Low-loss rib waveguides containing Si nanocrystals embedded in SiO2

We report on the study and modeling of the structural and optical properties of rib-loaded waveguides working in the 600-900-nm spectral range. A Si nanocrystal (Si-nc) rich SiO2 layer with nominal Si excess ranging from 10% to 20% was produced by quadrupole ion implantation of Si into thermal SiO2 formed on a silicon substrate. Si-ncs were precipitated by annealing at 1100°C, forming a 0.4-um-thick core layer in the waveguide. The Si content, the Si-nc density and size, the Si-nc emission, and the active layer effective refractive index were determined by dedicated experiments using x-ray photoelectron spectroscopy, Raman spectroscopy, energy-filtered transmission electron microscopy, photoluminescence and m-lines spectroscopy. Rib-loaded waveguides were fabricated by photolithographic and reactive ion etching processes, with patterned rib widths ranging from 1¿to¿8¿¿m. Light propagation in the waveguide was observed and losses of 11dB/cm at 633 and 780 nm were measured, modeled and interpreted.

Analysis of leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides

Power leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides (rib-ARROW) have been theoretically and experimentally studied as a function of wavelength and polarization of the light for different geometrical and optical parameters that characterize the rib-ARROW structure. Obtained results show that rib-ARROWs can only be fabricated with low losses in a wavelength range when determined rib configurations are adopted. Furthermore, these waveguides exhibit a polarization sensitivity that largely depends on the core-substrate refractive index difference. Together with the experimental results, theoretical calculations from different modeling methods are also presented and discussed.

Diffraction grating couplers milled in Si3N4 rib waveguides with a focused ion beam

Focused ion beam milling is a processing technology which allows flexible direct writing of nanometer scale features efficiently substituting electron beam lithography. No mask need results in ability for patterns writing even on fragile micromechanical devices. In this work we studied the abilities of the tool for fabrication of diffraction grating couplers in silicon nitride waveguides. The gratings were fabricated on a chip with extra fragile cantilevers of sub micron thickness. Optical characterization of the couplers was done using excitation of the waveguides in visible range by focused Gaussian beams of different waist sizes. Influence of Ga+ implantation on the device performance was studied.

Electrical pump & probe and injected carrier losses quantification in Er doped Si slot waveguides

Electrically driven Er3+ doped Si slot waveguides emitting at 1530 nm are demonstrated. Two different Er3+ doped active layers were fabricated in the slot region: a pure SiO2 and a Si-rich oxide. Pulsed polarization driving of the waveguides was used to characterize the time response of the electroluminescence (EL) and of the signal probe transmission in 1 mm long waveguides. Injected carrier absorption losses modulate the EL signal and, since the carrier lifetime is much smaller than that of Er3+ ions, a sharp EL peak was observed when the polarization was switched off. A time-resolved electrical pump & probe measurement in combination with lock-in amplifier techniques allowed to quantify the injected carrier absorption losses. We found an extinction ratio of 6 dB, passive propagation losses of about 4 dB/mm, and a spectral bandwidth > 25 nm at an effective d.c. power consumption of 120 μW. All these performances suggest the usage of these devices as electro-optical modulators.

Size dependence of refractive index of Si nanoclusters embedded in SiO2

he complex refractive index of SiO2 layers containing Si nanoclusters (Si-nc) has been measured by spectroscopic ellipsometry in the range from 1.5 to 5.0 eV. It has been correlated with the amount of Si excess accurately measured by x-ray photoelectron spectroscopy and the nanocluster size determined by energy-filtered transmission electron microscopy. The Si-nc embedded in SiO2 have been produced by a fourfold Si+ ion implantation, providing uniform Si excess aimed at a reliable ellipsometric modeling. The complex refractive index of the Si-nc phase has been calculated by the application of the Bruggeman effective-medium approximation to the composite media. The characteristic resonances of the refractive index and extinction coefficient of bulk Si vanish out in Si-nc. In agreement with theoretical simulations, a significant reduction of the refractive index of Si-nc is observed, in comparison with bulk and amorphous silicon. The knowledge of the optical properties of these composite layers is crucial for the realization of Si-based waveguides and light-emitting devices.

Er-Coupled Si Nanocluster Waveguide

Rib-loaded waveguides containing Er3+-coupled Si nanoclusters (Si-nc) have been produced to observe optical gain at 1535 nm. The presence ofSi-nc strongly improves the efficiency ofEr 3+ excitation but may introduce optical loss mechanisms, such as Mie scattering and confined carrier absorption. Losses strongly affect the possibility of obtaining positive optical gain. Si-nc-related losses have been minimized to 1 dB/cm by lowering the annealing time ofthe Er3+-doped silicon-rich oxide deposited by reactive magnetron cosputtering. Photoluminescence (PL) and lifetime measurements show that all Er3+ ions are optically active while those that can be excited at high pump rates via Si-nc are only a small percentage. Er3+ absorption cross section is found comparable to that ofEr 3+ in SiO 2.However, dependence on the effective refractive index has been found. In pump-probe measurements, it is shown how the detrimental role ofconfined carrier absorption can be attenuated by reducing the annealing time. A maximum signal enhancement ofabout 1.34 at 1535 nm was measured.

Electroluminiscence and optical amplification in silicon nanostructures: towards the integration of electronics and photonics

This line of research of my group intends to establish a Silicon technological platform in the field of photonics allowing the development of a wide set of applications. Particularly, what is still lacking in Silicon Photonics is an efficient and integrable light source such an LED or laser. Nanocrystals in silicon oxide or nitride matrices have been recently demonstrated as competitive materials for both active components (electrically and optically driven light emitters and optical amplifiers) and passive ones (waveguides and modulators). The final goal is the achievement of a complete integration of electronic and optical functions in the same CMOS chip. The first part of this paper will introduce the structural and optical properties of LEDs fabricated from silicon nanostructures. The second will treat the interaction of such nanocrystals with rare-earth elements (Er), which lead to an efficient hybrid system emitting in the third window of optical fibers. I will present the fabrication and assessment of optical waveguide amplifiers at 1.54 ¿m for which we have been able to demonstrate recently optical gain in waveguides made from sputtered silicon suboxide materials.