  A novel and simple model is proposed for the measurement of the linewidth
enhancement factor (LEF) {\alpha} of multiwavelengths semiconductor laser. It
is based on the suppression characteristics of an arbitrary mode while other
modes are optically injection locked individually. The proposed model can be
used to measure {\alpha} value of individual modes of multi-wavelengths laser
with large mode spacing. As a proof of the concept, the model is used to
experimentally measure {\alpha} of a mode of a slotted Fabry- P\'erot laser
source.
