München, Universiẗat der Bundeswehr, Diss., 2001.

In this study, we propose and demonstrate a flat-top birefringent optical interleavers utilizing a new ring-cavity as a phase-shift element. The uniform performance over entire C-band is a result of the unique ring-cavity architecture which utilizes Fresnel reflections of the prism-air interface to provide the partial reflections. Unlike dielectric mirrors with thin-film coatings, the reflectivities of Fresnel reflection are insensitive to wavelength variations in the transmission band. In the ring-cavity based birefringent interferometer (RCBI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 17.5 GHz (70% of the channel spacing), a 25-dB stopband greater than 17.5 GHz (70% of the channel spacing), a channel isolation better than 28 dB, and insertion loss lower than 2.2 dB. In the ring-cavity based birefringent Sagnac interferometer (RCBSI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 18.1 GHz (72.5% of the channel spacing), a 25-dB stopband greater than 18.1 GHz (72.5% of the channel spacing), a channel isolation better than 36 dB, and insertion loss lower than 1.5 dB. The RCBSI interleaver requires less number of optical components and hence results in more than 0.7 dB and 2.5% improvements in the insertion loss and band utilization, respectively, when compared to the RCBI interleaver. Therefore, the novel RCBSI interleaver can be used in dense wavelength division multiplexing (DWDM) applications.

Optical add/drop multiplexer (OADM) and optical wavelength cross-connect (WXC) are two key components to enable greater connectivity and flexibility in dense wavelength division multiplexing (DWDM) networks. Fiber Bragg grating (FBG) based components have several inherent advantages such as compact, low-insertion loss, high reflectivity, no-linearity effect, polarization insensitivity and wavelength tunability. We experimentally investigate the system power penalty induced by the chromatic dispersion of the FBG as a function of the wavelength detuning of the reflection spectrum for 10 Gb/s signals, which was reflected by cascade of FBGs. Such power penalty limits the number of cascaded gratings and restricts the allowable range of wavelength detuning. In our experiments, we have used several FBG filters with 3-dB bandwidth of 0.43 nm. According to the experimental results, power penalty increases from the central wavelength to the edge wavelength of the reflection spectrum. There are 0.4 dB and 7 dB power penalty for one single FBG and ten cascaded-FBG filter, respectively, when the central wavelength was detuned to ¡Ó0.2 nm and ¡V0.1/+0.14 nm. This study result may give a design guideline of fiber grating-based optical add-drop multiplexers or optical wavelength cross-connects in DWDM nodes.

In this thesis, we investigate the OTDR on-line monitoring feasibility of forward- and backward-pumping distributed Raman fiber amplifiers (FRAs) transmission systems with different OTDR probe lights. In the experiments, we choose the large effect area fiber ( LEAF ) with 50 km long as gain medium of Raman amplifiers. Two different OTDR probe lights with 1.31£gm and 1.65£gm wavelengths are separately used for on-line monitoring forward- and backward-pumping distributed FRAs. We find that the OTDR probe lights affect the optical gain of the 1.55 mm data signal. In the experiments, for the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal increases 0.2 dB, but for the backward-pumping scheme, that only increases 0.1 dB. In the forward-pumping scheme using 1.65£gm OTDR probe light on-line monitor, the optical gain of the 1.55 mm data signal decreases 0.6 dB, but for the backward-pumping scheme, that only decreases 0.2 dB. We also find the OTDR on-line monitoring distribution fiber Raman amplifiers Systems makes OTDR traces distortion. In an aspect of system BER performance, the system power penalty on account of the OTDR monitoring in both 10 Gb/s forward- and backward-pumping schemes is trivial¡@. In the forward-pumping scheme using 1.3£gm OTDR probe light on-line monitor, the power penalty is about 0.1 dB, but for the backward-pumping scheme that is about 0.05 dB. As the forward-pumping scheme using 1.65£gm OTDR probe light, the power penalty is about 0.2 dB, but for the backward-pumping scheme that is about 0.07 dB.

Dense wavelength-division multiplexing (DWDM) technology are the provide solutions to increase the capacity of network. With the growth of using the OADM in DWDM system, it is more and more important to research the fault-locating fiber-link in-service supervisory technique for enhance the system reliability. Optical Time Domain Reflectometer (OTDR) is a popular tool to offer an in-service fault-locating of fiber link in fiber-optic transmission systems. But in the DWDM network, this technique is never be used for in-service supervisory application on the system. Are different OADM structures will affect the in-service OTDR monitoring? Since OTDR operates with high peak powers, the stimulated Raman scattering (SRS) effect in the conventional transmission fiber gives rise to power depletion of the data signal, and may degrade the bit-error-rate (BER) performance. In this work, we investigate the in-service 1.65-£gm OTDR monitoring supported FBG-based OADM structures. We improved FBG sandwiched between a pair of three-port optical circulator and multi-port optical circulator (MOC) FBG-based OADM to support OTDR monitoring, and research the technique of in-service OTDR monitoring for FBG-based, MZ-FBG based OADM system. The system bit-error-rate due to the OTDR monitoring a 10-Gb/s long (> 80 km) distance fiber link is examined. Negligible system power penalty, due to the OTDR monitoring, of both structures in 10 Gb/s dense wavelength division multiplexing (DWDM) link is achieved. That is mean the system with OTDR monitoring should have the in-service fault-location monitoring capability to enhance network reliability. We also investigate the in-service OTDR 1.65-£gm OTDR monitoring on the distributed Raman application system.

This thesis describes single types of wavelength-division multiplex (WDM) according to the International Telecommunication Union (ITU-T). This work offers an overview of components and evaluation of critical parts of network design utilizing WDM technology. There are depicted typical properties, suitable components and channel spacing for each category. Suitable optic fibers according to ITU-T and characteristics of negative effects can be found in the work as well. Furthermore, there are presented most important optic sources, optic amplifiers, optic detectors with filters their requirements and application. They are especially important for achieving operation of WDM system. The fifth chapter considers impact of negative effects in fiber optics and their influence on the system. Then, a WDM system is designed along with management and monitoring the physical layer. The work also presents 1,33 Tbit/s (32 × 42,7 Gbit/s) WDM transmission over 300 km (with three 100 km spans) of post-compensated non-zero dispersion-shifted fiber (NZDSF) LEAF. The capacity of 400 Tbit/s×km is achieved in a single 25,6 nm C band using non-return-to-zero differential phase-shift-keyed modulation (NRZ-DQPSK), balanced detection and erbium-doped fiber amplification. Together with design of transmission system a several simulative analysis has been carried out in order to find the optimum configuration (such as number and distances between amplifiers, length of spans or the way of dispersion compensation) for a high bit rate optical transmission system. It was used a program OptiSystem 8.0.

University, Diss., 2001--Kaiserslautern.

With the technological shift towards big data, internet of things (IoT), 5G applications and cloud computing, the demand for high capacity networks is dramatically increasing. To avoid congestion and saturation, content and service providers are re-designing their network (backbone, metro and data-centers interconnects) connectivity using gridless optical line systems along with programmable coherent transponders. The latter are expected to transmit data at different data rates up to 400 Gb/s. In 2008, the first coherent receiver was commercially available [1]. By means of high-speed analog to digital converters and adaptive digital signal processing (DSP) algorithms, such revolution in modern optical communication was possible. That allowed a better spectral efficiency using higher order modulation formats and further signal reach by means of compensating both linear and nonlinear impairments. Another key development was leveraging light polarization-diversity, that permits to double the data rate at the expense of receiver complexity. To further increase the capacity of fiber links, gridless DWDM networks are being developed for deployment in the next few years. The key idea is to allow variable bandwidth signals to be allocated on optical links and by performing the appropriate network layer optimization improved throughput can be achieved. These innovations are driving new types of challenges for routing and assignment methods, as well, DSP algorithms such as clock recovery and compensation of fiber non-linearity. This thesis is organized as a collection of contributions and composed of five major parts. The first part, consisting of chapters 2 and 3. Chapter 4 deals with tracking of fast state of polarization transient, i.e. dynamic aspect of optical channels, in presence of polarization dependent loss (PDL) and filtering effects due to reconfigurable optical add-drop multiplexers (ROADMs). Chapters 5 and 6 study the impact of filtering effects, quasi-static effects in optical links and transponders, represented by ROADMs in fixed-grid and Silicon Photonics (SiPh) modulators in flexible-grid networks, respectively. Chapters 7, 8 and 9, are related to clock recovery in digital coherent receivers. They cover mitigation of jitter in gridless applications, improving jitter when deploying phase interpolators (PI) and jitter injection as a test-mean to evaluate performance.

The main goal of the diploma thesis is DWDM simulation of optical network, defined by recommandation ITU-T. Optical network includes 16 communication channels with length of fiber 50 km. Each channel have to be set with bandwith 50GHz and Bit rate with minimal value 10Gbit/s. The final simulation model includes 8 types of modulation techniques. The result of the thesis is comparison modulation techniques in terms of usability of bandwith and comparison of the quality of transfer

In wavelength division multiplexed (WDM) optical communication networks, signals are amplified periodically by optical amplifiers. Since the gain profiles of optical amplifiers are not flat, equalizers are usually used to maintain signal powers at different wavelengths in equal to avoid crosstalk and data loss. However, fixed attenuation can only compensate fixed input power and amplification. In active network, input power and amplifier gain change with time. Active level compensation at each wavelength is needed. An adaptive attenuator is a device with a chromatically variable transmissivity used to equalize channel powers in wavelength-division multiplexing (WDM) fiber-optic communication lines. In this thesis, a method of Fourier analysis of multi-beam interference is developed. It is shown that the total electric field and relative phase delay of each beam form a Fourier transform pair. Thus methods and properties of Fourier analysis are applicable in multi-beam interference analysis and design. Fourier transform based design is presented. Novel devices that apply such design principles are introduced. Principles and structures of novel adaptive attenuators based on various technologies such as segment deformable mirror, liquid crystal, phase modulation array are given. Simulation results for segment deformable mirror based adaptive attenuator are presented. / Master of Science