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Study on the Characteristics of High-Speed EAM-DFB Integrated Optical Source Based on OEIC Models

Author: WangShiKang
Tutor: PanZuo
School: Southwest Jiaotong University
Course: Microelectronics and Solid State Electronics
Keywords: Optical communication and optical device Optoelectronic integrated circuit Distributed-feedback laser Electro-absorption modulator Scattering parameter
CLC: TN248
Type: Master's thesis
Year: 2008
Downloads: 111
Quote: 2
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Abstract

The EAM-DFB is an integrated optical source which has the high performances, such as high-speed modulation characteristic, low drive voltage, low chirp, and small bulk. It is realized by electro-absorption modulator (EAM) modulating distributed-feedback semiconductor laser (DFB-LD) which with the single longitudinal mode characterisics. Because of these advantages, EAM-DFB has an important application in long-haul and high-capacity optical communication systems, and become the one kind of most promising optical source in nowadays. So, there is important meaning to research its characteristics.Based on the rate equation of DFB-LD and the absorption principle of EAM, aimed at the character of photoelectric mixing and scattering of ports in EAM-DFB, the analytical methods of typical parameters and scattering parameters based on optoelectronic integrated circuit (OEIC) model was advanced. The OEIC model of EAM-DFB including spontaneous emission, Auger recombination, parasitic efforts and isolation resistance was established by PSpice, the circuit-level simulation software. At the same time, for researching the scattering characteristic on integrated device, the model for calculating scattering parameter (S-Parameter), and the model of semiconductor optical amplifier (SOA) were also established. Based on these models, the typical paramters characteristics of EAM-DFB was simulated on circuit-level, the port scattering of device was investigated, and the integrated device based on the DFB-LD was discussed particularly.The numerical results indicated that, the parameters of EAM, cavity length and the transmission loss influenced the gain, for a longer cavity length, the gain decreased sharper as the frequency increasing. Based on the model, the relative absorption impedance of EAM decreased as the input optical power increasing, and its characteristic impedance changed more notable in low frequency. It also found that, the gain would increase and become flatness if load impedance was decreased.The simulation indicated that, EAM-DFB could generate short optical pulse (shorter than 25ps); increasing bias current could raise output power, spread line-width, enhance noise and induce the peak of noise to shift toward higher frequency. It also found that either decreasing spontaneous emission factor or increasing bias current and optical confinement factor could broaden modulation bandwidth. Compared with DFB-LD, EAM-DFB has more rapid light-current properties and wider modulation bandwidth with little noise increasing. Chirp was created along with the output of optical pulse, but it was restrained in EAM-DFB, the variation range of frequency chirp of DFB-LD and EAM-DFB was 3.8GHz～1.8GHz and 0.2GHz～0.1 GHz respectively.The researching of scattering characteristic indicated that, transmitted parameter of EAM-DFB is -25~-60dB, and decreased as frequency increasing when model was modulated, however, the reflected parameter increasing in this state. It also found that, whether decreasing spontaneous emission factor or increasing bias current and optical confinement factor could raise reflection and reduce transmission, but the reducing of transmission was more slowly and flatly, this could improve the modulation response.SOA has big bandwidth and flat gain curve when it worked independently, and increased rapidly as the facet reflectivity decreasing. The integrated device (DES) was composed by EAM-DFB integrating with SOA, because of the fluency of integration, the line-width of output pulse was spread, and modulation bandwidth was decreased. At the same time, the dynamic range of S-parameters increased in the same frequency bound. It indicated that the scattering of port between devices affected the performance of optical source.

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