Effect of optical elements on transmitted laser beam

Diplomová práca pojednáva o skalárnej teórii difrakcie a zavádza dôležité riešenie vlnovej rovnice a to elipticky symetrický Gaussov zväzok. V praktickej časti bude popísané modelovanie difrakcie na kruhovom otvore dvoma rôznymi prístupmi. Model bude experimentálne overený experimentom. V záverečnej časti bude kriticky pojednané o výsledkoch experimentu a simulácie.Master's thesis deals with scalar diffraction theory and introduces an important solution of wave equation – elliptically symetrical Gaussian beam. In practical part, two approaches of diffraction model are used. The model will be experimentaly confirmed during experiment. In the final part, results of this experiment and simulation are criticaly discussed.

Diffraction Effects in Transmitted Optical Beam

Dizertačná práca pojednáva o vlnových a elektromagnetických javoch, ku ktorým dochádza pri zatienení eliptického Gausovského zväzku kruhovou apretúrou. Najprv boli z Huygensovho-Fresnelovho princípu odvodené dva modely Fresnelovej difrakcie. Tieto modely poskytli nástroj pre zavedenie kontrastu difrakčného obrazca ako veličiny, ktorá kvantifikuje vplyv difrakčných javov na prevádzkové parametre optického spoja. Následne, pomocou nástrojov elektromagnetickej teórie svetla, boli odvodené štyri výrazy (dva presné a dva aproximatívne) popisujúce geometrický útlm optického spoja. Zároveň boli skúmané tri rôzne prípady odsmerovania zväzku - priečne posunutie a uhlové odsmerovanie vysielača, resp. prijímača. Bol odvodený výraz, ktorý tieto prípady kvantifikuje ako útlm elipticky symetrického Gausovského zväzku. Všetky vyššie uvedené modely boli overené v laboratórnych podmienkach, aby sa vylúčil vplyv iných javov. Nakoniec práca pojednáva o návrhu plne fotonického optického terminálu. Najprv bol ukázaný návrh optického vysielača nasledovaný vývojom optomechanickej sústavy prijímača. Pomocou nástrojov geometrickej a maticovej optiky boli vypočítané parametre spoja a odhad tolerancie pri zamierení spoja.The thesis was set out to investigate on the wave and electromagnetic effects occurring during the restriction of an elliptical Gaussian beam by a circular aperture. First, from the Huygens-Fresnel principle, two models of the Fresnel diffraction were derived. These models provided means for defining contrast of the diffraction pattern that can be used to quantitatively assess the influence of the diffraction effects on the optical link performance. Second, by means of the electromagnetic optics theory, four expressions (two exact and two approximate) of the geometrical attenuation were derived. The study shows also the misalignment analysis for three cases -- lateral displacement and angular misalignment of the transmitter and the receiver, respectively. The expression for the misalignment attenuation of the elliptical Gaussian beam in FSO links was also derived. All the aforementioned models were also experimentally proven in laboratory conditions in order to eliminate other influences. Finally, the thesis discussed and demonstrated the design of the all-optical transceiver. First, the design of the optical transmitter was shown followed by the development of the receiver optomechanical assembly. By means of the geometric and the matrix optics, relevant receiver parameters were calculated and alignment tolerances were estimated.

Modelling and analysis of FSO ground-to-train communications for straight and curved tracks

In this work, a free space optical (FSO) link for the ground-to-train communications is proposed. Analytical analysis is carried out for the case of the straight as well as curved rail tracks. We show that the transmitter divergence angle, the transmit power and the size of the concentration lens needs to increase for the curved section of the rail track compared to the straight track. We derive the analytical expression (11) for the received power level based on the link geometry for the cases of straight and curved tracks. The received power variation is compared for two cases showing a similar dynamic range. In the worst case scenario when the radius of curvature is 120 m, the transmit power at the optical base station (OBS) needs to increase by over 2 dB when the concentration lens radius is increased by 5 times. Analyses also show that received power increases with the radius of curvature. Finally, results are compared with the existing straight track model

POTREBA INTEGRIRANJA JAVNOG PUTNIČKOG PROMETA

The paper deals with the issue of supporting public passenger transport and integration in order to ensure the sustainable mobility of population. It highlights the importance of public passenger transport and the reasons why the population prefers cars. The objective of the paper is to analyse public passenger transport without mutual integration of individual transport systems resulting in the fact that it is not sufficiently able to compete with individual automobile transport. It is suggested the process of public passenger transport integration as well as the design of key elements in order to increase road safety. In addition, the paper confirms the hypothesis that by supporting of public passenger transport and increasing the number of individuals transported by public passenger transport, road safety increase can be achieved.Ovaj rad se bavi problematikom potpore javnog prijevoza kao i njegovom integracijom da bi se osigurala održiva mobilnost populacije. Ističe se značaj javnog prijevoza te se navode razlozi zašto generalna populacija preferira automobilski prijevoz. Cilj rada je analizirati javni putnički prijevoz izuzevši individualne načine prijevoza te se zaključuje da se javni ne može mjeriti sa individualnim automobilskim transportom (po broju putnika). U radu se predlaže način integracije javnog putničkog prijevoza i ističe ključne elemente za povećanje sigurnosti na cestama. Dodatno, ovo istraživanje potvrđuje hipotezu da se poboljšanjem javnog prijevoza kao i povećanim brojem korisnika istog povećava sigurnost na cestama

Quantifying the Effect of Atmospherically-Induced Pointing Errors in Optical Geostationary Satellite Feeder Links Using Transmitter Diversity

Optical links to geostationary (GEO) satellites suffer from atmospherically-induced beam wander which leads to pointing errors at the satellite causing deep fades. In this paper, we show the benefit of transmitter diversity in reducing the fades caused by beam wander. We derive an analytical expression for the reduction of overall scintillation index for a given number of transmitted beams with Gaussian profile in a multiple-input single-output (MISO) system considering solely the effect of beam wander. The transmitted power, beam divergence angle and pointing jitter are kept as free parameters as in the real situation. Moreover, the optimized ratio of transmitted powers between multiple beams is obtained though simulations for a two-fold transmitter diversity to obtain minimum overall power scintillation index (PSI)

Optical Technologies for Future Global Navigation Satellite Systems

Accurate, robust and reliable positioning and timing has become crucial for a wide spectrum of applications. New technologies will further improve the services offered by Global Navigation Satellite Systems (GNSSs). Optical technologies are promising candidates to achieve significant improvements in terms of accuracy, robustness and reliability of GNSSs in near future. First and foremost, optical inter-satellite links (OISLs) and optical clock technologies show enormous potential for future applications at the core of next generation GNSS architectures. Both technologies can be implemented independently from each other in current GNSS as the development lines may differ, in particular in terms of technology readiness. We will present different tracks on how optical key technologies could potentially be integrated in next generations of GNSS, and assess the corresponding improvements

Pre-correction Adaptive Optics performance of a 10 km Laser Link

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is likely to replace conventional RF links. To mitigate atmospheric turbulence, TNO and DLR propose Adaptive Optics (AO) to apply uplink pre-correction. In order to demonstrate the feasibility of AO pre-correction an FSO link has been tested over a 10 km range. This paper shows that AO pre-correction is most advantageous for low point ahead angles (PAAs), as expected. In addition, an optimum AO precorrection performance is found at 16 AO modes for the experimental conditions. For the specific test site, tip-tilt precorrection accounted for 4.5 dB improvement in the link budget. Higher order AO modes accounted for another 1.5 dB improvement in the link budget. From these results it is concluded that AO pre-correction can effectively improve highthroughput optical feeder links

Synchronnous detection of modulated optical signals

Bakalárska práca pojednáva o vlastnostiach systému pre synchrónnu detekciu slabých optických signálov. V práci budú rozobrané jednotlivé aspekty návrhu, ako aj jednotlivé časti systému. V závere bude navrhnutá celková schéma zapojenia systému, ktorá bude realizovaná a jej funkčnosť overená na optickom experimente.Bachelor’s thesis deals with common features of synchronous detection system of modulated optical signals. Theoretical aspects of design as well as separate parts of system design will be discussed. In conclusion, the complete circuitry design will be presented, realized and his functionality will be tested on optical experiment.

Curved Track Analysis of FSO Link for Ground-to-Train Communications

In this work, a free space optical (FSO) link for the ground-to-train (G2T-FSO) communications is proposed. Analytical analysis is carried out for the curved rail tracks. We show that the transmitter divergence angle, the transmit power and the size of the concentration lens need to increase for the curved section of the rail track compared to the straight track. We derive the analytical expression for the received power level based on the link geometry for the case of the curved track In the worst case scenario when the curvature radius is 120 m, the transmit power at the optical base station (BS) needs to increase by over 2 dB when the concentration lens radius is increased by 5 times. Analyses also show that the received power along the track increases with the curvature radius for the same transmit power and receiver optics illustrating the effect due to link geometry. Additionally, the signal-to-noise ratio (SNR) and the bit error rate (BER) performance of the system for the curved track with different curvature radii is analysed at data rates of 10 Mbps and 100 Mbps for an additive white Gaussian noise (AWGN) channel showing a good agreement between the theoretical and the simulated BER. Finally, effect of scintillations on the G2T-FSO link performance is discussed