Light spectral filtering based on spatial adiabatic passage

We present the first experimental realization of a light spectral filter based on the spatial adiabatic passage technique. We demonstrate
that a fully integrable CMOS-compatible system of three coupled identical total internal reflection silicon oxide waveguides with
variable separation along their propagation direction can be used simultaneously as a low- and high-pass spectral filter within the
visible range of wavelengths. Light is injected into the right waveguide, and after propagating along the system, long wavelengths are
transferred into the left output, whereas short wavelengths propagate to the right and central outputs. The stopband reaches values up
to 11 dB for the left output and approximately 20 dB for the right plus central outputs. The passband values are close to 0 dB for
both cases. We also demonstrate that the filtering characteristics of the device can be controlled by modifying the parameter values,
which define the geometry of the triple-waveguide system. However, the general filtering behavior of the system does not critically
depend on technological variations. Thus, the spatial adiabatic passage filtering approach constitutes an alternative to other integrated
filtering devices, such as interference or absorbance-based filters.