Cerium-doped Yttrium Iron Garnet Research Articles

Utilizing magneto-optical short-range surface plasmon resonance to enhance the performance of optical fiber sensor

Although the short-range surface plasmon resonance (SRSPR) has larger sensitivity than the long-range surface plasmon resonance (LRSPR) excited simultaneously, SRSPR is usually ignored in previous studies of the LRSPR sensors due to its much larger peak width. However, since the resonance peaks of both SRSPR and LRSPR narrow vastly when combined with the magneto-optical (MO) effect, SRSPR has the potential to reach much higher figure-of-merit (FOM) than LRSPR due to its higher sensitivity. In this work, the feasibility of utilizing magneto-optical short-range surface plasmon resonance (MOSRSPR), which is the combination of SRSPR and MO effect, to enhance FOM was verified first by analyzing the prism-based structure sensor with the transfer matrix method (TMM). Then a novel optical fiber sensor based on MOSRSPR was proposed. The structure of the proposed sensor is a D-shaped optical fiber coated with an MgF2 film, a thin silver film, and a MO material film of cerium-doped yttrium-iron garnet (CeYIG). The influence of the structural parameters including the MgF2, silver, and CeYIG film thicknesses was analyzed theoretically by the finite element method (FEM). With the optimal parameters, the FOM of the optical fiber MOSRSPR sensor is greatly enhanced to 10,750 RIU−1 in maximum and 2888 RIU−1 in average, which surpasses all reported optical fiber LRSPR sensors vastly. The miniaturized and simple design of the D-shaped fiber MOSRSPR sensor, coupled with its high performance, offers a significant reference for the study of optical fiber sensors with ultra-high FOM.

Optical fiber sensor based on magneto-optical surface plasmon resonance with ultra-high figure of merit

Compared to surface plasmon resonance (SPR), the sensors based on the magneto-optical SPR (MOSPR) technique have much higher figure-of-merit (FOM). However, there are no reports about applying MOSPR in the optical fiber structure now. In this work, a novel D-shaped optical fiber sensor based on the MOSPR technique is proposed. The D-shaped optical fiber is coated with a thin silver film and a magneto-optical (MO) material film of Cerium-doped Yttrium-Iron garnet (CeYIG). By applying a magnetic field on the sensing region, the magneto-optical Kerr effect (MOKE) of the CeYIG layer and the related MOSPR phenomenon could be excited when appropriate light is transmitted in the proposed optical fiber sensor. The influence of the structural parameters including the residual cladding thickness, silver and MO material film thicknesses are analyzed theoretically by the finite element method (FEM). With the optimal parameters, the sensor achieves the sensitivity of 5304 nm RIU−1. Since the peak width of MOSPR spectra is much narrower than that of the SPR spectra, the FOM of the sensor is largely enhanced to 3864 RIU−1 on average and 13260 RIU−1 in maximum, which surpasses the optical fiber SPR sensors vastly. The miniaturized and simple design of the D-shaped optical fiber MOSPR sensor, coupled with the ultra-high FOM, offers itself great potential in biochemical sensing applications.

Delineating magnetization dynamics in solution-processed doped yttrium iron garnet thin films

In this work, thin films of ruthenium-doped and cerium-doped yttrium iron garnet were deposited on silicon using solgel chemistry. Doped YIG could be produced in phase pure form up to a precursor stoichiometry of Y3Ru0.1Fe4.9O12 and Ce0.7Y2.3Fe5O12. Both dopants significantly increase the coercivity and anisotropy field of the materials either due to domain wall pinning or increased spin–orbit coupling from the dopant. To delineate these two effects, the dynamic magnetic properties were studied using strip line ferromagnetic resonance (FMR). The FMR linewidth was separated into intrinsic loss and inhomogeneous line broadening. Inhomogeneous line broadening was found to dominate the magnetic losses in all the films likely due to magnon scattering off grain boundaries, but the Gilbert damping remained fairly low. By comparing the two dopants, it was found that Gilbert damping increased more in Ce:YIG films than in Ru:YIG films. This finding was corroborated by changes in the anisotropy field of the films, indicating a larger contribution from spin–orbit coupling from cerium than from ruthenium. Surprisingly, while magnetic loss globally increased with higher substitution, adding a small amount of dopant actually reduced the inhomogeneous line broadening in both sets of films. This was corroborated by crystallite size. The damping in Ru:YIG also decreased with a small amount of the dopant, which has been predicted by Kittel for doped garnets. Thus, it follows that there is an ideal doping regime where solgel YIG can be doped at low levels without increasing magnetic loss.

Dysprosium Substituted Ce:YIG Thin Films for Temperature Insensitive Integrated Optical Isolator Applications.

Magneto-optical isolators are key components in photonic systems. Despite the progress of silicon-integrated optical isolators, the Faraday rotation of silicon-integrated magneto-optical materials, such as cerium-doped yttrium iron garnet (Ce:YIG), show a strong temperature dependence, limiting the temperature range for integrated nonreciprocal photonic device applications. In this work, we report dysprosium substituted Ce:YIG thin films (Dy2Ce1Fe5O12, Dy:CeIG) showing a low temperature coefficient of Faraday rotation. A temperature insensitive range of the Faraday rotation is observed in between 25 °C to 70 °C for this material, compared to 20% variation of the Faraday rotation in Ce:YIG thin films. A Dy:CeIG based temperature insensitive silicon-integrated optical isolator operating in the temperature range of 23 °C to 70 °C is experimentally demonstrated.

Integrated polarization-independent optical isolators and circulators on an InP membrane on silicon platform

In photonic integrated circuits (PICs), optical isolators and circulators are essential to prevent lasers from backreflections and to reroute the light flow. In this paper, an integrated polarization-independent device that can be operated as an optical isolator or an optical circulator, based on an InP membrane on silicon platform, is demonstrated. A cerium-doped yttrium iron garnet die is adhesively bonded on a Mach–Zehnder interferometer, in combination with four polarization converters. The device shows maximum optical isolations of 27.0 dB for transverse-electric (TE)-mode input and 34.0 dB for transverse-magnetic TM-mode input. The device also works as a four-port optical circulator. Optical isolations of at least 18.6 dB and 16.4 dB are measured between each circulator port pair for TE- and TM-mode input, respectively. This work could remove the optical interfaces between laser and isolator for robust production. It also provides a step forward toward a multifunctional and high-density PIC.

Crystal structure and magnetic properties of cerium-doped YIG: Effect of doping concentration and annealing temperature

We present a study of the effect of the substitution of Y3+ by Ce3+ on the crystal structure and magnetic properties of cerium-doped yttrium iron garnet (YIG), CexY3-xFe5O12 (0 ≤ x ≤ 0.5), which was synthesized using high-energy ball milling. In particular, we aimed to study the effect of the cerium concentration and the annealing temperature on the crystal structure and magnetic properties of the Ce-doped YIG. Fe2O3, Y2O3, and Ce2(CO3)3 were mixed in a stoichiometric ratio, milled for 5 h, and annealed at different temperatures, from 1000 to 1400 °C. The X-ray diffraction pattern confirmed the presence of CeO2 as a secondary phase, together with the formation of the YIG structure, at all studied temperatures and compositions. A complete solid solution of Ce3+ in the garnet structure was obtained for the samples annealed at 1400 °C. Increasing the Ce3+ content resulted in a consistent decrease in the saturation magnetization and a slight decrease in the coercivity, resulting from the insertion of Ce3+ into the YIG structure and the presence of CeO2 as a secondary phase.

Integration of bulk-quality thin film magneto-optical cerium-doped yttrium iron garnet on silicon nitride photonic substrates.

Cerium substituted yttrium iron garnet (Ce:YIG) films were grown on yttrium iron garnet (YIG) seed layers on silicon nitride films using pulsed laser deposition. Optimal process conditions for forming garnet films on silicon nitride are presented. Bulk or near-bulk magnetic and magneto-optical properties were observed for 160 nm thick Ce:YIG films grown at 640 °C on rapid thermal annealed 40 nm thick YIG grown at 640 °C and 2 Hz pulse rate. The effect of growth temperature and deposition rate on structural, magnetic and magneto-optical properties has been investigated.

Adhesively bonded Ce:YIG/SOI integrated optical circulator

A classical 3-port optical circulator is demonstrated on the silicon-on-insulator (SOI) platform. A garnet die with a magneto-optical cerium-doped yttrium iron garnet (Ce:YIG) layer is bonded on top of a Mach-Zehnder interferometer circuit using a thin adhesive bonding layer. The power transmission between different ports is characterized in the presence of an external magnetic field, transversal to the light propagation direction. An isolation of 22 dB is measured at a wavelength of 1562 nm.

Fabrications of cerium-substituted YIG thin films for magnetic field sensor by pulsed-laser deposition

We described the pulsed-laser deposition (PLD) and characterization of cerium doped yttrium iron garnet (Ce:YIG, Ce/sub 0.6/Y/sub 2.4/Fe/sub 5/O/sub 12/) thin films for magnetic field sensor applications. It was found that crystallized Ce:YIG films were obtained by the deposition at 900/spl deg/C substrate temperature and in 10 mtorr argon or oxygen ambient gas. The Faraday rotation angle was very large; 4.2 deg//spl mu/m at 430 nm wavelengths. The charge state control of cerium was important for the crystallinity and high Faraday rotation. The lower temperature or higher ambient gas pressure controlled the cerium charge state Ce/sup 4+/, because the oxygen and cerium released from an ablated target accelerated to form cerium oxide, the thin film was noncrystalline and no Faraday rotation occurred.

Magneto-optical garnet films made by reactive sputtering

Reactive radio frequency (RF) sputtering was used to grow cerium-doped yttrium iron garnet (YIG) films on magnesium oxide substrates. Magnesium oxide has been proven to be a good buffer material for semiconducting substrates. Reactive sputtering was not effective for cerium doping because the cerium target reacted with the oxygen in the sputtering gas. The films were amorphous as deposited. Stoichiometric compositions yielded smooth, polycrystalline garnet films on annealing. The effects of fluctuations in the yttrium-to-iron ratio were studied. Separate iron and yttrium targets were cosputtered in order to tailor the composition systematically along the iron-yttrium binary phase diagram. Oxygen content was found to be important in the formation of garnet and in the prevention of secondary phases. The garnet films had strong in-plane magnetizations and small coercive fields, which have promise for waveguide and switch devices, respectively.

Rare earth iron garnets and rare earth iron binary oxides synthesized by microwave monomode

Rare earth iron garnets (R3Fe5O12 or RIG, with R=Y, Sm, Eu, Gd, Dy, Ho, Er, and Yb) and rare earth orthoferrites RFeO3 have been synthesized from R2O3/Fe3O4 mixtures using the monomode microwave (MW) method. Such binary compounds are formed at a low temperature (T<900 K), in a few minutes at ambient atmosphere, whereas under conventional solid state reactions, all these binary oxides are synthesized at a much higher temperature (∼1800 K). The experimental conditions leading to nearly pure RIG are briefly discussed in relation to the nature of the rare earth and to the ratio R2O3/Fe3O4 in the starting mixture. This experimental method was extended to the synthesis of lanthanum- and cerium-doped yttrium iron garnet compounds. These results show that MW is a practical and economical procedure for chemical syntheses.

Integration of Yttrium Iron Garnet Films via Reactive RF Sputtering Bethanie

AbstractThis work aims to equip integrated optical circuits with important magneto-optical devices, such as isolators, that are currently available only as discrete components. Reactive rf sputtering was used to grow cerium-doped yttrium iron garnet films onto a variety of substrates, including SiO2-buffered Si, fused Si02 and MgO. MgO was used because it has proven to be a good buffer material for semiconducting substrates. Ce-doping was not effective via reactive sputtering due to a scale which formed on the Ce metal that prevented sufficient contact with the rf target. The films were amorphous as deposited. Stoichiometric Y3Fe5O12 films yielded smooth, polycrystalline garnet films upon annealing. A study of the effect of fluctuations in the Y:Fe ratio revealed that oxygen content is important for the prevention of secondary phases. Therefore, a high oxygen content should be used in the sputtering gas and subsequent annealing should be performed in oxygen.

Faraday rotation and MCD in Ce doped yig

The room temperature spectra of the Faraday rotation and magnetic circular dichroism in a cerium doped yttrium iron garnet (Ce: YIG) are presented. A dramatic change of the magnetooptical properties due to the substitution of Ce observed in the near infrared and visible regions originates from a strong paramagnetic transition centered near 1.41 eV (0.88 μm).