Collaborative Research: Magnetic Photonic Crystals

Texas State University - San Marcos, San Marcos TX

Investigators

Abstract

This collaborative project between Michigan Technological University (MTU) and Southwest Texas State University (SWT) focuses on the fabrication and testing of photonic crystals in magnetic oxides for novel integrated photonic device prototyping. The project responds to the growing interest in photonic crystals for device applications based on their unique optical band gap properties. While various novel optical band-gap structures have been fabricated in non-magnetic dielectric media for highly efficient waveguiding, filtering and resonator applications, very little work has been done on photonic crystals in magnetic systems. One-dimensional structures have received some attention, although this work is still very 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 project will consist of a one-year exploratory effort to assess the applicability of magnetic materials in photonic band-gap structures. The non-reciprocal properties of magnetic oxides, such as yttrium iron garnet (YIG), make these materials a unique choice for optical isolator and circulator fabrication. Optical fiber telecommunications have developed to the point where the monolithic integration of different optical components is a serious issue to reduce costs in local area networks and long-distance data transmittal. In particular, noise suppression 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 crystal structures provide a novel alternative to address this problem since they can significantly enhance the Kerr and Faraday response, making it possible to build smaller and cheaper isolators and circulators A 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 completely new and virgin field. Most of the work developed thus far has been theoretical, although a few experimental successes have been reported. Certain aspects of the sputtering work required for the fabrication of one-dimensional magnetic photonic crystals remain partly unexplored and may require particularly careful fine-tuning of the sputtering conditions. In particular, special attention must be paid to the formation of highly smooth interfaces in the magnetic photonic crystal stack given the large number of layers that make up these structures. The essence of the innovation presented by the use of photonic crystals in magneto-optic isolators is that of a tremendous reduction in length in the polarization rotator afforded by a corresponding enhancement in Faraday rotation. However, the impact of this program, if successful, would not be just the development 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 by the presence of linear birefringence in optical waveguides. The difficulty arises because waveguide dimensions 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 in device length envisaged by the use of photonic crystal structures promises to eliminate the phase matching stumbling block to the integration of isolators into photonic circuits. In that sense, this program has the potential to revolutionize optical communications technology, by allowing the on-chip fabrication of a critical component for communications systems.