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Study On The Optical Manipulation And All-silicon Long-wavelength Photodetection In Optical Communication Devices

Posted on:2018-02-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:J S GuoFull Text:PDF
GTID:1318330515969697Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
The silicon photonic integrated circuits have abilities of integrating diverse photonic components with high density and using CMOS-like fabrication to lower the cost,and silicon photonics is now widely accepted as a key technology in next-generation communications systems and data interconnects.Plasmonic optical structures can route and manipulate light at nanometer length scales,with the diffraction limit broken through,and thus provide new pathways to generate,guide,modulate and detect light with structures that are similar in size to state-of-the-art electronic devices.In this thesis,several optical simulation methods are used to study the optical manipulation issues including the mode-handling and non-reciprocal propagation in silicon integrated devices,as well as the light concentration in plasmonic photodetectors(PDs),besides,the high performance waveguide Schottky PDs which can be used in all-silicon long-wavelength photodetection,are designed.The common optical simulation methods are introduced with calculation principles and application properties.Focusing on the above issues,this work mainly contains the followings:Firstly,the mode hybridization in vertically-asymmetric waveguides is analyzed systematically.The mode hybridization can be used in the mode conversions in tapered waveguides,and this thesis throws lights upon the role played by mode hybridization in these mode conversion processes by analyzing the conversion properties with eigen-mode expansion method.For the reported inner-band mode conversion,we propose a curving tapered waveguide structure with length reduced by about 40%compared to the linear tapered structure.Besides,an easily fabricated inter-band mode convertor is presented by this work with high conversion efficiency,large bandwidth,and accepted fabrication tolerance.Both the proposed concepts are useful for high order modes control issues.Secondly,the silicon integrated magneto-optical non-reciprocal devices are studied.For the magneto-optical no-reciprocal phase shift devices,two calculation methods are used to evaluating the no-reciprocal phase shifts of different magneto-optical waveguides in this thesis,with waveguide mode properties taken into consideration.Two designs with compact sizes are proposed.One utilizes directional couplers for optical path switching,and the other utilizes mode conversion between TM mode and TE1 mode.The research includes some explorations in device fabrication.Thirdly,the plasmonic PDs with light concentration are studied.This type of devices with nano-scale active regions usually have limited optical absorptances.In this thesis,a design of plasmonic PD with high absorptance and nano-scale active regions is proposed.The material choosing,parameter optimizations,and light concentration mechanism are analyzed in detail.An optimized device has 3 dB bandwidth of 140 GHz and responsivity of 0.74 A/W at 1550 nm,and it can be coupled to fiber effectively,and fabricated by mature technologies.This design can be applied to both group III-V and IV materials.We can adjust the device parameters for particular operation wavelength covering the O-U bands.Among the plasmonic PDs with inherent high speeds but low absorptaces,this design makes the obvious progress on improving the optical absorptance.Finally,the integrated Schottky PDs based on silicon nanowire plasmonic waveguides have been designed and analyzed.Schottky photodetectors utilizing internal photoemission process use metals/silicides as absorption materials,and their responsivities are limited by the low internal quantum efficiencies(IQEs).By utilizing Si nano wire plasmonic waveguide with ultrathin metal/silicide stripes integrated,a type of Schottky PDs with high responsivities is proposed here.The mode characteristics of the plasmonic waveguide are systematically studied with diverse materials,and the silicides are classified to metal-like type and non-metal-like type.When using metal/metal-like silicide in the plasmonic waveguide,the aab0-quasi-TE hybrid modes are first use to absorb light efficiently.For example,a high absorptance of 95.6%(responsivity:0.146 A/W)is achieved in Au stripe with thickness of 5 nm and area of only 0.14 ?m2.This small contact area helps for getting a low dark current of 8.03 nA and a high 3dB bandwidth of 90 GHz.As for non-metal-like silicides,the quasi-TM mode should be used,and it is found that a relatively thicker and narrower silicide stripe leads to a lower dark current when the responsivity is fixed.These studies can promote the research of waveguide Schottky PDs.The studies on the magneto-optical devices and waveguide Schottky PDs benefit from the mode-handling study.In addition,the studies on both the surface-illuminated plasmonic PDs and waveguide Schottky PDs reflect the strong optical field confinement abilities of plasmonic structures.In short,the novelties of the thesis can be concluded as follows.The novel structures are proposed for mode conversions in Si waveguides.The size compression schemes of Si integrated magnet-optical devices are presented.The performance improvements of surface-illuminated plasmonic photodetectors are realized.Besides,the high performance Si integrated Schottky PDs,which can promote the researches on the all-silicon photodetection at telecom long wavelengths,are designed and analyzed.
Keywords/Search Tags:Silicon Photonics, Plasmonics, Finite-Difference Time-Domain(FDTD), Eigen-mode expansion method(EME), Mode conversion, Magneto-optic effect, Plasmonic photodetector, Schottky photodetector
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