Silicon photonics micro-ring resonator (MRR) and Mach-Zehnder waveguide based sensors have attracted much attention in recent years because of their capacity for high sensitivity, small footprint and mass-scalable (low cost) potential. This type of sensor is based on the detection of changes in optical amplitude/phase due to small changes in local, near-field refractive index (RI) in the environment surrounding the waveguide device. Sensitivity to ever smaller changes in RI are sought, e.g. for vapour/gas based sensing, which may be realised by designing devices based around the slot waveguide. Furthermore, tailoring resonant line-shapes to generate asymmetric (or Fano-like) modes through series, parallel or ‘nested’ arrangements of coupled MRRs also demonstrates the potential for such sensitivity enhancement. This type of device is likely to be of interest, for example where sensing of volatile organic compounds (VOCs) is important, e.g. in industrial process and environmental monitoring.
We demonstrate a number of such photonic sensing platforms, combining both the slot waveguide and both established and novel ‘photonic molecule’ structures, fabricated on silicon-on-insulator using standard foundry fabrication processes. Integrated TiN heaters provide the capacity for thermal tuning in order to manipulate the spectral characteristics of our devices and the sensitivity of the devices to a range of VOCs; benzene, toluene and xylene, are investigated as exemplars using a custom-made vapour delivery system. Sensor performance is established with the assistance of device modelling and comparison made with conventional single MRR devices as a reference. The potential of adding functional layers to the devices as a method for achieving chemical selectivity will also be discussed.
Silicon photonics has traditionally focused on near infrared wavelengths, with tremendous progress seen over the past decade. However, more recently, research has extended into mid infrared wavelengths of 2 μm and beyond. Optical modulators are a key component for silicon photonics interconnects at both the conventional communication wavelengths of 1.3 μm and 1.55 μm, and the emerging mid-infrared wavelengths. The mid-infrared wavelength range is particularly interesting for a number of applications, including sensing, healthcare and communications. The absorption band of conventional germanium photodetectors only extends to approximately 1.55 μm, so alternative methods of photodetection are required for the mid-infrared wavelengths. One possible CMOS compatible solution is a silicon defect detector. Here, we present our recent results in these areas. Modulation at the wavelength of 2 μm has been theoretically investigated, and photodetection above 25 Gb/s has been practically demonstrated.
Micro-ring modulators for use in high-speed telecommunication transceivers designed for silicon-on-insulator (SOI) for 2 μm wavelength operation are described and simulated with comparison to 1.55 μm. Device simulations show improved DC modulation performance due to the free-carrier effect described in the plasma dispersion relations which is stronger for longer wavelengths. WDM applications are described and simulated. Micro-ring modulator devices were designed and fabricated at A*STAR IME and are pending measurement.