  We present an alternative approach to the fabrication of highly efficient
superconducting nanowire single-photon detectors (SNSPDs) based on tungsten
silicide. Using well-established technologies for the deposition of dielectric
mirrors and anti-reflection coatings in conjunction with an embedded WSi
bilayer photon absorber structure, we fabricated a bandwidth-enhanced detector.
It exhibits system detection efficiencies (SDE) higher than
$\left(87.1\pm1.3\right)\,\%$ in the range from $1450\,\mathrm{nm}$ to
$1640\,\mathrm{nm}$, with a maximum of $\left(92.9\pm1.1\right)\,\%$ at
$1515\,\mathrm{nm}$. Our measurements indicate SDE enhancements of up to
$\left(18.4\pm1.7\right)\,\%$ over a single-absorber WSi SNSPD. The latter has
been optimized for 1550 nm for comparison and exhibits maximum SDE of
$\left(93.5\pm1.2\right)\,\%$ at 1555 nm. We emphasize that our technological
approach has been tested with, but is not limited to, the wavelengths and
absorber material presented here. It could be adapted flexibly for multi-color
detector systems from the ultraviolet to the mid-infrared wavelength range.
This bears the potential for significant improvements in many current quantum
optical experiments and applications as well as for detector commercialization.
