Study On Silicon-based Laser And Related Integrated Technology And Silicon-based Polarization?Mode Multiplexing Devices

With the rapid development of large capacity optical communication technology,the optoelectronic devices with high performance and conpact structure and the optoelectronic integrated systems with high performance and high integration have been widely concerned.Among them,the technology of silicon-based micro-nano optoelectronic devices and silicon-based optoelectronic integration based on SOI substrate have become the focus of research,which can realize large capacity optical communication system with low cost and low power consumption,because they are compatible with CMOS technology.However,due to the large mismatching of lattice constant,thermal expansion coefficient and antiphase domain,the realization of silicon-based laser has encountered great obstacles.In addition,in the ways of realizing silicon-based on-chip optoelectronic integration,compared with the way of silicon-based on-chip hybrid integration,the way of silicon-based on-chip monolithic integration can make full use of the advantages of simple package and large-scale production to significantly reduce the package cost and improve the reliability of the system.However,due to the complexity of fabrication process,it is still difficult to realize the on-chip integration of silicon-based laser and other optoelectronic devices by the way of monolithic integration.Besides,for silicon-based passive devices on SOI substrate,due to the large refractive index difference between silicon waveguide layer and silicon dioxide buried layer on SOI substrate,the devices show signigicant polarization correlation.Polarization beam splitter can solve this problem well.At the same time,in order to improve the system information transmission capacity,especially the single wavelength channel information transmission capacity,the mode multiplexing technology has been widely studied.And the mode converter is the most critical device to achieve the mode multiplexing.In particular,polarization multiplexing based on polarization beam splitter and mode multiplexing based on mode converter can be combined to further improve the system information transmission capacity.Therefore,it is very important to study polarization beam splitters and mode converters.Based on the above background,this thesis has carried out the researches of 1.55 ?m direct epitaxial silicon-based laser array,the on-chip optoelectronic integration of silicon-based lasers based on SOI substrate,polarization beam splitter and mode converter based on SOI substrate.The specific research contents and main innovations in this thesis are as follows:(1)A design of 1.55 ?m direct eptiaxial silicon-based laser array structure based on V-groove patterned substrate technology is proposed.The V-groove structure used in this scheme can effectively eliminate the antiphase domain and reduce the dislocation density produced by heteroepitaxy.Compared with the conventional laser array formed by etching multiple ridge laser units,this scheme can make the laser array be fabricated in the V-groove pattern substrate without the etching steps in the post process.The structure of the laser array is optimized from the point of the optical confinement factor of the active region.The calculation results show that the optical confinement factor of the active region is 9.3%when the period of the silicon-based laser array is 1 ?m,the width of the V-groove pattern is 0.6 ?m,and the height of the active region position is 0.3 ?m.Light in the active region of each laser unit in the array can be well confined.The calculation results are expected to provide theoretical guidance for the subsequent laser fabrication in the silicon-based V-groove patterned substrate.(2)A scheme of silicon-based laser on-chip optoelectronic integration on SOI substrate using monolithic integration method is proposed.Through the design,the on-chip optoelectronic integration of silicon-based III-V material square microcavity laser and waveguide type Ge detector and Si waveguide has been completed.Compared with the reported on-chip optoelectronic integration scheme of silicon-based laser using monolithic integration method,this scheme can utilize the advantages of SOI substrate to fabrication passive devices to achieve lower loss and higher integration,thus has more practical advantages.The device simulation and optimization of the integrated scheme show that when the side length of the square microcavity laser is 10 ?m,the thickness of the cover layer is 0.9 ?m,and the width of the silicon waveguide is 1.5 ?m,the coupling output efficiency of the laser is 11.8%,and the corresponding laser microcavity quality factor is 1804.The results show that the threshold current is 6.3 mA when the internal loss coefficient is 8 cm-1,and the output power is about 1.5?W when the injection current is 8 mA.At the same time,when the length of Ge detector is 5?m,the light absorption efficiency is 98%.And in the condition,when the reverse bias voltage is 2 V,the responsivity of the detector is 0.313 A/W.(3)A polarization beam splitter based on the three waveguide coupler is designed and fabricated on SOI substrate.In the design,a layer of silicon nitride is introduced into the middle waveguide of three waveguide coupler to realize the phase matching condition of TM polarization that TM polarization can be fully coupled and TE polarization can not be coupled,so as to realize polarization beam splitting.Compared with the same type of polarization beam splitters using three waveguide coupler structure,the designed polarization beam splitters have shorter device length(7 ?m).Moreover,the bandwidth with the extinction ratio greater than 30 dB is 100 nm(TE polarization)and 28 nm(TM polarization),and the insertion loss is less than 0.06 dB(TE polarization)and 0.35 dB(TM polarization).Among polarization beam splitters using three waveguide coupler with device length less than 10?m,the designed polarization beam splitter can achieve greater bandwidth and lower insertion loss.The performance of the device is lower than that of the design.If the accuracy of the device manufacturing process is improved,better test results can be obtained.(4)A method of mode-order conversion based on subwavelength grating structure is proposed,and three kinds of mode-order converters based on SOI substrate are designed.By introducing a sub-wavelength grating structure into the silicon waveguide on SOI substrate,the input fundamental mode is scattered to form a high-order mode.The three kinds of mode-order converters can be fabricated by one-step etching process,and the device fabrication is simple.Among them,the device length of TE0-to-TE1 and TE0-to-TE2 converters are less than 10 ?m,and the conversion efficiency calculated with the bandwidth of 100 nm is more than-0.25 dB.Compared with the same type of mode-order converters,the performances of the designed mode-order converters reach a better level.Moreover,the two kinds of mode-order converters are symmetrical which can realize the function of data exchange.(5)A polarization/mode-order converter is designed on SOI substrate by using hybrid plasmon waveguide.In this design,a metal layer is introduced into the silicon waveguide on SOI substrate,and the polarization/mode-order conversion of TE1-to-TM1 is realized.Compared with other polarization/mode-converter(TM0-to-TE1),the designed polarization/mode-order converter realizes a new polarization/mode-order conversion function(TE0-to-TM1),and the device length is smaller(11 ?m),the working bandwidth can cover the S+C+L bands.The calculated insertion loss of the device is less than 4.22 dB,the mode crosstalk is less than-13.36 dB,and the mode purity of TM1 mode in the output port is more than-0.6 dB.