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Study On Polarization Dependence And Wideband Characteristics Of Semiconductor Optical Amplifier

Posted on:2006-09-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:L R HuangFull Text:PDF
GTID:1118360182970606Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Semiconductor optical amplifier (SOA) is an important device in future all-optical communications due to its small volume, low cost and easy integration with other optoelectronic devices, etc. This dissertation makes deep theoretical and experimental investigations into the polarization dependence and wideband characteristics of SOAs. Gain insensitivity to polarization is a fundamental requirement for SOA in fiber optical communication. In this dissertation, based on energyband engineering theory, the influences on polarization dependent gain of various kind of strain, the magnitude of tensile strain, the well width and carrier density are investigated; A 1.55μm gain polarization-insensitive SOA with tensilely strained quantum wells active region and a 1.31μm gain polarization-insensitive SOA with mixed tensilely and compressively strained wells are designed. A novel scheme by optimal antireflection film is proposed to improve the gain polarization insensitivity of SOA, which can give SOA more flexibility in designing active region and waveguide to meet other performance requirements. The intrinsic birefringence and induced additional birefringence of SOA make optical phase shift sensitive to polarization state and give rise to unwanted effects in SOA. A calculation model which takes birefringence into account is set up; the polarization state changes are analyzed by Jones matrix method. The negative impact of birefringence on performances of SOA-based interferometer devices and the effect of birefringence on the spectrum broadening of ultrashort optical pulse in SOA are studied. And the necessity and possibility of fabricating SOA whose gain and phase modulation are both independent on polarization state are analyzed. The requirements for polarization dependence of phase modulation are different in various applications of SOAs. It is shown that both the impact of birefringence and the effect of cross-polarization modulation rely on the polarization dependence of differential refractive index. The different effects of strain in quantum well active region on the polarization dependence of differential refractive index is explored, and the results illustrate how to design the active region and waveguide structure in order to satisfy various needs in SOA's applications. Like other nonlinear effects such as cross-gain modulation, cross-phase modulation and four-wave mixing, cross-polarization modulation has opened up a new application field of SOAs. The theoretical and experimental researches on the relationship among cross-polarization modulation, cross-gain modulation and cross-phase modulation are made, and theoretical study on all-optical wavelength conversion based on cross-polarization modulation is also made, which is of practical significance to SOA's applications. In addition, detailed experiments on additional birefringence in SOA, which includes the polarization state changes caused by the change of input optical power or that of biased current, and the possible reasons for the polarization state change when the input light beam is pure TE or pure TM mode are investigated Furthermore, a systematical experimental and theoretical exploration is made into cross-polarization modulation, which involves the dependences of probe beam polarization state changes on the wavelength, input power and polarization state of pump beam. Optical sources with wide spectrum characteristics are needed in high-speed, large-capacity optical communications. As for the wide gain spectrum characteristics, broadening and flattening of gain spectrum by transition between different energy subband in quantum well, by dimensionally asymmetric quantum wells and by compositionally asymmetric quantum wells are discussed. As for the SOA incoherent optical source, the dissertation studies the effect of facet reflection spectrum on the broadness and flatness of output spectrum, and a novel scheme is presented to acquire wide and flat output spectrum with large spectrum power density, which makes use of the optimization of antireflection film. In addition, different requirements for gain saturation characteristics are needed in various applications. Based on the distribution rules of carrier concentration and photondensity along the cavity of SOA, a new scheme is proposed to improve the gain saturation characteristics by multi-electrode. For a multi-electrode SOA, it is very convenient to adjust the length ratio and injection current ratio between sections to meet various requirements in practice.
Keywords/Search Tags:Semiconductor optical amplifier (SOA), Polarization Dependence, Wideband Characteristics, Birefringence, Cross Polarization Modulation, Antireflection Film, Saturation Output Power
PDF Full Text Request
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