Collaborative Research: Magnetic Photonic Crystals

密歇根理工大学（MTU）和西南德克萨斯州立大学（SWT）之间的合作项目侧重于磁性氧化物中光子晶体的制造和测试，用于新型集成光子器件原型设计。基于光子晶体独特的光学带隙特性，该项目响应了人们对光子晶体器件应用日益增长的兴趣。虽然在非磁性介质中已经制造了各种新型的光学带隙结构，用于高效的波导，滤波和谐振器应用，但在磁性系统中的光子晶体方面做的工作很少。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，并且仍然主要是理论上的。更高维度的系统根本没有被研究过。鉴于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性工作，以评估磁性材料在光子带隙结构中的适用性。磁性氧化物的非互反性质，如钇铁石榴石（YIG），使这些材料成为光学隔离器和环行器制造的独特选择。光纤通信已经发展到这样的地步：为了降低局域网和远距离数据传输的成本，不同光器件的单片集成是一个严重的问题。特别是，源处的噪声抑制是片上光隔离器发展的重要驱动力。然而，利用非平面几何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，使构建更小、更便宜的隔离器和环行器成为可能。开发基于磁系统的光子晶体器件是一项高风险、高回报的事业。这是高风险的，因为光子晶体在磁系统中的应用是一个全新的、未开发的领域。到目前为止，大多数工作都是理论性的，尽管有一些实验成功的报道。制造一维磁性光子晶体所需的溅射工作的某些方面仍然部分未被探索，并且可能需要特别仔细地微调溅射条件。特别是，由于构成这些结构的大量层，必须特别注意在磁性光子晶体堆栈中形成高度光滑的界面。在磁光隔离中使用光子晶体所带来的创新的本质是由于法拉第旋转的相应增强而大大缩短了偏振旋转器的长度。然而，该计划的影响，如果成功的话，将不仅仅是超短隔离器的发展，而是使磁光隔离器的实际片上商业集成成为可能。这是因为这些器件在平面结构上的集成被光波导中线性双折射的存在所阻碍。由于波导尺寸与光波长相当，导致横向电（TE）和横向磁（TM）模式之间的相位失配，从而降低了隔离效率，因此出现了困难。利用光子晶体结构设想的定性缩短器件长度有望消除隔离器集成到光子电路中的相位匹配障碍。从这个意义上说，该计划有可能彻底改变光通信技术，通过允许在芯片上制造通信系统的关键组件。

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.