Time resolved bit error rate analysis of a fast switching tunable laser for use in optically switched networks

We investigate the use of different direct detection modulation formats in a wavelength switched optical network. We find the minimum time it takes a tunable sampled grating distributed Bragg reflector laser to recover after switching from one wavelength channel to another for different modulation formats. The recovery time is investigated utilizing a field programmable gate array which operates as a time resolved bit error rate detector. The detector offers 93 ps resolution operating at 10.7 Gb/s and allows for all the data received to contribute to the measurement, allowing low bit error rates to be measured at high speed. The recovery times for 10.7 Gb/s non-return-to-zero on–off keyed modulation, 10.7 Gb/s differentially phase shift keyed signal and 21.4 Gb/s differentially quadrature phase shift keyed formats can be as low as 4 ns, 7 ns and 40 ns, respectively. The time resolved phase noise associated with laser settling is simultaneously measured for 21.4 Gb/s differentially quadrature phase shift keyed data and it shows that the phase noise coupled with frequency error is the primary limitation on transmitting immediately after a laser switching event.

Time resolved bit error rate analysis of a fast switching tunable laser for use in optically switched networks

We investigate the use of different direct detection modulation formats in a wavelength switched optical network. We find the minimum time it takes a tunable sampled grating distributed Bragg reflector laser to recover after switching from one wavelength channel to another for different modulation formats. The recovery time is investigated utilizing a field programmable gate array which operates as a time resolved bit error rate detector. The detector offers 93 ps resolution operating at 10.7 Gb/s and allows for all the data received to contribute to the measurement, allowing low bit error rates to be measured at high speed. The recovery times for 10.7 Gb/s non-return-to-zero on–off keyed modulation, 10.7 Gb/s differentially phase shift keyed signal and 21.4 Gb/s differentially quadrature phase shift keyed formats can be as low as 4 ns, 7 ns and 40 ns, respectively. The time resolved phase noise associated with laser settling is simultaneously measured for 21.4 Gb/s differentially quadrature phase shift keyed data and it shows that the phase noise coupled with frequency error is the primary limitation on transmitting immediately after a laser switching event.

Recent advances in fundamentals and applications of random fiber lasers

Random fiber lasers blend together attractive features of traditional random lasers, such as low cost and simplicity of fabrication, with high-performance characteristics of conventional fiber lasers, such as good directionality and high efficiency. Low coherence of random lasers is important for speckle-free imaging applications. The random fiber laser with distributed feedback proposed in 2010 led to a quickly developing class of light sources that utilize inherent optical fiber disorder in the form of the Rayleigh scattering and distributed Raman gain. The random fiber laser is an interesting and practically important example of a photonic device based on exploitation of optical medium disorder. We provide an overview of recent advances in this field, including high-power and high-efficiency generation, spectral and statistical properties of random fiber lasers, nonlinear kinetic theory of such systems, and emerging applications in telecommunications and distributed sensing.

Temporal and spatio-temporal regimes of generation of Raman fibre lasers

Temporal dynamics of Raman fibre lasers tend to have very complex nature, owing to great cavity lengths and high nonlinearity, being stochastic on short time scales and quasi-continuous on longer time scales. Generally fibre laser intensity dynamics is represented by one-dimensional time-series, which in case of quasi-continuous wave generation in Raman fibre lasers gives little insight into the processes underlying the operation of a laser. New methods of analysis and data representation could help to uncover the underlying physical processes, understand the dynamics or improve the performance of the system. Using intrinsic periodicity of laser radiation, one dimensional intensity time series of a Raman fibre laser was analysed over fast and slow variation time. This allowed to experimentally observe various spatio-temporal regimes of generation, such as laminar, turbulent, partial mode-lock, as well as transitions between them and identify the mechanisms responsible for the transitions. Great cavity length and high nonlinearity also make it difficult to achieve stable high repetition rate mode-locking in Raman fibre lasers. Using Faraday parametric instability in extremely simple linear cavity experimental configuration, a very high order harmonic mode-locking was achieved in ò.ò kmlong Raman fibre laser. The maximum achieved pulse repetition rate was 12 GHz, with 7.3 ps long Gaussian shaped pulses. There is a new type of random lasers – random distributed feedback Raman fibre laser, which temporal properties cannot be controlled by conventionalmode-locking or Q-switch techniques and mechanisms. By adjusting the pump configuration, a very stable pulsed operation of random distributed feedback Raman fibre laser was achieved. Pulse duration varied in the range from 50 to 200 μs depending on the pump power and the cavity length. Pulse repetition rate scaling on the parameters of the system was experimentally identified.

Design and Fabrication of Perovskite Micro-Cavity Lasers

Thesis (Master's)--University of Washington, 2016-08

Experimental demonstration of a record high 11.25Gb/s real-time optical OFDM transceiver supporting 25km SMF end-to-end transmission in simple IMDD systems.

The fastest ever 11.25Gb/s real-time FPGA-based optical orthogonal frequency division multiplexing (OOFDM) transceivers utilizing 64-QAM encoding/decoding and significantly improved variable power loading are experimentally demonstrated, for the first time, incorporating advanced functionalities of on-line performance monitoring, live system parameter optimization and channel estimation. Real-time end-to-end transmission of an 11.25Gb/s 64-QAM-encoded OOFDM signal with a high electrical spectral efficiency of 5.625bit/s/Hz over 25km of standard and MetroCor single-mode fibres is successfully achieved with respective power penalties of 0.3dB and -0.2dB at a BER of 1.0 x 10(-3) in a directly modulated DFB laser-based intensity modulation and direct detection system without in-line optical amplification and chromatic dispersion compensation. The impacts of variable power loading as well as electrical and optical components on the transmission performance of the demonstrated transceivers are experimentally explored in detail. In addition, numerical simulations also show that variable power loading is an extremely effective means of escalating system performance to its maximum potential.

Significant improvements in optical power budgets of real-time optical OFDM PON systems.

Based on a comprehensive theoretical optical orthogonal frequency division multiplexing (OOFDM) system model rigorously verified by comparing numerical results with end-to-end real-time experimental measurements at 11.25Gb/s, detailed explorations are undertaken, for the first time, of the impacts of various physical factors on the OOFDM system performance over directly modulated DFB laser (DML)-based, intensity modulation and direct detection (IMDD), single-mode fibre (SMF) systems without in-line optical amplification and chromatic dispersion compensation. It is shown that the low extinction ratio (ER) of the DML modulated OOFDM signal is the predominant factor limiting the maximum achievable optical power budget, and the subcarrier intermixing effect associated with square-law photon detection in the receiver reduces the optical power budget by at least 1dB. Results also indicate that, immediately after the DML in the transmitter, the insertion of a 0.02nm bandwidth optical Gaussian bandpass filter with a 0.01nm wavelength offset with respect to the optical carrier wavelength can enhance the OOFDM signal ER by approximately 1.24dB, thus resulting in a 7dB optical power budget improvement at a total channel BER of 1 × 10(-3).

IMPROVED PEAK POWER METHOD FOR MEASURING FREQUENCY RESPONSES OF PHOTODETECTORS IN A SELF-HETERODYNE SYSTEM

An improved peak power method for measuring frequency responses of photodetectors in a self-heterodyne system consisting of a distributed Bragg reflector laser is proposed. The time-resolved spectrum technique is used to measure the peak power of the beat signal and the intrinsic linewidth of heat signal for calibration. The experimental results show that the impact of the thermal-induced frequency drift, which is the main reason for producing an error in measurement by conventional peak power method and spectrum power method, can be removed.

High-quality multiple quantum wells selectively grown on taper-patterned substrates by ultra-low-pressure MOCVD

High quality InGaAsP/InGaAsP multiple quantum wells ( MQWs) have been selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition. A large bandgap energy shift of 46 nm and photoluminescence with FWHM less than 30 meV were obtained with a rather small mask width variation (15-30 mu m). In order to study the uniformity of the MQWs grown in the selective area, novel tapered masks were employed, and the transition effect W the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated at larger ratios of the mask width to the tapered region length.

High-quality multiple quantum wells selectively grown with tapered masks by ultra-low-pressure MOCVD

An InGaAsP/InGaAsP multiple quantum wells (MQWs) selectively grown by ultra-low-pressure (22 mbar) metal-organic chemical vapor deposition was investigated in this article. A 46 nm photoluminescence peak wavelength shift was obtained with a small mask width variation (15-30 mu m). High-quality crystal layers with a photoluminescence (PL) ftill-width-at-half-maximum (FWHM) of less than 30 meV were achieved. Using novel tapered masks, the transition-effect of the tapered region was also studied. The energy detuning of the tapered region was observed to be saturated with the larger ratio of the mask width divided to the tapered region length. (C) 2005 Elsevier B.V. All rights reserved.

Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining (PM) fiber Mach-Zehnder (MZ) interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer,all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here, we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Tunable MQW-DBR lasers using selective area growth

The tunable ridge waveguide distributed Bragg reflector (DBR) lasers designed for wavelength-division-multiplex (WDM) communication systems at 1.55 um by using selective area growth (SAG) is reported. The threshold current of the DBR laser is 62mA and the output power is more than 8mW. The isolation resistance between the active region and the Bragg region is 30K Ohm. The total tuning range is 6.5nm and this DBR laser can provide 6 continuous standard WDM channels with 100GHz channel spacing; in the tuning range, the single mode suppression ratio (SMSR) is maintained more than 32dB and the maximum output power variation is less than 3dB.

An Adaptive Policy Management Approach to BGP Convergence

The Border Gateway Protocol (BGP) is the current inter-domain routing protocol used to exchange reachability information between Autonomous Systems (ASes) in the Internet. BGP supports policy-based routing which allows each AS to independently adopt a set of local policies that specify which routes it accepts and advertises from/to other networks, as well as which route it prefers when more than one route becomes available. However, independently chosen local policies may cause global conflicts, which result in protocol divergence. In this paper, we propose a new algorithm, called Adaptive Policy Management Scheme (APMS), to resolve policy conflicts in a distributed manner. Akin to distributed feedback control systems, each AS independently classifies the state of the network as either conflict-free or potentially-conflicting by observing its local history only (namely, route flaps). Based on the degree of measured conflicts (policy conflict-avoidance vs. -control mode), each AS dynamically adjusts its own path preferences—increasing its preference for observably stable paths over flapping paths. APMS also includes a mechanism to distinguish route flaps due to topology changes, so as not to confuse them with those due to policy conflicts. A correctness and convergence analysis of APMS based on the substability property of chosen paths is presented. Implementation in the SSF network simulator is performed, and simulation results for different performance metrics are presented. The metrics capture the dynamic performance (in terms of instantaneous throughput, delay, routing load, etc.) of APMS and other competing solutions, thus exposing the often neglected aspects of performance.

An Adaptive Management Approach to Resolving Policy Conflicts

The Border Gateway Protocol (BGP) is the current inter-domain routing protocol used to exchange reachability information between Autonomous Systems (ASes) in the Internet. BGP supports policy-based routing which allows each AS to independently define a set of local policies on which routes it accepts and advertises from/to other networks, as well as on which route it prefers when more than one route becomes available. However, independently chosen local policies may cause global conflicts, which result in protocol divergence. In this paper, we propose a new algorithm, called Adaptive Policy Management Scheme(APMS), to resolve policy conflicts in a distributed manner. Akin to distributed feedback control systems, each AS independently classifies the state of the network as either conflict-free or potentially conflicting by observing its local history only (namely, route flaps). Based on the degree of measured conflicts, each AS dynamically adjusts its own path preferences---increasing its preference for observably stable paths over flapping paths. APMS also includes a mechanism to distinguish route flaps due to topology changes, so as not to confuse them with those due to policy conflicts. A correctness and convergence analysis of APMS based on the sub-stability property of chosen paths is presented. Implementation in the SSF network simulator is performed, and simulation results for different performance metrics are presented. The metrics capture the dynamic performance (in terms of instantaneous throughput, delay, etc.) of APMS and other competing solutions, thus exposing the often neglected aspects of performance.

Fluoreszenz und Lasertätigkeit in dünnen amorphen Schichten von Spirobifluorenderivaten

Es wurden die optischen Eigenschaften einiger Spirooligophenylverbindungen untersucht. Bei den Verbindungen handelte es sich um lineare und verzweigte Derivate des Spirobifluorens. Es wurden dünne amorphe Schichten der Verbindungen mittels spincoating und Vakuumverdampfen (OMBD) auf unterschiedlichen Substraten hergestellt. Mit spektroskopischer Ellipsometrie konnten die Schichtdicken und optische Konstanten der dünnen Schichten bestimmt werden. Dafür sind die Extinktionsspektren mit Tauc-Lorentz-Oszillatoren modelliert worden. Auf diese Weise ließen sich die optischen Konstanten der amorphen Filme besser beschreiben als mit den üblicherweise verwendeten Gauß-Oszillatoren. In dünnen Filmen von Spirosexiphenyl konnte uniaxiale Anisotropie nachgewiesen werden. Im Bereich der pie,pie*-Bande beträgt das Verhältnis des ordentlichen zum außerordentlichen Extinktionskoeffizienten 2.09. Mit einer Integrationskugel wurden die absoluten Quantenausbeuten der Fluoreszenz in festen Filmen bestimmt. Dafür ist ein vereinfachtes Verfahren der Auswertung entwickelt worden. Im Vergleich der untersuchten Substanzen zeigt sich, dass die Verbindungen mit dem Sexiphenyl-Chromophor höhere Quantenausbeuten im Festkörper haben (31 % - 48 %) als die Verbindungen mit Quaterphenyl als Chromophor (15 % - 30 %). In den beiden Klassen haben jeweils die sterisch anspruchsvollen Octopusvarianten die höchsten Festkörperquantenausbeuten. Durch verdünnen mit m,m-Spirosexiphenyl konnte die Quantenausbeute von p,p-Spirosexiphenyl in dünnen festen Filmen bis auf 65 % (95 % m,m- und 5 % p,p-Spirosexiphenyl) gesteigert werden. Eine Korrelation der Quantenausbeuten in Lösung und im festen, unverdünnten Film wurde nicht festgestellt. Als dünne Filme in Wellenleitergeometrie zeigen Spirooligophenyle bei optischer Anregung verstärkte spontane Emission (ASE). Dies manifestiert sich in einer Einengung des Emissionsspektrums mit zunehmender Pumpleistungsdichte. Auch für stimulierte Emission sind die Verbindungen mit Sexiphenylchromophor besser geeignet. Die niedrigste Schwelle in einer unverdünnten Reinsubstanz wurde mit 0.23 µJ/cm² in einer aufgeschleuderten Schicht Spirosexiphenyl gemessen. Auch 4-Spiro³, Spiro-SPO und Octo-2 zeigten niedrige ASE-Schwellen von 0.45 µJ/cm², 0.45 µJ/cm² und 0.5 µJ/cm². Die ASE-Schwellwerte von Spiroquaterphenyl und seinen beiden Derivaten Methoxyspiroquaterphenyl und Octo-1 sind mit 1.8 µJ/cm², 1.4 µJ/cm² und 1.2 µJ/cm² höher als die der Sexiphenylderivate. Im gemischten System aus m,m- und p,p-Spirosexiphenyl konnte die ASE-Schwelle noch weiter gesenkt werden. Bei einer Konzentration von 5 % p,p-Spirosexiphenyl wurde ein Schwellwert von nur 100 nJ/cm² bestimmt. Durch Dotierung mit unterschiedlichen Farbstoffen in Spirosexiphenyl als Matrix konnte ASE fast über den gesamten sichtbaren Spektralbereich gezeigt werden. Mit der „variable Streifenlänge“ (VSL-) -Methode wurden die pumpleistungsabhängigen Gainspektren dünner aufgedampfter Proben gemessen. Hieraus konnten die Wechselwirkungsquerschnitte der stimulierten Emission der Substanzen ermittelt werden. In Übereinstimmung mit den Verhältnissen bei den Festkörperfluoreszenzquantenausbeuten und den Schwellwerten der ASE sind auch bei den Gainkoeffizienten reiner Spirooligophenyle die besten Werte bei den Sexiphenylderivaten gefunden worden. Der Wirkungsquerschnitt der stimulierten Emission beträgt für Methylspiroquaterphenyl und Octo-1 ca. 1.8*10^-17 cm². Für Spiro-SPO und Spirosexiphenyl wurden Wirkungsquerschnitte von 7.5*10^-17 cm² bzw. 9.2*10^-17 cm² bestimmt. Noch etwas größer waren die Werte im gemischten System aus m,m- und p,p-Spirosexiphenyl (1.1*10^-16 cm²) und für DPAVB dotiert in Spirosexiphenyl (1.4*10^-16 cm²). Der höchste Maximalwert des Gainkoeffizienten von 328 cm-1 bei einer absorbierten Pumpenergiedichte von 149 µJ/cm² wurde mit Spirosexiphenyl erreicht. Abschließend wurden DFB-Laser-Strukturen mit reinen und dotierten Spirooligophenylverbindungen als aktiven Materialien vorgestellt. Mit Spiroterphenyl konnte ein DFB-Laser mit der bisher kürzesten Emissionswellenlänge (361.9 nm) in einem organischen Festkörperlaser realisiert werden. Mit reinen Spirooligophenylverbindungen und Mischungen daraus habe ich DFB-Lasing bei Wellenlängen zwischen 361.9 nm und 479 nm aufgezeigt. Durch Dotierung mit DPAVB wurde der Bereich der erreichbaren Wellenlängen bis 536 nm erweitert, bei gleichzeitiger Erniedrigung der Schwellenergiedichten für Lasertätigkeit. Bei Emissionswellenlängen von 495 nm bis 536 nm blieb die Laserschwelle zwischen 0.8 µJ/cm² und 1.1 µJ/cm². Diese Werte sind für DFB-Laser zweiter Ordnung sehr niedrig und geben Anlass zu glauben, dass sich mit DFB-Strukturen erster Ordnung Schwellen im Nanojoule Bereich erzielen lassen. Damit würde man den Bedingungen für elektrisch gepumpten Betrieb nahe kommen.