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This thesis presents an investigation of the lasing dynamics and optical amplification devices using conjugated polymers. Spectroscopic studies of conjugated polymers and dendrimers were also performed. Conjugated polymers and dendrimers are materials with great potential as display materials and tuneable lasers due to their broad spectra and high optical gains. The effect of conjugation is studied in MEH-PPV and an anisotropy measurement of two different cored dendrimers has been shown to verify a theoretical prediction on their depolarisation. Singlet emission from a highly efficient phosphorescent dendrimer is also observed and is the first known report of fluorescence from this class of dendrimers. Conjugated polymers exhibit optical gain over broad spectral ranges, which has led to much interest in their potential as novel laser gain media. Investigations into lasing from conjugated polymers has been confined mainly to studying the lasing properties and not the temporal dynamics of the laser pulses. In this work an investigation into the lasing dynamics of a 2D-DFB conjugated polymer laser is demonstrated with the first subpicosecond laser pulses observed for a polymer laser. A novel encapsulated laser fabricated via a soft lithography route was also studied and exhibited laser pulse of 6 ps duration. The high gain observed over broad spectral ranges also means that these materials are suitable for use as optical amplifiers. Broadband gain in a conjugated polymer solution was demonstrated with a gain of 30 dB accessible across a 60 nm wavelength range. In the solid state the limited thickness of films (~ 100 nm) and the uneven nature of the film edges had limited the ability to study the amplification of a probe signal. The first practical solid state conjugated polymer amplifier has been demonstrated. The device uses grating structures to couple a probe signal into and out of the gain region. The gain dynamics of different length amplifiers were studied and an 18 dB gain was observed in a 300 µm device length using a conjugated polymer blend of RedF and F8BT. Further work on a conjugated polymer MEH-PPV led to a 21dB gain in a 1 mm device.

A dual-wavelength mode-locked semiconductor vertical-external-cavity-surface-emitting laser is demonstrated. A semiconductor saturable absorber mirror allows for simultaneous mode locking of pulses centered at two center wavelengths with variable frequency spacing. The difference-frequency control is achieved with an intracavity etalon. Changing the finesse of the etalon enables the adjustment of the pulse duration between 6 and 35 ps. The emitted two-color pulses are modulated by a beat frequency in the terahertz range. Self-starting mode-locking with 0.8-W average output power is demonstrated.

Q-switched operation of a holmium-doped fluoride fiber laser at 1.2 mu m wavelength induced by a semiconductor saturable absorber mirror (SESAM) is reported. 650 ns pulses with 0.13 mu J pulse energy at a repetition rate of 260 kHz were obtained.

by Hung Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 69-[73]). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- All Optical Multi-Access Network --- p.1 / Chapter 1.2 --- Multi-access Techniques --- p.2 / Chapter 1.2.1 --- Wavelength-Division Multi-access (WDMA) --- p.2 / Chapter 1.2.2 --- Subcarrier Multi-Access (SCMA) --- p.3 / Chapter 1.2.3 --- Time-Division Multi-Access(TDMA) --- p.3 / Chapter 1.3 --- Numerical Modelling of Semiconductor Mode-locked laser --- p.4 / Chapter 1.4 --- Objective of this Thesis --- p.5 / Chapter 2 --- Optical TDMA networks --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- OTDM --- p.8 / Chapter 2.3 --- Network Architecture --- p.9 / Chapter 2.3.1 --- Broadcast Networks --- p.9 / Chapter 2.3.2 --- Switch-based networks --- p.10 / Chapter 2.4 --- Key technologies for optical TDMA Network --- p.13 / Chapter 2.4.1 --- High Repetition Rate Short Pulse sources --- p.13 / Chapter 2.4.2 --- Multiplexer and de-multiplexers --- p.15 / Chapter 2.4.3 --- Optical Clock Recovery --- p.17 / Chapter 2.4.4 --- All optical logic gates --- p.18 / Chapter 2.5 --- Summary --- p.19 / Chapter 3 --- A Channel-Tunable Mode-locked Laser Transmitter for OTDM Networks --- p.20 / Chapter 3.1 --- Introduction --- p.20 / Chapter 3.2 --- Principle of Operation --- p.21 / Chapter 3.3 --- Experimental Demonstration --- p.23 / Chapter 3.4 --- The Channel Tuning Transient --- p.25 / Chapter 3.5 --- Experimental Investigation of channel-tuning transient --- p.28 / Chapter 3.6 --- Summary --- p.37 / Chapter 4 --- Modeling of Mode-Locked Semiconductor Laser --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Principle of Mode-Locking --- p.39 / Chapter 4.3 --- Simulation Model --- p.41 / Chapter 4.3.1 --- Travelling Wave Rate Equation Analysis --- p.41 / Chapter 4.3.2 --- Large Signal Time Domain Mode-locked Laser Model --- p.42 / Chapter 4.3.3 --- Modeling of Spontaneous Noise --- p.44 / Chapter 4.3.4 --- Modeling of Self-phase Modulation --- p.44 / Chapter 4.3.5 --- Frequency Dependent Gain Profile --- p.45 / Chapter 4.3.6 --- Computation Procedure --- p.45 / Chapter 4.4 --- Device Parameters --- p.47 / Chapter 4.5 --- Simulation Results on Passive Mode-locking --- p.48 / Chapter 4.5.1 --- Pulse Repetition Rate under Passive Mode-locking --- p.48 / Chapter 4.5.2 --- The effect of Differential Gain and Differential Absorption on Mode-locking Regimes --- p.50 / Chapter 4.5.3 --- The Effects of Linewidth Enhancement Factor and Ab- sorber Carrier Lifetime on Mode-locking Pulse Width --- p.53 / Chapter 4.6 --- Simulation Results on Hybrid and Subharmonic Mode-locking --- p.54 / Chapter 4.6.1 --- Modeling the Effect of Modulation on Absorber Section --- p.54 / Chapter 4.6.2 --- Modulation Phase Change Dynamics --- p.55 / Chapter 4.6.3 --- Subharmonc Mode-Locking Induced Amplitude Modulation --- p.62 / Chapter 4.7 --- Summary --- p.64 / Chapter 5 --- Conclusion --- p.66 / Chapter 5.1 --- Summary of the Thesis --- p.66 / Chapter 5.2 --- Future Work --- p.67 / Bibliography --- p.69

by Chow Kin Kee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgment --- p.v / Table of Contents --- p.vi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Ultra-short Pulse Generation in Semiconductor Lasers --- p.2 / Chapter 1.2 --- Wavelength Selection and Switching in Short Pulses Generated from Semiconductor Laser --- p.4 / Chapter 1.3 --- Structure of the Thesis --- p.6 / Reference --- p.8 / Chapter 2. --- Principles and Theories --- p.10 / Chapter 2.1 --- Principle of Wavelength Switching in Self-Seeded Laser --- p.11 / Chapter 2.2 --- Principle of Synchronous Injection Seeding of two Lasers --- p.15 / Chapter 2.3 --- Principle of Fast Spectral Improvement in DFB Laser with Optical Feedback --- p.17 / Chapter 2.4 --- Principle of Spectrally Resolved Analysis --- p.19 / Reference --- p.24 / Chapter 3. --- Switching Dynamics between Single-Mode and Dual-Mode Pulse Emissions from a Self-Seeded Laser Diode --- p.25 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Experimental Details and Discussion --- p.28 / Chapter 3.3 --- Summary --- p.37 / Reference --- p.38 / Chapter 4. --- Spectrally Resolved Analysis of Fast Tuning in Single-Mode Pulses Generated from Mutually Injection-Seeded Fabry- Perot Laser Diodes --- p.40 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental Details and Discussion --- p.42 / Chapter 4.3 --- Summary --- p.51 / Reference --- p.52 / Chapter 5. --- Fast Spectral Improvement in Gain-Switched Pulses Generated from a Distributed Feedback Laser with Weak Optical Feedback --- p.54 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Experimental Details and Discussion --- p.57 / Chapter 5.3 --- Summary --- p.65 / Reference --- p.66 / Chapter 6. --- Conclusion and Future Work --- p.67 / Chapter 6.1 --- Conclusion --- p.67 / Chapter 6.2 --- Future Works --- p.69 / Reference --- p.71 / Appendices --- p.A-l / Appendix A. List of Publications --- p.A-l / Appendix B. Modeling of Self-Seeded Fabry-Perot Laser --- p.A-2 / Appendix C. List of Figures --- p.A-4

This thesis presents studies of organic semiconductor lasers, including their operation when pumped by a light-emitting diode (LED), and their application as explosive sensors. The photophysics and amplified spontaneous emission (ASE) of star-shaped oligofluorene truxene molecules were investigated. These materials exhibit high gain and low optical loss in thin-film waveguides. Low ASE thresholds were achieved with the truxene T3 and T4. Second-order distributed feedback (DFB) lasers were fabricated, with pump threshold intensities below 0.5 kW/cm² and broad tunability of the emission. DFB lasers were demonstrated with a novel polymer BBEHP-PPV, pumped by a pulsed commercial InGaN LED. The laser emission occurred at 533 nm for peak drive current above 15 A. The output beams and pulse-dynamics of the lasers were investigated for the first time, along with a 'double-threshold' phenomenon that was observed in this long-pulse pumping regime. BBEHP-PPV lasers based on various types of diffractive resonators were also fabricated by UV nanoimprint-lithography (NIL). By optimising the resonator design and the fabrication, and the pump-beam geometry, polymer laser thresholds of ~60 W/cm², the lowest recorded for NIL lasers, were demonstrated, enabling them to be pumped by pulsed commercial LEDs and custom micro-LED arrays. One promising application of organic lasers is in explosive sensing. A polymer of intrinsic microporosity (PIM-1) was used to detect nitroaromatic vapours. Rapid detection of dinitrobenzene (DNB) of low vapour pressure was achieved by monitoring the photoluminescence and laser emission during exposure. In addition, a CMOS time-resolved fluorescence lifetime microsystem with a commercial green-emitting copolymer was used as a novel, portable sensor to detect DNB vapour. An InGaN LED pumped BBEHP-PPV laser was also used as a miniature sensor to detect 10 ppb of DNB. These highly sensitive hybrid sensors could be used in humanitarian demining, complementing existing technologies leading to improvement in the detection of hazardous objects.

Tang Wing-Wa. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Table of contents --- p.v / List of figure --- p.viii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- Introduction to ultrashort optical pulse generation --- p.2 / Chapter 1.2. --- Introduction to wavelength-tunable pulse generation --- p.5 / Chapter 1.3. --- Introduction to chapters --- p.7 / Chapter 2. --- Principles and Theories --- p.11 / Chapter 2.1. --- Principle of dispersion tuning --- p.12 / Chapter 2.2. --- SOA nonlinear optical loop mirror --- p.16 / Chapter 2.3. --- Principle of dispersion tuning in harmonically mode-locked fiber laser using nonlinear optical loop mirror --- p.19 / Chapter 2.4. --- Principle of re-configurable multi-wavelength pulses generationin a self-seeded laser diode incorporating SOA loop mirror --- p.22 / Chapter 3. --- Rational harmonic mode-locking of an optically triggered fiber laser incorporating a non-linear optical loop modulator --- p.25 / Chapter 3.1. --- Introduction --- p.26 / Chapter 3.2. --- Experiment --- p.27 / Chapter 3.3. --- Result and discussion --- p.30 / Chapter 3.4. --- Summary --- p.37 / Chapter 4. --- Generation of amplitude-equalized optical pulses from a rational harmonic mode-locked fiber laser incorporating a SOA loop modulator --- p.40 / Chapter 4.1. --- Introduction --- p.41 / Chapter 4.2. --- Experiment --- p.42 / Chapter 4.3. --- Result and discussion --- p.44 / Chapter 4.4. --- Summary --- p.47 / Chapter 5. --- Optically controlled dispersion-tuning in harmonically mode-locked erbium doped fiber laser using SOA nonlinear loop modulator --- p.49 / Chapter 5.1. --- Introduction --- p.50 / Chapter 5.2. --- Experiment --- p.51 / Chapter 5.3. --- Result and discussion --- p.54 / Chapter 5.4. --- Summary --- p.58 / Chapter 6. --- Alternate method of constructing harmonically mode-locked fiber laser incorporating SOA nonlinear loop modulator --- p.60 / Chapter 6.1. --- Introduction --- p.61 / Chapter 6.2. --- Experiment --- p.62 / Chapter 6.3. --- Result and discussion --- p.65 / Chapter 6.4. --- Summary --- p.69 / Chapter 7. --- Optically re-configurable multi-wavelength pulse source constructed from a self-seeded laser diode --- p.71 / Chapter 7.1. --- Introduction --- p.72 / Chapter 7.2. --- Experiment --- p.74 / Chapter 7.3. --- Result and discussion --- p.77 / Chapter 7.4. --- Summary --- p.82 / Chapter 8. --- Tunable alternating multi-wavelength pulse source constructed using non-linear optical control of wavelength switching in a self-seeded laser diode --- p.85 / Chapter 8.1. --- Introduction --- p.86 / Chapter 8.2. --- Experiment --- p.87 / Chapter 8.3. --- Result and discussion --- p.89 / Chapter 8.4. --- Summary --- p.92 / Chapter 9. --- Conclusion and future works --- p.94 / Chapter 9.1. --- Conclusion --- p.94 / Chapter 9.2. --- Possible future works --- p.98 / Appendix / List of publications --- p.A-1

Diode lasers have many advantages such as small size, high efficiency and small angular dispersion of the collimated beam. However they also have some problems like lack of frequency stability. They can not be tuned in wavelength. An external cavity can solve these problems and decrease the laser linewidth. To obtain a tunable, narrow linewidth light source, antireflection coatings were applied to commercial diode lasers which were then tested in an external cavity. Laser characteristics, such as threshold current, spectral behavior, I-V-curves, tuning range, and bandwidth were measured for the original diode laser and then compared to the measurements in an external cavity with and without antireflection (AR) coatings. The tuning range approximately doubled after AR coating. The modal stability was found to be better by a factor of 7 in the external cavity. The power amplification through the external cavity was as high as 50. It was also attempted to process laser diodes from material fabricated at OSU, however the resulting diodes showed a high series resistance and were not usable for this project. Additional work needs to be done in this area. The result of this work is a stable external cavity diode laser tunable over an 18 nm bandwidth which can be used as a tunable source in many applications. / Graduation date: 1995

It is estimated that, between the year 2000 and 2003, thenumber of online Internet users will grow from 250 millions to500 millions. This growth results in rapidly increasing demandfor fibre-optic communication bandwidth, occurring at alllevels: from access and local area networks (LANs) tometro-area networks (MANs). A now established solution for manyapplications such as interconnects and Gigabit Ethernet is thevertical cavity surface emitting laser (VCSEL). The advantagesof VCSELs are numerous: low fabrication and coupling costs,large modulation bandwidth, array integration and tunability.VCSEL-based modules, with speed up to 2.5 Gbit/s are nowcommercially available for multimode fibre (MMF) basedapplications. However, devices operating at long wavelength andhigher transmission rates (10Gbit/s and more) will be needed inthe near future. The purpose of the work presented in this thesis was toobtain an understanding of the high-speed properties of VCSELs,in order to extend the modulation frequency at which they canbe used in fibre optical communication systems. An approach forsystematic high-speed characterisation of VCSELs is presentedand both its potential benefits and problems are discussed. Itis shown that the VCSEL dynamics, under certain conditions, canbe well described by a small number of parameters that can beextracted from small signal measurements and used forfurtheroptimisation. The calibrated small-signal modulation responsesof VCSELs have been measured and fitted to an analyticaltransfer function allowing the estimation of the resonancefrequency, damping factor and parasitic cut-off at differentbias points. This data can be used to determine the relativeimportance of different bandwidth limiting effects due todamping, thermal heating and parasitics. Small signal analysis and transmission experiments wereperformed with a large sample of VCSELs covering the variousranges of applications. Visible VCSELs and resonant cavitylight emitting diodes (RCLEDs) for very short reach plasticoptical fibre (POF) applications, 850nm datacom VCSELs forshort distance multimode fibre networks, and long wavelengthVCSELs for long haul single mode fibre transmission. <b>Keywords:</b>Semiconductor lasers, VCSEL, high-speedmodulation, fibre optic networks, datacom, RCLED, plasticoptical fibre