  Periodic or gradient subwavelength structures are basic configurations of
photonic crystals and metamaterials. While the numerical simulations predict
trivial loss, but the fabricated photonic crystal waveguides by E-beam
lithography and standard dry etching shows unacceptable loss beyond 10 dB.
Nanofabrication variation introduced geometric inhomogeneity is considered as
the primary cause of the deleterious performance. The deep UV photolithography
in CMOS foundry is a large-scale parallel processing, which can significantly
suppress the fabrication-related inhomogeneous offsets and thus the optical
linear loss. Here we demonstrate ultra-low loss photonic crystal waveguides
with a 300 mm multi-project wafer run. For sub-millimetre long photonic crystal
W1 waveguides, consistent performance of 2 dB total loss and 40 dB extinction
ratio are observed across different dies.
