Class Note for OPTI 515 at UA
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Date Created: 02/06/15
Photonic Devices and Systems Lecture 35 17 Noise and Optical Amplifiers Sources of Noise in a Receiver with a PreAmplifier Optics Electronics gt I I Optical EleCTroniC Electronic EDFA preamplifier bandpass lowpass preamp fier ner filter I gt 39 m 39 39 m PIN A P lt2sigespongt p P P ltl spon spongt 5 73 lt 52gt lt39 shop lti mgt ASE ASE 0 lt Av 0 x gt y I A k i O gt lt f AW 23 Figure 1318 Receiver using EDFA as a preamplifier Photonic Devices and Systems Lecture 35 27 The signal and amplified spontaneous emission ASE spectra look like Electronic l lltf frequency band 25 20 QHZ 2A Optical Avf P filter 100 GHZ 1 nm ASE Aw 5 THz nolse 50 nm Figure 1320 Relative frequency ranges compared ASE noise optical filter and electronic frequency band Photonc Devices and Systems Lecture 35 37 We model the signal and ASE spectra with Signal GPs a E o G P ASE N l 0 121 v2 123 v4 v5 1 V Frequency 5 28 w Figure 1321 Division of continuous ASE noise spectrum into discrete ASE noise line spectra The current in the photodiode is N 2 it Escos27zvst SEncos27zvnt n and is made up of three parts 1 Signal current 2 Noise current due to the beats between the signal and the ASE noise whose beat frequencies fall within the electronic frequency bandwidth of the detector 3 Noise current due to the beats among the line spectra of the ASE noise whose beat frequencies fall within the electronic bandwidth of the detector 3 Photonic Devices and Systems Lecture 35 47 Signal to noise is a ratio of powers so we will compute 2 B Isigispongt 4GISGIASE A Vf 392 2 2 B B Isponispongt G ASE AVf AVf Other kinds of noise are 1 Shot noise 3101 2eGS IASE 4153 2 Thermal noise in the load resistor ism All57 L The signal to noise after amplification and detection is El N 0 GIS 2 B 4kBT B B 462 Gzl2 2 26 GI I I B sASEAVf ASE Avf Vf s ASE 1 RL Photonic Devices and Systems Lecture 35 57 Should I Use an Optical PreAmplifier EDFA Electronic preamplifier PIN detector preamplifier W BP lter I 7 LP filter I In ut i W if at Out ut L lgt L m 3 if m N J P 3 2 w mr 2 m A s 39 nspon 225 l 50 2 WSW G1556 Avf124 GHz 05 862 GHz T300K 1 Figure 1322 Physical layout when an EDFA is used as an optical preamplifier Signal to noise without a preamplifier ltiszhotgt 2633 216gtlt1O 1932gtlt1O 6 gtltO562gtlt 09A2 3174gtlt O 15A2 lt12 4ng 4138x10 2330062gtlt109 22053x10 12A2 50 Thermal noise in the load resistor is dominant Photonic Devices and Systems Lecture 35 67 s PSR2 32quO5AW2 W M 4138x10 2330062gtlt109 RL 5o 256x10 12A2 2053x10 12A2 2125 Signal to noise with a preamplifier The signalspontaneous emission beat noise is dominant PASE mtnspthv 2225663gtlt1O 34194X1O14124gtlt1O1 718X1O 9W ASE zgpm O5718gtlt1O 9 359x10 9A I B Iszigispongt 4GsGASE A Vf 7 62gtlt109 z 4155632gtlt1O 6 gtltO51556359gtlt1O m 278gtlt1O 8A2 The signal to noise after the preamplifier is Photonic Devices and Systems Lecture 35 E Z GPSR2 N igispon gt 1556x32uWgtltO5AW 2 8 2 223 278gtlt1O A So yes use an optical preamplifier 77
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