Short pulse generation from semiconductor lasers: characterization, modeling and applications

Esta Tesis describe el trabajo de investigación realizado sobre pulsos ópticos generados por láseres de semiconductor con duración de decenas de picosegundos. El trabajo se ha enfocado sobre diodos láser de cavidad vertical a 1550 nm, transmisores ópticos muy prometedores por sus ventajosas características en el entorno de las comunicaciones ópticas en fibra con modulación directa. El elevado ancho de banda previsto para las futuras redes ópticas requiere el conocimiento detallado de las propiedades eléctricas de los transmisores, así como de las propiedades de los pulsos generados por éstos que transportan la información binaria. En la presente Tesis, se describen los diferentes logros alcanzados en la caracterización de dicho tipo de láseres y de los pulsos generados por ellos, así como sus aplicaciones en un entorno de comunicaciones ópticas. Se han caracterizado láseres de cavidad vertical con emisión a 1550 nm, basados en pozos cuánticos y unión túnel, a través de medi¬das estáticas y dinámicas de la impedancia eléctrica y de la respuesta en modulación entre 0 y 10 GHz. Se han modelado los parásitos eléctricos y el circuito eléctrico equivalente de la estructura del dispositivo teniendo en cuanta los efectos de captura y escape de los portadores en los pozos cuánticos. Se han calculado los parámetros intrínsecos de los dispositivos a partir de las medidas realizadas. Se han empleado los dispositivos así caracterizados para la generación de pulsos con duraciones tan pequeñas como 55 ps a diferentes frecuencias de repetición, utilizando la técnica de conmutación de ganancia. Se ha medido la duración, la amplitud del pico, el "jitter" y el ancho espectral de los pulsos en función de los parámetros de conmutación de ganancia. Se ha investigado el efecto de la inyección óptica sobre los pulsos generados con dichos láseres de cavidad vertical conmutados en ganancia, obteniéndose una reducción del "jitter" en un amplio rango de los parámetros de inyección. Se ha diseñado e implementado un codificador de acceso múltiple por división de códigos ópticos (OCDMA) basado en líneas ópticas de retardo que emplea los pulsos generados por los dispositivos conmutados en ganancia. Finalmente, se ha propuesto y demostrado una novedosa implementación de la técnica de reconstrucción de fase por medio de la diferenciación óptica ultra rápida (PROUD), para la caracterización en amplitud y fase de pulsos ópticos. El diferenciador óptico necesario para la técnica ha sido realizado con un interferómetro birrefringente basado en fibra mantenedora de la polarización. Se ha medido la variación instantánea de la frecuencia ("time resolved chirp") de pulsos de diferente duración y forma, obtenidos con un laser conmutado en ganancia, y el factor de ensanchamiento de linea del laser utilizaso. Abstract This Thesis describes the research work that has been carried out on the generation of optical pulses, with duration of tens of picoseconds, from semiconductor lasers. The work is focused on 1550 nm Vertical Cavity Surface Emitting Lasers (VCSEL), which are promising optical transmitters due to their advantageous characteristics in the context of fiber optical communications with directly modulated sources. The high bandwidth expected for future optical networks requires the accurate knowledge of the transmitter electrical properties and of the laser generated optical pulses which carry the binary information. This Thesis describes the various achievements obtained in the characterization of these devices and the generated pulses, as well as their applications to an optical communications environment. VCSELs emitting at 1550 nm, based on quantum wells and tunnel junction, have been characterized by static and dynamic impedance measurements and modulation response between 0 and 10 GHz. The electrical parasitics and the equivalent circuit of the device have been modeled, taking into account the effects of capture and escape of carriers in quantum wells, and the laser intrinsic parameters have been calculated from the measurements. The VCSELs have been used for pulse generation using the gain switching technique, obtaining the shortest duration of 55 ps at different repetition frequencies. The duration, peak amplitude, jitter and spectral width of the pulses have been measured as a function of the gain switching conditions. The effect of optical injection on the pulses generated by gain switched VCSELs has been investigated, obtaining a jitter reduction over a wide range of injection parameters. An Optical Code Division Multiple Access (OCDMA) encoder based on optical delay lines has been designed and implemented, using the optical pulses generated by the gain switched devices. Finally, a novel implementation of the Phase Reconstruction using Optical Ultrafast Differentiation (PROUD) technique has been proposed and demonstrated for optical pulse characterization in amplitude and phase. The optical differentiator required in the PROUD technique has been realized with an interferometer based on birefringent polarization maintaining fiber. The instantaneous frequency, i.e. the time resolved chirp, of pulses with different durations and shapes obtained from a gain-switched laser, and the laser linewidth enhancement factor have been measured

Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Voltage properties of optically injected long wavelength VCSELs: Theory and experiment

Future high speed communications networks will transmit data predominantly over optical fibres. As consumer and enterprise computing will remain the domain of electronics, the electro-optical conversion will get pushed further downstream towards the end user. Consequently, efficient tools are needed for this conversion and due to many potential advantages, including low cost and high output powers, long wavelength Vertical Cavity Surface Emitting Lasers (VCSELs) are a viable option. Drawbacks, such as broader linewidths than competing options, can be mitigated through the use of additional techniques such as Optical Injection Locking (OIL) which can require significant expertise and expensive equipment. This thesis addresses these issues by removing some of the experimental barriers to achieving performance increases via remote OIL. Firstly, numerical simulations of the phase and the photon and carrier numbers of an OIL semiconductor laser allowed the classification of the stable locking phase limits into three distinct groups. The frequency detuning of constant phase values (ø) was considered, in particular ø = 0 where the modulation response parameters were shown to be independent of the linewidth enhancement factor, α. A new method to estimate α and the coupling rate in a single experiment was formulated. Secondly, a novel technique to remotely determine the locked state of a VCSEL based on voltage variations of 2mV−30mV during detuned injection has been developed which can identify oscillatory and locked states. 2D & 3D maps of voltage, optical and electrical spectra illustrate corresponding behaviours. Finally, the use of directly modulated VCSELs as light sources for passive optical networks was investigated by successful transmission of data at 10 Gbit/s over 40km of single mode fibre (SMF) using cost effective electronic dispersion compensation to mitigate errors due to wavelength chirp. A widely tuneable MEMS-VCSEL was established as a good candidate for an externally modulated colourless source after a record error free transmission at 10 Gbit/s over 50km of SMF across a 30nm single mode tuning range. The ability to remotely set the emission wavelength using the novel methods developed in this thesis was demonstrated

Aeronautical engineering: A continuing bibliography with indexes, supplement 103, December 1978

This bibliography lists 457 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1978

Aeronautical Engineering: A cumulative index to the 1980 issue

This bibliography is a cumulative index to reports, articles, and other documents introduced into the NASA scientific and technical information system. Abstracts for the entries cited appeared in issues 119 through 130 of Aeronautical Engineering: A Continuing Bibliography (NASA SP-7037). Subject, personal author, corporate author, contract number, and report/accession number indexes are provided

Psr1p interacts with SUN/sad1p and EB1/mal3p to establish the bipolar spindle

Regular Abstracts - Sunday Poster Presentations: no. 382During mitosis, interpolar microtubules from two spindle pole bodies (SPBs) interdigitate to create an antiparallel microtubule array for accommodating numerous regulatory proteins. Among these proteins, the kinesin-5 cut7p/Eg5 is the key player responsible for sliding apart antiparallel microtubules and thus helps in establishing the bipolar spindle. At the onset of mitosis, two SPBs are adjacent to one another with most microtubules running nearly parallel toward the nuclear envelope, creating an unfavorable microtubule configuration for the kinesin-5 kinesins. Therefore, how the cell organizes the antiparallel microtubule array in the first place at mitotic onset remains enigmatic. Here, we show that a novel protein psrp1p localizes to the SPB and plays a key role in organizing the antiparallel microtubule array. The absence of psr1+ leads to a transient monopolar spindle and massive chromosome loss. Further functional characterization demonstrates that psr1p is recruited to the SPB through interaction with the conserved SUN protein sad1p and that psr1p physically interacts with the conserved microtubule plus tip protein mal3p/EB1. These results suggest a model that psr1p serves as a linking protein between sad1p/SUN and mal3p/EB1 to allow microtubule plus ends to be coupled to the SPBs for organization of an antiparallel microtubule array. Thus, we conclude that psr1p is involved in organizing the antiparallel microtubule array in the first place at mitosis onset by interaction with SUN/sad1p and EB1/mal3p, thereby establishing the bipolar spindle.postprin

Removal of antagonistic spindle forces can rescue metaphase spindle length and reduce chromosome segregation defects

Regular Abstracts - Tuesday Poster Presentations: no. 1925Metaphase describes a phase of mitosis where chromosomes are attached and oriented on the bipolar spindle for subsequent segregation at anaphase. In diverse cell types, the metaphase spindle is maintained at a relatively constant length. Metaphase spindle length is proposed to be regulated by a balance of pushing and pulling forces generated by distinct sets of spindle microtubules and their interactions with motors and microtubule-associated proteins (MAPs). Spindle length appears important for chromosome segregation fidelity, as cells with shorter or longer than normal metaphase spindles, generated through deletion or inhibition of individual mitotic motors or MAPs, showed chromosome segregation defects. To test the force balance model of spindle length control and its effect on chromosome segregation, we applied fast microfluidic temperature-control with live-cell imaging to monitor the effect of switching off different combinations of antagonistic forces in the fission yeast metaphase spindle. We show that spindle midzone proteins kinesin-5 cut7p and microtubule bundler ase1p contribute to outward pushing forces, and spindle kinetochore proteins kinesin-8 klp5/6p and dam1p contribute to inward pulling forces. Removing these proteins individually led to aberrant metaphase spindle length and chromosome segregation defects. Removing these proteins in antagonistic combination rescued the defective spindle length and, in some combinations, also partially rescued chromosome segregation defects. Our results stress the importance of proper chromosome-to-microtubule attachment over spindle length regulation for proper chromosome segregation.postprin