The Effect of Spatial Correlation on the Linewidth Broadening in Tunable Laser Diodes

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Spectral linewidth broadening by carrier density fluctuations in electronically wavelength-tunable diodes is analyzed considering the spatial correlation of the fluctuations. The correlation over the entire cavity length occurs via currents flowing longitudinally along the highly conducting metal contacts. These currents link together first spatially independent potential fluctuations associated with the carrier density fluctuations. The analysis shows that at small tuning currents, an almost complete correlation occurs, while at large tuning currents, the most usual approximation of uncorrelated fluctuations is asymptotically approached. A genuine broadening mechanism in tunable laser diodes due to finite cladding layer resistance Rsis further discovered. Taking these effects into account, the present analysis contains the previous ones as limiting cases, and allows us to estimate their respective ranges of validity. The spectral broadening is calculated for typical tunable twin-guide (TTG) lasers, revealing an almost step-like onset of the broadening at small tuning currents. The most effective way to keep the broadening small is to reduce the internal resistances and to employ a low-impedance bias source.

Original languageEnglish
Pages (from-to)1799-1804
Number of pages6
JournalIEEE Journal of Quantum Electronics
Issue number6
StatePublished - Jun 1993
Externally publishedYes


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