Symposium Organizers
Bethanie Stadler University of Minnesota
Miguel Levy Michigan Technological University
Mathias Vanwolleghem Universite Paris-Sud
Vincent Fratello Integrated Photonics, Inc.
J1: Magneto-Photonic and Magnonic Crystals
Session Chairs
Tuesday PM, November 30, 2010
Room 201 (Hynes)
9:30 AM - **J1.1
Magnetophotonic Crystals - Their Functions and Applications.
Mitsuteru Inoue 1 , Alexander Baryshev 1 , Hiroyuki Takagi 2 , Taichi Goto 1 , Shi'ichiro Mito 1 , Seung Min Baek 1 , Kazuo Yayoi 3 , Kazuma Tobinaga 1 , Kotaro Yamada 1 , Yoji Haga 1 , Hironaga Uchida 4
1 , Toyohashi Univrersity of Technology, Toyohashi Japan, 2 , Toyota Natinal College of Technology, Toyota Japan, 3 , Ibaragi Natinal College of Technology, Toyota Japan, 4 , Tohoku Institute of Technology, Sendai Japan
Show AbstractIntroduction of artificial nano-scaled structures to magnetic materials gives us a variety of opportunities for controlling the light traveling in the structured materials. Magnetophotonic crystals (MPCs) can be classified into such materials, where optical-order periodic structures composed of magnetic and/or dielectric materials are introduced so as to create photonic band gap and to confine light in the vicinity of additional defects in the periodic structures. One- and two-dimensional MPCs have already found their optoelectronic applications such as magneto-optic (MO) spatial light modulator (MOSLM) and optical waveguide isolator. In this paper, overall functionalities of MPCs that have recently been demonstrated are described first, together with their applications in MOSLMs and waveguide circulator devices.Enhancement of MO Faraday and Kerr effects can be achieved by utilizing the surface plasmon resonance: For instance, when Au nano-particles are embedded in magnetic garnet thin film, the Faraday rotation angle of film shows considerable enhancement at the wavelength of plasmon resonance. This is also the case for Kerr rotation, suggesting that the MO responses can be manipulated by the use of localized evanescent field associated with the plasmon resonance. More sophisticated structures for the plasmon- assisted magnetophotonics have been also proposed and discussed mainly based upon our recent experimental studies.
10:00 AM - J1.2
Reprogrammable Forbidden Frequency Gaps in an Artificial Crystal Based on Periodic Magnetic Nanostructures.
Dirk Grundler 1 , Mikhail Kostylev 2 , Detlef Heitmann 3 , Jesco Topp 3
1 Physik Department, Lehrstuhl fuer Physik funktionaler Schichtsysteme, Technische Universitaet Muenchen, Garching b. Muenchen, Bavaria, Germany, 2 School of Physics, M013, University of Western Australia, Crawley, Western Australia, Australia, 3 Institut fuer Angewandte Physik und Mikrostrukturforschungszentrum, Universitaet Hamburg, Hamburg Germany
Show AbstractPeriodically patterned dielectrics and metal films have allowed one to create artificial band structures for photonic and plasmonic excitations, respectively. It is well known that in such artificial crystals the allowed minibands and forbidden frequency gaps are determined by the lateral size of the unit cell and the lattice symmetry. Artificial crystals made from magnetic materials are much less explored. Magnonic excitations in the GHz frequency regime, i.e., spin waves, exhibit a wavelength which is orders of magnitude shorter if compared to corresponding electromagnetic waves. Magnonic crystals thus open the perspective of advanced microwave devices operating on the nanoscale. We have fabricated one-dimensional (1D) magnonic crystals consisting of thin permalloy nanowires forming densely packed arrays. [1] The dynamic response is investigated by broadband GHz spectroscopy using miniaturized coplanar waveguides overlaying the ferromagnetic nanostructures. The spectra are consistent with allowed minibands and forbidden frequency gaps for spin waves propagating in transverse direction across the nanowire arrays. We substantiate the magnonic crystal behavior by theoretical modeling and micromagnetic simulations. The performance of such 1D magnonic crystals is found to go beyond the one of photonic and plasmonic crystals in that the magnonic minibands are reprogrammable in particular after fabrication.[2] The magnetic states of neighboring nanowires can be modified and thereby the relevant band structure. We show how to create an additional forbidden frequency gap in an otherwise allowed miniband using a small in-plane magnetic field. Such reprogrammable properties might be relevant for multifunctional and possibly nonreciprocal magnonic devices operating in the GHz frequency regime.The research work has received funding from SFB 668, “Nanosystems Initiative Munich (NIM)”, "NANO-SPINTRONICS" of the City of Hamburg, the Australian Research Council and the European Community via FP7/2007-2013 (Grant Agreement no. 228673, MAGNONICS). [1] J. Topp, J. Podbielski, D. Heitmann, and D. Grundler, Phys. Rev. B 78, 024431 (2008).[2] J. Topp, D. Heitmann, M.P. Kostylev, and D. Grundler, Phys. Rev. Lett. 104, 207205 (2010).
10:15 AM - J1.3
Polarization Rotation Based Optical Sensor in Magneto-photonic Crystals.
Neluka Dissanayake 1 , Miguel Levy 1 , Vincent Fratello 2 , Amir Jalali 1 3
1 Physics, Michigan Technological University, Houghton, Michigan, United States, 2 , Integrated Photonics, Inc., Hillsborough, New Jersey, United States, 3 , Electro-Optics Technology, Inc., Traverse City, Michigan, United States
Show AbstractIn this study we present an optical sensor based on refractive index detection utilizing Faraday-effect-active photonic band gap structures fabricated in iron garnet films. It is shown that magneto-photonic-crystal-enhanced polarization effects provide an interesting alternative platform to existing sensor techniques. Gyrotropic photonic-band gap structures can be made to yield large polarization rotations sensitive to the nature of the cladding in waveguide configurations. Strong near-band gap-edge polarization rotations serve as a sensitive probe to cover-index changes in birefringent magneto-optic waveguide photonic crystals. The one dimensional waveguide photonic crystals are fabricated on single-layer bismuth-substituted rare earth iron garnet films grown by liquid phase epitaxy on gadolinium gallium garnet (GGG) substrates. The polarization rotation of the output light from the photonic crystal is measured with respect to end-fire fiber coupled TE polarized input light. The sensor is tested through a wide range of cover indices from n=1.0 (air) to n=1.6. This study reveals that the device sensitivity improves with cover index increase. Experimental findings are verified with an extensive theoretical analysis of Bloch mode polarization states showing that large near stop-band edge rotations are induced by the magneto-photonic crystal. Bloch mode polarization states are found to vary strongly with cover index and to track the changes in experimentally-measured polarization rotations. The rate of change of polarization rotation with respect to cover index is much higher for the waveguide photonic crystal structure than that of plain waveguides fabricated on the same film. Experimental results also suggest that the combined effects of geometrical waveguide birefringence and Faraday rotation contribute to the strength of the sensor response.
10:30 AM - **J1.4
Gyrotropic Degenerate Bandgaps in Nonreciprocal Materials.
Alexander Merzlikin 1
1 , Institution of the Russian Academy of Sciences Institute for theoretical and applied electromagnetics RAS, Moscow Russian Federation
Show Abstract Recent technological developments have enabled the fabrication of numerous new types of artificial media. Particular interest is devoted to fabrication of periodic structures – photonic crystals that are extremely useful for manipulation with light propagation. A lot of attention has been focused on the possibility of managing its transparency or reflection by external means, as for example, by means of a magnetic field. The embedding of magneto-optic inclusions into the photonic crystal allows the control of its spectral properties: one may shift the dispersion curve and transmittance spectrum by application of a magnetic bias. But usually magnetization results in a shift of the dispersion curves for right- and left-circularly polarized waves in opposite directions thus making it impossible to simultaneously tune light of different polarizations or to manipulate unpolarized light. In this communication the results of investigation of 1D anisotropic magneto-photonic crystals are reported. The possibility to control unpolarized light by use of an external magnetic field is shown. The key feature of this control is the formation of a special type of band gap, namely, the formation of gyrotropic degenerate band gaps. These band gaps are formed by the coupling of ordinary and extraordinary Bloch waves upon application of an external magnetic field, which causes the transformation of linearly polarized eigenmodes into circulary polarized ones. The gyrotropic degenerate band gaps are formed inside the Brillouin zone, which makes it different from the common ones existing at the boundaries of the Brillouin zones. The main feature of such band gaps is polarization degeneracy of the Bragg reflection, i.e. these band gaps are simultaneously formed for both polarizations. The features of the degenerate band gaps, its interconnection with degenerate band edges and absence of Borrmann effect will be discussed.
J2: Nonreciprocity and Unidirectionality
Session Chairs
Tuesday PM, November 30, 2010
Room 201 (Hynes)
11:30 AM - **J2.1
Topologically-protected Photonic Crystal Edge States as ``One-way Waveguides.”
F. Duncan Haldane 1
1 Physics, Princeton University, Princeton, New Jersey, United States
Show AbstractA remarkable property of two-dimensional electron systems exhibiting the quantum Hall effect is their “chiral” edge states, which propagate unidirectionally and non-dissipatively around the edge of the quantum Hall region, travelling around obstacles without any backscattering. While the experimentally-realized quantum Hall effect involve charged fermions in high magnetic fields, and occurs (in its integer quantum Hall effect version) because of Landau quantization and the Bohm-Aharonov effect, I discovered in 1989 that the effect could in principle occur in the absence of a magnetic field in a periodic crystal with broken time-reversal symmetry as a consequence of Berry-curvature in k-space, when this leads to topologically-non-trivial bands with a non-vanishing Chern invariant. While it has not so far been experimentally seen , this “zero-field” or “anomalous quantum Hall effect” system (often now called the “Chern Insulator”) can now be recognized as the first example of a “Topological insulator” (albeit one with broken-time-reversal symmetry). In a 2005 preprint (finally published in 2008)[1]) with S. Raghu, I proposed that the analogous phenomenon could be reproduced in photonic crystals designed as metamaterials using non-reciprocal media to produce a topologically-non-trivial band structure. While the (integer) quantum Hall effect itself requires fermions obeying the Pauli principle, the unidirectional chiral edge states are a one-particle property that does not require Fermi statistics and can be reproduced in photonic systems. This maximally-non-reciprocal electromagnetic propagation has obvious potential for applications if suitable metamaterials can be designed, and experimental “proof of concept” realizations have already been reported. A spiral screw-dislocation in a three-dimensional version of a topologically-non-trivial Chern metamaterial would also carry the unidirectional mode, and is a possible model for a “unidirectional optical fiber.” I will review the translation of these concepts from electronic to photonics, where they are somewhat novel. [1] F. D. M. Haldane and S. Raghu, Phys. Rev. Lett. 100, 013904 (2008).
12:00 PM - J2.2
Modelling and Optimisation of an Integrated Optical One-way Magnetophotonic Crystal Mirror.
Mathias Vanwolleghem 1 , Kamil Postava 2 , Magdenko Liubov 1 , Lukas Halagacka 2 , Jaromir Pistora 2 , Pierre Beauvillain 1 , Beatrice Dagens 1
1 Institut d'Electronique Fondamentale (CNRS UMR8622), Université Paris Sud, Orsay France, 2 Dept. of Physics, Technical University Ostrava, Ostrava Czechia
Show AbstractThe absence of a miniaturized integrated version of an optical isolator is an issue that is becoming increasingly important in view of the always higher levels of integration in photonic integrated circuits. It has been shown that the intrinsic strength of the magneto-optical (MO) effects, necessary to induce optical non-reciprocity (NR), can be strongly enhanced in photonic crystals (PhC). We have demonstrated earlier the possibility to design uniformly magnetized magnetophotonic crystals that exhibit extremely enhanced NR under the form of one-way band gaps appearing inside the Brillouin zone [1]. By properly reducing the symmetry of the etched PhC motifs of a standard Bravais lattice in a MO layer (such as Bi3Fe5O12, BIG) this behaviour can be obtained without the need to use antisymmetric magnetic domains[2] or the need to use ternary PhC’s with three constitutent materials [3]. Using this novel unidirectional bandgap effect, we numerically demonstrated how a finite slice of such symmetry-reduced MOPhC behaves as an integrated one-way mirror for an TE mode incident from a uniform BIG layer, i.e. nearly totally reflecting upon backward illumination while partially transmitting upon forward illumination. The resulting device is an ultracompact integrated isolator showing 20dB isolation over merely 100 lattice periods (roughly corresponding to about 40 wavelengths).In this work we show first of all how the use of Shubnikovs dichromatic plane group theory allows us to identify all possible plane 2D symmetries that can exhibit one-way effects. In this way other competing MO PhC layouts can be identified that may lead to higher and/or technological even more flexible designs. Using an in-house developed fully vectorial anisotropic Fourier modal method we subsequently show how these designs can be optimized to improve their bandwidth and reduce their diffraction losses. Our earliest designs were hindered by high reflection and diffraction losses at the facets of the MO PhC slice. As a result an insertion loss (without taking substrate leakage into account) of already 6dB was sustained. These diffraction losses also limit the usable fraction of the one-way bandwidth of the MOPhC. By gradually adapting the filling factor and the motifs of the first few entrance and last few exit “crystal planes”, a better impedance matching for the forward modes is obtained without degrading the one-way band-gap. These optimization procedures have allowed us to design ultracompact one-way MOPhC mirrors for telecom wavelengths with a rejection rate of 25dB over a several hundreds GHz bandwidth and total diffraction losses lower than 1.5dB in a total number of crystal periods below 20. Fabrication of this novel type of isolator is ongoing and will also be shortly discussed.[1] M. Vanwolleghem et al., Phys. Rev. B 80, 121102(R) (2009)[2] Z. Yu, Z. Wang and S. Fan, Appl. Phys. Lett. 90, 121133 (2007).[3] A. Khanikaev and M. Steel, Opt. Express 17, 5265-5272 (2009).
12:15 PM - J2.3
Nonreciprocal Optical Bloch Oscillations in Magneto-optic Waveguide Arrays.
Pradeep Kumar 1 , Miguel Levy 1
1 Physics, Michigan Technological University, Houghton, Michigan, United States
Show AbstractThe present study explores nonreciprocal Bloch-like optical oscillations in transversely magnetized chirped waveguide arrays. Normal modes are shown to acquire different wave-numbers in opposite propagation directions. Bloch oscillatory motion is a remarkable phenomenon first predicted by F. Bloch and C. Zener in the 1930’s [1] consisting of oscillatory trajectories for particles subject to a constant force in periodic potentials. In optical systems this constant force is replicated by designing into the array a constant difference in waveguide mode index between adjacent waveguides. By embedding the system in a magneto-optic medium we demonstrate the possibility of optical modes akin to Wannier-Stark states, but having different properties upon propagation direction reversal. The presence of non-reciprocity in the system allows for normal-mode dephasing and the possibility of unidirectional Bloch oscillations. Differences in propagation constant between normal modes of the array in opposite propagation directions are established by imposing different vertical spatial index gradients at the substrate/core, and core/cover interfaces in the presence of transverse magnetization. Beam-propagation simulations show that light coupled into the central waveguide exhibits refocusing with Bloch-oscillation period Λ=2π/δβ, where δβ is the difference in propagation constant between adjacent waveguides. It is also shown that one can violate the conditions for Bloch oscillatory motion in one direction while maintaining a uniform wave-number step in the opposite. This can be done by adjusting the waveguide widths and periodically reversing the sign of the gyrotropic parameter g between adjacent waveguides. Conditions for the unidirectional breakdown in Bloch oscillations will be discussed.[1] C. Zener, “A theory of the electrical breakdown of solid dielectrics,” Proc. R. Soc. London A 145, 523-529 (1934).
12:30 PM - J2.4
One-way Electromagnetic Chiral Edge States and Slow Light.
Zheng Wang 1 2 , Yidong Chong 1 , John Joannopoulos 1 2 , Marin Soljacic 1 2
1 Department of Physics, MIT, Cambridge, Massachusetts, United States, 2 Research Laboratory of Electronics, MIT, Cambridge, Massachusetts, United States
Show AbstractRecent theoretical and experimental studies (Haldane, et al., Phys. Rev. Lett. 2008, Wang et al., Phys. Rev. Lett. 2008, Nature 2009) have shown that certain 2D magneto-optic photonic crystals support electromagnetic edge modes that propagate only in one direction, with backscattering prohibited even in the presence of disorder, analogous to chiral edge states in the integer quantum Hall effect. The resulting “Chiral edge states” are a unique class of states with unparalleled properties that have only been observed in electronic systems. In both the electronic systems and photonic systems, this unique form of unidirectional transport is a consequence of nontrivial topological properties of the bulk band structure. We have implemented a waveguide that supports these one-way modes, using a square photonic lattice of magnetized ferrite rods. At microwave operating frequencies, the waveguide exhibits strongly non-reciprocal propagation, with measured forward and backward transmission differing by up to 50 dB, even in the presence of very large obstacles, thus providing experimental evidence for non-zero topological Chern numbers in a photonic system. To extend the operational frequency of the one-way waveguides to higher frequencies, one must also consider the much greater absorption coefficient of magneto-optical materials at near-IR and visible wavelengths. Using numerical simulations and the coupled-mode theory, we show a fundamental trade-off exists between the operational bandwidth and the propagation loss. In addition, one important technological application of the complete suppression of the backward propagation is the reduction of loss in slow light structures, where the power of backscattering scales inversely with the square of the group velocity. We show that, for a given slow-light structure, its tolerance for propagation loss can be derived from the operational bandwidth. Analytical coupled-mode theory predictions and numerical results will be presented.
J3: Magneto-Optic Films: Fabrication and Applications
Session Chairs
Tuesday PM, November 30, 2010
Room 201 (Hynes)
2:30 PM - **J3.1
Magneto Optic Indicator Films for Forensics.
Charles Krafft 1 , Sergiy Tkachuk 2 , Garrett Lang 2 , Isaak Mayergoyz 2
1 , Laboratory for Physical Sciences, College Park, Maryland, United States, 2 Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractVisualization of magnetically recorded patterns provides important information for the forensic examiner. Although use of magnetic tape is diminishing, between legacy tape systems and old evidence there is still a need for magnetic media analysis tools for forensic applications. The epitaxially-grown magnetic garnet films provide a means of visualizing the recorded patterns which is non-destructive and allows direct observation without scanning. While simple in principal, achieving a suitable material design for the indicator films requires tradeoffs specific to the intended application. One goal is to achieve a featureless, artifact free garnet which responds with appropriate sensitivity to the media under observation, resolving submicron recorded features, but correlating events spanning distances orders of magnitude larger.In this paper, we report on a systematic approach to designing a suitable indicator film and present imaging results for a range of film compositions. We have previously shown that controlling the film thickness or etching of thicker films has resulted in improved imaging quality.[1] Depending on the media to be imaged, there is a difference in what constitutes an acceptable garnet, as intrinsic domain patterns in the garnet may obscure the image for high magnification work, but not affect the functionality at low magnification. We also report on the design of an imager stage which provides a convenient way to ensure good contact between the media and the garnet, but in a way that enables easy disengagement of the garnet from the media to examine different areas outside the microscope field of view. The garnet composition is carefully chosen to obtain optimal imaging performance. Although the majority of our films have been grown on (100)-oriented large lattice CMZ-GGG, we have also obtained some (110) oriented CMZ-GGG substrates which are of interest because of their easy plane of magnetization. Results were also obtained for films grown on a substrate with an intermediate lattice parameter, between GGG and CMZ-GGG. 1. S. Tkachuk, V.J. Fratello, C. Krafft, G. Lang, I. D. Mayergoyz, “Imaging Capabilities of Bismuth Iron Garnet Films With Low Growth-Induced Uniaxial Anisotropy,” IEEE Trans. Mag, 45, 4238 (2009).
3:00 PM - J3.2
Monolithically-grown Yttrium Iron Garnet Claddings on Silicon-on-insulator (SOI) Waveguides.
Samir Ghosh 2 , Sang-Yeob Sung 1 , Celso Cavaco 3 , Kristof Lodewijks 3 , Wim Van Roy 3 , Roel Baets 2 , Bethanie Stadler 1
2 , IMEC, Gent Belgium, 1 , U Minnesota, Minneapolis, Minnesota, United States, 3 , IMEC, Leuven Belgium
Show AbstractMagneto-optical isolators are an important missing link for the utilization of silicon-on-insulator (SOI) photonic devices because they are needed to protect undesirable reflections from impinging on active elements. Here, yttrium iron garnet (YIG) claddings were monolithically integrated onto SOI guides using reactive sputtering of either a yttrium-iron alloy target or separate yttrium and iron targets. The oxygen-argon plasma contained 10-20% oxygen in order to deposit amorphous oxide films without oxidizing the metallic targets. Subsequent rapid thermal annealing at 700-800C was required in an oxygen atmosphere to crystallize the garnet films as verified by X-ray diffraction. A critical parameter in high-quality garnet claddings is the area of contact between the waveguide and the cladding. This area was successfully reduced by using SOI guides with relatively vertical sidewalls and by a highly anisotropic deposition method. A sharp disconnect was found between the top cladding of the SOI guides and the rest of the garnet film. Therefore, although the areas between the guides exhibited cracking due to thermal stresses, the top claddings remained structurally sound. Interestingly, YIG-coated Si photonic crystals were also mechanically stable due to the nanostructuring of the substrate/film interface. Optical microscopy was used for initial characterization of the garnet top claddings. It was found that claddings of 50-320 nm thick could be deposited and annealed with few defects, and dark field microscopy was an effective means of confirming film quality. A polarizer was used to yield contrast between crystallized and amorphous regions of films that were annealed below 750C. Atomic force microscopy revealed that the garnet films were very smooth with only about 1nm RMS roughness. The garnet films were magnetically soft with coercivities of 10-50Oe. Faraday rotation and waveguide losses were measured in garnet films and guides on glass to characterize the garnet independent of the SOI structure. Faraday rotations of 0.2deg/um were measured along with waveguide losses of 1-2dB/mm. Next, garnet-cladded TE and TM SOI guides were measured and the losses due to the garnet compared to uncoated guides were measured to be as low as 0.7dB/mm.
3:15 PM - J3.3
Mechanical, Magnetic, and Optical Characterization of Magneto-optical Garnet Waveguides on Semiconducting Substrates.
Sang-Yeob Sung 1 , Anirudh Sharma 1 , Bethanie Stadler 1
1 , U Minnesota, Minneapolis, Minnesota, United States
Show AbstractMagneto-optical garnet is highly sought after in integrated photonics due to its non-reciprocal properties, but its mechanical properties do not match the Si-based materials of most photonic systems. Here, garnet films with thicknesses from 0.1 to 1.0 um and also waveguides with widths from 0.7 to 2.0um were grown onto Si in order to characterize the mechanical stresses that occur upon crystallization at 800C by rapid thermal anneal. Understanding of the stress mechanisms that cause cracking or blistering allowed subsequent fabrication of low-loss guides measured at 1.3 and 1.55um in the near infrared. The waveguide losses were 1.0-2.3 dB/mm at 1.3um and 0.9-1.7 at1.55um, increasing with waveguide width. Finite difference time domain (FDTD) simulations were used to estimate the number of modes in each guide, as well as the effective index and profile of each mode, in order to explain the trend in losses vs width. With Faraday rotations of 0.2dB/um and 1.0dB/mm loss, this integrated garnet has great potential for a multitude of photonic devices, including isolators, circulators and mode converters.
4:00 PM - **J3.4
Quasi-Phase Matching Magneto-Optical Waveguides.
David Hutchings 1 , Barry Holmes 1
1 School of Engineering, University of Glasgow, Glasgow United Kingdom
Show AbstractPhotonic integration has proved remarkably successful in combining multiple optical devices onto a single chip with the benefits of added functionality, and reduction in costs, arising from the replacement of manual assembly and alignment of individual components with lithographic techniques. However, the incorporation of optical isolators and related non-reciprocal devices within standard optoelectronic wafer platforms is exceptionally challenging. Preferred magneto-optic materials cannot be exploited as waveguide core layers on semiconductor wafers due to a lower refractive index. Another difficulty is the phase velocity mismatch as a consequence of the inherent structural birefringence associated with waveguide geometries.Our approach to the integration of an optical isolator with a III-V semiconductor laser involves combining a nonreciprocal mode converter with a reciprocal mode converter, based on an asymmetric profiled rib waveguide, fabricated by Reactive Ion Etching. We demonstrate that suitably tapered waveguides can be employed to connect the mode converter to other sections thereby avoiding problems caused by mode-matching and reflections from the section interfaces.The nonreciprocal mode converter is formed from a continuation of the III-V semiconductor waveguide core with a magneto-optic upper cladding so that Faraday rotation occurs through the interaction of the evanescent tail. The phase velocity mismatch due to the waveguide birefringence is overcome using a quasi-phase-matching approach. Lithography is used to pattern the top cladding so that the film immediately on top of the waveguide core alternates between magneto-optic and a non-magneto-optic dielectric of a similar refractive index. Our first demonstrations used a dielectric (silica or silicon nitride) patterned by etching, or lift-off, on top of a GaAs rib waveguide, over which was deposited a magneto-optic film. This film was deposited by sputtering from a Ce:YIG target and demonstrated magnetic hysteresis, but, as it was not annealed, it was believed to consist of Ce:YIG and/or gamma iron oxide microcrystallites embedded in an amorphous matrix. With quasi-phase-matching periods of 110-160 μm and a waveguide length of 8 mm, we were able to demonstrate up to 12% non-reciprocal TE- to TM-mode conversion around a wavelength of 1.3 μm using the remanent magnetisation.In order to enhance the magneto-optic effect it is desirable to anneal such films. However the mismatch in thermal expansion coefficients results in a catastrophic failure of samples with large area film coverage. This problem has been shown to be alleviated by patterning the YIG film. Unfortunately wet-etching of YIG also etches (Al)GaAs and, therefore, the development of a lift-off process for YIG deposition has been undertaken. Initial results are promising with ~100 μm × 2.5 μm YIG sections deposited on a GaAs layer which remain intact after an anneal in an oxygen atmosphere.
4:30 PM - **J3.5
Use of Ferrite Garnet Films in Magneto-optical Imaging (MOI).
Tom Johansen 1 , Atle Qviller 1 , Vitaliy Yurchenko 1 , Pietro Tierno 3 , Thomas Fischer 2 , Yuri Galperin 1
1 Dept. of Physics, University of Oslo, Oslo Norway, 3 , Universitat de Barcelona, Barcelona Spain, 2 , Universität Bayreuth, Bayreuth Germany
Show AbstractPhenomena creating intriguing traces of activity directly observable by visual methods are fascinating, and magneto-optical imaging (MOI) of flux dynamics in superconductors is one example. Using the Faraday effect of in-plane magnetized bismuth-substituted ferrite garnet films grown by liquid phase epitaxy on gadolinium gallium garnet substrates, we have discovered two modes of intermittent flux dynamics in superconducting films. One is characterized by rapid growth of branching dendritic flux structures, the other by flux needles abruptly penetrating along linear micro-defects in the superconductor. The results are analyzed theoretically, supporting that the two avalanche phenomena are of different physical origin. Fascinating dynamics is also found in the dynamics of polystyrene beads with superparamagnetic cores attracted to the magnetic walls of stripe domain uniaxial ferrite garnet films. Using MOI it is shown that by applying an ac-magnetic field monodisperse beads can hop coherently from one wall to the next in a ratchet-type of motion, demonstrating a huge potential of ferrite garnet films for particle manipulation and novel biomedical devices (Lab-on-a-chip).
J4: Poster Session: Magneto-Optic Films and Devices
Session Chairs
Vincent Fratello
Miguel Levy
Bethanie Stadler
Mathias Vanwolleghem
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - J4.1
Design of Optical Isolator with TiO2 / (CeY)3Fe5O12 Guiding Layer.
Hideki Yokoi 1 , Shintaro Ikeya 1 , Tsuyoshi Imada 1
1 , Shibaura Institute of Technology, Tokyo Japan
Show AbstractAn optical isolator employing a nonreciprocal phase shift is attractive because there is no need for phase matching or complicated control of the direction of magnetization. The nonreciprocal phase shift originates from an asymmetric structure of a waveguide. Therefore, a large nonreciprocal phase shift is expected when a magneto-optic waveguide has a high refractive index / magnetic garnet guiding layer. In this paper, we report on an optical isolator with a TiO2 / (CeY)3Fe5O12 guiding layer obtained using the nonreciprocal phase shift. The optical isolator includes an optical interferometer that consists of two multimode interference (MMI) couplers, nonreciprocal phase shifters in two arms and a reciprocal phase shifter in one of the arms. The nonreciprocal phase shift in the magneto-optic waveguide is calculated at a wavelength of 1.55 μm. The 1×2 MMI coupler in the optical isolator is designed to make a compact device. An interferometric optical isolator with distinct layer structures, which can be operated in a unidirectional magnetic field, is also designed.
9:00 PM - J4.2
Theoretical Analysis of Magnetophotonic Microcavities for Blue Light Modulation.
Taichi Goto 1 , Kotaro Yamada 1 , Hiroshi Sato 1 , Yuta Suzuki 1 , Hiroyuki Takagi 2 , Mitsuteru Inoue 1
1 , Toyohashi University of Technology, Toyohashi, Aichi Japan, 2 , Toyota National College of Technology, Toyota, Aichi Japan
Show AbstractThis paper describes theoretical performance of paramagnetic magnetophotonic microcavities that are functional for blue light intensity, polarization or phase modulations. The microcavities of our interest are composed of a paramagnetic Verde film such as Tb3Ga5O12 (TGG) and an electro-optic thin film such as LiTaO3, which are sandwiched between two anti-symmetric Bragg mirros with dielectric films. Typical structure of the film is expressed by (Ta2O5/SiO2)11/ TGG/ LiTaO3/ (SiO2/Ta2O5)20, where the optical thicknesses of the TGG and LiTaO3 films were chosen to be 10×λ/2 and 2×λ/2 with the localization wavelength of light λ (typically λ = 405 nm).Numerical computations with the matrix approach revealed that the TGG/LiTaO3 microcavity simultaneously provides a considerably high reflectivity (up to 90 %) and a large Kerr rotation angle (up to 150 degree) at the localized wavelength of 405 nm. The rotation angle of the film can be controlled with a small voltage (less than 1 V) applied to the LiTaO3 film, originating in a small change in refraction index of the film. Although the paramagnetic film is used for the microcavity, its magneto-optical effect can be manipulated as if a ferromagnetic one, suggesting that the magnetophotonic microcavity is an attractive constitutive material for various photonic devices including a blue-functional magneto-optic spatial light modulator.
9:00 PM - J4.3
Variable Birefringence on Artificially Designed Surface Gratings.
Yu-Ju Hung 1 , Jia-Hua Liou 1 , Jih-Young Tai 1 , Min-Hsiung Shih 2 , Yi-Jen Chiu 1
1 Department of Photonics, National Sun Yet-sen University, KaoHsung Taiwan, 2 Research Center for Applied Science, Academia Sinica, Taipei Taiwan
Show Abstract1.Introduction: Birefringence is necessary in many applications such as liquid crystal display or optical wave-plate applications. The artificially designed metamaterial [1] have shown fare amount of birefringence. The hyperlens concept proposed in [2-3] shows that positive or negative birefringence design is possible by simply varying the grating widths. In this report, we measured the polarization rotation caused by surface gratings on an Au film. The 1D grating acts like an uni-axial crystal. The manipulation of the polarity of Δn is achieved by changing the grating width ratios. This designed material has potential in optical data storage applications. 2. Experiment and Discussion:1D PMMA stripe gratings with 150nm thickness have been patterned on a 50nm thick gold film on a cover glass substrate. The Au film is intact under the PMMA gratings which periodicity is 500nm. Two different width ratios- PMMA grating stripe: Air = 1:1 and 3:7 have been fabricated. With a quarter wave plate, half wave plate, and polarizers, the output polarization state has been depicted on the Poincare sphere. The measured degree of polarization (DOP) is almost 1 which suggests that this 1D artificial structure is good linear uniaxial crystal-like material. Bare Au film and PMMA film on Au substrate don’t show any birefringence. The measured birefringence phenomenon simply comes from the interaction between gratings and Au film. The width ratio “r” between PMMA stripe and air shows that Δn=n∥-n⊥ can be > 0 and < 0 while r = 1 and 3/7 respectively. Our results suggest that PMMA/Au and PMMA/Air interfaces possess the effective refractive index n < 0 and n > 0 respectively. The origin of the polarity change on the effective refractive index comes from surface plasmon polariton effect. The dispersion curve on the two different interfaces shows n positive and negative relations. It is consistent with the indication comes from the hyperlens theory[2], experimental result[3] and multilayered formula[4]. 3. Conclusions:A variable birefringence effect has been observed with 1D PMMA surface gratings on a gold film substrate. By varying the ratio between PMMA grating stripe and air on the Au film, the birefringence value Δn changes rapidly spanned from positive to negative.4. Reference:[1] Aurelien Drezet, Cryiaque Genet, and Thomas W. Ebbesen, ‘Miniature Plasmonic Wave Plates’, Physical Review Letters 101, 043902, 2008.[2] Zubin Jacob, Leonid V. Alekseyev and Evgenii Narimanov, “Optical Hyperlens: far-field imaging beyond the diffraction limit,” Optics Express, V.14, No.18, 8247, 2006.[3] I. I. Smolyaninov, Y-J Hung, and C. C. Davis, Imaging and focusing properties of plasmonic metamaterial devices, Physical Review B,76,205424,2007.[4] S.M. Tytov, Electromagnetic Properties of a Finely Stratified Medium, Soviet Physics JETP, V.2 N3, p466, 1956.
9:00 PM - J4.4
On-chip Integration of Chalcogenide Glass/Iron Garnet Strip-loaded Waveguides for Integrated Non-reciprocal Photonic Device Applications.
Lei Bi 1 , Juejun Hu 1 , Gerald Dionne 1 , Lionel Kimerling 1 , Caroline Ross 1
1 DMSE, MIT, Cambridge, Massachusetts, United States
Show AbstractOn-chip integration of ferromagnetic iron garnets has been a challenging problem for integrated non-reciprocal photonic device applications due to their large lattice mismatch, thermal mismatch compared with semiconductor substrates and high thermal budget for crystallization. Using rapid thermal processing (RTP) and chemical etching, recent research shows the potential of using polycrystalline Y3Fe5O12 in on-chip planar photonic devices. It is therefore highly desired that ferromagnetic iron garnets such as Y3Fe5O12 (YIG), (Bi,Y)3Fe5O12 (Bi:YIG), and (Ce,Y)3Fe5O12 (Ce:YIG) can be integrated on a silicon platform using etch-free and fast prototyping techniques. Also as a starting point for non-reciprocal photonic device fabrication, the transmission loss and magneto-optical figure of merit of these devices need to be studied at the communication wavelengths.In this study, we report a novel route of integrating YIG and Bi:YIG polycrystalline films on a silicon platform using a chalcogenide glass (ChG)/iron garnet strip-loaded waveguide structure. Polycrystalline YIG films were deposited on an oxidized silicon substrate by pulsed laser deposition (PLD) followed by RTP. The film crystallized into the pure YIG phase with a crystal size of around 22nm. A saturation magnetization of 130emu/cm3 is achieved with an in-plane saturation field lower than 100 Oe. Bi:YIG films with two different Bi concentrations, i.e. Bi0.8Y2.2Fe5O12 (Bi0.8YIG) and Bi1.8Y1.2Fe5O12 (Bi1.8YIG) were deposited on oxidized silicon substrates by PLD on a 20nm thick polycrystalline YIG buffer layer. These films form single phase garnet with larger lattice constants and similar saturation magnetizations but higher saturation magnetic field up to ~500 Oe compared with pure YIG. 2μm to 8μm wide As2S3 and GeS2 chalcogenide glass channels were fabricated on top of the garnet layers using optical lithography, thermal evaporation and lift-off process to form strip-loaded waveguides. The optical transmittance spectra of these waveguides were characterized at a wavelength range of 1475nm to 1553nm, and the transmittance loss at 1550nm was determined by using the cut-back method. The ChG/YIG waveguides showed a transmission loss of ~10dB/cm which corresponded to a material loss of ~50dB/cm from the YIG layer; whereas a material loss of ~100dB/cm was estimated from Bi0.8YIG layer in the ChG/Bi0.8YIG waveguide, which is possibly due to particulate formation during PLD. By simulation, a maximum non-reciprocal phase shift of 36.8deg/cm and a figure of merit of 3.12 deg/dB are expected in a As2S3(280nm)/YIG(80nm) waveguide. Possible improvements on the device figure of merit will be discussed based on using Bi:YIG films with higher Faraday constants. Our study provides an etch-free and fast prototyping method to integrate magnetic garnets on silicon, which can be incorporated into integrated non-reciprocal photonic devices.
9:00 PM - J4.5
Structure and Magnetic, Magneto-optical Properties of Sr(Ti0.6-xGaxFe0.4)O3 Thin Films.
Peng Jiang 1 , Lei Bi 1 , Gerald Dionne 1 , Caroline Ross 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractRoom temperature ferrimagnetic garnets are widely used in discrete non-reciprocal photonic devices. However, garnets do not have a good lattice and thermal match with semiconductor substrates, such as Si or GaAs, which makes the integration of garnets challenging. In a search for alternative materials, we found that Sr(Ti1-xFex)O3 films show intrinsic ferromagnetism, high resistivity and a significant magneto-optical effect at near infrared wavelengths, as well as good lattice match to silicon, which make them promising candidates for integrated non-reciprocal photonic devices at the communication wavelengths. In order to further improve the figure of merit of this material for optical isolator or circulator applications, one needs to either increase the Faraday rotation or decrease the optical absorption. It is expected by introducing electronic defects in the Sr(Ti1-xFex)O3 lattice, the cation valence state can be controlled, the optical absorption can be reduced and the magneto-optical figure of merit can be enhanced.In this study, the structure, magnetic, magneto-optical and optical properties of epitaxial Sr(Ti0.6-xGaxFe0.4)O3 (x=0, 0.05, 0.1, 0.2, 0.3 and 0.4) thin films grown on (001) LSAT substrates by pulsed laser deposition were studied as a function of Ga concentration. X-ray diffraction and X-ray photoelectron spectroscopy were utilized for phase identification and electronic structure analysis. Films formed in a single phase epitaxial perovskite structure. The optical transmission spectra of 350nm thick Sr(Ti0.6-xGaxFe0.4)O3 films with different Ga concentrations were obtained within a wavelength range of 200–2000 nm by spectrophotometry. The films become increasingly transparent in the visible and near infrared wavelengths as the Ga content increases. The optical transmittance of the films around near infrared wavelengths (normalized to substrate transmittance) increases from 93% to 97% with increasing Ga. A significant enhancement of optical transmission is also observed in the visible range. The room temperature magnetic and magneto-optical properties were characterized by vibrating sample magnetometry and Faraday rotation at 1550nm wavelength. The saturation magnetization and Faraday rotation of these films decreased slightly by Ga doping. The saturation moment and saturation Faraday rotation at 1550nm wavelength of the film with x=0.2 are 0.64 μB/Fe and 0.102 deg/μm respectively, compared with the film x=0 for 0.68 μB/Fe and 0.154 deg/μm respectively. We believe that Ga (III) serves as an electronic acceptor which drives Fe and Ti ions to higher valence states and eliminates the optical absorption contribution from these ions at the lower valence states. The enhancement of material transparency and magneto-optical figure of merit makes this system a promising candidate for on-chip non-reciprocal photonic applications.
9:00 PM - J4.6
Waveguide Circulators Based on Two-Dimensional Magnetophotonic Crystals: Numerical Simulation for Structure Simplification and Experimental Results.
Kazuo Yayoi 1 , Kazuma Tobinaga 2 , Yusuke Kaneko 2 , Alaxander Baryshev 2 , Mitsuteru Inoue 2
1 , Ibaraki National College of Technology, Hitachinaka Japan, 2 , Toyohashi University of Technology, Toyohashi Japan
Show AbstractArtificial structures comprising altered dielectric and magnetic materials with a period on the scale of wavelength of light – so-called magnetophotonic crystals (MPCs) – are attractive due to possibility to control propagation of light by external magnetic fields. Two-dimensional MPCs are of interest because they are shown to be useful for such applications as magnetic superprisms and optical micro-circuits in waveguiding regime (bandpass filters, isolators and circulators). The 2D MPC with built-in magnetic materials is theoretically shown to act as a waveguide optical circulator [1]. The discussed model of a 2D MPC-based circulator has a complicated magnetization pattern and infinite dimensions that is why practical realization of the circulator is difficult. For 2D MPC circulators’ structure simplification, their propagation characteristics were numerically simulated and optimal structural parameters were defined.We propose magneto-optical circulators with the following structure working at the optical communication wavelength. A single domain magnetized magnetic defect was introduced into the center of a finite slab of 2D PC with the hexagonal lattice. The slab was Si with a 2D array of air holes. Ridge Si waveguides, optical input/output ports, were connected to three hexagonal sides of the slab. The air holes had a diameter of 462 nm, and a period of 2D lattice was 550 nm. Bismuth-substituted yttrium iron garnet (a Bi:YIG rod) was chosen as a nonreciprocal material to be embedded into the center of the slab. Si was considered to be the zero-loss material with ε = 12, and Bi:YIG had εxx = εyy = 4.4, εxy = −εyx = 0.02i. Numerical modeling of light propagation was done using a finite element computation, COMSOL.Result of the numerical simulations showed that the structure described above performed circulation of the flow of light. The isolation and the insertion loss of the 2D MPC circulator changed depending on the diameter of the Bi:YIG defect; the diameter was varied in a range of 100–650 nm. The spectrum of isolation in a range of 1400–1900 nm had two peaks where maximal isolation corresponding to certain diameters of Bi:YIG defects was obtained. Together with this effect, the insertion losses of the circulator gained their minima. We fabricated an experimental 2D MPC circulator and tested its characteristics. Si thin film was formed on glass substrate by sputtering, the 2D structuring was made using a focused ion beam (FIB) system, and a Bi:YIG rod was embedded by the micro-sampling method. Properties of the circulators were measured when coupling light to the circulator by a lensed fiber and detecting responses by the use of an optical measurement system.[1] Z. Wan and S. Fan, J. Appl. Phys. B, 81, 369–375 (2005)
9:00 PM - J4.7
Magnetophotonic Crystals with Metalized Surfaces for Biosensor Applications.
Kohei Kawasaki 1 , Alexander Baryshev 1 , Mitsuteru Inoue 1
1 , Toyohashi University of Technology, Tempaku, Hibari-Ga-Oka Japan
Show AbstractIn this work we demonstrate that tailoring of surfaces of magnetophotonic crystals (MPCs) provides a new approach to engineer their responses that can be useful for optical sensor applications. One-dimensional MPCs comprising magneto-optical garnets and terminated by a noble metal (gold) layer were fabricated using sputtering. Experimental samples had multilayer or microcavity structures, where the thickness of Au film did not exceed 50 nm. Parameters of these multilayers were chosen such that they supported spectrally narrow localized states. These states were spectrally located within photonic band gaps and were associated with a sharp reflection/transmission peak in measured spectra of the MPCs. Responses from the samples were studied in the regime of plasmon excitation (Kretschmann geometry) where optical resonances in reflection spectra spectrally overlapped with the plasmonic band. Tuning/detuning the overlapping of these two intrinsic resonances by a variation of analytes' refractive index resulted in the sharp change of measured optical and magneto-optical responses.
Symposium Organizers
Bethanie Stadler University of Minnesota
Miguel Levy Michigan Technological University
Mathias Vanwolleghem Universite Paris-Sud
Vincent Fratello Integrated Photonics, Inc.
J5: Magneto-Optic Isolators and Circulators
Session Chairs
Vincent Fratello
Miguel Levy
Bethanie Stadler
Mathias Vanwolleghem
Wednesday AM, December 01, 2010
Room 201 (Hynes)
9:30 AM - **J5.1
Design and Analysis of Integrated Magnetophotonic Circulators.
Wojciech Smigaj 1 , Liubov Magdenko 2 , Javier Romero-Vivas 3 , Sebastien Guenneau 1 , Boris Gralak 1 , Pierre Beauvillain 2 , Beatrice Dagens 2
1 , Institut Fresnel, CNRS, Aix-Marseille Université, Ecole Centrale Marseille, Marseille France, 2 , Institut d’Electronique Fondamentale, Université Paris-Sud, Orsay France, 3 Surface Physics Division, Faculty of Physics, Adam Mickiewicz University, Poznan Poland
Show AbstractA resonator-based circulator is a well-known microwave component. It consists of three waveguides coupled to a resonant cavity containing a ferromagnetic material. A static external magnetic field (SEMF) couples two otherwise degenerate cavity eigenmodes and splits their frequencies. The circulator’s operation bandwidth is proportional to the frequency splitting Δω, which in turn depends on the geometry of the cavity. A few years ago, Wang and Fan [1] presented a theoretical analysis of an optical-domain version of this device, based on two-dimensional photonic crystals (PCs). In comparison to commercially available optical isolators and circulators, typically several millimetres long [2], the footprint of this device could be very small, ~1 μm2. Having found typical PC cavities etched in a uniformly magnetised magneto-optical (MO) material to provide only a small Δω, Wang and Fan proposed to divide the MO material into several domains magnetised in opposite directions. Unfortunately, owing to the difficulty of fabricating domains of the required small size (~100–200 nm), such a device has never been manufactured. Here we propose several ways of simplifying this design, which should pave the way to an experimental realisation of a resonator-based optical circulator.First, we show that large Δω can be obtained in uniformly magnetised cavities. To this end, we study the restricted class of cavities composed of concentric rings and demonstrate analytically what choice of ring radii leads to the strongest SEMF-induced mode coupling [3]. Although such cavities can be adapted for integration in a PC, we argue that introduction of a periodic lattice is not necessary for a good in-plane light confinement. Abandoning the PC-based design, we obtain a much simpler geometry without sacrificing performance. We study next the issue of optimum waveguide-cavity coupling. Extending the original coupled-wave model of a circulator [1] to include the effects of radiation loss, we derive analytical constraints on the approximate optimum waveguide-cavity distance and the minimum quality factor of a cavity ensuring a sufficiently small insertion loss. We find these predictions to match well the results of numerical simulations. Lastly, we discuss the important issue of the influence of the multilayer structure on the out-of-plane radiation loss, not addressed in the previous publications [1, 3]. We show that this loss, while prohibitively large in cavities etched in bismuth-iron-garnet layers grown on gadolinium-gallium-garnet substrates and designed using the effective-index approximation, can be dramatically reduced in structures covered with a material having a refractive index close to that of the substrate. We also explore the experimentally attractive possibility of leaving the MO layer unetched.[1] Z. Wang and S. Fan, Opt. Lett. 30, 1989 (2005). [2] H. Doetsch et al., J. Opt. Soc. Am. B 22, 240 (2005). [3] W. Smigaj et al., Opt. Lett. 35, 568 (2010).
10:00 AM - **J5.2
Optical Isolation on Integrated Platforms – A Perspective.
Richard Osgood 1
1 Microelectronics Sciences Laboratory, Columbia University, New York, New York, United States
Show AbstractIn this talk, I review progress on integrated optical isolation devices and materials technology. The discussion will include careful magnetic thin-film engineering to form micrometer-scale waveguide magnetic fields, lift-off technology and other novel thin film processing methods to enable heterointegration of epitaxial garnet films, use of transverse magnetic fields for isolation, and finally nanooptical methods for isolation functionality. Finally I will present a recently demonstrated YIG/SOI isolator and discuss its performance. As will be brought out in the talk, this progress has been the result of major, key collaborations with other groups in the US, Germany, and Japan.
10:30 AM - **J5.3
Non-magnetic Optical Crculators and Isolators Using Dynamic Index Modulation.
Shanhui Fan 1 , Zongfu Yu 1
1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractWe show that non-reciprocal devices can be created dynamically, with the use of spatial-temporal refractive index modulation. Unlike other non-magnetic schemes previously considered, with proper design such dynamic photonic structures provide a linear response that can completely reproduce the functionalities of magneto-optical devices, including circulators and isolators.
11:30 AM - J5.4
Magneto-photonic Ring Circulator in Bismuth Iron Garnet Thin Film: Design and Fabrication.
Liubov Magdenko 1 2 , Elena Popova 3 , Wojciech Smigaj 4 , Pierre Beauvillain 1 2 , Niels Keller 3 , Boris Gralak 4 , Philippe Gogol 2 1 , Robert Megy 2 1 , Mathias Vanwolleghem 1 2 , Beatrice Dagens 1 2
1 , CNRS, IEF,UMR 8622, Orsay France, 2 , Univ Paris Sud, IEF, UMR 8622, Orsay France, 3 , Groupe d’Etude de la Matière Condensée, CNRS – UVSQ, Versailles France, 4 , Institut Fresnel, CNRS, Marseille France
Show AbstractNon-reciprocal functions like optical isolation or circulation are expected to significantly increase the integration capabilities and the size of photonic circuits. For example, the use of such functions in optical circuits allows inserting emitting sources like laser without risk of degradation due to internal feedback. For integrated optic, the most promising isolator or circulator principle consists in using transverse magneto-optical Kerr effect (MOKE), in garnet based devices [1] or in ferromagnetic metal based semiconductor amplifier [2]. Garnet based waveguide presents the advantage of low optical losses at telecom wavelength. But the relatively low magneto-optical strength has led to large devices like a several millimeter long interferometer [1]. Here we have focused our work on resonant ring circulator in order to obtain non-reciprocal behavior in a compact cavity [3]. We have simultaneously considered device design and fabrication in order to establish the best compromise between performance and technology. Designing an optical circulator is a first challenge due to the lack of simulation tools which take into account the non-diagonal permittivity tensor and the waveguiding multilayer structure. Here, we have considered first an analytical 2D approach based on perturbative model and multilayer effective index [3] which allows determining the number and the position of the cavity rings. Then thanks to 3D finite element calculation we have checked the optical confinement in the magneto-optical layer when the cavity structure is realized. Especially we have shown that the garnet layer has to be embedded in a silicon nitride layer. Finally through evaluation of the contra-circulating cavity modes quality factor in 3D calculation, we have determined an optimal design concerning the extinction ratio between different circulator outputs.The second challenge is the device fabrication. The aim is to also demonstrate the wafer-scale fabrication of such devices. We have fabricated garnet based circulator by adapting standard technological process to the particular case of oxide thin film nanostructuration. Bismuth-Iron garnet 300nm thick film was grown by pulsed laser deposition on Gadolinium-Gallium garnet (100) substrate. Design was defined by electronic lithography and transferred into a metallic mask before etching by chloride based ICP-RIE. Devices were cleaved for test on a fiber based optical bench. Optical and magneto-optical characterizations are pending.[1] H. Yokoi and T. Mizumoto, Electron. Lett. 33(21), 1787, 1997.[2] W. V. Parys, B. Moeyersoon, D. Van Thourhout, R. Baets, M. Vanwolleghem, B. Dagens, J. Decobert, O. Le Gouezigou, D. Make, R. Vanheertum, L. Lagae, Appl. Phys. Lett. 88, 071115, 2006[3] W. Smigaj, J. Romero-Vivas, B. Gralak, L. Magdenko, B. Dagens, M. Vanwolleghem, Optics Letters, 35 (4), pp568-570, 2010
11:45 AM - **J5.5
SOI Waveguide Optical Nonreciprocal Devices with Directly Bonded Garnet.
Tetsuya Mizumoto 1 , Ryohei Takei 1
1 Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Tokyo Japan
Show AbstractOptical isolators are indispensable to protect optical active devices from unwanted reflections. Magneto-optic materials are essential to obtain an optical nonreciprocal function. However, the platform used to construct photonic circuits is composed of non-magneto-optic materials, like III-V compound semiconductors, silicon and silica. Therefore, it is needed to develop the technology for integrating a magneto-optic material with them. A magneto-optic garnet is the best candidate in an optical fiber communication wavelength range because of its low absorption and large magneto-optic effect.We developed a surface activated direct bonding technique to integrate a magneto-optic garnet on III-V, silicon and silica. Using this technique, we fabricated an interferometric isolator that was composed of a GaInAsP guiding layer. The interferometer is designed so that the constructive and destructive interference occurs in the forward and backward direction, respectively, by employing the nonreciprocal phase shift. A similar approach was successfully taken to realize an optical isolator in a silicon waveguide fabricated on an SOI wafer. We demonstrated an isolation of 21 dB at 1559 nm in the silicon interferometric waveguide isolator, where a Ce:YIG cladding layer was directly bonded on a silicon rib waveguide. The surface activation process with plasma generated in O2 is used for bonding the garnet onto silicon at 250 OC. In these cases, relatively low temperature process is crucial for bonding dissimilar crystals by circumventing the problems associated with a mismatch in thermal expansion between two crystals. In this paper, we discuss the dependences of wafer pre-treatment and plasma conditions on the bonding of garnet and silicon.The direction-dependent phase difference in an interferometric waveguide is extended to realize a waveguide optical circulator. A silicon waveguide circulator is designed with a crosstalk < -20 dB and an insertion loss < 0.1 dB in a wavelength range between 1535 nm and 1560 nm. The length of device is 430 μm. The design detail of interferometric waveguide optical circulator is described in this paper.
12:15 PM - **J5.6
Magneto-optics in Diluted Magnetic Semiconductors and in Ferromagnetic-Metal/Semiconductor Hybrids.
Vadym Zayets 1 , Hidekazu Saito 1 , Shinji Yuasa 1 , Koji Ando 1
1 Spintronics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show AbstractPhotonics devices benefit from unique non-reciprocal properties of magneto-optical materials. Important optical components such as an optical isolator and circulator can be only made using the magneto-optical materials.Diluted magnetic semiconductors are attractive magneto-optical materials, because high crystal quality DMS films can be grown on semiconductor substrates. We achieved excellent performance of DMS isolator. Complete TE-TM mode conversion, a high Faraday rotation of 2000 deg/cm, a high isolation ratio of 27 dB, a low optical loss of 0.5 dB/cm, and a high magneto-optical figure-of-merit of 2000 deg/dB/kG were demonstrated in a wide 25-nm wavelength range for CdMnTe waveguide grown on GaAs substrate. These values are comparable or better to that of commercial discrete isolators. The propagation of waveguide mode in CdMnTe magneto-optical waveguide is very similar to the light propagation in magneto-optical bulk media. Therefore, non-reciprocal elements such as an optical isolator, circulator and polarization independent isolator can be fabricated by CdMnTe waveguides using a similar scheme as is used for free space components. Since DMS waveguides can be grown on semiconductor substrates, using DMS waveguides it is possible to integrated these non-reciprocal optical components into semiconductor-made optoelectronic integrated circuits.Optical waveguide isolators, either made of DMS or made of garnets, required high-crystal quality materials in order to have a low optical loss and a high value of Faraday rotation. The defect density in DMS or garnet film should be kept low until the end of the microfabrication process. For the fabrication of integrated optical circuits it is more convenient to use common fabrication technique like sputtering, e-beam evaporation and lift-off. Ferromagnetic metals, like Fe, Co or Ni are very attractive for this purpose. They have high magneto-optical constants and the microfabrication of these metals is simple and well established for optoelectronic integrated circuits. Semiconductor/metal hybrid waveguide optical isolator was predicted theoretically (Zayets PTL 1999) and demonstrated experimentally (Vanwolleghem APL 2004, Shimizu JJAP 2004, Zayets APL 2005). At present, the major limitation for practical applications of the hybrid isolator is relatively high current required to compensate the absorption of the metal. In our talk we will discuss the origin of non-reciprocal effect in hybrid isolator, the fabrication technology and performance of the isolator and the methods to reduce the operational current of the isolator in order to meet the requirements for the integration of the isolator into present optoelectronic integrated circuits.
J6: Magneto-Plasmonics
Session Chairs
Wednesday PM, December 01, 2010
Room 201 (Hynes)
2:30 PM - **J6.1
Transmission Magnetooptical Kerr Effect in Plasmonic Nanostructures.
Vladimir Belotelov 1 2 , Ilya Akimov 3 , Martin Pohl 3 , Arvind Vengurlekar 4 , Achanta Gopal 4 , Dmitry Yakovlev 3 , Vyatcheslav Kotov 5 2 , Anatoly Zvezdin 2 , Manfred Bayer 3
1 , M.V. Lomonosov Moscow State University, Moscow Russian Federation, 2 , A.M. Prokhorov General Physics Institute RAS, Moscow Russian Federation, 3 , Dortmund University, Dortmund Germany, 4 , Tata Institute of Fundamental Research, Mumbai India, 5 , V.A. Kotelnikov Institute of Radio Engineering and Electronics RAS, Moscow Russian Federation
Show AbstractNowadays, much effort is being made in the area of nanophotonics, which demands materials with outstanding optical performance and tunability at the nanosecond time scale. For these purposes, magnetooptical materials hold great potential since their optical properties can be easily altered via magnetic field. However, the magnetooptical effects are usually not sufficiently strong. Until recently, the streamline in the magnetooptical effects enhancement was on chemical side. In this paper we propose a new concept. It was revealed recently that surface plasmons lie at the root of the extraordinary optical transmission phenomenon in the metallic films periodically perforated with subwavelength hole or slit arrays. Surface plasmons also remain decisive in the proposed here nanoscale magnetooptical material. In this material a thin magnetic dielectric film is attached to the perforated metal, thus constituting a kind of metal-dielectric heterostructure with nanoscaled pattern. Unique features of the proposed material are high value of the magnetooptical constant and low optical losses. We demonstrate experimentally a significantly enhanced the transverse Kerr effect in transmitted light. Observation of this effect in transmission in smooth ferromagnets is extremely difficult because of its small value and/or ultra low detected light intensity. The new magnetoplasmonic material allowed to make the effect several orders larger and to observe it near the extraordinary transmission peaks. Furthermore, the effect is very sensitive to the properties of the surface plasmons and is shown to be an efficient method for in-depth studies of plasmonic systems. The other magnetooptical effects can be also enhanced by the same structure. It is possible to switch among the effects by applying magnetic field in different directions. It is of great importance for applications in the fields of telecommunication, computing and sensing.
3:15 PM - J6.3
Extraordinary Non-reciprocal Dichroism of the Bloch Modes in Transverse Magnetoplasmonic Waveguide Gratings.
Mathias Vanwolleghem 1 , Liubov Magdenko 1 , Pierre Beauvillain 1 , Beatrice Dagens 1
1 Institut d'Electronique Fondamentale (CNRS UMR8622), Université Paris Sud, Orsay France
Show AbstractOne of the most successful approaches to monolithically integrating isolation on standard telecom material platforms is based on the use of a transversely magnetized ferromagnetic metal cladding layer (for instance Co50Fe50). The magneto-optic Kerr effect will in this way induce a non-reciprocal (NR) loss for the guided light. Forward transparency can be achieved by current injection into an active layer of the III-V waveguide. We have reported monolithically integrated isolation of 13dB in a 2mm long device that is forward transparent under 160mA current injection [1]. These performances are close to what has been modelled as being theoretically optimally achievable with this approach. A further needed improvement has therefore to come from the introduction of a disruptive non-reciprocal physical effect. In the present study we report that such an enhancement can be obtained by patterning the MO metal layer into a chain of nanostripes. The discrete plasmonic modes of such a finite periodic chain are expected to lead to resonances in the nonreciprocal behaviour of the device. The behaviour of this device has been simulated using an in-house developed local NR eigenmode expansion method based on an aperiodic Fourier modal method [2,3]. Using a standard stable S-matrix algorithm on one period of the waveguide grating, we calculate the dispersion of the NR Bloch supermodes that are formed by evanescent coupling via a thin spacer layer between the plasmonic modes on the transversely magnetized ferromagnetic stripes and the standard TM slab modes of the III-V guide.This dispersion is studied both as a function of the geometrical waveguide grating parameters (metal height, fill factor, period, evanescent coupling layer) as well as a function of the wavelength. It is found that the NR loss of the fundamental Bloch modes in these structures exhibits a surprisingly strong dispersion, often even changing sign by simply varying a geometrical parameter under fixed magnetization and wavelength. This implies that the high loss direction can change from forward to backward without switching the magnetic field in the grating This sign change merely as a function of layer thickness is never observed in waveguides covered by continuous ferromagnetic films. We have found that this behaviour is linked to the coherent excitation of the strongly NR surface plasmons on the stripe surfaces at each grating indentation. The mechanisms of this NR plasmon generation will be discussed. It will be shown how this strong non-reciprocal loss dispersion as a function of geometrical parameters is accompanied by an extraordinary maximization of the NR phase difference of the Bloch modes in a manner that is reminiscent of a Kramers-Kronig relationship. We believe that this opens up new possibilities for integrated NR circuits.[1] M. Vanwolleghem et al., Appl. Phys. Lett., 85, 3980 (2004).[2] E. Silberstein et al. JOSA A 18, 2865 (2001).[3] L. Li, J. Mod. Optics 45, 1313 (1998).
3:30 PM - J6.4
Magnetoplasmonic Structures of Periodically Embedded Au Nanowires in Yttrium Iron Garnet.
Anirudh Sharma 1 , Sang-Yeob Sung 1 , Bethanie Stadler 1
1 Electrical and Computer Engineering, University of Minnesota, Twin Cities, Minneapolis, Minnesota, United States
Show AbstractNanostructures composed of plasmonic metals together with magneto-optic films such as yttrium iron garnet (YIG) are of special interest due to possible applications for controlling light at the sub-micron scale. Here, Au-filled periodic nanopores in YIG films were made using anodic aluminum oxide (AAO) templates that were ordered via nanoimprinting. First, imprint stamps with pillar diameters of 100nm and interpillar spacings of 400nm were made by ebeam lithography and reactive ion etching of 100nm-thick silicon nitride films, including both square and hexagonal patterns. These stamps were used to imprint aluminum films on Si wafers. The patterned aluminum was then anodized to make periodic arrays of holes onto which yttrium iron garnet (YIG) was deposited using reactive ion sputtering. The resulting films were annealed at 800C with rapid thermal annealing in oxygen to produce the garnet crystal structure. The AAO template was an excellent substrate for this easy nanostructuring of garnet as it remained stable throughout the process. Next, gold nanowires were electrochemically deposited into the pores, thus creating the desired magnetoplasmonic structure. Characterization of each step involved scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and UV-NIR transmission and reflectance spectra. In addition, vibrating sample magnetometry (VSM), Faraday rotation, and cathodoluminescence were used to characterize the magnetic and optical properties. Optimal long-range order was obtained in the AAO templates with an imprinting pressure of 1400psi and the stamps were reused 10-20 times, demonstrating reliability and cost effectiveness. XRD and optical microscopy indicated that the garnet films were fully crystallized, and the stoichiometry and underlying AAO pattern transfer was observed with EDS/SEM. These films were transparent from about 500nm (bandgap of YIG) to 3.1nm. The garnet films were soft magnetically with coercivities of 20-100 Oe, and they were measured (without nanostructuring) to have Faraday rotations of 0.2 deg/um. The gold nanowires had cathodoluminescence counts of 3.4x10^4 compared to 4.5x10^3 for the background. The plasmonic resonance of the Au nanowires was shown to shift with an applied magnetic field.