ece228 lecture 10

ece228 lecture 10 - Bowers ECE 228A Transmitters Lecture...

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Bowers ECE 228A Transmitters Lecture #10 John Bowers ECE 228A Read Chapter 3 Midterm Tuesday, May 4 hursday May 6: Start at 12:45 Thursday, May 6: Start at 12:45
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Bowers ECE 228A Kerr Effects A A A 2 3 2 1 1 ptical power in the fiber (Silica) can alter A A j t t j A z 3 3 2 2 6 2 Optical power in the fiber (Silica) can alter the index of refraction • All the resulting effects are generically Kerr Effect term called as “Kerr effects” • In general, Kerr effect induces a phase odulation on the signal that is n = n 0 + n 2 I modulation on the signal that is proportional to its instantaneous power level • The phase modulation is then converted to amplitude modulation by fiber dispersion
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Bowers ECE 228A Self-Phase Modulation (SPM) Optical power in the fiber (Silica) can alter the index of refraction and therefore the phase of the optical signal via the nonlinear Kerr Optical effect: Single Channel (SPM) Silica Fiber n = n 0 + n 2 (P opt /A eff ) P opt  2 6 5 2 2  P A L n opt eff eff SPM 1 dB/km 0.25 = and m 1.55 for , ) ( ) ( 4 035 . 0 mW P m w hase modulation ectral broadening P opt ( t )   ( t ) phase modulation spectral broadening 1 A. R. Chraplyvy, IEEE JLT, Vol. . 8, No. 10, p. 1548, Oct. 1990.
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Bowers ECE 228A Cross-Phase Modulation (XPM) In multichannel propagation (WDM), the phase of a given channel can be affected by ther channels in the fiber leading to XPM The strength of this effect depends on the other channels in the fiber leading to XPM. The strength of this effect depends on the alignment of bits between channels and fiber dispersion (pulse walk-off). 5 2 n 2 L eff or 2 Channels Multi-Channel (XPM)  XPM 2 SPM 3 A eff P opt , For 2 Channels XPM XPM N ( m ), For N channels m 2 XPM combines in a very complex way with dispersion, due to the walk-off yp y p , effect among bits in adjacent channels As a rule of thumb, the resulting XPM effect is inversely proportional to the (local) dispersion value 1 1 A. R. Chraplyvy et. al., IEEE JLT , Vol. 2, No. 1, 1984. 2 A. R. Chraplyvy, IEEE JLT , Vol. . 8, No. 10, p. 1548, Oct. 1990. D
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Bowers ECE 228A Fiber Four-Wave Mixing (FWM) • Four-wave mixing in optical fibers is a complicated rocess that produces nonlinear harmonics process that produces nonlinear harmonics • Two optical frequencies at 1 and 2 will generate light at two new frequencies   and . • When more than two channels are present, these new frequencies can interfere as crosstalk with existing channels as shown below.
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This note was uploaded on 05/18/2010 for the course ECE 228a taught by Professor Bowers,j during the Spring '08 term at UCSB.

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ece228 lecture 10 - Bowers ECE 228A Transmitters Lecture...

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