We present the development of SOI waveguides with low-loss (~1.5 dB/cm) single-moded guidance over an octave of frequency. Broadband single-moded guidance is needed for on-chip mid-infrared spectroscopy and this cannot be provided by conventional waveguide geometries in standard material platforms. The reported waveguides require a simple fabrication process flow and will be widely applicable to different mid-infrared wavelength bands for a variety of sensing applications. We further present a low-loss bend design (0.179 ± 0.031 dB/90°) that overcomes the inherently large bending loss of the waveguides, which is a limiting factor in the utility of the waveguides. We consider different prospective designs for the use of these waveguides in a circuit for a sensing device.
We review our recent results on modulators and detectors for the 2μm range, which may become very relevant for future communications, and on the development of mid-IR broadband devices for sensing applications. We show Mach-Zehnder and Michelson based modulators operating at data rates up to 25 Gb/s and Ge based detectors operating up to 12.5 Gb/s. For longer wavelengths relevant for sensing applications, we present broadband waveguides and splitters, waveguide integrated bolometers, and the realisation of a mid-infrared sensor.
The interest in developing high-performance optical modulator to meet the growing demands of data processing speed has increased over the last decade. While there have been significant research efforts in developing standalone silicon modulators, works on integrating those with electronics is limited, which is necessary for the practical implementation of short-reach optical interconnects.
In contrast to previous work in the field where electronic–photonic integration was mostly limited to the physical coupling approach, we have introduced a new design philosophy, where photonics and electronics must be considered as a single integrated system in order to tackle the demanding technical challenges of this field.
In this work, I shall present our recent 100Gb/s silicon photonics transmitter, where photonic and electronic devices are co-designed synergistically in terms of device packaging, power efficiency, operation speed, footprint and modulation format.
In this work, potential ways of accessing a greater spectral range at mid-infrared (MIR) wavelength ranges in silicon photonics are explored, in particular for sensing applications that use on-chip spectroscopy. To utilise the full low-loss transmission of silicon, silicon membranes are transfer printed onto MIR-transparent substrates for waveguides with no absorption from the substrate. A Y-junction splitter with low loss across a
1 µm optical bandwidth is also designed and experimentally demonstrated.
In this paper we present silicon and germanium-based material platforms for the mid-infrared wavelength region and we report several active and passive devices realised in these materials. We particularly focus on devices and circuits for wavelengths longer than 7 micrometers.
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.
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.
Group IV platforms can operate at longer wavelengths due to their low material losses. By combining graphene and Si and Ge platforms, photodetection can be achieved by using graphene’s optical properties and coplanar integration methods. Here, we presented a waveguide coupled graphene photodetector operating at a wavelength of 3.8 μm.
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.
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.
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