similar performance to the existing methods referring now to fig4 showing a ta 101 without wavelength selector and some transponders linked to the ta 102 103 the ta 101 receives the input signals from different input ports degrees of the node 104 105 and use a wavelength selective switch 106 to select the wdm channels that need to be dropped in the ta the maximum number of dropped channels for the ta is denoted as n these channels are illustrated in the spectrum 107 these signals are amplified by an optical amplifier 108 and sent to a 1 n optical splitter 109 each of the n splitter outputs 110 has the same number of drop channels as 107 each splitter output is connected to the input of a transponder such as 102 103 the receiver 111 of the transponder uses coherent receiving technique it contains a coherent mixer or called 90 degree optical hybrid it can be polarization insensitive coherent mixer or polarization diversity coherent mixer 112 which mixes the input dropped signal 110 and a cw signal from a local oscillator laser 113 since this is for colorless roadm each transponder is colorless which means that the local oscillator laser is tunable its wavelength is tuned to a single particular wdm channel 114 which has the wavelength of the targeted drop channel using the technique despite the transponder receives multiple wdm channels from the ta only the specific target channel will be received due to coherent receiving technology the coherent mixer produces different vectorial additions of the lo and the targeted drop channel.