Improvement and Mitigation of Kerr Effects on Multichannel ‎Communication Systems Using Efficient Optical Method

في هذا البحث، تم دراسة توليد طريقة التخفيف البصري لتعويض التشوهات في نقل الألياف البصرية لمسافات طويلة الناتجة عن التشتت اللوني وعدم خطية كير في الأنظمة متعددة القنوات. يتم استخدام طريقة هجينة جديدة تُعرف باسم اقتران الطور البصري (OPC) باستخدام الألياف غير الخطية مع مضخم رامان كجزء من عملية تحسين أداء أنظمة الاتصالات باستخدام إشارة أحادية النمط القياسي لوصلة الألياف أحادية الوضع بطول 800 كيلومتر. في هذا العمل، نقدم طريقتين يتم فيهما استخدام تضخيم رامان الخلفي بالتزامن مع اقتران الطور البصري لتحسين أداء ارتباط بصري يبلغ 1.728 تيرابايت / ثانية عبر ستة عشر قناة مع تباعد قناة قدره 50 جيجا هرتز. من خلال استخدام اقتران الطور البصري المتعدد، فأن أداء أنظمة نقل مضاعف تقسيم الطول الموجي الكثيف (DWDM) مع قنوات 16 × 108 جيجا بت في الثانية 8-QAM يمكن تحسينه بشكل كبير مقارنة بالأنظمة التي تحتوي إما على اقتران طور بصري واحد متوسط المدى أو بدون اقتران طور بصري. استراتيجية استخدام OPCs متعدد فعال عبر مجموعة متنوعة من وصلات الإرسال. تم تحسين العتبة غير الخطية (إشارة الطاقة المثالية) في نظام الإرسال المقترح بمقدار 4 ديسيبل عند استخدام OPCs متعدد، مقارنة بالحالة التي لا تحتوي على OPC، وبنسبة 2 ديسيبل عند استخدام OPC متوسط المدى. تظهر نتائج المحاكاة أنه بالمقارنة مع السيناريو دون استخدام نهج التعويض، تم تحسين عامل جودة الإشارة (Q)، وأداء معدل الخطأ في البت (BER)، والطول الإجمالي لوصلة النقل من خلال استخدام هذه الطريقة البصرية للتعويض غير الخطي.This paper studies the generation of an optical mitigation method for compensation of distortions in long distance fiber optic transmission caused by chromatic dispersion and the nonlinear Kerr effect in multi-channel systems. A hybrid new method known as Optical Phase Conjugation (OPC) based highly nonlinear fiber with Raman amplifier is used as part of the process of improving the performance of communication systems with an 800 km standard single mode fiber link Single Polarization Quadrature Amplitude Modulation (SP-QAM) signaling. This work presents two scenarios in which backward Raman amplification is employed in conjunction with OPC to improve the performance of an optical link of 1.728 Tb/s over sixteen channels with a channel spacing of 50 GHz. In this study, through the use of multiple OPC, the performance of dense wavelength division multiplexing (DWDM) transmission systems with 16 ×108 Gbps 8-QAM channels can be significantly improved over that of systems with either a mid-span optical phase conjugation or no optical phase conjugation. The strategy of using multiple OPCs is effective over a variety of transmission links. The nonlinear threshold in the proposed transmission system was enhanced by 4 dB when employing multiple OPCs, compared to the case with no OPC, and by 2 dB when using a mid-span OPC. The simulation results show that compared to the scenario without employing the compensation approach, the Q-factor, Bit Error Rate (BER) performance, and total length of the transmission link are all improved by utilizing this optical method of nonlinearity compensation

Digital electronic predistortion for optical communications

The distortion of optical signals has long been an issue limiting the performance of communication systems. With the increase of transmission speeds the effects of distortion are becoming more prominent. Because of this, the use of methods known from digital signal processing (DSP) are being introduced to compensate for them. Applying DSP to improve optical signals has been limited by a discrepancy in digital signal processing speeds and optical transmission speeds. However high speed Field Programmable Gate Arrays (FPGA) which are sufficiently fast have now become available making DSP experiments without costly ASIC implementation possible for optical transmission experiments. This thesis focuses on Look Up Table (LUT) based digital Electronic Predistortion (EPD) for optical transmission. Because it is only one out of many possible implementations of EPD, it has to be placed in context with other EPD techniques and other distortion combating techniques in general, especially since it is possible to combine the different techniques. Building an actual transmitter means that compromises and decisions have to be made in the design and implementation of an EPD based system. These are based on balancing the desire to achieve optimal performance with technological and economic limitations. This is partly done using optical simulations to asses the performance. This thesis describes a novel experimental transmitter that has been built as part of this research applying LUT based EPD to an optical signal. The experimental transmitter consists of a digital design (using a hardware description language) for a pair of FPGAs and an analogue optical/electronic setup including two standard DAC integrated circuits. The DSP in the transmitter compensated for both chromatic dispersion and self phase modulation. We achieved transmission of 10.7 Gb/s non-return-to-zero (NRZ) signals with a +4 dBm launch power over 450 km keeping the required optical-signal-to-noise-ratio (OSNR) for a bit-error-rate of 2x10^{-3} below 11 dB. In doing so we showed experimentally, for the first time, that nonlinear effects can be compensated with this approach and that the combination of FPGA-DAC is a viable approach for an experimental setup

High Data Rate Coherent Optical OFDM System for Long-Haul Transmission

The growth in internet traffic has driven the increase in demand for bandwidth and high data rates. Optical Orthogonal Frequency Division Multiplexing is considered as a promising technology to satisfy the increased demand for bandwidth in broadband services. Optical OFDM received a great attention after proposing it as a modulation technique for the long-haul transmission in both direct and coherent detection. However, Coherent Optical OFDM (CO-OFDM) is the next generation technology for the optical communications, since it integrates the advantages of both coherent systems and OFDM systems. It has the ability to overcome many optical fiber restrictions such as chromatic dispersion (CD) and polarization mode dispersion (PMD). Moreover, Integrating the Coherent Optical OFDM with Wavelength Division Multiplexing (WDM) systems will provide the transmission system with a high bandwidth, a significant data rates, and a high spectral efficiency without increasing the cost or the complexity of the system. WDM systems help to enhance the capacity and the data rate of the system by sending multiple wavelengths over a single fiber. This research focuses on the implementation and performance analysis of high data rate coherent optical OFDM for long-haul transmission. The study starts with a single user and extends to the implanting of the WDM system. OptiSystem-12 simulation tool is fully used to design and implement the system. The system utilizes to carry range of data rates start from 10 Gbps to 1 Tbps, 4-QAM (2 bits-per-symbol) is used a modulation type for the OFDM signal, Optical I/Q modulation is employed at the transmitter and coherent detection is employed at the receiver. The performance of the system is studied and analyzed system in terms of Bit-Error-Rate (BER), the effect of the transmission distance on the Optical-Signal-to-Noise-Ratio (OSNR), and the relation of BER and OSNR with regard to the transmission distance

Coexistence of optical systems on a physical layer

Tato diplomová práce se zabývá koexistencí optických systémů na společné fyzické vrstvě. Cílem této práce je analýza interakcí mezi různými optickými systémy na fyzické vrstvě, přičemž dílčím cílem je porovnání integrace těchto systémů za různých provozních podmínek. Data pro tuto práci byla získána pomocí simulačního prostředí Optsim. Na základě výsledků koexistence různých systémů za různých provozních podmínek lze vyvodit závěr, zda je možné systémy sloučit či se tato varianta nasazení nedoporučuje.This thesis deals with coexistence of optical systems on a physical layer. The main objective of this thesis is to analyse interactions between multiple optical systems at the physical layer, while partial goal is to compare the integration of these systems under different system conditions. Data for this study were obtained by computer simulation in Optsim environment. On the basis of the resulting models of coexistence of different transmission systems under various system conditions it can be concluded, whether it is recommended to combine certain systems or not

Fixed-point realization of fast nonlinear Fourier transform algorithm for FPGA implementation of optical data processing

The nonlinear Fourier transform (NFT) based signal processing has attracted considerable attention as a promising tool for fibre nonlinearity mitigation in optical transmission. However, the mathematical complexity of NFT algorithms and the noticeable distinction of the latter from the “conventional” (Fourier-based) methods make it difficult to adapt this approach for practical applications. In our work, we demonstrate a hardware implementation of the fast direct NFT operation: it is used to map the optical signal onto its nonlinear Fourier spectrum, i.e. to demodulate the data. The main component of the algorithm is the matrix-multiplier unit, implemented on field-programmable gate arrays (FPGA) and used in our study for the estimation of required hardware resources. To design the best performing implementation in limited resources, we carry out the processing accuracy analysis to estimate the optimal bit width. The fast NFT algorithm that we analyse, is based on the FFT, which leads to the O(N log^{2}_{2} N) method’s complexity for the signal consisting of N samples. Our analysis revealed the significant demand in DSP blocks on the used board, which is caused by the complex-valued matrix operations and FFTs. Nevertheless, it seems to be possible to utilise further the parallelisation of our NFT-processing implementation for the more efficient NFT hardware realisation

Approaching the non-linear Shannon limit

We review the recent progress of information theory in optical communications, and describe the current experimental results and associated advances in various individual technologies which increase the information capacity. We confirm the widely held belief that the reported capacities are approaching the fundamental limits imposed by signal-to-noise ratio and the distributed non-linearity of conventional optical fibres, resulting in the reduction in the growth rate of communication capacity. We also discuss the techniques which are promising to increase and/or approach the information capacity limit

Fabrication and characterization of copper oxide thin film by thermal CVD for ethanol sensor application

A gas sensor is a device used to warn us of dangerous gases Gas sensors based on metal oxides semiconductors are important devices in modern technologies. Gas sensors play critical roles in many fields such as industrial production, environmental pollution, and traffic safety. Cupric oxide (CuO) thin films were prepared on a glass and FTO substrates by thermal CVD method. The substrate, deposition temperature, oxygen flow rate, and substrate were varying during deposition. The morphological, optical and electrical properties of CuO films were characterized by FE-SEM, atomic force microscopy (AFM), ultra-violet visible spectrophotometer, respectively, two point probe techniques and Keithley system. The FE-SEM result showed that spherical and uniform shaped were obtained on a glass substrate while the porous structure was obtained on FTO. AFM showed well organized morphology with the highest root mean square surface roughness for CuO thin films on glass and FTO substrates were 23 and 27nm, respectively. The optical direct band gap energy of the CuO film grown on glass and FTO substrate were in the range 1.8-l.86eV. The current-voltage characteristic has been formed with the threshold voltage (V th) of 2V and breakdown voltage (Vs) of -SV. The highest value of resistance was obtained which is 6.99xl06 0 when the CuO sensing element is contacted with to ethanol liquid. This work has successfully demonstrated the formation of optimized copper oxide thin films and for ethanol sensing application

Deep Learning-Based Phase Retrieval Scheme for Minimum-Phase Signal Recovery

We propose a deep learning-based phase retrieval method to accurately reconstruct the optical field of a single-sideband minimum-phase signal from the directly detected intensity waveform. Our method relies on a fully convolutional Neural Network (NN) model to realize non-iterative and robust phase retrieval. The NN is trained so that it performs full-field reconstruction and jointly compensates for transmission impairments. Compared to the recently proposed Kramers-Kronig (KK) receiver, our method avoids the distortions introduced by the nonlinear operations involved in the KK phase-retrieval algorithm and hence does not require digital upsampling. We validate the proposed phase-retrieval method by means of extensive numerical simulations in relevant system settings, and we compare the performance of the proposed scheme with the conventional KK receiver operated with a 4-fold digital upsampling. The results show that the 7% hard-decision forward error correction (HD-FEC) threshold at BER 3.8e-3 can be achieved with up to 2.8 dB lower carrier-to-signal power ratio (CSPR) value and 1.8 dB better receiver sensitivity compared to the conventional 4-fold upsampled KK receiver. We also present a comparative analysis of the complexity of the proposed scheme with that of the KK receiver, showing that the proposed scheme can achieve the 7% HD-FEC threshold with 1.6 dB lower CSPR, 0.4 dB better receiver sensitivity, and 36% lower complexity