| Optical switches and arrays are key components in optical interconnection, optical add/drop multiplexer and optical router, which plays an important role in optical communication systems. Compared with inorganic electro-optic materials, poled polymer materiallas have wide application in the fabrication of electro-optic devices, such as electro-optic switch and electro-optic modulator, due to the advantages including high electro-optic coefficient, fast response, easy control on refractive index, low-cost and simple processing technology. Micro-ring resonators (MRRs) are widely used as filtering, multiplexing/demultiplexing, etc, due to small dimension, easy phase match, etc. In view of the above considerations, this paper will investigate MRR-assisted electro-optic switch and wavelength-selective passive optical switch array based on filtering characteristics of MRR, design novel device structure, propose analysis theory and optimization method, and calculate and simulate device performance. This work will provide certain basis for the fabrication of such kind of or similar devices.The meanings for studying polymer MRR switch and array was first described. The functions of optical switch and array in optical communication networks were discussed, and the classification of optical switch was given in detail. Research progresses on two kinds of non-reasonance waveguide optical switches were demonstrated, including non-reasonance electro-optic switch and non-reasonance thermos-optic switch. Furthermore, research status as well as characteristics of reasonance switch and array was presented. In the following, for the rectangular waveguide structure to be used in the proposed devices, mode characteristics were analyzed on the five-layer slab waveguide on high-index substrate, double-metal-cladding slab waveguide, and medium absorption rectangular waveguide using perturbation method and differential method. Through thorough theoretical, derivation, expressions of mode characteristic equation and amplitude attentuation coefficient were obtained for all the waveguide structures. Microring resonator thwory was available to lay a basis for the optimical design and analysis similation of MRR optical switch and array.Utilizing coupled mode theory, microring resonance theory and electro-optic modulation theory, three kinds of scalable optical switches or arrays were designed, analyzed and simulated. Details are below:First, a kind of polymer optical switch using N-th order microring resonator side-coupled Mach-Zehnder interferometer (MRR-SC-MZI) was designed and optimized. Formulation and expression of output power, insertion loss, crosstalk and 3 dB modulation bandwidth were derived, and detailed design and optimization were carried out unde 1550 nm wavelength. Dependence of characteristics on N was summarized. Analytical results indicate that all the devices for N≥1 can perform normal switching function, and 8≥N≥ 2 is preferred for dropping the driving voltage below 5 V. For the seven MRR-SC-MZI EO switches (N=2～8), their cross-state voltages are within 0-2.32 V, their bar-state voltages are within 0.96-4.83 V; their insertion losses are within 0.35-0.85 dB at bar state, whereas those are within 0.14～1.70 dB at cross state; their crosstalk are within -20.79～-31.11 dB at bar state, whereas those are within -13.86～-20.36 dB at cross state; their 3-dB electrical bandwidth are within 18.5-28.0 GHz, and 3-dB optical bandwidths for the two output ports are within 18.1-40.0 and 32.0-55 GHz, respectively. Comparison indicates that the driving voltages of the proposed MRR-SC-MZI switching devices are 10-250 times smaller than those of the traditional MZI EO switches with the same EO region length, device length and structural parameters.Second, a kind of (2N+1)-th order polymer microring resonator Mach-Zehnder interferometer (MRR-MZI) electro-optic (EO) switch was designed and optimized. Formulas and expressions of output power, insertion loss and crosstalk were derived. Detailed design and optimization were carried out under the wavelength of 1550 nm. Relation between switching characterictics and N was studied. Analytical results indicate that, except for the first order MRR-MZI EO switch (N=0), other devices for N≥1 can all perform normal switching function, and 5≥N≥2 is preferred for dropping the crosstalk below -10 dB. For the four MRR EO switches (N=2～5), their switching voltages are 0.99,0.73,0.57 and 0.47 V, respectively; their insertion losses are within the range of 1.15～2.26 dB at bar state, whereas those are within the range of 1.95～2.42 dB at cross state; their crosstalk are within the range of -11.04～-17.82 dB at bar state, whereas those are within the range of -10.34～-12.51 dB at cross state. Compared with the traditional MZI EO switch, the voltage-length product (0.21 V-mm) of this switching element is decreased by ～111.7 times under the same waveguide parameters.Third, based on three different basic routing elements, including cross-coupling one microring resonator (CCO-MRR), cross-coupling two microring resonators (CCT-MRR) and parallel-coupling one microring resonator (PCO-MRR), three kinds of four-port optical routers with the same routing function were designed. The three arrays can be N-stage cascaded, through which the operation wavelength number can be increased to 3N. The structural parameters of the routing elements were optimized Detailed routing topologies of the three routers are presented, and a thorough comparison among them is made on their routing performances. The used MRR numbers of the CCO-MRR-based and PCO-MRR-based routers (4 rings) are half of that of the CCT-MRR-based router (8 rings); the PCO-MRR-based router depicts the minimum insertion loss (0.02-0.6 dB); the CCT-MRR-based router reveals the minimum crosstalk (<-38 dB) and the best spectral selectivity; the CCT-MRR-based and CCO-MRR-based routers have the similar perfect N-stage cascading structure (still with four ports) for expanding the number of wavelength-channel to 3N; however, the PCO-MRR-based router cannot be cascaded easily because of too many unavoidable waveguide crossings.Regarding the MRR optical switch and array, the proposed scalable generic structure model, related formulations and analysis method were not reported in detail, and therefore they are of certain novelty and can provide model and theoretical basis for the design, simulation and fabrication of specific device. The novelties of this paper are as below:(1) Generic model and analysis theory were proposed for a kind of polymer optical switch using N-th order microring resonator side-coupled Mach-Zehnder interferometer (MRR-SC-MZI). Dependence of characteristics on N was summarized. The driving voltages of the proposed MRR-SC-MZI switching devices are 10～250 times smaller than those of the traditional MZI EO switches with the same EO region length, device length and structural parameters.(2) Generic model and analysis theory were proposed for a kind of (2N+1)-th order polymer microring resonator Mach-Zehnder interferometer (MRR-MZI) electro-optic (EO) switch. Relation between switching characterictics and N was obtained. For the four MRR EO switches (N=2～5), their switching voltages are below 1.0 V. Compared with the traditional MZI EO switch, the voltage-length product (0.21 V-mm) of this switching element is decreased by ～111.7 times under the same waveguide parameters.(3) Based on three different basic routing elements, three kinds of four-port optical routers with the same routing function were designed. A novel N-stage cascading structure was presented, through which the operation wavelength number can be increased from 3 for the 1-stage array to 3N for the N-stage array. The structural parameters of the routing elements were optimized Detailed routing topologies of the three routers are presented, and a thorough comparison among them is made on their routing performances. The used MRR numbers of the CCO-MRR-based and PCO-MRR-based routers (4 rings) are half of that of the CCT-MRR-based router (8 rings); the PCO-MRR-based router depicts the minimum insertion loss (0.02-0.6 dB); the CCT-MRR-based router reveals the minimum crosstalk (<-38 dB) and the best spectral selectivity; the CCT-MRR-based and CCO-MRR-based routers have the similar perfect N-stage cascading structure (still with four ports) for expanding the number of wavelength-channel to 3N; however, the PCO-MRR-based router cannot be cascaded easily because of too many unavoidable waveguide crossings. Therefore, the proposed stuctures have potential applications for routing and switching wideband optical signals in complex optical networks-on-chip.
|
PDF Full Text Request