We report the selected-area epitaxy of rare-earth iron garnet crystalline and amorphous straight ridge patterns, from 4μm to 8μm in width, deposited on Gd3Ga5O12 single crystal substrates. These samples were fabricated via a sputter epitaxial method on substrates that were partially etched by ion-beam bombardment. The strip pattern direction has given the considerable influence on the crystal-graphic formation of the sidewall of the grown ridge. The ridge shapes were similar to results that have been reported for the dissolution forms of garnet crystals in phosphoric acid and the facet of garnet crystals grown from flux. Furthermore, we have successfully grown both an epitaxial garnet film onto an amorphous film and an amorphous straight ridge with a triangular shape surrounded by crystal.

Co-doped Bi3Fe5O12 garnet (BIG) films were prepared on Gd3(ScGa)5O12(GSGG) substrates using two types of ion-beam-sputtering (IBS) technique. In the films deposited by sputtering the Co and the BIG source targets alternately with short periodicity, the interface exchange coupling of BIG and Co-spinel ferrite was characteristically observed in the Faraday hysteresis loop. The magnetic and the Faraday hysteresis loops were found to have different coercivity. In the films deposited by conventional IBS method using the BIG target doubly substituted by Co and Ge, Co2+ ions were highly replaced up to 0.7 atoms/formula unit for Fe3+ in BIG. The specific Faraday rotation angle (θ F) at a wavelength of 1.5 μ m was 1.1 deg/μm/Co atom. The magnetic easy direction was normal to the film plane.

We describe our recently developed integrated isolators. Their structure is simple, in that it consists solely of a single-mode channel magneto-optic waveguide. The operating principle is that a backward fundamental TM mode wave is converted to higher-order or radiation TE modes while a forward fundamental TM mode wave propagates with no mode conversion. These isolators are realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. We obtain 13-27 dB isolation around a wavelength of 1.55 μm. We also review our recent study on a hybrid-integrated polarization-independent optical circulator based on a nonreciprocal Mach-Zehnder interferometer which does not need a polarization-beam splitter. We obtain 14.1-23.7 dB isolation at λ = 1.55 μm.

Nonreciprocal rib waveguide structures can be used to realize integrated optical isolators. The nonreciprocal phase shift is the difference between the forward and backward propagation constants of TM modes in magneto-optic waveguides. It can be optimized with respect to absolute value and temperature dependence if double layer waveguides with different magnetic and nonmagnetic layers are prepared. In this paper we propose an improved design for two different Mach-Zehnder interferometer isolators the nonreciprocal parts of which are formed by such double layer waveguides. One concept utilizes a nonreciprocal and a reciprocal arm. In the other case both arms are nonreciprocal but with opposite sign of the nonreciprocal phase shift. A particular property of both concepts is that the lengths of the nonreciprocal arms are well defined. The rest of the interferometer is made by reciprocal rib waveguides. Therefore, the nonreciprocal phase shift is well known. The concepts are compared with regard to isolation ratio, forward losses and fabrication tolerances. Moreover, we simulate the entire isolator by a finite difference beam propagation calculation.

Three-guide couplers with multimode central waveguides allow for remote coupling between optical channels. A simple three mode approximation turns out to be sufficient for the description of the main features of the power transfer behavior. The specific form of the relevant modes suggests the design of integrated optical isolators and circulators based on magnetic garnet materials. These novel devices are superior to conventional nonreciprocal couplers with respect to the total length and admissible fabrication tolerances. We characterize the isolation performance and the transmission loss for the proposed devices by propagating mode simulations and estimate the influence of geometry parameter deviations.

The most recent advances in the integration architecture and diffraction efficiency of magnetostatic wave (MSW)-based guided-wave magnetooptic (MO) Bragg cell modulators in yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) waveguides are reported. A curved ion-milled hybrid waveguide lens pair has been integrated with a MO Bragg cell modulator in a taper waveguide with dimensions of 6.0x16.0mm2 to facilitate the collimation and focusing functions. An enhancement in the Bragg diffraction efficiency by two-to six-fold has been accomplished using a non-uniform bias magnetic field. An oscillator-based MO Bragg cell modulator has also been constructed and has provided a Bragg diffraction efficiency which is higher by a factor of two to four than that of a conventional delayline-based modulator.

A novel magnetooptic (MO) Bragg cell modulator that utilizes a magnetostatic forward volume wave (MSFVW) oscillator is presented. The carrier frequency of the MSFVW signals involved in the MO interaction is tuned linearly from 2.112 to 3.274 GHz by increasing an external bias magnetic field from 2350 to 2900 Oe. Compared with a conventional magnetostatic wave (MSW) delay line-based MO Bragg cell modulator, the proposed modulator can provide significantly higher diffraction efficiency owing to reduction of insertion losses in the MSFVW oscillator. Furthermore, the oscillator-type MO modulator can be more easily integrated with other MMIC devices.

Although discovered over 150 years ago, it was not until the 1970's that materials were developed that enabled magneto-optic (Faraday) effect devices of practical sizes. These developments are: magneto-optic materials with high Verdet constants, and the rare-earth magnet materials, capable of extremely high magnetic fields.

The magneto-optic effect has enabled development of equipment used in diverse laser applications, from industrial use to fiber-optic telecommunications.

The principle of operation of optical isolators and circulators is described herein, as well as descriptions of critical components in such equipment, such as the polarizers and the magnets.

We have developed a novel lens-free and mirror-free fiber integrated optical magnetic field sensor. The use of a bent optical fiber and chip optical components allows easy assembly with no alignment. The linearity error and temperature dependence of the sensitivity of this sensor were less than ±1% and +2%, respectively.

Amorphous alloys of the heavy rare earth elements with cobalt and iron have magnetic and optical properties that make them ideally suited for magneto-optical mass storage media. These materials are used in all commercial erasable (MO) optical disk systems and in optically assisted magnetic storage such as the recordable music minidisk. The important properties of these materials for this application are: 1/ ferrimagnetic exchange with a magnetic compensation point near room temperature, 2/ perpendicular easy axis anisotropy when prepared under suitable conditions as thin films, 3/low media noise as compared to polycrystalline films, 4/low processing temperatures compatible with polymer substrates and 5/thermally stable when cycled repeatedly to the Curie temperature. The magneto-optical Kerr effect that is used to read the information off the disk is large at the 800 nm wavelength used in current devices but low at 400 nm. Since the areal storage density is set by the diffraction limit, improvements in shorter wavelength device performance are needed.

The amorphous rare earth - transition metal (RE-TM) thin film alloys and nanolayered materials exhibit numerous properties advantageous for optical recording, including perpendicular anisotropy, high coercivity and low magnetization at room temperature, low noise, and easily adjustable Curie and compensation points. As a result these materials have been employed in all commercial magneto-optic (MO) media. On the other hand, the MO effect of these materials is relatively small and tends to decrease with decreasing wavelength. It is important to understand the useful limits of these materials in MO media, and to determine if their MO figure of merit can be substantially increased through appropriate doping or nanolayering. In this paper we discuss experimental techniques for measuring MO properties, a theoretical approach for analyzing the data and designing optical thin film stacks, and results for a variety of RE-TM thin film materials.

Nano-size R2BiAlxFe5-xO12 (R: Dy, Gd, Th) particles were prepared with a coprecipitation and annealing method. The coating films of the particles were prepared with a coating technique. The magnetic and magneto-optical properties of the particles and films were investigated. The coercive force Hc of the particles and films was increased and saturation magnetization Ms. dropped with the Al content x. The Hc of the coating films was about 200 Oe at the compositions of dispersed particles for which the Ms was almost zero. These results suggest that the increase was made with magnetic compensation. The BiTb2A10.6Fe4.4O12 coating film shows Faraday rotation spectra. The figure of merit of the film is about 0.5 at 520 nm. The coating BiTb2A10.6Fe4.4O12 film is one of the candidate materials for a new economical magneto-optical storage medium.

The purpose of this work is to obtain spherical particles YIG from micrometric to nanometric scales. The spherical particles were obtained from cation hydrolysis in acid medium by adding urea or ammonia in order to carry out a homogeneous nucleation process up to 90°C. Different composition and morphology were achieved by changing reactant concentrations, precipitation agent and stabilizing agent. X-ray diffractometry, electrophoretic mobility, transmission and scanning electron microscopies were carried out on these particles to investigate the phase identification, mobility, morphology and particle size. Crystalline YIG, with spherical characteristics, was obtained. The surface potential presented different characteristics for different dispersion media.

Two recent topics on high density recording are reviewed in this paper on conventionally structured MO disk by magnetic field modulation. One topic is the MO disk with a capacity of 650 MB/ φ 64 mm. Using a light wavelength of 650 nm and an numerical aperture of an objective lens of 0.52, a track pitch of 0.95 μm and a bit length of 0.34 μm for (1,7) RLL coding has been applied to achieve 650 MB within a size of a Mini Disc(MD). Groove conditions such as the depth and groove duty in a 1.2-mm thick polycarbonate substrate are optimized to reduce the cross-talk from adjacent tracks. As a result, the recording power margin of ± 20% is obtained. The disk tilt margin is ± 0.82 deg and ± 0.63 deg in the radial and tangential direction, respectively.

The other topics is land/groove recording using an optical phase shifter. A maximum carrier level and a minimum cross-talk are achieved simultaneously when an optical phase shifter is inserted into the optical path before an analyzer. The optimum phase shift is 40 deg for recording on land and -40 deg for recording in groove. Recording on 0.5 μm land/0.5 μm groove with 1.2-mm thick substrate is investigated with a bit length of 0.35 μm for (1,7) RLL code using a light wavelength of 693 nm and a numerical aperture of 0.55. MO recording using an optical phase shifter is promising for an areal density of 3.7 Gb/in2. Furthermore, when an optical phase shifter is applied to recording on 0.36 jim land/0.36 μm groove with a bit length of 0.258 μm, light wavelength of 642 nm, and NA of 0.7, a capability of 7.0 Gb/in2 using conventionally structured MO disk is shown.

A novel near-field magneto-optic fiber probe (NF-MOFP) for readback of ultra high density magnetic recording, or high resolution imaging of magnetic domains is described. This NFMOFP consists of a partially metalized tapered fiber, as used in conventional near-field scanning optical microscopy (NSOM), with the subwavelength sized aperture coated with a reflective magneto-optic (MO) film. This device is then used in a manner similar to conventional NSOM. The properties of the MO film deposited on the fiber tip, the NFMOFP's response to applied fields, and images of magnetic domains taken with the device are described.

Magnetic field induced second harmonic generation (MSHG) is suggested as a nonlinear-optical readout for magnetic film-based memories: Systematic studies of the nonlinear-optical magnetic Kerr effect and MSHG interferometry are carried out for (i) magnetic rare-earth iron garnet films, (ii) Gd-containing Langmuir-Blodgett films and (iii) CoxCu1-x granular films. The magneto-induced nonlinear-optical properties of thin films being used for recording the information can be easily distinguished by the MSHG nondestructive probe. An estimation of the signal-to-noise ratio (readout error) shows an acceptable value of the magnetic contrast for this potential readout.

We review the properties of diluted magnetic semiconductor (DMS) thin films and multilayers, with special attention to their usefulness in magneto-optical device applications. We begin with the most widely studied DMS family, i.e., alloys of II-VI semiconductors involving Mn ions. Prospects and challenges are discussed for achieving II1-xMnxVI-based non-reciprocal devices; and for devices operating in the far infrared. We also consider the unique advantages which DMSs offer for probing the properties of semiconductor heterostructures. We then discuss ferromagnetic DMSs, including those based on the III-V semiconductor family. And we briefly review the status of hybrid ferromagnetic-semiconductor structures achieved through recent advances in epitaxy of new materials.

We propose to use a paramagnetic diluted magnetic semiconductor Cd1-xMnxTe for magneto-optic waveguides, which can be integrated with semiconductor optic devices. Single crystal Cd1-xMnxTe films are epitaxially grown on GaAs substrates by molecular beam epitaxy method. A good optical confinement is obtained in the waveguide by using a Cd1-yMnyTe clad layer with Mn concentration higher than that of the waveguide core layer.

Cr substituted dilute magnetic semiconductor Cd1-xCrxSe films were grown onto fused silica and sapphire (00 · 1) substrates by vapor deposition technique. The films with wurtzite structure were obtained at composition of 0 ≤ × ≤ 0.66. Saturation magnetization and magnetic susceptibility increased as x increased. In comparison with Mn-DMS system, the initial magnetization curves saturate easily. This tendency is different from most DMS materials in which magnetic ions interact with each other antiferromagnetically. It is possible that ferromagnetic interactions exist in Cd1-xCrxSe.

A solution flow system for hydrothermal-electrochemical synthesis has been constructed in our laboratory. This equipment can operate at 20°-200°C, under the pressure of 1-50 atm., at flow rate of 1-50 cm3/min. Applicability of the flow system for low-temperature, hydrothermalelectrochemical synthesis of single-layer and multilayered thin films has been demonstrated using the BaTiO3-SrTiO3 system as an example. Single phase thin films as well as double layers have been deposited at 150°C, current density of 1 mA/cm2, and flow rates of 1-50 cm3/min. The flow rate is an important parameter allowing additional control of the films' morphology by affecting the growth rate. The multilayers can be prepared in only one experiment by simply changing the flowing solution. Processing using the solution flow cell may serve as an inexpensive and environmentally friendly way of fabricating any multilayered thin films, including magneto-optic films.