| The booming of big data and cloud computing leads to a continuous demand for the capacity of traditional fiber communication facilities.At present,the optical fiber communication systems based on standard single-mode fiber are rapidly reaching their ultimate capacity.The space division multiplexing（SDM）based on multiplexing fiber such as weakly coupled multi-core fiber and few-mode fiber can make full use of the spatial dimension,the number of modes and wavelengths,which has become the key technology to break the capacity bottleneck.The performance of multiplexing fiber affects the transmission capacity of fiber communication systems and the complexity of multiple input multiple output（MIMO）digital signal processing（DSP）at the receiver.Therefore,the investigation of multiplexing fiber is of great significance to realize the next generation fiber communication systems with large capacity and low complexity.In addition,the multiplexing fiber supports multi-channel and multi-wavelength transmission,showing good compatibility with the multi-wavelength reflective optical antenna array.The dissertation focuses on the research of multiplex fiber and its application in multiplex systems and multi-wavelength reflective optical antenna array,and the main achievements are as follows:（1）In this dissertation,a seven hollow core Bragg fibers array is proposed.The coupled-power theory of the seven-core fiber is derived,and the calculation method of the aperiodic Bragg structure in the seven-core fiber is proposed.The transmission matrix method and finite element method are combined to design,analyze and optimize the fiber.The seven-core fiber introduces the advantages of low material dispersion and low nonlinearity of traditional Bragg fiber.The confinement loss of each core in Bragg fibers array with proper inter-fiber separation is greatly lower than that of traditional Bragg fiber with the same parameters.When the alternate dielectric layer N=13,the Bragg fibers array can be realized with low crosstalk of below-30 d B for 55.4 km space division multiplexing propagation,and the confinement loss of its center core is only 0.1 d B/km.In addition,it is proved that the crosstalk and confinement loss of the seven-core fiber can be further reduced by increasing the number of alternate dielectric layers.The fabrication method of the seven-core fiber is presented.The analytical methods and conclusions in this dissertation provide some constructive suggestions for the design of optical devices such as Bragg fibers array laser and omnidirectional emitting laser.（2）In this dissertation,an air-trenches/holes assisted depressed-core 12-mode fiber is proposed.The fiber is characterized by some asymmetric air trenches and air holes around the step index core.The air-trenches and depressed-core can produce great contribution in separating the non-degenerated LP modes and the degenerated spatial modes,thus suppressing the crosstalk efficiently.The simulation results indicate that this fiber can support 12 spatial modes with the effective index difference between adjacent LP modes larger than 1.03×10-3 and the effective index difference between adjacent spatial modes larger than 1.24×10-4.The bending loss values of the proposed fiber can be satisfied with the ITU-T recommendations of G.654.The proposed fiber shows small birefringence effect and it is feasible to be fabricated with the Stack-and-Draw technique.The proposed fiber possesses stable comprehensive broadband characteristics such as large effective refractive index difference,small chromatic dispersion,and large effective mode area over the whole C and L band.The few mode fiber has great application potential in 2×2 MIMO mode division multiplexing and mature wavelength division technology,thus further enlarging optical communication capacity and simplifying the systems complexity.（3）In this dissertation,a nanopore-assisted 7-mode fiber is proposed.The 7-mode fiber consists of a nanopore,a Ge O2-doped core and a silica cladding.The nanopore produces great contribution in separating the non-degenerated mode groups（MGs）,thus simplifying the MIMO process.The simulation results indicate that the 7-mode fiber can support 7 MGs with the min effective index difference of 2.2×10-3 at the wavelength of1550 nm,which breaks through the trade-off between mode spacing and the number of MGs.In addition,the min effective index difference of larger than 2.0×10-3 can be achieved over a wide wavelength range from 1500 nm to 1650 nm.In addition,in the wide wavelength range from 1500 nm to 1650 nm,the dispersion of all MGs is less than42 ps/nm/km,and the effective mode field areas of 7 MGs（except MG4）are larger than109μm2.The bending-induced confinement loss of the highest vector mode is lower to1.9×10-9 d B/m at the bending radius of 30 mm.The 7-mode fiber can be readily fabricated through normal MCVD technology,drill method and drawing process.The few mode fiber is targeted at applications in 4×4 MIMO mode division multiplexing and mature wavelength division technology,thus enlarging the capacity of optical communication systems and simplifying the systems complexity.（4）In this dissertation,the model of the nanopore assisted seven-mode fiber-optical antenna array multiplexing optical communication system is established,and two schemes of designing a conic lens pair or a positive-negative conic lens pair to optimize the transmission performance of the system are proposed.Based on the three-dimensional vector refraction and reflection theory,the ray tracing and transmission efficiency of the system are studied.Combined with the transmission matrix method,the multi-layer film with high total reflection is designed for the optical antenna array.The results show that after several practical factors such as the dispersion,the transmissivity and chamfering are considered,two schemes can still increase the transmission efficiency of single-channel in the modeled system to 92.37%and 95.54%.The two schemes proposed in this dissertation can match the optical antennas array with different sizes,which is more practical in improving the transmission efficiency of the system.In contrast,although the transmission efficiency of the system with a conic lens pair is slightly lower,it does not have internal chamfering and the machining process is simpler. |
