A. Chelnokov

Efficient Directional Coupling between Silicon and Copper Plasmonic Nanoslot Waveguides: toward Metal−Oxide−Silicon Nanophotonics

Coupling plasmonics and silicon photonics is the best way to bridge the size gap between macroscopic optics and nanodevices in general and especially nanoelectronic devices. We report on the realization of key blocks for future plasmonic planar integrated optics, nano-optical couplers, and nanoslot waveguides that are compatible both with the silicon photonics and the CMOS microelectronics. Copper-based devices provide for very efficient optical coupling, unexpectedly low propagation losses and a broadband sub-50 nm optical confinement. The fabrication in a standard frontline microelectronic facilities hints broad possibilities of hybrid opto-electronic very large scale integration.

Giant coupling effect between metal nanoparticle chain and optical waveguide.

We demonstrate that the optical energy carried by a TE dielectric waveguide mode can be totally transferred into a transverse plasmon mode of a coupled metal nanoparticle chain. Experiments are performed at 1.5 μm. Mode coupling occurs through the evanescent field of the dielectric waveguide mode. Giant coupling effects are evidenced from record coupling lengths as short as ~560 nm. This result opens the way to nanometer scale devices based on localized plasmons in photonic integrated circuits.

Subwavelength Grating-Mirror VCSEL With a Thin Oxide Gap

A new vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength grating mirror and a thin oxide gap is suggested and numerically investigated. The structure is shown to exhibit similar threshold gain, suppression of higher order transverse modes, and polarization stability as a grating-mirror VCSEL reported in the literature based on a thick air gap. The thin oxide gap structure has a number of advantages including easier fabrication, better mechanical stability, and very strong single-mode properties.

Two-dimensional photonic crystals with Ge/Si self-assembled islands

Two-dimensional photonic crystals were fabricated on silicon-on-insulator waveguides with self-assembled Ge/Si islands deposited on top of the upper silicon layer. The photonic crystals consist of triangular lattices of air holes designed to exhibit a forbidden band around 1.5 μm. Different hexagonal photonic crystals microcavities were processed whose optical properties are probed at room temperature with the Ge/Si island photoluminescence. Quality factors larger than 200 are measured for hexagonal H3 cavities. A significant enhancement of the Ge/Si island photoluminescence is achieved in the 1.3–1.55 μm spectral region using the photonic crystal microcavities. We show that the energy resonance of the defect modes can be tuned with the filling factor of the photonic crystal.

Toward controllable photonic crystals for centimeter- and millimeter-wave devices

In this paper, we present several experimental and theoretical studies showing the feasibility of active photonic crystal controlled either by electrical elements or by light. The controllability of photonic crystals at centimeter wavelengths is proposed with the periodic insertion of diodes along the wires of a two-dimensional (2-D) metallic structure. For only three crystal periods with commercially available devices, more than 30 dB variations of the crystal transmission are predicted over a multigigahertz range by switching the diodes. From calculation models, a tight analogy is shown between these crystals and those consisting of discontinuous metallic rods with dielectric inserts. The numerical models as well as the proposed technology are validated by experimental measurements on 2-D crystals with either continuous or discontinuous metallic rods. The partial control of a 3-D layer-by-layer dielectric structure at millimeter wavelengths is also demonstrated in the second part of the work. A laser light is used to modulate the transmission level of defect modes by photo-induced free carrier absorption. The overall results are expected to contribute to further developments of switchable electromagnetic windows as well as to tunable waveguide structures in the microwave and millimeter wave domains.

Recent Advances Toward Optical Devices in Semiconductor-Based Photonic Crystals

Photonic crystals, artificial, wavelength-scale multidimensional periodic structures, have given birth to a number of realizations in semiconductors. Photonic integrated circuits, especially around new integrated lasers, are challenging directions of research for miniaturization and new functions in optical telecommunications. We review the basic physics behind such applications and underline the current status of this very active research field worldwide

Two-dimensional photonic crystals in macroporous silicon: from mid-infrared (10 /spl mu/m) to telecommunication wavelengths (1.3-1.5 /spl mu/m)

We present a detailed study of two-dimensional (2D) photonic crystals based on macroporous silicon technology, showing a broad range of wavelengths accessible for applications with this material. In this work, we have reached 1.55 /spl mu/m, this certainly represents a decisive issue for this technology. First, the reflection performances of a hexagonal and a triangular lattice of air holes are compared. The triangular lattice reduces technological requirements because the complete photonic bandgap (PBG) results from the overlap of broader forbidden bands of lower order. Second, a combined experimental and theoretical study is presented of the reflection properties of a 2D photonic crystal in a three-dimensional (3D) optical environment. This reveals the critical parameters that can degrade the performances of such 2-D structures. Reflection coefficients up to 98% are obtained with optical quality interfaces. Finally, a complete PBG centered at 1.55 /spl mu/m is demonstrated with a submicrometer period triangular lattice defined by holographic lithography. The influence of the air filling factor on the band position and the interface quality is analyzed by reflection measurements. The overall results show the high flexibility of the macroporous silicon technology and its applicability to integrated optics at telecommunication wavelengths.

Fabrication of 2-D and 3-D silicon photonic crystals by deep etching

Deep etching methods applied to semiconductors allow the fabrication of two-dimensional and three-dimensional photonic crystals. The use of chemical, plasma, and focused ion beam etch applied to silicon is reviewed.

Fabrication of three-dimensional photonic structures with submicrometer resolution by x-ray lithography

We report on the fabrication of diamond-like photonic structures in PMMA resist and their use as porous templates for transferring three-dimensional patterns to metals or dielectrics. Following the original “three drilling holes” approach first proposed by Yablonovitch, we used three consecutive exposures of PMMA resist to an x-ray beam through a triangular lattice of holes. A submicronic patterning was thus obtained in thick PMMA layers (>6 μm). Optical characterizations of 1.3 μm period templates showed a well-defined photonic gap in the midinfrared. The pattern transfers from the PMMA templates to a metal (copper) and a high refractive index dielectric (titania) were achieved by the electrodeposition and sol–gel filling techniques, respectively. Three-dimensional metallic structures of 1.3 μm lattice constant were obtained with extreme regularity over a thickness of ∼6 μm, thereby providing a way to build submicrometer photonic band gap materials for optical wavelengths.

1.9% bi-axial tensile strain in thick germanium suspended membranes fabricated in optical germanium-on-insulator substrates for laser applications

High tensile strains in Ge are currently studied for the development of integrated laser sources on Si. In this work, we developed specific Germanium-On-Insulator 200 mm wafer to improve tolerance to high strains induced via shaping of the Ge layers into micro-bridges. Building on the high crystalline quality, we demonstrate bi-axial tensile strain of 1.9%, which is currently the highest reported value measured in thick (350 nm) Ge layer. Since this strain is generally considered as the onset of the direct bandgap in Ge, our realization paves the way towards mid-infrared lasers fully compatible with CMOS fab technology.