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JOURNAL OFCHEMISTRYMaterialsFeature ArticleFrom molecules to opto-chips: organic electro-optic materialsLarry R. Dalton,*ab William H. Steier,c Bruce H. Robinson,a Chang Zhang,b Albert Ren,bSean Garner,c Antao Chen,c Timothy Londergan,a Lindsey Irwin,a Brenden Carlson,aLeonard Fifield,a Gregory Phelan,a Clint Kincaid,a Joseph Amenda and Alex JendaDepartment of Chemistry, University of Washington, Seattle, WA 98195–1700, USAbLoker Hydrocarbon Research Institute, University of Southern California, Los Angeles, CA90089–1661, USAcDepartment of Electrical Engineering, University of Southern California, Los Angeles, CA90089–0483, USAdDepartment of Chemistry, Northeastern University, 360 Huntington Avenue, Boston, MA 02115,USAReceived 1st April 1999, Accepted 26th May 1999Recent advances in polymeric electro-optic materials andby electronic state lifetimes in contrast to polymeric modu-device fabrication techniques have significantly increasedlators where response times are essentially limited by electronicthe potential for incorporation of these materials andphase relaxation times (corresponding to a few tens of femtose-devices into modern high bandwidth (fiber and wireless)conds). Polymeric modulators also avoid energy loss that istelecommunication, information processing, and radar sys-normally associated with absorptive processes. Since suchtems. Charge transfer p-electron chromophores charac-modulators operate in regions of high transparency, very littleterized by molecular first hyperpolarizability (second orderheating results. Light scattering is typically the only opticaloptical non-linearity) values approaching 3000×10−30 esuloss mechanism of consequence.have been synthesized. Elucidation of the role of intermol-Of course, bandwidth by itself is not enough to ensure theecular electrostatic interactions in inhibiting the efficientwidescale commercial utilization of polymeric electro-optictranslation of molecular optical non-linearity to macro-modulators. Other crucial material characteristics include thescopic electro-optic activity has permitted systematic modi-magnitude of electro-optic activity (which translates into drivefication of materials to achieve electro-optic coefficientsvoltage, Vp, requirements), optical loss, stability (includingapproaching 100 pm V−1. Improvements in the optical lossthermal, mechanical, chemical and photochemical stability),of polymeric materials at wavelengths of 1.3 and 1.55 mmand ease of integration with silica fiber optics and very largehave been effected. Mode matching of passive transmissionscale integration ( VLSI) semiconductor electronic circuitry.and active electro-optic waveguides has been addressed,Moreover, each application of electro-optic modulators,permitting a dramatic reduction in insertion loss. Theranging from cable television (CATV ),1 to backplane intercon-putative ability of polymeric electro-optic materials to benects between high-speed parallel processors,2 to gyroscopesefficiently integrated with very large scale integration semi-conductor electronic circuitry and with passive optical for missile guidance,3 has different material requirements.circuitry has been demonstrated. Several devices of varyingRequirements are summarized for several applications indegrees of complexity have been fabricated and evaluatedTable 1. It is beyond the scope of this article to discuss into operational frequencies as high as 150 GHz. The oper-detail the numerous applications that are currently beingational stability of polymeric devices is very competitiveexplored for polymeric electro-optic modulators; however, inwith devices fabricated from lithium niobate and galliumthe course of it we will illustrate several sophisticated devicearsenide.structures and their associated performance characteristics.Our attention is restricted to polymer electro-optic modulatormaterials that are being developed for application at theApplications of electro-optic materials: from CATVtelecommunication wavelengths of 1.3 and 1.55 mm.to gyroscopesLike the silicon diode, electro-optic modulators can beconfigured to perform a variety of functions from electrical toThe demand for electro-optic modulators has, to a largeoptical signal transduction, to optical switching, to millimeterextent, been driven by the desire for greater bandwidth, forwave signal generation, to optical beam steering, to radiofre-high capacity local area networks (LANs), for video trans-quency (also microwave and millimeter wave) detection, tomission, for optical detection of radar and phased-array radar,phase control, to power splitting, to wavelength divisionfor radiofrequency (and microwave to millimetre wave) distri-multiplexing ( WDM ). For each of these applications, electro-bution, and for ultrafast information processing such asoptic modulators must compete with established alternativeanalog-to-digital conversion. Both fiber and wireless communi-technologies; however, as drive voltage requirements and losscation systems are experiencing increased bandwidth demands;characteristics of modulators improve and as the bandwidthelectro-optic modulators can perform numerous discrete band-width-dependent functions in these systems effectively improv-ing overall system bandwidth.1 Fortunately, high bandwidthTable 1 Bandwidth and drive voltage requirements for several(i.e. >300 GHz) is readily obtained with polymeric electro-applications of electro-optic modulatorsoptic modulators due to low relative permittivities and rela-Application Bandwidth Drive voltage/Vtively frequency(wavelength)-independent refractive indicesand relative permittivities (permitting radiofrequency andCable TV, datacom Lower GHz 5–10optical waves to co-propagate significant distances without de-Telecom Higher GHz 2–3phasing). Competing technologies for signal transduction,RF Photonics Higher GHz <1such as modulated lasers, often suffer from bandwidths definedJ. Mater. Chem., 1999, 9, 1905–1920 1905requirements of various applications increase, modulators aremore likely to become the technological approach of choice.Hopefully, the ultimate competition to electro-optic modu-lation will come from all-optical processing based on the Kerreffect. Such all-optical processing depends upon third order,rather than second order, optical non-linearity. The magni-tudes of third order optical non-linearities are not adequateat the present time.Pockell’s effect: the macroscopic phenomenon ofelectro-optic


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CU-Boulder CHEM 6321 - From molecules to opto-chips

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