Achieving monolithic integration of nonreciprocal photonic devices on semiconductor substrates has been long sought by the photonics research society. One way to achieve this goal is to deposit high quality magneto-optical oxide thin films on a semiconductor substrate. In this paper, we review our recent research activity on magneto-optical oxide thin films toward the goal of monolithic integration of nonreciprocal photonic devices on silicon. We demonstrate high Faraday rotation at telecommunication wavelengths in several novel magnetooptical oxide thin films including Co substituted CeO2−δ, Co- or Fe-substituted SrTiO3−δ, as well as polycrystalline garnets on silicon. Figures of merit of 3~4 deg/dB and 21 deg/dB are achieved in epitaxial Sr(Ti0.2Ga0.4Fe0.4)O3−δ and polycrystalline (CeY2)Fe5O12 films, respectively. We also demonstrate an optical isolator on silicon, based on a racetrack resonator using polycrystalline (CeY2)Fe5O12/silicon strip-loaded waveguides. Our work

https://www.mdpi.com/1996-1944/6/11/5094/pdf

Magneto-Optical Thin Films for On-Chip Monolithic Integration of Non-Reciprocal Photonic Devices

Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 μm≦λ≦1.9 μm by thin-film interference for λ ≳0.52 μm and by ellipsometry forλ≲0.52 μm. The Y3−x−yBixPbyFe5−zPtzO12 films contain bismuth in the range O≦x ≦1.42, lead in the range 0.01 ≦y≦0.08 and platinum in the range 0.005<=z≦0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.

Measurement of the Refractive Index and Optical Absorption Spectra of Epitaxial Bismuth Substituted Yttrium Iron Garnet Films at uv to Near-ir Wavelengths

The invention relates to a planar optical isolator having a magneto optical gyrotropic layer and an anisotropic birefringent layer which are proportioned so that the non-reciprocal rotation of polarisation of the light (Faraday rotation) resulting from the action of a magnetic field in the forward direction of the isolator is at least substantially negatively equal to the reciprocal rotation of polarisation as a result of the birefringence, so that a TE-mode in the forward direction is guided with low damping, measures being taken for the intensive attenuation of at least one TM-mode. An isolator having a high isolating effect in which magneto optical gyrotropic layers and anisotropic birefringent layers can be connected epitaxially is obtained in that the waveguiding core layer comprises two rare earth-iron garnet (YIG) layers which are differently doped to obtain different specific birefringence.

Planar optical isolator

High‐quality iron‐garnet films of composition Gd3−vBivFe5−w−x−yGdw GaxAlyO12−zArz with 1.02≤v≤1.45, 0.01≤w≤0.36, 0.22≤x≤0.24, 0.26≤y≤0.38, and 0.002≤z≤0.014 have been grown epitaxially on (111)‐ and (110)‐oriented gallium garnet substrates with the lattice constant in the range 1.2475≤a0(nm)≤1.2553 by rf magnetron sputtering in argon plasma. For the study of the optoelastic and magnetoelastic properties of these sputter‐epitaxial films the lattice mismatch Δa⊥=as−a⊥f has been varied in the range −1.7<Δa⊥(10−2 nm)<0.5 by using substrates with various lattice constants. The near‐infrared optical anisotropy normal to (Δnxy) and in the plane (Δnyz) of (110)‐oriented films turn out to depend linearly on Δa⊥ over this large range of lattice misfits. No growth‐induced contribution has been observed. The same behavior is found for the induced uniaxial (K⊥) and in‐plane (K∥) magnetic anisotropy constants at room temperature. The optoelastic coefficients P44 and ΔP, as well as the magnetostriction constants λ111 an...

Magnetoelastic and optoelastic coupling in (111)‐ and (110)‐oriented bismuth‐iron garnet films prepared by sputter epitaxy

Isolator conditions are derived by a perturbation method for optical slab isolators in which magnetooptical crystal and anisotropic dielectric crystal films are integrated for reciprocal and non-reciprocal TE-TM mode conversion functions. The general expressions show that isolator conditions can be satisfied for any combination of wavelength, normalized frequency, waveguide thickness, and gyrotropic constant of the magnetooptical crystal by appropriate choice of the magnitude of the birefringence of the top layer film and its crystal orientation angle. Design examples of single-mode isolators with waveguide thicknesses of 4, 4.5, and 5 μm are given at 1.55 μm wavelength. It is also pointed out that isolators of the above design can be fabricated with Y 3 Fe 5 O 12 , Y 1.5 Gd 1.5 Fe 3 O 12 , and Tm 3 Fe 5 O 12 crystal films as magnetooptical materials and a solid solution of LiNbO 3 and LiTaO 3 as an anisotropic film. Tolerance in the required film thickness becomes less stringent with this design. Isolation of more than 20 dB with an insertion loss of less than 0.12 dB is feasible without any parameter adjustment, even when there is as much as a ten percent deviation in the film thickness.

M. Tateda

Papers

Design feasibility of a single-mode optical isolator