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Very high amplitude, minimal chirp optical pulse generation at 1.55 ?m using multicontact DFBs and an erbium doped fibre amplifier
Electronics Letters
Abstract
A novel method of obtaining chirp minimised gain switched pulses of very high amplitude and contrast ratio is presented. 75 ps wide pulses at a 1.5 GHz repetition rate, with a -20 dB bandwidth of 4.7 AA are demonstrated. This is the first time that chirp has been minimised for DFB lasers without the compromise of the pulse definition.
We investigated the gas-phase reaction between trimethylamine alane (TMAA) and triethylgallium (TEG) in chemical beam epitaxy (CBE) using a quadrupole mass analyzer (QMA). When they were premixed to form a single beam, the overall intensity of the mass spectrum for the mixtures was much lower than that for each source, which was consistent with the observed growth rate of each layer. In contrast, such reduction was remarkably suppressed when they formed individual beams. These results indicated that gas-phase reaction to produce nonvolatile materials occurred in the premixing region. Therefore, premixing must be prevented during growth using TMAA and TEG.
Le développement important des transmissions sur fibre optique utilisant les solitons nécessite de disposer a la longueur
ď onde de 1,5 μm ď impulsions optiques picoseconde proche de la limite de la transformation de Fourier. Dans ce but, une analyse
des lasers a semiconducteur en régime impulsionnel est proposée. Les auteurs évaluent les performances que ľ on peut attendre
des deux méthodes qui sont classiquement utilisées pour générer ces impulsions avec des lasers à semiconducteur : le blocage
de modes et la commutation de gain. Le but de la dernière partie est de discuter la réalisation et les performances des sources
spécialement conçues pour les applications soliton ainsi que de présenter le principe de fonctionnement ď une source monolithique
utilisant un laser multisection. Les premiers résultats obtenus avec un composant dbr à trois sections seront discutés.
Recent developments in soliton transmission on optical fiber require picosecond pulses at 1.5 μm which are as close as possible
to the Fourier transform limit. In the present paper, semiconductor lasers in pulsed regime are studied for this purpose.
Thus, performances achievable by using the most usual methods, mode-locking and gain-switching, are evaluated. The aim of
the last part is to discuss the design and performances of sources dedicated to soliton transmission as well as to present
the principle of operation of a monolithic source based on a two- or three-section laser. The first results obtained with
a three sections dbr laser are given.
Mots clésLaser semiconducteur-Impulsion ultracourte-Fibre optique-Soliton-Laser verrouillage mode-Réflexion Bragg répartie
Key wordsSemiconductor laser-Ultrashort pulse-Optical fiber-Soliton-Mode locked laser-Distributed Bragg reflection
High power bandwidth-limited picosecond pulses with peak powers in excess of 200 mW have been generated using 1.5 mu m multicontact distributed feedback laser diodes for the first time. The pulses have widths typically less than 10 ps, time-bandwidth products of as little as 0.24, and can be generated on demand at generator limited repetition rates of up to 140 MHz.
A three contact multiquantum well (MQW) distributed feedback (DFB) laser has been gain switched to generate tunable picosecond optical pulses with substantially reduced chirp (as low as 0.6 AA) when compared with that possible using equivalent single contact devices. This spectral performance is achieved by using the central device region to control the wavelength of the picosecond pulses generated through modulation of the end contacts. Near Fourier limited duration-bandwidth products as low as 0.26 are observed.
Calculations of modulation induced line-width broadening in 1.55 mu m DFB lasers are reported. Voltage controlled intracavity loss modulation has significant performance advantages compared with conventional large signal current modulation schemes.
High-peak-power picosecond pulses with ultralow jitter of 65 fs (50-500 Hz) have been generated by Q-switching multi-quantum-well (MQW) distributed-feedback (DFB) and Fabry-Perot (FP) multicontact lasers. Peak pulse powers of 80 mW have been measured for pulses having durations of 26 ps and repetition rates of 1.25 GHz.< >
The first generation of bandwidth‐limited, single‐mode ultrashort optical pulses with excellent coherency from a distributed feedback InGaAsP diode laser at 1.3 μm by the method of strong rf modulation superimposed on the dc bias current is reported. It was realized only by the laser diode itself with no requirement of any other optical elements or external cavity or careful optical control. The measurement of time‐bandwidth product of the generated coherent picosecond pulses at 500‐MHz modulation gave the value of 0.38 for Lorentzian pulse shape with a full width at half‐maximum of nearly 34 ps, which proved definitely the Fourier‐transform‐limited character. By changing the dc bias current from positive to negative, the pulse width was demonstrated to be continuously controllable over a range of approximately twice to three times depending upon the modulation frequency.
A simple and novel sampling technique for optical timedivision multiplexing circuit and packet switched data is proposed using a gain-switched distributed feedback semiconductor laser and lithium niobate modulators. System error rate measurements on a two-channel system multiplexing data at 140 Mbit/s and 50 Mbit/s are given and operating penalties analysed.
VPTDFB semiconductor lasers have been shown to exhibit particularly low transient frequency chirp resulting in record distances for dispersive fibre transmission at 2 to 4 Gbit/s rates. The letter reports experimental study of chirping in 1.55 μm VPTDFB lasers under the demanding situation of high-speed modulation with high pulse on/off ratios. The laser was modulated with 100 ps current pulses from a comb generator, or with high-frequency RF at 4 GHz. It is found that the laser's chirped linewidth is between 2 to 8 Å for modulation on/off ratios from 4:1 to more than 20:1. We infer that at high laser pulse on/off ratios there will be significant pulse distortion at 8 to 10 Gbit/s rates for fibre distance of ⩾60 km even with these low chirp VPTDFB lasers. However, the exact nature of this distortion and its system impact in dispersive fibre transmission may depend in detail on the specific laser parameters and system operating conditions.