,*,*,The Sch.Of Information Engineering,WHUT,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,单击此处编辑母版标题样式,CONTENT,Chapter11 Optical Amplifier,11/20/2024,1,The Sch.Of Information Engineering,WHUT,Chapter11 Optical Amplifier8,Used routinely for loss compensation since 1995,Amplify the input signal but also add some noise,Several kinds of amplifiers have been developed,semiconductor optical amplifier,raman-based fiber amplifier,erbium-doped fiber amplifier,EDFAs are used most commonly for lightwave system,Raman amplifiers work better for long-haul system,11/20/2024,2,The Sch.Of Information Engineering,WHUT,8/5/20232The Sch.Of Informati,OUTLINE,Basic concepts,Semiconductor optical amplifier(SOA),Raman amplifier,Erbium doped fiber amplifier,System application of optical amplifier,11/20/2024,3,The Sch.Of Information Engineering,WHUT,OUTLINEBasic concepts8/5/20233,11.1 Basic concepts,11.1.1 Gain spectrum and bandwidth,11.1.2,Gain saturation,11.1.3 Amplifier noise,11.1.4 Amplifier applications,11/20/2024,4,The Sch.Of Information Engineering,WHUT,11.1 Basic concepts11.1.1 Gain,11.1.1 Gain spectrum and bandwidth,Amplifier pumped optically or electrically to realize optical gain.,Optical gain has the general form:,is the peak value of the gain,is the optical frequency of the incident signal,is the atomic transition frequency,is the optical power of the signal being amplified,is the saturation power,11/20/2024,5,The Sch.Of Information Engineering,WHUT,11.1.1 Gain spectrum and bandw,In the unsaturated regime,Lorentzian spectrum with bandwidth,Typically (40nm or so),11/20/2024,6,The Sch.Of Information Engineering,WHUT,In the unsaturated regime8/5/2,11/20/2024,7,The Sch.Of Information Engineering,WHUT,8/5/20237The Sch.Of Informati,Use with initial condition,signal power grows as,Amplification factor also depends on frequency as,Amplifier bandwidth is defined as the FWHM of,It is related to gain bandwidth as,It is easy to show that,11/20/2024,8,The Sch.Of Information Engineering,WHUT,Use with init,11.1.2 Gain saturation,If G=G0/2,11/20/2024,9,The Sch.Of Information Engineering,WHUT,11.1.2 Gain saturationIf G=G0/,11.1.3 Amplifier noise,Optical amplifiers introduce noise and degrade SNR.,Source of noise:Spontaneous emission,Noise spectral density,Population inversion factor,Amplifier noise figure is defined as,11/20/2024,10,The Sch.Of Information Engineering,WHUT,11.1.3 Amplifier noiseOptical,11.1.4 Amplifier applications,11/20/2024,11,The Sch.Of Information Engineering,WHUT,11.1.4 Amplifier applications8,11.2 Semiconductor Optical Amplifier,11.2.1 Amplifier design,11.2.2,Amplifier characteristics,11.2.3,Problems of SOAs,11/20/2024,12,The Sch.Of Information Engineering,WHUT,11.2 Semiconductor Optical Amp,11.2.1 Amplifier design,A laser biased below threshold acts as a FP amplifier.,Feedback at facets provides most gain near FP resonances.,Amplification factor obtained considering multiple reflections:,1.FPA,11/20/2024,13,The Sch.Of Information Engineering,WHUT,11.2.1 Amplifier designA laser,is the single pass amplification factor.,reduces to G when,Amplifier bandwidth set by sharpness of cavity resonances.,11/20/2024,14,The Sch.Of Information Engineering,WHUT,is the single pass ampl,2.Traveling wave amplifiers,FP amplifiers not suitable because of their narrow bandwidth.,Feedback at the cleaved facets must be suppressed.,Common to coat facets with an antireflection coating.,AR coating should be good enough to suppress FP resonances.,11/20/2024,15,The Sch.Of Information Engineering,WHUT,2.Traveling wave amplifiersFP,11/20/2024,16,The Sch.Of Information Engineering,WHUT,8/5/202316The Sch.Of Informat,11.2.2 Amplifier characteristics,11/20/2024,17,The Sch.Of Information Engineering,WHUT,11.2.2 Amplifier characteristi,Wide gain spectrum with negligible ripples.,High gain(25dB)at low currents.,Output saturation power in the range 5-10 mW.,Noise figure in the range 5-7dB.,11/20/2024,18,The Sch.Of Information Engineering,WHUT,Wide gain spectrum with neglig,11.2.3 Problems with SOAs,11/20/2024,19,The Sch.Of Information Engineering,WHUT,11.2.3 Problems with SOAs8/5/2,SOA provide Polarization dependent gain:,several schemes can solve this problem partially.,Large coupling losses(6-8 dB or more).,Relatively large noise figure.,11/20/2024,20,The Sch.Of Information Engineering,WHUT,SOA provide Polarization depen,11.3 Raman amplifier,11.3.1 Raman gain and bandwidth,11.3.2 Raman gain saturation,11.3.2 Raman amplifier design,11/20/2024,21,The Sch.Of Information Engineering,WHUT,11.3 Raman amplifier11.3.1 Ram,Pumped optically in the forward or backward direction.,Use stimulated raman scattering for signal amplification.,Can work at any wavelength with suitable pumping.,Fiber used for data transmission can itself be used.,Gain can be made polarization independent using orthogonally polarized pumps at each wavelength.,11/20/2024,22,The Sch.Of Information Engineering,WHUT,Pumped optically in the forwar,11.3.1 Raman gain and bandwidth,11/20/2024,23,The Sch.Of Infor