  Dense waveguide arrays with half-wavelength-pitch, low-crosstalk, broadband,
and flexible routing capability are essential for integrated photonics.
However, achieving such performance is challenging due to the relatively weaker
confinement of dielectric waveguides and the increased interactions among
densely packed waveguides. Here, leveraging the artificial gauge field
mechanism, we demonstrate half-wavelength-pitched dense waveguide arrays,
consisting of 64 waveguides, in silicon with -30dB crosstalk suppression from
1480nm to 1550nm. The waveguide array features negligible insertion loss for
90-degree bending. Our approach enables flexibly routing a large-scale dense
waveguide array that significantly reduces on-chip estate, leading to a
high-density photonic integrated circuit, and may open up opportunities for
important device performance improvement, such as half-wavelength-pitch OPA and
ultra-dense space-division multiplexing
