Search

Purpose When wearable and implantable devices first arose in the 1970s, they were rigid and clashed dramatically with our soft, pliable skin and organs. The past two decades have witnessed a major upheaval in these devices. Traditional electronics are six orders of magnitude stiffer than soft tissue. As a result, when rigid electronics are integrated with the human body, severe challenges in both mechanical and geometrical form mismatch occur. This mismatch creates an uneven contact at the interface of soft-tissue, leading to noisy and unreliable data gathering of the body’s vital signs. This paper aims to predict the role that discreet, seamless medical devices will play in personalized health care by discussing novel solutions for alleviating this interface mismatch and exploring the challenges in developing and commercializing such devices. Design methodology/approach Since the form factors of biology cannot be changed to match those of rigid devices, conformable devices that mimic the shape and mechanical properties of soft body tissue must be designed and fabricated. These conformable devices play the role of imperceptible medical interfaces. Such interfaces can help scientists and medical practitioners to gain further insights into the body by providing an accurate and reliable instrument that can conform closely to the target areas of interest for continuous, long-term monitoring of the human body, while improving user experience. Findings The authors have highlighted current attempts of mechanically adaptive devices for health care, and the authors forecast key aspects for the future of these conformable biomedical devices and the ways in which these devices will revolutionize how health care is administered or obtained. Originality/value The authors conclude this paper with the perspective on the challenges of implementing this technology for practical use, including device packaging, environmental life cycle, data privacy, industry partnership and collaboration.

The first page of this article is displayed as the abstract

We have previously presented a novel spatial light modulator appropriate for use in transparent, flat-panel holographic display applications. Our architecture consists of an anisotropic leaky-mode coupler and integrated Bragg reflection grating as a monolithic device implemented in lithium niobate and is fabricated using direct femtosecond laser writing techniques. In this paper, we present a methodology for the experimental characterization of holographically-reconstructed point spread functions from sample devices.

We have previously introduced a femtosecond laser micromachining-based scheme for the fabrication of anisotropic waveguides and isotropic Bragg reflection gratings in lithium niobate for application in future integrated-optic spatial light modulators. In this paper, we depict progress in fabrication and characterization of anisotropic Bragg reflection gratings fabricated in lithium niobate via Type I femtosecond laser-based permittivity modulation. We furthermore depict an electromagnetic analysis of such multilayer grating structures based around coupled-wave theory for thick holographic gratings.

We have previously introduced a monolithic, integrated optical platform for transparent, flat-panel holographic displays suitable for near-to-eye displays in augmented reality systems. This platform employs a guided-wave acousto-optic spatial light modulator implemented in lithium niobate in conjunction with an integrated Bragg-regime reflection volume hologram. In this paper, we depict analysis of three key system attributes that inform and influence the display system performance: 1) single-axis diffraction-driven astigmatism, 2) strobed illumination to enforce acousto-optic grating stationarity, and 3) acousto-optically driven spatial Nyquist rate.

Near-to-eye holographic displays act to directly project wavefronts into a viewer’s eye in order to recreate 3-D scenes for augmented or virtual reality applications. Recently, several solutions for near-to-eye electroholography have been proposed based on digital spatial light modulators in conjunction with supporting optics, such as holographic waveguides for light delivery; however, such schemes are limited by the inherent low space-bandwidth product available with current digital SLMs. In this paper, we depict a fully monolithic, integrated optical platform for transparent near-to-eye holographic display requiring no supporting optics. Our solution employs a guided-wave acousto-optic spatial light modulator implemented in lithium niobate in conjunction with an integrated Bragg-regime reflection volume hologram.

We have previously introduced a femtosecond laser micromachining-based scheme for the fabrication of anisotropic waveguides in lithium niobate for use in a guided-wave acousto-optic spatial light modulator. This spatial light modulation scheme is extensible to off-plane waveguide holography via the integration of a Bragg reflection grating. In this paper, we present femtosecond laser-based direct-write approaches for the fabrication of (1) waveguide in-coupling gratings and (2) volume Bragg reflection gratings via permanent refractive index changes within the lithium niobate substrate. In combination with metal surface-acoustic-wave transducers, these direct-write approaches allow for complete fabrication of a functional spatial light modulator via femtosecond laser direct writing.

Recently, the fabrication of high-resolution silver nanostructures using a femtosecond laser-based direct write process in a gelatin matrix was reported. The application of direct metal writing towards feature development has also been explored with direct metal fusion, in which metal is fused onto the surface of the substrate via a femtosecond laser process. In this paper, we present a comparative study of gelatin matrix and metal fusion approaches for directly laser-written fabrication of surface acoustic wave transducers on a lithium niobate substrate for application in integrated optic spatial light modulators.

We have previously introduced an anisotropic leaky-mode modulator as a waveguide-based, acousto-optic solution for spatial light modulation in holographic video display systems. Waveguide fabrication for these and similar surface acoustic wave devices relies on proton exchange of a lithium niobate substrate, which involves the immersion of the substrate in an acid melt. While simple and effective, waveguide depth and index profiles resulting from proton exchange are often non-uniform over the device length or inconsistent between waveguides fabricated at different times using the same melt and annealing parameters. In contrast to proton exchange, direct writing of waveguides has the appeal of simplifying fabrication (as these methods are inherently maskless) and the potential of fine and consistent control over waveguide depth and index profiles. In this paper, we explore femtosecond laser micromachining as an alternative to proton exchange in the fabrication of waveguides for anisotropic leaky-mode modulators.

Waveguide holography refers to the use of holographic techniques for the control of guided-wave light in integrated optical devices (e.g., off-plane grating couplers and in-plane distributed Bragg gratings for guided-wave optical filtering). Off-plane computer-generated waveguide holography (CGWH) has also been employed in the generation of simple field distributions for image display. We have previously depicted the design and fabrication of a binary-phase CGWH operating in the Raman-Nath regime for the purposes of near-to-eye 3-D display and as a precursor to a dynamic, transparent flat-panel guided-wave holographic video display. In this paper, we describe design algorithms and fabrication techniques for multilevel phase CGWHs for near-to-eye 3-D display.

Doping is a process in which atomic impurities are intentionally added to a host material to modify its properties. It has had a revolutionary impact in altering or introducing electronic, magnetic, luminescent, and catalytic properties for several applications, for example in semiconductors. Here we explore and demonstrate the extension of the concept of substitutional atomic doping to nanometre-scale crystal doping, in which one nanocrystal is used to replace another to form doped self-assembled superlattices. Towards this goal, we show that gold nanocrystals act as substitutional dopants in superlattices of cadmium selenide or lead selenide nanocrystals when the size of the gold nanocrystal is very close to that of the host. The gold nanocrystals occupy random positions in the superlattice and their density is readily and widely controllable, analogous to the case of atomic doping, but here through nanocrystal self-assembly. We also show that the electronic properties of the superlattices are highly tunable and strongly affected by the presence and density of the gold nanocrystal dopants. The conductivity of lead selenide films, for example, can be manipulated over at least six orders of magnitude by the addition of gold nanocrystals and is explained by a percolation model. As this process relies on the self-assembly of uniform nanocrystals, it can be generally applied to assemble a wide variety of nanocrystal-doped structures for electronic, optical, magnetic, and catalytic materials.