Filtering of directly modulated laser signals by arrayed wavelength grating (de-)multiplexers.
|Student Report - Yi An - February 2006 |
Student report, COM-DTU, Department of Communications, Optics and Materials, Technical University of Denmark, Kgs. Lyngby, Denmark.
17 February 2006. Supervisors: Christophe Peucheret
, Jorge Seoane
Cost effective Wavelength Division Multiplexing (WDM) networks call for the use of 10 Gbit/s directly modulated lasers. However, the inherent frequency chirp of directly modulated lasers acts as a limiting factor on the performance of lightwave systems. The effective bandwidth of cascaded filters is smaller than that of any individual filter. The random misalignment between the center frequency of the light source and the filters will have a severe degradation on the system and even blind it, as it is combined with the concatenation. I report the computer simulation results of the signal quality and misalignment tolerance of directly modulated laser (DML) signals and externally modulated laser (EML) signals filtered by cascaded ideal Gaussian filters and Arrayed Waveguide Grating de-multiplexer produced by Ignis Photonyx. DML lasers with adiabatic and transient chirp characteristic at 2.5 Gbit/s and 10 Gbit/s are investigated. We found that the adiabatic chirp dominated laser shows an asymmetric sensitivity response to the frequency shift, whereas the response transient chirp dominated laser is symmetric. The pass-band flattened AWG de-multiplexer shows a better detuning tolerance than the ideal Gaussian filter with the same 3-dB bandwidth. And I report the experimental results of filtering the DML and EML signals by an AWG de-multiplexer. The response of the AWG filter appears better than the simulation results on EML signals and the results of filtering DML signals show a good match with the simulation results. The extinction ratio for the adiabatic chirp dominated laser can be improved by appropriate misalignment between the laser and the filter center frequencies.
Yi_An_Special_Course.pdf (only available from COMĽDTU)
Record created 2007-07-04, last modified 2008-10-15
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