Diffractive optical elements in single crystal diamond.

We demonstrate the design, fabrication, and experimental characterization of near-field binary phase transmission diffractive optical elements (DOEs) in single crystal diamond. Top-hat and arbitrary pattern DOE beam shapers were numerically optimized using an iterative Fourier transform algorithm (IFTA). Commercially available single crystal diamond plates (3mm×3mm×0.3mm) were patterned using hardmask deposition (α-Si), e-beam lithography, and O2 plasma-based diamond reactive ion etching. The resulting binary phase relief patterns were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental characterization of the single crystal diamond DOEs in transmission at λ=532nm confirms excellent uniformity of the resulting top-hat beam profile as required in copper welding applications.

High-quality single crystal diamond diffraction gratings fabricated by crystallographic etching.

We demonstrate a novel method for fabricating single crystal diamond diffraction gratings based on crystallographic etching that yields high-quality diffraction gratings from commercially available <100> diamond plates. Both V-groove and rectangular gratings were fabricated and characterised using scanning electron microscopy and atomic force microscopy, revealing angles of 57° and 87° depending on the crystal orientation, with mean roughness below Ra = 5 nm on the sidewalls. The gratings were also optically characterised, showing good agreement with simulated results. The fabrication method demonstrated in this contribution shows the way for manufacturing high-quality diamond diffractive components that surpass existing devices both in quality and manufacturability.

Silicon Photonic MEMS Phase-Shifter.

We present a design for an analog phase shifter based on Silicon Photonic MEMS technology. The operation principle is based on a two-step parallel plate electrostatic actuation mechanism to bring a vertically movable suspended tapered waveguide in a first step into proximity of the bus waveguide and to tune the phase of the propagating coupled mode in a second step by actuation of the suspended waveguide to tune the vertical gap. In the coupled state, the effective index of the optical supermode and the total accumulated phase delay can be varied by changing the vertical separation between the adiabatically tapered suspended and the fixed bus waveguides. Simulations predict that π phase shift can be achieved with an actuation voltage of 19 V, corresponding to a displacement of 19 nm. With an adiabatic coupler geometry, the optical signal can be coupled between the moving waveguide and the bus waveguide with low loss in a wide wavelength range from 1.5 µm to 1.6 µm keeping the average insertion loss below 0.3 dB.

Precision micro-mechanical components in single crystal diamond by deep reactive ion etching.

The outstanding material properties of single crystal diamond have been at the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. In particular, the extreme mechanical hardness, the highest elastic modulus of any bulk material, low density, and the promise for low friction have spurred interest most notably for micro-mechanical and MEMS applications. While reactive ion etching of diamond has been reported previously, precision structuring of freestanding micro-mechanical components in single crystal diamond by deep reactive ion etching has hitherto remained elusive, related to limitations in the etch processes, such as the need of thick hard masks, micromasking effects, and limited etch rates. In this work, we report on an optimized reactive ion etching process of single crystal diamond overcoming several of these shortcomings at the same time, and present a robust and reliable method to produce fully released micro-mechanical components in single crystal diamond. Using an optimized Al/SiO2 hard mask and a high-intensity oxygen plasma etch process, we obtain etch rates exceeding 30 µm/h and hard mask selectivity better than 1:50. We demonstrate fully freestanding micro-mechanical components for mechanical watches made of pure single crystal diamond. The components with a thickness of 150 µm are defined by lithography and deep reactive ion etching, and exhibit sidewall angles of 82°-93° with surface roughness better than 200 nm rms, demonstrating the potential of this powerful technique for precision microstructuring of single crystal diamond.

A Multimodal, SU-8 - Platinum - Polyimide Microelectrode Array for Chronic In Vivo Neurophysiology.

Utilization of polymers as insulator and bulk materials of microelectrode arrays (MEAs) makes the realization of flexible, biocompatible sensors possible, which are suitable for various neurophysiological experiments such as in vivo detection of local field potential changes on the surface of the neocortex or unit activities within the brain tissue. In this paper the microfabrication of a novel, all-flexible, polymer-based MEA is presented. The device consists of a three dimensional sensor configuration with an implantable depth electrode array and brain surface electrodes, allowing the recording of electrocorticographic (ECoG) signals with laminar ones, simultaneously. In vivo recordings were performed in anesthetized rat brain to test the functionality of the device under both acute and chronic conditions. The ECoG electrodes recorded slow-wave thalamocortical oscillations, while the implanted component provided high quality depth recordings. The implants remained viable for detecting action potentials of individual neurons for at least 15 weeks.