Inscription of 3D waveguides in diamond using an ultrafast laser

Abstract

Three dimensional waveguides within the bulk of diamond are manufactured using ultrafast laser fabrication. High intensities within the focal volume of the laser cause breakdown of the diamond into a graphitic phase leading to a stress induced refractive index change in neighboring regions. Type II waveguiding is thus enabled between two adjacent graphitic tracks, but supporting just a single polarization state. We show that adaptive aberration correction during the laser processing allows the controlled fabrication of more complex structures beneath the surface of the diamond which can be used for 3D waveguide splitters and Type III waveguides which support both polarizations.Diamond has long found use as a material with extreme mechanical properties, and is now rapidly gaining interest for photonic applications 1 . High transmission over a very large spectral window and a high refractive index are attractive for light manipulation. Diamond also acts as a stable basis for a host of color centers which are promising for quantum enhanced technologies 2,3 . The nitrogen vacancy (NV) center is proving particularly useful not just for quantum processing 4 but, also for a range of sensors with extreme sensitivity to magnetic field and temperature 5-7 . The strong Raman coefficient is effective for Raman lasers generating low cost lasing solutions at unusual wavelengths 8,9 . The high Raman coefficient is also useful for implementing solid state quantum memories, a vital component for any quantum optical technology enabling the storage and retrieval of quantum information 10 . In addition, diamond serves as an ideal platform for biophotonics due to a high level of biocompatibility 11 . The efficiency of many of these technologies would be improved by the ability to confine and route light using a network of optical waveguides 12 .Previous demonstrations of waveguiding within diamond have been based upon the principle of selectively removing regions of diamond to generate an air-diamond interface.Surface RIB waveguides have previously been fabricated using reactive ion etching (RIE) with photolithographic patterning 13,14 . Elegant nanobeam waveguides have recently been demonstrated through either angled 15 or undercut RIE etching 16 . Alternatively, direct ion microbeam writing has been used to create shallow subsurface multimode waveguides 17 . All of these approaches are constrained to the diamond surface, require extensive material processing to the potential detriment of the diamond and are difficult to interface with optical fibers. However, a different method for generating guiding structures in crystals has emerged over the past decade, whereby an ultrashort pulsed laser is used to modify the material 18 . In the majority of implementations, light is confined in regions of stress neighboring laser induced damage tracks, which is designated as waveguide based upon a Type II modification 19 . Previously this has been successfully applied to a range of crystals such as lithium niobate 20,21 , KDP 22 , KTP 23 and T...

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