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Bragg gratings in thin-film LiNbO3 waveguides
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.ORCID iD: 0000-0001-7242-7300
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
Show others and affiliations
2017 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Optics Express, ISSN 1094-4087, Vol. 25, no 26, p. 32323-32332Article in journal (Refereed) Published
Abstract [en]

We design, fabricate and characterize sidewall corrugated Bragg gratings in a high confinement integrated optics lithium niobate platform, comprising submicrometric photonic wires, tapers and grating couplers to interface off-chip standard telecom optical fibers. We analyze the grating performance as band-rejection filter for TE-polarized signals in the telecom C-band, considering both rectangular and sinusoidal sidewall profiles, and demonstrate record extinction ratios as high as 27 dB and rejection bandwidths as narrow as 3 nm. The results show the potential for an efficient integration of novel photonic functionalities into low-footprint LiNbO3 nonlinear and electro-optical waveguide devices.

Place, publisher, year, edition, pages
Optical Society of America, 2017. Vol. 25, no 26, p. 32323-32332
Keywords [en]
Lithium niobate; Integrated optics devices; Bragg reflectors; Thin film devices and applications; Waveguides
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-220908DOI: 10.1364/OE.25.032323ISI: 000418893200009Scopus ID: 2-s2.0-85039046273OAI: oai:DiVA.org:kth-220908DiVA, id: diva2:1172163
Note

QC 20180110

Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-10-04Bibliographically approved
In thesis
1. Photonic MEMS for optical information technologies
Open this publication in new window or tab >>Photonic MEMS for optical information technologies
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photonic integrated circuits (PICs) combine hundreds of optical components on a chip, and can enable fast communications, high-performance computing, and improved sensing. PICs, made by miniaturized optical waveguides, require many reconfigurable elements to enable programmable functionalities and to compensate for fabrication variations and environmental factors. However, current reconfiguration methods consume large amounts of electrical power, which is a bottleneck for their scalability, and limits their applications. A promising technology to alleviate this bottleneck is photonic microelectromechanical systems (MEMS), which provides low-power reconfiguration of PICs using electromechanical actuation. This thesis reports on several photonic MEMS devices and technologies that enable low-power reconfiguration for PICs, and bring new functionalities towards efficient nonlinear optics, optical beam steering, and photonic Lab-on-chips (LoCs). A fundamental element of reconfigurable PICs is the phase shifter, and this thesis introduces novel photonic MEMS phase shifters with low power consumption, low optical losses, and linear actuation, and applies them to reconfigurable filtering. Moreover, photonic MEMS bring novel functionalities arising from the mechanical movement of waveguide components, and, in this thesis, a method to tune waveguide dispersion for efficient nonlinear optics in silicon, and two types of reconfigurable waveguide gratings for low-power optical beam steering are developed. The photonic MEMS platform introduced in this thesis can be combined with polarization diversity schemes by using a novel suspended polarization beam splitter. In addition, other technologies addressing challenges in integrated photonics are introduced, such as a lithium niobate on insulator (LNOI) platform that combines grating couplers, high confinement waveguides, and Bragg gratings, for electro-optic modulation and efficient nonlinear optics; and a cost-efficient method to integrate photonic sensors into LoCs for healthcare applications. The technologies introduced in this thesis have potential to enable large-scale, power-efficient, and highly functional PICs, with prospects for more efficient and more functional optical information technologies.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. iii-xi, 79
Series
TRITA-EECS-AVL ; 2018:55
Keywords
Micro-electro-mechanical systems (MEMS), photonics, silicon photonics, photonic integrated circuits (PIC), lithium niobate photonics, ring resonator, polarization beam splitter (PBS), microfluidic integration, lab-on-chip (LoC), optical beam steering, nonlinear optics
National Category
Nano Technology Other Physics Topics
Research subject
Electrical Engineering; Physics; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-235069 (URN)978-91-7729-910-3 (ISBN)
Public defence
2018-10-12, M2, Brinellvägen 64, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
VR-HETMORPHIC
Funder
Swedish Research Council, 621-2012-5364EU, Horizon 2020, 780283
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-14 Last updated: 2018-09-17Bibliographically approved
2. 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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