Elmanova, A., An, P., Kovalyuk, V., Golikov, A., Elmanov, I., & Goltsman, G. (2020). Study of silicon nitride O-ring resonator for gas-sensing applications. In J. Phys.: Conf. Ser. (Vol. 1695, 012124).
Abstract: In this work, we experimentally studied the influence of different gaseous surroundings on silicon nitride O-ring resonator transmission. We compared the obtained results with numerical calculations and theoretical analysis and found a good agreement between them. Our results have a great potential for gas sensing applications, where a compact footprint and high efficiency are desired simultaneously.
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Komrakova, S., Kovalyuk, V., An, P., Golikov, A., Rybin, M., Obraztsova, E., et al. (2020). Effective absorption coefficient of a graphene atop of silicon nitride nanophotonic circuit. In J. Phys.: Conf. Ser. (Vol. 1695, 012135).
Abstract: In this paper, we demonstrate the results of a study of the optical absorption properties of graphene integrated with silicon nitride O-ring resonator. We fabricated an array of O-ring resonators with different graphene coverage area atop. By measuring the transmission spectra of nanophotonic devices with and without graphene, we calculated the effective absorption coefficient of the graphene on a rib silicon nitride waveguide.
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Prokhodtsov, A., Kovalyuk, V., An, P., Golikov, A., Shakhovoy, R., Sharoglazova, V., et al. (2020). Silicon nitride Mach-Zehnder interferometer for on-chip quantum random number generation. In J. Phys.: Conf. Ser. (Vol. 1695, 012118).
Abstract: In this work, we experimentally studied silicon nitride Mach-Zehnder interferometer (MZI) with two directional couplers and 400 ps optical delay line for telecom wavelength 1550 nm. We achieved the extinction ratio in a range of 0.76-13.86 dB and system coupling losses of 28-44 dB, depending on the parameters of directional couplers. The developed interferometer is promising for the use in a compact random number generator for the needs of a fully integrated quantum cryptography system, where compact design, as well as high generation speed, are needed.
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Venediktov, I. O., Elezov, M. S., Prokhodtsov, A. I., Kovalyuk, V. V., An, P. P., Golikov, A. D., et al. (2020). Study of microheater’s phase modulation for on-chip Kennedy receiver. In J. Phys.: Conf. Ser. (Vol. 1695, 012117).
Abstract: In this work we describe phase modulators for several Mach-Zehnder interferometers (MZI) on silicon nitride platform for telecomm wavelength (1550 nm). We obtained current-voltage and phase-voltage curves for these modulators. MZI are needed for experimental realisation of various quantum receivers that can distinguish weak coherent states of light with extremely low error. Thermo-optical (TO) modulation is ensured by microheaters on one of the arms of MZI, which enables the change of the refractive index of the material with temperature. This approach allows to apply the necessary voltage to the golden microheaters to obtain the required phase change. For the on-chip microheaters we demonstrate the dependence of the phase shift on the voltage applied to our on-chip microheaters.
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Elmanov, I., Sardi, F., Xia, K., Kornher, T., Kovalyuk, V., Prokhodtsov, A., et al. (2020). Development of focusing grating couplers for lithium niobate on insulator platform. In J. Phys.: Conf. Ser. (Vol. 1695, 012127).
Abstract: In this paper, we fabricate and experimentally study focusing grating couplers for lithium niobate on an insulator photonic platform. The transmittance of a waveguide equipped with in- and out-couplers with respect to the grating period is measured with and without silicon dioxide cladding applied. Our results show the influence of silicon dioxide cladding on the efficiency and the central wavelength of grating couplers and can be used to improve grating coupling efficiency. Our study is supported by numerical simulations.
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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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An, P., Kovalyuk, V., Golikov, A., Zubkova, E., Ferrari, S., Korneev, A., et al. (2018). Experimental optimisation of O-ring resonator Q-factor for on-chip spontaneous four wave mixing. In J. Phys.: Conf. Ser. (Vol. 1124, 051047).
Abstract: In this paper we experimentally studied the influence of geometrical parameters of the planar O-ring resonators on its Q-factor and losses. We systematically changed the gap between the bus waveguide and the ring, as well as the width of the ring. We found the highest Q = 5×105 for gap 2.0 μm and the ring width 2 μm. This work is important for further on-chip SFWM applications since the generation rate of the biphoton field strongly depends on the quality factor as Q3
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Golikov, A., Kovalyuk, V., An, P., Zubkova, E., Ferrari, S., Pernice, W., et al. (2018). Silicon nitride nanophotonic circuit for on-chip spontaneous four-wave mixing. In J. Phys.: Conf. Ser. (Vol. 1124, 051051).
Abstract: Here we present an integrated nanophotonic circuit for on-chip spontaneous four-wave mixing. The fabricated device includes an O-ring resonator, a Bragg noch-filter as well as a nine-channel arrayed waveguide gratings (AWG) operated in the C-band wavelength range (1550 nm). The measured optical losses of the device (-6.8 dB) as well as a high Q-factor (> 1.2×105) shows a good potential for realizing the spontaneous four-wave mixing on the silicon nitride chip.
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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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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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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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Benz, A. O., Bruderer, S., van Dishoeck, E. F., Stäuber, P., Wampfler, S. F., Melchior, M., et al. (2010). Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system. Astron. Astrophys., 521, L35 (1 to 5).
Abstract: Context. Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays.
Aims. We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation.
Methods. W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (2500 s) in 8 spectral regions.
Results. The target lines including CH, NH, H3O+, and the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J = 1–0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds.
Conclusions. The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.
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Decin, L., Justtanont, K., De Beck, E., Lombaert, R., de Koter, A., Waters, L. B. F. M., et al. (2010). Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen by Herschel/HIFI. Astron. Astrophys., 521, L4.
Abstract: During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H216O and the rarer isotopologues H217O and H218O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of $6.6 \times 10^{-5}$, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.
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Mookerjea, B., Giesen, T., Stutzki, J., Cernicharo, J., Goicoechea, J. R., De Luca, M., et al. (2010). Excitation and abundance of C3 in star forming cores. Herschel/HIFI observations of the sight-lines to W31C and W49N. Astron. Astrophys., 521, L13.
Abstract: We present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy ν2 bending mode at frequencies between 1654–1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel's HIFI instrument. We detect C3 in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C3 absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (Trot) of ~50-70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived Trot, we get column densities N(C3) ~ 7–9 × 1014 cm-2 and abundance x(C3) ~ 10-8 with respect to H2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C3) = 10-8, Tkin = 30–50 K, N(C3) = 1.5 × 1015 cm-2 fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis.
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Wampfler, S. F., Herczeg, G. J., Bruderer, S., Benz, A. O., van Dishoeck, E. F., Kristensen, L. E., et al. (2010). Herschel observations of the hydroxyl radical (OH) in young stellar objects. Astron. Astrophys., 521, L36.
Abstract: Aims. “Water In Star-forming regions with Herschel†(WISH) is a Herschel key program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature (T 250 K) chemistry connects OH and H2O through the OH + H2 H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O through H2O + γUV OH + H.
Methods. High-resolution spectroscopy of the 163.12 μm triplet of OH towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory. The low- and intermediate-mass protostars HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) on Herschel in four transitions of OH and two [O i] lines.
Results. The OH transitions at 79, 84, 119, and 163 μm and [O i] emission at 63 and 145μm were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 μm was detected in absorption. With HIFI, the 163.12 μm was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM 11 km s-1) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [O i] flux and the bolometric luminosity, as found in our sample. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources.
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