Methods and structures are disclosed demultiplexing optical signals
transmitted over an optical fiber into a silicon substrate and to
multiple detectors. The silicon substrate has two spaced-apart surfaces
and a diffractive element disposed adjacent to one of the surfaces. Each
of the optical signals corresponds to one of multiple wavelengths. The
optical signals are directed into the silicon substrate along a path
through the first surface to be incident on the diffractive element. The
path is oriented generally normal with the first surface and/or with the
diffractive element, which angularly separates the optical signals such
that each of the wavelengths traverses through the substrate in a
wavelength dependent direction to the first surface. Each optical signal
is steered from the first surface towards the second surface to be
incident on different optical elements that direct them generally normal
to the first surface to be incident on one of the detectors.