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We have studied the effects of introducing phaseshifts in the active section of a 1.5 µm phaseshift-controlled DFB wavelength tunable filter on tuning range, peak power transmissivity and side-mode suppression ratio (SMSR). The analysis indicates that when φ 1 = φ 4 = π/2 the filter wavelength tuning range is 22.1 Å for the grating coupling coefficient κ = 6 mm −1 while maintaining almost constant transmissivity (gain) of more than 35 dB. The filter SMSR ranges from 11.1 to 25.4 dB. The results for asymmetric values of φ 1 and φ 2 are also given.

A new wavelength‐tunable optical filter which is based on a phase‐shift‐controlled distributed feedback structure with two phase shifts along its active layer has been studied, in particular, the effects of phase shifts on tuning range, peak power transmissivity, and side‐mode suppression ratio (SMSR). The analysis indicates that when ϕ1=ϕ4=π/2, the filter wavelength tuning range is 22.1 Å for the grating coupling coefficient κ=6/ mm while maintaining almost constant transmissivity (gain) of more than 35 dB. The filter SMSR ranges from 11.1 to 25.4 dB. The results for asymmetric values of ϕ1 and ϕ4 are also given. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 119–122, 1997.