Research On Optical Switch Based On Graphene Modulating Electrode And Integrated Technology

With the continuous development of society,the signal processing volume of information and communication networks is rapidly increasing,and the energy demand for equipment is also constantly increasing.High-energy consumption has become one of the main bottlenecks restricting the sustainable development of information technology.Optical switches and switch arrays are important components for building optical communication systems.Especially in the backbone lines of high-speed broadband communication networks utilizing dense wavelength division multiplexing（DWDM）or mode division multiplexing（MDM）technology,complex network architecture requires flexible and reliable network management.Optical switches and switch arrays have functions of optical domain optimization,routing,and protection in optical networks,and are the key technologies of optical add-drop multiplexer（OADM）and optical cross connect（OXC）.Therefore,how to reduce the power consumption of optical switches has become an important problem that urgently needs to be addressed,which is of great significance for reducing the energy consumption of information infrastructure.Waveguide-type optical switches are currently the most widely used optical switches in optical communication networks.The materials used to fabricate waveguide-type optical switches are primarily categorized into inorganic materials and organic polymer materials.Compared with inorganic materials,organic polymer materials have advantages of simple fabrication process,lower cost,adjustable refractive index,strong anti-electromagnetic interference capability,and unparalleled high electro-optic and thermo-optic coefficients.Therefore,organic polymer have gradually become the fundamental materials with great development and application prospects for achieving low-cost and high-performance photonic devices.In addition,the most prominent advantage of organic polymer materials is their strong fabrication process and integration ability,which can flexibly mix and integrate with other material systems,waveguides,and electrode structures.Therefore,exploring and studying high-performance,low-power consumption,miniaturized,and integrated optical switch devices using organic polymer materials has important theoretical significance and application value.For traditional optical switch devices,in order to avoid optical absorption loss caused by metal electrodes,a certain thickness of cladding material needs to be added between the metal electrodes and the waveguide core,which can also limit the modulation efficiency of the electrodes on the optical field in the waveguide core.To address this problem,this thesis mainly combines the excellent electrical,optical,and mechanical properties of graphene with the simple and flexible processing advantages of organic polymer waveguides.Through the research on graphene transfer technology and the design of waveguide fabrication processes,the graphene electrodes are buried inside the organic polymer waveguide.Based on the graphene/polymer hybrid waveguide structure,a series of studies on optical switch devices have been conducted.The main contents of this thesis are as follows:（1）The theoretical model of the graphene/polymer hybrid waveguide was established,and the anisotropy model and interface model of graphene was also analyzed.The advantages of interface model in simulation efficiency was utilized to simulate the optical absorption loss of graphene/polymer hybrid waveguide structure on TE and TM fundamental mode,demonstrating that the optical absorption loss of the TE mode was significantly greater than that of the TM mode.Then,a wet transfer process for single-layer graphene was developed,and a polarizer based on the graphene/polymer hybrid waveguide was designed and fabricated.Further experimental verification was conducted on the polarization dependence of optical absorption for the graphene/polymer hybrid waveguide structure.The measure results show that the device exhibits a significant difference in optical absorption loss of TE polarization mode and TM polarization mode,with values of 20 d B and 5 d B,respectively,achieving an extinction ratio of 15 d B and good stability within the1525～1620 nm wavelength range.（2）Based on the low absorption loss characteristic of graphene/polymer hybrid waveguides under TM polarization mode,a graphene/polymer hybrid waveguide optical switch with graphene modulation electrodes is proposed.Firstly,a polymer waveguide thermo-optic switch based on graphene heating electrodes was researched.Utilizing the simple and flexible processing technology of polymer waveguide,a new method was developed to bury and pattern the graphene heating electrodes within the waveguide core by combining a stripe-loaded waveguide structure and developed wet transfer process for graphene.The graphene heating electrodes can effectively enhance the overlap integral factor between the heating electrodes and the optical field without introducing additional absorption losses,thereby improving the heating efficiency of the electrode and reducing the power consumption of the device.Furthermore,an air isolation trench is introduced in the fabrication process of graphene electrodes,which can effectively concentrate the heat generated by the electrode in the waveguide core,further reducing the power consumption of the device.The measure results show that the switching power of the device using graphene heating electrodes is only 3.28 m W,which is approximately three times lower than that of the traditional structure thermo-optic switch using Al heating electrodes.The device exhibits a transmission loss of 6.2 d B,the extinction ratio of 25d B,and the rise and fall times of 96μs and 112μs,respectively.Secondly,the application of graphene modulating electrodes in polarized polymer electro-optic switch was researched.In order to reduce the voltage division in the waveguide cladding and enhance the polarization and modulation efficiency of the electrode,graphene is used as the ground electrode and buried between the waveguide core and lower cladding.Meanwhile,a metal electrode was employed as the modulation electrode and placed on the surface of the waveguide upper cladding,proposing an electro-optic switch structure based on metal-graphene composite modulating electrodes.Utilizing the cladding-modulated electro-optic switch structure and wet etching processes,an MZI electro-optic switch based on metal-graphene composite modulating electrodes was fabricated,with the switching speed of 17 ns.（3）Utilizing the electro-absorption effect of graphene,a mode-selective optical switch based on the graphene/polymer hybrid waveguides is proposed.To achieve flexible modulation of spatial modes in the MDM systems,the interaction between graphene capacitors and TE-polarized mode is employed,and combined with the optical field distribution and normalized electric field intensities of the TE₁₁,TE₁₂,and TE₂₁modes,four graphene capacitors were buried at different positions in polymer few mode waveguide.By optimizing the size and buried positions of each graphene capacitor,the selectable modulation of TE₁₁,TE₁₂,and TE₂₁modes is achieved.Simulation results show that the power consumption for modulating the three modes is 12.6 p J/bit,126.0 p J/bit,and 94.5 p J/bit,respectively,with corresponding switching times of 31 ps,357 ps,and 250 ps.In the C-band,the optical absorption loss of graphene for the three modes exceeds 20 d B/cm.By designing the length of the graphene capacitors,the extinction ratios of each mode can reach 23 d B,and enabling stable operation of the device across a wide wavelength range while maintaining modulation capabilities.Meanwhile,the performance of the device as an electro-refractive phase modulator was analyzed,and the lengths of graphene capacitors required to regulate TE₁₁,TE₁₂,and TE₂₁modes to achieveπphase are 3.3mm,9.1 mm,and 9.3 mm,respectively.（4）Based on the graphene/polymer hybrid waveguide structure,a mode-insensitive optical switch utilizing the electro-absorption effect of graphene is further proposed.To achieve insensitive modulation of various spatial modes in the MDM systems,we have combined the optical field distribution characteristics of TE₁₁,TE₁₂,TE₂₁,and TE₂₂modes,and conducted a comparative analysis of the impact of different capacitor structures,sizes,and burying positions on the absorption loss and modulation efficiency of each mode,greatly reducing the difference in modulation various modes and achieving mode-insensitive modulation.Simulation results show that the structure of two graphene capacitors sharing the lower layer graphene can effectively reduce the difference in optical absorption loss of graphene for each mode.In the C-band,the optical absorption loss of graphene for each mode is maintained consistently at 150d B/cm.During the switching process between the“ON”and“OFF”states of the device,the required voltage is 1.84 V,the power consumption is about 38.4 p J/bit,and the corresponding switching time is about 115 ps.