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You searched for subject:(Holographic beam steering). Showing records 1 – 2 of 2 total matches.

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University of Oxford

1. Tran, Tuan-Anh. Multiple-input multiple-output optical wireless communications.

Degree: PhD, 2013, University of Oxford

Visible-light optical wireless communications (OWC) is a potential technology that can help resolve the crowdedness of the radio-frequency bands, whilst conveniently exploiting energy-saving light-emitting diodes (LEDs) as transmitters for both illumination and communications. Since there usually are many LEDs in a lighting unit, OWC has a multi- input multi-output (MIMO) geometry which, thanks to its channel diversity, can offer wireless local networks at data-rates many times higher than possible with single-channel systems. In such systems, MIMO-detection methods to separate the different optical channels play an important role in improving the system performance by helping reduce cross-talk between channels. To measure the performance of a particular geometry for MIMO communications, a simulation study, reported in this thesis, found that, amongst the signal- independent metrics, the condition number may be used as a rough predictor of the performance, whilst the channel Signal-to-Interference-and-Noise Ratio (SINR) is the most appropriate for geometry assessment. Combined with the fact that the overall performance of a MIMO system is mostly dominated by its worst channel, this indicates that the most effective way to improve the system performance is to maximise the worst channel’s SINR. One of the possible solutions to improving the SINRs is to use holograms to steer the transmitter images such that their distributions over the photo-detectors reduce overlaps. As LEDs emit partially-coherent light, the beam steering has to be carried out with partially- coherent illumination. By using two lenses to parallelise and collect partially-coherent light before and after the hologram, respectively, the source and image intensity distributions, and the autocorrelation of the hologram can be related in a succinct mathematical relationship. This leads to the development of three computational algorithms based on the autocorrelation function to obtain a quantised hologram with the desired beam-steering capability. These algorithms have their cost functions and performance comparison done at the hologram plane instead of the image plane, which therefore takes less time than traditional image-based methods. Specifically, one of these algorithms is able to save significant time over both the other autocorrelation-based algorithms and the direct binary-search, by 33% and by 50% respectively. A simulation-based study and a corresponding experiment, both reported in this thesis, found that the one of the proposed algorithms had poor power efficiency, whilst the other two were both highly effective in generating digital holograms with precise and power-efficient beam-steering performance. Of these two algorithms, one had superior time performance and was likely the best of the three proposed autocorrelation-based algorithms for generating beam-steering holograms. MIMO-OWC simulation also demonstrated the capability of using beam-steering holograms to design the channel and improve the system performance. Combining reported…

Subjects/Keywords: 621.382; Optoelectronics; Atomic and laser physics; Visible light communications; Holographic; Beam-steering; Channel matrix; Optimisation

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Tran, T. (2013). Multiple-input multiple-output optical wireless communications. (Doctoral Dissertation). University of Oxford. Retrieved from http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595975

Chicago Manual of Style (16th Edition):

Tran, Tuan-Anh. “Multiple-input multiple-output optical wireless communications.” 2013. Doctoral Dissertation, University of Oxford. Accessed March 08, 2021. http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595975.

MLA Handbook (7th Edition):

Tran, Tuan-Anh. “Multiple-input multiple-output optical wireless communications.” 2013. Web. 08 Mar 2021.

Vancouver:

Tran T. Multiple-input multiple-output optical wireless communications. [Internet] [Doctoral dissertation]. University of Oxford; 2013. [cited 2021 Mar 08]. Available from: http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595975.

Council of Science Editors:

Tran T. Multiple-input multiple-output optical wireless communications. [Doctoral Dissertation]. University of Oxford; 2013. Available from: http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595975

2. Persson, Martin. Advances in Holographic Optical Trapping.

Degree: 2013, University of Gothenburg / Göteborgs Universitet

Holographic optical trapping (HOT) is a technique for non-invasive dynamic anipulation of multiple microscopic objects, which has been used for many applications in the life sciences during the past decade. The technique uses holographic beam steering with a spatial light modulator (SLM) to direct light to the desired positions of optical traps. In many cases, the control of the optical intensity of the traps is impaired by imperfections in the SLM. This has limited the use of HOT for applications sensitive to variations in the trap intensities, such as optical force measurement (OFM). Also, the algorithms for optimization of holograms used in HOT are computationally demanding, and real-time manipulation with optimized holograms has not been possible. In this thesis, four different methods for improving the accuracy of holographic beam steering are presented, along with a novel application for the combination of HOT and position measurement. The control of trap intensities is improved by compensating for crosstalk between pixels, and for spatial variations of the phase response of the SLM; and by dumping a controlled amount of light to specified regions away from the traps. Variations in trap intensities occurring when updating the SLM with new holograms are suppressed by enforcing a stronger correlation between consecutive holograms. The methods consist of modifications of the algorithm used for hologram generation, or alternative methods for post-processing of generated holograms. Applications with high stability requirements, such as OFM with HOT, will benefit from the presented improvements. A method for reducing computation time for hologram optimization is also presented, allowing the accuracy improvements to be used also for time critical applications. Further, it is shown that position measurement of nanowires, held by multiple optical traps, can be used to probe the orientational structure and defects in liquid crystal materials.

Subjects/Keywords: Optical tweezers; Holographic optical trapping; Optical force measurement; Spatial light modulators; Holographic beam steering; Liquid crystals

…5 5 7 8 9 3 Holographic Beam Steering 3.1 Scalar Diffraction… …image plane of the microscope. Chapter 3 Holographic Beam Steering o control optical traps… …optical system. 11 12 3.1.1 Holographic Beam Steering The Rayleigh-Sommerfelt Diffraction… …microscope is given exactly by its image near the target plane. 14 Holographic Beam Steering… …x29;/Id,m ) (3.11) 16 Holographic Beam Steering where Id,m is the… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Persson, M. (2013). Advances in Holographic Optical Trapping. (Thesis). University of Gothenburg / Göteborgs Universitet. Retrieved from http://hdl.handle.net/2077/32606

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Persson, Martin. “Advances in Holographic Optical Trapping.” 2013. Thesis, University of Gothenburg / Göteborgs Universitet. Accessed March 08, 2021. http://hdl.handle.net/2077/32606.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Persson, Martin. “Advances in Holographic Optical Trapping.” 2013. Web. 08 Mar 2021.

Vancouver:

Persson M. Advances in Holographic Optical Trapping. [Internet] [Thesis]. University of Gothenburg / Göteborgs Universitet; 2013. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/2077/32606.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Persson M. Advances in Holographic Optical Trapping. [Thesis]. University of Gothenburg / Göteborgs Universitet; 2013. Available from: http://hdl.handle.net/2077/32606

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.