Waveguide coupling gratings for high-sensitivity biochemical sensors

Grating coupling is now currently used in evanescent-wave biochemical sensors as a waveguide coupling element or as the sensing element. In most coupling cases of practical interest, the Rayleigh-Fourier method is valid, and leads to physically meaningful analytical solutions allowing grating coupling to be designed in simple terms. In the present paper the emphasis is placed on the grating as a waveguide coupling element

Sensitivity enhancement in evanescent optical waveguidesensors

It is shown, that the sensitivity of the effective refractive index on the cladding index in evanescent optical waveguide sensors, can be larger than unity. This implies that the attenuation of a guided wave propagating in a waveguide immersed in an absorptive medium can be made larger than that of a free-space wave propagating through the same medium. The conditions and physical explanation for this puzzling behavior are identified and as a practical application, an absorption sensor, based on a suspended silicon slab waveguide, is proposed where the sensitivity is enhanced by a factor of 1.3

Guided-mode triggered switching between TE orders of a metal-based grating-waveguide

An undulated metal-based dielectric slab waveguide is shown to exhibit a high contrast broadband switching effect in the angular spectrum between the 0^th order Fresnel reflection and the propagating -1^st reflected diffraction orders. The switching trigger is the synchronous collinear coupling of an incident TE plane wave to the close-to-cutoff forward- and backward-propagating fundamental TE_0 mode of the waveguide via the +1^st and -2^nd order of the periodic undulation

Duty cycle tolerant binary gratings for fabricable short period phase masks

Wavelength scale 1D binary gratings of rectangular corrugation profile are often used as diffractive elements acting on incident free space waves under different incidence angle, wavelength and polarization. Their optical function is best understood by considering the interplay of the grating modes propagating up and down the periodic walls and slits of the segmented structure. The interference conditions between modes depend on the difference between the effective index of the interfering modes and on their relative amplitude. This difference and relative amplitude depend critically on the ratio between the wall and slit widths which is difficult to control technologically. The condition for a wide tolerance of the effective index difference and for a balanced mode excitation on the wall/slit ratio is found analytically and once for all for a wide class of 1D gratings. It is also found that TE interference elements may exhibit a very wide wall/slit ratio tolerance domain

Flying phase mask for the printing of long submicron-period stitchingless gratings

International audienceLong and stitchingless gratings are printed by means of a read/write head comprising a phase mask illuminated by an intensity modulated laser beam and a reference grating displacement sensor which dictates the modulation period real time. A nearly perfect grating copying is achieved by fixing the sensor grating scale and the written grating substrate on a long platform sliding under the read/write hea