Yohann Franz

Kerr nonlinear switching in a hybrid silica-silicon microspherical resonator.

A hybrid silicon-core, silica-clad microspherical resonator has been fabricated from the semiconductor core fiber platform. Linear and nonlinear characterization of the resonator properties have shown it to exhibit advantageous properties associated with both materials, with the low loss cladding supporting high quality (Q) factor whispering gallery modes which can be tuned through the nonlinear response of the crystalline core. By exploiting the large wavelength shift associated with the Kerr nonlinearity, we have demonstrated all-optical modulation of a weak probe on the timescale of the femtosecond pump pulse. This novel geometry offers a route to ultra-low loss, high-Q silica-based resonators with enhanced functionality.

Material properties of tapered crystalline silicon core fibers

Crystalline silicon optical fibers are emerging as a promising platform for a wide range of optoelectronic applications. Here we report a crystallographic study of the material properties within silicon fibers that have been post-processed via a tapering procedure to obtain small, few micron-sized core diameters. Our results reveal that the tapering process can improve the polysilicon quality of the core through the formation of large, centimeter long crystal grains, thus significantly reducing the optical losses.

Laser annealing of low temperature deposited silicon waveguides

We report the fabrication of low temperature deposited polysilicon waveguides using a laser annealing process. Micro-Raman and XRD measurements reveal the quasi-single crystal-like quality of the material, which exhibits low optical losses of 5.13 dB/cm.

Tapered silicon core fibers with nano-spikes for optical coupling via spliced silica fibers

Reported here is the fabrication of tapered silicon core fibers possessing a nano-spike input that facilitates their seamless splicing to conventional single mode fibers. A proof-of-concept 30 µm cladding diameter fiber-based device is demonstrated with nano-spike coupling and propagation losses below 4 dB and 2 dB/cm, respectively. Finite-element-method-based simulations show that the nano-spike coupling losses could be reduced to below 1 dB by decreasing the cladding diameters down to 10 µm. Such efficient and robust integration of the silicon core fibers with standard fiber devices will help to overcome significant barriers for all-fiber nonlinear photonics and optoelectronics.

Advancing silicon photonics by germanium ion implantation into silicon

We review our recent developments of the trimming techniques for correcting the operating point of ring resonator and Mach-Zehnder Interferometers (MZIs). This technology has been employed to fine-tune the effective index of waveguides, and therefore the operating point of photonic devices, enabling permanent correction of optical phase error induced by fabrication variations. Large resonance wavelength shift of ring resonators was demonstrated, and the shift can be tuned via changing the laser power used for annealing. A higher accuracy trimming technique with a scanning laser was also demonstrated to fine-tune the operating point of integrated MZIs. The effective index change of the optical mode is up to 0.19 in our measurements, which is approximately an order of magnitude improvement compared to previous work, whilst retaining similar excess optical loss.

Dataset for: Ion implantation in silicon for trimming the operating wavelength of ring resonators

In recent years, we have presented results on the development of erasable gratings in silicon to facilitate wafer scale testing of photonics circuits via ion implantation of germanium. Similar technology can be employed to control the operating wavelength of ring resonators, which is very sensitive to fabrication imperfections. Ion implantation into silicon causes radiation damage resulting in a refractive index increase, and can therefore, form the basis of multiple optical devices. In this paper, we discuss design, modeling, and fabrication of ring resonators and their subsequent trimming using ion implantation of germanium into silicon, followed by either rapid thermal annealing or localized laser annealing. The results confirm the ability to permanently tune the position of the resonant wavelength to any point inside the free spectral range of the ring resonator, thus, greatly reducing the amount of power required for active tuning of these devices.

Phase trimming of Mach-Zehnder interferometers by laser annealing of germanium implanted waveguides

We demonstrate a new post-fabrication trimming technique to fine-tune the phase of integrated Mach-Zehnder Interferometers (MZIs), enabling permanent correction of typical fabrication based phase errors. Preliminary results demonstrate a phase trimming accuracy of 0.146π.

Laser annealed low temperature deposited polysilicon waveguides for nonlinear photonics

The intrinsic properties of silicon (Si) make it an excellent material for integrated photonics devices with small footprints [1]. To date, most of the reported devices have been based on crystalline silicon (c-Si), but this material suffers from difficult integration with electronic layers due to fabrication constraints. Subsequently, there has been growing interest in alternative forms of Si, such as hydrogenated amorphous silicon (a-Si:H), silicon nitride (SiN) and polysilicon (poly-Si) [2]. Among these materials, only poly-Si has the potential to exhibit both optical and electronic properties that are equivalent to c-Si. However, to achieve good material quality, poly-Si is typically deposited at temperatures higher than 900°C, rendering it incompatible with most CMOS fabrication processes. Thus there is a growing drive to develop new techniques to deposit poly-Si at low temperatures (<450°C) [2], but so far the optical losses in these materials have been high, limiting its use in all-optical systems employing nonlinear optical processing. In this work, we report the fabrication and characterisation of laser annealed, low temperature deposited silicon waveguides with low optical losses. Our results represent the first demonstration of nonlinear propagation in a poly-Si waveguide suitable for integration.

Laser writing of polycrystalline Si ridge waveguides

Polycrystalline silicon (poly-Si) has attracted significant interest in the area of silicon photonics because of its potential for combining good optical transmission, electronic functionality and low fabrication cost, which makes it an attractive material for commercial applications [1]. In addition, it was shown recently that by laser processing of amorphous Si (a-Si) it is possible to obtain very large grain poly-Si [2] resulting in a material with superior optical and electronic performance.

Dataset for: Post-fabrication Phase Trimming of Mach-Zehnder Interferometers by Laser Annealing of Germanium Implanted Waveguides

We demonstrate a new post-fabrication trimming technique to fine-tune the phase of integrated Mach-Zehnder Interferometers (MZIs), enabling permanent correction of typical fabrication based phase errors. Preliminary results demonstrate a phase trimming accuracy of 0.146π.