We present a fabrication method to obtain freestanding optical microcavities in Single Crystal Diamond (SCD), based on a combination of Reactive Ion Etching (RIE) and multidirectional Focused Ion Beam (FIB) milling, and we report for the first time experimental optical characterization of freestanding diamond optical microdisk resonators obtained by this fabrication method. Patterning of the optical microcavities is achieved by contact photolithography on single crystal CVD diamond plates (3 mm x 3 mm x 0.15 mm), using a SiO2 hard mask and optimized O2 diamond plasma etching, resulting in multiple circular pillars in a single etch step. Individual pillars are subsequently undercut by multi-directional FIB milling from two orthogonal directions, shaping the anchor to the bulk substrate. Sequential FIB thinning and smoothing of the disks allows obtaining freestanding optical microcavities. During FIB milling, an Al/Cr layer (50 nm/75 nm) is used to ground the diamond substrate, simultaneously limiting ion implantation and reducing FIB induced edge rounding. We experimentally probe the cavities by a tunable laser, coupled to the resonator by a tapered single mode fiber. The spectral response of a typical microdisk (diameter 5.9 μm, thickness 800 nm) in transmission over the tuning range of the laser (1485 nm to 1550 nm) reveals multiple optical resonances with a Free Spectral Range of 52.5 nm and optical Q-factors attaining up to 1500 (at 1496 nm). To our knowledge, this is the first time that freestanding optical microdisk resonators are demonstrated in Single Crystal Diamond by a combination of RIE and multidirectional FIB milling, providing a path for high-Q optical cavities in diamond.
Single Crystal Diamond has been recognized as a prime material for optical components in high power applications due to low absorption and high thermal conductivity. However, diamond microstructuring remains challenging. Here, we report on the fabrication and characterization of optical diffraction gratings exhibiting a symmetric trapezoidal profile etched into a single crystal diamond substrate. The optimized grating geometry diffracts the transmitted optical power into precisely defined proportions, performing as an effective beam splitter.
We fabricate our gratings in commercially available single crystal CVD diamond plates (2.6mm x 2.6mm x 0.3mm). Using a sputter deposited hard mask and patterning by contact lithography, the diamond is etched in an inductively coupled oxygen plasma with zero platen power. The etch process effectively reveals the characteristic {111} diamond crystal planes, creating a precisely defined angled (54.7°) profile. SEM and AFM measurements of the fabricated gratings evidence the trapezoidal shape with a pitch of 3.82μm, depth of 170 nm and duty cycle of 35.5%. Optical characterization is performed in transmission using a 650nm laser source perpendicular to the sample. The recorded transmitted optical power as function of detector rotation angle shows a distribution of 21.1% in the 0th order and 23.6% in each ±1st order (16.1% reflected, 16.6% in higher orders).
To our knowledge, this is the first demonstration of diffraction gratings with trapezoidal profile in single crystal diamond. The fabrication process will enable beam splitter gratings of custom defined optical power distribution profiles, while antireflection coatings can increase the efficiency.
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