Research On Techniques Of Optical Delay Based On Slow Light Of Stimulated Brillouin Scattering In Optical Fibers

Techniques of optical delay are utilized to provide tunable delays for opticalsignals via optical mechanisms. They play key roles in many fields, such as opticalcommunication, optical computing, radar and so on. With the capabilities ofworking at room temperature, compatible with current communication systems,easy to adjust the amount of time delay, techniques of optical delay based on slowlight effect of stimulated Brillouin scattering (SBS) in fibers are promising forpractical applications. The purpose of the dissertation focus on solving the two mainproblems existing in this technology, i.e.: how to increase the amount of time delayand how to broad the slow light bandwidth.Using the coupled-wave equations of SBS, the theoretical model of opticaldelay based on SBS slow light under the pump with discrete lines spectrum isestablished. Using this model, the effects of SBS slow light delay under the pumpwith single-line spectrum and multi-line spectrum are studied numerically. First, thecharacteristics of time delay, waveform distortion and broadening for pulses withvarious durations under the pump with narrow bandwidth spectrum are studied.Then the delay effects of broadband SBS slow light by using the pump withmulti-line spectrum are studied, starting with the analysis of the influences on theBrillouin gain spectrum by changing the number of spectral lines and the intervalbetween two adjacent spectral lines. With fixed spectral interval, the characteristicsof slow light delay are studied under the pumps with different numbers of spectrallines. The results show that the waveform distortion and broadening are suppressedefficiently under the pump with multi-line spectrum. The fidelity of the delayedwaveform is increased as increasing the width of the pump spectrum, while theefficiency of the delay is decreased.A dual-channel hybrid optical delayer based on SBS slow light is proposed.The delayer combines the nonlinear delay deriving from SBS slow light and thelinear travel delay using a two-ring configuration, which extends the delay in a greatamount. In experiment, a maximum SBS slow light delay of468ns is obtained inthe active ring for a43-ns pulse, which indicates that the hybrid delayer is capableof providing a tunable delay up to18microseconds. Besides, a method of measuringintrinsic Brillouin gain linewidth is proposed based on SBS slow light. In thismethod, the intrinsic Brillouin linewidth is measured by measuring waveformsunder different gains.In order to realize broadband delay, two methods are proposed. One method torealize broadband SBS slow light delay is to use the pump with multi-line spectrum generated via multi-frequency intensity modulation. In theory, the maximumnumber of the discrete lines generated is only limited by the bandwidths of therelated instruments. Limited by the2-GHz free spectral range of the F-Pinterferometer used in experiment, a spectrum consisting of65lines with the intervalof30MHz is demonstrated, which indicates that it can extend the bandwidth of thepump up to2GHz. Using this method, the effects of SBS slow light delay for4.0-nspulse and2.0-ns pulse are studied under the pump with the7-line,11-line and21-linespectrums. The results prove that the method of generating multi-line spectrum viamulti-frequency intensity modulation is valid for achieving broadband SBS slow light,which is capable of delaying short pulses.Another method of utilizing chirped pump to realize broadband SBS slow lightdelay is proposed. It features asynchronous amplification in frequency domain. Byusing the effect of the second order frequency shifting of an intensity modulator, thefrequency of the pump can be changed step by step with a high speed. Because onlythe matched frequency component of the signal can be amplified, the signal isamplified asynchronously in frequency domain. If the scanning range of the pumpcovers the whole Brillouin loss region for a given signal, the signal experiencesbroadband amplification. In experiment, for4.0-ns pulse and2.0-ns pulse, the effectsof SBS slow light delay are studied using the pump with6-step and10-step frequencytunings. The experimental results fit with the simulations of the model of SBS slowlight delay with multi-line pump established in Chapter2. It proves that it is feasibleto achieve broadband slow light by using asynchronous amplification. The maximumbandwidth generated via this method is limited by the bandwidth of the optical filter.A34-step frequency tuning pump is obtained in experiment, which extends the pumpbandwidth up to1GHz. In the end, by using the method of frequency agility, dynamicdistributed Brillouin optical fiber sensing is realized. In experiment, the measurementof vibration with the frequency of33Hz is demonstrated over a50-mpolarization-maintaining Panda fiber.