Collaborative Research: Magnetic Photonic Crystals

这个由密歇根理工大学(MTU)和西南得克萨斯州立大学(SWT)合作的项目专注于用于新型集成光子器件原型的磁氧化物中光子晶体的制造和测试。该项目基于光子晶体独特的光学带隙特性，回应了人们对光子晶体在设备应用中日益增长的兴趣。虽然人们已经在非磁性介质中制作了各种新型的光学带隙结构，用于高效的波导、滤波和谐振器，但在磁性系统中的光子晶体方面的工作还很少。一维结构已经得到了一些关注，尽管这项工作仍然非常有限，主要仍然是理论上的。高维系统还没有被研究过。考虑到磁性系统在光子晶体应用领域的新颖性，拟议的项目将包括为期一年的探索工作，以评估磁性材料在光子带隙结构中的适用性。磁性氧化物的非互易性质，如YIG，使这些材料成为制造光隔离器和环行器的唯一选择。光纤通信已经发展到了这样一个地步：为了降低局域网和远程数据传输的成本，不同光学元件的单片集成是一个严重的问题。特别是，源端的噪声抑制是片上光隔离器发展的重要驱动力。然而，使用非平面几何结构的传统系统既笨重又昂贵。光子晶体结构为解决这一问题提供了一种新的选择，因为它们可以显著增强Kerrand Faraday响应，使制造更小、更便宜的隔离器和环行器成为可能。这是高风险的，因为在磁性系统中使用光子晶体是一个全新的、未开发的领域。到目前为止，大多数工作都是理论上的，尽管有少数实验成功的报道。制造一维磁性光子晶体所需的溅射工作的某些方面仍有部分未被探索，可能需要对溅射条件进行特别仔细的微调。尤其需要特别注意的是，由于构成这些结构的层很多，所以在磁性光子晶体叠层中形成高度光滑的界面必须特别注意。在磁光隔离器中使用光子晶体所呈现的创新的本质在于，通过相应地增强法拉第旋转角，极大地缩短了偏振旋转器的长度。然而，这一计划的影响，如果成功，将不仅仅是超短隔离器的开发，而是使磁光隔离器的实际片上商业集成成为可能。这是因为光波导中线性双折射的存在阻碍了这些器件与平面结构的集成。困难的出现是因为与光学波长相当的波导尺寸导致横电(TE)和横磁(TM)模式之间的相位失配，从而降低了隔离效率。利用光子晶体结构所设想的定性缩减索引长度有望消除将隔离器集成到光子电路中的相位匹配绊脚石。从这个意义上说，该项目通过允许在芯片上制造通信系统的关键部件，有可能给光通信技术带来革命性的变化。

This collaborative project between Michigan Technological University (MTU) and SouthwestTexas State University (SWT) focuses on the fabrication and testing of photonic crystals in magneticoxides for novel integrated photonic device prototyping. The project responds to the growing interest inphotonic crystals for device applications based on their unique optical band gap properties. While variousnovel optical band-gap structures have been fabricated in non-magnetic dielectric media for highly efficientwaveguiding, filtering and resonator applications, very little work has been done on photonic crystals inmagnetic systems. One-dimensional structures have received some attention, although this work is stillvery limited and remains mostly theoretical. Higher dimensional systems have not been investigated at all.Given the novelty of the field of magnetic systems in photonic crystal applications, the proposed projectwill consist of a one-year exploratory effort to assess the applicability of magnetic materials in photonicband-gap structures.The non-reciprocal properties of magnetic oxides, such as yttrium iron garnet (YIG), make thesematerials a unique choice for optical isolator and circulator fabrication. Optical fiber telecommunicationshave developed to the point where the monolithic integration of different optical components is a seriousissue to reduce costs in local area networks and long-distance data transmittal. In particular, noisesuppression at the source is an important driver for the development of on-chip optical isolators. However,conventional systems utilizing non-planar geometries are both bulky and expensive. Photonic crystalstructures provide a novel alternative to address this problem since they can significantly enhance the Kerrand Faraday response, making it possible to build smaller and cheaper isolators and circulatorsA program to develop photonic crystal devices based on magnetic systems is a high-risk high-payoff undertaking. It is high-risk because the use of photonic crystals in magnetic systems is a completelynew and virgin field. Most of the work developed thus far has been theoretical, although a fewexperimental successes have been reported. Certain aspects of the sputtering work required for thefabrication of one-dimensional magnetic photonic crystals remain partly unexplored and may requireparticularly careful fine-tuning of the sputtering conditions. In particular, special attention must be paid tothe formation of highly smooth interfaces in the magnetic photonic crystal stack given the large number oflayers that make up these structures.The essence of the innovation presented by the use of photonic crystals in magneto-optic isolatorsis that of a tremendous reduction in length in the polarization rotator afforded by a correspondingenhancement in Faraday rotation. However, the impact of this program, if successful, would not be just thedevelopment of ultra-short isolators but the enabling of actual on-chip commercial integration of magneto-optic isolators. This is because the integration of these devices onto planar structures has been hindered bythe presence of linear birefringence in optical waveguides. The difficulty arises because waveguidedimensions comparable to the optical wavelength induce a phase mismatch between transverse-electric(TE) and transverse-magnetic (TM) modes, degrading the isolation efficiency. The qualitative reduction indevice length envisaged by the use of photonic crystal structures promises to eliminate the phase matchingstumbling block to the integration of isolators into photonic circuits. In that sense, this program has thepotential to revolutionize optical communications technology, by allowing the on-chip fabrication of acritical component for communications systems.