Many novel materials and device designs have been proposed as photonic analogs to electrical diodes over the last four decades. This paper seeks to revisit these materials and designs as advanced technologies may enable experimental realization that was not possible upon conception of several of these designs. The background behind integration challenges, including waveguide birefringence, fabrication tolerances, garnet/semiconductor mismatch, and optimized interfaces will hopefully spark new ideas that will finally enable the realization of integrated optical isolators and circulators.

Integrated Magneto-Optical Materials and Isolators: A Review

A compact waveguide optical isolator whose input and output light are TE or TM mode has been realized by making adjacent nonreciprocal and reciprocal TE‐TM mode converters in a (BiGdLu)3(FeGa)5O12 film. Designed configurations of the magnetization directions were produced by making use of local laser annealing of the film grown on a Gd3Ga5O12 substrate of which the face normal is tilted from the [111] axis. The laser‐annealed and nonannealed regions worked as the nonreciprocal and reciprocal mode converters, respectively. The observed isolation agreed with theoretical calculation. An isolation ratio of 12.5 dB was achieved at a wavelength λ=1.15 μm.

Waveguide magneto‐optic isolator fabricated by laser annealing

Realization of magnetostatic forward volume wave (MSFVW)-based guided-wave magneto-optic (MO) Bragg cells and their applications to communications and signal processing are reported. Bragg diffraction of guided-optical waves from the MSFVW in a noncollinear coplanar geometry is analyzed. The design of microstrip line transducers that facilitate wideband MO Bragg diffraction with electronically tunable microwave carrier frequencies (2.0 to 12.0 GHz) are briefly discussed. Experimental results obtained with the resulting Bragg cells in both pure and bismuth-doped yttrium-iron-garnet (YIG) waveguides and a comparison to the theoretical predictions are presented. Applications of the Bragg cells to light beam modulation, scanning/switching, and RF spectral analysis are presented in detail. >

Magnetostatic-forward-volume-wave-based guided-wave magneto-optic Bragg cells and applications to communications and signal processing

Wideband noncollinear coplanar guided‐wave magneto‐optic diffraction and mode conversion by magnetostatic surface waves at multigigahertz (3–7 GHz) carrier frequencies in yttrium iron garnet‐gadolinium gallium garnet waveguides have been observed and measured in detail for the first time. Interaction configuration, physical mechanisms, summary of a theoretical treatment, and some experimental results obtained at 1.152 μm optical wavelength are presented. This noncollinear coplanar magneto‐optic interaction configuration should result in a number of integrated optic devices for wideband communications and signal processing applications at electronically tunable microwave carrier frequencies. The potential advantages of the resulting magneto‐optic devices over the existing acousto‐optic devices are also discussed.

Noncollinear coplanar magneto‐optic interaction of guided optical wave and magnetostatic surface waves in yttrium iron garnet‐gadolinium gallium garnet waveguides

Highly Bi‐substituted garnet films (BiLu)3Fe5O12 (Bi=0.89/f.u.) have been grown on (111)‐oriented Gd3Ga5O12 substrates by liquid‐phase epitaxy with only Bi2O3 as a flux. The specific Faraday rotation θF attains −0.14 deg/μm at 1.3 μm. Guided‐optical‐wave propagation loss of 0.6 dB/cm at 1.3 μm is obtained by doping an appropriate amount of MgO in the melt. Magnetostatic backward volume wave (MSBVW) is launched efficiently into the film as expected from the measured small ferromagnetic resonance linewidth of 0.7 Oe, whereas magnetostatic surface wave and magnetostatic forward volume wave are subject to the severe attenuation due to their coupling to spin‐wave modes. The interaction between guided optical wave and MSBVW is investigated in a transverse configuration where the input optical wave passes almost orthogonal to MSBVW. The TM‐TE optical‐mode conversion induced by MSBVW is observed over the frequency range of 3.5–7.5 GHz. Its efficiency, as high as 47%/0.8 W at 4 GHz, is obtained for the interaction...

TM‐TE optical‐mode conversion induced by a transversely propagating magnetostatic wave in a (BiLu)3Fe5O12 film

TE-TM mode conversion, in magneto-optic guides for integrated optics, requires TE-TM mode overlap and phasematching. This two properties are analyzed with circular and linear magnetic birefringence dependence. In application an experimental 95% TE-TM mode conversion efficiency is presented for an uniform longitudinal magnetization.

Coupling and phase matching coefficients in a magneto-optical TE-TM mode converter

Very large energy exchange (more than 97%) between TE and TM modes of YIG : Tb,Al guides have been obtained for short propagation lengths (less than 2 mm) in the near infrared (1.152 μm). These performances are better than those of YIG : Gd,Ga layers (97% in 4 mm). With such guides we can reduce M.O. device dimensions; they can be used in the integrated magneto‐optics. Also high nonreciprocal conversions (9% conversion in one propagation direction and 93% in the opposite direction) have been obtained in YIG : Gd,Ga films. A nonreciprocity theory is discussed for monosection uniform waveguides. This theory shows that the guides in which we obtained the nonreciprocity cannot be monosection but multisections.

L. Courtois

Papers

Coupling and phase matching coefficients in a magneto-optical TE-TM mode converter

Reciprocal and nonreciprocal high TE‐TM modes conversions in Tb,Al and Gd,Ga substituted garnet films

High Optical Mode Conversions Induced by the Epitaxy Birefringence in Gd and Tb Substituted Garnet Films