Magneto‐Optical Bi:YIG Films with High Figure of Merit for Nonreciprocal Photonics

Abstract

lator devices is commonly a MO iron garnet material, in particular yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) with substituents such as Ce or Bi to increase the MO performance. [5][6][7][8][9][10][11][12][13][14][15] However, the integration of garnets on a Si (or other semiconductor) platform is challenging due to the incompatible lattice parameters and the thermal expansion mismatch between garnets and common semiconductor substrates. [6][7][8][9][10][11][12][13][14][15][16] Moreover, crystallization of the garnet phase usually requires a high thermal budget. Garnets formed on semiconductor substrates are polycrystalline and exhibit higher optical absorption than single crystal films. Furthermore, impurity phases such as YFeO 3 , Fe 2 O 3 , and Bi 2 O 3 can form during the crystallization process, [17] which contributes to optical loss. These factors result in inferior optical performance of polycrystalline MO garnet films compared to the bulk garnet material, and a lower figure of merit (FoM), defined as the ratio of the Faraday rotation to the absorption coefficient per length of the material.Considerable work has been done on growth of garnet films on semiconductors to enable demonstrations of isolators and modulators. [6][7][8][9][10][11][12][13][14][15][16] The first monolithically integrated optical isolator [6] used 80 nm thick Ce:YIG which was grown by pulsed laser deposition (PLD) on a pre-annealed 20 nm thick YIG seed layer to induce crystallization of the Ce:YIG. A simplified PLD process was introduced by Sun et al. [11] where the YIG seed layer was placed on top of the MO garnet and both layers were crystallized simultaneously by rapid thermal annealing (RTA). This top-seedlayer process places the MO garnet in direct contact with the underlying Si waveguide, maximizing the coupling of light from the waveguide to the MO cladding, but it has only been applied to Ce:YIG. Recently rare-earth garnets have been developed that crystallize on Si and quartz without a seed layer, including sputter-deposited terbium iron garnet (TIG) and Bi-doped TIG (Bi:TIG). [18,19] Growth of MO materials on the sidewall of the waveguide can enable a wider range of device designs, including isolators for transverse electric (TE) polarization. Integrated semiconductor lasers emit TE-polarized light, and TE mode isolation using NRPS requires placement of the MO material on the sidewall of the waveguide to break left-right symmetry. [18,20,21] However, the NRPS-based integrated optical isolators that have been experimentally demonstrated are made with the MO material on the top or bottom surface of the waveguide, which isolates only the transverse magnetic (TM) polarization. [6][7][8][11][12][13][14] It is therefore essential to establish deposition conditions that yield Thin film magneto-optical (MO) materials are enablers for integrated nonreciprocal photonic devices such as isolators and circulators. Films of polycrystalline bismuth-substituted yttrium iron garnet (Bi:YIG) have been grown on silicon substrates and waveguide d...

Dysprosium Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy on Silicon

“…Thin films of the archetypical yttrium iron garnet (Y 3 Fe 5 O 12 ,YIG) and rare-earth iron garnets (RE 3 Fe 5 O 12 , REIG) have attracted considerable attention recently for studies of spin torques, [1][2][3][4] spin waves, [5][6][7][8] and magneto-optical effects. [9][10][11] Selection of the rare-earth ion enables tuning of the saturation www.advelectronicmat.de temperature used to crystallize the films after growth. [20,23,37] Considerable work was done on thin film polycrystalline REIGs for bubble memory in the 1960-1970s, where PMA was promoted by lowering the magnetization and therefore the shape anisotropy (e.g., by Al or Ga substitution for Fe), and from a growth-induced anisotropy.…”

High Figure of Merit Magneto‐Optical Ce‐ and Bi‐Substituted Terbium Iron Garnet Films Integrated on Si

“…[73] The high FoM and the single-layer growth process make Ce and especially Bi-substituted TbIG attractive materials for integrated nonreciprocal photonic devices or for other applications requiring MO materials such as magnetophotonic crystals or other nonreciprocal MO metamaterials. [74,75] [12] of 99.999% pure Tb 2 O 3 , CeO 2 , Bi 2 O 3 , and Fe 2 O 3 powders. The films were grown at a repetition rate of 10 Hz and laser fluence of 1.5 and 2.5 J cm −2 .…”

“…ferrimagnetic yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) offer a desirable combination of a high Faraday rotation and low optical absorption. Cerium-and bismuth-substituted yttrium iron garnet (CeYIG, BiYIG) have an excellent MO figure of merit (FoM, the ratio of Faraday rotation to optical absorption), [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and bismuth iron garnet and paramagnetic terbium gallium garnet are both used in bulk optical isolators.…”

“…Crystallization of CeYIG or BiYIG without secondary phases can be accomplished by depositing then annealing the film directly or by annealing a bilayer consisting of a YIG seedlayer placed either above or below the active MO layer. [12,13] When a seed layer is included, a top seed layer is preferable as it maximizes coupling of the MO garnet with an optical mode propagating through an underlying waveguide.Like YIG, rare earth garnets such as terbium iron garnet (TbIG) or dysprosium iron garnet [19,20] can crystallize directly on non-garnet substrates to form polycrystalline films. TbIG is a thermodynamically stable phase like YIG [21,22] which promotes garnet-phase crystallization without a seed layer.…”

All-dielectric magnetophotonic gratings for maximum TMOKE enhancement

“…The growth of MO garnet films on Si and other photonic substrates is possible by the recent methods. 34,35 The working wavelength is set to l = 630 nm, for which there is a wide availability of laser sources. The permittivity values, considered at room temperature, are used (at l = 630 nm) as e Si = 14.969 + i0.12588 36 and e SiO 2 = 2.123 37 for the Si and SiO 2 materials, whilst for Bi:YIG we used e Bi:YIG = 8.24 +i0.024 for the diagonal components of the permittivity tensor ẽ; Bi:YIG .…”