Choy Man Ting. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 66-69). / Abstracts in English and Chinese. / Acknowledgments --- p.ii / Abstract --- p.v / Table of Contents --- p.vii / List of figures --- p.viii / Chapter Chapter 1 --- p.12 / Chapter 1.1 --- OBS Network Architecture --- p.3 / Chapter 1.2 --- Offset Time and Reservation Schemes --- p.5 / Chapter 1.3 --- Research Objectives --- p.7 / Chapter 1.4 --- Overview --- p.8 / Chapter Chapter 2 --- p.9 / Chapter 2.1 --- WDM crossbar architectures --- p.9 / Chapter 2.2 --- Switch Based on Optical Crossbars --- p.10 / Chapter 2.3 --- Switch Based on Wavelength Grating Routers --- p.11 / Chapter Chapter 3 --- p.14 / Chapter 3.1 --- Basics of Dual Shuffle Exchange Network --- p.14 / Chapter 3.2 --- Dual Shuffle-exchange Network --- p.16 / Chapter 3.3 --- Proposed Architecture based on DSN --- p.19 / Chapter 3.4 --- Analysis on blocking due to output contention --- p.20 / Chapter 3.5 --- Implementation issues on the 4x4 switching module --- p.23 / Chapter 3.6 --- Analysis: Non-blocking versus banyan --- p.25 / Chapter Chapter 4 --- p.30 / Chapter 4.1 --- First Scheme --- p.30 / Chapter 4.2 --- Simulation on the first scheme --- p.33 / Chapter 4.3 --- Second Scheme: Tunable wavelength converter --- p.37 / Chapter 4.4 --- Third Scheme: Route to specific wavelength port --- p.42 / Chapter 4.5 --- Analysis on blocking due to insufficient stages --- p.46 / Chapter Chapter 5 --- p.49 / Chapter 5.1 --- Delay analysis of DSN --- p.49 / Chapter 5.2 --- Vertical Expansion --- p.51 / Chapter 5.3 --- Simulation results on vertical expansion --- p.52 / Chapter 5.4 --- Building DSN with 8x8 MEMS switches --- p.54 / Chapter 5.5 --- Prove of the proposed Quarter shuffle network --- p.56 / Chapter 5.6 --- Comparison between Quarter shuffle and doubled links approaches --- p.58 / Chapter Chapter 6 --- p.64 / Conclusion --- p.64 / Bibliography --- p.66

The monitoring and study of the earth�s atmosphere is becoming an increasingly important task given the current uncertainties in climate prediction. Areas where lidar has been used to further understanding of the atmosphere include monitoring of greenhouse gases, global warming, stratospheric ozone depletion, photochemical smog and aerosol photochemistry. However, the potentially severe long term effects of anthropogenic aerosols on earth�s biosphere are poorly understood. This project seeks to apply state of the art laser technology to develop an innovative multiwavelength lidar system capable of providing new information and new insights into the field of tropospheric aerosol lidar. Several novel tunable laser and laser-like sources have been investigated and developed for the purpose of tropospheric aerosol lidar at The National Institute of Water and Atmospheric Research (Niwa), Central Otago. Multiwavelength operation in the visible and near infrared portion of the spectrum has been emphasised with the sources developed collectively spanning the wavelength interval of 400-1369 nm. The laser sources investigated were the LiF:F2+ colour centre, Titanium Sapphire (Ti:sapphire) and barium nitrate Raman lasers. In addition to the laser sources, the β-barium borate optical parametric oscillator (BBO OPO) was characterised. For each of the sources, lidar relevant aspects were studied. The results recorded include conversion efficiency with respect to the pump source, linewidth and tuning characteristics, beam quality, temporal behaviour, and device reliability and ruggedness. It was found that the LiF:F2+ laser offered significantly lower threshold, broader tuning and higher output pulse energies than the Ti:sapphire laser in the 900-1000 nm region. The high optical gain of the LiF:F2+ medium facilitated cavity optical alignment and operation of the system. The high gain also resulted in temporal behaviour well suited to the existing Niwa lidar detection scheme. When using a 5 ns pump source, amplified spontaneous emission (ASE) was found to limit the laser tuning range and efficiency. The barium nitrate Raman laser was based on a simple linear cavity arrangement which resulted in a compact and robust device with no moving components. The stimulated Raman scattering process offers relatively narrow linewidth laser operation at the first and second Stokes wavelengths of 1197 nm and 1369 nm respectively. This laser offered efficient operation once the high operation threshold was reached. Second harmonic generation was used to extend the number of potential lidar transmitter lines produced. The barium nitrate Raman laser possessed high beam divergence and a maximum of three discrete transmitter wavelengths. The BBO OPO used a type I collinear signal resonant configuration. A plane-plane cavity configuration with pump reflection was found to provide simplicity of design, low threshold, highly efficient operation and output pointing stability. The BBO OPO signal wavelength could be tuned over the wavelength interval of 400-700 nm. The disadvantage of the plane cavity was high output beam divergence. However, this was successfully brought within the required limits through the use of a 40 mm long cavity in conjunction with an expanding and collimating telescope. As a result of the study, a Tunable lidar Transmitter (TLT) system based on the BBO OPO was designed and constructed at the Physics Department. The TLT was computer-controlled using custom written software and constructed in a self contained modular manner with all required mechanical, electrical and optical components. A user manual was also written to accompany the TLT. The TLT was installed at Niwa and was successfully used to gather preliminary multiwavelength lidar data. The TLT BBO OPO threshold occurred for a pump energy of 5.2 mJ (10.6 MW/cm2) and had a maximum slope efficiency of 53%. Signal efficiency varied from 24-41-35% over the intervals of 410-500-600 nm. A maximum signal energy of 21 mJ was obtained for a signal wavelength of 492 nm when using the maximum available pump energy of 42 mJ. OPO signal linewidth varied from 0.1-1-8 nm over the signal wavelength intervals of 400-600-700 nm. The associated OPO finesse varied between 370 and 100 as the signal wavelength was tuned over the wavelength interval of 400-600 nm. The temporal behaviour of the BBO OPO was a slowly varying function of pump energy and closely followed the temporal behaviour of the pump laser, making it well suited to the existing Italian lidar detection and timing scheme.

The communication system using Wavelength-division multiplexing (WDM) allows for better utilization of the spectral bandwidth. Photonic crystals (PhCs) exhibit photonic bandgap (PBG) due to the periodic variation of the dielectric constant and photons with a range of frequencies within the PBG cannot travel through the crystal. By introducing defects into PhCs, it is possible to control the light propagation along certain paths. In this thesis, the characteristics of coupled cavity waveguides (CCWs) and drop filter are discussed. Then we propose a multi-channel WDM system based on CCWs. It can be applied in FTTH to filter the wavelengths of 1310, 1490 and 1550 nm in different CCWs and also can make the bandwidth of output wavelength become narrow to filter more wavelengths. In addition, by modulating the size of the resonator on the PhCs, it can drop the particular wavelength into the waveguide. Finally, we proposed a multi-channel drop filter with FHWM 0.8 nm. This device design is leading the way to achieve CWDM specification with 100% drop efficiency, high quality factor and almost no crosstalk. The operations of such an ultra-compact demultiplexer and drop filter based on PhCs are suitable to be used in WDM optical communication systems.

Optical communication networks are becoming the backbone of both national and international telecommunication networks. With the progress of optical communication systems, and the constraints brought by WDM transmissions and increased bit rates, new ways to convert the binary data signal on the optical carrier have been proposed. There are different factors that should be considered for the right choice of modulation format, such as information spectral density (ISD), power margin, and tolerance against group-velocity dispersion (GVD) and against fiber nonlinear effects like self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM), and stimulated Raman scattering (SRS). In this dissertation, the several very important modulation formats such as Non Return to Zero (NRZ), Return to Zero (RZ), Chirped Return to Zero (CRZ), Carrier Suppressed Return to Zero (CSRZ), Differential Phase Shift Keying (PSK) and Carrier Suppressed Return to Zero- Differential Phase Shift Keying (CSRZ-DPSK) will be detailed and compared. In order to make performance analysis of such modulation formats, the simulation will be done by using VPItransmissionMakerTM WDM software.

A single-mode fused biconical 2¡Ñ2 coupler for polarization beamsplitting is fabricated in this thesis. We use simple fused and tapered method to fabricate the polarization beamsplitter(PBS) stably, and then we can get polarization maintaining in the output fibers. Without changing the manufacturing process, we design the device with special combination of fabrication parameters. We have achieved an extinction ratio of 25.78dB at the throughput port and 27.16dB at the coupled port. A usable spectral window as broad as 37nm and 27nm with an extinction ratio larger than 15dB for both ports is obtained. The excess loss is about 0.3dB. Based on a full-wave numerical approach, the performance of the PBS can be well modeled. We get good agreement between the measured and simulated results.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 77-79). Also available in electronic version. Access restricted to campus users.

Στην συγκεκριμένη εργασία παρουσιάζεται ένα μοντέλο προσομοίωσης των Πολυμερών Οπτικών Ινών και συγκεκριμένα των GI-POF ικανό να υπολογίζει την κρουστική απόκριση και τη διασπορά των συγκεκριμένων ινών. Επίσης ακολουθούν προσομοιώσεις 2 απλών συστημάτων μετάδοσης μέσω POF με λέιζερ και φωτοδιόδους χιονοστοιβάδας και ένα πλήρες προσομοιωμένο σύστημα μετάδοσης 2 καναλιών με πολυπλεξία μήκους κύματος μέσω των POF. Σχολιάζονται τα αποτελέσματα και η δυνατότητα χρήσης των ινών στη δομή του δίκτυου Μετάδοσης Κινητής Τηλεφωνίας. Επίσης αναλύονται όλα τα πιθανά πρωτόκολλα για τοπικά οπτικά δίκτυα και όλες οι πληροφορίες για τις POF, τους κατάλληλους πομπούς και δέκτες που μπορούν να χρησιμοποιηθούν σε μελλοντικές εφαρμογές. / In the specific project it is presented a simulation model of Polymer Optical Fibers and especially of GI-POF capable of calculating the impulse response and the dispersion of the specific fibers. Also next, simulations were realised of 2 simple transmission systems via POF with laser and avalange photodiodes, and a complete simulated transmission system with 2 channels with Wavelegth Division Multiplexing via POF. Results are being discussed as also the possibility of POF use in structure of Transmission Network of Cellular Telephony. In addition, all available protocols for local optical networks are described and all necessary information about POF, suitable transmitters and receivers that can be used in future applications.

Coarse Wavelength Division Multiplexing (CWDM) is becoming a popular way to increase the optical throughput of fibers for short to medium haul networks at a reduced cost. The International Telecommunications Union (ITU) has defned the CWDM network to consist of eighteen channels with channel spacings of 20 nm starting at 1270 nm and ending at 1610 nm.Four and eight channel AWGs on InP, suitable for CWDM, were fabricated using a novel and versatile S-shape design. The standard horseshoe layout will not work on semiconductor for AWGs with a free spectral range (FSR) larger than 30 nm. The AWG design provides operation insensitive to thermal and polarization fluctuations, which is key for low cost operation and packaging. It will be shown thatrefractive index changes over the large operating wavelength band produced negligible effects in the transmission spectrum.Standard AWG design assumes refractive index is a constant over the operating wavelength band. As a result, the output waveguide separations are held constant on the second star coupler. As the channel number increases, secondary focal dispersion causedfrom a changing refractive index can have detrimental effects on performance. A new design method will be introduced which includes refractive index dispersion by allowing the output waveguide separations to vary. The new design is consistent with standard design but is applicable in materials with a linear index dispersion over an arbitrarily large wavelength band.Lastly, a method for increasing the transmission using multimode waveguides is discussed. Traditionally, single mode waveguides are required in order to prevent higher order waveguide modes creating ghost images in the output spectrum. Using bend loss and waveguide junction offsets, higher order modes can be filtered from the output,thereby eliminating ghost images and at the same time, increase transmission.

No description available.

The monitoring and study of the earth�s atmosphere is becoming an increasingly important task given the current uncertainties in climate prediction. Areas where lidar has been used to further understanding of the atmosphere include monitoring of greenhouse gases, global warming, stratospheric ozone depletion, photochemical smog and aerosol photochemistry. However, the potentially severe long term effects of anthropogenic aerosols on earth�s biosphere are poorly understood. This project seeks to apply state of the art laser technology to develop an innovative multiwavelength lidar system capable of providing new information and new insights into the field of tropospheric aerosol lidar. Several novel tunable laser and laser-like sources have been investigated and developed for the purpose of tropospheric aerosol lidar at The National Institute of Water and Atmospheric Research (Niwa), Central Otago. Multiwavelength operation in the visible and near infrared portion of the spectrum has been emphasised with the sources developed collectively spanning the wavelength interval of 400-1369 nm. The laser sources investigated were the LiF:F2+ colour centre, Titanium Sapphire (Ti:sapphire) and barium nitrate Raman lasers. In addition to the laser sources, the β-barium borate optical parametric oscillator (BBO OPO) was characterised. For each of the sources, lidar relevant aspects were studied. The results recorded include conversion efficiency with respect to the pump source, linewidth and tuning characteristics, beam quality, temporal behaviour, and device reliability and ruggedness. It was found that the LiF:F2+ laser offered significantly lower threshold, broader tuning and higher output pulse energies than the Ti:sapphire laser in the 900-1000 nm region. The high optical gain of the LiF:F2+ medium facilitated cavity optical alignment and operation of the system. The high gain also resulted in temporal behaviour well suited to the existing Niwa lidar detection scheme. When using a 5 ns pump source, amplified spontaneous emission (ASE) was found to limit the laser tuning range and efficiency. The barium nitrate Raman laser was based on a simple linear cavity arrangement which resulted in a compact and robust device with no moving components. The stimulated Raman scattering process offers relatively narrow linewidth laser operation at the first and second Stokes wavelengths of 1197 nm and 1369 nm respectively. This laser offered efficient operation once the high operation threshold was reached. Second harmonic generation was used to extend the number of potential lidar transmitter lines produced. The barium nitrate Raman laser possessed high beam divergence and a maximum of three discrete transmitter wavelengths. The BBO OPO used a type I collinear signal resonant configuration. A plane-plane cavity configuration with pump reflection was found to provide simplicity of design, low threshold, highly efficient operation and output pointing stability. The BBO OPO signal wavelength could be tuned over the wavelength interval of 400-700 nm. The disadvantage of the plane cavity was high output beam divergence. However, this was successfully brought within the required limits through the use of a 40 mm long cavity in conjunction with an expanding and collimating telescope. As a result of the study, a Tunable lidar Transmitter (TLT) system based on the BBO OPO was designed and constructed at the Physics Department. The TLT was computer-controlled using custom written software and constructed in a self contained modular manner with all required mechanical, electrical and optical components. A user manual was also written to accompany the TLT. The TLT was installed at Niwa and was successfully used to gather preliminary multiwavelength lidar data. The TLT BBO OPO threshold occurred for a pump energy of 5.2 mJ (10.6 MW/cm2) and had a maximum slope efficiency of 53%. Signal efficiency varied from 24-41-35% over the intervals of 410-500-600 nm. A maximum signal energy of 21 mJ was obtained for a signal wavelength of 492 nm when using the maximum available pump energy of 42 mJ. OPO signal linewidth varied from 0.1-1-8 nm over the signal wavelength intervals of 400-600-700 nm. The associated OPO finesse varied between 370 and 100 as the signal wavelength was tuned over the wavelength interval of 400-600 nm. The temporal behaviour of the BBO OPO was a slowly varying function of pump energy and closely followed the temporal behaviour of the pump laser, making it well suited to the existing Italian lidar detection and timing scheme.