Microfluidics and Raman microscopy: current applications and future challenges

Raman microscopy systems are becoming increasingly widespread and accessible for characterising chemical species. Microfluidic systems are also progressively finding their way into real world applications. Therefore, it is anticipated that the integration of Raman systems with microfluidics will become increasingly attractive and practical. This review aims to provide an overview of Raman microscopy-microfluidics integrated systems for researchers who are actively interested in utilising these tools. The fundamental principles and application strengths of Raman microscopy are discussed in the context of microfluidics. Various configurations of microfluidics that incorporate Raman microscopy methods are presented, with applications highlighted. Data analysis methods are discussed, with a focus on assisting the interpretation of Raman-microfluidics data from complex samples. Finally, possible future directions of Raman-microfluidic systems are presented

Microwave and RF signal processing based on integrated soliton crystal optical microcombs

Microcombs are powerful tools as sources of multiple wavelength channels for photonic RF signal processing. They offer a compact device footprint, large numbers of wavelengths, and wide Nyquist bands. Here, we review recent progress on microcomb-based photonic RF signal processors, including true time delays, reconfigurable filters, Hilbert transformers, differentiators, and channelizers. The strong potential of optical micro-combs for RF photonics applications in terms of functions and integrability is also discussed

Ridge Resonance: A new Resonance Phenomenon for Silicon Photonics Harnessing Bound States in the Continuum

We present a new resonant behavior based on bound states in the continuum in a guided wave silicon platform. The continuum has the form of a collimated beam of light which is confined vertically in a TE mode of a silicon slab. The bound state is a discrete TM mode of a ridge on the silicon slab. The coupling between the slab and ridge modes results in a single sharp resonance at the wavelength where they phase match. We experimentally demonstrate this phenomenon on a silicon photonic chip using foundry compatible parameters and interface it on-chip to standard single mode silicon nanowire waveguides. The fabricated chip exhibits a single sharp resonance near 1550 nm with a line width of a few nanometer, an extinction ratio of 25 dB and a thermal stability of 19.5 pm/C. We believe that this is the first demonstration of bound states in the continuum resonance realized using guided wave components

Media 1: Dielectric resonator nanoantennas at visible frequencies

Originally published in Optics Express on 14 January 2013 (oe-21-1-1344

Controlled Electrochemical Deformation of Liquid-Phase Gallium

Pure gallium is a soft metal with a low temperature melting point of 29.8 °C. This low melting temperature can potentially be employed for creating optical components with changeable configurations on demand by manipulating gallium in its liquid state. Gallium is a smooth and highly reflective metal that can be readily maneuvered using electric fields. These features allow gallium to be used as a reconfigurable optical reflector. This work demonstrates the use of gallium for creating reconfigurable optical reflectors manipulated through the use of electric fields when gallium is in a liquid state. The use of gallium allows the formed structures to be frozen and preserved as long as the temperature of the metal remains below its melting temperature. The lens can be readily reshaped by raising the temperature above the melting point and reapplying an electric field to produce a different curvature of the gallium reflector

Synthesis of Self-Assembled Island-Structured Complex Oxide Dielectric Films

A self-assembly driven process to synthesize island-structured dielectric films is presented. An intermetallic reaction in platinized silicon substrates provides preferential growth sites for the complex oxide dielectric layer. Microscopy and spectroscopy analyses have been used to propose a mechanism for this structuring process. This provides a simple and scalable process to synthesize films with increased surface area for sensors, especially those materials with a complex chemistry. The ability of these island-structured dielectric films to improve sensitivity by a factor of 100 compared to continuous films in applications as substrates for surface-enhanced Raman scattering (SERS) is demonstrated

Optical chirality from dark-field illumination of planar plasmonic nanostructures

Dark-field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction analogous to true chiral scatterers. Circular dichrosim is experimentally observed at the maximum scattering of single oligomers consisting rotationally symmetric arrangements of gold nanorods, with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the geometric projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark-field that is normally incident on a glass substrate. Owing to this geometric origin, the wavelength of the peak chiral response is also experimentally shown to shift depending on the separation between nanoparticles. All presented oligomers have physical dimensions less than the operating wavelength, and the applicable extension to closely packed planar arrays of oligomers is demonstrated to amplify the magnitude of circular dichroism. The realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark-field illumination

Applications of integrated optical microcombs

Optical microcombs represent a new paradigm for generating laser frequency combs based on compact chip-scale devices, which have underpinned many modern technological advances for both fundamental science and industrial applications. Along with the surge in activity related to optical micro-combs in the past decade, their applications have also experienced rapid progress, not only in traditional fields such as frequency synthesis, signal processing, and optical communications, but also in new interdisciplinary fields spanning the frontiers of light detection and ranging (LiDAR), astronomical detection, neuromorphic computing, and quantum optics. This paper reviews the applications of optical microcombs. First, an overview of the devices and methods for generating optical microcombs is provided, which are categorized into material platforms, device architectures, soliton classes, and driving mechanisms. Second, the broad applications of optical microcombs are systematically reviewed, which are categorized into microwave photonics, optical communications, precision measurements, neuromorphic computing, and quantum optics. Finally, the current challenges and future perspectives are discussed

Improved second harmonic performance in periodically poled LNOI waveguides through engineering of lateral leakage

In this contribution we investigate the impact of lateral leakage for linear and nonlinear optical waveguides in lithium niobate on insulator (LNOI). Silicon nitride (SiN) loaded and direct patterned lithium niobate cross-sections are investigated. We show that lateral leakage can take place for the TE mode in LNOI ridge waveguides (X-cut lithium niobate), due to the birefringence of the material. This work gives guidelines for designing waveguides in LNOI that do not suffer from the lateral leakage effect. By applying these design considerations, we avoided the lateral leakage effect at the second harmonic wavelength of a nonlinear optical waveguide in LNOI and demonstrate a peak second harmonic generation conversion efficiency of ~1160% W-1cm-2

Emerging applications of integrated optical microcombs for analogue RF and microwave photonic signal processing

We review new applications of integrated microcombs in RF and microwave photonic systems. We demonstrate a wide range of powerful functions including a photonic intensity high order and fractional differentiators, optical true time delays, advanced filters, RF channelizer and other functions, based on a Kerr optical comb generated by a compact integrated microring resonator, or microcomb. The microcomb is CMOS compatible and contains a large number of comb lines, which can serve as a high performance multiwavelength source for the transversal filter, thus greatly reduce the cost, size, and complexity of the system. The operation principle of these functions is theoretically analyzed, and experimental demonstrations are presented