Bangor University DOCTOR OF PHILOSOPHY All-dielectric superlens and applications Yan, Bing Award date: 2018 Awarding institution: Bangor University Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 09. Oct. 2021 ALL-DIELECTRIC SUPERLENS AND APPLICATIONS Bing Yan School of Electronic Engineering Bangor University A thesis submitted in partial fulfilment for the degree of Doctor of Philosophy May 2018 IV Acknowledgements First and foremost, I would like to express my sincere gratitude to my supervisor Dr Zengbo Wang for giving me this opportunity to work on such an exciting topic, and for his constant support during my entire PhD study and research. His guidance helped me in all time of research and writing of this thesis. I could not have imagined having a better advisor and mentor for my PhD study. During my PhD study, I have visited Swansea University and worked with many fascinating people for six months. Therefore, my sincere thank goes to Prof. Owen Guy, for his support and the use of equipment in their clean room. I would also like to thank Prof. Perumal Nithiarasu for his valuable guidance on the simulation works. So many interesting results were produced during that period. I have to say that I had an unforgettable half-year studying experience in Swansea University. I would like to thank the Sêr Cymru National Research Network for the financial support during this research. In addition, I want to thank my colleagues in Bangor: Dr Liyang Yue, Dr Rakesh Dhama Mr James Norman Monks, Dr Yanhua Hong and Dr Paul Sayers for their continuous support in research and friendly helps in my daily life. Also, I thank my friends Chen Liu, Songkun Ji, Mingliang Deng, Yixian Dong who are PhD students from different research groups in School of Electronic Engineering at Bangor University. They let me, an overseas student, have the feeling of hometown during my three-year intensive PhD life. Without my parents I would have never accomplished so much. I would like to thank them, for giving birth to me and encouraging and supporting me financially and spiritually throughout my life. Thank you, my wife Aijun, who is always there for me, no matter the best and the worst, the difficult and the easy. No words can express my gratitude to you. Thank you, my son Ethan, your smile is my biggest driving force. V Abstract One of the great challenges in optics is to break the diffraction limit to achieve optical super- resolution for applications in imaging, sensing, manufacturing and characterization. In recent years we witnessed a number of exciting developments in this field, including for example super-resolution fluorescent microscopy, negative-index metamaterial superlens and super- oscillation lens. However, none of them can perform white-light super-resolution imaging until the development of microsphere nanoscopy technique, which was pioneered by the current PhD’s research group. The microscope nanoscopy technique was developed based on all-dielectric microsphere superlens which is fundamentally different from metal-based superlenses. In this research, we aim to significantly advance the technology by: (1) increasing superlens resolution to sub- 50 nm scale and (2) improving superlens usability and demonstrate application in wider context including lab-on-chip devices. Our longer-term vision is to bring the all-dielectric superlens technology to market so that each microscope user can have superlens in hand for their daily examination of nanoscale objects including viruses. To improve the superlens resolution, a systematic theoretical study was first carried out on the optical properties of dielectric microsphere superlens. New approaches were proposed to obtain precise control of the focusing properties of the microsphere lens. Using pupil mask engineering and two-material composite superlens design, one can precisely control the focusing properties of the lens and effectively surpass the diffraction limit λ/2n. To further improve the resolution, we incorporated the metamaterial concept in our superlens design. A new all-dielectric nanoparticle metamaterial superlens design was proposed. This is realized by 3D stacking of high-index nanoparticles to form a micro-sized particle lens. This man-made superlens has unusual optical properties not found in nature: highly effective conversion of evanescent wave to propagating wave for unprecedented optical super-resolution. By using 15 nm TiO2 nanoparticles as building blocks, the fabricated 3D all-dielectric metamaterial-based solid immersion lens (mSIL) can produce a sharp image with a super-resolution of at least 45 nm under a white-light optical microscope, significantly exceeding the classical diffraction limit and previous near-field imaging techniques. In additional to mSIL where only one kind of nanoparticle was used, we also studied two- VI nanomaterial hybrid system. High-quality microspheres consisting of ZrO2/polystyrene elements were synthesised and studied. We show precise tuning of the refractive index of microspheres can effectively enhance the imaging resolution and quality. To increase superlens usability and application scope, we proposed and demonstrated a new microscope objective lens that features a two times resolution improvement over conventional objective. This is accomplished by integrating a conventional microscope objective lens with a superlensing microsphere lens with a customised lens adaptor. The new objective lens was successfully demonstrated for label-free super-resolution static and scanning imaging of 100 nm features in engineering and biological samples. In an effort to reduce superlens technology entrance barrier, we studied several spider silks as naturally occurring optical superlens. These spider silks are transparent in nature and have micron-scale cylinder structure. They can distinctly resolve λ/6 features with a large field-of- view under a conventional white-light microscope. This discovery opens a new door to develop biology-based optical systems and has enriched the superlens category. Because microsphere superlenses are small in size, their application can be extended to lab- on-chip device. In this thesis, microsphere superlens was introduced to a microfluidic channel to build an on-chip microfluidic superlensing device for real-time high-resolution imaging of biological objects. Several biological samples with different features in size, transparency, low contrast and strong mobility have been visualised. This integrated device provides a new way to allow researchers to directly visualise details of biological specimens in real-time under a conventional white light microscope. The work carried out in this research has significantly improved the microsphere superlens technology which opens the door for commercial exploitation. VII VIII Table of Contents 1.1 Optical super-resolution ..................................................................................................... 1 1.2 Aim and objectives .............................................................................................................. 2 1.3 Thesis outline ....................................................................................................................... 4 2.1 Optical diffraction limit ....................................................................................................... 7 2.2 Super-resolution with near-field optics .............................................................................. 8 2.3 Super-resolution techniques ............................................................................................... 9 2.3.1 Near-field Scanning Optical Microscope (NSOM or SNOM) ................................ 9 2.3.2 Metal-based Metamaterial Superlens and Hyperlens (M-MSH) ....................... 11 2.3.3 Super-Oscillation Lenses .................................................................................... 14 2.3.4 Structured Illumination Microscopy (SIM) ........................................................ 16 2.3.5 Super-resolution Fluorescent Microscopy ......................................................... 17 2.3.6 Other techniques ............................................................................................... 19 2.4 Microsphere super-resolution imaging technique .......................................................... 21 2.4.1 Photonic nanojet ................................................................................................ 21 2.4.2 Wide-field microsphere superlens ..................................................................... 23 i 2.4.3 Confocal microsphere superlens ....................................................................... 25 2.4.4 Scanning microsphere superlens ......................................................................