EC524 2013 4 1 1 Sheets

 

ARAB ACADEMY ACADEMY FOR SCIENCE & TECHNOLOGY & MARITIME MARITIME TRANSPORT

COLLEGE OF ENGINEERING & TECHNOLOGY  Electronics and Communications Departmen t

Lecturer: Prof. Dr. Moustafa Husse!   Dr. He%a A. Fae'

O"tca# Co$$u!cato!s Course ( EC)*+ Ter$: ,t- & /t-

S-eet 012 333333333333333333333333333333 333333333333333 333333333333333333333333333333 33333333333333333333333333333333 33333333333333333333333333 333333333 O"tca# F%er Co!!ecto!4 O"tca# Sources a!' O"tca# F%er Sste$s 333333333333333333333333333333333333333 1] An optical fiber has a core refractive index of 1.5. Two lengths of the fiber with smooth and perpendicular (to the core axes) end faces are butted together. Assuming the fiber axes are perfectly aligned calculate the optical loss in decibels at the !oint (due to "resnel reflection) when there is a small air gap between the fiber end faces. (#.$% d&) '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ] A silica multimode step index fiber has a core refractive index of 1.%. *etermine *etermine the optical loss in decibels due to "resnel reflection at a fiber !oint with+ a. a small air gap. b. an index matching epoxy which has a refractive index of 1.#. ,t may be assumed that the fiber axes and end faces are perfectly aligned at the !oint.   (#.$1 d&  $.-x1#'$ d&) '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' $] The "resnel reflection at a butt !oint with an air gap in a multimode step index fiber is #.% d&. *etermine the refractive index of the fiber core.   (1.5)   '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ] A ruby laser contains a crystal length  cm with a refractive index of 1./-. The pea0 emission wavelength from the device is #.55 µm. *etermine the number of longitudinal modes and their freuency separation.   (.%x1#5  .1 234) '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 5] The longitudinal modes of a gallium arsenide in!ection i n!ection laser emitting at a wavelength of #.-/ µm are separated in freuency by /- 234. *etermine the length of the optical cavity and the number of longitudinal modes emitted. The refractive index of gallium arsenide is $.%. (15#µm  11) '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' %] An An optical fiber lin0 of length  0m comprises a fiber cable with an attenuation of 5 d&.0m'1. The splice losses for for the lin0 are estimated estimated at  d&.0m d&.0m'1 and the connector losses at the source and detector are $.5 and .5 d& respectively. ,gnoring the effects of dispersion on the lin0 determine the total channel loss. ($ d&) ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 

/] The following parameters are established for a long'haul single'mode optical fiber system operating at a wavelength of 1.$ µm. Mean power launched from the laser transmitter Cabled fiber loss Splice loss Connector llo osses at th the tr transmitter an and receiver Mean power reuired at the !"# recei receiver$ ver$ -+ when operatin% at 3& Mbit's (B)* 10 , when operatin% at 400 Mbit's (B)* 10 -+, *euired safet mar%in

- 3 dBm 0.4 dB.km-1 0.1 dB.km-1 1 dB each - && dBm - 44 dBm  dB

stimate+ a. the maximum possible lin0 length without repeaters when operating at $5 6bit7s (&8 1#'). ,t may be assumed that there is no dispersion'euali4ation dispersion'euali4ation penalty at this bit rate. b. the maximum possible lin0 length without repeaters when operating at ## 6bit7s (&8 1#') and assuming no dispersion'euali4ation penalty at this bit rate. c. the reduction in the maximum maximum possible lin0 length without repeaters of (b) when there is a dispersion'euali4ation dispersion'eua li4ation penalty of 1.5 d&. ,t may be assumed for the purposes of this estimate that the reduced lin0 length has the 1.5 d& penalty. (-% 0m  % 0m  $ 0m) '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' -] 9omponents 9omponents are chosen for a digital optical fiber lin0 of overall length / 0m and operat operating ing at '1 a # 6bit.s  using an 8: code. ,t is decided that an ;* emitting at #.-5 µm with graded index fiber to a p'i'n photodiode is suitable choice for the system compo components nents giving no dispersion'euali4ation penalty. An ;* which is capable of launching an average of 1## µ< of optical power (including connector loss) into a 5# µm core diameter graded index fiber is chosen. The proposed fiber cable has an attenuation of .% d&.0m'1 and reuires splicing every 1 0m with a loss of #.5 d& per splice. There is also connector loss at the receiver receiver of 1.5 d&. d&. The The receiver receiver reuires mean mean incident power of ' 1 d&m d&m in in order to '1# give the necessary &8 of 1#  and it is predicted that a safety margin margin of % d& will be reuired. 0ew rays are accepted into a large core diameter (compared to the wavelength of the transmitted transmitte d light) step index fiber in air at a maximum maximum axial axial angle of  o. nellGs ;aw 9ritical Angel

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