Guido Niederer

Tunable, oblique incidence resonant grating filter for telecommunications

We have designed a tunable, oblique-incidence resonant grating filter that covers the C band as an add-drop device for incident TE-polarized light. We tune the filter by tilting a microelectromechanical systems platform onto which the filter is attached. The fabrication tolerances as well as the role of finite incident-beam size and limited device size were addressed. The maximum achievable efficiency of a finite-area device as well as a scaling law that relates the resonance peak width and the minimum device size is derived. In good agreement with simulations, measurements indicate a negligible change in shape of the resonance peak from 1526 nm at a 45 degrees angle of incidence to 1573 nm at a 53 degrees angle with a full width at half-maximum of 0.4 nm. In this range the shift of the peak wavelength is linear with respect to changes in the angle of incidence.

Design and characterization of a tunable polarization-independent resonant grating filter

We present the design, analysis and characterization of a polarization-independent tunable resonant grating filter. Polarization independence is achieved by setting the plane of incidence parallel to the grating grooves and optimizing the fill factor to obtain a strong reflection peak for all incident polarization states. Experimental measurements show that approximate angular insensitivity to the input polarization orientation concurrent with tunability over a wavelength range of roughly 1530 nm to 1560 nm is achieved. Modulation of the reflectivity peak shape with variations in the orientation of the incidence plane are observed, and found to be in qualitative agreement with theoretical predictions.

Tilting out-of-plane platform for optical applications

In this paper we present a novel concept for a tiltable optical platform. The platform is electrostatically actuated using two vertical comb drives that run through the whole thickness of the wafer causing out-of-plane deflection. The platform measures 2/spl times/2 mm/sup 2/ with a through-hole of 1.6/spl times/1.8 mm/sup 2/. For a first demonstrator an optical filter showing an angular dependency of the reflected wavelength will be glued onto the platform in order to act as a channel add/drop device for telecom applications.

MEMS tunable filter for telecom applications

We report on an angle-tunable oblique incidence resonant grating filter that can be used to drop individual channels from the C-band for incident TE-polarized light. For tuning purpose, the filter is glued onto a tiltable platform of a MEMS device. Continues scanning of the platform allows to monitor channel presence and power. The reflected wavelength is tuned by changing the angle of incidence of the resonant grating filter, which is composed of two thin films with a grating pattern on top of it. The first layer on a glass substrate acts as a waveguide, and the second layer separates the waveguide from the grating. The grating has been patterned by holographic recording and dry etching. The filter works over a wavelength range of 1520-1580 nm and its response has a Lorentian shape with 0.5 nm FWHM peak width. The MEMS part is based on SOI technology and is processed in only two DRIE steps. The platform measures 2 x 2 mm2 with a through-hole of 1.6 x 1.8 mm2 for light transmission. Two arrays of combs attached to the platform as well as a set of four static combs are used to electrostatically incline the platform by ± 4° with a driving voltage of about 60 V.

Resonant grating filters at oblique incidence

We designed a tunable, oblique incidence resonant grating filter covering the c-band as drop device. Our resonant grating filter consists of a planar waveguide on a glass substrate covered by low index medium that separates the waveguide from the grating on top of it. With these 3 layers we reach a finesse of more than 3000, which would require much more layers in traditional thin film technology. The drop filter can be tuned by tilting the MEMS platform on which the filter will be glued. Tuning over the c-band will require tilt angles of 3° of the MEMS platform in both directions. Measurements indicate a resonance peak shift of 1.2% and a negligible shape change of 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 peak wavelength shift is linear with respect to the change of the AOI.

Resonant grating filter for a MEMS based add-drop device at oblique incidence

A reflective tunable resonant grating filter with a full width at half maximum (FWHM) of 0.5 nm at 1545 nm for TE polarization was investigated. The tunability is achieved by placing the filter on a tiltable MEMS platform. The filter was designed to accommodate fabrication tolerances and since we work in microsystems the minimum filter size was analyzed, as well as the needed tilt angle for the platform. The device works at 45/spl deg/ incidence angle, thus a separation of the reflected and incident light is easily possible.

Submicro-optics: big effects on a small scale

Recent results of our studies into optical effects where sub-micron length scales play a pivotal role are presented. We start with a discussion of fine optical features produced by relatively large objects, and then move on to consider the big effects that can be produced by sub-micron structures. Topics covered include fine structure in the optical field of microlenses and gratings, and then further down in length scale from microstructured surfaces to resonant filters, photonic crystal waveguides and metallic nanoparticles. For each step we demonstrate potential applications in which such a length scale can present important advantages, as well as discussing some of the disadvantages and challenges in the design and fabrication of such elements. We particularly highlight the sensitivity of many of the structures to small variations in optical situation (e.g. geometry, orientation, material, polarization) leading significant optical effects for small-scale changes. Methods for the characterization of optical fields produced by objects at these smaller dimensions are also presented.

Design and measurement of a tunable resonant grating filter at oblique incidence

The aim is to use a resonant grating filter (RGF) in a tunable add-drop device. The tuning is achieved by placing the RGF on a tillable MEMS platform. The reflection peak wavelength shifts as a function of the angle of incidence. The filter works at oblique incidence since filter applications imply constant peak linewidth, and this also provides better beam separation. The measurements were performed with a HP8168 tunable laser source. Thus the experimental proof of the working principle of the resonant grating filter has been carried out.

One-dimensional and two-dimensional periodic structures for security devices, resonant filters, and photonic crystals

We present recent applications of one-dimensional (1D) and two-dimensional (2D) periodic structures. The structures were designed using rigorous diffraction theory and produced by modern micromachining techniques (electron beam writing, optical lithography). In addition, interferometric recording of periodic structures was investigated in order to fabricate periodic structures with arbitrary profile shapes.