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Significance: Detailed biochemical and morphological imaging of the plaque burdened coronary arteries holds the promise of improved understanding of atherosclerosis plaque development, ultimately leading to better diagnostics and therapies. Aim: Development of a dual-modality intravascular catheter supporting swept-source optical coherence tomography (OCT) and frequency-domain fluorescence lifetime imaging (FD-FLIM) of endogenous fluorophores with UV excitation. Approach: We instituted a refined approach to endoscope development that combines simulation in a commercial ray tracing program, fabrication, and a measurement method for optimizing ball-lens performance. With this approach, we designed and developed a dual-modality catheter endoscope based on a double-clad fiber supporting OCT through the core and fluorescence collection through the first cladding. We varied the relative percent of UV excitation launched into the core and first cladding to explore the potential resolution improvement for FD-FLIM. The developed catheter endoscope was optically characterized, including measurement of spatial resolution and fluorescent lifetimes of standard fluorophores. Finally, the system was demonstrated on fresh ex vivo human coronary arteries. Results: The developed endoscope was shown to have optical performance similar to predictions derived from the simulation approach. The FLIM resolution can be improved by over a factor of 4 by primarily illuminating through the core rather than the first cladding. However, time-dependent solarization losses need to be considered when choosing the relative percentage. We ultimately chose to illuminate with 7% of the power transmitting through the core. The resulting catheter endoscope had 40-μm lateral resolution for OCT and <100 μm lateral resolution for FD-FLIM. Images of ex vivo coronary arteries are consistent with expectations based on histopathology. Conclusions: The results demonstrate that our approach for endoscope simulation produces reliable predictions of endoscope performance. Simulation results guided our development of a multimodal OCT/FD-FLIM catheter imaging system for investigating atherosclerosis in coronary arteries.

The refractive index is one of the most important quantities that characterize a material's optical properties. However, it is hard to measure this value over a wide range of wavelengths. Here, we demonstrate a new technique to achieve a spectrally broad refractive index measurement. When a broadband pulse passes through a sample, different wavelengths experience different delays. By comparing the delayed pulse to a reference pulse, the zero path difference position for each wavelength can be obtained and the material's dispersion can be retrieved. Our technique is highly robust and accurate, and can be miniaturized in a straightforward manner.

This paper presents a method to characterize the effective properties of inertial acoustic metamaterial unit cells for underwater operation. The method is manifested by a fast and reliable parameter retrieval procedure utilizing both numerical simulations and measurements. The effectiveness of the method was proved to be self-consistent by a metamaterial unit cell composed of aluminum honeycomb panels with soft rubber spacers. Simulated results agree well with the measured responses of this metamaterial in a water-filled resonator tube. A sub-unity density ratio and an anisotropic mass density are simultaneously achieved by the metamaterial unit cell, making it useful in implementations of transformation acoustics. The metamaterial, together with the approach for its characterization, are expected to be useful for underwater acoustic devices.

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Flat optics for spatially resolved amplitude and phase modulation usually rely on 2D patterning of layered structures with spatial thickness variation. For example, Fabry–Perot-type multilayer structures have been applied widely as spectral filter arrays. However, it is challenging to efficiently fabricate large-scale multilayer structures with spatially variable thicknesses. Conventional photo/eBeam-lithography-based approaches suffer from either low-efficiency and high-cost iterative processes or limitations on materials for spectral tunability. In this work, an efficient and cost-effective grayscale stencil lithography method is demonstrated to achieve material deposition with spatial thickness variation. The design of stencil shadow masks and deposition strategy offers arbitrarily 2D thickness patterning with low surface roughness. The method is applied to fabricate multispectral reflective filter arrays based on lossy Fabry–Perot-type optical stacks with dielectric layers of variable thickness, which generate a wide color spectrum with high customizability. Grayscale stencil lithography offers a feasible and efficient solution to overcome the thickness-step and material limitations in fabricating spatially thickness-varying structures. The principles of this method can find applications in micro-fabrication for optical sensing, imaging, and computing.

We demonstrated high-resolution pixelated quantum dots (QDs)/thiol-ene photopolymer color converters patterned by projection lithography on microLEDs. The material composite and patterning technology enable high-efficiency, wide-gamut and low cross-talk color conversion compared to drop-cast QDs.

X-ray computed tomography (XCT) can be used to measure the internal and external surfaces of an object non-destructively and with micron-level spatial resolution. XCT is therefore an appealing method for measuring and characterising the internal surface roughness of additively manufactured parts that cannot be accessed by traditional tactile and optical surface roughness instruments. In this work, an additively manufactured aluminium spherical surface roughness sample is designed, fabricated and its surface roughness measured via a focus variation microscope, the sample is then XCT scanned when embedded in varying thicknesses of surrounding material. A quantitative and qualitative comparison between the optical and XCT surface roughness measurements is made; the results show that the Sa of the XCT-based surface roughness measurements increases as a function of surrounding material thickness.