PhD Student in Photonics (ESR 10): Efficient nonlinear broadband light sources in photonic...

Updated: 3 months ago
Job Type: FullTime
Deadline: 22 May 2020

We seek a highly talented and ambitious PhD student to join, in the framework of the ECLAUSion cotutelle programm (see below), our project aiming at creating Efficient nonlinear broadband light sources in photonic integrated circuits.

In the past two decades, silicon photonics has emerged as a mature technological platform allowing for multiple optical functions to be integrated onto the same chip. Electro-optic modulators, SiGe photodetectors and low-loss silicon waveguides are now available. However, when it comes to light emission or nonlinear functions, silicon turns out to be intrinsically limited. The heterogeneous integration of III-V materials onto silicon has already provided a way to realize efficient LED or laser devices. Similarly, several material candidates are investigated for their nonlinear properties, with the aim to integrate them onto the mature silicon photonic platform. The nonlinear optical response of materials can enable attractive optical devices such as all-optical switches and even amplifiers that can directly control light signals with other light signals. These all optical nonlinear devices are much faster than their optoelectronic counterparts and perhaps more importantly, they can enable completely new functions such as wavelength conversion, the generation of frequency combs or supercontinuum light. More generally, a wide range of nonlinear devices can be realized for information processing using light control signals.

Despite the high application potential of nonlinear optics for all-optical information processing, no nonlinear material candidate has emerged as a clear choice to complement silicon photonics so far. On the one hand, wide band gap semiconductors have been investigated, but their integration onto silicon photonics is not straightforward. Glass materials have also been explored, but their relatively weak nonlinearity precludes the realization of compact devices. Lithium niobate (LiNBO3) possesses both a second-order (c(2)) and third-order (c(3)) nonlinearity, which proves useful for both electro-optical modulation and also all-optical signal processing devices. However, it has been very difficult to create high performance nanophotonic devices due the low index contrast typically offered by this technology.

Very recently, thin-film lithium niobate on insulator wafers have become commercially available and emerged as a highly promising platform for integrated nonlinear optics. Most importantly, this platform supports tightly confining waveguide geometries, a boost for nonlinearities, while additionally opening opportunities for dispersion engineering, which is key to device efficiency and broadband processes, such as frequency combs and supercontinuum. The combination of both c(2)and c(3) responses can, in contrast with silicon where only c(3) does exist, provide new ways of electrically tuning all-optical nonlinear functions. Furthermore, the birefringence of lithium niobate and ferroelectric domain inversion capabilities provide opportunities for phase matching and quasi phase matching, which is critical for frequency conversion processes, such as four-wave mixing or high-order harmonic generation.

RMIT has developed a complementary route towards high performance thin-film lithium niobate based devices that exploits strip loading of another thin film, silicon nitride (Si3N4) for instance, which is patterned instead of the lithium niobate so as to support low loss guided modes.

The specific objectives of this PhD study will be (1) to exploit strip-loaded lithium niobate on insulator waveguides and resonators to design and realize highly efficient c(3) nonlinear devices with anomalous dispersion for frequency conversion as well as supercontinuum and frequency comb generation, (2) to experimentally demonstrate the integration of electro-optical modulators with c(3) ring resonators on a single chip, where the modulation frequency of the modulator can be tuned to match the free spectral range of the ring resonator, which will enable the efficient generation of optical frequency combs, (3) explore the alternative path offered by c(2) nonlinear optics via quasi-phase matching in lithium niobate for the generation of optical frequency combs and (4) use the c(2) response of lithium niobate to realize tunable nonlinear functions.

Expected original contributions:

  • Contribution to the development of a generic integrated photonic platform made of strip-loaded thin-film lithium niobate on insulator for high performance nonlinear optics on a chip
  • Demonstration of all-optical signal processing devices and broadband supercontinuum using low-power pump sources
  • Contribution to the field of frequency combs, by investigation of the potential interplay between electro-optic and Kerr combs as well as using c(2) for comb generation

Research program and methodology:

The PhD student will be involved in the design, fabrication and test of the lithium niobate on insulator nonlinear devices at telecom wavelengths (l~1,55mm). This will include the patterning of the strip-loaded silicon nitride material deposited on top of the thin-film lithium niobate on insulator wafer for producing the nanophotonic devices by traditional clean-room nanofabrication (nanolithography, etching) at the NANOLYON nanotechnology platform and the MNRF Melbourne (for waveguide structures and periodic poling). The PhD student will also drive the characterization efforts of the resulting optical devices using the characterization setups available at INL (both linear and nonlinear optical test-beds) and RMIT.

The student will be working with the Nanophotonics research group at INL hosted by Ecole Centrale de Lyon, the Integrated Photonics and Applications Centre (InPAC) by Prof. Arnan Mitchell at RMIT for integrated photonic devices. The student will benefit from INL's and RMIT’s resources and expertise in silicon photonics, non-linear optics and lithium niobate periodic poling, both in terms of device design and on technology and clean room manufacturing aspects for the production of the first basic demonstrators. S/he will contribute to develop an original nonlinear integrated platform with as long-lasting impact for Datacom and telecom applications.

The cotutelle ECLAUSion program

We seek talented and ambitious PhD students to join our new cotutelle PhD program ECLAUSion. ECLAUSion will build on ECL and RMIT outstanding reputation of research excellence, state of the art research facility in micro-nanofabrication and nanotechnology platform, and the rich Lyon and Melbourne area ecosystem in biotechnology and ICT industries to offer a multidisciplinary, cutting edge research program initially centered around 4 topics impacted by nanotechnologies i) functional materials, ii) electronics and computing architecture, iii) photonics and photovoltaics, iv) biotechnology and healthcare. ECLAUSion, with their strong academic researchers, programs and industrial support for the first time gathered within a single flag, provides a unique opportunity to develop global (across continents) crossdisciplinary PhD training & research with impact ranging from fundamental science to original technological innovation underpinned by nanotechnology. The domains of application cover key economic sectors for investment and growth and have been flagged as research collaboration priority in the Australian-EU S&T roadmap: semiconductors, microelectronics and photonics, telecommunications, ICTs in general, energy, health and well-being, biosensors.

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