We report an experimental validation of a machine learning-based design method that significantly accelerates the development of all-dielectric complex-shaped meta-atoms supporting specified Mie-type resonances at the desired wavelength, circumventing the conventional time-consuming approaches. We used machine learning to design isolated meta-atoms with specific electric and magnetic responses, verified them within the quasi-normal mode expansion framework, and explored the effects of the substrate and periodic arrangements of such meta-atoms. Since the implemented method allowed for the swift transition from design to fabrication, the optimized meta-atoms were fabricated, and their corresponding scattering spectra were measured using white light spectroscopy, demonstrating an excellent agreement with the theoretical predictions.
Structural coloration generates colors by the interaction between incident light and micro- or nano-scale structures. It has received tremendous interest for decades, due to advantages including robustness against bleaching and environmentally friendly properties (compared with conventional pigments and dyes). As a versatile coloration strategy, the tuning of structural colors based on micro- and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays, anti-counterfeiting, and coating. However, scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost, scalability, and fabrication. In this review, we analyze the key challenges and opportunities in the development of structural colors. We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration. The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market. Finally, we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas.
Optical metasurfaces are engineered 2D electromagnetic structures enabling flat optical elements with properties not readily found in nature. Their unit cells, meta-atoms, usually are represented by a set of electric and magnetic multipoles. All-dielectric-based metasurfaces have recently attracted significant attention owing to their virtually lossless transmission properties at optical frequencies. A majority of reported dielectric metamaterials are composed of relatively simple meta-atoms such as spheres, cubes, and cylinders, whose electromagnetic response is dominated by the electric dipole. However, magnetic dipoles and higher-order multipoles may enable new optical properties and functionalities, including directional scattering, beam steering, and new frequency generation. Despite impressive progress in the field of optical metamaterials and nanofabrication technologies, engineering meta-atoms that support such higher-order resonances is still challenging. Here, we demonstrate that designed titanium dioxide meta-atoms can enable dominant magnetic dipole response. We apply a machine-learning model to predict a meta-atom shape with a strong magnetic dipole resonant mode at the operating wavelength of 750 nm. Using finite-element-based numerical simulations implemented in COMSOL Multiphysics, we found that the optimized meta-atom is robust against experimental variations and conditions such as a non-perfectly collimated incident beam, nanofabrication inaccuracies, and an added substrate. The meta-atoms have been fabricated using two approaches, focused ion beam lithography and an electron beam lithography followed by reactive ion etching, and characterized using white light spectroscopy. To the best of our knowledge, this is the first experimental realization of a machine-learning-based optimization of a magnetic dipole mode at optical frequencies.
Quantum technologies rely on creating and manipulating entangled sources, which are essential for quantum information, communication, and imaging. By integrating quantum technologies and all-dielectric metasurfaces, the performance of miniature display devices can be enhanced to a higher level. Miniature display technology, such as virtual reality display, has achieved original commercial success, and was initially applied to immersive games and interactive scenes. While the consumer market has quickly adopted this technology, several areas remain for improvement, including concerns around bulkiness, dual-channel display, and noise reduction. Here, we experimentally realize a quantum meta-hologram concept demonstration of a miniature display. We fabricate an ultracompact meta-hologram based on 1 μm thick titanium dioxide (TiO2). The meta-hologram can be remotely switched with heralding technique and is robust against noise with the quantum entangled source. The platform can alter the miniature display channel by manipulating heralding photons’ polarization, removing speckles and multiple reflective light noise, improving imaging contrast, and potentially decreasing device weight. Imaging contrast increases from 0.36 dB under speckle noise influences to 6.8 dB in quantum correlation imaging. This approach has the potential to miniaturize quantum displays and quantum communication devices.
In recent years, Meta-lens has become a new type of optical device, showing excellent performance and novel applications. The nanoantennas of meta-lens can be used to control the phase, amplitude, and polarization at well. The phase part is the most important part of the function of the meta-lens. However, so far, the phase distribution of meta-lenses has not been directly measured, which further hinders the quantitative evaluation of their performance. We have developed an interferometric imaging phase measurement system for meta-lens and meta-devices. This system can measure the phase distribution by shooting the interference pattern. The phase distribution of meta-lenses can be measured to quantitatively characterize the imaging performance. Our meta-lens phase measurement system can help for designers to optimize the design, for manufacturers to identify defects, thereby improving the manufacturing process. This work will pave the way for meta-lens in industrial applications.
Solution-based perovskite nanoparticles have been intensively studied in the past few years due to their applications in both photovoltaic and optoelectronic devices. Here, based on the common ground between solution-based perovskite and random lasers, we have studied the mirrorless lasing actions in self-assembled perovskite nanoparticles. After synthesis from a solution, discrete lasing peaks have been observed from optically pumped perovskites without any well-defined cavity boundaries. We have demonstrated that the origin of the random lasing emissions is the scattering between the nanostructures in the perovskite microplates. The obtained quality (Q) factors and thresholds of random lasers are around 500 and 60 μJ/cm2, respectively. Both values are comparable to the conventional perovskite microdisk lasers with polygon-shaped cavity boundaries. From the corresponding studies on laser spectra and fluorescence microscope images, the lasing actions are considered random lasers that are generated by strong multiple scattering in random gain media. In additional to conventional single-photon excitation, due to the strong nonlinear effects of perovskites, two-photon pumped random lasers have also been demonstrated for the first time. We believe this research will find its potential applications in low-cost coherent light sources and biomedical detection.
We report for the first time to our knowledge, the random laser emission from surface corrugated waveguides. Discrete lasing modes, super narrow spectral linewidth, and the existence of lasing threshold behavior have been observed. A theoretical model combining transfer matrix method and effective refractive index method was presented to explain the random lasing phenomena.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.