We are demonstrating the use of Low temperature PECVD silicon nitride based materials used for applications ranging from non-linear functionalities in the C band, wavelength division multiplexing in the O band and post fabrication light based refractive index tuning for in-situ device trimming. These materials are demonstrated for waveguide ranging from 300 nm up to 1 micron in thickness with refractive indices varying between 1.9 and 2.55.
Electrical annealing of erasable directional couplers (DCs) was realized. Titanium nitride (TiN) micro-heaters were used to electrically heat up and anneal the Ge-ion implanted regions in silicon, which are used as the coupling waveguides in the erasable DCs. The refractive index of implanted silicon was reduced rapidly by electrical annealing, so that the DCs were effectively erased. The whole annealing process can be accomplished in about 2 seconds. Based on the simulation results, the implanted region can be heated up to about 700 °C.
In recent years, we have presented results on the development of a variety of silicon photonic devices such as erasable gratings and directional couplers, tunable resonators and Mach-Zehnder interferometers, and programmable photonic circuits using germanium ion implantation and localised laser annealing. In this paper we have carried out experiments to analyse a series of devices that can be fabricated using the same technology, particularly silicon-on-insulator racetrack resonators which are very sensitive to fabrication imperfections. Simulation and experimental results revealed the ability to permanently optimise the coupling efficiency of these structures by selective localised laser annealing.
We reviewed our recent developments on the post-fabrication trimming techniques and programmable photonic circuits based on germanium ion implanted silicon waveguides. Annealing of ion implanted silicon can efficiently change the refractive index. This technology has been employed to fine-tune the optical phase, and therefore the operating point of photonic devices, enabling permanent correction of optical phase error induced by fabrication variations. High accuracy phase trimming was achieved with laser annealing and a real-time feedback control system. Erasable waveguides and directional couplers were also demonstrated, which can be used to implement programmable photonic circuits with low power consumption.
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.
Ion implantation into silicon causes radiation damage. If a sufficient dose is implanted, complete
amorphisation can result in any implanted part of an optical device. Amorphous silicon has a refractive index
that is significantly different higher than that of crystalline silicon (~10-1), and can therefore form the basis of
a refractive index change in optical devices. This refractive index change can be partially or completely
removed by annealing. In recent years we have presented results on the development of erasable gratings in
silicon to facilitate wafer scale testing of silicon photonics circuits. These gratings are formed by amorphising
selected areas of silicon by utilising ion implantation of Germanium. However, we have now used similar
technology for trimming of integrated photonic components. In this paper we discuss design, modelling and
fabrication of ring resonators and their subsequent trimming using ion implantation of Germanium into silicon
followed by annealing.
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 develop a range of optical devices that are reported in this paper. Ion implantation into silicon causes radiation damage resulting in a refractive index increase, and can therefore form the basis of multiple optical devices. We demonstrate the principle of a series of devices for wafers scale testing and have also implemented the ion implantation based refractive index change in integrated photonics devices for device trimming.
A crucial component of any large scale manufacturing line is the development of autonomous testing at the wafer scale. This work offers a solution through the fabrication of grating couplers in the silicon-on-insulator platform via ion implantation. The grating is subsequently erased after testing using laser annealing without affecting the optical performance of the photonic circuit. Experimental results show the possibility for the realisation of low loss, compact solutions which may revolutionise photonic wafer-scale testing. The process is CMOS compatible and can be implemented in other platforms to realise more complex systems such as multilayer photonics or programmable optical circuits.
Hyperuniform disordered solids are a new class of designer photonic materials with large isotropic band gaps
comparable to those found in photonic crystals. The hyperuniform disordered materials are statistically isotropic and
possess a controllable constrained randomness. We have employed their unique properties to introduce novel
architectures for optical cavities that achieve an ultimate isotropic confinement of radiation, and waveguides with
arbitrary bending angles. Our experiments demonstrate low-loss waveguiding in submicron scale Si-based hyperuniform
structures operating at infrared wavelengths and open the way for the realization of highly flexible, disorder-insensitive
optical micro-circuit platforms.
In this paper we present silicon photonics devices designed for the 3-4μm wavelength region including waveguides,
MMIs, ring resonators and Mach-Zehnder interferometers. The devices are based on silicon on insulator (SOI) platform.
We show that 400-500 nm high silicon waveguides can have propagation losses as low as ~ 4 dB/cm at 3.8μm. We also
demonstrate MMIs with insertion loss of 0.25 dB, high extinction ratio asymmetric Mach-Zehnder interferometers, and
SOI ring resonators. This combined with our previous results reported at 3.4μm confirm that SOI is a viable platform for
the 3-4 μm region and that low loss mid-infrared passive devices can be realized on it.
Group IV mid-infrared photonics is attracting more research interest lately. The main reason is a host of potential
applications ranging from sensing, to medicine, to free space communications and infrared countermeasures. The field is,
however, in its infancy and there are several serious challenges to be overcome before we see progress similar to that in
the near-infrared silicon photonics. The first is to find suitable material platforms for the mid-infrared. In this paper we
present experimental results for passive mid-infrared photonic devices realised in silicon-on-insulator, silicon-on-sapphire,
and silicon on porous silicon. We also present relationships for the free-carrier induced electro-refraction and
electro-absorption in silicon and germanium in the mid-infrared wavelength range. Electro-absorption modulation is
calculated from impurity-doping spectra taken from the literature, and a Kramers-Kronig analysis of these spectra is used
to predict electro-refraction modulation. We examine the wavelength dependence of electro-refraction and electro-absorption,
finding that the predictions suggest longer-wave modulator designs will in many cases be different than those
used in the telecom range.
The mid-infrared spectral region is interesting for bio-chemical sensing, environmental monitoring,
free space communications, or military applications. Silicon is relatively low-loss from 1.2 to 8 μm and from
24 to 100 μm, and therefore silicon photonic circuits can be used in mid- and far- infrared wavelength ranges.
In this paper we investigate several silicon based waveguide structures for mid-infrared wavelength region.
In this paper, we investigate athermal and low propagation loss silicon-on-insulator (SOI) rib waveguides. Propagation
losses have been modeled for different dimensions of ridge waveguides achieving good agreement with experimental
measurements. At certain waveguide widths, it is possible to obtain low propagation losses for both TE (transverse
electric) and TM (transverse magnetic) modes. Racetrack ring resonator structures based on ridge waveguides covered
by a polymer have been fabricated, aiming for an athermal design and therefore, a very small temperature dependent
wavelength shift. Design guidelines for temperature insensitive and small propagation loss ridge waveguides are
presented in this paper together with experimental data.