光纖通信第九講-課件

1、 Analog Transmission SystemsCHAPTER9Digital system : telecommunication , e.g. voice, dataAnalog system : microwave multi-signals , video distribution, radar signal processingThe general operational aspects and componentsCarriertonoise ratio, quantum noise effectSubcarrier modulation tech., harmonic

2、and intermodulation(IM) distortionWe will discuss the followingNoise contributors in an analog link Overview of Analog LinksCHAPTER9.1Analog modulation tech.AM, FM, PMPhotodetector with good linearnity Carrier-to-Noise ratioCHAPTER9.1CNR=Carrier powerSource+photodiode+amp+intermodulation noiseP(t)=P

3、t1+ms(t)m=Ppeak/Pt Carrier-to-Noise ratioCHAPTER9.1=RIN(A0P)2BRIN=/P2L=2q(Ip+ID)M2F(M)BC 0.5 (mA0MP)2 N RIN(A0P)2B+2q(Ip+ID)M2F(M)B+4KBTBFt/Req=4KBTBFt/Req=Examples of RIN effects Relative Intensity NoiseCHAPTER9.2.3RIN (IB/Ith-1) -3CNR versus optical power level Limiting ConditionsCHAPTER9.2.5C 0.5

4、 (mA0MP)2 N 4KBTBFt/Req)1=(C 0.5 m2 A0PN 2qF(M)B)2=(C 0.5 (mM)2 N RINB)3=( Standard FDM technique Multichannel Transmission Tech.CHAPTER9.3For example. CATV networksfrequency range : 50 88MHz ,120550MHzTech: amplitude-modulation-vestigial-sideband (AM-VSB)Channel bandwidth: 6MHzNonlinear DeviceCHAPT

5、ER9.3Provided a number M of simultaneously present sinusoids lying between ,the second-order terms at frequencies appear.In general a1 a2 a3 = It seems the second-order terms are more harmful than the third terms.If we make will lie completely outside the band two-tone third-order terms (because the

6、re are only two distinct frequencies) triple-beat (CTB)Define: Composite second order (CSO) distortion Composite triple-beat (CTB) distortionIn general CTB distortion is larger than CSO distortion.IM products on the r-th carrier for 2fi-fj D1,2=1/2N-2-1/21-(-1)N(-1)rIM products on the r-th carrier f

7、or fi+ fj -fkD1,1,1=r/2(N-r+1)+1/4(N-3)2-5-1/21-(-1)N(-1)N+rTwo-tone are spread through the passband, The triple-beat be concentrated in the middle of passbandrN1234567810200301041221524442646776476910111096891214151514129The number of third-order triple-beat IMrN123456781020031014111152121262222227

8、3232323833333333The number of third-order two-tone IMPredicted CSO for 60 CATV channels Predicted CTB for 60 CATV channelsMultichannel FMCHAPTER9.3For AM C/N40dB , very stringent requirements on laser and receiver linearityFor FM3644dBThe reduce C/N will make FM less susceptible to laser and receiverthan AMRIN versus optical modulation index Effects Of Nonline