Bond orbital description of the strain induced second order optical susceptibility in silicon

We develop a theoretical model, relying on the well established sp3 bond-orbital theory, to describe the strain-induced $\chi^{(2)}$ in tetrahedrally coordinated centrosymmetric covalent crystals, like silicon. With this approach we are able to describe every component of the $\chi^{(2)}$ tensor in terms of a linear combination of strain gradients and only two parameters $\alpha$ and $\beta$ which can be estimated theoretically. The resulting formula can be applied to the simulation of the strain distribution of a practical strained silicon device, providing an extraordinary tool for optimization of its optical nonlinear effects. By doing that, we were able not only to confirm the main valid claims known about $\chi^{(2)}$ in strained silicon, but also estimate the order of magnitude of the $\chi^{(2)}$ generated in that device

Optical Gain in Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be promising material for nanophotonics and optoelectronics. Due to the possibility of tuning their direct band gap and controlling excitonic recombinations in the near-infrared wavelength range, s-SWNT can be used as efficient light emitters. We report the first experimental demonstration of room temperature intrinsic optical gain as high as 190 cm-1 at a wavelength of 1.3 {\mu}m in a thin film doped with s-SWNT. These results constitute a significant milestone toward the development of laser sources based on carbon nanotubes for future high performance integrated circuits.Comment: 4 figure

A theoretical comparison of strip and vertical slot-waveguide

For biosensing applications where small refractive index variations of the surrounding medium are monitored, light needs to have a strong interaction with such a surrounding biological medium. This is not the case for classical rib and strip waveguides where light is predominantly guided in the high index material. However, in slot waveguides, light is confined in a low index slot region sandwiched between two high index rails and due to the discontinuity of the electric field at the interface between the rails and slot, a significant fraction of the electromagnetic field is localized in the slot. As such slot waveguides present an interesting alternative for biosensing applications especially when made using silicon nitride which permits slot widths of up to 200nm and as such reachable fabrication tolerances, and reduced propagation losses compared to silicon slot waveguides with its higher refractive index contrast. Furthermore, for biosensing, the wider slot facilitates sample transport and using a multiple-slot structure, further enhancement of the optical confinement in low index slot regions is possible. In this paper we present work in progress of theoretical modeling for strip, slot and multiple-slot waveguides and compare their characteristics for sensing purposes

Frequency-tuning dual-comb spectroscopy using silicon Mach-Zehnder modulators

[EN] Dual-comb spectroscopy using a silicon Mach-Zehnder modulator is reported for the first time. First, the properties of frequency combs generated by silicon modulators are assessed in terms of tunability, coherence, and number of lines. Then, taking advantage of the frequency agility of electro-optical frequency combs, a new technique for fine resolution absorption spectroscopy is proposed, named frequency-tuning dual-comb spectroscopy, which combines dual-comb spectroscopy and frequency spacing tunability to measure optical spectra with detection at a unique RF frequency. As a proof of concept, a 24 GHz optical bandwidth is scanned with a 1 GHz resolution.Agence Nationale de la Recherche (ANR-17-CE09-0041, ANR-18-CE39-0009).Deniel, L.; Weckenmann, E.; Pérez-Galacho, D.; Alonso-Ramos, C.; Boeuf, F.; Vivien, L.; Marris-Morini, D. (2020). Frequency-tuning dual-comb spectroscopy using silicon Mach-Zehnder modulators. Optics Express. 28(8):10888-10898. https://doi.org/10.1364/OE.390041S108881089828

A general approach for robust integrated polarization rotators

Integrated polarization rotators suffer from very high sensitivity to fabrication errors. A polarization rotator scheme that substantially increases fabrication tolerances is proposed. In the proposed scheme, two tunable polarization phase shifters are used to connect three rotator waveguide sections. By means of properly setting the polarization phase shifters, fabrication errors are compensated and perfect polarization rotation is achieved. Analytical conditions are shown that determine the maximum deviation that can be corrected with the proposed scheme. A design example is discussed, where the thermo-optic effect is used to provide the required tunable polarization phase shifting. Calculated 40dB extinction ratio is shown in presence of fabrication errors that would yield a 4dB extinction ratio in the conventional approach. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.The authors want to aknowledge Universidad de Málaga alaga, Campus de Excelencia Internacional Andalucia Tech for their support

Simplified model enabling optimization of silicon modulators

International audienceIn this work, the simplified modeling of silicon phase modulators is presented along with a comparison among different options of modulators. The proposed simplified model enables a substantial reduce in computational effort while maintaining a good accuracy. The presented model is validated against complete 3D-simulations by means of the design of four different modulators. Furthermore, with the help of the model a deep insight on the performances tradeoffs in the choose and design of silicon modulators is provided

Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures

The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugations widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a single-etch, $\mathbf{220\,nm}$ thick, Si Bragg filter featuring a corrugation width of $\mathbf{150\,nm}$, a rejection bandwidth of $\mathbf{1.1\,nm}$ and an extinction ratio exceeding $\mathbf{40\,dB}$. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch counterparts with similar bandwidths

Silicon nitride waveguide-integrated Ge/SiGe quantum wells optical modulator

Silicon-based photonics has generated a strong interest in recent years, mainly for optical interconnects and sensing on photonic integrated circuits. The main rationales of silicon photonics are the reduction of energy consumption and photonic system costs via integration on a standard Si chip. Waveguide-integrated silicon based-optoelectronic modulators have been particularly studied as a key building block. Ge-rich Ge/SiGe quantum well waveguides are promising for compact and low energy consumption modulators thanks to the demonstration of direct gap related optical transitions in these structures, while silicon nitride (SiN) waveguide could be a promising alternative to Si waveguide. This paper studies an integration approach between passive SiN waveguide and active Ge/SiGe multiple quantum wells (MQWs) optoelectronic modulators. Photocurrent measurements at different bias voltages demonstrated strong optical modulation within the O-band wavelength (1.26 - 1.36 μm) from Ge/SiGe MQWs, while 3D-FDTD calculations confirm a compact and efficient integration with SiN waveguide on Si wafer