Impacts Of Nonlinear Stimulated Raman Scattering On The Performance Of Optical Codedivision Multiple-Access Transmission Systems

Code-division multiple access (CDMA) is a well-known scheme for multiplexing communication channels that is based on the method of directsequence spread spectrum. This concept was introduced into fiber optic communication systems in the middle of 1980’s as optical CDMA (OCDMA), where encoding and decoding operations are all performed in optical domain using optical devices and large number of users with asynchronous access capability. In addition to the good performance at high number of users and asynchronous access to the network, OCDMA systems provide the users with high security by coding the data before transmission and at the same time using this code to recover the data at the receiver. However, there are various nonlinear effects that limit the performance of OCDMA systems. In particular, nonlinear stimulated Raman scattering (SRS) causes the optical power from one mode to be transferred in the forward direction to the same, or other modes, at a different frequency. The process of SRS can severely limit the performance of multi-channel communication systems through the transfer of energy between the signals at different wavelengths. The main motivation behind this research is the need to understand signal distortion due to SRS in OCDMA transmission systems. Specially, there is no real attention paid to investigate this issue in OCDMA systems while most of researches that study nonlinear effects are based on wavelength-division multiplexing (WDM) systems. Therefore, this work is attempting to understand SRS effects on the performance of OCDMA systems as a function of system design parameters (i.e. power per chip, transmission distance, and number of users), and hence, to determine the fundamental transmission limits in OCDMA systems in the presence of SRS nonlinear effects. The system performance is evaluated by measuring the bit-error-rate (BER) and tilt ratio which indicates the power transfer between the chips at different wavelength. It is demonstrated through numerical simulations that the performance of OCDMA systems, at high input powers, large number of users and/or long transmission distances, is significantly degraded due to SRS effects. Furthermore, the transmission limits to keep the performance of the system under study within acceptable levels in the presence of SRS effects is estimated according to the BER threshold of 10-9 and 10-12

Measurements of stimulated-Raman-scattering-induced tilt in spectral-amplitude-coding optical code-division multiple-access systems

We measure the stimulated Raman scattering (SRS)-induced tilt in spectral-amplitude-coding optical code-division multiple-access (SAC–OCDMA) systems as a function of system main parameters (transmission distance, power per chip, and number of users) via computer simulations. The results show that SRS-induced tilt significantly increases as transmission distance, power per chip, or number of users grows

Signal distortion due to stimulated Raman scattering in optical CDMA transmission systems

In this paper, the signal distortion due to stimulated Raman scattering (SRS) in incoherent optical code-division multiple-access (OCDMA) transmission systems is evaluated at different transmission distances. A number of computer simulations have been conducted for this purpose. It is shown that as the total transmit power exceeds Raman threshold level, the SRS will cause severe signal deterioration over long distances even in the absence of the other signal impairment factors

Optical power limitations in spectral-amplitude- coding optical code-division multiple-access systems due to stimulated Raman scattering

In is paper, the maximum power per chip to keep the Stimulated Raman Scattering (SRS)- induced tilt below a specific level in Spectral-Amplitude-Coding Optical Code-Division Multiple-Access (SAC-OCDMA) is evaluated for different number of users. A number of computer simulations have been conducted for this purpose. It is shown that as number of users grows, the power per chip must be decreased to control the SRS-induced tilt and to keep it below acceptable levels. It is also shown that SRS-induced tilt can significantly limit the power per chip levels when the number of users is large. This is the first time such a study is reported for OCDMA systems

Numerical investigation of the performance of an SPR-based optical fiber sensor in an aqueous environment using finite-difference time domain

We investigate a surface plasmon resonance (SPR)-based optical fiber sensor using 2-D finite-difference time domain (FDTD) simulations. The optical sensor is designed by polishing a single-mode optical fiber by symmetrically removing a portion of its cladding forming two sensing regions. We analyze the effects of two physical parameters of the sensor in an aqueous medium, i.e. the thickness of the metal layer and the amount of residual cladding using numerical simulations. The results show that a good transmission dip can be obtained by optimizing these parameters. Thus, the sensor structure can be deployed as an optical biosensor in aqueous environments

Influence of design parameters on the performance of a refractive index sensor based on SPR in plastic optical fibers

We report a refractive-index sensor based on surface plasmon resonance in etched plastic optical-fibers. Impact of fiber residual thickness and sensing length on the sensor's sensitivity is experimentally investigated

Investigation of a SPR based refractive index sensor using a single mode fiber with a large D shaped microfluidic channel

In this work, a highly sensitive surface plasmon resonance (SPR) sensor based on a single mode fiber (SMF) incorporating a large microfluidic channel (MFC) for refractive index (RI) sensing is designed and optimized using a full-vectorial finite element method (FEM). The fluidic channel size can be varied according to the requirement due to the availability of the large cladding diameter of SMF, which makes it simple and easy to fabricate. The proposed novel sensor is favourable to both analytes and metallic strips. The D-shaped hollow section above the core is filled with the measurand analytes and a gold (Au) strip is deposited on the base of the MFC, as it is known as the most attractive metal for SPR. Our numerical simulations illustrate that the confinement loss of the designed sensor is highly influenced by the distance of the MFC from the core along with the width and thickness of the Au strip. The designed sensor shows an average sensitivity of 1350 nm/RIU and maximum sensitivity of 8250 nm/RIU in the sensing range of 1.33-1.35 and 1.41-1.43, respectively. However, for a small variation of na at a step of 0.005, within ranges like 1.415, 1.420, and 1.425, we have achieved a maximum sensitivity of 7000 nm/RIU, 9000 nm/RIU and 11000 nm/RIU, respectively. This novel SPR sensor with MFC can open up a new opportunity in the application of chemical and biological sensing

The religious establishment in Ithna'ashari Shi'ism: A study in scholarly and political development.

This thesis deals mainly with the historical development of the religious institution of Ithna ashari Shi'ism in both its scholarly and political aspects. It is divided into six chapters. The word "school" has been used to describe the place in which such an institution had flourished due to the activities of its fuqaha ' in response to their turbulent history, whether it was in Iraq, in Bilad al-Sham (Greater Syria, i.e. Syria and Lebanon) or in Iran. Chapter one deals with the Baghdad School. It includes a study of the scholarly development right from the begining of the fuqaha' institution during Shaykh al-Mufid's times (d. 413/1022) and ending with Shaykh al-Tusi (d. 460/1068). Chapter two follows the development of this scholarly renaissance at the hands of the Hilla fuqaha starting with Ibn Idris al-Hilli's time (d. 598/1201) and ending with Fakhr al-Muhaqiqqin ibn al-'Allama al-Hilli (d. 771/1369), and investigates the relationship between the religious institution and the Mongol invaders of Iraq and the ideological influence of the Ithna'ashari fuqaha' on the leaders of the invaders. Chapter three, on the Jabal 'Amil school, deals in part with the unsettled period of the Mamluk state, its struggle against the Mongols and the internal situation of the Shi'a vis-a-vis the Mamluks. It also deals in part with the influence of the Jabal 'Amil fuqaha' on the Safawid state after these fuqaha' had migrated there. Particular attention is paid to the role of Shaykh al-Karaki (d. 940/1533) and his attempt to build a religious institution inside Safawid Iran, and the opposition that he met. The chapter ends with a study of the Akhbari Movement in its first stage, during the time of Muhammad Amin al-Astarabadi (d. 1033/1624). Chapter four focuses on the Najaf School, which had started about two hundred years before as an intellectual school. The development and activities of this school from the beginning of the thirteenth/nineteenth century, are discussed, as is its position regarding the emergence of the Wahhabi Movement, the Akhbari Movement (in its second phase) and the Shaykhi Movement. The chapter also deals with the political activity of the fuqaha' in their struggle against the Qajari state, which had been manifested in the fatwa prohibiting tobacco and in the Constitutional Movement. Chapter five deals with the struggle of the Najaf fuqaha' from the start of the Republican period (1958) until the beginning of the 1990s. This is preceded by an introductory remark concerning the position taken by the fuqaha' towards the British forces who entered Iraq after the First World War and the events of the Iraqi Revolution of 1920. Chapter six has been dedicated to a study of the Qumm school. It looks at the historical development of that city, with particular attention to the role of Shaykh 'Abd al-Karim al-Ha'iri al-Yazdi (d. 1355/1936) in supervising an elite of mujtahids who have participated in the renewal of this city. (Abstract shortened by ProQuest.)

Deterministic Raman crosstalk effects in amplified wavelength division multiplexing transmission

We study the deterministic effects of Raman-induced crosstalk in amplified wavelength division multiplexing (WDM) optical fiber transmission lines. We show that the dynamics of pulse amplitudes in an N-channel transmission system is described by an N-dimensional predator-prey model. We find the equilibrium states with non-zero amplitudes and prove their stability by obtaining the Lyapunov function. The stability is independent of the exact details of the approximation for the Raman gain curve. Furthermore, we investigate the impact of cross phase modulation and Raman self and cross frequency shifts on the dynamics and establish the stability of the equilibrium state with respect to these perturbations. Our results provide a quantitative explanation for the robustness of differential-phase-shift-keyed WDM transmission against Raman crosstalk effects.Comment: 34 pages and 12 figures. Revised paper. Submitted to Optics Communication