional optical code division multiple access (2D-OCDMA) system using an underwater wireless optical (UWO) medium is assessed in this work. The optical source is an LED with a working wavelength of 532 nm, and the optical detector is a p-in photodiode. When calculating the bit error rate (BER), the phase-induced intensity noise (PIIN), thermal noises, and shot sounds are taken into account. The user code address is set using 2D perfect difference (2D-PD) codes. Link distance, inclination angle, beam divergence angle, transmitter power, and the number of concurrent users are all taken into account when determining the BER performance. For various water media, such as pure sea water (PSW), clear ocean water (CLOW), and coastal ocean water (CSOW), the performance of the suggested system is examined.

An optical dynamic spectral encoding code division multiple access ͑CDMA͒ communication system is proposed. In this system, an electrically controlled tunable optical filter ͑TOF͒ is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code, named functional code, is also proposed based on a shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for a sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The system is modeled and analyzed taking into account the multiple access interference, phase-induced intensity noise ͑PIIN͒, and thermal noise. The performance of this system is shown to be better compared with a fast frequency hopping ͑FFH͒ system and a spectral amplitude coding ͑SAC͒ system that uses either a Hadamard code, a modified quadratic congruence ͑MQC͒ code, or a modified frequency hopping ͑MFH͒ code.

In this work, we present the results for thermal gradient measurements using constant period UV written longperiod gratings (LPG) in photosensitive and SMF-28 fibers. We have studied theoretically and experimentally the effect of thermal gradients on the spectrum of LPGs. It has been shown theoretically and confirmed experimentally that thermal gradients lead to changes of the depth of the grating spectrum while changes of the mean temperature cause shifts of the resonance wavelength. Thus thermal gradients and average temperature can be independently measured using a single LPG. Sensitivities to temperature difference and to average temperature for LPGs in air have been found to be higher than in water.

The perfect difference codes minimize the Phase Induced Intensity Noise (PIIN) and cancel the multiple access interference. Earlier researchers analyze the performance of OCDMA systems considering three noises namely PIIN, shot and thermal noise for 3D Perfect Difference Codes (PDC) for OCDMA system. In this research paper we have considered two more noises i.e. 1/f and generation recombination noise for 3D PDC based OCDMA system. Mathematical analysis has been done and the performance of the system has been evaluated for higher data rates i.e. 1Gbps to 10Gbps for minimum BER −9 .

This paper presents the comparative performance of different detection and coding schemes for spectral-amplitude-coded optical code division multiple access (SAC-OCDMA) system. SAC-OCDMA systems are receiving more attention because of their ability to completely eliminate multiple access interference (MAI). Fiber Bragg grating (FBGs) are used as encoder/decoder. Experimental simulation was carried out using OptiSystem version 5.0 and performance of OCDMA network is characterized through bit error rate (BER) received power and no of filters required for a particular code.

A tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of 200 GHz arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP/InGaAsP material for operation at wavelengths around 1.55 µm, and has an optical bandwidth of 36 nm. Multimode inputs to the waveguide gratings are used to flatten their optical passbands, leading to a fourfold decrease in pulse ringing. The device is able to (pre-) compensate dispersion values of 0.2 ps/nm for 300 fs pulses, which is a suitable value for applications in e.g. biomedical multi-photon imaging.

Phase-induced intensity noise in optical networks that employ directly modulated laser sources is observed to be bit-sequence dependent. This dependence is explained by optical frequency variations that are due to the heating history of the laser chip and is accurately modeled. This effect may permit suppression of phase-induced intensity noise in many types of fiber system with multipaths.

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

We present a novel characterization method for semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) switches which combines a pump-probe measurement with an interferometer bias scan. This enables optimal bias identification and better understanding of switching dynamics.

The ultrafast limit of the response of arrayed waveguide gratings is studied both theoretically and experimentally. We present new experimental results that show that interference occurs inside of an arrayed waveguide pulse shaper even when pulses that travel through different paths do not overlap. A comprehensive discussion of this extreme case is presented.

In this paper, the channel capacity for different models of Poisson optical communication channels has been derived. The closed form expression for the single input single output (SISO) Poisson channel-derived by Kabanov in 1978, and Davis in 1980-will be investigated. In addition, we derive closed form expressions for the capacity of the parallel Poisson channel and the capacity of the multiple access Poisson Channel (MAC) under the assumption of constant shot noise. The optimum power allocation is also derived for the different models; results have been analyzed in the context of information theory and optical communications. We then provide a set of simulation results establishing a comparison between Gaussian channels and Poisson Channels.

We propose a solution for pointing and tracking an optical terminal using one or more beacons and a slowly varying background image. The primary application is a deep space optical communication terminal, where multiple source tracking provides robustness against beacon outage. Our solution uses optical orthogonal codes modulated on each beacon to separate the signal from each source for centroiding. This technique allows calculation of the transmit pointing vector from each beacon location as well as from the background image. The latter can be used to track during beacon outages. We present a simple algorithm for performing this separation, and apply it to experimental data from a photon-counting detector illuminated by two beacons and one constant source. Our results show that the photon flux from each source can be accurately estimated even in the low signal, high background regime.

An all-semiconductor-optical-amplifier loop device with a multimode interference (MMI) coupler was fabricated with the deep UV cryo-etching technique. Efficient power-dependent switching was observed. With continuous-wave signals, nonlinear switching occurred due to the combined effect of the nonlinear coupling in the MMI coupler and the lateral wave field redistribution caused by the loop structure. Simulation results showed good agreement in trend with the experimental data.

In order to solve the problem of one-dimensional code length, two-dimensional code spatial length, phase induced intensity noise PIIN effect, improved system capacity, and increased the number of simultaneous users, a new three-dimensional spectral/time/spatial variable weight zero cross correlation code for non-coherent spectral amplitude coding-optical code division multiple access (3D-VWZCC-SAC-OCDMA) is proposed in this paper. Its construction is based on a one-dimensional (1D) spectral sequence and two-dimensional (2D) temporal/spatial sequences, which are characterized by the property of zero cross correlation ZCC. The simulation results demonstrate that our code proves high immunity against PIIN noise and shot noise, it increases multiplexing ability when the passage is from (1D) and (2D) to (3D) up to 5.112 and 2.248 times, and it saves −7.04 dBm and −5.9 dBm of the receiver power due to simple detection at the receiver; furthermore, the 3D-VWZCC system capacity has outperfo...

This paper discusses the problem of single channel speech enhancement in stationary environments, and proposes Wiener filtering with the recursive noise estimation algorithm. The Wiener filter is a linear estimator and minimizes the mean-squared error between the original and enhanced speech. The algorithm is implemented in the frequency domain and depends on the filter transfer function from sample to sample based on the speech signal statistics; the local mean and the local variance. For the noise estimation, the recursive noise estimation approach is used. In this approach, the noise estimation is done by past and present spectral power values, using a smoothing parameter. The value of smoothing parameter is selected in between [0 1]. For the performance evaluation of the proposed speech enhancement algorithm objective evaluations with informal listening tests are conducted for the speech sentences, pronounced by male and female speakers from the NOIZEUS corpus, degraded by White as well as Pink noise types at different SNR levels. For objective measures, signal to noise ratio, segmental signal to noise ratio, and the perceptual evaluation of speech quality are used. The measures prove that the speech enhanced by proposed algorithm is more pleasant to the human ear for both noise conditions in comparison to the conventional speech enhancement method.

In this paper, we propose a new teletraffic model for the calculation of blocking probabilities in an Optical Code Division Multiple Access (OCDMA) Passive Optical Network (PON) supporting multiple service-classes of Poisson traffic. OCDMA is a promising candidate of PON configuration for the provision of moderate security communications with large dedicated bandwidth to each end user. The PON accommodates multiple service-classes that are differentiated by either different data-rates or different Quality of Service levels. Parameters related to the additive noise, multiple access interference and user activity are incorporated into our analysis. Based on a twodimensional Markov chain, we propose a recursive formula for the calculation of the number of in-service codewords, when the OCDMA PON guarantees Quality of Service (QoS), or not. To evaluate the proposed model, the analytical results are compared with simulation results to reveal that the model's accuracy is quite satisfactory.

Abstract: In this paper, we propose a new teletraffic model for the calculation of blocking probabilities in an Optical Code Division Multiple Access (OCDMA) Passive Optical Network (PON) supporting multiple service-classes of Poisson traffic. OCDMA is a promising candidate of PON configuration for the provision of moderate security communications with large dedicated bandwidth to each end user. The PON accommodates multiple service-classes that are differentiated by either different data-rates or different Quality of Service ...

Reduction of bit error rates in optical transmission systems is an important task that is difficult to achieve. As speeds increase, the difficulty in reducing bit error rates also increases. Channels have differing characteristics, which may change over time, and any error correction employed must be capable of operating at extremely high speeds. In this paper, a linear support vector machine is used to classify large-scale data sets of simulated optical transmission data in order to demonstrate their effectiveness at reducing bit error rates and their adaptability to the specifics of each channel. For the classification, LIBLINEAR is used, which is related to the popular LIBSVM classifier. It is found that is possible to reduce the error rate on a very noisy channel to about 3 bits in a thousand. This is done by a linear separator that can be built in hardware and can operate at the high speed required of an operationally useful decoder.

Spectrum scarcity and the inefficient use of the electromagnetic spectrum motivated the development of Cognitive Radio (CR), which aims to extend the spectral efficiency, with opportunistic access to the available frequency bands. Energy Detection (ED) is the most adopted spectrum sensing technique for cognitive radio applications due to its simplicity. However, fading effects are usually simplified or discarded when evaluating the energy detector performance in spectrum sensing. This paper presents the performance evaluation of cognitive spectrum sensing, based on energy detector, for fading channels. The objective is to analyze how the use of various fading models affect the spectral detection in cognitive networks. Rayleigh, Rice, Nakagami-m and Lognormal fading channels are considered, and the results favor the use of ED when the channel is subject to Lognormal fading.

In this paper, we investigate the performance of Spectral Amplitude Coding Optical Code Division Multiple Access technique based on Free Space Optical channel. SAC OCDMA is one of the most popular multiplexing techniques since many years and FSO is gaining popularity and is very useful especially in point to point communication. The system presented in this paper utilizes Walsh Hadamard code as signature code. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). This system focuses on the performance analysis of FSO based systems for subtropical regions. This paper demonstrates the error rate performance in the form of eye diagrams/BER under varying channel gain and link distances. Five cases have been taken which shows that SAC OCDMA FSO system is reliable even for distances sufficient to overcome the last mile problem.