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The lecture commenced with a warm welcome and brief speaker introduction by Prof. CHEN Qingyan, Director of PAIR. Prof. Russell kickstarted his presentation by giving a brief overview of the historical development of photonic crystal fibre (PCF), highlighting how advancements in optical fibres, Bragg scattering, photonic bandgaps and drawing towers laid the foundation for PCF breakthroughs. Prof. Russell shared that he proposed in 1991 a glass fibre with a periodic array of microscopic hollow channels running along its length might guide light in novel ways, and many PCFs emerged from drawing towers at universities in subsequent years. Next, he elaborated on the advantages of PCF, explaining how it offers enhanced control over the propagation light, and how this property has enabled valuable applications. He shared his research in light-guiding PCF, hollow core PCF filled with gas, and twisted PCF, reviewing how some of the scientific discoveries made possible by PCF have evolved into real-world applications.

More than one hundred years ago, Albert Einstein published his Theory of General Relativity (GR). One year later, Karl Schwarzschild solved the GR equations for a non-rotating, spherical mass distribution; if this mass is sufficiently compact, even light cannot escape from within the so-called event horizon, and there is a mass singularity at the center. The theoretical concept of a 'black hole' was born, and was refined in the next decades by work of Penrose, Wheeler, Kerr, Hawking and many others. First indirect evidence for the existence of such black holes in our Universe came from observations of compact X-ray binaries and distant luminous quasars. I will discuss the forty-year journey, which my colleagues and I have been undertaking to study the mass distribution in the Center of our Milky Way from ever more precise, long-term studies of the motions of gas and stars as test particles of the space time. These studies show the existence of a four million solar mass object, which must be a single massive black hole, beyond any reasonable doubt.