Choon Kong Lai

The University of Sydney · School of Physics

Surface acoustic wave devices are ubiquitously used for signal processing and filtering, as well as mechanical, chemical, and biological sensing and show promise as quantum transducers. While surface acoustic waves (SAWs) are primarily excited and driven using electromechanical coupling and interdigital transducers, there is a strong desire for nov...

Efficient and extended light storage mechanisms are pivotal in photonics, particularly in optical communications, microwave photonics, and quantum networks, as they offer a direct route to circumvent electrical conversion losses and surmount bandwidth constraints. Stimulated Brillouin Scattering (SBS) is an established method to store optical infor...

Microwave photonics (MWP) has unlocked a new paradigm for Radio Frequency (RF) signal processing by harnessing the inherent broadband and tunable nature of photonic components. Despite numerous efforts made to implement integrated MWP filters, a key RF processing functionality, it remains a long-standing challenge to achieve a fully integrated phot...

We present the first experimental observation of reversible 1550 nm-induced Bragg gratings and stimulated Brillouin scattering (SBS) in a planar waveguide made of high-index chalcogenide material, arsenic triselenide (As2Se3). The temporary grating is inscribed by the two-photon absorption (TPA)-induced refractive index change along the waveguide,...

Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their div...

Non-reciprocal optical components such as isolators and circulators are crucial for preventing catastrophic backreflection and controlling optical cross talk in photonic systems. While non-reciprocal devices based on Brillouin intermodal transitions have been experimentally demonstrated in chip-scale platforms, harnessing such interactions has requ...

Microwave photonics offers a promising solution for frequency converting microwave signals, however, demonstrations so far have either been bulky fibre implementations or lacked rejection of interfering image signals. Here, we demonstrate the first microwave photonic mixer with image rejection of broadband signals utilising chip-based stimulated Br...

We present the experimental observation of 1550 nm laser-induced Hill-type gratings in As 2 Se 3 rib waveguides. Such gratings exhibit narrow reflection bandwidth and highly tailorable resonant wavelengths, allowing versatile functionalities in nonlinear integrated circuits.

We heterogeneously integrate As2S3 Brillouin waveguides and Si modulators, enabling a compact chip-based RF photonic filter with 50 dB rejection. This level of photonic integration facilitates novel on-chip processing, increasing RF gain by 16 dB.

Non-reciprocal optical components such as isolators and circulators are crucial for preventing catastrophic back-reflection and controlling optical crosstalk in photonic systems. While non-reciprocal devices based on Brillouin intermodal transitions have been experimentally demonstrated in chip-scale platforms, harnessing such interactions has requ...

The low optical loss of ${{\rm Ge}_2}{{\rm Sb}_2}{{\rm Se}_4}{{\rm Te}_1}$ G e 2 S b 2 S e 4 T e 1 (GSST) makes it a potential functional material for all-optical multilevel photonics memory devices that can operate in the optical telecommunication wavelength band. However, the same characteristic also restricted the tolerance of GSST phase change...

A new methodology for realizing fabrication-tolerant planar directional couplers is proposed and experimentally demonstrated. Performance of power splitting and WDM couplers can be made highly tolerant to typical process errors when an appropriate center-to-center spacing is chosen due to changes in the mode area compensating waveguide edge to edge...

The polarization response of graphene oxide (GO)-coated planarized optical waveguides is used to determine the complex refractive index of GO film. GO films with thicknesses between 0.10 and 0.71 µm were coated on planarized optical waveguides. GO-coated waveguides exhibit large polarization dependent losses—and the polarization response depends st...

This paper aims to study the amorphous-to-crystalline phase transition characteristics of novel optical phase change material: Ge2Sb2Se4Te1 using excitation wavelength situated in the low absorption window of the phase change material. The GSST thin film is 300 nm thick and is coated on a glass substrate. The excitation wavelength used is situated...

On‐chip stimulated Brillouin scattering (SBS) in arsenic trisulfide (As2S3) planar waveguides lead to a range of outstanding demonstrations in microwave photonics signal generation and processing. However, the lack of other integrated functionalities, high back reflections, and large in‐ and out‐fiber coupling losses in high index contrast waveguid...

We propose a planarized optical waveguide structure functionalized with 2D materials that exhibits strong polarization dependent light interaction. Numerical study on both TE – and TM-polarized lights propagation in the 2D material coated optical waveguide is carried out. The effective index, neff of optical waveguide increases with the increase of...

An abrupt change in optical transmission characteristic of a graphene oxide (GO) coated optical planar waveguide was observed. This observation was based on the peculiar characteristics of the graphene oxide film, namely its high transverse-electric polarized light propagation loss, highly selective permeability of water, and change in optical prop...

A configurable optical waveguide polarizer using graphene oxide (GO) as a polarizing element has been demonstrated. The propagation characteristics of the GO-coated optical waveguide are changed from TM-pass to TE-pass by controlling the GO coating thickness in the sub-micron range during the deposition process. The highest extinction ratio measure...

In this paper, an optical waveguide polarizer based on molybdenum diselenide (MoSe2) coating is proposed and demonstrated. By applying drop-casting method, MoSe2 is coated onto an optical polymer waveguide. The extinction ratio is recorded at wavelength of 980 nm, 1310 nm, 1480 nm and 1550 nm. The highest extinction ratio obtained through this expe...

Precise detection of dopamine is essential in medical applications to diagnose many diseases such as Parkinson’s disease. Here, a new optical approach based on surface plasmon resonance (SPR) is presented to detect dopamine down to 50 pM. A four-layer coating structure is developed including SU8 waveguide, platinum, platinum nanoparticles, and plas...

GO doped SU-8 waveguides have been fabricated and characterized. The GO doped SU-8 can be processed using standard photolithography parameters. The optical characteristics of the developed waveguides are determined using fibre-butt coupling and cut-back method. Propagation loss of 1.9 dB/cm and a coupling loss of 4 dB per point measured at 1550 nm...

A variety of photonic device functionalities has now been demonstrated using both graphene and more-or-less reduced versions of the closely related compound material, graphene oxide (GO). Graphene oxide can readily be produced with a range of degrees of oxidation — and it is then generically called reduced graphene oxide (rGO). It is also important...

An approach is presented to make new waveguide-based sensors aiming to improve the sensitivity. In this approach, the sensor benefits from both optical and electrical properties of the coated material on the waveguide. The approach was applied on graphene oxide for purpose of humidity sensing. The results show that the sensitivity is improved betwe...

Generally, in a waveguide-based humidity sensors, increasing the relative humidity (RH) causes the cladding refractive index (RI) to increase due to cladding water absorption. However, if graphene oxide (GO) is used, a reverse phenomenon is seen due to a gap increase in graphene layers. In this paper, this interesting property is applied in order t...

Increased absorption of transverse-magnetic (TM) - polarised light by a graphene-oxide (GO) coated polymer waveguide has been observed in the presence of transverse-electric (TE) - polarised light. The GO-coated waveguide exhibits very strong photo-absorption of TE-polarised light - and acts as a TM-pass waveguide polariser. The absorbed TE-polaris...

An on-chip optical humidity sensor using Nano-anatase TiO2 coating is presented here. The coating material was prepared so that the result is in solution form, making the fabrication process quick and simple. Then, the solution was effortlessly spin-coated on an SU8 straight channel waveguide. Investigating the sensitivity and performance (response...