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Polymer Components for Photonic Integrated Circuits
KTH, School of Engineering Sciences (SCI). (Optics and Photonics)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Optical polymers are a subject of research and industry implementation for many decades. Optical polymers are inexpensive, easy to process and flexible enough to meet a broad range of application-specific requirements. These advantages allow a development of cost-efficient polymer photonic integrated circuits for on-chip optical communications. However, low refractive index contrast between core and cladding limits light confinement in a core and, consequently, integrated polymer device miniaturization. Also, polymers lack active functionality like light emission, amplification, modulation, etc. In this work, we improved a performance of integrated polymer waveguides and demonstrated active waveguide devices. Also, we present novel Si QD/polymer optical materials.

In the integrated device part, we demonstrate optical waveguides with enhanced performance. Decreased radiation losses in air-suspended curved waveguides allow low-loss bending with radii of only 15 µm, which is far better than >100 µm for typical polymer waveguides. Another study shows a positive effect of thermal treatment on acrylate waveguides. By heating higher than polymer glass transition temperature, surface roughness is reflown, minimizing scattering losses. This treatment method enhances microring resonator Q factor more than 2 times. We also fabricated and evaluated all-optical intensity modulator based on PMMA waveguides doped with Si QDs.

We developed novel hybrid optical materials. Si QDs are encapsulated into PMMA and OSTE polymers. Obtained materials show stable photoluminescence with high quantum yield. We achieved the highest up to date ~65% QY for solid-state Si QD composites. Demonstrated materials are a step towards Si light sources and active devices.

Integrated devices and materials presented in this work enhance the performance and expand functionality of polymer PICs. The components described here can also serve as building blocks for on-chip sensing applications, microfluidics, etc.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 60
Series
TRITA-FYS, ISSN 0280-316X ; 2017:66
Keywords [en]
integrated photonics, polymers, optical communications, microfabrication, optical waveguides, microring resonators, silicon, Si nanocrystals, photoluminescence
National Category
Engineering and Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-219556ISBN: 978-91-7729-576-1 (print)OAI: oai:DiVA.org:kth-219556DiVA, id: diva2:1163572
Public defence
2017-11-24, Sal C, Isafjordsgatan 22, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20171207

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2017-12-07Bibliographically approved
List of papers
1. Air-Suspended SU-8 Strip Waveguides With High Refractive Index Contrast
Open this publication in new window or tab >>Air-Suspended SU-8 Strip Waveguides With High Refractive Index Contrast
2016 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 28, no 17, p. 1862-1865Article in journal (Refereed) Published
Abstract [en]

Integrated polymer photonics is efficient and cheap solution for many applications, such as optical communications and sensors. Waveguides are basic elements of photonic integrated circuits, and their performance directly influences optical circuit efficiency. However, it is a challenge to develop small footprint polymer waveguides with reasonable losses due to low refractive index comparing to cladding. In this letter, we present free-standing SU-8 waveguides with high refractive index contrast. SiO2 cladding is selectively etched, leaving only air as a cladding material; waveguides are supported by thin pillars. Removal of SiO2 cladding eliminates light leakage to substrate and provides better light confinement. Straight and bending SU-8 waveguides are numerically simulated and experimentally verified lambda = 1550 nm. We also report reduced propagation and bending losses in discussed waveguides.

Place, publisher, year, edition, pages
IEEE, 2016
Keywords
Optical polymers, optical strip waveguides
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-190548 (URN)10.1109/LPT.2016.2573960 (DOI)000379881800017 ()2-s2.0-84978926966 (Scopus ID)
Note

QC 20160815

Available from: 2016-08-15 Created: 2016-08-12 Last updated: 2017-12-11Bibliographically approved
2. Thermal reflow engineered cylindrical polymer waveguides for optical interconnects
Open this publication in new window or tab >>Thermal reflow engineered cylindrical polymer waveguides for optical interconnects
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Integrated polymer photonics brings low cost and high fabrication flexibility to optoelectronic industry. However, this platform needs to overcome several issues to be efficient enough for practical applications. In this work, we experimentally demonstrate a decrease of propagation losses and polarization sensitivity of polymer waveguide-based devices as a result of thermal treatment. Heating of poly(methyl methacrylate) (PMMA) strip optical waveguides above the glass transition temperature initiates a waveguide surface reflow due to a decrease of a polymer viscosity and surface tension energy. This results in a decrease of surface roughness and shape change from rectangular to cylindrical; thus, scattering losses and polarization sensitivity are minimized.

National Category
Engineering and Technology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-219567 (URN)
Note

QC 20171211

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2017-12-11
3. Free carrier absorption modulation in polymer waveguides doped with Si nanocrystals
Open this publication in new window or tab >>Free carrier absorption modulation in polymer waveguides doped with Si nanocrystals
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

This work demonstrates all-optical intensity modulation in integrated optical polymer waveguides doped with Si nanocrystals. The modulation here is based on free carrier absorption of 1550 nm probe signal in Si nanocrystals with excited carriers. Optical 405 nm pump was used to increase free carrier concentration. By applying pulsed pump excitation, -1.55 dB deep intensity modulation was achieved in 5 mm long waveguides. The modulation bandwidth is limited to few kHz due to excited carrier relaxation time (τ ~ 100 μs). Demonstrated all-optical reconfigurable polymer waveguides are a promising potential alternative to thermo-optical switches.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-219568 (URN)
Note

QC 20171211

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2017-12-11
4. Photostable Polymer/Si Nanocrystal Bulk Hybrids with Tunable Photoluminescence
Open this publication in new window or tab >>Photostable Polymer/Si Nanocrystal Bulk Hybrids with Tunable Photoluminescence
Show others...
2016 (English)In: ACS Photonics, E-ISSN 2330-4022, Vol. 3, no 9, p. 1575-1580Article in journal (Refereed) Published
Abstract [en]

Solid polymer/Si nanocrystal bulk nanocomposites were fabricated from solutions of alkene- and hydride-terminated silicon nanocrystals (NCs) in toluene. The photoluminescence peak position of hydride-terminated SiNCs before polymerization was tuned by photoassisted hydrofluoric acid etching. Optical properties of obtained PMMA/NC hybrids, such as quantum yield, luminescence lifetime, and dispersion factor, were evaluated over time. Photostability of these transparent bulk polymer/SiNC hybrids over months was confirmed. The emission covers the visible to near-infrared range with a quantum yield of similar to 30-40% for yellow-red nanocomposites.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
Keywords
silicon nanocrystals, photoluminescence, polymers, poly(methyl methacrylate), nanocomposites
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-194275 (URN)10.1021/acsphotonics.6b00485 (DOI)000384040900009 ()2-s2.0-84988647909 (Scopus ID)
Note

QC 20161025

Available from: 2016-10-25 Created: 2016-10-21 Last updated: 2018-06-14Bibliographically approved
5. Light Converting Polymer/Si Nanocrystal Composites with Stable 60-70% Quantum Efficiency and their Glass Laminates
Open this publication in new window or tab >>Light Converting Polymer/Si Nanocrystal Composites with Stable 60-70% Quantum Efficiency and their Glass Laminates
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2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252Article in journal, Letter (Refereed) Published
Abstract [en]

Thiol-ene polymer/Si nanocrystal bulk hybrids were synthesized from alkyl-passivated Si nanocrystal (Si NC) toluene solutions. Radicals in the polymer provided a co-passivation of “dark” Si NCs, making them optically active and leading to a substantial ensemble quantum yield increase. Optical stability over several months was confirmed. The presented materials exhibit the highest photoluminescence quantum yield (~65%) of any solid-state Si NC hybrid reported to date. The broad tunability of thiol-ene polymer reactivity provides facile glass integration, as demonstrated by a laminated structure. This, together with extremely fast polymerization, makes the demonstrated hybrid material a promising candidate for light converting applications.

Keywords
Si nanocrystals, polymers, photoluminescence, photovoltaics, hybrids, laminates, OSTE
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-213457 (URN)10.1021/acsami.7b09265 (DOI)000411043600006 ()2-s2.0-85029458862 (Scopus ID)
Note

QC 20170831

Available from: 2017-08-31 Created: 2017-08-31 Last updated: 2017-12-11Bibliographically approved

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