The ability to actively precisely control the absorption, emission, and flow of light is one of the main features of nanophotonics research. Phase change materials (PCMs) hold promise for achieving energy efficient, set-and-forget reconfigurability over long times which can be used for a range of applications in optical memory, neural networks, trimming, programmable and reconfigurable photonics. To achieve non-volatile control over optical phase without inducing large losses, a next generation of low-loss optical PCMs is needed. Recently, antimony-based materials Sb2S3 and Sb2Se3 have been introduced as a family of PCMs of particular interest for applications in telecoms, near-infrared and visible range. I will present an overview of our work on exploring the properties of Sb2Se3 including time resolved switching, endurance, and applications in silicon photonics and free space optical devices.
Adaptable, reconfigurable and programmable are key functionalities for the next generation of silicon-based photonic processors, neural and quantum networks. Phase change technology offers proven non-volatile electronic programmability, however the materials used to date have shown prohibitively high optical losses which are incompatible with integrated photonic platforms. Here, we demonstrate the capability of the previously unexplored material Sb$_2$Se$_3$ for ultralow-loss programmable silicon photonics. The favorable combination of large refractive index contrast and ultralow losses seen in Sb$_2$Se$_3$ facilitates an unprecedented optical phase control exceeding 10$\pi$ radians in a Mach-Zehnder interferometer. To demonstrate full control over the flow of light, we introduce nanophotonic digital patterning as a conceptually new approach at a footprint orders of magnitude smaller than state of the art interferometer meshes. Our approach enables a wealth of possibilities in high-density reconfiguration of optical functionalities on silicon chip.
Exploration of the Moon and Mars calls for robots that are increasingly capable in regolith, or granular soil. Beyond traversing and avoiding entrapment, future robots will excavate and process regolith as a resource. This work distinguishes concerns governing the performance of regolith operations, based on load-haul-dump tasks motivated by in situ resource utilization and lunar outpost site work. Payload ratio (mass of regolith payload capacity normalized by robot mass) and driving speed are identified as key parameters governing the productivity of small site work robots. Other parameters, such as number of wheels, are not as important. Experiments with a small robotic excavator and task-level simulations (for which a modeling framework is described) determine the relative sensitivity of productivity to changes in these variables. These findings provide direction for the development of future lightweight robotic excavators.
The emerging fields of on-chip photonic data processing, neuromorphic computing, and quantum technology are enabled by mature integrated photonics platforms. Silicon is considered the material of choice and silicon photonics is rapidly becoming a mainstream industrial platform. One of the key elements lacking is the availability of non-volatile programmable materials compatible with silicon photonics which could be used to reconfigure and program circuits without requiring continuous power to maintain its state. Recently, a new family of phase change materials Sb2S3 and Sb2Se3 have gained interest for their properties including a refractive index close to silicon, large switching of refractive index at telecommunications wavelength and ultralow optical losses. I will present here our results in developing the materials and their integration into new types of reconfigurable silicon photonics devices.
In this talk, we give an overview of our chalcogenide material and device capabilities and the applications they are driving, scaling from bulk glasses to two-dimensional films. Using a melt-quench technique, we routinely manufacture a family of Ga:La:S semiconducting glasses which offer considerable advantages over commercially available chalcogenides, expanding uses in defense, medical and sensing. We use these glasses to produce optical fibers using extrusion, rod and crucible drawing. We are also developing these materials further, for example by incorporating selenium resulting in improved infrared transmission, enabling both thermal and visible imaging for object recognition. Transition metal dichalcogenides (TMDCs) are promising alternatives to graphene, with bandgaps tunable through composition and number of layers. Today’s challenge remains in the fabrication of large area atomically thin TMDCs on desired substrates. We have developed chemical vapor and atomic layer deposition techniques to deposit highly crystalline TMDCs, from nanometers down to a monolayer on up to 6 inch wafers. We recently developed novel patterning techniques that result in defect free devices. Our applications range from 3D photonic crystals to photovoltaics and transistors. Finally we deposit chalcogenide thin films via sputtering and demonstrate applications which exploit their phase change and thermoelectric properties.
Data comprising Numerical simulation results and deep learning results to supprot article N. J. Dinsdale, P. R. Wiecha, M. Delaney, J. Reynolds, M. Ebert, I. Zeimpekis, D. J. Thomson, G. T. Reed, P. Lalanne, K. Vynck, O. L. Muskens Deep learning enabled design of complex transmission matrices for universal optical components. ACS Photonics (2020). Each figure has a Readme file attached.
We propose a reconfigurable and non-volatile Bragg grating in the telecommunication C-band based on the combination of novel low-loss phase-change materials (specifically Ge2Sb2Se4Te1 and Sb2S3) with a silicon nitride platform. The Bragg grating is formed by arrayed cells of phase-change material, whose crystallisation fraction modifies the Bragg wavelength and extinction ratio. These devices could be used in integrated photonic circuits for optical communications applications in smart filters and Bragg mirrors and could also find use in tuneable ring resonators, Mach-Zehnder interferometers or frequency selectors for future laser on chip applications. In the case of Ge2Sb2Se4Te1, crystallisation produces a Bragg resonance shift up to ∼ 15 nm, accompanied with a large amplitude modulation (insertion loss of 22 dB). Using Sb2S3, low losses are presented in both states of the phase change material, obtaining a ∼ 7 nm red-shift in the Bragg wavelength. The gratings are evaluated for two period numbers, 100 and 200 periods. The number of periods determines the bandwidth and extinction ratio of the filters. Increasing the number of periods increases the extinction ratio and reflected power, also narrowing the bandwidth. This results in a trade-off between device size and performance. Finally, we combine both phase-change materials in a single Bragg grating to provide both frequency and amplitude modulation. A defect is introduced in the Sb2S3 Bragg grating, producing a high quality factor resonance (Q ∼ 104) which can be shifted by 7 nm via crystallisation. A GSST cell is then placed in the defect which can modulate the transmission amplitude from low loss to below -16 dB.
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