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An asymmetry in the output power and the low-frequency noise emitted from the rear and front facets of index-guided semiconductor lasers with a large percentage of optical feedback into the front facet is reported. Transitions from coherent to incoherent feedback-induced properties by modulation of the feedback path length can be distinguished in the output power versus current (L-I) curve. A cross-over point is found only in the front facet L-I curve corresponding to a minimum in the noise. A model is presented which correctly describes the asymmetry between the L-I curve of the front and rear facets. It also predicts the observed cross-over point in the front facet L-I curve. [ABSTRACT FROM AUTHOR]