| Optical switch and array have important applications in optical communicationnetworks, such as Micro-opto-electro-mechanical Systems (MOEMS) switch, liquidcrystal optical switch, and so on. Compared with these optical switches, the opticalswitch using waveguide has obvious advantages and potential applications, because ithas no mechanical moving parts, so it is more reliable. Thermo-optical switch is oneof the hot areas of the waveguide switch, it has some advantages of small size,scalability, good stability. Response time and power consumption are keyperformance of thermo-optical switch, and developing a thermo-optical switch withfast response, low power consumption is very important.In recent years, in order to speed up response time and reduce powerconsumption, Si/SiO2thermo-optic switch and polymer thermo-optical switch havebeen reported. Silicon has a large thermal conductivity, therefore, Si/SiO2thermo-optical switch has faster response, but its switching power consumption isgenerally higher. Although in order to solve the shortcoming about large powerconsumption in inorganic waveguide optical switch, various of waveguide structuresof thermo-optical swiches have been studied, such as a suspended phase armwaveguide, the fabricating process is extremely complex, and the experimental resultsare not very satisfactory. Compared with inorganic materials thermo-optical switch,polymer thermo-optical switch has low power consumption and simple fabricatingprocess, but it has slower response time of milliseonds.In order to fabricate a switch with low power consumption and fast responsespeed, the advantages of both organic and inorganic have been used. In this paper, thepolymeric materials of SU-8and polymethyl methacrylate (PMMA) as the core andthe upper cladding layer of the waveguides, respectively, an inorganic material ofSiO2were used as the lower cladding layer of the waveguides on the Si substrate, we fabricated varieties of organic/inorganic hybrid thermo-optical switches. On the onehand, SU-8has larger thermal-optical coefficient of1.8×10-4K-1, which can reduce thedriving power of the device, on the other hand, the refractive index differencebetween PMMA (n3=1.4798@1550nm) and SU-8(n1=1.5742@1550nm) is bigenough. The upper cladding layer was fabricated as thin as2μm, which could speedup the heat conduction between electrode and the core, and because of the largethermal conductivity of SiO2, which would accelerate heat dissipation of the core, onthis way, it was conducive to shorten the rise and fall time of the device. The mainwork and innovation of this paper is as follows:1、The full vector, half-vector, scalar eigenvalue equations and their boundaryconditions were obtained from the Maxwell’s equations, and their derive their finitedifference equations were also ratiocinated by finite difference method. The opticalfield intensity distribution and the mode effective refractive index of three-slabwaveguide had been resolved from the horizontal Helmholtz equation. Utilizing theanalytical method of solving three-slab waveguide mode, the effective refractiveindex of the rectangular waveguide was obtained combining with effective indexmethod, in addition, all-vector, semi-vector and scalar finite difference method werealso analysised for comparing. The analytical method of ridge waveguide was same asrectangular waveguide. Using the analytical method and semi-vectorial finitedifference method, two-dimensional slot waveguide modes were analyzed, and usingsemi-vectorial finite difference method, three-dimensional slot waveguide wasanalyzed. Heat conduction equation in general form and steady form and their finitedifference form were ratiocinated.2、Polymer has some characteristices such as big thermo-optical coefficient, lowthermal conductivity, simple fabricating process and low cost, while the inorganicmaterial has a relatively small thermo-optical coefficient, big thermal conductivitycoefficient, relatively complex preparation process and high cost. So the organic-inorganic composite waveguide structure was proposed, and different types ofMach-Zehnder interferometer (MZI) thermo-optical switch was fabricated:1) Makinguse of the advantages of organic and inorganic materials,1×1MZI thermo-optical switch was fabricated by wet etching process. The core, upper cladding and undercaladding of the waveguide were SU-8, PMMA and SiO2, respectively. Thethickneses of upper and lower cladding were3μm and2μm by theoretical optimizing,respectively. Calculating with finite difference method, the light field and the heatdistribution of the optical switch was obtained. The driving power was only4mWand the extinction ratio was up to29.6dB at1550nm, the rise time and fall time were73.5μs and96.5μs, respectively.2)1×2organic-inorganic hybrid waveguidemultimode interferometer (MMI) MZI thermo-optical switch was proposed. Theswitch power is9.6mW, and the crosstalk is-23dB, the rise time and fall time were264μs and444μs, respectively.3)1×2organic-inorganic hybrid waveguidedirectional coupler (DC) MZI thermo-optical switch was proposed. The switch poweris10.7mW, and the crosstalks under bar state and cross state were-11.5dB and-23dB. The rise time and fall time of port1were170μs and560μs, and the rise time andfall time of port2were200μs and560μs.4)2×2organic-inorganic hybrid waveguideDC-MZI thermo-optical switch was proposed. The switch power is7.2mW, and thecrosstalks under bar state and cross state were-22.8dB and-26.5dB.3、 In order to study the capacity of noise tolerance characteristics oforganic-inorganic hybrid waveguide thermo-optical switch, a driving-noise-tolerantmethod was proposed on1×1MZI thermo-optical switch and2×2DC-MZIthermo-optical switch. When ignored the changes caused by temperature fluctuations,a1×1MZI device with a extinction ratio up to32.6dB was chooseed to study thedriving-noise-tolerant characteristic. Experimental results showed that when theacceptable minimum extinction ratio was bigger than10dB, the maximum allowablenoise amplitude was1.1V. For2×2DC-MZI thermo-optical switch, which crosstalkwere-22.8dB and-26.5dB on cross state and bar state, respectively. When a squarewave noise signal with a frequency of2KHz and a peak-peak value of2.5V wassuperimposed on driving signal, the smallest extinction ratio was about11.3dB.When a square wave noise signal with a frequency of5KHz and a peak-peak value of2.5V was superimposed on driving signal, the smallest extinction ratio was about24.1dB. The minimum extinction ratio increased with the increasing of peak-peak value of noise. When the noise amplitude was immovable, the minimum extinctionratio increased with the decreasing of frequency. However, when the frequency of thenoise is large enough, the change of the minimum extinction ratio almost did notchange, it was proved the device is insensitive to high frequency signals.4、An organic-inorganic hybrid total internal reflection2×2switch was porposed.When the signal input from input port1, the crosstalk were-24dB and-26dB oncross state and bar state, respectively. When the signal input from input port2, thecrosstalk were-25.7dB and-26.3dB on cross state and bar state, respectively. Thepower consumption of the switch was about100mW when the extinction ratio wasgreater than26dB. By optimizing the size of the device, the power consumption wasreduced to59.7mW, the crosstalk on cross state and bar state were-27.6dB and-35dB, respectively. When the total internal reflection switch matrix is blocking, itrequires2×(N-1)-1total internal reflection2×2switches. When the total internalreflection switch matrix is non-blocking, it requiresN2total internal reflection2×2switches.5、 As the general MZI switch usually has very narrow spectrum, Athermo-optical switch with broad spectrum was proposed. A3-dB coupler composedby phase-generating coupler (PGC) was used to replace general DC3-dB coupler,which phase difference was also changed with the wavelength drift, and thischaracteristic could compensate the drift of modulation region. Simulation resultsshowed that the two output ports of designed models had a wavelength range of110nm, in which the extinction ratio was greater than30dB. |
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