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Zubkova, E., Golikov, A., An, P., Kovalyuk, V., Korneev, A., Ferrari, S., et al. (2019). CWDM demultiplexer using anti-reflection, contra-directional couplers based on silicon nitride rib waveguide. In J. Phys.: Conf. Ser. (Vol. 1410, 012179).
Abstract: We report on the development and fabrication of a 9-channel coarse wavelength-division multiplexing for telecommunication wavelengths (1550 nm) using anti-reflection contra-directional couplers, based on silicon nitride (Si3N4) rib waveguide. The transmitted and reflected spectrum in each channel of the demultiplexer were measured. The average full width at half maximum of the transmitted (reflected) spectra is about 3 nm.
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Zubkova, E., An, P., Kovalyuk, V., Korneev, A., Ferrari, S., Pernice, W., et al. (2017). Integrated Bragg waveguides as an efficient optical notch filter on silicon nitride platform. In J. Phys.: Conf. Ser. (Vol. 917, 062042).
Abstract: We modeled and fabricated integrated optical Bragg waveguides on a silicon nitride (Si3N4) platform. These waveguides would serve as efficient notch-filters with the desired characteristics. Transmission spectra of the fabricated integrated notch filters have been measured and attenuation at the desired wavelength of 1550 nm down to -43 dB was observed. Performance of the filters has been studied depending on different parameters, such as pitch, filling factor, and height of teeth of the Bragg grating
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Zubkova, E., An, P., Kovalyuk, V., Korneev, A., Ferrari, S., Pernice, W., et al. (2018). Optimization of contra-directional coupler based on silicon nitride Bragg rib waveguide. In J. Phys.: Conf. Ser. (Vol. 1124, 051048).
Abstract: We report on the development and fabrication of a contra-directional coupler based on the Bragg waveguide on Si3N4 platform. Transmitted and reflected by the contra-directional coupler spectra were measured. The reflected spectra exactly matches the one notched by the main channel of the coupler. Losses are about 3dB, coupling to the directing branch of the coupler is practically lossless. FWHM of the transmitted (reflected) spectra is 3.46 nm.
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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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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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Prokhodtsov, A., An, P., Kovalyuk, V., Zubkova, E., Golikov, A., Korneev, A., et al. (2018). Optimization of on-chip photonic delay lines for telecom wavelengths. In J. Phys.: Conf. Ser. (Vol. 1124, 051052).
Abstract: In this work, we experimentally studied optical delay lines on silicon nitride platform for telecomm wavelength (1550 nm). We modeled the group delay time and fabricated spiral optical delay lines with different waveguide widths and radii as well as measured their transmission. For the half etched rib waveguides we achieved the losses in the range of 3 dB/cm.
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Polyakova, M., Semenov, A. V., Kovalyuk, V., Ferrari, S., Pernice, W. H. P., & Gol'tsman, G. N. (2019). Protocol of measuring hot-spot correlation length for SNSPDs with near-unity detection efficiency. IEEE Trans. Appl. Supercond., 29(5), 1–5.
Abstract: We present a simple quantum detector tomography protocol, which allows, without ambiguities, to measure the two-spot detection efficiency and extract the hot-spot interaction length of superconducting nanowire single photon detectors (SNSPDs) with unity intrinsic detection efficiency. We identify a significant parasitic contribution to the measured two-spot efficiency, related to an effect of the bias circuit, and find a way to rule out this contribution during data post-processing and directly in the experiment. From the data analysis for waveguide-integrated SNSPD, we find signatures of the saturation of the two-spot efficiency and hot-spot interaction length of order of 100 nm.
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Lobanov, Y., Shcherbatenko, M., Semenov, A., Kovalyuk, V., Kahl, O., Ferrari, S., et al. (2017). Superconducting nanowire single photon detector for coherent detection of weak signals. IEEE Trans. Appl. Supercond., 27(4), 1–5.
Abstract: Traditional photon detectors are operated in the direct detection mode, counting incident photons with a known quantum efficiency. Here, we have investigated a superconducting nanowire single photon detector (SNSPD) operated as a photon counting mixer at telecommunication wavelength around 1.5 μm. This regime of operation combines excellent sensitivity of a photon counting detector with excellent spectral resolution given by the heterodyne technique. Advantageously, we have found that low local oscillator (LO) power of the order of hundreds of femtowatts to a few picowatts is sufficient for clear observation of the incident test signal with the sensitivity approaching the quantum limit. With further optimization, the required LO power could be significantly reduced, which is promising for many practical applications, such as the development of receiver matrices or recording ultralow signals at a level of less-than-one-photon per second. In addition to a traditional NbN-based SNSPD operated with normal incidence coupling, we also use detectors with a travelling wave geometry, where a NbN nanowire is placed on the top of a Si 3 N 4 nanophotonic waveguide. This approach is fully scalable and a large number of devices could be integrated on a single chip.
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Kuzin, A., Kovalyuk, V., Golikov, A., Prokhodtsov, A., Marakhin, A., Ferrari, S., et al. (2019). Efficiency of focusing grating couplers versus taper length and angle. In J. Phys.: Conf. Ser. (Vol. 1410, 012181).
Abstract: Here we experimentally studied dependence of a focusing grating coupler efficiency versus taper length and angle on silicon nitride platform. As a result, we obtained a dependence for the efficiency of a focusing grating coupler on the parameters of the taper length and angle.
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Kovalyuk, V., Kahl, O., Ferrari, S., Vetter, A., Lewes-Malandrakis, G., Nebel, C., et al. (2018). On-chip single-photon spectrometer for visible and infrared wavelength range. In J. Phys.: Conf. Ser. (Vol. 1124, 051045).
Abstract: Here we show our latest progress in the field of a single-photon spectrometer for the visible and infrared wavelengths ranges implementation. We consider three different on-chip approaches: a coherent spectrometer with a low power of the heterodyne, a coherent spectrometer with a high power of the heterodyne, and an eight-channel single-photon spectrometer for direct detection. Along with high efficiency, spectrometers show high detection efficiency and temporal resolution through the use of waveguide integrated superconducting nanowire single-photon detectors.
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