Ch4sec6 - THE FIBER FORUM Fiber Optic Communications...

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THE FIBER FORUM Fiber Optic Communications JOSEPH C. PALAIS PRESENTED BY
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Joseph C. Palais 4.6 2 Section 4.6 Integrated Optic Components 4.6.1 Passive Devices Integrated Optic Directional Coupler Substrate L P 1 P 2 P 3 P 4
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Joseph C. Palais 4.6 3 Passive Devices For an ideal (lossless) coupler the relative output powers are given by: P 2 /P 1 = cos 2 ( π L/2L c ) P 3 /P 1 = sin 2 ( π L/2L c ) where L c is called the coupling length . Any splitting ratio between the two output ports is possible by appropriate choice of length L.
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Joseph C. Palais 4.6 4 Passive Devices Example: If the actual length L of the coupling region is L c /2, compute the output coupling. P 2 /P 1 = cos 2 ( π /4) = (0.707) 2 = 0.5 P 3 /P 1 = sin 2 ( π /4) = (0.707) 2 = 0.5 50% of the power exits both of the output ports. Since 10 log P 2 /P 1 = 10 log 0.5 = 3 dB this is a 3-dB coupler
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Joseph C. Palais 4.6 5 For the ideal coupler, the coupling to port 4 (the isolated port) is zero. Thus, 10 log P 4 /P 1 = 10 log 0 = - Passive Devices
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Joseph C. Palais 4.6 6 An integrated optic power splitter is constructed with the waveguide pattern indicated below: Passive Devices P in /2 P in P in /2
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Joseph C. Palais 4.6 7 Multiport splitters can be constructed by cascading 2-port couplers as indicated schematically below: Passive Devices 1 x 8 Coupler
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Ch4sec6 - THE FIBER FORUM Fiber Optic Communications...

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