Laser Nanopatterning of Colored Ink Thin Films for Photonic Devices

Nanofabrication through conventional methods such as electron beam writing and photolithography is time-consuming, high cost, complex, and limited in terms of the materials which can be processed. Here, we present the development of a nanosecond Nd:YAG laser (532 nm, 220 mJ) in holographic Denisyuk reflection mode method for creating ablative nanopatterns from thin films of four ink colors (black, red, blue, and brown). We establish the use of ink as a recording medium in different colors and absorption ranges to rapidly produce optical nanostructures in 1D geometries. The gratings produced with four different types of ink had the same periodicity (840 nm); however, they produce distant wavelength dependent diffraction responses to monochromatic and broadband light. The nanostructures of gratings consisting of blue and red inks displayed high diffraction efficiency of certain wavelengths while the black and brown ink based gratings diffracted broadband light. These gratings have high potential to be used as low-cost photonic structures in wavelength-dependent optical filters. We anticipate that the rapid production of gratings based on different ink formulations can enable optics applications such as holographic displays in data storage, light trapping, security systems, and sensors

Toward biomaterial-based implantable photonic devices

Optical technologies are essential for the rapid and efficient delivery of health care to patients. Efforts have begun to implement these technologies in miniature devices that are implantable in patients for continuous or chronic uses. In this review, we discuss guidelines for biomaterials suitable for use in vivo. Basic optical functions such as focusing, reflection, and diffraction have been realized with biopolymers. Biocompatible optical fibers can deliver sensing or therapeutic-inducing light into tissues and enable optical communications with implanted photonic devices. Wirelessly powered, light-emitting diodes (LEDs) and miniature lasers made of biocompatible materials may offer new approaches in optical sensing and therapy. Advances in biotechnologies, such as optogenetics, enable more sophisticated photonic devices with a high level of integration with neurological or physiological circuits. With further innovations and translational development, implantable photonic devices offer a pathway to improve health monitoring, diagnostics, and light-activated therapies. Keywords: biomaterials; biocompatible; biodegradable; optics; photonicsUnited States. Department of Defense (Award FA9550-13-1-0068)National Institutes of Health (U.S.) (Award P41-EB015903)National Institutes of Health (U.S.) (Award R01-CA192878)National Science Foundation (U.S.) (Award CBET-1264356)National Science Foundation (U.S.) (Award ECCS-1505569

Glucose sensing with phenylboronic acid functionalized hydrogel-based optical diffusers

Phenylboronic acids have emerged as synthetic receptors that can reversibly bind to cis-diols of glucose molecules. The incorporation of phenylboronic acids in hydrogels offers exclusive attributes; for example, the binding process with glucose induces Donnan osmotic pressure resulting in volumetric changes in the matrix. However, their practical applications are hindered because of complex readout approaches and their time-consuming fabrication processes. Here, we demonstrate a microimprinting method to fabricate densely packed concavities in phenylboronic acid functionalized hydrogel films. A microengineered optical diffuser structure was imprinted on a phenylboronic acid based cis-diol recognizing motif prepositioned in a hydrogel film. The diffuser structure engineered on the hydrogel was based on laser-inscribed arrays of imperfect microlenses that focused the incoming light at different focal lengths and direction resulting in a diffused profile of light in transmission and reflection readout modes. The signature of the dimensional modulation was detected in terms of changing focal lengths of the microlenses due to the volumetric expansion of the hydrogel that altered the diffusion spectra and transmitted beam profile. The transmitted optical light spread and intensity through the sensor was measured to determine variation in glucose concentrations at physiological conditions. The sensor was integrated in a contact lens and placed over an artificial eye. Artificial stimulation of variation in glucose concentration allowed quantitative measurements using a smartphone’s photodiode. A smartphone app was utilized to convert the received light intensity to quantitative glucose concentration values. The developed sensing platform offers low cost, rapid fabrication, and easy detection scheme as compared to other optical sensing counterparts. The presented detection scheme may have applications in wearable real-time biomarker monitoring devices at point-of-care settings

Three-dimensional microstructured lattices for oil sensing

Monitoring of environmental contamination, including oil pollution, is important to protect marine ecosystems. A wide range of sensors are used in the petroleum industry to measure various parameters, such as viscosity, pressure, and flow. Here, we create an optical lattice mesh structure that can be used as an oil sensor integrated with optical fiber probing. The principle of operation of the sensor was based on light scattering, where the tested medium acted as a diffuser. Three different mesh-patterned structures were analyzed by optical imaging, light transmission, and scattering in the presence of supercut, diesel, and stroke oil types. The meshes were used as a medium for different types of oils, and the optical diffusion and transmission were studied in the visible spectrum. Angle-resolved measurements were carried out to characterize the light scattering behavior from the mesh structures. Different types of oils were identified on the basis of the optical behavior of the lattice structure. The fabricated mesh structures can be used as a low-cost measurement device in oil sensing

Laser-inscribed contact lens sensors for the detection of analytes in the tear fluid

Tears exhibit compositional variations as a response to ocular and systemic metabolic conditions, and they can therefore be used for the assessment of physiological health. Here, microfluidic contact lenses were developed as wearable platforms for in situ tear pH, glucose, protein, and nitrite ions sensing. The microfluidic system was inscribed in commercial contact lenses by CO2 laser ablation. The microchannel consisted on a central ring with four branches, and biosensors were embedded within microcavities located at the branches ends. The device was tested with artificial tears and colorimetric readouts were performed using a smartphone-MATLAB algorithm based on the nearest neighbor model. Sensors responded within a time range of 15 s, and yielded sensitivities of 12.23 nm/pH unit, 1.4 nm/mmol L−1 of glucose, 0.49 nm/g L−1 of proteins, and 0.03 nm/μmol L−1 of nitrites. Contact lens sensing platforms may provide on-eye tears screening with applications in the monitoring of the ocular health both in clinics and at point-of-care settings

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

Carbon Nanotube Array Based Binary Gabor Zone Plate Lenses

Diffractive zone plates have a wide range of applications from focusing x-ray to extreme UV radiation. The Gabor zone plate, which suppresses the higher-order foci to a pair of conjugate foci, is an attractive alternative to the conventional Fresnel zone plate. In this work, we developed a novel type of Beynon Gabor zone plate based on perfectly absorbing carbon nanotube forest. Lensing performances of 0, 8 and 20 sector Gabor zone plates were experimentally analyzed. Numerical investigations of Beynon Gabor zone plate configurations were in agreement with the experimental results. A high-contrast focal spot having 487 times higher intensity than the average background was obtained

Holographic Writing of Ink-Based Phase Conjugate Nanostructures via Laser Ablation

Abstract The optical phase conjugation (OPC) through photonic nanostructures in coherent optics involves the utilization of a nonlinear optical mechanism through real-time processing of electromagnetic fields. Their applications include spectroscopy, optical tomography, wavefront sensing, and imaging. The development of functional and personalized holographic devices in the visible and near-infrared spectrum can be improved by introducing cost-effective, rapid, and high-throughput fabrication techniques and low-cost recording media. Here, we develop flat and thin phase-conjugate nanostructures on low-cost ink coated glass substrates through a facile and flexible single pulsed nanosecond laser based reflection holography and a cornercube retroreflector (CCR). Fabricated one/two-dimensional (1D/2D) nanostructures exhibited far-field phase-conjugated patterns through wavefront reconstruction by means of diffraction. The optical phase conjugation property had correlation with the laser light (energy) and structural parameters (width, height and exposure angle) variation. The phase conjugated diffraction property from the recorded nanostructures was verified through spectral measurements, far-field diffraction experiments, and thermal imaging. Furthermore, a comparison between the conventional and phase-conjugated nanostructures showed two-fold increase in diffracted light intensity under monochromatic light illumination. It is anticipated that low-cost ink based holographic phase-conjugate nanostructures may have applications in flexible and printable displays, polarization-selective flat waveplates, and adaptive diffraction optics