ECE227A Final Solutions 2005

ECE227A Final Solutions 2005 - Final ECE 227A December 7,...

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Unformatted text preview: Final ECE 227A December 7, 2005 Department of Electrical and Computer Engineering Universin of California, Santa Barbara (40 pts) 1. Two different types of DFB lasers are fabricated from the same 1.55 pm wavelength wafer that contains a uniform grating and 2 pm wide BH lateral waveguides. The first are stande AR—coated DFB lasers with a 500 nm length. The threshold current on these is measured to be 30 mA and the differential efficiency, considering both ends, is found to be 0.5. As expected two degenerate axial modes are observed. The second type of laser is formed by cleaving out 250 um length devices from this same wafer, and then applying AR coatings to only one end. In this case the spectra of some devices show marginal MSRs, while others show relatively good MSRs. The devices with the best MSRs are measured, and these provide threshold currents of 30 mA and differential efficiencies, considering both ends, of 0.6. From other measurements is also determined that the threshold modal gain of these shorter lasers is twice that of the longer lasers. 3 a What is m. the internal efficiency? i 6 b. What is <a,->, the incremental modal loss? a c. What is K, the grating coupling coefficient? 9 d. Assuming a gain characteristic of the form, I'g = Fgo 1n(J/J,,), what are Fgo and J,? 8 e. What MSR would be expected in the better 250 um devices, if operated at twice threshold with a, q, = 105? : t I!“ - 0,03A : k/L “L ill.) I ETA - 732m”: '94.“ ‘ fl“ [‘3 '2 [V0 5%: Farl§gl_ [5. $611.4 = W?!) (131mm 12"; _ P w 51:: '6’??? [y/ 31} : “77/604 "W3 A: e = my»? 1/ 711’5 IS 6/ 14! ' Mumwmifi>flfié % afifip %_' (Ulflu; QMA LW( IfMQw) ; A / /“44 7470745» $404435; 233% fl$éfiw) 2 50 04'“. 6d FHO‘M,’ (7:1I_ Fig/7 :ZZJ" 2%m/MJ (P —«,\z = mar/(5 M “’5” W _ t X 6 , ., gfla" 5/ 3L3! 0%» ,77 v! /o / X r: 14 G 14x) '2 g,£fX/o.y4~_l 6w" ; 1 IVER-r... ? fl“??- /'7 Barn-«(NJ 4'5 .— 7’523‘ I a»- M— :) 35,3413 MQW and inirrors. g (b) What is the internal efficiency? (0) What is the one-pass intemal modal loss, Lpu<q~>? ’1 (d) What is the confinement factor? ’1 (e) Assuming a gain characteristic of the form, g = go [nu/1,), what is go and J,, within each QW? @ /¢¢ M2 332 fi q’m): % ’71:”? / f :71: §.Vé I ‘ C 0‘) o. ?757.(‘ 77%): A 5%! = 0,00%; ¢ J— : 270/15 > a" N / 77") / am; @ [3 NW 05/: 7’03): 0,0/200 , J— : $5.33 -_ I '75) C /://J a. 0,7:‘L0.él M7471? / / MA: 11",?) pay/A; Ar} / F ,‘_ fi—(dgxeg (“>10m "L : i— + (7’ 7m 7m 7w 5907')’%‘z/’0755 f‘fi/JC) 4:! M 575/ if 41 dame/<7? "‘ W cm 3 w 4.04M _, ,5ng <0 dflvefiw’i“ (Io/J32!) LY A I . .éL _ 2,; 4447 - 01522;; AK 20/.é—Y123 “3‘27 = 10—020;- . /l P, ,w\ ! 0.60652.‘-r : W4. [-zmz = 3449: + 2: RIM” : 2 g6ox~ yam-2.93) + QZfT'é") + 5D,,” 2 275-1311!) + } SDM‘ 3 //‘/3>p_q I ’. (0(5) : g7cm—/ W.» 4479: =90“): ’ F, = (3400“: 03775” “7 W (turf/v “9 CW€¢n/'Ac 42 - I I r 4 L o, 727 (‘ghm 1m - 0.00052 r 0.009% : glam/3 {bf/91m t 6.0065’2-4- (10/200 : 0,0/33’2 f—L Pips/L 2 a” La. : /I?(30h|)»: (5/77)” - ,O/l : i = o </Y [m 6.0V7Z 51/57»; ’— 2 [26' Afi/ 362 \ x u - 0, 0/351 31,05) * W : 3 L/gO‘MV ;/./ZY r25) 0.05.3 //— 77’,(2)(/o"9 Em" 2:75 K ova/h» (25W) 3. An edge-emitting, InP-based, l550nm wavelength DBR laser, similar to Fig. 3.16, is formed with gain. phase and grating sections measuring 400, 100, and 200 microns in length, respectively. The modal loss in the gain section is known to be 15 cm“, and it is found to be 5 cm" in the passive phase and minor secn'ons. The internal efficiency is assumed to be 0.75, and the DBR power reflection and transmission are found to be 0.2 and 0.7, respectively. The other mirror is a cleaved facet. é (a) What is the axial mode spacing? 7 (b) What are the differential efficiencies out of each end? Q (c) Ifwe wish to move the DBR Bragg wavelength by 5 run, by how much does the effective index of the minor need to be shifted? Md) By how much would an axial mode shit! for the index shifl of (c)? ,lc/mm /l. :o.7\( I 0‘7 1/23/1— 256 0404 5p,“ «IL/[ra/Lafl'fill 44 ink“ Z t [a I - K. P / 7(0” 7‘- ;- [Cf/3447577..» Fur 0x111 “17,5 Silt? r7{// )Itld/ 2%? flax/mg 4,5, (“Maia/z Mu #444,, I W5 - 0 (WM 714292? 4/ A.“ [face day «4 “75%; It'qu > M1 M mask“ .— Ink): _ 0,2 war» 04%?) w r / _ 2i I}a 5.7 ~ 477/7 ‘— , , , X 2 0.5M ' - 0572 " A] / X, 002». ’ 9'56‘5/ ...
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ECE227A Final Solutions 2005 - Final ECE 227A December 7,...

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