In this thesis, we investigate the design and amplification characteristics of discrete fiber Raman amplifier (FRA), and discuss with amplification characteristics of FRA by employing multi-pumping-wavelength configuration. Recently, because of the invention of high output power of pump laser diodes, so discrete FRA can be practically employed in optical fiber communication system. The fiber Raman amplifier has two merits. One is the low noise characteristic and the other is the arbitrary spectral gain band, so it will play an important role in optical communication system. In this study, we employ backward pumping configurations in the experiment and simulation of discrete FRA. By comparing with results of experiment and simulation, we prove that the simulation results quite agree with the experimental data of four pumping wavelengths configuration, we have successfully designed an L-band gain flattened discrete FRA by using four pumping wavelengths configuration. The experimental results showed that the amplifier, for the input of seven optical channel each with ¡V16 dBm input power level, has an optical gain of >10 dB of each channel with good gain uniformity (<1 dB) in the 1565-1595 nm wavelength region.

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.

Optical fiber access technology is the key to realize a broadband communication for everyone, and the passive optical network (PON) is enabling customers to enjoy high-speed internet access now. As the demand for the broadband access is still growing, a study to find out technologies to realize wider bandwidth for the access system is quite important. At this moment, wavelength division multiplexing (WDM) PON is the most promising technology for the future optical fiber access system. Current PON system covers a reach of within 20km from a central office, because the market of the access system is focusing on well-populated area. It is required to extend the reach of the PON system to enhance the applicable area, because there are many regions in the world where are not so highly populated. Therefore, this master thesis is focusing on to enhance the reach of the WDM-PON system. A little more specifically, a single fiber bidirectional 80 km WDM PON system with symmetric up-and-downstream data rate of 10.66Gb/s is reported. In order to enhance the reach of the WDM-PON system, Raman amplifier is utilized. As the Raman amplifier can amplify both directional optical signals simultaneously, it is quite effective to enhance the reach of the WDM-PON system. Even though, there are several effects that cause performance degradations of the system by introducing the Raman amplifier. It is important to clarify such effects and to provide solutions. This thesis discusses these issues also. One factor to degrade the system performance is the Rayleigh backscattering. As the Raman amplifier amplifies the Rayleigh backscattering, it interferes to the signal and causes the crosstalk penalty. At first, an experimental study has been conducted to clarify the significance of the Rayleigh backscattering, and the method to overcome the crosstalk penalty is presented. Then, another experiment to realize 80km WDM PON system with Raman amplifier is conducted, and it demonstrates a feasibility of such system. Finally, this thesis is concluded by a successful demonstration of the WDM-PON system with an enhanced reach.

We consider the boundary control problem to stabilize the power of a signal and a pump propagating down a Raman amplifier. This is essentially an initial-boundary value problem (IBVP) of a hyperbolic system with Lotka-Volterra type nonlinearities. We treat the system as a control problem with states in the function space and use Lyapunov-based analysis to demonstrate asymptotic stability in the C_0 and the L_2-sense. The stability conditions are derived for closed-loop systems with a proportional controller and a dynamic controller, and confirmed by simulations in MATLAB.

We consider the boundary control problem to stabilize the power of a signal and a pump propagating down a Raman amplifier. This is essentially an initial-boundary value problem (IBVP) of a hyperbolic system with Lotka-Volterra type nonlinearities. We treat the system as a control problem with states in the function space and use Lyapunov-based analysis to demonstrate asymptotic stability in the C_0 and the L_2-sense. The stability conditions are derived for closed-loop systems with a proportional controller and a dynamic controller, and confirmed by simulations in MATLAB.

Aim of this Master´s thesis is to describe and compare most common types of optical amplifiers used in today’s networks. The first section focuses on problematic of optical transmissions and phenomenon which cause degradation of transmitted signal. It is also explained in this section why there is a need to deploy optical amplifiers. Next section describes basic principles, structure and properties of individual types of optical amplifiers. Following section describes simulations which were made to compare the performance of transmission systems with each individual type of optical amplifier. The last section contains a design of optical metropolitan network with wavelength multiplex. Based on simulations from preceding part best amplifier type and optimal amplifier placement was selected. Functionality of the design was tested and simulations described in final section.

Interest in Raman amplification has undergone a revival due to the rapidly increasing bandwidth requirements for communications transmission, both for long haul and local area networks, and recent developments in the telecom fiber industry and diode laser technology. In contrast to rare earth doped fiber amplifiers, for which the range of wavelengths is fixed and limited, Raman gain bandwidths are larger and the operating wavelength is fixed only by the pump wavelength and the bandwidth of the Raman active medium. In this context, glasses are the material of choice for this application due to their relatively broad spectral response, and ability of making them into optical fiber. This dissertation summarizes findings on different oxide-based glasses that have been synthesized and characterized for their potential application as Raman gain media. Two main glass families were investigated: phosphate-based glass matrices for broadband Raman gain application and TeO2-based glasses for high Raman gain amplification. A phosphate network was preferred for the broadband application since the phosphate Raman active modes can provide amplification above 1000 cm-1, whilst TeO2-based glasses were selected for the high gain application due to their enhanced nonlinearities and polarizabilities among the other oxide-based network formers. The results summarized in this dissertation show that phosphate-based glasses can provide Raman amplification bandwidths of up to 40 THz, an improvement of almost 5 times the bandwidth of SiO2. On the other hand, tellurite-based glasses appear to be promising candidates for high gain discrete Raman applications, providing peak Raman gain coefficients of up to 50 times higher than SiO2, at 1064 nm. Although, visible spontaneous Raman scattering cross-section measurement is the most frequently used tool for estimating the strength and spectral distribution of Raman gain in materials, especially glasses, there are some issues that one needs to be aware when conducting these measurements near the absorption band edge of the material. This led to the detection of an inherent frequency-dispersion in the Raman susceptibility and a resonant enhancement phenomenon when measurements were conducted near the absorption edge of the material.

This thesis presents a novel technique named "Core Suction" for fabricating optical fiber preforms for manufacturing highly doped fibers (HDFs) for optical amplification (Raman effect based or Erbium fiber based). The technique involves drawing the molten non-conventional core glass material into the silica cladding tube to form the preform. The developed technique is simple, inexpensive and shows great potential for fabricating preforms of highly nonlinear non-conventional multi-component glasses as the core material. Preforms were made with various core glasses such as Schott SF6, Lead-Tellurium-Germanate, Lead-Tellurium-Germanate- Neodymium -Erbium and MM2 in silica cladding tubes and then pulled into fibers. The fabricated fibers were measured for refractive index profile, loss spectrum and spontaneous Raman spectra. Elemental analysis of the fiber samples was also performed using an electron microprobe. Erbium doped fiber amplifiers (EDFAs) were setup using 30 cm, 5cm and 1 cm lengths of fabricated erbium doped fibers and their gain spectra measured. The distributed gain spectrum for an EDFA was also measured using an optical frequency domain reflectometery (OFDR) technique. Commercial dispersion compensated fiber (DCF) with very high GeO2 doping was used to setup a Raman amplifier and the gain spectrum measured. One of the needs of Raman amplification in optical fibers is to predict an accurate Raman gain, based on the fiber's refractive index profile. A method of predicting Raman gain in GeO2 doped fibers is presented and the predicted Raman gain values are compared with the measured ones in the same fibers. Raman gain issues like the dependence of the Raman gain on the GeO2 concentration, polarization dependence were taken into account for the gain calculations. An experimental setup for Raman gain measurements was made and measurement issues addressed. Polarization dependence of the Raman gain in one kilometer of polarization maintaining fiber was also measured. / Ph. D.

Fiber Raman amplification using the transmission line is a promising technology to increase the repeater distance as well as the capacity of the communication systems. Because of the growing importance of fiber Raman amplification, it is desired to predict the magnitude and shape of the Raman gain spectrum from the doping level and refractive index profiles of different fiber designs. This thesis develops a method to predict the Raman gain coefficients and spectra for a pure silica core fiber and two different types of GeO2-doped silica fibers given their index profiles. An essential feature of the model is the inclusion of the variation in Raman gain coefficient over the mode field due to the variation in the Ge concentration across the fiber core. The calculated Raman gain coefficients were compared with measurements of the peak Raman gain on a step-index GeO2-doped fiber and with published measurements from various sources. Agreement between the calculated and measured peak gain for the step-index fiber was excellent. There was qualitative agreement with published measurements but there were significant differences between the calculated and published gain coefficients, which are not understood. Part of the work sought a way of predicting Raman gain coefficients from a standard gain curve given only the fiber type and the effective area. This approach appears promising for moderately-doped fibers with the proper choice of effective area. / Master of Science