having the combined wavelengths e g u03bb 1 u03bb 2 u03bb 3 u03bb 4 fig5 shows a sandwiched structure 500 that embeds the two stages of couplers 502 in the depolarizers specifically fig5 shows four input signals are depolarized first the outputs therefrom are coupled to the couplers 502 the output from the couplers 502 are further depolarized by one or more of the depolarizers as far as the couplers are concerned there are also ways to combine two inputs fig6 a and fig6 b show respectively two possibilities respectively referred to as inner cross over structure and outer cross over structure beside using the above described combination of a spectrum combiners e g couplers and separate depolarizers 2 u00d7 2 couplers may be used to serve the same purpose of the spectrum combining function and depolarizing function in a more integrated way fig7 shows an embodiment 700 based on 2 u00d7 2 couplers with 50 coupling ratio various 2 u00d7 2 couplers are formed to provide inner and outer feed back loops the depolarizing functions are thus achieved through feed forward lines from other 2 u00d7 2 couplers the first group 702 including 16 couplers form a basic unit this unit can be cascaded further to further perform spectrum combination and depolarization by changing the two inputs and.