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Silicon-based Photonic Devices: Design, Fabrication and Characterization
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The field of Information and Communication Technologies is witnessing a development speed unprecedented in history. Moore’s law proves that the processor speed and memory size are roughly doubling each 18 months, which is expected to continue in the next decade. If photonics is going to play a substantial role in the ICT market, it will have to follow the same dynamics. There are mainly two groups of components that need to be integrated. The active components, including light sources, electro-optic modulators, and detectors, are mostly fabricated in III-V semiconductors. The passive components, such as waveguides, resonators, couplers and splitters, need no power supply and can be realized in silicon-related semiconductors. The prospects of silicon photonics are particularly promising, the fabrication is mostly compatible with standard CMOS technology and the on-chip optical interconnects are expected to increase the speed of microprocessors to the next generation.

This thesis starts with designs of various silicon-based devices using finite-difference time-domain simulations. Parallel computation is a powerful tool in the modeling of large-scale photonic circuits. High Q cavities and resonant channel drop filters are designed in photonic crystal platform. Different methods to couple light from a single mode fiber to silicon waveguides are studied by coupled-mode theory and verified using parallel simulations. The performance of waveguide grating coupler for vertical radiation is also studied.

The fabrication of silicon-based photonic devices involves material deposition, E-beam or optical lithography for pattern defining, and plasma/wet-chemistry etching for pattern transfer. For nanometer-scaled structures, E-beam lithography is the most critical process. Depending on the structures of the devices, both positive resist (ZEP520A) and negative resist (maN2405) are used. The proximity and stitch issues are addressed by careful dose correction and patches exposure. Some examples are given including photonic crystal surface mode filter, micro-ring resonators and gold grating couplers. In particular, high Q (2.6×105), deep notch (40 dB) and resonance-splitting phenomenon are demonstrated for silicon ring resonators.

It is challenging to couple light into photonic integrated circuits directly from a single-mode fiber. The butt-coupled light-injecting method usually causes large insertion loss due to small overlap of the mode profiles and large index mismatch. Practically it is not easy to cleave silicon sample with smooth facet where the waveguide exposes. By adding gold gratings to the waveguides, light can be injected and collected vertically from single-mode fiber. The coupling efficiency is much higher. There is no need to cleave the sample. The access waveguides are much shortened and the stitch problem in E-beam lithography is avoided.

In summary, this thesis introduces parallel simulations for the design of modern large-scale photonic devices, addresses various issues with Si-based fabrication, and analyses the data from the characterization. Several novel devices using silicon nanowire waveguides and 2D photonic crystal structures have been demonstrated for the first time.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , 58 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:5
Keyword [en]
Photonic Devices, Silicon Photonics, Parallel Computation, Nanofabrication, Electron Beam Lithography, Optical Characterisation
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-4647OAI: oai:DiVA.org:kth-4647DiVA: diva2:13238
Public defence
2008-03-07, N1, Electrum 3, Isafjordsgatan 28, Kista, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2010-09-23Bibliographically approved
List of papers
1. Small-volume waveguide-section high Q microcavities in 2D photonic crystal slabs
Open this publication in new window or tab >>Small-volume waveguide-section high Q microcavities in 2D photonic crystal slabs
2004 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, no 17, 3988-3995 p.Article in journal (Refereed) Published
Abstract [en]

A series of microcavities in 2D hexagonal lattice photonic crystal slabs are studied in this paper. The microcavities are small sections of a photonic crystal waveguide. Finite difference time domain simulations show that these cavities preserve high Q modes with similar geometrical parameters and field profile. Effective modal volume is reduced gradually in this series of microcavity modes while maintaining high quality factor. Vertical Q value larger than 106 is obtained for one of these cavity modes with effective modal volume around 5.40 cubic half wavelengths [(lambda/2n(slab))(3)]. Another cavity mode provides even smaller modal volume around 2.30 cubic half wavelengths, with vertical Q value exceeding 10(5).

Keyword
Computer simulation, Crystal lattices, Finite difference method, Light reflection, Microstructure, Optical resonators, Optical waveguides, Time domain analysis, Finite difference time domain (FDTD) simulation, Microcavities, Microstructure devices, Photonic crystals (PC)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8017 (URN)10.1364/OPEX.12.003988 (DOI)000223469000014 ()2-s2.0-4644371173 (Scopus ID)
Note
QC 20100922 QC 20110923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
2. Influence of structural variations on high-Q microcavities in two-dimensional photonic crystal slabs
Open this publication in new window or tab >>Influence of structural variations on high-Q microcavities in two-dimensional photonic crystal slabs
2005 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 13, 1713-1715 p.Article in journal (Refereed) Published
Abstract [en]

The influence of some critical structural variations in high-Q microcavities in two-dimensional photonic crystal slabs is investigated. All the cavities studied maintain a high Q in a wide range of structural variations, while the resonant frequencies shift on a relatively large scale when the structural variations are comparable to the physical sizes of the cavities.

Keyword
Approximation theory, Computer simulation, Crystalline materials, Finite difference method, Lattice constants, Natural frequencies, Optical design, Optical systems, Photons, Time domain analysis
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8018 (URN)10.1364/OL.30.001713 (DOI)000230193000039 ()2-s2.0-22144446757 (Scopus ID)
Note
QC 20100920Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
3. Compact in-plane channel drop filter design using a single cavity with two degenerate modes in 2D photonic crystal slabs
Open this publication in new window or tab >>Compact in-plane channel drop filter design using a single cavity with two degenerate modes in 2D photonic crystal slabs
2005 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, no 7, 2596-2604 p.Article in journal (Refereed) Published
Abstract [en]

A compact in-plane channel drop filter design in 2D hexagonal lattice photonic crystal slabs is presented in this paper. The system consists of two photonic crystal waveguides and a single cavity with two degenerate modes. Both modes are able to confine light strongly in the vertical dimension and prove to couple equally into the waveguides. Three dimensional finite difference time domain simulations show that the quality factor is around 3,000. At resonance, power transferred to the drop waveguide is 78% and only 1.6% remains in the bus waveguide. We also show that by carefully tuning the drop waveguide boundary, light remaining in the bus can be further reduced to below 0.4% and thus the channel isolation is larger than 22dB.

Keyword
defect-wave-guide, microcavities, emission, states
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-14658 (URN)10.1364/OPEX.13.002596 (DOI)000228180800038 ()2-s2.0-21244464730 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Coupled mode analysis of in-plane channel drop filters with resonant mirrors
Open this publication in new window or tab >>Coupled mode analysis of in-plane channel drop filters with resonant mirrors
2005 (English)In: Photonics and Nanostructures-Fundamentals and Applications, ISSN 1569-4410, Vol. 3, no 2-3, 84-89 p.Article in journal (Refereed) Published
Abstract [en]

A channel drop filter system that consists of two waveguides and three cavities is studied. One cavity couples with both waveguides, while the other two work as resonant mirrors to reflect the selected channel back into the system. The operation of this configuration is analyzed, using coupled mode theory. The conditions to achieve 100% in-plane channel transfer are derived. A method to suppress the side lobes of reflection and backward drop is also proposed. The direct coupling between the cavities is not required. The analysis is verified by two-dimensional finite difference time domain simulations in 2D hexagonal photonic crystals.

Keyword
optical filters, photonic crystals, integrated optics, 2-dimensional photonic-crystal, design, slabs
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-15331 (URN)10.1016/j.photonics.2005.09.002 (DOI)000236935600005 ()2-s2.0-28244464435 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-09-22Bibliographically approved
5. Coupled-mode analysis of a resonant channel drop filter using waveguides with mirror boundaries
Open this publication in new window or tab >>Coupled-mode analysis of a resonant channel drop filter using waveguides with mirror boundaries
2006 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 1, 104-113 p.Article in journal (Refereed) Published
Abstract [en]

The operation of resonant channel drop filters is analyzed using coupled-mode theory. The resonator is chosen to support a single standing-wave mode, and, in the ideal case, one can realize 100% in-plane channel transfer by properly applying mirror boundaries to the waveguides. The presence of the mirrors causes the resonant frequency to shift, and the system Q factor also changes accordingly. The two variables are related by a closed curve depending on the phase introduced by the reflection and wave propagation between the two ports. When one works on different regions of the curve, the system can be tuned to work at different resonant frequencies with minimum Q-factor variations or vice versa. The mirror can be frequency selective. The same single-mode cavity can be used as a resonant mirror to terminate the waveguide. The combined system is analyzed, and we find the conditions to achieve 100% channel transfer as well as to maintain a simple Lorentzian line shape of the transmission spectra. The analysis is verified by two-dimensional (2D) finite-difference time-domain simulations in 2D hexagonal photonic crystals.

Keyword
Cavity resonators, Computer simulation, Crystals, Finite difference method, Mirrors, Natural frequencies, Optical waveguides, Reflection, Time domain analysis
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8021 (URN)10.1364/JOSAB.23.000104 (DOI)000234528900015 ()2-s2.0-33644510447 (Scopus ID)
Note
QC 20100907Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
6. Parallel Power Computation for Photonic Crystal Devices
Open this publication in new window or tab >>Parallel Power Computation for Photonic Crystal Devices
2006 (English)In: Methods and Applications of Analysis, ISSN 1073-2772, E-ISSN 1945-0001, Vol. 13, no 2, 149-156 p.Article in journal (Refereed) Published
Abstract [en]

Three-dimensional finite-different time-domain (3D FDTD) simulation of photonic crystal devices often demands large amount of computational resources. In many cases it is unlikely to carry out the task on a serial computer. We have therefore parallelized a 3D FDTD code using MPI. Initially we used a one-dimensional topology so that the computational domain was divided into slices perpendicular to the direction of the power flow. Even though the speed-up of this implementation left considerable room for improvement, we were nevertheless able to solve largescale and long-running problems. Two such cases were studied: the power transmission in a two-dimensional photonic crystal waveguide in a multilayered structure, and the power coupling from a wire waveguide to a photonic crystal slab. In the first case, a power dip due to TE/TM modes conversion is observed and in the second case, the structure is optimized to improve the coupling. We have also recently completed a full three-dimensional topology parallelization of the FDTD code.

Keyword
Photonic crystals, the Maxwell equations, FDTD, MPI parallelization
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8022 (URN)
Note
QC 20100922Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
7. Optical filter based on two-dimensional photonic crystal surface-mode cavity in amorphous silicon-on-silica structure
Open this publication in new window or tab >>Optical filter based on two-dimensional photonic crystal surface-mode cavity in amorphous silicon-on-silica structure
Show others...
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 4, 041108- p.Article in journal (Refereed) Published
Abstract [en]

An optical filter based on side coupling between silicon wire waveguide and two-dimensional photonic crystal surface-mode cavity is presented. The design is optimized numerically by parallel three-dimensional finite-different time-domain simulations. The device is then fabricated on amorphous silicon-on-silica structure. The drop wavelength is observed around 1580 nm. The extinction ratio of the filter is larger than 10 dB and the intrinsic quality factor of the surface-mode cavity is approximately 2000.

Keyword
Computer simulation, Finite difference method, Optical filters, Silica, Silicon on insulator technology, Time domain analysis, Extinction ratio, Silicon wire waveguides, Silicon-on-silica structure
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8023 (URN)10.1063/1.2432228 (DOI)000243789600008 ()2-s2.0-33846579251 (Scopus ID)
Note
QC 20100922Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
8. Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide
Open this publication in new window or tab >>Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide
2007 (English)In: Chinese optics letters, ISSN 1671-7694, Vol. 5, no 10, 577-579 p.Article in journal (Refereed) Published
Abstract [en]

Coupling between subwavelength-diameter silica wires and silicon-based waveguides is studied using the parallel three-dimensional (3D) finite-different time-domain method. Conventional butt-coupling to a silica-substrated silicon wire waveguide gives above 40% transmission at the wavelength range from 1300 to 1750 nm with good robustness against axial misalignments. Slow light can be generated by counter-directional coupling between a silica wire and a two-dimensional (2D) silicon photonic crystal slab waveguide. Through dispersion-band engineering, 82% transmission is achieved over a coupling distance of 50 lattice constants. The group velocity is estimated as 1/35 of the light speed in vacuum.

Keyword
Alignment, Finite difference time domain method, Optical waveguides, Parallel algorithms, Silicon, Three dimensional, Axial misalignments, Silicon based waveguides, Subwavelength diameter silica wires
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8024 (URN)000255024400006 ()2-s2.0-36248989245 (Scopus ID)
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2010-09-23Bibliographically approved
9. Subwavelength-diameter Silica Wire and Photonic Crystal Waveguide Slow Light Coupling
Open this publication in new window or tab >>Subwavelength-diameter Silica Wire and Photonic Crystal Waveguide Slow Light Coupling
2007 (English)In: Active and Passive Electronic Components, ISSN 0882-7516, E-ISSN 1563-5031, Vol. 2007, 78602- p.Article in journal (Refereed) Published
Abstract [en]

Counter-directional coupling between subwavelength-diameter silica wire and single-line-defect two-dimensional photonic crystal slab waveguide is studied numerically using parallel three-dimensional finite-different time-domain method. By modifying silica wire properties or engineering photonic crystal waveguide dispersion band, the coupling central wavelength can be moved to the slow light region and the coupling efficiency improves simultaneously. One design gives 82 peak power transmission from silica wire to photonic crystal waveguide over an interacting distance of 50 lattice constants. The group velocity is estimated as 1/35 of light speed in vacuum.

Keyword
Finite difference method, Photonic crystals, Power transmission, Time domain analysis, Waveguides, Wire, Coupling central wavelength, Photonic crystal waveguides, Waveguide dispersion band
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8025 (URN)10.1155/2007/78602 (DOI)2-s2.0-38849182436 (Scopus ID)
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
10. Optically Tunable Delay Line in Silicon Microring Resonator Based on Thermal Nonlinear Effect
Open this publication in new window or tab >>Optically Tunable Delay Line in Silicon Microring Resonator Based on Thermal Nonlinear Effect
Show others...
2008 (English)In: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 14, no 3, 706-712 p.Article in journal (Refereed) Published
Abstract [en]

We experimentally demonstrate optically tunable delay fine in a silicon microring resonator with a 20-mu m radius. The delay-tuning mechanism is based on the red shift of the resonance induced by thermal nonlinear effect. We investigate the delay performance of three modulation formats-non-return-to-zero (NRZ), return-to-zero (RZ), and differential phase-shift keying (DPSK) signals at different data rates. Tunable delay is achieved by controlling the power of the continuous-wave (CW) pump with very low tuning threshold, which could be used in microring-resonator-based slow-light structure.

Keyword
buffer, microring resonator, silicon photonics, thermal nonlinear effect
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8026 (URN)10.1109/JSTQE.2008.916240 (DOI)000256624900020 ()2-s2.0-41649115586 (Scopus ID)
Note
QC 20100923. Uppdaterad från in press till published (20100923).Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved
11. High-quality-factor micro-ring resonator in amorphous-silicon on insulator structure
Open this publication in new window or tab >>High-quality-factor micro-ring resonator in amorphous-silicon on insulator structure
Show others...
2008 (English)In: ECIO'08 Eindhoven - Proceedings of the 14th European Conference on Integrated Optics and Technical Exhibition, Contributed and Invited Papers, 2008, 329-332 p.Conference paper, Published paper (Refereed)
Abstract [en]

Micro-ring resonators have been fabricated in hydrogenated amorphous silicon on silica structure. The intrinsic quality factor is estimated as 56,000 and the notch depth is ̃ 30dB. The intrinsic loss per unit length is 15.3dB/cm, comparable to 9.16dB/cm in the single-crystalline silicon ring of the same geometry.

Keyword
Exhibitions, Integrated circuits, Integrated optics, Optical materials, Optical resonators, Photonics, Resonators, Silica, Crystalline silicons, Hydrogenated amorphous silicons, Intrinsic losses, Intrinsic quality factors, Notch depths, Per unit lengths, Ring resonators, Silica structures, Silicon on insulator structures
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8027 (URN)2-s2.0-58149105797 (Scopus ID)
Note
QC 20100923Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2010-09-23Bibliographically approved
12. Resonance-splitting and enhanced notch depth in SOI ring resonators with mutual mode coupling
Open this publication in new window or tab >>Resonance-splitting and enhanced notch depth in SOI ring resonators with mutual mode coupling
2008 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 7, 4621-4630 p.Article in journal (Refereed) Published
Abstract [en]

Resonance-splitting and enhanced notch depth are experimentally demonstrated in micro-ring resonators on SOI platform as a result of the mutual mode coupling. This coupling can be generated either by the nanometer-scaled gratings along the ring sidewalls or by evanescent directional coupling between two concentric rings. The transmission spectra are fitted using the time-domain coupled mode analysis. Split-wavelength separation of 0.68 nm for the 5-mu m-radius ring, notch depth of 40 dB for the 10-mu m-radius ring, and intrinsic Q factor of 2.6 x 10(5) for the 20-mu m-radius ring are demonstrated. Notch depth improvement larger than 25dB has been reached in the 40-39-mu m-radius double-ring structure. The enhanced notch depth and increased modal area for the concentric rings might be promising advantages for bio-sensing applications.

Keyword
Directional couplers, Resonators, Time domain analysis, Wavelength, Mutual mode coupling, SOI ring resonators
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8028 (URN)10.1364/OE.16.004621 (DOI)000255100400026 ()2-s2.0-41649120161 (Scopus ID)
Note
QC 20100923. Uppdaterad från submitted till published (20100923).Available from: 2008-02-22 Created: 2008-02-22 Last updated: 2017-12-14Bibliographically approved

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