Nicolas A Jaeger
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Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Sub-wavelength gratings (SWGs) and periodic waveguides play important roles in integrated optics. These periodic structures have been employed in integrated optical power couplers and wavelength filters which are key components for optical communication and sensing systems. This dissertation is a theoretical and experimental study of high performance silicon photonic SWG-based adiabatic couplers, SWG contra-directional couplers (SWG CDCs), and polarization-rotating Bragg grating (PRBG) filters that use these periodic structures. Mode-evolution-based couplers, also known as adiabatic couplers, are fundamental building blocks for optical communications applications such as broadband optical switches and electro-optic modulators. In this thesis, to begin with, adiabatic 3 dB couplers using conventional silicon-on-insulator (SOI) ridge and strip waveguides are studied and demonstrated for 100-mm-long mode-evolution regions and 100 nm operating bandwidths with splitting imbalances 30 nm and sidelobe suppression ratios >50 dB. PRBGs are proposed and demonstrated using periodic corner corrugations on single-mode SOI strip waveguides for polarization-insensitive wavelength filtering. A PRBG band-rejection filter is demonstrated with a 3 dB bandwidth of 2.63 nm, an extinction ratio (ER)>27 dB, and a low IL
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This dissertation presents theoretical and experimental results for silicon optical ring resonator filters that meet many of the typical commercial specifications for dense wavelength-division multiplexing (DWDM) filters. First, we theoretically demonstrate a silicon quadruple Vernier racetrack resonator that meets 4-port filter commercial specifications for a clear window of 0.08 nm and a channel spacing of 0.8 nm while being tolerant to typical fabrication variations. Next, we experimentally demonstrate a silicon quadruple Vernier racetrack resonator that meets many 3-port filter commercial specifications for a clear window of 0.048 nm and a channel spacing of 0.8 nm. Then, enhanced resonant tuning range using the Vernier effect is theoretically and experimentally demonstrated using a thermally tunable silicon quadruple Vernier racetrack resonator. Also, we sent 12.5 Gbps data through a thermally tunable silicon quadruple Vernier racetrack resonator and show open eye diagrams in both the drop port and through port of the filter, even within one of the minor through port notches. We then present theoretical and experimental results on a high performance silicon double microring resonator filter using Mach-Zhender interferometer-based coupling that meets numerous 3-port filter commercial specifications for a clear window of 8 GHz and a channel spacing of 200 GHz as well as having an FSR larger than the span of the C-band and low through port passband dispersion. Next, we present a FSR-eliminated silicon Vernier racetrack resonator filter. We demonstrate the performance of this filter both theoretically and experimentally. The FSR of this filter is eliminated by using contra-directional grating couplers (contra-DCs) to suppress all but one of the notches and peaks of the filter's spectra. Lastly, a process calibration procedure is demonstrated that accurately determines the coupling coefficients of fabricated contra-DCs and is used to design a FSR-eliminated silicon Vernier racetrack resonator filter that meets 3-port filter commercial specifications for a clear window of 13 GHz and a channel spacing of 200 GHz. This filter also has low drop port dispersion and low dispersion within the passbands of the through port.
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In the last decade, silicon photonics has become a strategic technology for the development of telecommunications and sensors. Due to its compatibility with well-developed complementary metal oxide semiconductor (CMOS) fabrication processes, silicon on insulator (SOI) wafers can be processed to create thousands of devices per die in a fast and inexpensive way. Being solid state devices with no movable parts, optical gyroscopes have longer life expectancies and shock resistance compared to micro-electro-mechanical gyroscopes. Thus, the implementation of SOI-based gyroscopes is desirable for large-scale, low-cost production. This thesis presents a study of the feasibility of implementing optical gyroscopes in SOI technology. A comprehensive theoretical study has been carried out to develop a device-level optimization and robustness analysis, showing that the most crucial resonator parameter is the propagation loss, followed by length and coupling. For a given propagation loss, there is an optimal resonator size, beyond which the angular speed resolution is severely degraded. On the system level, the impact of signal-to-noise ratio and insertion loss on the resolution are described.Given that the propagation loss is the most important parameter, strategies were proposed to reduce it as much as possible while still using CMOS-compatible processes. The quality factor, Q was chosen as the figure of merit to be maximized during the design iterations. As a result, the largest Q factors reported to date on SOI, using standard CMOS-compatible processes, were achieved. These Q factors are comparable to, or exceed, those of optical resonators intended for gyroscopic applications that are fabricated in materials such as indium phosphide (InP). Innovative approaches to compensate for fabrication variations are proposed, such as thermally-tuneable coupling and reference rings for differential measurements. Complex mechano-opto-electrical measurement setups were designed and implemented to characterize SOI gyroscopes, both at rest and under rotation. As a result, the Microsystem Integration Platform for Silicon-Photonics (Si-P MIP) was created. This characterization platform is now being commercialized by CMC Microsystems for academic and industrial applications. The main practical and theoretical challenges regarding the implementation of optical ring gyroscopes on SOI have been identified. Schemes to address them and suggestions for future work are proposed.
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Significant advances in the growth, measurement, and characterization methods in the field of nanoengineering have made Co-based magnetic hybrid (ferromagnetic and non-magnetic) nanostructures increasingly important for the development of giant magnetoresistance (GMR) sensors and high magnetic-moment biocompatible nanoparticles for use in the future magnetic technology. This thesis presents the growth, measurement, and characterization of magnetic hybrid nanostructures (multilayers, alloys, and nanoparticles) that exhibit interesting magnetoresistance (MR) and magnetic properties, which are significant in the development of state-of-the-art magnetic technology for use in the electronics and biomedical sectors. Firstly, Co/Au multilayers have been grown on glass substrates using e-beam evaporation, and then Co/Ag and Co/Cu multilayers have been grown on polyimide substrates using pulsed-current deposition. All of these multilayers exhibited the GMR effect at room temperature. The maximum MR for Co/Au, Co/Ag, and Co/Cu multilayers was 2.1 %, 9.1 %, and 4.1 %, respectively. The e-beam evaporated multilayers exhibited strong magnetic anisotropy when the films were deposited at the angle of 45 degrees. The electrodeposited multilayers exhibited strong magnetic anisotropy when strain was introduced externally. In both the cases, the GMR is strongly influenced by the ferromagnetic and nonmagnetic layer thicknesses and interfacial states between layers. Secondly, novel nanocomposites Co nanoparticles embedded in Au matrix have been developed using pulsed-current deposition on polyimide substrates. They exhibited interesting MR, grain size, and saturation magnetization characteristics. The maximum room temperature GMR found was 4.6 %. X-ray diffraction, magnetization, and low temperature measurements suggest that a smaller grain size formed during higher current density correlates with the larger MR values for these nanocomposites. Thirdly, high-magnetic-moment biocompatible FeCo nanostructures have been developed using pulsed-current deposition. The nanostructures exhibited saturation magnetization of up to 240 emu/g, which is much larger than the saturation magnetization of either Co or Fe. The less expensive and highly sensitive GMR sensors if coated with specific probes, and if the target biomolecules are labelled with high-moment biocompatible nanoparticles presented in this thesis, the GMR sensors have potential for use in improving the early detection and treatment of chronic diseases (e.g., prostate and lung cancer) using biomagnetic technology.
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This thesis is a theoretical and experimental study of novel silicon photonic filters, such as traveling-wave resonators (TWRs) and grating-assisted, contra-directional couplers (contra-DCs), for on-chip wavelength-division-multiplexing (WDM) systems and sensing applications. To measure optical losses of photonic components such as Y-branch splitters and waveguide crossings, we have developed a ring-resonator based technique which is accurate, simple, and space-efficient. A number of novel devices have been demonstrated using commercial CMOS-photonics fabrication foundries, with the aim of developing large-scale photonic integrated circuits using the standard process development tools. Two types of wavelength-selective, TWR-based reflective filters have been demonstrated for applications such as remote sensing and tunable lasers. Ultra-compact, high-Q microdisk resonators have been demonstrated, with radii of down to 1.5 µm, free spectral ranges (FSRs) of up to 71 nm, loaded Q's of up to 88,000, and unloaded Q's of over 100,000.Contra-DCs have been studied using coupled-mode theory. An add-drop filter designed using contra-DCs in slab-modulated rib waveguides has been proposed and demonstrated, which shows a flat-top response and a narrow bandwidth of 50--100 GHz, promising for dense-WDM applications. Also, we proposed an out-of-phase grating design to suppress the intra-waveguide reflection in contra-DCs. Using this novel anti-reflection (AR) design, we have demonstrated an add-drop filter with a single-band, flat-top response and a wide channel bandwidth of 6.5 nm, which enables athermal operation in a large temperature span of > 70 K. This AR contra-DC can be used to build an on-chip coarse-WDM system for power-efficient, ultra-high-speed optical interconnects. Furthermore, we have proposed and demonstrated an electrically tunable phase-shifted contra-DC.In order to overcome the challenges facing microring resonators, such as limited FSRs and difficulty in controlling the bus-resonator coupling, we have proposed to integrate contra-DCs with microring resonators for selective bus-resonator coupling. Using this method, we have demonstrated a single dominant resonant mode in a microring resonator that originally has a small FSR of 1.3 nm. This grating-coupled microring resonator is promising for applications that need a huge free spectral range, such as cascaded resonator sensor arrays and ultra-high-bandwidth WDM systems.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Silicon-on-insulator (SOI) microring resonator (MRR)-based modulators and filters have been researched extensively for use in wavelength-division multiplexing (WDM) systems due to their attractive spectral characteristics and small device footprints. However, an inherent drawback of using MRRs in WDM systems is their free-spectral-ranges (FSR). The FSR limits the aggregate data rate of the system, as it limits the number of channels that can be selectively modulated in a WDM transmitter, or simultaneously de-multiplexed in a WDM receiver. The goal of this thesis is to present and demonstrate SOI, MRR-based modulators and filters with FSR-free responses. We first experimentally demonstrate an SOI, FSR-free, MRR-based filter with a reconfigurable bandwidth. The device uses a grating-assisted coupler integrated into the MRR cavity to achieve an FSR-free response. Here, we demonstrate a nonadjacent channel isolation, for 400-GHz WDM, greater than 26.7 dB. A thermally tunable coupling scheme is utilized to compensate for fabrication variations and to demonstrate the reconfigurable filter bandwidth. We then demonstrate how lithography effects affect the performance of SOI devices, which include grating-based components. Using lithography models developed for deep ultraviolet lithography processes, we analyze the effects of lithography on the performance of an MRR with an integrated, grating-assisted coupler. We show that, if the effects of lithography are not taken in account during device design flow, large discrepancies result between the predicted “as fabricated” and “as-designed” device performance. We also demonstrate how to use the lithography models to compensate for lithographic-effects in future device designs. Lastly, we experimentally demonstrate an FSR-free, MRR-based, coupling modulator. We demonstrate open eye diagrams at 2.5 Gbps and discuss how the effects of DUV lithography limited the electro-optic bandwidth of the fabricated modulator to 2.6 GHz. We also discuss the effects of lithography on the modulation crosstalk of the device and how to significantly improve the electro-optic bandwidth and how to minimize crosstalk in future implementations of the device.
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In this thesis, we present and study the use of bent couplers in silicon-on-insulator(SOI) microring resonator (MRR) based filters. MRR based filters are attractive candidates in wavelength division-multiplexing (WDM) transceivers because of their compactness and low power consumptions. However, they suffer from drawbacks that include a limited free spectral range (FSR) which limit the number of channels that can be simultaneously multiplexed and/or demultiplexed. Our work investigates SOI single-ring MRR filters with bent couplers that have extended FSRs, enhanced filter performance (such as bandwidth, out-of-band rejection ratio,side-mode suppression, extinction ratio, and insertion loss) while maintaining compact footprints. Our aim is to make these filters attractive candidates to the current state-of-the-art WDM transceivers.We first demonstrated a 2.75 μm radius MRR filter that employs bent directional couplers in its coupling regions. This MRR filter was fabricated using a 248 nm photolithography process. Our filter has a 33.4 nm FSR and a 3-dB bandwidth of 25 GHz. Also, our MRR achieved an out-of-band-rejection ratio of 42 dB, an extinction ratio of 19 dB, and a drop-port insertion loss that is less than 1 dB. Lastly, our MRR filter has a tuning efficiency of 12 mW/FSR. Then, we theoretically and experimentally demonstrated an MRR filter with bent contra-directional couplers that exhibits an FSR-free response, at both the drop and through ports, while achieving a compact footprint. Also, using bent contra-directional couplers in the coupling regions of MRRs allows us to achieve larger side-mode suppressions than MRRs with straight CDCs. The fabricated MRR filter has a minimum suppression ratio of more than 15 dB, a 3dB-bandwidth of ~23 GHz, a through-port extinction ratio of ~18 dB, and a drop-port insertion loss of ~1 dB. High-speed data transmission through the MRR filter is demonstrated at data rates of 12.5 Gbps, 20 Gbps, and 28 Gbps.
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Sinusoidal anti-coupling (AC) symmetric waveguides provide a means to design dense waveguide arrays that have minimal inter-waveguide crosstalk for high-density integration of photonic circuits. Also, the polarization sensitivity of sinusoidal AC symmetric waveguides and the reduction of wavelength dependence that is achieved by the sinusoidal waveguides can be used to design broadband polarization beam splitters (PBSs) for polarization diversity systems. In this thesis, I demonstrate the use of sinusoidal bends to suppress the optical power exchange between pairs of symmetric strip waveguides for both transverse-electric (TE) and transverse-magnetic (TM) modes as well as to separate the TE and TM modes into two output symmetric strip waveguides on a silicon-on-insulator platform. I design, model, simulate, and analyze sinusoidal AC symmetric waveguide pairs for both the TE and TM modes. Then, based on the TE sinusoidal AC waveguide structure, I design, simulate, and analyze a PBS using a symmetric directional coupler (DC) with sinusoidal bends. I also compare the modal dispersions of the sinusoidally-bent symmetric DC, which is used in the PBS, with the modal dispersions of an equivalent straight symmetric DC. I measure the fabricated test devices and evaluate their performances.The TE sinusoidal AC device, which has a gap width of 200 nm, has an average crosstalk suppression ratio (SR) of 38.2 dB, and the TM sinusoidal AC device, which has a gap width of 600 nm, has an average crosstalk SR of 34.9 dB over an operational bandwidth of 35 nm. The PBS has a small coupler length of 8.55 μm, has average extinction ratios of 12.0 dB for theTE mode and of 20.1 dB for the TM mode, and has average polarization isolations of 20.6 dB for the through port (the TE mode over the TM mode) and of 11.5 dB for the cross port (the TM mode over the TE mode) over a broad operational bandwidth of 100 nm. All of my devices are easy to fabricate and compatible with complementary metal-oxide-semiconductor technologies.
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In this thesis, we demonstrate long transverse magnetic (TM) Bragg gratings wrapped compactly using spiral waveguides on the silicon-on-insulator (SOI) platform. We developed three types of TM spiral Bragg grating waveguides (SBGWs) including uniform spiral Bragg grating (U-SBGWs), phaseshifted spiral Bragg grating (P-SBGWs), and chirped spiral Bragg gratings (C-SBGWs). Our spiral waveguides are space-efficient, requiring an area of only 189 x 189 μm² to accommodate 1 cm long Bragg grating waveguides and, thus, are less susceptible to fabrication non-uniformities. Due to these factors, the TM U-SBGWs are able to successfully obtain narrow bandwidths and high extinction ratios (ERs), as narrow as 0.09 nm and as large as 52 dB respectively. Also, the TM P-SBGWs can obtain sharp resonance peaks with high quality factors of 78790. Finally, we demonstrate the TM C-SBGWs, which exhibit group delays that are linear functions of the wavelengths over their passbands. Traditionally, due to the large coupling coefficients and the flexibility for achieving desired spectral characteristics, short Bragg grating waveguides for transverse electric (TE) modes on the SOI platform have been developed forapplications in optical communication and sensing systems. In contrast, TM modes Bragg gratings on SOI platform have small coupling coefficients and, therefore, the grating lengths need to be much longer than TE mode devices, in order to obtain large ERs. However, such TM mode Bragg gratings can achieve very narrow bandwidths. Creating long gratings in regular straight waveguides suffer from the fabrication non-uniformity effects caused by the wafer thickness. As is shown here, spiral-shaped waveguides can be used to increase the grating length, while still being made using little on chip real estate, thus reducing the effects of fabrication non-uniformity.
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A dumbbell shape micro-ring resonator reflector fabricated using the silicon-on-insulator (SOI) technology for use as a reflective notch filter is presented. The development of this dumbbell micro-ring reflector is motivated by the increasing demand for highly confined resonant structures as integrated optical components in modern optical communication and sensor applications. In this thesis, we have analyzed and simulated the reflection properties of dumbbell micro-ring reflectors based on SOI strip waveguides. We have optimized our design based on the analytic modeling and simulation results and had our devices fabricated at a foundry. An automated optical probe station has been developed for characterizing the performance of the fabricated dumbbell micro-ring reflectors. Measurement results on the reflection spectrum showed an extinction ratio of 20 dB with a quality factor of ~11,000. Thermal tuning responses showed the potential for those resonators in sensor applications.
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Wavelength-division multiplexing (WDM) using silicon-on-insulator (SOI) waveguides have become an attractive area of research to decrease the footprint of optical interconnects as well as to ensure high speed data transmission. Specifically, research into using SOI ring resonator add-drop filters for WDM applications have been increasingly pursued. A ring resonator coupled on both sides by straight waveguides enables one to add (multiplex) or drop (demultiplex) wavelengths. Using series-coupled ring resonators, with each resonator having a different length, enables better spectral performance than single ring resonators. In this thesis, we have analyzed the properties of SOI strip waveguides and directional couplers. We have compared different spectral properties of single and series-coupled ring resonators and showed the advantages of using series-coupled ring resonators. SOI strip waveguide series-coupled racetrack resonators exhibiting the Vernier effect were designed by us and fabricated at a leading edge foundry. The free spectral range was 36 nm, which is comparable to the span of the optical C-band. The drop port response showed interstitial peak suppression between 9 dB and 17 dB and minimal resonance splitting.
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An electro-optic modulator containing a single SiGe/Si quantum-well has been designed for operation at λ₀= 1.55 µm. This single quantum-well modulator has a lower VπLπ than the 3 quantum-well modulator recently designed and optimized by Maine et al. for operation at λ₀= 1.31 µm, for which the VπLπ product was 1.8 V•cm [25]. Both modulators are derived from the detailed design given for their modulator in [40]. This single quantum-well modulator contains a Si₀.₈Ge₀.₂ quantum-well with Non-Intentionally Doped (NID) and P⁺ highly doped layers on either side. With no field applied, holes from the P⁺ layers are captured by and confined in the quantum-well and when a reverse bias is applied holes are released from the quantum well and drift to the P⁺ contact layer. Variations of the hole distribution lead to changes in the free-carrier absorption and the refractive index of each layer and subsequently to phase modulation of guided TE modes. The VπLπ product of the single quantum-well modulator is estimated 1.09 V•cm for low voltage linear modulation and 1.208 V•cm for 0 to 1.6 V digital modulation, whereas the 3 quantum-well modulator gives a VπLπ of 2.039 V•cm for 0 to 6 V digital modulation for operation at λ₀= 1.55 µm. Also, the optical loss in the single quantum-well (5.36 dB/cm at V=0 V) is lower than that of the 3 quantum-well structure (5.75 dB/cm at V=0 V). This single quantum-well modulator should also offer higher frequency operation than the 3 quantum-well modulator.
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A new type of broadband impedance transformer loaded with capacitive fins (ITF) and suitable for use up to 100 GHz is presented. The development of ITF is motivated due to the growing demand for the ever increasing transmission speed in the telecommunications industry. At millimetre wave frequencies, impedance matching is crucial to reduce reflections between mismatched loads, allowing for cleaner signal transfer and higher bit rates.Conventional tapered impedance transforms have been used in the past to achieve wideband impedance matching. In order to improve the performance of tapered impedance transformers, we adopted a slow-wave electrode design approach. A typical ITF structure utilizes capacitive loading fins to control the impedance along the line. This increases the effective microwave index of the impedance transformer. Compared with conventional, unloaded, tapered impedance transformers, ITF structures extend the impedance matching range and the operating bandwidth for the same amount of on-chip real-estate. We have designed ITFs capable of impedance matching resistive loads from ~ 10 Ω to ~ 229 Ω, on a 650 μm thick GaAs substrate, for frequencies up to 70 GHz. Several design examples are used to demonstrate the performance and flexibility of these ITF structures. The ITF design technique can be used to make impedance transformers that operate up to 100 GHz.
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