DBR active optical filters: transfer function and noise characteristics

A theoretical model of distributed Bragg reflector (DBR) active filters is presented and verified experimentally through measurements of the transfer function and the noise spectra. The theory allows simple yet accurate evaluation of the transmission transfer function and of the noise properties of this class of filters. A conventional DBR laser device used as a filter is shown, experimentally and theoretically, to have two drawbacks: a multilobe transfer function and small gain (less than 10 dB facet-to-facet). It is shown how both problems can be overcome via reduction of two key device parameters: the grating coupling coefficient and the physical length of the active and/or phase control sections. This technique can lead to devices with attractive properties, having a gain of 35 dB, sidelobe suppression of 32 dB, and bandwidth as narrow as 1 GHz.<
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