No description available.

Photonic crystal (PC) technology potentially offers lossless control of light propagation at a size scale near the order of the wavelength of light. The advantages and benefits of using such a technology in commercial devices are staggering. Yet, the commercial development of PC structures has been slow. Challenges associated with the repeatable fabrication and testing of structures has been identified as one cause of the slow development pace. To address these challenges, a development methodology that utilizes PC structures operating in the long-wavelength infrared is presented. One-dimensional PC structures, consisting of alternating regions of silicon and air are fabricated and characterized by measuring the transmittance or reflectance of the structure over the wavelength range from 5 쭠to 15 쭮 For the measurements, a model of the focused infrared beam is developed, tested and employed to characterize the structures. A novel measurement method, enabling the calculation of the single-angle plane-wave transmittances and reflectances from composite, multiple-angle transmittance and reflectance measurements, is formulated, tested and applied to PC structures. A new spectral characterization tool using a discretely tunable carbon-dioxide laser is presented and demonstrated. A measurement apparatus employing an FTIR microspectroscopy system is developed and measurements are recorded for the single-angle plane-wave characterization method. Single-angle plane-wave transmittances and reflectances calculated from composite multiple-angle measurements are shown to be in excellent agreement with theory. The results of this research are analyzed to identify the advantages and limitations of the long-wavelength infrared method.

The Long Wavelength Array (LWA) is a large multi-purpose radio telescope, operating in frequencies between 10 and 88 MHz, designed for both long-wavelength astrophysics and ionospheric science. The LWA will eventually consist of 53 "stations", each consisting of 256 pairs of crossed-dipole antennas whose signals are formed into beams. The Monitoring and Control System (MCS), a subsystem of each LWA station, controls the station's subsystems and also monitors their status. This thesis addresses the interface-related features of MCS. The physical interface of the MCS with each subsystem is a Gigabit Ethernet connection and the interface protocol is User Datagram Protocol (UDP). An analysis of the throughput obtained through the interface using UDP is compared to that achieved using Transmission Control Protocol (TCP). It is seen that the throughput with UDP is 15\% better than with TCP, and that UDP is a better choice for the given requirements. Implementation of a new ionospheric calibration scheme requires that the MCS be capable of repointing between astronomical sources on a 5 ms time scale. The rate at which beams can be repointed is analyzed. It is confirmed that MCS is at least 2 orders of magnitude faster than necessary, and is limited by the ethernet network throughput. Python software that facilitates the development and testing of MCS and other subsystems have been developed, and are described. / Master of Science

Long-wavelength magnetic anomalies (LWMA) are broad scale magnetic fields that are usually observed at satellite altitudes. The origin of these fields have been assumed to be solely from the crust, disregarding possible contributions from the upper mantle. Using data from magnetic mantle xenoliths, the possible mantle contribution to LWMA was investigated for different regions including Siberian craton, Kamchatka subduction zone fore-arc, Hawaii hotspot, and French Massif Central plume. To do this, a MATLAB-based forward-modeling of magnetic anomalies from tectonic regions with different upper mantle geotherms and magnetized mantle geometries was developed. This model incorporated the increase in Curie temperature of magnetite with pressure, the current geotherms of the specific regions, and the statistical distributions of magnetic data from xenoliths in the specific regions. A Monte-Carlo method of random selection of values and repeated calculations was utilized in constraining the range of potential mantle contributions to satellite-observable LWMA. The Siberian craton shows the highest possible contribution to satellite magnetic anomalies with amplitudes ranging from 2 nT to 9 nT, with a wavelength equivalent to the long-axis of the craton. The Hawaii hotspot region displays a significant contribution of its upper mantle to satellite measured magnetic anomalies with an amplitude of the order of 2 nT, while the Massif Central plume regions shows an insignificant contribution of its upper mantle to satellite magnetic anomalies with potential total magnetic anomaly amplitude of 0.07 nT. Finally, the mantle portion of Kamchatka subduction zone shows a sizeable contribution to magnetic anomalies measurable at satellite altitude with an amplitude up to 1.3 nT. These results when compared with lithospheric total field intensity model derived from SWARM satellite data, show that the upper mantle can contribute significantly to LWMA depending on (a) the average remanent magnetization in xenoliths from such regions, (b) the thickness of magnetized mantle, and (c) the size of the region under consideration.

This project successfully designed, fabricated and characterized two highly reflective distributed Bragg reflectors for use with long wavelength vertical cavity surface emitting lasers. The first reflector consisted of 20 pairs of alternating lnP/Ino.64Gao.36Aso.777Po.223 layers grown on an InP substrate with a theoretically predicted normal incident reflectivity of 96.6% at a center wavelength of 1550nm. The second DBR had 20 pairs of alternating GaAs/Ino.484Gao.5i6P layers grown on a GaAs substrate with a theoretically predicted reflectivity of 94.9% at a center wavelength of 1550nm for normal incident light. Experimental results obtained using a specially designed reflectivity measurement setup confirmed reflectivity models and predictions at both normal and variable incident light angles. However, these measurements revealed a discrepancy between theoretical and experimental layer thickness values for both DBR structures. Applying perturbations to the theoretical models, the actual layer thicknesses ofthe DBRs were determined. X-ray analysis was employed to examine the periodicity of the super-lattices along with the accuracy of lattice matching to the substrate. Transmission electron microscopy revealed that no detectable drift in layer thickness was apparent during growth of the DBR structures. Photoluminescence was used to investigate any compositional variations ofthe quaternary layers in the first DBR stack. / Thesis / Master of Applied Science (MASc)

We used the first station of the Long Wavelength Array (LWA) to observe giant pulses (GPs) from pulsars and search for other radio transients. Using the LWA with a bandwidth of 16 MHz at 39 MHz, we made a 24-hour observation of pulsar radio pulses from PSR B0950+08. The average pulse ux density and pulse width (dominated by "normal" pulses) are consistent with previous studies by others. Using techniques we developed for searching for radio transients, in this observation we detected 119 giant pulses (with signal-to-noise ratios 10 times larger than for the mean pulse). The giant pulses have a narrower temporal width (17.8 ms, on average) than the mean pulse (30.5 ms). Giant pulses occur at a rate of about 5.0 per hour, or 0.035% of the total number of pulse periods. The strength and rate of giant pulses is less than observed by others at ~100 MHz. The probability distribution of the cumulative pulse strength is a power law, but deviates from the Gaussian distribution of normal pulses. These results suggest PSR B0950+08 produces less frequent and weaker giant pulses at 39 MHz than at 100 MHz. We detected no other transients in this observation within a dispersion measure (DM) range from 1 to 90 pc cm³. Furthermore, we conducted observations of giant pulses from PSR B0950+08 in a separate set of observations of 12 hours made simultaneously at 42 and 74 MHz. In these observations we detected a total of 275 at 42 MHz and a total of 465 giant pulses at 74 MHz. Giant pulses with double-peak temporal structure have a shorter peak-to-peak separation compared to the average pulse. Once again, PSR B0950+08 appears to produce less frequent and weaker giant pulses than reported at 100 MHz. Giant pulses are identified with signal-to-noise ratios 10 times larger than for the mean pulse, and the probability distribution of the cumulative pulse strength is a power law, but deviate from the Gaussian distribution of normal pulses, for both frequencies. There were only 128 giant pulses detected simultaneously at 42 and 74 MHz, which implies that more than half of them are narrow-band radio pulses. Using these observations we analyzed the effect of scattering due to the interstellar medium on pulses with signal-to-noise ratio > 7 and the average pulse using a CLEAN-based algorithm, assuming a thin-screen scattering model. The scatter-broadening time constant τ ∝ ν^α, where ν is the observing frequency. The resulting α as calculated from pulses with signal-tonoise ratio > 7 and for the average pulses is found to be α = −1.45±0.14 and −0.14±0.03, respectively. These results indicate differences along the line of sight from a Kolmogorov spectrum for electron density uctuations. We calculated the altitude of the emission region for the pulsar using the dipolar magnetic field model. We found a similar magnitude for the emission region altitudes of normal and giant pulses. We detected no other transient pulses in a wide DM range from 1 to 4990 pc cm⁻³. We also conducted another a 12-hour observational study of PSR B0031−07 at 38 and 74 MHz, simultaneously. Giant pulses were identified with ux densities of a factor of ≥ 90 and ≥ 80 times that of an average pulse, at 38 and 74 MHz. The cumulative pulse strength distribution follows a power law, and has a much more gradual slope than a Gaussian distribution for the normal pulses. We found 158 of the observed pulses at 38 MHz qualified as giant pulses. At 74 MHz a total of 221 of the observed pulses were giant pulses. Only 12 giant pulses were detected within the same pulse period at both 38 and 74 MHz, meaning that the majority of them are narrow-band radio pulses. No other radio transients were detected within a DM range 1 to 4990 pc cm⁻³. We used the same data processing pipeline for observations of pulsar GPs to search within the pulsar observations for fast radio bursts (FRBs). We did not detect any nonpulsar signals with signal-to-noise ratio larger than 10. When the radio transient signals propagate through the interstellar medium, they are affected by propagation effects such as dispersion and scattering. Scattering may limit the detectability of radio transients. By examination of archived pulsar profiles, we investigated the impact of scattering on observed pulses. We utilized a CLEAN-based strategy to decide the scatter-broadening time, τ , under both the thin-screen and uniform-medium scattering models and to determine the scatter-broadening time frequency scaling index, α, where τ ∝ ν^α. In most cases the scattering tail was not large compared to the pulse width at half maximum. Still, we deconvolved 1342 pulse profiles from 347 pulsars assuming a Kolmogorov spectrum of the interstellar medium turbulence. For a subset of 21 pulsars the scattering-boarding tails were suficiently long to be estimated at the lowest frequencies. Since the scatter-broadening times were only determined distinctly for the subset of pulsars at the lowest observed frequency, we were restricted to utilizing upper limits on scatter-broadening times at higher frequencies for the assessment of the scatter-broadening-time frequency dependence. We include three new direct scatter-broadening time measurements at low frequencies and they are consistent with previous studies which were scaled from higher frequencies. Our findings are consistent with a relationship between the DM and scatter-broadening time which can range over more than two orders of magnitude in DM. One of the potential reasons that we did not detect FRBs is that transients may be highly scatter-broadened at low frequencies for high DM values. / Ph. D.

Vertical-cavity surface-emitting lasers (VCSELs) areattractive as potential inexpensive high-performance emittersfor fibre-optical communication systems. Their surface-normalemission together with the small dimensions are beneficial forlow-cost fabrication since it allows on-wafer testing,simplified packaging and effective fibre-coupling. Forhigh-speed data transmission up to hundreds of metres, 850-nmVCSELs are today the technology of choice. For higher bandwidthand longer distance networks, emission at long-wavelength(1.3-1.55 µm) is required. Long-wavelength VCSELs are,however, not available since no materials system offershigh-index-contrast distributed Bragg reflectors (DBRs) as wellas high-gain active regions at such wavelengths.High-performance DBRs may be built up from AlGaAs/GaAsmultilayers, but long wavelength quantum wells (QWs) are onlywell established in the InP system. Therefore, the bestperforming devices have relied on wafer-fusion betweenInP-based QWs and AlGaAs-DBRs. More recently, however, the mainefforts have been shifted towards all-epitaxial GaAs-baseddevices, employing 1.3-µm GaInNAs QWs. In this thesis, different processing technologies forlong-wavelength VCSELs are described. This includes a thoroughinvestigation of wafer-fusion between InP and GaAs regardingelectro-optical as well as metallurgical properties, and thedevelopment of a stable low-pressure process for the selectiveoxidation of AlAs. Optimised AlGaAs/GaAs DBRs were designed andfabricated. An important and striking observation from thatstudy is that n-type doping potentially is much moredetrimental to device performance than previously anticipated.These investigations were exploited in the realisation of twonew VCSEL designs. Near-room-temperature continuous-waveoperation of a single-fused 1.55-µm VCSEL was obtained.This demonstrated the potential of InGaAsP/InP DBRs inhigh-performance VCSELs, but also revealed a high sensitivityto self-heating. Further efforts were therefore directedtowards all-epitaxial GaAs-based structures. This resulted in ahigh-performance 1215-nm VCSEL with a highly strained InGaAssingle QW. This can be viewed as a basis for longer-wavelengthVCSELs, i.e., with an emission wavelength approaching 1300 nm,either by an extensive device detuning or with GaInNAs QWs. <b>Keywords</b>: VCSEL, vertical cavity laser, semiconductorlaser, long-wavelength, DBR, oxidation, wafer fusion, InGaAs,semiconductor processing

Vertical cavity lasers (VCLs) are of great interest aslow-cost, high-performance light sources for fiber-opticcommunication systems. They have a number of advantages overconventional edge-emitting lasers, including low powerconsumption, efficient fiber coupling and wafer scalemanufacturing/testing. For high-speed data transmission overdistances up to a few hundred meters, VCLs (or arrays of VCLs)operating at 850 nm wavelength is today the technology ofchoice. While multimode fibers are successfully used in theseapplications, higher transmission bandwidth and longerdistances require single-mode fibres and longer wavelengths(1.3-1.55 µm). However, long-wavelength VCLs are as yetnot commercially available since no traditional materialssystem offers the required combination of bothhigh-index-contrast distributed Bragg reflectors (DBRs) andhigh-gain active regions. Earlier work on long-wavelength VCLshas therefore focused on hybrid techniques, such as waferfusion between InP-based QWs and AlGaAs DBRs, but more recentlythe main interest in this field has shifted towardsall-epitaxial GaAs-based devices employing novel 1.3-µmactive materials. Among these, strained GaInNAs/GaAs QWs aregenerally considered one of the most promising approaches andhave received a great deal of interest. The aim of this thesis is to investigate monolithicGaAs-based long-wavelength (&gt;1.2 µm) VCLs with InGaAsor GaInNAs QW active regions. Laser structures - or partsthereof - have been grown by metal-organic vapor phase epitaxy(MOVPE) and characterized by various techniques, such ashigh-resolution x-ray diffraction (XRD), photoluminescence(PL), atomic force microscopy, and secondary ion massspectroscopy (SIMS). High accuracy reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs DBRs than previously anticipated. Asystematic investigation was also made of the deleteriouseffects of buried Al-containing layers, such as AlGaAs DBRs, onthe optical and structural properties of subsequently grownGaInNAs QWs. Both these problems, with their potential bearingon VCL fabrication, are reduced by lowering the DBR growthtemperature. Record-long emission wavelength InGaAs VCLs were fabricatedusing an extensive gain-cavity detuning. The cavity resonancecondition just below 1270 nm wavelength occurs at the farlong-wavelength side of the gain curve. Still, the gain is highenough to yield threshold currents in the low mA-regime and amaximum output power exceeding 1 mW, depending on devicediameter. Direct modulation experiments were performed on1260-nm devices at 10 Gb/s in a back-to-back configuration withopen, symmetric eye diagrams, indicating their potential foruse in high-speed transmission applications. These devices arein compliance with the wavelength requirements of emerging10-Gb/s Ethernet and SONET OC-192 standards and may turn out tobe a viable alternative to GaInNAs VCLs. <b>Keywords:</b>GaInNAs, InGaAs, quantum wells, MOVPE, MOCVD,vertical cavity laser, VCSEL, long-wavelength, epitaxy, XRD,DBR

<p>Vertical-cavity surface-emitting lasers (VCSELs) areattractive as potential inexpensive high-performance emittersfor fibre-optical communication systems. Their surface-normalemission together with the small dimensions are beneficial forlow-cost fabrication since it allows on-wafer testing,simplified packaging and effective fibre-coupling. Forhigh-speed data transmission up to hundreds of metres, 850-nmVCSELs are today the technology of choice. For higher bandwidthand longer distance networks, emission at long-wavelength(1.3-1.55 µm) is required. Long-wavelength VCSELs are,however, not available since no materials system offershigh-index-contrast distributed Bragg reflectors (DBRs) as wellas high-gain active regions at such wavelengths.High-performance DBRs may be built up from AlGaAs/GaAsmultilayers, but long wavelength quantum wells (QWs) are onlywell established in the InP system. Therefore, the bestperforming devices have relied on wafer-fusion betweenInP-based QWs and AlGaAs-DBRs. More recently, however, the mainefforts have been shifted towards all-epitaxial GaAs-baseddevices, employing 1.3-µm GaInNAs QWs.</p><p>In this thesis, different processing technologies forlong-wavelength VCSELs are described. This includes a thoroughinvestigation of wafer-fusion between InP and GaAs regardingelectro-optical as well as metallurgical properties, and thedevelopment of a stable low-pressure process for the selectiveoxidation of AlAs. Optimised AlGaAs/GaAs DBRs were designed andfabricated. An important and striking observation from thatstudy is that n-type doping potentially is much moredetrimental to device performance than previously anticipated.These investigations were exploited in the realisation of twonew VCSEL designs. Near-room-temperature continuous-waveoperation of a single-fused 1.55-µm VCSEL was obtained.This demonstrated the potential of InGaAsP/InP DBRs inhigh-performance VCSELs, but also revealed a high sensitivityto self-heating. Further efforts were therefore directedtowards all-epitaxial GaAs-based structures. This resulted in ahigh-performance 1215-nm VCSEL with a highly strained InGaAssingle QW. This can be viewed as a basis for longer-wavelengthVCSELs, i.e., with an emission wavelength approaching 1300 nm,either by an extensive device detuning or with GaInNAs QWs.</p><p><b>Keywords</b>: VCSEL, vertical cavity laser, semiconductorlaser, long-wavelength, DBR, oxidation, wafer fusion, InGaAs,semiconductor processing</p>

<p>Vertical cavity lasers (VCLs) are of great interest aslow-cost, high-performance light sources for fiber-opticcommunication systems. They have a number of advantages overconventional edge-emitting lasers, including low powerconsumption, efficient fiber coupling and wafer scalemanufacturing/testing. For high-speed data transmission overdistances up to a few hundred meters, VCLs (or arrays of VCLs)operating at 850 nm wavelength is today the technology ofchoice. While multimode fibers are successfully used in theseapplications, higher transmission bandwidth and longerdistances require single-mode fibres and longer wavelengths(1.3-1.55 µm). However, long-wavelength VCLs are as yetnot commercially available since no traditional materialssystem offers the required combination of bothhigh-index-contrast distributed Bragg reflectors (DBRs) andhigh-gain active regions. Earlier work on long-wavelength VCLshas therefore focused on hybrid techniques, such as waferfusion between InP-based QWs and AlGaAs DBRs, but more recentlythe main interest in this field has shifted towardsall-epitaxial GaAs-based devices employing novel 1.3-µmactive materials. Among these, strained GaInNAs/GaAs QWs aregenerally considered one of the most promising approaches andhave received a great deal of interest.</p><p>The aim of this thesis is to investigate monolithicGaAs-based long-wavelength (>1.2 µm) VCLs with InGaAsor GaInNAs QW active regions. Laser structures - or partsthereof - have been grown by metal-organic vapor phase epitaxy(MOVPE) and characterized by various techniques, such ashigh-resolution x-ray diffraction (XRD), photoluminescence(PL), atomic force microscopy, and secondary ion massspectroscopy (SIMS). High accuracy reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs DBRs than previously anticipated. Asystematic investigation was also made of the deleteriouseffects of buried Al-containing layers, such as AlGaAs DBRs, onthe optical and structural properties of subsequently grownGaInNAs QWs. Both these problems, with their potential bearingon VCL fabrication, are reduced by lowering the DBR growthtemperature.</p><p>Record-long emission wavelength InGaAs VCLs were fabricatedusing an extensive gain-cavity detuning. The cavity resonancecondition just below 1270 nm wavelength occurs at the farlong-wavelength side of the gain curve. Still, the gain is highenough to yield threshold currents in the low mA-regime and amaximum output power exceeding 1 mW, depending on devicediameter. Direct modulation experiments were performed on1260-nm devices at 10 Gb/s in a back-to-back configuration withopen, symmetric eye diagrams, indicating their potential foruse in high-speed transmission applications. These devices arein compliance with the wavelength requirements of emerging10-Gb/s Ethernet and SONET OC-192 standards and may turn out tobe a viable alternative to GaInNAs VCLs.</p><p><b>Keywords:</b>GaInNAs, InGaAs, quantum wells, MOVPE, MOCVD,vertical cavity laser, VCSEL, long-wavelength, epitaxy, XRD,DBR</p>