Optical Fiber Communication
Optical Fiber Communication EE 230
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This 25 page Class Notes was uploaded by Amiya Haley on Monday September 7, 2015. The Class Notes belongs to EE 230 at University of California - Santa Cruz taught by Staff in Fall. Since its upload, it has received 62 views. For similar materials see /class/182339/ee-230-university-of-california-santa-cruz in Electrical Engineering at University of California - Santa Cruz.
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Date Created: 09/07/15
AuAu Sn l I W p I l n I I lt W gt i l b l n 39 3 E substrate 2 I u I I I l x W l l Distance 1 a 39 I b FIGURE 45 39 a A pi n photodiode together with the electric eld distribution inside various layers under reverse bias b Design of an InGaAs p i n photodiode PHO ODIODES 145 Absorption Gain l I I l Vt W p l p I m 1 W I l 39 l I 1 1 s is s 39 Eu 5 s 39 I A k Distance a b HGURE 47 a An APD together with the electric eld distribution inside various layers under reverse bias b Design of a silicon reachthrough APD 1o3 rj1r H OPTIMUM APD GAIN 10 i11 40 35 30 25 20 INCIDENT OPTICAL POWER dBm Figure 417 Optimum APD gain Mopt as a function of the incident optical power P1n for several values of 194 Parameter values corresponding to a typical 155pm InGaAs APD receiver were used 7 Features n Applications 2 Advantage Disadvantage quot1 Short distance Easy Large low bit rate coupling dispersion Local area An 05 1 0 a Multimode stepindex fiber a b Medium distance Easy Moderate medium bit rate coupling dispersion Local area An 0510 b Gradedindex fiber Long distance Wideband Difficult high bit rate coupling Wide area Long distance immune Difficult high bit rate to H2 or coupling ray gu39gfngfnae irradiation Extremely short distance Easy H39gh loss coupling Robotic circuits Large I Process control d39spers39on Data link ghpower Single ow dispersion Ernaterial Large core Local oscillator No Higher loss Sensor polarization Pigtail for jitter integrated optics g Polarization preserving fiber Figure 1110 Various kinds of optical fibers gure MA Modi ed Chemical vapor deposition MCVD method Soot Motor 1 Q39 9193 19191919 QXQLOLOKOXOLOXQXOXOZQ191919191919399191919191 2919191939OXOXOXOE m K919 19191 29239 v 239 I I 39 39 quot 1 r E 3 39 39 5 Carbon or ceramic rod for easy release Advance screw 7 a innerI ner mag 439 V Material gas r 02 Poe3 Figure 3 L48 Outside vapor depes tierr OVD methed Fireform rod o Advance screw Argon gas shield against 1 oxygen gas to prevent I I oxidation of carbon Zigzag carbon heater OD meter Servo control UVcurable rein Cavity 1 wrth confocal 39 reflector 7 a Rubber belt Figure 1150 Apparatus for drawing a fiber a MATERIAL DISPERSION C MODAI DISTORTION in 1 s 4 IT f1 Figure 546 Schematic description of the three contributions to pulse spreading The space occupied by an entering pulse is shown on the left At some later time this pulse exits the fiber occupying the space indicated on the right side of the figure a Pulses at different wavelengths have different velocities b Pulses at different wavelengths but propagating in the same mode must travel at slightly different angles resulting in a difference in net axial velocities c A pulse at a single wavelength splits its power into modes that travel at different axial velocities because of the path differences 0 4348 V J 1 t 20 t3to R U Figure 13 Schematic plot of the eld amplitude illustrating the propagation of the wave packet in the regime where Eq 152 is valid and the pulse shape remains undistorted q T 1 i 4 4 1 1 10 Irilij I T 08 06 39U FYl39Yr39 UzT 04 02 I7IYTIU TTo Fig 31 Dispersioninduced broadening of a Gaussian pulse inside a ber at z ZLD nd 4L0 The dispersion length L0 T5 I 32 I where 32 is the GVD parameter imhed curve shows the incident pulse a z O I Group velocity vg a Group delay I 9g 60 6 6k Dispersion D 2 62 82 quotC0k21 2A1 17 Since A ltlt1 the term in brackets is approximately equal to 1 2A1 bA2l b2 1 All quot19l2 So 5 nCOk A1 b This has two terms and we need to take the derivative of each one with respect to k in order to determine the group delay First term is nk and its derivative is nkdndk This is called the group index N1 In wavelength units it is equal to nMdndlt It has nothing to do with the waveguide it s the material dispersion term Second term is nkAl b and its derivative is quotco quotmi dk which can be rewritten in terms of V rather than k as nee I W W This term is called NW the waveguide index So we now have the total expression for 1 equal to lcN1Nw To determine the dispersion we have to take the derivative of this with respect to it We see already that the material term involves the second derivative of index with respect to 7t so if a material s index changes linearly with it there will be no material dispersion We need to take derivatives with respect to it so we need to write V in terms of X V 2 n o nil so dVdk Vt This helps us take the wavelength derivative of the ddV term since ddlt VltddV We end up with 11166 page 752 D dVZ 22 6w2 id2nw VnCOA 512023 272390 am 0 d f cl The last derivative on the right is the GVD parameter D depends upon the dispersion of the core material assumes that this is equal to the dispersion in the cladding material depends upon the mode b and the waveguide parameters V index of refraction Putse amplitude Input pulses 3 Output pulses Distance along fiber 393 33 1 4600 1 4575 1 4550 1 4525 1 4500 1 4475 1 4450 l 1 60 1 4425 39 39 39 060 080 1 00 1 20 Wavelength pm 1 40 34 There is a formula that very nicely ts the wavelength dependence of the index of refraction of pure silica glass 11 3 a n21Z 39 1111 with a 06961663 b 0004629148 a2 04079426 72 001351206 1112 a 08974994 93 97934062 This formula is known as Sellmeier s formula As shown in Fig 118the measured index of refraction of the glass has two regions of steep slope in the range of 004 40 ttm The steep slope in the region of 7 15 pm is due to the dispersion caused by vibration of the Si O lattice in the crystalThe electronic transition bands around 01 pm are responsible for the steep slope in the region of 007 015 pm Each term 2 11 13 12 b 39 Lattice absorption bands Refractive index n Electronic absorption bands i J 1 1 I I i 004 007 01 02 04 07 10 2 4 7 1O 20 4O Wavelength A um Figure 118 Refractive index variation offused silica Afters Ft Nagel corresponds to a peak at A abi and the sum of the terms nicely represents the index of refraction except in very close proximity to A v 19 where the associated term becomes in nite Figure 117 was obtained by expanding the vertical scale in the region between 03 and 3 pm nN 149 148 147 146 145 144 120 80 4O 40 120 I 1 I 1 I 15 5 pskmnm 752 IDEs ANDI DISPERSION iN OPTICAL FIBERS 22 I I 21 T Top section is in Fig 1137 20 I I I I I I 1 18 I I I I I I I 1 mm 16 d2Vb W 14 dV2 for LP11 d2Vb 12 10 e I 0 s 06 04 02 9 r9 I I o 39 1 133 2 i V koanif 2405 Figure 1133 Values of b dVbdV and Vd2VbdV2 These values are used in the design of dispersionshifted fibers and dispersion oompensators The graph of Vd2VbdV2 is shown for both the LPm and LP11 modes After D Gloge 37 20 39 1 I 1 I 1 7 1 1 i T 81 51 61 71 16 52 41 32 42 31 33 21 22 2339 11 1 1392 I I 1239 13 r 701 l V Iquot 139 39 a 39 02 O3 14 k 0 8 04 L a 04 1 l 0 1 L 1 1 L J L L 0 2 4 6 8 10 12 V FIGURE 314 The group delay arising from waveguide dispersion as a function of the V number for a stepindex optical ber The curve numbers jm designate the LPjm modes Reproduced with permission from Gloge37 Elspersion pskm nm 40 i 1 1 l l l Material dispersion I e 20 L Total dispersion D39 a g I 39 O Waveguide f 4 20 dispersion a 4O A AC 10 pm 6O Core Ge02 Slog A Cladding Sioz l i i l l 1 o 10 11 12 13 14 15 16 17 Mum 39 Figure 119 Dispersion of a single mode fiber After D B Keck 12 Figure 26 State of polarization in a birefringent ber over one beat length Input beam is linearly polarized at 45 with respect to the slow and fast axes 20 i i I 2 10 w Standard g Dispersion flattened E o C 9 g Dispersion shifted Q 10 20 J l l l I 11 12 13 14 15 16 17 Wavelength um FIGURE 211 Typical wavelength dependence of the dispersion parameter D for standard dispersion shifted and dispersion attened bers a d e i f FIGURE 216 Several index pro les used in the design of single mode bers Upper and lower rows correspond to standard and dispersionshifted bers respectively l rquot b l quot 39 C m 7 Optical guide with grating Bragg re ector l i I N Either reflector or grating 39 Figure 1430 Distributed Bragg reflection DBR laser V Tilted to suppress AR coating of FP mode M4 SiN film to suppress FP mode thicai guide Figure 1431 Distariibuiz ieedbacik IDFi laser Optical output 1w n Contact SiSio2 mirror 39 substrate 39 quot InGa ASP aetiiie tcg39ion 39 Current blocking region SiA1203 mirror Au heat sink FIGURE 427 Basic architecture of a vertical cavity surfaceemitting laser mirror Negative electrode Cavity lt6 1 3yum nAvlo a GaolAs Active GaAs P39A39l39oe GaO7AS Insulator Figure 1429 Surface emitting SE laser Semetimes this laser is called a vertical cavity surfaceemitting laser VCSEL
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