Resonant gratings are high-index structures in a low-index environment with periods slightly below the wavelength of light (approx. λ/2 up to λ). Particularly gratings with high-index contrast (high contrast gratings) have attracted recent interest in applications ranging from mirrors in semiconductor lasers (vertical-cavity surface-emitting lasers), filters for particle sensors and highly efficient polarizers up to low-noise optical components for high precision metrology. For the latter particularly highly reflective monolithic gratings made of crystalline silicon are interesting because they promise a reduction of Brownian thermal noise compared to conventional multilayer based mirrors. For the detection of gravitational waves this can result in an enhancement of the detection probability by up to a factor of 1000. In order to evaluate the suitability of waveguide gratings for future detectors different silicon based grating topologies for cavity mirrors and diffractive beam splitters are investigated.
Making use of the broadband reflectivity of silicon based resonant gratings it is also possible to design transmissive optical filters that provide a defined selectivity with respect to polarization, wavelength and angle of incidence. By means of the geometric grating parameters the transmission window can be adjusted to a desired target angle of wavelength. The large spectral bandwidths of the silicon gratings can also be utilized to realize band blockers for sensor applications. They allow for a decomposition of optical signals into a desired number of channels, e.g. in multispectral cameras.

mono 1D_SK
SEM-Image of monolithic waveguide grating with 1D periodicity.(rights: IAP)
mono 2D_SK
SEM-Image of monolithic waveguide grating with 2D periodicity.(rights: IAP)

SEM-Image of a stacked waveguide grating with 1D periodicity.(rights: IAP)
SEM-Image of angular bandpass filter based on a resonant silicon grating.(rights: IAP)

Angular dependent transmittance of the realized bandpass filter.(rights: IAP)

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