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Scalable Fabrication of Integrated Nanophotonic Circuits on Arrays of Thin Single Crystal Diamond Membrane Windows Afaq H. Piracha, Patrik Rath, Kumaravelu Ganesan, Stefan Kuehn, Wolfram HP Pernice, and Steven Prawer Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b00974 • Publication Date (Web): 25 Apr 2016 Downloaded from http://pubs.acs.org on April 27, 2016
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Scalable Fabrication of Integrated Nanophotonic Circuits on Arrays of Thin Single Crystal Diamond Membrane Windows Afaq H. Piracha,†,⊥ Patrik Rath, §,#,⊥ Kumaravelu Ganesan,† Stefan Kühn,$ Wolfram H.P. Pernice,§,#,* Steven Prawer †,* †
School of Physics, University of Melbourne, Victoria 3010, Australia
§
Institute of Nanotechnology (INT), Karlsruhe Institute of Technology, Hermann-vonHelmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
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Institute of Physics, University of Münster, Heisenbergstr. 11, Münster, Germany
$
Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany ABSTRACT. Diamond has emerged as a promising platform for nanophotonic, optical and quantum technologies. High quality, single crystalline substrates of acceptable size are a prerequisite to meet the demanding requirements on low-level impurities and low absorption loss when targeting large photonic circuits. Here we describe a scalable fabrication method for single crystal diamond membrane windows which achieves three major goals with one fabrication method: providing high quality diamond, as confirmed by Raman spectroscopy; achieving homogeneously thin membranes, enabled by ion implantation; and providing compatibility with established planar fabrication via lithography and vertical etching. On such suspended diamond membranes we demonstrate a suite of photonic components as building blocks for nanophotonic circuits. Monolithic grating couplers are used to efficiently couple light between photonic circuits and optical fibers. In waveguide coupled optical ring resonators we find loaded quality factors up to 66 000 at a wavelength of 1560 nm, corresponding to propagation loss below
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7.2 dB/cm. Our approach holds promise for the scalable implementation of future diamond quantum photonic technologies and all-diamond photonic metrology tools.
KEYWORDS: Single crystal diamond, integrated optics, photonic circuits, optical microresonators
Integrated photonic circuits1, 2 are of growing interest for a number of applications such as high performance non-linear optics3, 4, optomechanics5-10, sensing11 and metrology12,
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. To enable
applications beyond traditional classical optics, innovative materials are necessary to provide the tools for chip-based quantum information processing14-17. Diamond is a particularly attractive candidate material because of a unique combination of desirable material properties, including a high refractive index (n ≈ 2.4), exceptionally high thermal conductivity (2 × 103 W (m × K)–1) and high Young’s modulus. Due to its large bandgap (5.5 eV) diamond also offers low absorption in a wide transmission window ranging from ultraviolet (UV) to infrared (IR) wavelengths2. Most importantly for non-classical applications, diamond can host a range of color centers2, such as the Silicon Vacancy (SiV)18 and the Nitrogen Vacancy Center (NV)19. These defects are stable single photon emitters at room temperature20 and suitable for coupling to nanophotonic devices15, 21, 22. Diamond as a material platform therefore enables applications in a range of fields, including quantum networks3, 15, 17, 23 and quantum computing24-27. In particular the NV center has attracted much attention because it enables long lived spin memory with optical read out28, 29, long coherence time30, 31, and provides the means for metrology with high sensitivity32-34. In order to bring laboratory demonstrations closer to real-world application two key challenges need to be addressed: 1) high quality diamond substrates are mostly available
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only in small sizes and not as thin films which are necessary for photonic technologies; and 2) methods for processing diamond at larger scales have yet to be established. Large-area diamond films to date are predominantly produced in polycrystalline form. Polycrystalline diamond (PCD) thin films can be grown heteroepitaxially on a wafer scale on various substrates5,
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and are commercially available. Integrated optical devices from PCD
thin films have successfully been demonstrated,35, 36 however, some of the intrinsic features of PCD such as grain boundaries and interfacial stresses, as well as the incorporation of higher concentrations of dopants at the grain boundaries lead to inferior properties, such as increased scattering and absorption of light as compared to single crystal diamond
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. Individual color
centers in particular are absent in PCD and thus prevent its use for monolithic quantum photonics. Single crystalline diamond (SCD), on the other hand, with a potentially perfect carbon lattice, is highly suitable for photonics applications and in addition also hosts the aforementioned single colour centers. Unfortunately, macroscopic size single crystal diamond films can only be grown homoepitaxially on existing SCD substrate which inhibits wafer scale processing. In order to take full advantage of nanophotonic circuits the thickness of SCD thin films need to be submicron (
