H. Dammann

Yttrium iron garnet single-mode buried channel waveguides for waveguide isolators

Magneto‐optic single‐mode buried channel waveguides in substituted yttrium iron garnet suitable for waveguide isolators have been prepared. The channels are fabricated in a three‐step procedure: starting with multiple‐layer planar single‐mode waveguides, rib waveguides are wet etched and then overgrown with top cladding. Such waveguides show mode profiles well matched to that of single mode fibers. In mode conversion experiments, an extinction ratio of 20 dB was obtained. Waveguides coupled to single‐mode fibers on both sides showed an overall insertion loss of about 4 dB.

Phase matching in symmetrical single‐mode magneto‐optic waveguides by application of stress

Tuning of the propagation constant difference Δβ=βTM−βTE in single‐mode symmetrical yttrium iron garnet (YIG) film waveguides over a range of 250°/cm by means of external stress is demonstrated. An a posteriori, precise setting of phase match Δβ→0, which is a precondition for nonreciprocal mode coupling type components, can be achieved by this method.

45° waveguide isolators with phase mismatch

45° waveguide isolators based on magneto‐optic channel waveguides with phase mismatch can be realized simply by choosing a proper orientation of the input polarization. This is demonstrated theoretically by visualizing the magneto‐optic mode coupling as ‘‘coupling tracks’’ on the Poincare sphere, and is verified experimentally for real waveguides with considerable phase mismatch. More than 30 dB isolation is feasible in practical devices.

Growth of buried garnet channel waveguides by liquid phase epitaxy

Abstract Buried magneto-optic garnet channel waveguides with a core shaped in a symmetrical parallel trapezium are prepared by liquid phase epitaxy on etched double layers.

Light guidance and mode conversion in magneto-optic buried channel waveguides

The optical and magneto‐optical properties of weakly guiding single‐mode buried channel waveguides in substituted yttrium iron garnet have been investigated experimentally. The propagation constant difference Δβ of the two coupled TE and TM modes, which is of particular interest for waveguide isolator application, is found to be strongly dependent on waveguide geometry. Measured results can be explained by the specific growth of the top cladding layer, which occurs into different crystallographic directions around the etched waveguide core. This leads to a local variation of the refractive index, which effects the guidance of light, and to a local variation of birefringence, which effects Δβ. The measured variation of Δβ is shown to be primarily caused by growth induced birefringence. It is demonstrated that Δβ can be controlled to small values at selectable waveguide widths as required for waveguide isolator application simply by an appropriate setting of fabrication parameters.

Growth of magneto-optic garnet layers on structured surfaces

Abstract Local inhomogeneities in layers grown on structured surfaces are studied by electron probe microanalysis and X-ray diffraction. They are explained by variations of the growth rate due to differences in the diffusion length and the orientation dependent growth resistivities. Conclusions for the improvement of the properties of buried channel waveguides are drawn.

Buried Channel Waveguides In Magneto-Optic Materials

Buried channel waveguides in magneto-optic yttrium iron garnet have been prepared for application to waveguide isolators. The channel waveguides are fabricated in a three-step procedure: planar single-mode waveguides are grown, then rib waveguides are wet-etched into the planar waveguides and successively overgrown with top cladding. Light propagation and mode conversion characteristics of such waveguides have been investigated.

Non-Reciprocal Waveguides

Materials and growth processes for magneto-optic garnet film wavequides are described. The realization and characterization of single-mode waveguide structures is explained, and experimental methods for the investigation of the non-reciprocal mode conversion are discussed. Applications for waveguide isolators are briefly mentioned.