Lecture7-228a

Lecture7-228a - ECE 228A Fall 2011 Daniel J Blumenthal 7.1...

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Unformatted text preview: ECE 228A Fall 2011 Daniel J. Blumenthal 7.1 Lecture 7 - Dispersion and Chirp ECE 228A Fall 2011 Daniel J. Blumenthal 7.2 General Dispersion Formula This formula can be used to derive dispersion limits in several different transmission scenarios ➥ If we take into account more realistic source and ¡ber effects † ➥ we include β 3 ➥ source with a generic spectral width σ ω σ ( z ) σ = 1 + C β 2 z 2 σ 2 # $ % & ' ( 2 + 1 + V 2 ( ) β 2 z 2 σ 2 # $ % & ' ( 2 + (1 + C 2 + V 2 ) 2 1 2 β 3 z 4 σ 3 # $ % & ' ( 2 ) * + ,- . 1 2 † D. Marcuse, Applied Optics, Vol. 19, p. 1653, 1980 and Vol. 20, p. 3573, 1981. Where V = 2 σ σ ω ECE 228A Fall 2011 Daniel J. Blumenthal 7.3 Dispersion Limits First solution: use a single frequency laser, then spectral width is 0.1 nm and the limit is 167 Gbps km. Second solution: Use dispersion shifted ¡ber, so D~1 ps/nm km. This was done in Japan. Then, the limit is 2500 Gbps km Third solution: Use external modulators. Then Note: Nonlinearity and four wave mixing are big problems in ¡bers with low dispersion 2 / / 1 4 . 4 / 17 / 17 / 4 . 3 . 8 / / 1 1 . 4 1 kmB nm ps nm GHz L nm GHz B B km GHz kmB nm ps nm L • • < = • = • • < σ ECE 228A Fall 2011 Daniel J. Blumenthal 7.4 Dispersion Bit Rate Limitations ➥ Assume V >> 1, C = 0 and β 3 = 0, defne the pulse broadening ¡actor σ D σ = σ 2 + σ D 2 ( ) 1 2 σ D = β 2 L σ ω = D L σ λ ➥ Assume that the bit slot is T B ¡or a bit rate B ➥ Assume that the pulse width at the receiver must not be greater than 1/4 o¡ T...
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This note was uploaded on 11/24/2011 for the course ECE 228a taught by Professor Bowers,j during the Fall '08 term at UCSB.

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Lecture7-228a - ECE 228A Fall 2011 Daniel J Blumenthal 7.1...

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