| Summary: | 博士 === 國防大學中正理工學院 === 應用物理研究所 === 90 === Semiconductor optical amplifiers (SOA) have many features such as: compact size, high gain, broad band and low threshold current, etc. SOA’s play an important role in developing all-optical switching devises and logic gates. The nonlinear switching properties of SOA based on nonlinear polarization rotation and nonlinear coupling have great potential in ultrafast signal processing and optical communication.
We investigated the nonlinear polarization switching in SOA’s with a multiple quantum well (MQW) structure. With the differences of selection rules and optical confinement factors between the TE mode and TM mode, differences in gain and absorption are expected.
By comparing the properties of output optical signals with continuous wave, picosecond pulses and femtosecond pulses input into the MQWSOA samples, nonlinear polarization switching due to gain saturation, absorption saturation and some other ultrafast mechanisms (spectral hole burning and carrier heating) was observed.
We also investigated the propagation of optical signals in multimode interference (MMI) structure of MQWSOA samples. Optical nonlinear properties due to gain saturation, absorption saturation and some ultrafast mechanisms are always accompanied by variation of refractive index. Phase-matching condition for linear coupling is changed as the input power is increased. The nonlinear coupling switching of the MMI sample has also been observed.
In the experiments, SOA samples with AlGaAs/GaAs multiple quantum well structure have been used.
A Ti:sapphire laser, fabricated by us, with wide tunable wavelength range (790nm~950nm), was used as the light source. This laser can generate continuous wave, picosecond pulses and femtosecond pulses. By using the autocorrelator and spectrum analyzer, we can verify that the shortest output pulse is unchirped with pulse width of 50 femtoseconds.
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