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Photoinduced Enhanced Raman from Lithium Niobate on Insulator Template
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0001-7242-7300
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 36, p. 30871-30878Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018. Vol. 10, no 36, p. 30871-30878
Keywords [en]
Raman, SERS, chemical enhancement, ferroelectric, photoinduced
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-235752DOI: 10.1021/acsami.8b10076ISI: 000444793000096PubMedID: 30107124Scopus ID: 2-s2.0-85052314803OAI: oai:DiVA.org:kth-235752DiVA, id: diva2:1253066
Note

QC 20181004

Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2020-03-09Bibliographically approved
In thesis
1. Integrated Nanophotonic Devices in Lithium Niobate
Open this publication in new window or tab >>Integrated Nanophotonic Devices in Lithium Niobate
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 92
Series
TRITA-SCI-FOU ; 2018:44
Keywords
Lithium niobate (LN), LN-on-insulator, photonic integrated circuits, nonlinear optics, electro-optics, waveguides, propagation losses, Bragg gratings, grating couplers, polarization-insensitive, LN for life sciences
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-235753 (URN)978-91-7729-977-6 (ISBN)
Public defence
2018-10-26, FA32, Roslagstullsbacken 21, Stockholm, 10:00 (English)
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Note

QC 20181004

Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-10-04Bibliographically approved

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