1,720,993 research outputs found
Advanced Bragg grating based integrated optical devices for wavelength division multiplexing systems
No full textThis thesis presents experimental and theoretical work towards the development of advanced integrated planar optical devices for wavelength division multiplexing (WDM) applications in optical communication systems. The presented work lies within a broad range of research areas, namely: design and simulation of novel Bragg grating based WDM passive devices, their performance characterization in simulated optical communication systems, fabrication and characterization of photosensitive thin films and finally device fabrication using ultraviolet induced refractive index changes. A complete model for the analysis of Bragg grating assisted devices in waveguide structures has been developed. Bragg grating based optical Add/Drop multiplexers (OADM) have been simulated and studied by using this modelling tool. A fully optimised design for an OADM based on null coupler and tilted Bragg grating has been proposed. This device can exhibit optimised Add and Drop actions with suppressed backreflections and crosstalk to a level lower than -40 dB. A novel interferometric OADM configuration based on a full cycle full (100%) coupler is also proposed. This design exhibits fully optimised and symmetrical Add/Drop actions in contrast to the compromised performance of traditional interferometric configurations. A software simulation tool has also been developed and employed for the theoretical characterization of optical filters, linking this way the proposed devices to real communication system issues related to high bit rate WDM networks. The effect of group delay ripple in WDM filters is studied for different modulation formats and a simplified figure of merit is proposed for the characterization of the effect. For the fabrication of photosensitive thin film structures, a prototype in-house Flame Hydrolysis Deposition facility was built and it was initially characterized. Further experimental work involved detailed analysis and characterization of highly photosensitive Lead Germanate glasses grown by Pulsed Laser Deposition. A developed direct UV-writing facility is presented and major issues around the functionality of the technique are discussed, by demonstrating solutions for the control of the optical system. A rapid heat treatment technique is also proposed for locking the enhanced photosensitivity in deuterium loaded germanosilicate glasses and successful preliminary results are demonstrated. This method should allow finally the fabrication of complex all-UV-written devices, which has been limited to date by the degrading photosensitivity during UV writing, due to rapid deuterium outdiffusion
Characterization of optical add drop multiplexers in high bit rate WDM networks
No full textCharacterization of Optical Add Drop Multiplexers (OADMs) in High Bit Rate Wavelength Division Multiplexing (WDM) systems is presented using theoretical systems simulations. Firstly the interferometric full-coupler based OADM is modelled in various configurations using coupled mode theory. Implications of the inherent non-optimum overall performance of this device in conjunction with additional system issues like filter misalignments and cascading are analysed. Filters with typical degraded spectral characteristics in the Drop or Add action exhibits at least 0.15 dB higher Eye Opening Penalty (EOP) compared to filter with optimized flat spectral response. For this kind of OADMs we found also that the Intra-Band dispersion EOP performance in a cascaded 'Add-and-Drop operation' - in a single-wavelength-processing-node - for a specific OADM is insensitive to the arrangement of the Bragg grating in the coupler waist and consequently to the individual spectral characteristics of the Add or Drop actions
Bragg grating design method for the implementation of an optimised symmetric add/drop multiplexer
No full textAn efficient and simple method is proposed for the design of a novel Bragg grating based optical add/drop multiplexer. Central to this method is the existence of generic engineering curves that relate for any BG of a specific apodization profile, its penetration slope α = Lp/Lg to its reflectivity. The implemented by this method, interferometric device based on a full-cycle waveguide coupler exhibits symmetric and simultaneously optimised add/drop responses, of zero loss
Design considerations in optical add/drop multiplexers based on grating-assisted null couplers
No full textThe performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V2 /V1 ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications
Novel full-cycle-coupler-based optical add-drop multiplexer and performance characteristics at 40-Gb/s WDM Networks
Full text linkA novel configuration of an interferometric device, based on a full-cycle full (100%) coupler structure, loaded with a Bragg grating symmetrically placed into the uniform coupler waist, is proposed for use as an optical add-drop multiplexer (OADM) with simultaneously optimized add and drop actions. A general method for designing a suitable Bragg grating for optimal inscription in to the uniform coupler waist is also proposed for use in to the device design and development. The performance of the device is characterized at 40-Gb/s wavelength-division-multiplexing (WDM) networks using theoretical systems simulations and is compared directly with other alternative OADM architectures
Performance comparison of Bragg grating-based optical add-drop multiplexers in WDM transmission systems
No full textThe filtering performance of Bragg grating-based optical add-drop multiplexers (OADMs) is studied using theoretical system simulations. The implications of the non-optimum spectral characteristics of the coupler-based OADM are quantified and compared with other filter configurations. Simulation of the performance of a non-fully optimised add/drop filter of this type, in an intensity modulation/direct detection communication system at 40 Gbit/s transmission speed, where filter/laser source misalignments and cascading operations are present, suggests an excessive eye-opening penalty of at least 0.15dB compared to the case where fully optimised spectrally flat filters are deployed
Effect of in-band group delay ripple on WDM filter performance
No full textThe effects of time-delay-ripple period and amplitude in 25GHz and 100GHz filters for operation at 10Gb/s and 40Gb/s, respectively, are studied. It is shown that maximum transmission penalties occur at time-delay periods of ~75% of the -20dB data bandwidth
Optimization of OADM's based on grating-assisted mode conversion in null couplers
No full textThe performance of a fully optimised OADM, based on null couplers and tilted Bragg gratings, is studied. The device exhibits drop action with < -40dB channel cross-talk and shows < -40 dB backreflections at the input port
Continuous wave ultra violet laser induced frustration of etching in congruent lithium niobate
No full textSurface relief patterns have been fabricated on the z face of congruent lithium niobate single crystals by illumination of the surface with continuous wave 244 nm laser radiation followed by chemical etching with hydrofluoric acid
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