电光聚合物调制器的发展(特邀)

Development of Electro-Optical Polymer Modulators(Invited)

作为电信号到光信号的转换枢纽,高性能电光调制器在高速光互连系统的升级换代以及促进集成光子学发展等方面具有重要的科学意义与广袤的实用前景。电光聚合物调制器在近年来获得了高度关注,其具有调制电压<0.1 V(器件长度为1 cm)、调制带宽>150 GHz、易与硅、SiN、金属等衬底异质集成等优点。本文深入剖析了电光聚合物材料及其调制器的发展历程。首先,综述了电光高分子材料的研究进展,重点介绍了几种代表性的电光聚合物,并探讨了材料结构与性能之间的关系;其次,着重介绍了基于电光聚合物的马赫曾德尔干涉(MZI)型电光调制器和微环调制器,详细分析了其在国内外的研究现状,并对这两类调制器的研究现状进行了总结;最后对材料与器件的商用化进行了展望。

Significance The information industry has profoundly affected people’s lives due to advancements in technologies such as 5G,optical computing,the internet,sensing technologies,artificial intelligence,and multimedia/data/signal processing.These innovations have spurred major changes and opportunities within the optoelectronic device industry.One critical challenge is the demand for high-speed communication,which requires the rapid transformation of electronic signals into optical signals.Progress The heart of this transformation lies the development of high-performance electro-optical(EO)modulators.These devices translate electrical signals into the optical realm,which facilitates the transmission of high-bandwidth information while minimizing electrical interference.EO modulators are essential in optical communication systems,where they regulate optical signals.As the demand for faster EO signal conversion grows,the requirements for EO modulators become increasingly stringent.Key criteria include:1)low drive voltage;2)minimal optical loss;3)low energy consumption;4)high bandwidth,among others.EO polymers offer distinct advantages over other materials for modulator fabrication.They can achieve an EO coefficient(r33)exceeding 300 pm/V in neat-film and over 100 pm/V in device.In contrast,commercial lithium niobate,a common modulator material,typically shows lower EO coefficients.The high r33 value of EO polymers indicates their ability to achieve significant modulation with lower voltages,which makes them highly efficient for high-speed applications.Additionally,EO polymers exhibit a low microwave/optical velocity mismatch,which simplifies the design of modulator electrodes for achieving rapid modulation.These characteristics enable EO polymer modulators to operate at frequencies exceeding 100 GHz,ideal for applications requiring rapid data transmission and processing.Moreover,EO polymers can be processed and integrated with various materials and components,including semiconductor light sources,detectors,low-voltage CMOS drivers,and both inorganic and polymeric waveguides.This integration capability enhances the versatility of EO polymer modulators,thus allowing for customized optimization to meet specific application and device configurations.In 2002,Mark Lee and his colleagues demonstrated ultra-high bandwidth modulation ranging from 25 to 145 GHz in EO polymer MZI modulators(Fig.12).With advancements in materials science,the EO coefficient of EO polymers can exceed 100 pm/V,resulting in a VπL of around 1 V·cm(Fig.13).Integrating EO polymers with silicon slot waveguides helps foster the development of more compact modulators.Modulation speed of up to 112 Gb/s has been realized using a 1.5 mm long slot waveguide.EO polymers have also been combined with metal plasmonic structures.By filling the polymer into the metal slots,both electric and optical fields can be concentrated within the metal slots,thereby enhancing the EO interaction.Modulators with an effective phase shift length of only 6μm correspond to Vπ=10 V and a modulation bandwidth of 70 GHz.Additionally,ring resonator modulators with high bandwidth and high EO tunability have been developed.Conclusions and Prospects Based on advancements in organic molecular science,guided optics,and microwave theory,EO polymer materials,and their modulator structures have made enormous progress over the past decade.In terms of materials,scientists have systematically addressed several challenging issues through innovations in polymer compositions,chromophores,and host materials.These advancements provide a robust material foundation for the practical implementation of related devices and chips.In terms of device development,researchers from Japan,Germany,Switzerland,and China have successively pioneered“cladding-free structures”,“ultra-thin silicon structures”,“silicon-based slot structures”,“metal plasmonic structures”,and“silicon nitride micro-ring structures”.These innovations fully leverage the unique advantages of EO polymers,including high EO coefficients,broad intrinsic bandwidths,and good compatibility with multiple material systems.These breakthroughs have effectively overcome the limitations of traditional modulation techniques in terms of energy consumption and bandwidth.