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Unformatted text preview: 8.1 Dry ﬁbers have acceptabie losses over a spectrai region extending from 1.3 to 1.6 ,um. Estimate the capacity of a WDM system covering this entire region using 40—Gb/s channels spaced apart by
50 GHZ. We ﬁrst convert the 300mn wavelengih range to frequency range as c c mamW)
Amm—_ﬂ3 ﬁ—Ww~=@ﬂnc
V M a “Gamma Z For a channel spacing of 0.05 THz, the number of channels N is given by Nmﬁﬂmﬁ:%5 Thus the WDM system capacity is NB m 865 X 40 2 34.6 Tia/s. 8.3 A 128 X 128 broadcasz star is made by using 2 X 2 directional couplets, each having an insertion loss of 0.2 (113. Each Channei Iransmiis 1 mW of average power and requires 1 jLL‘W of average received power for operation a: I Gb/s. What is the mimum transmission distance for each channeI? Assume
a cabfe loss of 0.25 dBﬂcm and a loss of 3 dB from connectors and splices. For a broadcast star made by using 2 x 2 directionai coupiers, the power from each port is obtained
using Eq. (5.2.2) or
PN = (Pr/MU w area”. The 0.2 dB insertion loss of each directional coupier transiates into i w 5 "2 0.955. Using PT : 1 mW,
and N m 228, we ﬁnd PN : 5.66 yW or "222.47 dBm. Since receiver requires E ,LLW or —30 dBm,
total E05365 should be be at most 7.53 dB, or afLmi am 2: 7.53 dB. for given values of losses, me m 18.} km. 8.5 A Fabrwaerotﬁlter is used IO select 100 channels Spaced. apart by 0.2 nm. What should be the length and the mirror reﬂectivizies of the ﬁlter? Assume IO—Gb/s bit rate, a refractive index of 1.5 and an. operating wavelength of 1.55 34m. The free spectral range (FSR) corresponds to the spacing among transmission peaks. For the like: to be able to select all N channels, FSR should be larger than NAvCh, where Avg;2 is the channei spacing. Using FSR = Cf (2311.) > NAvck, we obtain
L < 6/ (ERNAVCh). The 0.1mm channel spacing corresponds to Avch : L‘(A}LCh)/l2 m 25 GHz. Using this value with ' n 2 1.53110 N: 3000, we: obtain L < 80 pm. The mirror reﬂectivity R of the ﬁlter is obtained from Eq. (8.2.2): min/'1?
_. 1 l N<ngFm where “as m B/Avm. Using B m 10 Gin/s and n5 2 0.4,. we obtain R > 98.7% f0; N = 100. 8.12 Use a single ﬁber coupler and two ﬁber gratings Io design an addmdrop ﬁfter. Explain how such a device ﬁrzcrions. Figure 842(1)) of the textbook shows a design that requires two ﬁber couplers and two ﬁber gratings. Its operation is based on a Mach~Zehnder interferometer. If we remove the second coupier, the device can still be used to drop a channel at port 2‘ However, it cannot be used to add a channel by launching
it at port 2. Thus, the only solution is to fabricate the two gratings within the two cores of a ﬁber coupler. The
gratings would reflect only one channel at the Bragg wavelength, which will appear at the unused
inpot port. The remaining channel will appear at one of the output ports. We can also add the channel at the Bragg wavelength by launching it from the second output port. b 3 er: 7 \
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This note was uploaded on 03/06/2012 for the course ENGINEERIN 605 taught by Professor Rahmir during the Spring '11 term at Wisconsin.
 Spring '11
 Rahmir

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