Research On Polymer Optical Waveguide Mode Converters And Switches

In recent years,with the rapid growth of internet traffic and the emergence of new applications,the need to increase the transmission capacity of optical fibers is very urgent.The mode-division-multiplexing?MDM?technology is currently considered as an effective method to increase the transmission capacity.In the mode-division-multiplexing system,each mode is an independent transmission channel.The mode converters that realize the mutual conversion between the fundamental mode and higher order modes can play an important role in the mode-division-multiplexing system.Mode converters realized by electro-optical or thermo-optical effects can be used as reconfigurable mode switches to flexibly realize mode conversion.This dissertation takes polymer optical waveguides as the research topic,and aims at the realization of broadband mode converters and mode conversion switches with low switching voltage.The research contents of this dissertation are summarized as follows:?1?To improve the bandwidth of mode coverters,a length-apodized long period grating is employed to increase the operating bandwidth of the grating-based waveguide mode converter.Using organic polymer materials,we designed and fabricated LP₀₁-LP_11a mode converter based on sidewall grating and LP₀₁-LP_11b mode converter based on surface grating.The fabricated LP₀₁-LP_11a and LP₀₁-LP_11b mode converters provide the conversion efficiency higher than 99%over a bandwidth of¹20 nm and¹50 nm,respectively,or the conversion efficiency higher than 90%over a bandwidth of¹80 nm and³00 nm,respectively.And these two mode converters are insensitive to temperature and polarization variations.The ultra-broadband mode converters can be integrated with other devices and play an important role in MDM system.?2?To pole the electro-optic polymer films,the scheme that using graphene as poling electrodes is proposed.The graphene film embedded in a low-index-contrast waveguide does not induce a significant loss to the transverse-magnetic?TM?waves,so graphene electrodes can replace conventional metal electrodes to realize the poling of organic electro-optic materials.Without using buffer layer between elctro-optic polymer film and electrode,the poling voltage is largely reduced.410 V voltage is applied to pole 3.8?m thick film,after poling,the electro-optic coefficient can be 82 pm/V in1550 nm,and in 1300 nm,the electro-optic coefficient can be 110 pm/V.Moreover,the graphene electrodes do not introduce excessive loss after poling,and then the graphene electrodes can be used as modulation electrodes.Using the graphene electrodes to pole the electro-optic polymer materials can simplify the design and fabrication of electro-optic devices.?3?In order to solve the problem that the graphene supported by PMMA film cannot be transferred onto the substrate that is not resistant to acetone,the scheme that alcohol-soluble supporting materials are used to replace PMMA to complete the transfer of graphene is proposed.Alcohol-soluble PVP-co-PMMA and PMMA double-layer films are used to realize the transfer of graphene.This transfer method can achieve large-area and high-quality graphene films.Graphene films are transferred onto the electro-optic polymer film by using this transfer method,after poling,the PVP-co-PMMA and PMMA double-layer films can be peeled off by the ethanol solvent.This transfer method can transfer the graphene films onto substrates that are not resistant to acetone,such as electro-optic polymer films and organic semiconductor materials,and expands the application of graphene films.?4?In order to obtain mode switches with low voltage and broad bandwidth.The scheme of electro-optic mode switch designed by using graphene films and organic electro-optic polymer materials is proposed.Utilizing the property that graphene electrodes does not induce a significant loss to the TM waves in the low-index-contrast waveguide and the advantage that graphene electrodes can efficiently pole organic electro-optic polymer films,LP₀₁-LP_11a and LP₀₁-LP_11b1b mode switches based on graphene grating electrodes and electro-optic materials are designed.By optimizing the size of core,refractive indices of cladding and core materials and the design of grating electrodes,the mode switches with low voltage?low loss and high conversion efficiency are designed.And the ultra-broadband mode switch is designed by using length-apodized long-period grating electrode.