High quality 64 channel 15 km AM-FDM transmission using low distortion characteristics DFB laser module

The distortion mechanism of distributed-feedback (DFB) laser modules has not yet been studied extensively. The authors report an additional distortion degradation characteristic, which is caused by the etalon interference effect in a laser module. This effect occurs between two or more reflection facets of the optical components in a module, such as optical lens, polarizers, Faraday crystal, and fiber facet. The calculation results for the second-harmonic distortions (HM2) show that less than 0.1% power reflection from both etalon facets can degrade HM2 up to 50 dB in certain conditions. It is notable that HM2 and HM3 values change periodically against the center wavelength change, and that HM2 and HM3 take two peaks in the free spectral range (FSR) of the etalon cavity.<>