New Garnet Films for Magneto-Optical Photonic Crystals
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New Garnet Films for Magneto-Optical Photonic Crystals S.I. Khartsev, A.M. Grishin Condensed Matter Physics, Royal Institute of Technology SE-164 40 Stockholm-Kista, SWEDEN
ABSTRACT Epitaxial La3Ga5O12 (LGG) garnet films and Bi3Fe5O12/La3Ga5O12 (BIG/LGG) heteroepitaxial structures have been synthesized on Gd3Ga5O12(GGG,111) single crystal. LGG films were grown by Pulsed Laser Deposition (PLD) technique whereas rf-magnetron sputtering was used to grow BIG films. We demonstrate LGG is a promising material to be integrated with a giant Faraday rotator Bi3Fe5O12 in magneto-optical photonic crystals. LGG has a lattice constant 12.772 Å that is bigger than that in GGG (12.384 Å) and closer to that in BIG (12.626 Å). Heteroepitaxial Bi3Fe5O12(2µm)/La3Ga5O12(300nm) structures grown on the GGG(111) single crystal show the Faraday rotation as high as 5.74 deg/µm compared to 5.46 deg/µm in BIG/GGG at λ = 655 nm. Fitting LGG reflectivity spectra to Fresnel formulas yields LGG refractive index n = 1.981 compared to 1.963 in GGG at 655 nm. Dispersion of LGG refraction index follows Sellmeier formula n2 = 1 + 2.78/[1 – (138nm/λ)2] in the range from 400 nm to 1000 nm.
INTRODUCTION Over the past few years photonic crystals have formed rapidly expanding niche of photonics. Having enormous potential for light guiding, filtering and switching, exceptional dispersion properties (superprism effect) they promise to overcome limits in scaling of CMOS devices as well as to bring new mathematics in signal processing thus surpass significantly the speed of electronic circuits. Magnetic photonic band gap materials attract special interest since they possess nonreciprocal properties [1]. The first magneto-optic photonic crystals have been composed of Bi-substituted iron garnet layers alternated with Ta2O5/SiO2 dielectric spacers [2]. Recently all garnet Bi3Fe5O12/Y3Fe5O12 photonic crystal has been synthesized on Gd3Ga5O12 substrate [3]. Remarkable phenomenon of “frozen mode” has been predicted in photonic crystals which combine ferroelectrics with ferromagnetics to break both the time reverse symmetry (t→ t) and the centre inversion symmetry (r → - r) [4]. To develop high performance magnetically and electrically tunable photonic crystals one needs to fabricate a crystalline superlattices in one and two dimensions. Nowadays we have very limited arsenal of materials suitable for this purpose. Therefore, this is a challenging task to engineer new materials with high electro-optic and magneto-optic effects as well as materials which are non-active but crystalline and optically compatible to the acknowledged premiers. In this paper we present results on processing and characterization of novel garnet La3Ga5O12 (LGG) crystal. LGG films of epitaxial quality were synthesized on standard Gd3Ga5O12(GGG,111) single crystal by Pulsed Laser Deposition (PLD) technique. Lattice constant in LGG (12.772 Å) was found to be bigger than that in GGG (12.384 Å) and closer to that in BIG
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(12.626 Å). At 655 nm LGG refractive index n = 1.981 appear
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