Wavelength-Dependent Femtosecond Pulse Amplification in Wide Band Tapered-Waveguide Quantum Well Semiconductor Optical Amplifiers

Mingjun Xia, Hooshang Ghafouri-Shiraz

Research output: Contribution to journalAbstractpeer-review


In this paper, we have studied the wavelength-dependent amplification in three different wide-band quantum well semiconductor optical amplifiers (QWA) having conventional, exponentially tapered and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in quantum well is established based on quantum well transmission line modelling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the tapered-waveguide QWA provides higher saturation gain and the output spectra of amplified pulse in all the three structures exhibit an apparent red shift and bandwidth narrowing due to the reduction of carrier density however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplifications of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependent of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of femtosecond pulse train, the linear tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs.
Original languageEnglish
Pages (from-to)10524-10531
JournalApplied Optics
Issue number35
Publication statusPublished - 10 Dec 2015


  • Semiconductor optical amplifiers, Quantum-well, -wire and -dot devices), Femtosecond phenomena, Pulse propagation and temporal solitons


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