Method of extending the capture range of a wavelength monitor and a wavelength monitor and laser system therefor

The invention relates to a method of extending the capture range (CR) of a wavelength monitor for the lasers of a wavelength division multiplex (WDM) transmission system wherein the capture range (CR) comprises one wavelength period (FSR) of a periodic error signal (E) generated with the aid of the wavelength filter (4), the capture range contains a desired wavelength (₀) of a plurality of equidistant wavelengths (_i, _i+1, _i+2, . . . ), each of the lasers of the WDM transmission system is set at a desired wavelength (₀) by comparing the error signal (E) with an comparison value (C1 or C2), that is unique in the capture range (CR) for a chosen slope sign, the wavelength period (FSR) of the error signal (E) is set such that it corresponds to double the wavelength spacing (A) of two adjacent wavelengths of the WDM transmission system and the desired wavelength (₀) is set taking into account the slope sign of the error signal (E), and further relates to a wavelength monitor and laser system therefor.