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Title: Spatial light modulator technologies for WDM
Author: Cohen, Adam David
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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The research outlined in this dissertation relates to the application of spatial light modulators (SLMs) to dynamic wavelength division multiplexing (WDM) network components. The work includes an investigation into the relative merits of the material basis of the modulation with particular emphasis on the comparison of liquid crystalline and polymeric materials. The principal component functionality demonstrated is that of a wavelength filter, in which the slightly wavelength-dispersive SLM acts in conjunction with a highly wavelength-dispersive fixed diffraction element in a free-space architecture. An existing commercially available SLM based on ferroelectric liquid crystals (FLCs) is used to display computer general holograms, which are pre-calculated binary-phase (0 or π) modulation patterns. The filter is also configured in a fibre ring containing a gain medium - an erbium-doped fibre amplifier (EDFA) - to create a tuneable laser. Previous work in this area established single-wavelength filtering and lasing having an apparent intrinsic 1.3-nm stepping resolution. The hologram generation algorithm has been modified to provide fine tuning of the spectral location of the lasing mode or filter passband centre. Further algorithm modifications have yielded holograms having several, variable-amplitude constructive replay angles within the first diffraction order. This has afforded expansion of the filter to a dynamic multi-channel spectral equaliser for up to eight channels, with suppression of EDFA amplified spontaneous emission between channels and at unused channel locations. These results represent the first demonstration of dynamic holographic spectral equalisation. An associated development reported in the dissertation is the facility to provide spectral shaping of the filter passband, i.e. the generation of a transmission function having a 'flat top' and an overall form that is more nearly rectangular. The filter parameters can be readily modified to ensure conformance to telecommunications standards. The molecular motion involved in typical FLC switching limits practical SLM frame rates to the order of 100 kHz. An FLC-SLM-based network component would provide adequate reconfiguration speed for application to circuit switching or restoration, but reconfiguration at the packet rate in a multiplexed data stream would require an alternative basis for spatial light modulation. X(2) non-linear optical polymers (NLOPs) can provide modulation through the linear electro-optic effect and present a number of practical advantages, including low dielectric constant, ease of processing, compatibility with silicon integrated circuit fabrication processes and scope for bespoke chemical synthesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available