Prabesh Dulal

Growth Parameters of Fully Crystallized YIG, Bi:YIG, and Ce:YIG Films With High Faraday Rotations

We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such films have historically been challenging to grow due to either cracking or incomplete crystallization of the films. We have established the proper growth parameters by tuning seed layer thickness to an optimum of 45 nm. These films were then used as seed layers for growth of films of Bi:YIG and Ce:YIG. Bi:YIG films show a Faraday rotation of 1700 °/cm, and Ce:YIG films show a Faraday rotation of 3700 °/cm.

Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Strategies are developed for obtaining nonreciprocal polarization mode conversion, also known as Faraday rotation, in waveguides in a format consistent with silicon-on-insulator or III-V semiconductor photonic integrated circuits. Fabrication techniques are developed using liftoff lithography and sputtering to obtain garnet segments as upper claddings, which have an evanescent wave interaction with the guided light. A mode solver approach is used to determine the modal Stokes parameters for such structures, and design considerations indicate that quasi-phase-matched Faraday rotation for optical isolator applications could be obtained with devices on the millimeter length scale.

Monolithically-Integrated TE-mode 1D Silicon-on-Insulator Isolators using Seedlayer-Free Garnet

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the ‘missing link’ in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and 4 dB were obtained, and future designs are identified capable of isolation ratios >30 dB with losses <6 dB.

Faraday polarisation mode conversion in semiconductor waveguides incorporating periodic garnet claddings

We report on our progress towards the integration of nonreciprocal optical elements in, for example, an integrated optical waveguide isolator on conventional semiconductor photonic platforms. Our approach uses an evanescent interaction with a magneto-optic iron garnet upper cladding. Specifically, cerium- and bismuth- substituted yttrium and terbium iron garnets were investigated. Device fabrication incorporates RF sputtering, mask lift-off to form a grating for a quasi-phase-matched interaction and thermal anneal. A non-reciprocal polarisation-mode conversion was observed.

Demonstration of Magnetooptic Latching Router for All-Optical Networking Applications

In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted yttrium iron garnet (Bi:YIG) is presented. Experimentation shows that nearly 90° of rotation of the state of polarization of incident light occurs between material latching states upon application of an external magnetic field greater than 500 G. This amount of rotation is enough to cause sufficient routing at the output of an optical interferometer of Sagnac configuration, which is presented in this paper. Due to the high coercivity of the Bi:YIG, the material remains in its magnetized state for very long periods of time and is thus latched. Reversing the applied magnetic field changes the state of the material, unlatching it. This capability has great importance for nonreciprocal all-optical devices requiring low power operation. In addition, having such control of the state of the nonreciprocal elements can allow for a wider diversification of small-scale and large-scale optical network design. A discussion of the experimental setup, the resulting measurement data, and its implication for future low power applications is presented.

Si-integrated ultrathin films of phase-pure Y3Fe5O12 (YIG) via novel two-step rapid thermal anneal

ABSTRACT Traditional one-step annealing of ultrathin amorphous Y–Fe–O films on Si has been reported to yield ‘incomplete crystallization’. Here, it is shown that films produced by standard anneals (e.g.: 800°C, 3 min) actually contain yttrium iron garnet (YIG) crystallites in a nanocrystalline non-garnet matrix. During in situ TEM laser annealing, a low-temperature pre-anneal enabled subsequent YIG crystallization at velocities of 280 nm/s that prevented the formation of the nanocrystalline matrix. From these results, a two-step rapid thermal anneal was identified (400°C, 3 min; 800°C, 3 min) that successfully produces phase-pure garnet films on SiO2 on Si. GRAPHICAL ABSTRACT IMPACT STATEMENT A novel two-step anneal discovered through in situ TEM laser annealing produces phase-pure, fully crystallized ultrathin YIG films grown on SiO2 on Si.

Transmission Electron Backscatter Diffraction (tEBSD) analysis of Au Thin Films

Identifying and characterizing nanoscale crystallographic features is vital for understanding deformation in plasmonic devices and developing more robust plasmonic structures. Here, advanced characterization processes using transmission Electron Back Scatter Diffraction (tEBSD) were developed to analyze thin film crystal structure and its role in plasmonic device stability. The specific crystalline features of interest are film texture, grain boundary configuration and grain size. These results will hopefully contribute to the successful implementation of Heat Assisted Magnetic Recording (HAMR) as well as improve plasmonic device reliability in other applications.[1]

Faraday polarisation rotation in semiconductor waveguides incorporating periodic garnet claddings

Nonreciprocal polarisation mode conversion is demonstrated in semiconductor waveguides with an alternating periodic upper cladding incorporating a segmented magneto-optic iron garnet fabricated with a novel lift-off process and crystallised by rapid thermal annealing.