Augmented reality glassed based on waveguides with diffraction gratings are the technology of choice for many device makers. They have evolved to provide excellent picture quality and large field of view to the users. However, the field of view is a key criterion for such waveguides and to further increase it the refractive index of the used materials has to be increased. With current manufacturing methods mostly nanoimprinted permanent polymers with inorganic high refractive nanoparticles are used. Commercial materials can already achieve refractive index of n=1.9 but it seems difficult to achieve refractive indices of n=2.0 and above. On the other side the glass substrates or coating are already available with a refractive index n=2.0 and higher and thus could be utilized directly for structuring the needed diffraction gratings. In this case a pattern transfer by etching is required which should enable binary grating designs as well as slanted grating. In this work the nanoimprint lithography patterning is investigated in combination with subsequent etching processes to achieve binary or slanted nanograting in high refractive TiO2 and glasses.
The need for forming gratings (for example used in VR headsets) in materials such as SiO2 has seen a recent surge in the use of Ion beam etching techniques. However, when using an argon-only beam, the selectivity is limited as it is a physical process.
Typically, gases such as CHF3, SF6, O2 and Cl2 can be added to argon in order to increase selectivity; depending on where the gas is injected, the process is known as Reactive Ion Beam Etching (RIBE) or Chemically Assisted Ion Beam Etching (CAIBE). The substrate holder can rotate in order to provide an axisymmetric etch rate profile. It can also be tilted over a range of angles to the beam direction. This enables control over the sidewall profile as well as radial uniformity optimisation. Ion beam directionality in conjunction with variable incident beam angle via platen angle setting enables profile control and feature shaping during nanopatterning. These hardware features unique to the Ion Beam etching methods can be used to create angled etch features. The CAIBE technique is also well suited to laser diode facet etch (for optoelectronic devices); these typically use III-V materials like InP.
Here, we report on materials such as SiO2 etched without rotation and at a fixed platen angle allowing the formation of gratings and InP etched at a fixed angle with rotation allowing the formation of nanopillars and laser facets.
Ion Beam Sputter Deposition (IBSD) is a versatile technique particularly suited to applications requiring high quality, high performance layer materials as it allows independent and accurate control of the process parameters. Vanadium oxides, used for example in the fabrication of microbolometers, optical switches or optical storage, exhibit interesting properties such as a high Temperature Coefficient of Resistance (TCR), relatively low 1/f noise and a semiconductormetal phase transition close to room temperature. However, it is very challenging to control the stoichiometry of the deposited film as there are at least 25 different oxidation states of vanadium, few of which display the required electrical characteristics. In the present study, vanadium oxide thin layers were deposited by IBSD using an Oxford Ionfab300+ and analyzed with regard to their electrical properties. The impact of the system parameters on the resistance repeatability, wafer-to-wafer and batch-to-batch, was thoroughly investigated to provide the end user with a clear understanding of the factors affecting film resistivity while ensuring at the same time a steep variation of resistance with temperature, as notably required for uncooled bolometers. These parameters were balanced to also achieve a good deposition rate, throughput and uniformity over large device areas, compatible with the requirements of industrial applications.
The conventional wisdom to guarantee high purity thin films in IBSD has been to use a large vacuum chamber usually in excess of 1 m3. The chamber size was important to minimise the effect of reflected high energy particles from the target surface sputtering chamber materials onto the substrate and to allow the use of large targets to avoid beam overspill onto chamber furniture. An improved understanding of beam trajectories and re-sputtered material paths has allowed the deposition of thin films with very low metallic impurity content in a chamber volume below 0.5 m3. Thus, by optimizing the sputter ion source, target and substrate configuration, and by arranging suitable shielding made of an appropriate material in the process chamber, the levels of contaminants in the deposited films have been reduced to a minimum. With this optimum hardware arrangement, the ion beam process parameters were then optimized with respect to the ppm levels of contaminants measured in the films by SIMS analysis. Using the deposition of SiO2 as a standard material for DSIMS composition analysis and impurity level determination, it has been shown that our IBS deposition tool is capable of depositing films with contamination levels of <50ppm for the total of all metal impurities in the deposited films.
A semiconductor laser coupled to a gallium-made non linear mirror may exhibit pulse regime. In order to better understand this coupled cavity, stationary solutions and dynamics are described following the standard Lang and Kobayashi equations for a semiconductor laser submitted to nonlinear optical feedback. It is shown that the nonlinearity distorts the ellipse on which lied the stationary solutions, with a "higher" part corresponding to lower reflectivity and a "lower" part to higher reflectivity. Bifurcation diagrams and nonlinear analysis are presented while the conditions for pulsed operation are discussed.
We have found recently that Gallium, confined at an interface with silica, responds dramatically to low power optical excitation when held at temperatures close to its melting point (29.8oC). Intensities of just a few kW/cm2 can reversibly modulate the intensity (by up to 40%) and phase (by as much as several degrees) of reflected light as the result of a light-induced structural transition occurring in a layer of gallium of only a few nm thick. Here, we report that this concept - of achieving a nonlinearity via a light-induced transformation in a confined solid at a temperature close to a phase transition temperature - can also be applied to gallium nanoparticles. We present the transient all-optical switching characteristics of gallium nanoparticle films comprising particles, typically 80 nm in diameter, which were formed directly on the ends of optical fibers using a new light-assisted self-assembly technique. We also report, for the first time, that this light-induced structural transition in gallium confined at an interface with silica underlies a new mechanism for photoconductivity. In our opinion, the exploitation of the light-induced phase transition in gallium may be a means of enabling the development of nanoscale photonic devices.