Taichi Goto

Optical Tamm States in One-Dimensional Magnetophotonic Structures

We demonstrate the existence of a spectrally narrow localized surface state, the so-called optical Tamm state, at the interface between one-dimensional magnetophotonic and nonmagnetic photonic crystals. The state is spectrally located inside the photonic band gaps of each of the photonic crystals comprising this magnetophotonic structure. This state is associated with a sharp transmission peak through the sample and is responsible for the substantial enhancement of the Faraday rotation for the corresponding wavelength. The experimental results are in excellent agreement with the theoretical predictions.

Magneto-optical properties of cerium substituted yttrium iron garnet films with reduced thermal budget for monolithic photonic integrated circuits

Thin films of polycrystalline cerium substituted yttrium iron garnet (CeYIG) were grown on an yttrium iron garnet (YIG) seed layer on Si and Si-on-insulator substrates by pulsed laser deposition, and their optical and magneto-optical properties in the near-IR region were measured. A YIG seed layer of ~30 nm thick processed by rapid thermal anneal at 800°C provided a virtual substrate to promote crystallization of the CeYIG. The effect of the thermal budget of the YIG/CeYIG growth process on the film structure, magnetic and magnetooptical properties was determined.

Vacuum annealed cerium-substituted yttrium iron garnet films on non-garnet substrates for integrated optical circuits

Polycrystalline cerium-substituted yttrium iron garnet (CeYIG) showing large Faraday rotation (FR) in the near-IR region was grown on non-garnet (synthetic fused silica, Si, and Si-on-insulator) substrates by sputtering followed by thermal annealing in vacuum. The FR of the films is comparable to the single crystal value. Structural characterization, magnetic properties, refractive index, extinction coefficient, surface topography, and FR vs. wavelength were measured and the magnetooptical figure of merit was compared with that of CeYIG films on garnet substrates.

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

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

A nonreciprocal racetrack resonator based on vacuum-annealed magnetooptical cerium-substituted yttrium iron garnet.

Vacuum annealed polycrystalline cerium substituted yttrium iron garnet (CeYIG) films deposited by radio frequency magnetron sputtering on non-garnet substrates were used in nonreciprocal racetrack resonators. CeYIG annealed at 800°C for 30 min provided a large Faraday rotation angle, close to the single crystal value. Crystallinity, magnetic properties, refractive indices and absorption coefficients were measured. The resonant transmission peak of the racetrack resonator covered with CeYIG was non-reciprocally shifted by applying an in-plane magnetic field.

Faraday rotation of a magnetophotonic crystal with the dual-cavity structure

We demonstrated optical properties of a one-dimensional magnetophotonic crystal (MPC) which comprises two magnetic defects built into a dielectric multilayer. This MPC with the so-called dual-cavity structure exhibited resonant transmittance and enhancement of the Faraday rotation at a designed wavelength. A double peak that is intrinsic feature of dual cavities was observed in the spectrum of the Faraday rotation. However, the peak of resonant transmission had a bell-type shape. These results are in agreement with our theoretical consideration where a structural disorder in the experimental sample was taken into account.

Novel magnetophotonic crystals controlled by the electro-optic effect for non-reciprocal high-speed modulators

We present a new type of electro- and magneto-optical spatial light modulators (e-MOSLMs) utilizing the concept of photonic crystals (PCs) – such e-MOSLMs have a microcavity structure. They comprise a magneto-optical (MO) and electro-optical (EO) constituents that can control the direction of the polarization plane, when applying voltage and/or external magnetic fields. Optical spectra of e-MOSLMs were analyzed by using the matrix approach. Calculations showed that e-MOSLMs can change the direction of polarization over a considerably large range of angles at relatively low power consumption and with no significant change of the light intensity.

Magnetophotonic Crystals: Experimental Realization and Applications

The most striking feature of photonic crystals, compared with homogeneous optical materials, is the existence of photonic band gaps. The band gaps are responsible for resonant light coupling to constituents of photonic crystals in both the cases where periodicity is ideal or broken by defects introduced intentionally. What if photonic crystals are made of magnetic materials? May magnetism bring about new advances in the field of photonic crystals where not only amplitudes but also polarization states are controlled by the spin subsystem? Below we will discuss magnetophotonic crystals and show that light confinement in their non-reciprocal magnetic constituents results in new magneto-optical phenomena. This chapter reviews studies on magnetophotonic crystals with various designs; it focuses on their experimental realizations, theoretical analysis and application to spatial light modulators.

Magnetic domains driving a Q-switched laser

A 10-mm cavity length magnetooptically Q-switched Nd:GdVO4 laser was demonstrated using a single-crystalline ferrimagnetic rare-earth iron garnet film. To design the Q-switching system, the magnetic, optical, and magnetooptical properties of the garnet film were measured. The diode pumped solid-state laser cavity was constructed using a 190-μm-thick garnet film with 58% transmittance. The garnet film had maze-shaped magnetic domains, and the domain walls disappeared when a field of over 200 Oe was applied. Therefore, the polarization state of the transmitted light was modified by modulating the magnetization, and a Q-switched pulse output with a pulse width of 5 ns and peak power of 255 W was achieved in the 10-mm-long cavity. The physical limitation of the pulse width was discussed with the calculated results.

Thermomagnetic writing into magnetophotonic microcavities controlling thermal diffusion for volumetric magnetic holography.

Holographic memory is expected to become a high-capacity data storage. Magnetic volumetric holograms are rewritable holograms that are recorded as magnetization directions through thermomagnetic recording. However, the effective depth of magnetic holograms is limited by thermal diffusion that causes merging of magnetic fringes. In this study, we propose the insertion of heat-sink layers (HSLs) for retaining well-defined magnetic fringes during volumetric writing. Magnetophotonic microcavity media were used for demonstrating the HSL effect, and the structural design principle was established in numerical calculations. The results indicate that deep and clear magnetic fringes and an improvement in the diffraction efficiency can be achieved by the insertion of HSLs.