| 1. |
- Al-Shammari, Rusul M., et al.
(författare)
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Photoinduced Enhanced Raman from Lithium Niobate on Insulator Template
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:36, s. 30871-30878
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced enhanced Raman spectroscopy from a lithium niobate on insulator (LNOI)−silver nanoparticle template is demonstrated both by irradiating the template with 254 nm ultraviolet (UV) light before adding an analyte and before placing the substrate in the Raman system (substrate irradiation) and by irradiating the sample in the Raman system after adding the molecule (sample irradiation). The photoinduced enhancement enables up to an ∼sevenfold increase of the surface-enhanced Raman scattering signal strength of an analyte following substrate irradiation, whereas an ∼threefold enhancement above the surface-enhanced signal is obtained for sample irradiation. The photoinduced enhancement relaxes over the course of ∼10 h for a substrate irradiation duration of 150 min before returning to initial signal levels. The increase in Raman scattering intensity following UV irradiation is attributed to photoinduced charge transfer from the LNOI template to the analyte. New Raman bands are observed following UV irradiation, the appearance of which is suggestive of a photocatalytic reaction and highlight the potential of LNOI as a photoactive surface-enhanced Raman spectroscopy substrate.
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| 2. |
- Baghban, Mohammad Amin, 1983-, et al.
(författare)
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Impact of longitudinal fields on second harmonic generation in lithium niobate nanopillars
- 2016
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Ingår i: APL Photonics. - : American Institute of Physics (AIP). - 2378-0967. ; 1:6
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Tidskriftsartikel (refereegranskat)abstract
- An optimized focused ion beam process is used to fabricate micrometer-long LiNbO3 nanopillars with diameters varying between 150 and 325 nm. Polarimetric mappings of second harmonic generation from a wavelength of 850 nm demonstrate the ability to modify the polarization features of the nonlinearresponse through a fine adjustment of the pillar size. The effect is ascribed to the non-negligible contribution of the longitudinal fields associated with sub-wavelength light confinement in the LiNbO3nanopillars. The results also highlight the importance of a fine control over the nanopillar size in order to effectively engineer their nonlinear response.
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| 3. |
- Baghban, Mohammad Amin, 1983-
(författare)
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Integrated Nanophotonic Devices in Lithium Niobate
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium niobate (LN) is a ferroelectric crystal offering a broad transparency spectrum, together with excellent electro-optic and nonlinear optical properties. Thanks to them, LN is setting the standard for quantum optics and telecommunications in critical applications such as ultrafast modulation and frequency conversion. The development of a reliable nanophotonic platform in LN can be expected to effectively leverage all such appealing functionalities in compact and integrated formats and provide important and complementary functionalities to current silicon-photonics platforms.This thesis encompasses systematic and consistent efforts with the goal to achieve the key building blocks for a comprehensive integrated nanophotonic platform in LN. It involves work on the technology side, sustained and complemented by modelling and experiments, ultimately leading to the demonstration of a few novel devices.Ultrahigh field confinement in nanophotonic waveguides is accompanied by the appearance of non-negligible longitudinal components in the guided optical fields. By fabricating high-quality LN nanopillars and analyzing with theory and experiments their second harmonic generation (SHG) response, we provide evidence for the existence of longitudinal field components and demonstrate the possibility to reshape the SHG polar emission properties of these submicrometric waveguides by fine-tuning the nanopillar size.This thesis also presents a different technological approach, allowing the fabrication of photonic wires as small as 250 nm with lengths up to 1 cm on LN-on-insulator (LNOI), suitable for upscaling to photonic integrated circuit (PIC) architectures. By optimizing the fabrication process, the propagation losses of single-mode waveguides at telecom wavelengths on this platform were brought down from 76 to 1.13 dB/cm. Fine-pitch waveguide structuring was also successfully achieved, enabling LNOI-to-fiber grating couplers and waveguide Bragg gratings, the latter featuring record extinction ratios in LNOI (45 dB), comparable to the state of the art in silicon.The thesis involves also theoretical work on the design of photonic wires where the interplay between LN and waveguide birefringence is used to achieve polarization-insensitive operation for the fundamental guided modes.Finally, two demonstrators are provided for novel and emerging applications of LN to the life sciences, using LNOI surface-patterned templates for enhanced Raman spectroscopy and LN templates for controlled neuron growth and manipulation in microfluidic environments, respectively.
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| 4. |
- Baghban, Mohammad Amin, 1983-, et al.
(författare)
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Phase-Shifted Bragg Grating Resonators in Thin-Film Lithium Niobate Waveguides
- 2019
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Ingår i: 2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO).
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Konferensbidrag (refereegranskat)abstract
- We demonstrate narrowband integrated filters with 0.23 mm-long phase-shifted Bragg gratings in corrugated single-mode thin-film LiNbO3 photonic wires, achieving quality factors of 1.24x10(4) and extinction ratios up to 24 dB at telecom wavelengths.
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| 5. |
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| 6. |
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| 7. |
- Kilinc, D, et al.
(författare)
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Charge and topography patterned lithium niobate provides physical cues to fluidically isolated cortical axons
- 2017
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 110:5
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Tidskriftsartikel (refereegranskat)abstract
- In vitro devices that combine chemotactic and physical cues are needed for understanding how cells integrate different stimuli. We explored the suitability of lithium niobate (LiNbO3), a transparent ferroelectric material that can be patterned with electrical charge domains and micro/ nanotopography, as a neural substrate. On flat LiNbO3 z-surfaces with periodically alternating charge domains, cortical axons are partially aligned with domain boundaries. On submicron-deep etched trenches, neurites are aligned with the edges of the topographical features. Finally, we bonded a bicompartmental microfluidic chip to LiNbO3 surfaces patterned by etching, to create isolated axon microenvironments with predefined topographical cues. LiNbO3 is shown to be an emerging neuron culture substrate with tunable electrical and topographical properties that can be integrated with microfluidic devices, suitable for studying axon growth and guidance mechanisms under combined topographical/chemical stimuli.
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| 8. |
- Neumayer, Sabine M., et al.
(författare)
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Surface Chemistry Controls Anomalous Ferroelectric Behavior in Lithium Niobate
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:34, s. 29153-29160
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Tidskriftsartikel (refereegranskat)abstract
- Polarization switching in ferroelectric materials underpins a multitude of applications ranging from nonvolatile memories to data storage to ferroelectric lithography. While traditionally considered to be a functionality of the material only, basic theoretical considerations suggest that switching is expected to be intrinsically linked to changes in the electrochemical state of the surface. Hence, the properties and dynamics of the screening charges can affect or control the switching dynamics. Despite being recognized for over 50 years, analysis of these phenomena remained largely speculative. Here, we explore polarization switching on the prototypical LiNbO3 surface using the combination of contact mode Kelvin probe force microscopy and chemical imaging by time-of-flight mass-spectrometry and demonstrate pronounced chemical differences between the domains. These studies provide a consistent explanation to the anomalous polarization and surface charge behavior observed in LiNbO3 and point to new opportunities in chemical control of polarization dynamics in thin films and crystals via control of surface chemistry, complementing traditional routes via bulk doping, and substrate-induced strain and tilt systems.
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| 9. |
- Prencipe, Alessandro, et al.
(författare)
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Tunable Ultranarrowband Grating Filters in Thin-Film Lithium Niobate
- 2021
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:10, s. 2923-2930
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Tidskriftsartikel (refereegranskat)abstract
- Several applications in modern photonics require compact on-chip optical filters with a tailored spectral response. However, achieving subnanometric bandwidths and high extinction ratios is particularly challenging, especially in low-footprint device formats. Phase-shifted Bragg gratings implemented by the sidewall modulation of photonic nanowire waveguides are a good solution for on-chip narrowband operation with reasonable requirements in fabrication and scalability. In this work we report on their implementation and optimization in thin film lithium niobate, a photonic platform that affords reconfigurability by exploiting electrooptic effects. The phase-shifted Bragg grating filters have a footprint smaller than 1 mu m x 1 mm and operate at telecom wavelengths, featuring extinction ratios up to 25 dB. We demonstrate transmission bandwidths as narrow as 14.4 pm (Q = 1.1 x 10(5)) and 8.8 pm (Q = 1.76 x 10(5)) in critically coupled structures and multiwavelength Fabry-Perot configurations, respectively, in full agreement with theoretical predictions. Moreover, by taking advantage of the strong electro-optic effect in lithium niobate, in combination with the tight light confinement of nanophotonic wires and the ultranarrow spectral resonances of optimized grating structures, we demonstrate an electric tunability in peak wavelength and transmission of 25.1 pm/V and 2.1 dB/V, respectively, and a 10.5 dB contrast at CMOS voltages. The results pave the way for reconfigurable narrowband photonic filters with a small footprint and low consumption, to be exploited toward on-chip quantum and nonlinear optics, as well as optical sensing and microwave photonics.
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| 10. |
- Prencipe, Alessandro, et al.
(författare)
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Wavelength meter on thin film lithium niobate based on superconducting single photon detectors
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Photonic integrated circuits (PICs) present significant benefits with respect to table-top optical systems regarding footprint, stability, and power consumption. Among the materials used to fabricate PICs, thin film lithium niobate (TFLN) is one of the most attractive ones, as its χ(2) nonlinearity and electro-optic properties allow to implement on-chip light generation and routing [1]. On-chip detection of light has also been demonstrated on TFLN, based on the waveguide integration of superconducting nanowire single photon detectors (SNSPDs) [1]. Combining efficient detectors with TFLN nanophotonic waveguides holds promises for the realization of quantum photonics experiments fully on-chip. On the other hand, the sensitivity of SNSPDs changes with the wavelength of the detected photons [2], setting a boundary to the longest detectable wavelength and limiting the use of the wide transparency window of TFLN. However, this wavelength dependency in the response of SNSPDs can be leveraged to achieve new on-chip functionalities. In this work, by performing a straightforward analysis of the light signal measured at different bias currents [2], we operate hairpin SNSPDs on TFLN as waveguide-integrated wavelength-meters in the telecom bandwidth.
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| 11. |
- Prencipe, Alessandro, et al.
(författare)
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Wavelength-Sensitive Superconducting Single-Photon Detectors on Thin Film Lithium Niobate Waveguides
- 2023
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 23:21, s. 9748-9752
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Tidskriftsartikel (refereegranskat)abstract
- Lithium niobate, because of its nonlinear and electro-optical properties, is one of the materials of choice for photonic applications. The development of nanostructuring capabilities of thin film lithium niobate (TFLN) permits fabrication of small footprint, low-loss optical circuits. With the recent implementation of on-chip single-photon detectors, this architecture is among the most promising for realizing on-chip quantum optics experiments. In this Letter, we report on the implementation of superconducting nanowire single-photon detectors (SNSPDs) based on NbTiN on 300 nm thick TFLN ridge nano-waveguides. We demonstrate a waveguide-integrated wavelength meter based on the photon energy dependence of the superconducting detectors. The device operates at the telecom C- and L-bands and has a footprint smaller than 300 × 180 μm2 and critical currents between ∼12 and ∼14 μA, which ensures operation with minimum heat dissipation. Our results hold promise for future densely packed on-chip wavelength-multiplexed quantum communication systems.
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| 12. |
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| 13. |
- Steinhauer, Stephan, et al.
(författare)
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NbTiN thin films for superconducting photon detectors on photonic and two-dimensional materials
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118.
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Tidskriftsartikel (refereegranskat)abstract
- Integration of superconducting devices on photonic platforms opens up a wide range of functionalities and applications. We report on NbTiN thin films deposited on SiO2, Si3N4, GaAs, LiNbO3, and AlN as well as on a monolayer of hexagonal boron nitride, using a universal reactive co-sputtering recipe. The morphology and the superconducting properties of the NbTiN thin films with a thickness of 10 nm were characterized by atomic force microscopy and electrical transport measurements. Superconducting strip photon detectors were fabricated using a design suitable for waveguide integration and compared in terms of their internal quantum efficiency and detection pulse kinetics. Our results show well-comparable performances for detectors integrated on different platforms, while also demonstrating that reactive co-sputter deposition of NbTiN at room temperature provides a robust method for realizing superconducting devices on various materials.Superconducting materials are the fundamental building block for a wide variety of devices such as Josephson junctions, magnetic field probes, and electromagnetic radiation detectors. Moreover, they form a platform for quantum computing as well as neuromorphic circuit architectures. To utilize the full potential of superconducting thin films and take advantage of their versatile functionalities, fabrication processes suitable for integration on different platforms are required. For instance, superconducting strip photon detectors1 (SSPDs; nomenclature according to the International Standard IEC is used,2 whereas in the literature, these devices are also referred to as superconducting nanowire single-photon detectors) have been demonstrated with different thin film systems on multiple substrate materials and have evolved into the leading technology for single-photon detection.3,4 They offer a wide wavelength sensitivity range,5 high detection efficiency, low dark count rate, and high time resolution6–9 and can be integrated on waveguides in photonic integrated circuits.10 However, integration of SSPDs is often complicated by application-specific restrictions and dedicated growth processes using high temperatures or intermediate buffer layers. While amorphous materials such as WSi are associated with high detection efficiencies and a forgiving fabrication process resulting in a good detector fabrication yield,11 it is challenging to achieve low timing jitter12 and detector operation typically requires sub-Kelvin temperatures. On the other hand, the nitride-based superconductors NbN and NbTiN excel in time resolution but are less forgiving in terms of fabrication yield due to their nanocrystalline structure, often requiring deposition at elevated temperatures.In this Letter, we show the integration of NbTiN-based SSPD devices on photonic and monolayer two-dimensional materials using a universal reactive co-sputtering process at room temperature. Six substrate materials were studied: silicon dioxide (SiO2), silicon nitride (Si3N4), gallium arsenide (GaAs), lithium niobate (LiNbO3), aluminum nitride (AlN), and hexagonal boron nitride (hBN). SiO2 is commonly used for the fabrication of free-space or fiber-coupled SSPDs due to the refractive index difference between SiO2 and the Si substrate underneath forming a weak optical cavity.13 Si3N4 is a CMOS-compatible material that offers a wide transparency window from the visible to the mid-infrared and is suitable for efficient photonic waveguiding. SSPDs can be integrated either before Si3N4 growth as embedded detectors14 or on top of the photonic circuit.15 AlN is used as a piezo-electric material, for instance, in resonators, transducers, and actuators. Superconducting detectors were also fabricated using a pick and place technique16 and by NbN deposition at high temperatures.17 LiNbO3 as an optically non-linear material with a large transparency window and electro-optical properties allows for second-harmonic generation and electro-optic modulation. SSPDs were demonstrated on planar substrates,18,19 whereas superconducting transition-edge sensors were realized on titanium in-diffused waveguides.20 GaAs is a common photonic platform that also allows for the fabrication of quantum dot-based non-classical light sources. The integration of NbN SSPDs requires precise control of deposition temperature to preserve the substrate integrity21–23 or the use of a buffer layer.24 Finally, two-dimensional crystals and van der Waals heterostructures have emerged as optoelectronic platforms with unique characteristics.25 hBN, in particular, is an important building block that is used as a dielectric, for passivation or for its optical properties in the ultraviolet range.26 However, SSPDs realized on two-dimensional crystals as substrate material have remained unexplored so far.We realized NbTiN thin films by reactive co-sputtering from separate Nb and Ti targets at room temperature. We developed a universal recipe for the deposition of 10 nm NbTiN on all six material platforms without substrate-dependent adaptation. The deposition rate and nominal film thickness were monitored in situ using a rate monitor calibrated for SiO2/Si substrates (uncertainty 5%). The magnetron sources were operated at a DC bias of 120 W and a RF bias of 240 W for Nb and Ti, respectively, using an Ar/N2 ratio of 10 and a sputtering pressure of 3 mTorr. These deposition conditions result in polycrystalline films with a Nb/Ti ratio around 60% suitable for high-efficiency SSPDs with a sub-20 ps timing jitter, as reported previously for SiO2/Si substrates.27 The following samples were used: thin film SiO2 on Si (150 nm thermal oxide), thin film Si3N4 on SiO2/Si (250 nm low pressure chemical vapor deposition; Rogue Valley Microdevices), bulk GaAs wafer (Wafer Technology); bulk LiNbO3 wafer (x-cut; CasTech), thin film AlN on Si (200 nm plasma vapor deposition; Kyma Technologies), and monolayer hBN on SiO2/Si (chemical vapor deposition growth and PMMA transfer, oxide thickness 285 nm; Graphene Supermarket). Measurements of NbTiN step heights by atomic force microscopy in tapping mode suggested well-comparable thicknesses for films on SiO2 compared to Si3N4, GaAs, LiNbO3, and AlN with relative differences below 4% (hBN was excluded from the step height analysis due to surface irregularities resulting from the transfer process). Furthermore, the surface morphology of all substrates was assessed (Fig. 1), characterizing areas with NbTiN as well as bare substrate areas covered during the deposition. The root mean square surface roughness Rq was extracted and is summarized for all the cases in Table I. Sputtering of 10 nm NbTiN at room temperature had a negligible influence on the surface roughness, confirming the homogeneity of film deposition. Low Rq values of 0.3–0.6 nm were found for SiO2, Si3N4, and GaAs, whereas larger values were measured for LiNbO3 (0.9 nm), hBN (1.0 nm), and AlN (1.2 nm). In the latter case of AlN, the surface roughness was determined by its distinct grain morphology [Fig. 1(e)]. Note that for the monolayer hBN substrate, circular surface irregularities were present, which were excluded from the roughness analysis.
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