报告题目： Why do therefractive indexes of different materials differ so little and are also sodifficult to change?
报告人：Jacob Khurgin（约翰霍普金斯大学教授）
报告时间：2025年3月12日（星期三）上午9:00—10:30
报告地点：物理与光电学院18号楼213报告厅
主办单位：物理与光电学院
报告人简介：
Jacob Khurgin, a professor of electrical and computerengineering at Johns Hopkins University, is known for his diverse and eclecticresearch in the areas of optics, electronics, condensed matter physics, andtelecommunications. He has published eight book chapters, 40 patents, 340papers in refereed journals. He is a member of the American Physical SocietyJoint Council on Quantum Electronics and has served as a technical programcommittee member for more than 60 academic conferences. He has held visitingprofessorships at numerous institutions, including Princeton, UCLA, Brown, ETHin Zurich, and Ecole Normale Superieure in Paris. He was named a Fellow by theAmerican Physical Society and the Optical Society of America.
报告摘要：
For too long the functionality of opticaldevices and systems has been severely restricted by the very limited range ofrefractive indices at the disposal of designers. These limitations becomeespecially constricting in the currently most active areas of optics –integrated photonics, photonic crystals, metamaterials and metasurfaces. Asimple increase of the value of refractive index by 50% can result indisproportionally large improvement in performance (i.e. smaller size, lesscross-talk, higher resolution, and so on, depending on application) With that in mind, I explore what are thefundamental limits that limit the scope of refractive indices as a function ofwavelength, explain why higher index materials have not yetmaterialized and point out a few tentative directions for the search of theseelusive materials, be they natural or artificial.
In the secondpart of the talk, I investigate a closely related issue: changing refractiveindex to achieve effective modulation. There exist many methods of index modulation, starting with Pockels andKerr electro-optic effects, acousto-optic and opto-mechanical effect, opticalnonlinearities, thermal, carrier injection/depletion, etc. In my talk I willtry to provide a comprehensive analysis that will show that independent of themodulation technique, one must supply and maintain (but not necessarilydissipate) anywhere between few times 103 and 105 J/cm3 of energy in order toachieve relative index change on the order of 50-100% (with energy requirementsincreasing in sync with the increase of operating frequency). The generalconclusion is that unless radically new material systems are developed, theimprovement of the performance of existing modulation techniques will haveevolutionary rather than revolutionary character with no order of magnitudeimprovement in sight. I will try to argue for using collective effects and fastphase transitions to achieve future breakthroughs.
