A hybrid structure combining square and hexagonal photonic crystal lattices is presented. This structure, which we refer to as heterostructure, offers the ability to tailor, optimize, and match the band structure of different lattices. The availability of heterostructures in photonic crystals opens abroad range of possibilities for optical device development. In particular, heterostructure photonic crystals are well suited for the application of optical beam splitting (Y coupler) and combining. Numerical experiments performed by use of the finite-difference time-domain method are shown to illustrate the device implemented in both unistructure and heterostructure lattices.