Ultra-Small Bent Meta-Waveguide Filters

This paper demonstrates the capability of locally resonant metamaterials (LRMs) for creating compact metallic waveguide E- and H-bends, which are simultaneously working as bandpass filters. For creating these bent meta-filters, we use composite pin-pipe waveguides (CPPWs), which are a type of LRMs made from resonant pins inserted in a rectangular waveguide. Like linear-shaped CPPWs, the subwavelength spatial dispersion in E- and H-bent CPPWs can nucleate a hybridization bandgap and subwavelength modes with custom frequency and bandwidth. To guarantee compatibility with standard waveguides and to improve the matching, we design subwavelength metamaterial ports. Finally, we build and test narrow and wideband H-bent CPPW filters, compatible with WR75 (10-15GHz) interfaces. Our measurements demonstrate the excellent performance of the small bent meta-filters and the customizability of the bandwidth. Our findings enable us to merge assembly components, such as bends and filters, in an ultra-small volume. It may find applications for reducing the size of waveguide networks with complex geometries in telecommunication and radar applications.

Subwavelength Metawaveguide Filters and Metaports

Romain Christophe Rémy Fleury, Maliheh Khatibi Moghaddam

This paper proposes an alternative technique for the design of miniaturized waveguide filters based on locally resonant metamaterials (LRMs). We implement ultrasmall metamaterial filters (metafilters) by exploiting a subwavelength (sub-λ) guiding mechanism in evanescent hollow waveguides, which are loaded by small resonators. In particular, we use composite pin-pipe waveguides (CPPWs) built from a hollow metallic pipe loaded by a set of resonant pins, which are spaced by deep-subwavelength distances. We demonstrate that, in such structures, multiple resonant scattering nucleates a sub-λ mode with a customizable bandwidth below the induced hybridization band gap (HBG) of the LRM. The sub-λ guided mode and the HBG, respectively, induce pass and rejection bands in a finite-length CPPW, creating a filter, the main properties of which are largely decoupled from the specific arrangement of the resonant inclusions. To guarantee compatibility with existing technologies, we propose a subwavelength method to match the small CPPW filters to standard waveguide interfaces, which we call a metaport. Finally, we build and test a family of low- and high-order ultracompact aluminum CPPW filters in the X and Ku bands (10–18 GHz). Our measurements demonstrate the customizability of the bandwidth and the robustness of the passband against geometrical scaling. The three-dimensional printed prototypes, which are 1 order of magnitude smaller and lighter than traditional filters and are also compatible with standard waveguide interfaces, may find applications in future satellite systems and 5G infrastructures.

2021

Tunable and Broadband Nanostructured Photonic Devices

Pierre-Yves Baroni

The main topic of this thesis is the fabrication and characterization of structures smaller than the wavelength of light, for operation in the visible or near infrared spectral range. In the first part of this thesis, the fabrication of periodic structures in one and two dimensions with an interference photolithography technique is described in detail. The structure periodicities that have been fabricated with this process ranges between 270 nm and a few microns on areas that can be as large as 100 cm2. Typical structure thicknesses are approximately equal to the period. In particular, a square lattice of pillars with a period of 270 nm has been created on the (non-flat) surface of a quartz microlens array and exhibits anti-reflective properties. Experimental results show a 15 % attenuation of the reflectivity and a 3 % enhancement of the transmissivity over the visible spectral range. In the second part of the thesis the structures are fabricated by e-beam lithography to ensure very precise devices shapes. The experimental results are obtained in the infrared range with two different structures, called photonic crystals. The first structure, a superprism, is a triangular lattice of pillars infiltrated by liquid crystals. A displacement of the output light spot is measured to be 20.5 µm for a wavelength variation of 27 nm. The structure length is 70 µm. The device, based on standard silicon technology, should allow integration of the device as a multiplexer/demultiplexer system into optical micro-circuits. The second structure, a tunable resonant cavity, is a wavelength filter working in the near infrared spectrum. The active area is composed of a photonic waveguide with a triangular lattice made of sub-micrometer holes. Additional nanostructuring in the light waveguide acts as a resonant cavity. The tunability of the device is obtained due to the liquid crystals which are infiltrated into the nanostructure. A 32 nm shift of the transmitted light peak inside the photonic band gap is measured by changing the temperature from room temperature to 45 °C.

EPFL2010

High spectral resolution waveguide spectrometer with enhanced throughput for space and commercial applications

Mohammadreza Madi

This dissertation presents the results concerning the development of an innovative high spectral resolution waveguide spectrometer, from the concept to the prototype demonstration and the test results. The main innovative aspects of this instrument are the enhanced throughput and the large spectral bandwidth in a static design without mechanism. These innovations are based on the customized pattern of nano-samplers fabricated on the surface of a planar waveguide, which allow enhancing the throughput and to increase the measurement points of the interferogram necessary for increasing the spectral bandwidth in a static way. On the other hand, the propagation in the unconfined direction of the planar waveguide is controlled using an adapted front-end optics to maintain the superposition of forwarding and reflected beams to form the interferogram under the nano-samplers. Polymeric- and silicon oxynitride-based planar waveguides were manufactured, evaluated and tested for studying mode profile in planar waveguides. The nano-samplers are gold nanodisks of few tens of nanometers in diameter and thickness, optimized for sampling the visible light coupled in the waveguide module of the spectrometer. A waveguide spectrometer prototype is made in silicon oxynitride/silicon dioxide technology and characterized in visible range at 633 and 685 nm using stable monochromatic laser sources. This waveguide spectrometer shows a nominal bandwidth of 256 nm thanks to a custom pattern of nanodisks providing 0.25 ÎŒm sampling interval at central wavelength of 633 nm. The targeted prototype in the near future is a highly integrated spectrometer, with an approximate footprint of a few cubic millimeters, excluding the volume required by the front-end optics and the detector electronics. This new type of instrument can be adapted for various spectral ranges where the material for the waveguide, the nano-samplers and the detectors are available and compatible (from ultraviolet to mid-infrared). This instrument has the potential to be used for numbers of space applications, for instance for the applications where the sample is in a close proximity to the spectrometer (e.g. mineralogy from a rover or active gas detection in a capsule or space station), or in remote sensing applications (e.g. atmospheric observations from a satellite). In addition, the principle idea is to group several of such spectrometers to allow hyperspectral imaging: a 1D array of spectrometers to form an acquisition line to image with lateral scanning, heading towards a full cube of spectrometers in a 2D image acquisition scheme to probe directly a complete scene (the concept of "FPAS" - focal plane array spectrometer). This technology is also adaptable for vast commercial applications in tele-surveillance, optical metrology, genomics and medical domain. At the system level, the full instrument optimization is taken into account in this dissertation, including front-end optics and the detector. Different subsystems are evaluated, developed and tested in order to integrate and demonstrate a complete prototype.