Optoelectronic Devices Based On Transparent Conducting Materials

With the rapid development of information technology,opto-electronic integrated devices are facing higher requirement.Current opto-electronic devices,especially the optical modulators that are key components for optical networks,have some limitations in terms of integration density,power consumption,operating speed,etc.So it is urgent to have some breakthroughs in the materials and devices field.New concept device,which integrated transparent conducting materials?TCMs?such as indium-tin-oxide?ITO?or graphene in the silicon chip or fiber,can increase the performance of the opto-electronic devices,thus becomes the research hot topic.In this thesis,we investigated ITO-and graphene-assisted chip-based and fiber-based polarization-insensitive optical modulators?PIMs?and electro-absorption optical modulators?EAMs?,respectively.These optical modulators are attributed with compact footprint,low power budget,large extinction ratio and small insertion loss,fast modulation and ultra-wide spectral bandwidth.Four optical modulators were studied,and the graphene's intensity-dependent optical nonlinearity was investigated by using2-Dimensional full-vectorial finite-element-method.The main research work of this thesis can be concluded as following:1)Graphene-assisted electro-absorption optical modulator using D-microfiber was investigated.Dual-graphene lamellae separated by dielectric spacer is mechanically transferred over flat surface of D-microfiber to induce electro-absorption?EA?effect.The light-graphene interaction quantified by effective mode index?EMI?change is comparatively³ times higher than reported similar model.The active length of 80?m–long modulator offers extinction ratio?ER?as high as 17.80 dB,insertion loss?IL?of 2.71 dB,modulation bandwidth of 97.26 GHz and operates at C-band of communication wavelength at the expense of 24.30 fJ/bit.2)Graphene-assisted chip-integrated polarization-insensitive optical modulator was studied.dual-graphene lamella separated by dielectric spacer with 90obent corner is transferred over inner silicon rib,followed by outer silicon and outer silica onto silica substrate that ensures identical absorption between transverse-electric?TE?and transverse-magnetic?TM?modes.The PIM is capable of offering ER=18.87 dB,IL=2.32 dB and figure-of-merit?FOM?=8.14 for TE-mode.Concurrently,for TM-mode ER=19.39 dB,IL=2.41 dB and FOM=8.04.f_3dB is as high as 62.74 GHz at the expense of 1.28 fJ/bit for 12?m–long modulator.The operating wavelength ranges between¹500 nm and¹590 nm with optical bandwidth excess of 90 nm.The polarization-sensitive loss?PSL?at ON-State of modulator is as low as 0.1 dB,and mode power attenuation?MPA?tolerance between TE-and TM-modes is 0.82 dB.3)ITO-assisted D-fiber modulator was investigated.The identical modulating ability between TE-and TM-modes is achieved by transferring Al/HfO₂/ITO/HfO₂ stack exactly around the core region of D-fiber.The modulator is attributed with microscale length and low PSL loss.It can offer ER=23.71 dB,IL=1.01 dB for TE-mode.Concurrently,for TM-mode are 23.93 d B and 1.07 dB.The PSL of⁰.056 dB ensures identical modulating ability between fundamental optical modes.f_3dB=45.85 GHz at the expense of 0.39 pJ/bit for 10?m–long modulator.The operating wavelength ranges between¹475 nm and¹625 nm with optical bandwidth excess of 150 nm.4)ITO-assisted chip-integrated EAM wads studied.The efficient modulator is realized by maintaining balance between ER-IL that ensure higher FOM,low power consumption and wider modulation bandwidth.The balance between ER-IL is maintained by device architecture?using sidewall angled silicon waveguide?and choosing ON-state of the modulator at lower carrier concentration regime.EAM comprised of Si/ITO/HfO₂/Si stack upon silica substrate can offer ER=6.81 dB/?m,IL=0.019 dB/?m,FOM=337.f_3dB=78.85 GHz at the expense of 20 fJ/bit.The 3-dB modulation length is⁴40 nm operating between¹440 nm and¹660 nm with optical bandwidth excess of 220 nm.FOM is¹10%higher and 3-dB modulation length is²9.26%shorter than reported similar model.5)We studied the graphene's intensity-dependent optical nonlinearity.A single graphene lamella is incorporated with D-microfiber,and nonlinear parameters are investigated by engineering Fermi level and geometry of the waveguide.The net utility of nonlinear coefficient is harnessed up to a very high value of 10⁶ W^-1m^-1,which is²orders of magnitude larger than in similar waveguide model.The highly dispersive nature of the waveguide and large FOM_NL have raised the possibilities of utilizing slow light structures to operate devices at few watts power level with microscale length.