Magneto-optical response of a one-dimensional all-garnet photonic crystal in transmission and reflection

  • PDF / 402,595 Bytes
  • 12 Pages / 612 x 792 pts (letter) Page_size
  • 89 Downloads / 208 Views

DOWNLOAD

REPORT


J1.3.1

Magneto-optical response of a one-dimensional all-garnet photonic crystal in transmission and reflection S. Kahl and A. M. Grishin Microelectronics and IT, Royal Institute of Technology, S-16440 Stockholm, Sweden ABSTRACT We present spectra of transmittance, reflectance, and Faraday rotation of transmitted and reflected light for a periodic garnet multilayer structure with a central defect layer. The multilayer consists of alternating layers of bismuth and yttrium iron garnet, is 1.5 µm thick, and was prepared by pulsed laser deposition. For the reflection measurements, a silver mirror was evaporated on top of the multilayer. Faraday rotation is strongly enhanced at resonances in transmission and reflection. The peak value obtained at 748 nm in transmission is 5.3 deg and at 733 nm in reflection is 18 deg. A single layer BIG film of equivalent thickness shows 2.2 deg Faraday rotation at 748 nm. We find rather good agreement between measured and calculated spectra. Using calculations of the distributions of light intensities at different wavelengths inside the multilayer, we are able to give consistent qualitative explanations for the enhancement of Faraday rotation. We also find numerically that - at moderate strengths of the optical resonances - a linear relation exists between Faraday rotation and the intensity integrated over all magneto-optically active layers, if absorption is neglected. We suggest to modify the usual sensor film for magneto-optical imaging by introducing a Bragg mirror consisting of heteroepitaxial garnet layers between the substrate and sensor film. For one example situation, we show by calculation that the quality factors of image contrast and optical efficiency can be higher for heteroepitaxial garnet multilayers than for single-layer iron garnet films currently in use as sensor films. 1 INTRODUCTION Transparent multilayers with periodic regions where single layers have thicknesses of a quarter wavelength in the respective material can be denoted one-dimensional photonic crystals [1]. The term ’magnetophotonic crystal’ (MPC) was coined by the researchers who presented the first concepts and experimental realizations of one-dimensional photonic crystals that contained magneto-optical (MO) layers [2]. Since then, more advanced theoretical concepts have been proposed, aiming especially at possible applications in optical isolators [3–5]. In MPCs, it is possible to enhance the MO rotation of the polarization plane of incident linearly polarized light by means of optical resonances. Iron garnets exhibit low absorption and strong Faraday rotation in visible and/or infrared light. The MO effect is enhanced by different substitutions, e.g., when the material contains bismuth. Iron garnets are therefore the materials of choice for MPCs. The first MPC contained iron garnet in a defect layer (i.e., in a layer of a thickness that breaks the periodicity of the photonic crystal) of the MPC and nonmagnetic dielectric materials in the periodic regions [2], while we have recently reported an all-garnet MPC [6]. The op