a tri - mode co - boresighted seeker including a primary collecting mirror assembly having a parabolic surface and a forwardly located dielectric secondary mirror assembly including a dielectric mirror coating which reflects infrared energy to an ir detector assembly located on a central longitudinal axis on one side of the secondary mirror while providing substantially unobstructed propagation of millimeter wave rf energy and laser energy in a joint or common signal path therethrough to means located on the other side of the secondary mirror for extracting and diverting laser energy away from the common rf - optical signal path to a laser sensor assembly while causing little or no disturbance to the rf signal as it propagates to a co - located bifurcated waveguide assembly which couples the rf energy to an rf sensor means located behind the primary mirror .