Characteristics and Applications of Semiconductor Lasers and Semiconductor Optical Amplifiers
Date Issued
2006
Date
2006
Author(s)
Chang, Wei-Che
DOI
zh-TW
Abstract
With the increase of blooming information and data transmission of internet, the perspective of fiber-optic communication becomes more and more prospect in the future. In this dissertation, we focus on the use and design of quantum well (QW) and quantum dot (QD) devices to achieve broadband emission characteristics and higher modulation bandwidth of semiconductor laser diodes (LD) and semiconductor optical amplifiers (SOA).
First, we propose a new simple method to measure the broadband gain spectrum with a two-section device. Without any other external tunable lasers and complicated setup, we measured broadband gain spectrum of quantum-dot amplifiers. The quantum dots give positive gain for the spectral range near 480nm, covering from 950nm to 1400nm. The maximum gain could be 42.83cm-1.
Besides, we find out the infrared emission in the second quantized state device. The reason is supposed to be the free electron’s intersubband transition in the conduction band. By the small energy band gap, the emission of the QDs has the infrared wavelength.
In Addition, we propose a new mechanism for direct modulation of laser diode by using second quantized state device. Lasing at the second quantized state can be induced by increasing the total cavity loss, which can be practically accomplished either by decreasing the length of cavity, increasing the material loss, or by decreasing the facet reflectivity. In our experiment, the bandwidth of the QD device lasing at the second quantized state highest could achieve 2.78GHz. Furthermore, it also enhanced the modulation speed over 2.6 times more than the first quantized state. In addition, we also analysis this result using theoretical model. It helps us to figure out the mechanism of the carriers and the photons.
Finally, we continue to measure the direct modulation of laser diode by using carrier redistribution inside nonidentical multiple quantum wells (MQWs). With proper design of the nonidentical MQW structure, a device with two-section waveguide Fabry-Perot laser diodes can be switched between two widely separated lasing wavelengths at high frequency. The switched intensity can have extinction ratio of 20dB within 5mA of current variation. Carriers redistribute inside nonidentical MQWs and contribute to different lasing wavelengths. Because the transport time between quantum wells is much smaller than the diffusion and drift time in SCH layer of carriers, the modulation bandwidth of two-section laser is expected to surpass the relaxation frequency of conventional laser diode. This new mechanism will greatly improve the transmitter speed and lower the cost in optical communication system.
Subjects
量子點
量子井
半導體
雷射
光放大器
增益
頻譜
調變
Quantum-dot
Quantum-well
Semiconducter
Laser Diodes
Optical Amplifiers
Gain
Spectrum
Modulation
Type
thesis
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