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This thesis presents an engineering project measuring the effective wavelength of the CHARA Classic beam combiner on the CHARA Array. Knowing the actual effective wavelength of light observed is very important because that value is necessary for determining astrophysical parameters of stars. Currently, the value used for CHARA Classic data comes from a model of the system and is based on numbers published by the manufacturer of the filter; it is not derived from measurements done on the system directly. We use two data collection methods to observe standard stars of different spectral types and calculate the wavelength of light recorded by the instrument for each star. We find the best estimate of the effective wavelength for the CHARA Classic K′-band configuration to be 2.138±0.003μm, a 0.56% decrease from the previously adopted value of 2.150μm. Our result establishes the first estimate of the uncertainty in the effective wavelength.

The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany. Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements. When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m2) and the peak wavelength were maximum luminescence occurred. The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected. When irradiance of the excitation light was approx. 8 W/m2 the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m2. The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample. The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.

This thesis utilized pulse shaping and Gerberg-Saxton algorithm to develop high power tunable narrowband terahertz radiation and applications. By the way of using Freezing algorithm and Gerberg-Saxton, pulse width, pulse duration, pulse position and pulse number can be controlled. The pulse train can be pumping source of high power tunable narrowband terahertz radiation, by avoid the saturations and different pulse duration. The simulation shown the result can have 5GHz narrowband width closing to commercial product. Besides, we demonstrated the THz multi-wavelength interference method by using THz-TDS (terahertz time domain spectroscopy) to measure the liquid crystal cell gap. We have also used THz-TDS to investigate the complex optical constants and birefringence of cholesteric liquid crystal mixture BL006. The extraordinary (ne) and ordinary (no) indices of refraction at are 1.784-1.817 and 1.516-1.555 giving rise to a birefringence of 0.25¡V0.29 in 0.2THz~1.6THz.

The communication system using Wavelength-division multiplexing (WDM) allows for better utilization of the spectral bandwidth. Photonic crystals (PhCs) exhibit photonic bandgap (PBG) due to the periodic variation of the dielectric constant and photons with a range of frequencies within the PBG cannot travel through the crystal. By introducing defects into PhCs, it is possible to control the light propagation along certain paths. In this thesis, the characteristics of coupled cavity waveguides (CCWs) and drop filter are discussed. Then we propose a multi-channel WDM system based on CCWs. It can be applied in FTTH to filter the wavelengths of 1310, 1490 and 1550 nm in different CCWs and also can make the bandwidth of output wavelength become narrow to filter more wavelengths. In addition, by modulating the size of the resonator on the PhCs, it can drop the particular wavelength into the waveguide. Finally, we proposed a multi-channel drop filter with FHWM 0.8 nm. This device design is leading the way to achieve CWDM specification with 100% drop efficiency, high quality factor and almost no crosstalk. The operations of such an ultra-compact demultiplexer and drop filter based on PhCs are suitable to be used in WDM optical communication systems.

Optical Wireless Communication systems use lasers offering larger bandwidth, which facilitates higher data rates, comparing with radio communication systems. However, its performance is limited by atmospheric conditions, and is a function of wavelength. The objective of this study is the determination of the wavelength interval(s) at which the atmospheric transmittance is relatively high and has relatively low dependence on variations in temperature, relative humidity, wind speed and atmospheric pressure under the conditions such as path altitude of 10 meters, path geometry of horizontal to the Earth&rsquo / s surface and clean (includes no fog, rain or snow etc.) over sea surface atmosphere. The path length is taken to be 15 km. Alanya was assignated as geographical region and the required information about the atmospheric constituents and meteorological parameters was collected. Then, the variations in atmospheric transmittance due to the periodically measured meteorological parameters were calculated (for summer and winter seasons). Finally, individually calculated effects of these parameters on atmospheric transmittance are assembled in order to determine the desired wavelength interval(s). As a result, the most suitable wavelength interval was determined to be about between 3.99 &micro / m and 4.02 &micro / m. In addition, dependencies of atmospheric pressure, temperature, relative humidity, and wind speed on atmospheric transmittance have been established for both winter and summer seasons. Atmospheric transmittance is found to be inversely proportional to temperature, relative humidity and wind speed. The effect of pressure is relatively small comparing with other parameters.

Optical communication networks are becoming the backbone of both national and international telecommunication networks. With the progress of optical communication systems, and the constraints brought by WDM transmissions and increased bit rates, new ways to convert the binary data signal on the optical carrier have been proposed. There are different factors that should be considered for the right choice of modulation format, such as information spectral density (ISD), power margin, and tolerance against group-velocity dispersion (GVD) and against fiber nonlinear effects like self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), and stimulated Raman scattering (SRS). In this dissertation, the several very important modulation formats such as Non Return to Zero (NRZ), Return to Zero (RZ), Chirped Return to Zero (CRZ), Carrier Suppressed Return to Zero (CSRZ), Differential Phase Shift Keying (PSK) and Carrier Suppressed Return to Zero- Differential Phase Shift Keying (CSRZ-DPSK) will be detailed and compared. In order to make performance analysis of such modulation formats, the simulation will be done by using VPItransmissionMakerTM WDM software.

In this thesis, several machining strategies to remove axially symmetric form error with small wavelength by Hydrodynamic Polishing process (abbreviated as HDP) were proposed. Three strategies were proposed progressively in the study so as to remove axially symmetric form error with small wavelength. The first and second tactics were based on a basic algorithm, say, directly solving of a set of simultaneous equations. In the first strategy, a set of simultaneous equations was constructed by relating the total machining action of each dwelling point to the corresponding initial error. Subsequently, a set of dwelling time was obtained by directly solving the simultaneous equations. The second strategy evaluates solutions in a similar way like the first one but more restrictions were concerned in solution evaluation. The third strategy is an optimal based method. A set of dwelling time was obtained by minimizing an objective function with given constraints. A series of computer simulations were conducted to estimate the residual error and examine the validity of the strategies. From the computer simulation, the first and second strategies were confronted with negative-time problem, so that merely limited improving of form precision was obtained. The proposed optimal strategy was shown to have high potential for improving the machining precision by the HDP process. Based on the proposed strategies, a better form precision of the work surface with small wavelength can be obtained.

A single-mode fused biconical 2¡Ñ2 coupler for polarization beamsplitting is fabricated in this thesis. We use simple fused and tapered method to fabricate the polarization beamsplitter(PBS) stably, and then we can get polarization maintaining in the output fibers. Without changing the manufacturing process, we design the device with special combination of fabrication parameters. We have achieved an extinction ratio of 25.78dB at the throughput port and 27.16dB at the coupled port. A usable spectral window as broad as 37nm and 27nm with an extinction ratio larger than 15dB for both ports is obtained. The excess loss is about 0.3dB. Based on a full-wave numerical approach, the performance of the PBS can be well modeled. We get good agreement between the measured and simulated results.

<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>