  In this paper, by cascading several bichromatic photonic crystals we
demonstrate that the quality factor can be much larger compared with that in an
isolated cavity without increasing the total size of the device. We take
lithium niobate photonic crystal as an example to illustrate that the simulated
quality factor of the cascaded cavity can attain 10^5 with a 70{\deg} slant
angle, which is an order of magnitude larger than that in isolated cavity. The
device can be fabricated easily by current etching technique for lithium
niobate. We have fabricated the proposed device experimentally including holes
with 70{\deg} slant angle. This work is expected to provide guidance to the
design of photonic crystal cavity with high-quality factor.
