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Modal birefringence-free lithium niobate waveguides
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. (Nonlinear and Quantum Photonics)
2017 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 18, p. 3578-3581Article in journal (Refereed) Published
Abstract [en]

We investigate polarization-insensitive waveguide designs afforded by the interplay of material and waveguide birefringence in LiNbO3-on-insulator photonic wires. Fundamental mode birefringence-free operation in the 0.8-1.8 mu m spectral range is predicted for a suitable choice of waveguide widths in the 375-600 nm range. Optimized buried waveguide designs yield broadband (1350-1625 nm) index matching between TE00 and TM00 modes. Furthermore, simultaneous phase- and group-velocity matching at infrared wavelengths appears feasible for pulse durations as short as 100 fs.

Place, publisher, year, edition, pages
Optical Society of America, 2017. Vol. 42, no 18, p. 3578-3581
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-215363DOI: 10.1364/OL.42.003578ISI: 000410921000018PubMedID: 28914906Scopus ID: 2-s2.0-85029410908OAI: oai:DiVA.org:kth-215363DiVA, id: diva2:1148121
Funder
Swedish Research Council, VR 612-2014-5407; VR 622-2010-526
Note

QC 20171010

Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2019-01-28Bibliographically 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)
Opponent
Supervisors
Note

QC 20181004

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

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