Research On Control And Transmission Characteristics Of Silicon-based Optical Switch Chips

Optical switching system is an essential part in optical communication network.In current network,commercial large-scale optical switching nodes are usually realized in the electrical domain through optical-electronic-optical(O-E-O)conversion.However,with the increasing of data rate in communication network,the electronic bottleneck and power consumption for this method are becoming two critical problems,while all-optical switching structure based on silicon photonics technology is regarded as an effective solution.Silicon-based integrated photonic chips can reduce the size and power consumption of resulting devices,and also can save costs due to the compatibility with complementary metal oxide semiconductor(CMOS)processes.In this thesis the design and module package of large-scale silicon-based optical switching chips are studied,and their performance and transmission characteristics are also investigated.The main work of this thesis includes the four aspects as follows:1.The performance of the integrated optical switch units based on the Mach-Zehnder interferometer(MZI)and micro-ring resonator is simulated and tested.Each optical switch unit is integrated with an n-i-n thermal resistor and a p-i-n junction.The extinction ratio of the MZI switch with carrier injection is 21 dB;the extinction ratio of the micro-ring switch based on thermo-optic effect is 18 dB.Furthmore,by comparison with the performances of several typical optical switching topology structures,the design and packaging of the optical switching chip modules based on the Benes structure are accomplished.The electrical package is achieved through gold wire-bonding to connect the chip p-i-n junctions,and the optical package is implemented through grating array to couple optical signals.In order to further improve the stability of the optical switching chip,a temperature control module is designed and manufactured.The overall temperature fluctuation of the chip can be controlled within ±0.03 °C.2.For large-scale high-speed optical switching chips,the author developed the high-precision thermal control and electronic control circuits to compensate for fabrication induced errors and fast switching,respectively.They can be combined flexibly by board interconnection to meet the requirements of driving different optical switching chip.The output accuracy of the control circuits is 10 mV,and the switching time is about 40 ns.A group of circuits with 112 control outputs that meet the drive requirements of 16×16 optical switching chip are developed,and the related experiments have been conducted.A synchronous driving scheme of the MZI optical switch is proposed.When carriers are injected into the p-i-n junction of one arm to change the switching state,along with heat generation,the thermal voltage of the other arm is drived synchronously to balance heat of the two arms,and then the switching performance is improved.Experimental results show that,compared with the traditional drive scheme,the proposed synchronous drive scheme can improve the extinction ratio of a single switch unit by 1 dB,along with a better output waveform.3.An optical switching node resulting from the MZI chip module is developed,which is mainly composed of an optical switching chip module,a driving circuit group,a control module and input/output interface.In order to act on network service requests,a modified looping algorithm linked with the optical switch performance is proposed and implemented for the rearranging non-blocking Benes switching network,which can be applied for the cases with deterioration or partial failure of the switching elements.An optical switching experimental system consisting of four edge nodes and one core node is built and tested in the intelligent communication network of Huawei Technologies Co.,Ltd..The third-party's measurement shows that the insertion loss of the 16×16 switching system is in the range of 21.3~30.6 dB,and the crosstalk is less than-8.96 dB.4.In order to verify the large-capacity transmission capability of the resulting optical switching node,a WDM communication system is built up using a comb as light source to perform a large-capacity communication system.The optical frequency comb source with a single soliton state was obtained by generating a local dispersion jump using an auxiliary ring,which only requires fixed-speed unidirectional pump frequency sweeping to achieve single soliton state.Statistic analysis shows that it has an excellent determinacy as high as 98.7%.A WDM transmission system is built up using a comb as light source,where the optical signal to noise ratio(OSNR)is degraded by an average of 4.4 dB.Theoretically 1.5 Tb/s per channel of the optical switching chip can be achieved.Considering that the existence of special nonlinear phenomenon induced by free-carrier in silicon waveguide,a chip interconnection scheme with EDFA is proposed for larger switching dimension,and a 64×64 optical switching matrix is built up based on 16×16 switch chips.Analysis shows that,compared with the 16×16 switching chips,the OSNR and receiver sensitivity of the resulting 64×64 optical switching matrix have been improved by 0.6 dB and 0.2 dB,respectively.