Faculté des sciences

Resonant grating filters for microsystems

Niederer, Guido ; Herzig, Hans-Peter (Dir.)

Thèse de doctorat : Université de Neuchâtel : 2004 ; 1745.

In the present work we report on the design and characterization of a tunable optical filter for use in a compact add-drop multiplexer. The optical filter is a resonant grating filter (RGF) consisting of a planar waveguide and a grating parallel to the surface. A resonance occurs when the incoming light is diffracted by the grating and matches a mode in the waveguide. Numerous aspects of the... Plus

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    Summary
    In the present work we report on the design and characterization of a tunable optical filter for use in a compact add-drop multiplexer. The optical filter is a resonant grating filter (RGF) consisting of a planar waveguide and a grating parallel to the surface. A resonance occurs when the incoming light is diffracted by the grating and matches a mode in the waveguide. Numerous aspects of the modeling, design optimization, fabrication tolerances and characterization are addressed. A particular emphasis is given to miniaturization of the device for use in a MEMS microsystem. We have investigated tunable, oblique incidence resonant grating filters covering the C-band as add-drop devices for incident TE-polarized light. The fabrication tolerances as well as the role of the finite incident beam size and limited device size are addressed. The maximum achievable efficiency of a finite-area device as well as a scaling law relating the resonance peak width and the minimum device size are derived. In a filter application it is important to have negligible shape changes over the tuning range. This is shown in theory as well as in experiments, where we measured the resonance peak from 1526nm at 45° angle of incidence to 1573nm at 53° with a full width at half maximum of 0.4nm. In this range the shift of the peak wavelength is linear with respect to a change in the incidence angle. Infinite beams and devices show ideal performance. The performance decreases for smaller systems. We present the limits of miniaturization. Theoretical modeling shows that the minimum size is in the millimeter range. Additional aspects, such as the influence of wavefront distortion of the reflected and transmitted beams are studied. Wavefront distortions are important for fiber coupling. Finally polarization independent configurations are studied, leading to a novel tunable design