temperature t 1 as a result a different wavelength signal or set of wavelengths represented by u03bb t is reflected to a circulator 46 b where the wavelength signal u03bb t is sent to a detector 48 b an embodiment of the present invention showing multiple filter elements is shown in fig5 wavelengths u03bb 1 u03bb 2 u03bb n enter for example a 1 u00d7 4 filter element 60 that has one optical fiber 62 coming in four optical fibers collectively shown as numeral 64 and filtered wavelengths coming out and one optical fiber 66 with unfiltered wavelengths coming out the filter element 60 is held at temperature t 1 this filter removes four of the wavelengths from the stream u03bb 1 and three others determined by the total number of channels n and the channel spacing the wavelengths that aren 39 t removed by this first filter then pass on to the second filter element 70 held at temperature t 2 this filter is manufactured in exactly the same way as the first filter but removes different wavelengths through optical fibers 72 as it is held at a different temperature the unfiltered wavelengths pass through an optical fiber 76 into a filter element 80 held at a temperature t n 4 1 the reflected wavelengths signal u03bb n 4 1 passes out through optical fiber 82 eventually the unfiltered wavelengths pass through a filter element 90 heated to a temperature t n 4 and thereby reflects a corresponding wavelength signal through optical fiber 92.