We demonstrate ultrasmall five-port channel drop filters (CDFs) based on a two-dimensional photonic crystal slab. We combine seven photonic crystals with different lattice constants and use light reflections at the different photonic crystal boundaries to control the interference process and achieve a high dropping efficiency. We operate the CDFs in two modes; one requires careful control of the interference process, whereas the other does not. The former can output a narrower signal spectrum than the latter, and CDF design is easier with the latter. Both CDFs achieve a high dropping efficiency and can function in the CL-band.