Magneto-optic Waveguide Research Articles

Magnetic control of optical spatial solitons.

Calculations involving the propagation of a pair of bright, spatial solitons in magneto-optic waveguides are presented. It is shown that an external magnetic field can force bright solitons from a state of attraction to each other into isolation from each other. It is also shown that TE-TM conversion, a typical magneto-optic phenomenon, can be controlled by the input power. Finally, an elegant Hamiltonian analysis of the critical points of the phase space is used to prove that various stable, or unstable, regimes can be established.

Beam-propagation in magnetooptic waveguides

The propagation of modes in magnetooptic waveguides distinguishes between the forward and the backward direction. This effect is applied to the realization of integrated optical isolators and circulators. The paper presents a finite-difference beam propagation simulation of such devices. Two different directions of the waveguide magnetization are considered. Finally, some consequences with respect to the practical realization of nonreciprocal integrated optical components are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Preparation of Magneto-Optic Single-Mode Buried Channel Waveguides of Lanthanum- and Gallium-Substituted Yttrium Iron Garnet

Magneto-optic single-mode buried channel waveguides are prepared using lanthanum- and gallium-substituted yttrium iron garnet [(La, Ga):YIG] liquid-phase-epitaxial film. The film growth conditions, film properties and the core ridge fabrication method are described. The refractive index of the film is controlled with the film growth temperature. The core ridge size is well controlled using ion beam etching. The obtained waveguides provide low loss coupling with a silica-based waveguide, which is a platform waveguide for a hybrid optical integrated circuit. Magneto-optic mode conversion is observed in a weak applied magnetic field, and the conversion efficiency R max and isolation ratio are evaluated. The relationship between R max and the stress-induced birefringence is discussed.

Geometric phases in magnetooptic channel waveguide devices

Geometric phases, generated by a coupling process between TE and TM polarizations through anisotropic chiral media-magnetooptic channel waveguides-are determined. In fact, many of the conventional phase and frequency shifters are based on this geometrical effect, nevertheless, the physical origin of these phase factors (spatial and temporal ones) has never been explained. In this work a physical interpretation, based on the topological phases theory, is given. Likewise, an integrated interferometer is proposed for both generating and checking these phases by changing the characteristics of the channel waveguides. The relationship between geometric factors and phase and frequency shifters is shown in the work.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical waveguide isolator based on nonreciprocal radiation

A new waveguide isolator which has a simple structure is proposed and experimentally demonstrated. The isolator operates on the basis of nonreciprocal guided-radiation mode conversion in a channel magneto-optic waveguide. The isolator was realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. 13.3 dB isolation was obtained at a wavelength near 1.55 μm.

Magneto-optic channel waveguides in Ce-substituted yttrium iron garnet

This article describes the demonstration of magneto-optic channel waveguides in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. The rib waveguides are successfully produced by employing a new etching technique, which is a reactive ion etching method using BCl3 gas. The nonreciprocal phase shift in the magneto-optic waveguides is measured by using a new improved measurement method. These waveguides exhibit the largest nonreciprocal phase shift ever reported of 21.1 rad/cm (λ=1.55 μm).

Mode conversion in a magnetooptical waveguide with a band domain structure

The solutions of the equations of coupled modes, describing the propagation and conversion of waveguide modes in a magnetooptical planar waveguide with a band domain structure, are obtained in the two-mode approximation. Dispersion relations are derived for unidirectional and oppositely traveling modes. The mode coupling as a function of the parameters of the structure and the orientation of the magnetization in the domains is investigated for different types of magnetization distribution in the domain structure. Wave-guide-mode conversion is analyzed taking the linear magnetooptical coupling into account.

Phase-matching in magneto-optic waveguides with W-shaped refractive index profile

A new experimental set-up is proposed to observe TE-TM mode conversion in magneto-optical waveguides. The phase matching is achieved by using the splitting of the eigenvalues that occurs as two identical waveguides are brought into close proximity. Each TE and TM mode is split into two compound modes whose propagation constants are shifted up and down relative to their original values. A symmetrical W-structure can be obtained by stacking up two identical slab waveguides with their guiding films placed next to each other.

An efficient finite-element analysis of magnetooptic channel waveguides

A finite-element method based on the scalar-wave approximation is developed for the analysis of magnetooptic waveguides. A simple and efficient iterative method is proposed for solving a nonlinear eigenvalue equation derived from the scalar finite-element approach. To show the validity and usefulness of this method, examples are computed for magnetooptic rib-type and ridge-type waveguides. The waveguide structures which have larger nonreciprocal phase shift are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Permanent magnet-based guided-wave magnetooptic Bragg cell modules

Compact magnetostatic forward volume wave-based guided-wave magnetooptic (MO) Bragg cell modules have been realized by utilizing a pair of small samarium-cobalt permanent magnets together with a pair of current-carrying coils. A highly uniform DC magnetic field, has been obtained in the air gap where yttrium iron garnet-gadolinium gallium garnet (YIG-GdGG) waveguide samples are inserted. A tunable DC magnetic field as large as 2446 Oe corresponding to a tunable carrier frequency band of 6.85 GHz has been achieved. The resulting MO Bragg cell modules, at the optical wavelength of 1.303 mu m, with carrier frequencies ranging from 2.0 to 12.0 GHz have provided performance characteristics comparable to those obtained by using a bulk electromagnet. Compact MO Bragg cell modules have potential applications, such as scanning, switching of light beams, and real-time processing of wide-band microwave signals without requiring frequency down-conversion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polarization-rotated conversion in magneto-optic waveguide using coupling coefficient reversal

Transverse-electric transverse-magnetic (TE-TM) mode conversion in a magnetooptic waveguide by use of a reversal of a coupling coefficient is addressed. A transmission matrix treatment for a class of coupled mode systems is used for the design of an experimental arrangement. The reversal method used is proved qualitatively to be advantageous to improve an incomplete conversion by the experiment using a (YLa)/sub 3/(FeGa)/sub 5/O/sub 12/ rib channel waveguide at 1.15 mu m wavelength. The method was previously investigated with a slab waveguide by the authors, and its usefulness was qualitatively confirmed. In the present work attention is paid to quantitative verification.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

RF MAGNETIZATION OF MAGNETOSTATIC FORWARD VOLUME WAVE IN A YIG-GGG LAYERED STRUCTURE WITH APPLICATION TO DESIGN OF HIGH-PERFORMANCE GUIDED-WAVE MAGNETOOPTIC BRAGG CELLS

Explicit expressions for the RF magnetization of magnetostatic forward volume waves (MSFVW) generated by a microstrip line transducer in a Yttrium Iron Garnet-Gadolinium Gallium Garnet (YIG-GGG) layered structure sandwiched between two finite ground planes have been derived for the first time. The behavior of the RF magnetization as a function of various physical and geometrical parameters and its influence on the design of high-performance guided-wave magnetooptic (MO) Bragg Cells are studied in detail. The effects of DC bias magnetic field and geometrical parameters on the RF magnetization and thus the MO Bragg diffraction or mode-conversion efficiency and the bandwidth are presented in plots generated using a computer. A good agreement between computed and experimental results has been obtained.

Measurements of Faraday effect in iron garnet optical waveguide at near infrared wavelengths

The Faraday rotation constants in a magneto-optic channel waveguide whose magnetization aligns along the direction of propagation are measured by a novel method developed by the authors. The tested sample is a lanthanum and gallium substituted yttrium iron garnet optical channel waveguide prepared by the liquid phase epitaxial and the ion milling techniques. The proposed method is more practical than the previously reported one because of determination of the parameters with one time measurement. In the previous method we needed to know the phase constant difference between the orthogonally polarized waves to determine the Faraday coefficient. Using the presented technique we successfully measure the magneto-optic coefficients in the iron garnet waveguide at the near infrared wavelengths: 1.15, 1.3, and 1.55 μm. We confirm the validity of the proposed method by comparing with other methods: the previously reported method and the Faraday modulation method conventionally used for measuring the Faraday rotation. We also demonstrate the waveguide isolator operation.

Light guidance and mode conversion in magneto-optic buried channel waveguides

The optical and magneto-optical properties of weakly guiding single-mode buried channel waveguides in substituted yttrium iron garnet have been investigated experimentally. The propagation constant difference Δβ of the two coupled TE and TM modes, which is of particular interest for waveguide isolator application, is found to be strongly dependent on waveguide geometry. Measured results can be explained by the specific growth of the top cladding layer, which occurs into different crystallographic directions around the etched waveguide core. This leads to a local variation of the refractive index, which effects the guidance of light, and to a local variation of birefringence, which effects Δβ. The measured variation of Δβ is shown to be primarily caused by growth induced birefringence. It is demonstrated that Δβ can be controlled to small values at selectable waveguide widths as required for waveguide isolator application simply by an appropriate setting of fabrication parameters.

Broadband magneto-optic waveguide isolator

Isolation ratios between −32 and −37 dB have been measured on a magneto-optic waveguide isolator over a wavelength range from 1.43 to 1.58 μm. This tunable broadband operation was achieved by rotating the input polarization angle by 22.5° from the waveguide surface of a 45° Faraday rotator to overcome the harmful effects of moderate linear birefringence. The output polarizer was then rotated to maximize the isolation ratio at each wavelength. The excess forward loss introduced by this procedure was 10% or less over this wavelength range. It is shown that excellent isolation and moderate excess forward loss (1 dB or less) can be achieved with triple garnet film, single-mode ridge waveguides over a wavelength range of ±0.2 μm around the etch-tuned wavelength, and over a temperature range of ±30 °C, which greatly enhances the usefulness of these waveguide isolators.

Integrated optical isolator based on nonreciprocal-mode cut-off

A concept of an integrated optical isolator is presented which uses the TM(0) mode propagating perpendicular to the in-plane magnetization of a planar magnetooptical waveguide. The cut-off thickness of the waveguide depends on the propagation direction. If the magnetic film has a strong Faraday rotation and is weakly guiding, the cut-off thicknesses for forward and backward propagation differ markedly. Operating close to cut-off yields a large difference between coupling efficiencies to the waveguide for forward and backward propagation.

45° waveguide isolators with phase mismatch

45° waveguide isolators based on magneto-optic channel waveguides with phase mismatch can be realized simply by choosing a proper orientation of the input polarization. This is demonstrated theoretically by visualizing the magneto-optic mode coupling as ‘‘coupling tracks’’ on the Poincaré sphere, and is verified experimentally for real waveguides with considerable phase mismatch. More than 30 dB isolation is feasible in practical devices.

Double-layered magnetooptic channel waveguide for waveguide isolator application

TE-TM mode conversion based on the nonreciprocal Faraday effect for waveguides fabricated by liquid-phase epitaxially grown (YBiCa)/sub 3/Fe/sub 5/O/sub 12/ films is discussed. The phase mismatch is controlled by constructing a double-layer channel waveguide with an intermediate cladding layer of refractive index slightly lower than the core. Care must be taken to compensate any birefringence of materials, e.g. stress- and growth-induced birefringence. It is shown that such a structure is effective in decreasing the effect of waveguide shape deformation on the phase-matching degree. The analysis of the double-layered channel waveguide and experimental results are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Waveguide analysis of multisectional magneto-optical isolator

A wave optics analysis of light propagation in a multisectional magnetooptical waveguide isolator is performed. The action of the whole element can be mathematically described as the multiplying of complex matrices. Specifically, a simple stepwise isolator design with input TE (transverse electric) polarization is analyzed. The dependence of the output TM (transverse magnetic) power on the length of one full sector is computed. >

Improvements in the differential phase shift of magneto-optic waveguides by loading with high refractive index overlayers

Experimental results are presented for a nonreciprocal phase shift of vertically polarized waves in four-layer magneto-optic rib waveguides. The structure consists of a high refractive index nonmagnetic layer of titanium oxide on top of a magneto-optic film (a lanthanum and gallium substituted yttrium iron garnet film on a gadolinium gallium garnet substrate) to improve differential phase characteristics. The difference of phase constants for waves traveling in opposite directions is evaluated by observing the variation in the polarization coupled out of a straight waveguide when simultaneously exciting both horizontally and vertically polarized waves with equal amplitudes and phases. The phase shift difference varies with the thickness of the nonmagnetic film, and is larger than that of a previous three-layer waveguide in the overlayer thickness range 0.15–0.45 μm. The maximum phase shift obtained is 2.5 times as large as that of uncoated waveguides.