Light spectral filtering based on spatial adiabatic passage

Abstract

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. Researchers have developed a waveguide-based scheme for filtering different wavelengths of light that suits chip-level integration. The approach, developed by Ricard Menchon-Enrich and co-workers from Barcelona, Spain, and Lausanne, Switzerland, relies on wavelength-dependent coupling between three closely spaced silicon oxide waveguides. When white visible light is launched into the right waveguide input, the red spectral components are transferred to the left waveguide output while green and blue components propagate to both right and central outputs. This ‘spatial adiabatic passage filter’ represents an alternative to filters that rely on either absorption or interference, which can be lossy or inconvenient to implement. Furthermore, because this filter is compatible with complementary metal–oxide–semiconductor fabrication, it could potentially be combined with other optical and electronic devices in a monolithic photonic integrated circuit.