| In recent years,emerging technologies such as big data,cloud computing and 5G communication have developed rapidly,and human society has entered a new information age.The age not only brings great convenience to human life and facilitates human communication,but also makes good interconnect with each other and develop toward the direction of intelligence.These changes promote the demand of modern society for information transmission and processing.It will urge the development of optical network to high integration,low power consumption,big bandwidth,and low latency.As an important component in the field of optical network,optical waveguide devices have important application potential and have been widely paid attention and studied all over the world.As for optical waveguide devices,their structures are various,and different structures can realize the personalized modulation of optical signals.In general,different functions can be achieved by designing different structures.Among the many optical waveguide structures,MZI(Mach-Zehnder Interferometer)is a common and simple structure in the design of optical waveguide devices.Because of its simple production process,it has been widely applied in optical switches,optical sensors,filters,wavelength division multiplexers,and mode division multiplexers,etc.Based on the MZI structure and the thermo-optic effect,different types of optical switches(applying at1550 nm and 850 nm)and optical sensors(length-asymmetric,width-asymmetric and refractive index-asymmetric)are designed,in this paper.Moreover,the polymer material has many advantages,such as high thermo-optic coefficient,low cost,biological compatibility,and easy to fabricate.This paper utilizes these advantages of polymer materials to reduce the power consumption of thermo-optical switches or increase the sensitivity of temperature sensors.The work include structural design,theoretical analysis,fabrication process,and functional measurement,etc.The main work of the paper is summarized as follows:1.In the stage of theoretical analysis,we first take the theory of planar optical waveguide as the basis,by means of the effective refractive index calculation method to infer the mode features of asymmetric three-layer planar waveguide,rectangular waveguide,and ridge waveguide.Then the thermo-optic effect involved in the optical waveguide devices are introduced in detail and its formulas are analyzed.Finally,MZI structure and its principle are introduced based on the optical switch.2.At 1550 nm wavelength,polymer optical waveguide thermo-optic switch was fabricated on silicon substrate by traditional semiconductor process.By using polymer material NOA 73 with high thermo-optic coefficient as the waveguide core and the inorganic material Si O2with high thermal conductivity as the waveguide under-layer,the power consumption is reduced and the response time is reduced at the same time.In addition,we introduced an air trench structure on the sides of two parallel transmission arms and optimized the electrode width to further reduce the power consumption.During measurement,the power consumption is 1.7 m W,the extinction ratio is 23.27 d B,the rise time and fall time are 177.5?s and 175.7?s,respectively.3.At 850 nm wavelength,the influences of the waveguide core size,upper/under-layer thickness and electrode width on the performances of thermo-optic switch are studied.And then thermo-optic switches with different electrode widths are fabricated using the optimized waveguide sizes.The cladding and core layers of the waveguide are fabricated by using all polymer materials and only by wet etching,which greatly simplifies the process of device fabrication.The device is made of all polymer materials,which is expected to be used in flexible display,wearable devices and other fields.During measurement,the power consumption is 4.5 m W,the extinction ratio is 26.5 d B,the rise time and fall time are 400.0?s and 600.0?s,respectively4.A length-asymmetric temperature sensor based on MZI structure is designed.Although the large length difference is beneficial to increase the sensitivity of the sensor,it will also cause the loss and the size of the device increase.Firstly,the optimal length difference is obtained theoretically.Then the sensors with different length differences and waveguide core materials are fabricated to verify the influence of length difference between the two interference arms of MZI and waveguide core materials on the temperature sensitivity of the devices.Finally,through optimization,the maximum sensitivity of the designed temperature sensor of-431 pm/°C can be obtained in the range of 25°C-75°C.The structure of the temperature sensor has many advantages of simple structure,easy to fabrication,low cost,and large temperature detection range.These advantages make it more widely used.5.A width-asymmetric temperature sensor based on MZI structure is designed.The influence of the width differences between the two interferometer arms and the waveguide upper-layer materials on the sensitivity of the sensor is studied by the full-vector finite lelment mode solver.Finally,through optimization,the maximum temperature sensitivity of 30.8 nm/°C can be obtained in the range of 25°C-27°C.This increases the sensitivity of the temperature sensor by orders of magnitude,and thus makes it extremely sensitive to the change of ambient temperature.This sensor has the characteristics of high sensitivity,simple structure,low cost and flexibility.But also because of its large sensitivity,the temperature range is limited.It can be applied to biological and chemical sensing field.6.A refractive index-asymmetric temperature sensor based on MZI structure is designed.The sensitivity to temperature is demonstrated that when the two interferometer arms are filled with two materials with different thermo-optic coefficient and similar refractive indices.In this design,for the application of microfluidic system,we set the test temperature to change from 37.0?to 37.6?to meet the temperature range required by the culture environment in the process of biological culture.During the fabrication of the device,PMMA grooves are etched and then the asymmetric waveguide structure was obtained by twice filling different core materials.Two polymer materials Epo Clad and NOA 73 which have silimar refractive index are selected to realize the lower loss caused by material conversion in the transmission process of the optical signal.During measurement,a typical fabricated device present a large temperature sensitivity of-1.685°C-1,the rise time and the fall time are 511.6?s and 551.9?s,respectively.This result enables the designed sensor to be applied to real-time and high-precision monitoring of the temperature of biological culture environment. |
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