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Structured light just got colorful

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A new publication from Opto-Electronic Advances; DOI 10.29026/oea.2022.210174 discusses nonlinear optics with structured light.

Light can be tailored, much like cloth, weaving and stitching a pattern into the very fabric of light itself.  This so-called structured light allows us to access, harness and exploit all light’s degrees of freedom, for seeing smaller in imaging, focusing tighter in microscopy and packing more information into light for classical and quantum communications.  In this work, the authors showcase the recent advances in replacing the traditional linear optical toolkit with nonlinear control.  Historically, nonlinear optics is associated with the wavelength control, but here the authors show that the landscape is far more colourful than just the colour of the light, affecting all degrees of freedom in sometimes counter-intuitive ways. The advanced toolkit promises novel applications from classical to quantum, ushering in a new chapter in structured light.

The authors of this article review the recent progress in using nonlinear optics as a new tool for the creation, control and detection of structured light, offering new insights and perspectives on this nascent topic.  Structured light seeks to harness light’s many degrees of freedom, to impact “structure” to the light.  This could be in amplitude, phase, polarisation or even more exotic degrees of freedom such as path, orbital angular momentum and even spatiotemporal control.  To date, this has mostly been achieved with a linear optical toolkit, with nonlinear optics used to change the colour of the light (its wavelength and frequency).  The focus of attention has been on “how much light do I have?”, with efficiency questions in mind.  Today the focus is on “what does the light look like?”, the structure of the light.  In this article, the authors show how structured light with nonlinear optics can surpass the linear toolkit, mixing degrees of freedom in unusual ways, altering selection rules and producing sometimes counter-intuitive results.  For instance, to diffract light in a linear system requires a physical object with some obscuration, for example, a pin hole or slits.  But in the nonlinear regime, one structure of light itself can appear to be the amplitude object that diffracts another, for new propagation dynamics of structured fields.   Excitingly, new forms of structured light can be produced by the product of fields in nonlinear optics rather than just their sum. Quantum control of light can get a boost by replacing the ubiquitous linear beam splitter with nonlinear crystals, which has shown to enhance imaging and offer a new roadmap to high-dimensional teleportation.  Interestingly, the light-matter interaction in nonlinear optics means that advanced structured matter can be used to customized structured light, for instance, the use of advanced artificial materials such as metasurfaces and metamaterial, offering unparalleled nonlinear efficiency.

The authors unpack the physics of nonlinear optics in the context of structured light, the first report to do so, and offer a holistic introduction to the topic from fundamentals to applications.  They provide novel insights and perspectives based on their long track record in structured light, revealing how this new field is rapidly accelerating, and suggest what the future may hold when present challenges are transformed into exciting applications.

Article reference: Buono WT, Forbes A. Nonlinear optics with structured light. Opto-Electron Adv 5, 210174 (2022). doi: 10.29026/oea.2022.210174 

Keywords: wave mixing / parametric conversion / high harmonic generation / structured light / photonic crystals / holography / nonlinear optics / second harmonic generation / metasurfaces

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Prof. Forbes heads the Structured Light Laboratory at the University of the Witwatersrand (South Africa) which has pioneered the field of structured light, with the hope of harnessing light for a brighter future.  The team seeks to control light in all its degrees of freedom, in space and time.  The team have pioneered this topic, and specifically the all-digital control of light.  This control is sought directly at the source for novel lasers, with bright classical light using conventional lasers, as well as with single photons and quantum entangled light. With this control in hand, the team aims for impact both in fundamental science and applications.  Their fundamental research is based on the premise of challenging paradigms by asking simple questions that require considerably effort to answer, for example: how many photons does it take to form an image of an object? How much information can a photon hold? How do we get the information in and out? Photonics knows no boundaries, and the exciting science requires a blending of disciplines. The vision is structured light as an enabling tool, the vehicle by to tour the scientific landscape.  Understanding leads to invention, and invention with a focus leads to innovation.   Applications of the technological advances presently underway include an all-digital toolbox for industrial light-based processes, non-invasive nanoscale optical metrology, lab-on-a-chip chemistry for detecting water pollutants, designing our future communication networks for fast and quantum-enabled security, and imaging complex (living) structures with a quantum microscope.

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Opto-Electronic Advances (OEA) is a high-impact, open access, peer reviewed monthly SCI journal with an impact factor of 9.682 (Journals Citation Reports for IF 2020). Since its launch in March 2018, OEA has been indexed in SCI, EI, DOAJ, Scopus, CA and ICI databases over the time and expanded its Editorial Board to 36 members from 17 countries and regions (average h-index 49).

The journal is published by The Institute of Optics and Electronics, Chinese Academy of Sciences, aiming at providing a platform for researchers, academicians, professionals, practitioners, and students to impart and share knowledge in the form of high quality empirical and theoretical research papers covering the topics of optics, photonics and optoelectronics.

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