Advances in cost-effective integrated spectrometers

The proliferation of Internet-of-Things has promoted a wide variety of emerging applications that require compact,lightweight,and low-cost optical spectrometers.While substantial progresses have been made in the miniaturization of spectrometers,most of them are with a major focus on the technical side but tend to feature a lower technology readiness level for manufacturability.More importantly,in spite of the advancement in miniaturized spectrometers,their performance and the metrics of real-life applications have seldomly been connected but are highly important.This review paper shows the market trend for chip-scale spectrometers and analyzes the key metrics that are required to adopt miniaturized spectrometers in real-life applications.Recent progress addressing the challenges of miniaturization of spectrometers is summarized,paying a special attention to the CMOS-compatible fabrication platform that shows a clear pathway to massive production.Insights for ways forward are also presented.

Nonlinear,tunable,and active optical metasurface with liquid film

Optical metamaterials and metasurfaces,which emerged in the course of the last few decades,have revolutionized our understanding of light and light–matter interaction.While solid materials are naturally employed as key building elements for construction of optical metamaterials mainly due to their structural stability,practically no attention was given to study of liquid-made optical two-dimensional(2-D)metasurfaces and the underlying interaction regimes between surface optical modes and liquids.We theoretically demonstrate that surface plasmon polaritons and slab waveguide modes that propagate within a thin liquid dielectric film trigger optical self-induced interaction facilitated by surface tension effects,which leads to the formation of 2-D optical liquid-made lattices/metasurfaces with tunable symmetry and can be leveraged for tuning of lasing modes.Furthermore,we show that the symmetry breaking of the 2-D optical liquid lattice leads to phase transition and tuning of its topological properties,which allows the formation,destruction,and movement of Dirac-points in the k-space.Our results indicate that optical liquid lattices support extremely low lasing threshold relative to solid dielectric films and have the potential to serve as configurable analogous computation platform.

Fabrication-tolerant Fourier transform spectrometer on silicon with broad bandwidth and high resolution

We report an advanced Fourier transform spectrometer(FTS)on silicon with significant improvement compared with our previous demonstration in[Nat.Commun.9,665(2018)].We retrieve a broadband spectrum(7 THz around 193 THz)with 0.11 THz or sub nm resolution,more than 3 times higher than previously demonstrated[Nat.Commun.9,665(2018)].Moreover,it effectively solves the issue of fabrication variation in waveguide width,which is a common issue in silicon photonics.The structure is a balanced Mach–Zehnder interferometer with 10 cm long serpentine waveguides.Quasi-continuous optical path difference between the two arms is induced by changing the effective index of one arm using an integrated heater.The serpentine arms utilize wide multi-mode waveguides at the straight sections to reduce propagation loss and narrow single-mode waveguides at the bending sections to keep the footprint compact and avoid modal crosstalk.The reduction of propagation loss leads to higher spectral efficiency,larger dynamic range,and better signal-to-noise ratio.Also,for the first time to our knowledge,we perform a thorough systematic analysis on how the fabrication variation on the waveguide widths can affect its performance.Additionally,we demonstrate that using wide waveguides efficiently leads to a fabrication-tolerant device.This work could further pave the way towards a mature silicon-based FTS operating with both broad bandwidth(over 60 nm)and high resolution suitable for integration with various mobile platforms.

Thin liquid film as an optical nonlinear-nonlocal medium and memory element in integrated optofluidic reservoir computer

Understanding light–matter interaction lies at the core of our ability to harness physical effects and to translate them into new capabilities realized in modern integrated photonics platforms.Here,we present the design and characterization of optofluidic components in an integrated photonics platform and computationally predict a series of physical effects that rely on thermocapillary-driven interaction between waveguide modes and topography changes of optically thin liquid dielectric film.Our results indicate that this coupling introduces substantial self-induced phase change and transmittance change in a single channel waveguide,transmittance through the Bragg grating waveguide,and nonlocal interaction between adjacent waveguides.We then employ the self-induced effects together with the inherent built-in finite relaxation time of the liquid film,to demonstrate that the light-driven deformation can serve as a reservoir computer capable of performing digital and analog tasks,where the gas–liquid interface operates both as a nonlinear actuator and as an optical memory element.

Subnanometer imaging and controlled dynamical patterning of thermocapillary driven deformation of thin liquid films

Exploring and controlling the physical factors that determine the topography of thin liquid dielectric films are of interest in manifold fields of research in physics,applied mathematics,and engineering and have been a key aspect of many technological advancements.Visualization of thin liquid dielectric film topography and local thickness measurements are essential tools for characterizing and interpreting the underlying processes.However,achieving high sensitivity with respect to subnanometric changes in thickness via standard optical methods is challenging.We propose a combined imaging and optical patterning projection platform that is capable of optically inducing dynamical flows in thin liquid dielectric films and plasmonically resolving the resulting changes in topography and thickness.In particular,we employ the thermocapillary effect in fluids as a novel heat-based method to tune plasmonic resonances and visualize dynamical processes in thin liquid dielectric films.The presented results indicate that lightinduced thermocapillary flows can form and translate droplets and create indentation patterns on demand in thin liquid dielectric films of subwavelength thickness and that plasmonic microscopy can image these fluid dynamical processes with a subnanometer sensitivity along the vertical direction.

Novel spectral-shaping building block:a narrowband Mach-Zehnder interferometer

We present an experimental demonstration of notch filters with arbitrary center wavelengths capable of tunable analog output power values varying between full extinction of 15 and 0 dB.Fach filter is composed of highly modular apodized four-port Bragg add/drop filters to reduce the crosstalk between concatenated devices.The constructed photonic integrated circuit experimentally demonstrates spectra shaping using four independent notch filters.Fach notch filter supports a bandwidth of^2 nm and is shown to be suitable for realization of programmable photonic integrated circuits.