Churin, E.G.; (2004) Analysis and design of concave grating-based devices for multi-wavelength optical networks. Doctoral thesis , University of London.

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Abstract

This thesis is focused on the analysis and design of concave holographic gratings for applications in wavelength division multiplexed (WDM) optical network devices, such as multi/demultiplexers, routers and channel equalizers. The main advantage of this approach is that a single optical element can perform both functions of dispersion and imaging. However, the design of such gratings for operation in optical fibre communication networks requires the understanding and control of dominant optical aberrations, stray light, and polarization sensitivity. The solution of these problems forms the basis of the work in this thesis. Chapter 1 presents the motivation for the work, describes the major objectives and lists the main original contributions. Chapter 2 reviews related works in the field of WDM optical networks. Different published methods and techniques used for channel separation are described. Chapter 3 describes the analysis of crosstalk in free-space WDM demultiplexers and wavelength routers due to aberrations, diffraction at the aperture, and diffuse scattering from non-uniformities. It is demonstrated experimentally that holographic grating can give background crosstalk as low as -60 dB. Holographic grating-based wavelength routers are shown to be absolutely scalable from the coherent crosstalk point of view, allowing a large number of subscribers/nodes to be interconnected. Chapter 4 presents aberration analysis of concave grating. New general analytic formulae that define the parameters of concave grating mounts providing stationary and superstationary astigmatism are derived. These mounts offer diffraction-limited imaging within operating spectral range of WDM demultiplexers. A novel retro-reflective scheme of demultiplexer with concave grating and convex mirror resulting in double dispersion and large image field is proposed and analyzed. Chapter 5 describes in detail all stages of design and adjustment of an athermal 49-channel demultiplexer. The method for accurate calculation of transmission spectra is developed. Tolerances and environmental stability are analyzed and the experimentally measured performance characteristics of fully packaged device are presented. Chapter 6 presents the design and analysis of 91x91 wavelength router with 0.33 nm channel spacing based on stationary anastigmatic Littrow mount of concave grating. The problem of additional complexity with respect to a demultiplexer relating to the wide field of view in dispersion direction is successfully solved. Chapter 7 describes the design, analysis and experimental verifications of WDM channel equalizer based on concave grating. In chapter 8, novel method of flattening and broadening demultiplexer passband is proposed. The final chapter, presents a summary of the research, and provides suggestions for future work.

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