A four-fiber collimator is coupled to the optics of a single interleaver to produce the functionality of two co-packaged interleavers. Two fibers of the collimator are coupled to the core optics of a single interleaver to produce two pairs of output beams. The other two fibers of the collimators are coupled to receive the reflection output beams. The geometry of the optical fibers in the bundle is controlled to produce interleaver outputs with no offset. In another embodiment two fibers of the four-fiber collimator are coupled as inputs to and the other two fibers as outputs from a Fabry-Perot etalon. The geometry of the fibers and the focal length of the collimator are controlled to produce two outputs with peaks offset by a predetermined amount.