Integrated Optics – Projects

Novel silicon photonic devices harnessing new leakage behaviour

Silicon photonics is emerging as the technological salvation for the continued advancement of integrated electronics. Together with our collaborators at the Center for Optical Technologies, Lehigh University, we have recently discovered new, important characteristics of high index contrast silicon waveguides: lateral leakage loss and leakage resonance. This leakage behaviour presents challenges for traditional circuit design but also presents exciting opportunities for new devices harnessing the leakage. In this project, we investigate a completely new class of waveguide device incorporating leakage behaviour in both the linear and nonlinear regimes.

This is a collaborative research project with the Center for Optical Technologies, Lehigh University in the USA. The project is supported by an Australian Research Council (ARC) Discovery Project grant and a DIISR International Science Linkage grant.

Silicon photonic platform for quantum encryption and communications

Silicon photonics is explored as a platform to realise integrated transmitter and receiver systems for exchanging of quantum cryptographic keys. A recent demonstration using discrete devices works well, but is too large and costly. This project will exploit compact waveguide technology and novel polarisation control techniques to integrate the entire transmitter and receiver systems onto a single chip. The use of CMOS compatible processes will enable prototype fabricated by a commercial foundry, and may even allow integration of custom quantum signal processing electronics. The technology from this project will pave the way for a revolutionary quantum communications module which is low-cost, compact and highly manufacturable.

This project is supported by a Linkage Project grant from the Australian Research Council (ARC) and QuintessenceLabs.

Active control of light for nonlinear photonic devices

All-optical signal processing and routing stands as one of the most important goals of photonics, with promise for increasing the speed of current communication system. The fundamental challenge, however, is to achieve precise, high-speed manipulation of light in both space and time. This can only be done with active control of the optical properties of the host material.

This project will realize novel, micro and nano-scale periodic photonic structures with high-speed electro-optic tuning and optical nonlinearity to achieve ultimate control of spatiotemporal propagation of high-speed, broad-spectrum pulses. The outcomes of this project will form the fundamental knowledge basis for new active signal routing and processing devices.

This is a collaborative research project with ANU and is supported by an Australian Research Council (ARC) Discovery Project grant.

Silicon-on-insulator (SOI) photonic device as a bio-sensing platform

Evanescent field optical waveguide sensors are gaining increased interest for biological sensing. These sensors are based on the interaction of the tails of guided light with the surrounding environment, resulting in small changes to the waveguide effective index or loss. These changes can be detected, for example, by monitoring the variation of the resonant wavelength of a ring resonator.

To achieve high sensitivity, waveguides with strong evanescent field are preferable. Thin-ridge SOI waveguide exhibits an extremely strong evanescent field and is therefore a very good candidate for evanescent field sensing applications. In addition, this waveguide has a new, important characteristic: lateral leakage resonance. By applying a thin sensing layer on the waveguide surface, the guiding properties may be modified in response to chemical/biomolecules adsorbed on the waveguide surface.

In this project, we are collaborating with researchers in the School of Applied Science to combine thin-ridge SOI devices with novel leakage behaviour and an active bio-sensing layer to achieve an innovative sensing platform.

Periodically poled lithium niobate waveguides for transverse second harmonic generation

Optical communications at present takes place in the C band of the IR spectrum which has the wavelength range 1530-1565 nm. Here the optical signals are transmitted over optical fibres in the form of optical pulses. There are many occasions where we would like to examine the wavelength spectrum on the fibre to help understand system operation and to diagnose faults and also monitor the optical pulses. At present optical spectrum analysers are very expensive around $40,000-$50,000 because of the expensive IR detectors and complex electronic equipment which does the signal processing.

There has been research into implementing transverse (or surface emitting) second harmonic generation (SHG) as means to spectral analysis and pulse monitoring using counter propagating pulses. This configuration is very effective as the second harmonic which is emitted from the surface can be easily captured using a visible optical detector like a cheap web-camera and pictures captured can easily be processed using rapid image processing algorithms which could be done easily by any standard PC. Using established Lithium Niobate processing platforms and newly established etching and waveguide fabrication techniques this research intends to investigate Lithium Niobate as a potential material that could be used in a low cost optical signal processing and testing system.

Non-linear polarisation phenomena in lithium niobate waveguides

This project involves the investigation of non-linear phenomena in lithium niobate waveguides. The particular focus of this research is the polarisation dependence of the Photorefractive effect and seeing if there is a way we can harness these processes by using tuneable periodic perturbations integrated into the nonlinear waveguides.

To realise the periodic perturbations we will utilise stress-induced long period gratings, which will allow phase matching and therefore coupling between the two fundamental polarisations. The Photorefractive effect in this device should allow for self-tuning of the polarisation coupling within the devices.

The expected outcome of this work is the observation of a spectral soliton, a steady state reached by two competing nonlinear processes. Such devices would be operating only in the optical domain. Possible applications for this might may be some form of self-tuning wavelength filter.

Planar fluid-infiltrated waveguide platform

The detection and analysis of biological specimen such as viruses or cells requires sensors of very high precision. The fluid infiltrated waveguide project is exploring the combination of microfluidics with integrated optics to investigate the refractive index of fluids based on optical effects. This optofluidic interplay leads the path highly sensitive and compact sensors with a short response time to perform real-time analysis of refractive index changes in biological or chemical compositions.

The fluid-infiltrated waveguide arrays are designed, constructed and fabricated at RMIT University. The waveguides are manufactured at micro-metre scale using a combination of photo lithography and polymer dry film lamination.

Fluid-infiltrated waveguides based on a low-cost planar polymer architecture illustrate a promising platform for ultra-sensitive refractive index measurements. The novel platform also supports biological and chemical analysis in a lab-on-chip environment.

Surface machining LiNbO₃ using Ti-diffusion technique

The project investigates a novel technique for realizing smooth micro-scale etched features on lithium niobate. Etching of lithium niobate is observed when annealing two wafers in contact with an intermediate titanium strip. A variety of etching characteristics result when the two wafers are different combinations of X, +Z, and -Z crystal orientations. The physical mechanism causing etching is also investigated. Evidence suggests that the etching is in fact hydrogen plasma etching that occurs in the proximity of the diffusing titanium strip. Control over etch depth was achievable through parameters that affect titanium diffusion such as annealing duration, titanium film thickness and patterned titanium strip widths.

Optical waveguiding was observed under the etched trenches of narrow widths. These impurity free waveguides support both the ordinary and the extra-ordinary polarizations with modest transmission losses. This optical waveguiding phenomenon has been attributed to residual stress and offers great potential for high power handling and compact waveguiding.

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