two mdcs can be combined with mcgs to form an exemplary low loss add drop multiplex device as shown schematically in fig7 fibers 71 72 73 and 74 are single mode fibers all other fibers are multimode channels u03bb 1 u03bb 2 u03bb n all 0 1 enter the device on fiber 71 with channels u03bb 2 u03bb n propagating through the device substantially without attenuation to appear at fiber 74 the u03bb 1 radiation is reflected at grating 75 and transformed into 1 1 it propagates to grating 76 where it is reflected and transformed into 0 1 which propagates to fiber 72 where it is available for detection or other utilization add channel u03bb 1 0 1 propagates from fiber 73 to grating 77 where it is reflected in the 1 1 mode the 1 1 radiation propagates to grating 75 where it is reflected and transformed to 0 1 which then propagates to fiber 74 where it is available for utilization together with u03bb 2 u03bb n all as 0 1 the add channel is designated u03bb 1 to indicate that the wavelength is the same as that of the drop channel but that the information content is different those skilled in the art will appreciate that the above described embodiments.