The excess linewidth broadening of continuously tunable InGaAsP/InP laser diodes at 1.5 &mgr;m wavelength is investigated. Terminal electrical and FM noise measurements indicate that the recombination processes in the forward biased tuning region produce significant 1/fcarrier noise. Below 1 MHz the 1/fnoise dominates yielding a noise enhancement of about 30 dB at 1 kHz. The discrepancy observed so far between theoretically expected and measured spectral linewidth can be well resolved by taking into account this additional noise source. ©1997 American Institute of Physics.