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Kovalyuk, V., Hartmann, W., Kahl, O., Kaurova, N., Korneev, A., Goltsman, G., et al. (2013). Absorption engineering of NbN nanowires deposited on silicon nitride nanophotonic circuits. Opt. Express, 21(19), 22683–22692.
Abstract: We investigate the absorption properties of U-shaped niobium nitride (NbN) nanowires atop nanophotonic circuits. Nanowires as narrow as 20nm are realized in direct contact with Si3N4 waveguides and their absorption properties are extracted through balanced measurements. We perform a full characterization of the absorption coefficient in dependence of length, width and separation of the fabricated nanowires, as well as for waveguides with different cross-section and etch depth. Our results show excellent agreement with finite-element analysis simulations for all considered parameters. The experimental data thus allows for optimizing absorption properties of emerging single-photon detectors co-integrated with telecom wavelength optical circuits.
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Ferrari, S., Kahl, O., Kovalyuk, V., Goltsman, G. N., Korneev, A., & Pernice, W. H. P. (2015). Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires. Appl. Phys. Lett., 106(15), 151101 (1 to 5).
Abstract: We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents.
W. H. P. Pernice acknowledges support by the DFG Grant Nos. PE 1832/1-1 and PE 1832/1-2 and the Helmholtz society through Grant No. HIRG-0005. The Ph.D. education of O. Kahl is embedded in the Karlsruhe School of Optics and Photonics (KSOP). G. N. Goltsman acknowledges support by Russian Federation President Grant HШ-1918.2014.2 and Ministry of Education and Science of the Russian Federation Contract No.: RFMEFI58614X0007. A. Korneev acknowledges support by Statement Task No. 3.1846.2014/k. V. Kovalyuk acknowledges support by Statement Task No. 2327. We also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN) within subproject A6.4. We thank S. Kühn and S. Diewald for the help with device fabrication as well as B. Voronov and A. Shishkin for help with NbN thin film deposition and A. Semenov for helpful discussion about the detection mechanism of nanowire SSPD's.
The authors declare no competing financial interests.
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Rath, P., Vetter, A., Kovalyuk, V., Ferrari, S., Kahl, O., Nebel, C., et al. (2016). Travelling-wave single-photon detectors integrated with diamond photonic circuits: operation at visible and telecom wavelengths with a timing jitter down to 23 ps. In J. - E. Broquin, & G. N. Conti (Eds.), Integrated Optics: Devices, Mat. Technol. XX (Vol. 9750, pp. 135–142). Spie.
Abstract: We report on the design, fabrication and measurement of travelling-wave superconducting nanowire single-photon detectors (SNSPDs) integrated with polycrystalline diamond photonic circuits. We analyze their performance both in the near-infrared wavelength regime around 1600 nm and at 765 nm. Near-IR detection is important for compatibility with the telecommunication infrastructure, while operation in the visible wavelength range is relevant for compatibility with the emission line of silicon vacancy centers in diamond which can be used as efficient single-photon sources. Our detectors feature high critical currents (up to 31 μA) and high performance in terms of efficiency (up to 74% at 765 nm), noise-equivalent power (down to 4.4×10-19 W/Hz1/2 at 765 nm) and timing jitter (down to 23 ps).
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Vetter, A., Ferrari, S., Rath, P., Alaee, R., Kahl, O., Kovalyuk, V., et al. (2016). Cavity-enhanced and ultrafast superconducting single-photon detectors. Nano Lett., 16(11), 7085–7092.
Abstract: Ultrafast single-photon detectors with high efficiency are of utmost importance for many applications in the context of integrated quantum photonic circuits. Detectors based on superconductor nanowires attached to optical waveguides are particularly appealing for this purpose. However, their speed is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. Here, we solve this problem by aligning the nanowire, contrary to usual choice, perpendicular to the waveguide to realize devices with a length below 1 mum. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess subnanosecond decay ( approximately 120 ps) and recovery times ( approximately 510 ps) and thus show potential for GHz count rates at low timing jitter ( approximately 32 ps). The small absorption volume allows efficient threshold multiphoton detection.
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Shcherbatenko, M., Lobanov, Y., Semenov, A., Kovalyuk, V., Korneev, A., Ozhegov, R., et al. (2016). Potential of a superconducting photon counter for heterodyne detection at the telecommunication wavelength. Opt. Express, 24(26), 30474–30484.
Abstract: Here, we report on the successful operation of a NbN thin film superconducting nanowire single-photon detector (SNSPD) in a coherent mode (as a mixer) at the telecommunication wavelength of 1550 nm. Providing the local oscillator power of the order of a few picowatts, we were practically able to reach the quantum noise limited sensitivity. The intermediate frequency gain bandwidth (also referred to as response or conversion bandwidth) was limited by the spectral band of a single-photon response pulse of the detector, which is proportional to the detector size. We observed a gain bandwidth of 65 MHz and 140 MHz for 7 x 7 microm2 and 3 x 3 microm2 devices, respectively. A tiny amount of the required local oscillator power and wide gain and noise bandwidths, along with unnecessary low noise amplification, make this technology prominent for various applications, with the possibility for future development of a photon counting heterodyne-born large-scale array.
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