Both gain transient and dynamic gain control devices were also designed and fabricated as photonic integrated circuits (PICs). Silicon-based PICs were able to perform dynamic gain tilt compensation by thermo-optic effect. Helium doped SOI rib waveguides were used for power monitoring and is potentially used as monolithic gain tilt compensation device with arrayed waveguide grating (AWG). / Dynamic gain tilt induced by wavelength dependent gain of EDFA leads to power penalty in wavelength division multiplexed systems. Using optical filter with known spectral response, it is possible to detect dynamic gain tilt and a per-band compensation scheme using electronic variable optical attenuators. This was implemented for dynamic gain tilt compensation (DGTC). / Dynamic provisioning of bandwidth and re-configurable optical networks can potentially allow efficient and cost effective deliveries of services based on the actual bandwidth requirement. Optical add/drop multiplexers (OADM) and optical cross-connects (OXC) will be used for such networks but the dynamic provisioning of optical channels may introduce optical power transients because of the slow gain dynamics of erbium doped fiber amplifiers. In this dissertation, the potential problems on using Erbium Doped Fiber Amplifiers (EDFA) in future reconfigurable optical networks are studied and possible solutions are assessed. In particular, the problems of gain transient and dynamic gain tilt were studied experimentally and theoretically. / In saturated EDFA channel add/drop can produce average power fluctuations, in timescales in the microsecond range. The thesis describes how gain transients can be minimized in gain clamped EDFA by optimizing erbium concentrations of EDF. Both simulations and experiments demonstrate that highly doped EDF minimize the transient in gain clamped EDFA. For unclamped EDFA, all-optical feedforward constant output power compensation has been successfully demonstrated using electronic variable optical attenuator (EVOA). / Chan Po Shan. / "August 2006." / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1813. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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Rather than measuring aberrations at several locations across the field to quantify the alignment of an optical system, we show how a simple measurement of the pupil mapping can be used to measure the off-axis performance of the system. This method uses the Abbe sine condition to relate the mapping between the entrance and the exit pupils, where the violations of the generalized sine condition are used to determine the pupil mapping error. From this pupil mapping, the linearly field-dependent aberrations can be calculated. One of the advantages to this method is that all of the test equipment can be aligned to the center of the field while making measurements of the off-axis performance, which reduces the uncertainty of the measurement. This advantage is particularly evident with systems or sub-systems that have large inherent aberrations where off-axis alignment tolerances are very tight. Additionally, in the Sine Condition Test (SCTest), the test equipment can be designed to compensate for the native Siedel coma in the system. This makes it more straightforward to measure the linearly field dependence of the aberrations. By reducing or removing coma, the measurement uncertainty is further reduced. This work begins by explaining the background of the Abbe sine condition, derivation of the pupil mapping error, and an overview of linearly field-dependent astigmatism that arises from misalignment. Next, the general method of implementation is discussed, and expanded further by exploring the two different source options: a point source with a grating or a flat-panel display. Experimental results from proof of concept systems are shown for both cases. Next, this dissertation explains how the SCTest can be implemented on more complex systems. Last, this dissertation shows how the linear aberrations, along with constant field-dependent aberrations, can be used to align a system. Here, the application of the alignment version of the SCTest on a three mirror anastigmat (TMA) is discussed. Using simulation, this dissertation then investigates the behavior of the alignment SCTest for various levels of mirror misalignment, mirror fabrication errors, and misalignment of the test equipment. All of these tests show that the alignment SCTest can successfully align an optical system.

M.Ing. / This thesis is about the gain equalization of erbium doped fibre amplifiers (EDFA), which is a key technology for enabling wavelength-division multiplexed (WDM) optical communication systems. In order to flatten dynamically the EDFA gain spectrum, a tuneable long-period grating filter was demonstrated. Long-period gratings were fabricated by using a KrF excimer laser combined with the metal amplitude mask technique. The transmission spectrum characteristic of the long- period grating was simulated theoretically by the coupled-mode theory. The coupling between the core and cladding modes of the long-period grating was investigated both experimentally and theoretically. The EDFA was constructed by using the forward pumping configuration consisting of pump laser source, WDM couplers, an optical isolator, and the erbium-doped fibre. The EDFA was characterized theoretically and experimentally for WDM applications. The tuneable long-period grating filter design is based on the tuneable coupler that uses the Mach-Zehnder interferometer configuration. The tuneable filter was demonstrated by equalizing the EDFA gain spectrum and the amplified spontaneous emission (ASE) source. The main advantage of this filter compared to other optical filters is its tuneability of the attenuation over a wide range of pump power.

M.Ing. / Long distance optical communication systems experience a large degree of attenuation due to fibre losses, necessitating signal amplification. Erbium Doped Fibre Amplifiers (EDFAs) have found widespread use as all-fibre optical amplifiers, but exhibit unequal amplification of different wavelengths. Since the gain spectrum is signal-power and pump-power dependent, each EDFA spectrum may differ considerably, and a tuneable gain equalizer is required. A tuneable long-period grating (LPG) can be implemented as a gain equalizer for EDFAs. This dissertation deals with the design of an integrated optic version of the tuneable equalizing filter. The various components of which the device comprises, including optical couplers, Mach-Zehnder interferometers and an LPG, are investigated. The integrated optics designs of these components are then done using the BeamPROP software package. The use and optical properties of germania-doped silica as photosensitive waveguide material is studied. The production of the films for the gain equalizer, using electron-cyclotron resonance plasma-enhanced chemical vapour deposition, is discussed. Characterization of these films was carried out using spectroscopic ellipsometry and infrared spectroscopy. The optical constants, thickness, germania content and hydroxyl absorption was calculated using these measurements.

M.Ing. (Electrical And Electronic Engineering) / Please refer to full text to view abstract

This thesis examines the performance of a custom built deep UV laser (257.5nm) for Raman spectroscopy and the advantages of Raman spectroscopy with a laser in the deep UV over a laser in the visible range (532 nm). It describes the theory of resonance Raman scattering, the experimental setup for Raman spectroscopy and a few Raman spectroscopy measurements. The measurements were performed on biological samples oak tree leaf and lactobacillus acidophilus and bifidobacteria from probotioc medicinal capsules. Fluorescence free Raman spectra were acquired for the two samples with 257.5 nm laser. The Raman spectra for the two samples with a 532nm laser was masked with fluorescence. Raman measurements for an inorganic salt sodium nitrate showed a resonance Raman effect with 257.5 nm laser which led to enhancement in the Raman intensity as compared to that with 532 nm laser. Therefore we were able to demonstrate two advantages of deep UV Raman spectroscopy. First one is the possibility of acquiring fluorescence free spectra for biological samples. Second is the possibility of gaining enhancement in Raman intensity due to resonance Raman effect. It was observed that 257.5 nm laser requires optimization to reduce the bandwidth of the laser to get better resolution. The 257.5 nm laser also needs to be optimized to obtain higher power to get better signal to noise ratio. The experimental setup can also be further improved to obtain better resolution. If the improvements required in the setup are implemented, the deep UV Raman setup will become an important tool for spectroscopy.

Fiber optic networks are no longer just pipelines for transporting data in the long haul backbone. Exponential growth in traffic in metro-regional areas has pushed higher capacity fiber toward the edge of the network, and highly dynamic patterns of heterogeneous traffic have emerged that are often bursty, severely stressing the historical "fat and dumb pipe" static optical network, which would need to be massively over-provisioned to deal with these loads. What is required is a more intelligent network with a span of control over the optical as well as electrical transport mechanisms which enables handling of service requests in a fast and efficient way that guarantees quality of service (QoS) while optimizing capacity efficiency. An "agile" optical network is a reconfigurable optical network comprised of high speed intelligent control system fed by real-time in situ network sensing. It provides fast response in the control and switching of optical signals in response to changing traffic demands and network conditions. This agile control of optical signals is enabled by pushing switching decisions downward in the network stack to the physical layer. Implementing such agility is challenging due to the response dynamics and interactions of signals in the physical layer. Control schemes must deal with issues such as dynamic power equalization, EDFA transients and cascaded noise effects, impairments due to self-phase modulation and dispersion, and channel-to-channel cross talk. If these issues are not properly predicted and mitigated, attempts at dynamic control can drive the optical network into an unstable state. In order to enable high speed actuation of signal modulators and switches, the network controller must be able to make decisions based on predictive models. In this thesis, we consider how to take advantage of Software Defined Networking (SDN) capabilities for network reconfiguration, combined with embedded models that access updates from deployed network monitoring sensors. In order to maintain signal quality while optimizing network resources, we find that it is essential to model and update estimates of the physical link impairments in real-time. In this thesis, we consider the key elements required to enable an agile optical network, with contributions as follows: *Control Framework: extended the SDN concept to include the optical transport network through extensions to the OpenFlow (OF) protocol. A unified SDN control plane is built to facilitate control and management capability across the electrical/packet-switched and optical/circuit-switched portions of the network seamlessly. The SDN control plane serves as a platform to abstract the resources of multilayer/multivendor networks. Through this platform, applications can dynamically request the network resources to meet their service requirements. *Use of In-situ Monitors: enabled real-time physical impairment sensing in the control plane using in-situ Optical Performance Monitoring (OPM) and bit error rate (BER) analyzers. OPM and BER values are used as quantitative indicators of the link status and are fed to the control plane through a high-speed data collection interface to form a closed-loop feedback system to enable adaptive resource allocation. *Predictive Network Model: used a network model embedded in the control layer to study the link status. The estimated results of network status is fed into the control decisions to precompute the network resources. The performance of the network model can be enhanced by the sensing results. *Real-Time Control Algorithms: investigated various dynamic resource allocation mechanisms supporting an agile optical network. Intelligent routing and wavelength switching for recovering from traffic impairments is achieved experimentally in the agile optical network within one second. A distance-adaptive spectrum allocation scheme to address transmission impairments caused by cascaded Wavelength Selective Switches (WSS) is proposed and evaluated for improving network spectral efficiency.

This dissertation explores frequency comb spectroscopy and, in particular, its extension to the vacuum-ultraviolet (VUV) and extreme-ultraviolet (XUV) wavelength regimes through a technique called intracavity high harmonic generation (IHHG). By combining the techniques of passive pulse amplification in an enhancement cavity with high harmonic generation, IHHG enables the direct conversion of near-infrared radiation to the VUV/XUV while still maintaining the underlying comb structure .As part of this work, a series of numerical simulations was performed to investigate the plasma that is formed in the IHHG process and its implications for the resulting VUV comb. It was demonstrated that a fundamental limitation to the performance of IHHG experiments is due to the single-pass ionization phase shift acquired by the pulse circulating in the enhancement cavity. Furthermore, we showed that a static background plasma accumulates between pulses and complicates cavity stabilization. Insights gained from the simulations led to the development of a novel pump-probe technique using the enhancement cavity that allowed a direct measurement of the intracavity plasma and its decay dynamics in real-time. Because the plasma lifetime plays such a crucial role in the operation of these cavities, it was important to have a method to test ways of reducing it. To build on our initial IHHG results showing record-level powers in the XUV, we implemented a fully phase-coherent dual comb spectrometer consisting of two identical IHHG systems operating in parallel. The system is designed for precision spectroscopy in the VUV and is based on a pair of homemade ytterbium fiber lasers that use a parabolic amplification scheme to achieve 80 fs pulses after amplification to 50 W of average power. Initial dual comb data showing system performance at the fundamental frequency and third harmonic are presented.