Research On Reconfigurable Optical Waveguide Encoder Based On Fluorinated Photopolymer

Today’s social communication technology is booming.In reconfigurable communication systems,optical switching networks have received more and more attention as effective alternatives to electrical switching networks.Free-space optics and planar optics are used to implement a variety of two main types of optical cross-connect switching networks.Compared with free-space optical switching structure,planar optical switching network has higher integration and faster signal response,which is more suitable for single-chip multifunctional photonic modules with good compatibility and high efficiency.In particular,a thermo-optic（TO）device with a planar optical waveguide structure is more useful for implementing an on-chip planar lightwave circuit as a key part of an optical code division multiple access（OCDMA）network system.With the ability of asynchronous operation,capacity expansion and enhanced privacy,these highly integrated optical modules for OCDMA technology are playing an increasingly important role in contemporary society.The Multimode Interference（MMI）unit structure can provide a more compact architecture.The interaction area between the electrodes and the waveguide is more suitable for large-scale and efficient optical coding systems for multifunctional photon integration modules.This article uses MMI as the basic structural unit,and innovatively proposes two structures of planar reconfigurable optical waveguide encoders,which respectively encode the phase and wavelength of light,and work on the working principles and functions.Based on detailed analysis and discussion,epoxy-terminated copolycar-bonate（AF-Z-PC EP）and polymethyl methacrylate（PMMA）were used as waveguide core and cladding materials.The electrode structure is introduced in the integrated waveguide chip to realize the device’s dual choice of signal and wavelength.The main work of this paper is summarized as follows:Theoretically,MMI was used as the basic unit,and the two structures of phase and wavelength encoder were designed respectively.The two structures were simulated using Rsoft software.1.Regarding the phase encoder:a structure formed by cascading five-MMI couplers with the same structure is designed,and the length of the entire device is 1cm.The basic functional unit of each MMI coupler could be controlled by the corresponding heating electrode to achieve the channel selection and switching characteristics.We optimized and simulated the structural parameters of the MMI unit and the added electrodes,and finally determined the length and width of the MMI basic unit to 1918μm and 36μm,respectively.The relationship between the output efficiency change of the MMI and the electrode heating power at different electrode lengths was explored,and the electrode length Le was finally set to 300μm.At this time,the power of the electrode heater was less than 20 mW.By controlling the driving power of the corresponding five electrodes,the state of the chip’s binary-coded optical switch matrix was??analyzed and defined,and the transmission matrix converted between different power matrices was obtained.2.About the wavelength encoder:Design a wavelength encoder structure formed by cascading MMI and delay lines of 7 different structures.After optimizing the size and structure of the unit element and simulating the function of the partial wave,after finally realizing the input of the band with a center wavelength of 1550 nm,the output of the output could be modified the electrodes on the input MMI and the delay line.The functions were centered on 1538 nm and 1564 nm,and the output wavelengths were 3.2 nm and 7.2 nm.Experimentally:Based on the basic technology of polymer planar optical waveguides,we prepared thermo-optical reconfigurable MMI phase encoders formed by cascading multi-mode interferometers.The light absorption characteristics of the fluorinated photopolymer material used in the core were characterized and plotted.According to the actual structural characteristics of the device,a PCB board is designed and prepared that conforms to the structural characteristics of the device and is convenient for actual testing.A test system was built for measuring.The light from the tunable laser at a wavelength of 1550 nm is coupled into the chip through a single-mode fiber,and then the output optical signal is collected into an optical power meter or an infrared photodetector connected to an oscilloscope through another single-mode fiber.The adjustable coding function of the device is modulated by the electronic control system（ECS）through electrode heaters,and five MMI-based switches are modulated by corresponding electrical signals.When an electric signal corresponding to the driving power control matrix A₁ was loaded in the electrode heater,the near-infrared field photo（×80）of the relevant output of the chip was measured by an infrared CCD camera,and the crosstalk between O₁ and O₂ was measured as-32.2 dB,and the crosstalk value between O₃ and O₄ was-31.5 dB,and the maximum crosstalk in adjacent channels was less than-30 dB.A small square wave voltage signal with a frequency of 400 Hz generated from the signal generator wass loaded on the electrode heater corresponding to E₅,and then a 150 mV DC bias was loaded to increase the A₂[1001]state,the switching time including rise time and fall time were both close to 220μs.With the same code in the state of A₂[1001],when the varying direct current P₅ is continuously loaded on the corresponding electrode heater,the relationship between the driving electric power and the output optical power of different channels was measured.You can convert the encoding of A₂[1001]to A₂[1010]state.The measured extinction ratio was 21.5 dB.The insertion loss of Channel 1 was 7.1 dB.When the switching matrix was??set to the coding state A₂[1100],the output power of the O₂ channel was measured in a temperature range of 20 to 55°C.The change in device insertion loss over this temperature range was less than 1.5 dB.This device had good performance,realizesed the coding function of the switching matrix,and could be adjusted and applied to the implementation of an OCDMA network encoder.