Air-clad suspended nanocrystalline diamond ridge waveguides

Abstract

A hybrid group IV ridge waveguide platform is demonstrated, with potential application across the optical spectrum from ultraviolet to the far infrared wavelengths. The waveguides are fabricated by partial etching of sub-micron ridges in a nanocrystalline diamond thin film grown on top of a silicon wafer. To create vertical confinement, the diamond film is locally undercut by exposing the chip to an isotropic fluorine plasma etch via etch holes surrounding the waveguides, resulting in a mechanically stable suspended air-clad waveguide platform. Optical characterization of the waveguides at 1550 nm yields an average optical loss of 4.67 ± 0.47 dB/mm. Further improvement to the fabrication process is expected to significantly reduce this waveguide loss.

Isotropic silicon etch characteristics in a purely inductively coupled SF6 plasma

“…23 We have earlier demonstrated the use of SF 6 isotropic etching to form suspended nanocrystalline diamond waveguides. 24 Isotropic etching in SF 6 and a comparison of different fluorine-based etchants and their etch rates 15 have been reported. While the SF 6 isotropic etch has been investigated in regard to surface roughness in the presence of polymer masks 25 and for applications such as creating microlenses, 26 basic data on the effect of aperture size on the etch characteristics does not seem to be readily available.…”

Nanocrystalline diamond-glass platform for the development of three-dimensional micro- and nanodevices

“…During growth, dopants such as nitrogen and silicon can also be incorporated in diamond to form color centers for quantum technologies [9,10]. After growth, NCD films can be processed to form two or three-dimensional suspended structures [11,12] and the surface of an NCD film can be functionalized with a variety of (bio)molecules for use in biosensors [13] and solar cells [14]. Due to these excellent properties, NCD based devices such as micromechanical resonators of high Q-factor [15,16], pressure sensors for harsh environments [17,18], tunable optical lenses [19], biosensors that, for example, can detect influenza [20,21], optically transparent electrodes [22,23], CO 2 reducing electrodes [24], superconducting quantum interference devices [25], and conducting atomic force microscope tips are being developed [26].…”

Suspended nanocrystalline diamond ridge waveguides designed for the mid-infrared

“…Due to the wide spectral design range (2.5-16 µm), three different film thickness for different overlapping ranges were assumed: 520 nm for wavelengths between 2.5 and 5 µm, 1000 nm for wavelengths between 4 and 9 µm and 2000 nm for wavelengths between 8 and 16 µm. The choice of 520 nm for the shorter wavelengths is to preserve comparative continuity with our previous work [9]. Growth of thin film NCD with thicknesses of more than a few microns and low top surface roughness is challenging, so we limited our maximum film thickness to 2000 nm.…”

“…This method is quite promising in terms of large area fabrication and scalability and results in film thicknesses in the required range for optical waveguiding. However, the surface roughness of the films can lead to large optical scattering losses at shorter infrared wavelengths [9,18,19]. To some extent this can be alleviated through suitable polishing techniques [17,20].…”