Analysis and fabrication of corner cube array based on laser direct writing technology

Mechanically Tunable Flexible Photonic Device for Strain Sensing Applications

Flexible photonic devices based on soft polymers enable real-time sensing of environmental conditions in various industrial applications. A myriad of fabrication techniques have been established for producing optical devices, including photo and electron-beam lithography, nano/femtosecond laser writing, and surface imprinting or embossing. However, among these techniques, surface imprinting/embossing is simple, scalable, convenient to implement, can produce nanoscale resolutions, and is cost-effective. Herein, we utilize the surface imprinting method to replicate rigid micro/nanostructures onto a commonly available PDMS substrate, enabling the transfer of rigid nanostructures into flexible forms for sensing at a nanometric scale. The sensing nanopatterned sheets were mechanically extended, and the extension was remotely monitored via optical methods. Monochromatic light (450, 532, and 650 nm) was transmitted through the imprinted sensor under various force/stress levels. The optical response was recorded on an image screen and correlated with the strain created by the applied stress levels. The optical response was obtained in diffraction pattern form from the flexible grating-based sensor and in an optical-diffusion field form from the diffuser-based sensor. The calculated Young's modulus in response to the applied stress, measured through the novel optical method, was found in a reasonable range compared to the reported range of PDMS (360-870 kPa) in the literature.

Investigation of ultra-precision planing process to fabricate high luminance retroreflector based on cutting force and tool vibration analysis

In ultra-precision planing process, the analysis of the critical depth of cut (DOC) is required to reduce the edge blunt and micro burrs produced by size effect which decreases of the effective area for high luminance retroreflector. However, since the machining characteristics are different according to cutting tool shape, machining material, and cutting condition, determine of the critical DOC is difficult without a comparison of machined surfaces under various DOC measured by ultra-high resolution measuring instrument. In this study, the critical DOC was analyzed using cutting force and tool vibration signals. The specific cutting energy was calculated by cutting force and cross-sectional area to analyze the stress variation according to DOC. Also, acceleration signals were converted to frequency spectrum that analyze dominant vibrating direction of the cutting tool by variation of cutting characteristic. It was confirmed that the method of using tool vibration more effective and accurate than specific cutting energy through validation of the comparison between results from analyze of the vibration signals and direction measuring surfaces. The master mold with area of 250 mm² was manufactured by applying analyzed critical DOC. In addition, the high luminance characteristic of a retroreflection film press formed by the master mold was confirmed.

Lateral and Vertical Flow Assays for Point-of-Care Diagnostics

Lateral flow assays (LFAs) have been the pillar of rapid point-of-care (POC) diagnostics due to their simplicity, rapid process, and low cost. Recent advances in sensitivity, selectivity, and chemical stability enhancement have ensured the foothold of LFAs in commercial POC diagnostics. This paper reviews recent developments in labeling strategies and detection methods of LFAs. Moreover, vertical flow assays (VFAs) have emerged as an alternate paper-based assay due to faster detection time and unique multiplexing capabilities. Smartphones as LFA readers have been transformed into a universal integrated platform for imaging, data processing, and storage, providing quantitative results in low-resource settings. Commercial LFAs and VFAs products are evaluated with regards to their performance, market trends, and regulatory issues. The future outlook of the flow-based assays for POC diagnostics is also discussed.

Flexible corner cube retroreflector array for temperature and strain sensing

Optical sensors for detecting temperature and strain play a crucial role in the analysis of environmental conditions and real-time remote sensing. However, the development of a single optical device that can sense temperature and strain simultaneously remains a challenge. Here, a flexible corner cube retroreflector (CCR) array based on passive dual optical sensing (temperature and strain) is demonstrated. A mechanical embossing process was utilised to replicate a three-dimensional (3D) CCR array in a soft flexible polymer film. The fabricated flexible CCR array samples were experimentally characterised through reflection measurements followed by computational modelling. As fabricated samples were illuminated with a monochromatic laser beam (635, 532, and 450 nm), a triangular shape reflection was obtained at the far-field. The fabricated flexible CCR array samples tuned retroreflected light based on external stimuli (temperature and strain as an applied force). For strain and temperature sensing, an applied force and temperature, in the form of weight suspension, and heat flow was applied to alter the replicated CCR surface structure, which in turn changed its optical response. Directional reflection from the heated flexible CCR array surface was also measured with tilt angle variation (max. up to 10°). Soft polymer CCRs may have potential in remote sensing applications, including measuring the temperature in space and in nuclear power stations.

A flexible corner cube retroreflector (CCR) array based passive dual sensing is demonstrated to measure external stimuli (temperature/mechanical force as weight suspension).

Phase-conjugated directional diffraction from a retroreflector array hologram

A corner cube retroreflector (CCR) consists of three perpendicular flat surfaces and reflects the incident light back to its source.

Suspended, micron-scale corner cube retroreflectors as ultra-bright optical labels

Corner cube retroreflectors are objects with three mutually perpendicular reflective surfaces that return light directly to its source and are therefore extremely bright and easy to detect. In this work, we have fabricated suspended corner cube retroreflectors, 5 microns in size, consisting of a transparent epoxy core and three surfaces coated with gold as ultra-bright labels for use in a rapid, low-labor diagnostic platform. The authors have demonstrated that individual cubes are easily imaged using low-cost, low numerical aperture objectives in suspension and that they remain suspended over long periods of time. Moreover, we have demonstrated that the gold outer surfaces can be decorated with proteins, and that individual cubes can be bound to magnetic sample preparation particles bearing antibodies which recognize these proteins. The bound cubes can be imaged and tracked as they move through solution in response to an external magnetic field, and we have, as such, demonstrated the principle of the new biosensing approach.