Metalorganic Chemical Vapor Deposition of Magneto-Optical Ce:YIG Thin Films
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The advantages of thin film isolators integrated with lasers are: (1) light from a laser can remain in a guided mode as it passes through the thin film, eliminating the need for collimating lenses and complex alignment procedures typically required of nonintegrated approaches; (2) films need only be a few microns thick in the planar waveguide configuration, rather than over 200 microns required of conventional isolators in which the light passes transversely through the thick film, (3) the magnetic field required to saturate a planar magnetic thin film is much smaller than that required to saturate a bulk crystal, which allows the use of thin film permanent magnets; and (4) these waveguides can act as building blocks for other integrated optic devices such as circulators, switches, modulators, polarization controllers and magnetic field sensors. APPLICATIONS OF MAGNETO-OPTICAL GARNET THIN FILMS A. Waveguide Isolators
Many early development works on YIG thin film waveguide isolators were done by Ray Wolf s group at AT & T Bell Laboratories (1-4) and H. Dammann et. al. in Germany (5-6). The details of these works was reviewed by Wolf in Reference 7. Fig. 1 shows a prototype waveguide isolator which consist of three LPE YIG layers on GGG substrates to promote a highquality single-mode waveguiding. By rotating the input and the output polarizer 22.5' in opposite direction as shown in the Fig. 1, excellent isolator performance can be achieved even if the linear birefringence is not zero. The isolation spectrum of such a waveguide isolator is shown in Fig. 2, isolation ratios of more than 32 dB have been achieved over a broad band of wavelengths of 1.43-1.59 tim.
Fig. 1 Magneto-optical waveguide isolator: REIG, rare earth iron garnet. A triple film of magnetic garnet provide a single mode waveguiding and rotates the plane of .5 polarization by 450. Input and output -22 5polarization rotate 22.50 in opposite
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Fig. 2. Isolation ratio vs wavelength using the arrangement in Fig. 1: e experimental results for reverse isolation; 0 forward results, corresponding to slight extra loss; theoretical fit to the results with the input polarization parallel to the film plane.
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1.50 WAVELENGTH (mrn)
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B. Magneto-optical recording Bi substituted yttrium iron garnet is an attractive candidate for magneto-optic recording media because of its large carrier-to-noise ratio (CNR). The work utilizing in-situe crystallization of BiYIG thin films showed large mark CNR of 58 dB at 488 nm onto a grooved gadolinium gallium garnet (GGG) disk (8). The readout signal for BiYIG is compared with other material such as (Co/Pt) and TbFeCo in Fig. 3 (9). The drawback with Bi-garnet is that hightemperature crystallization (- 650'C) is needed. This limits the choice of substrate materials, which may prevent the development of low-cost media.
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Fig. 3. Readout signal f
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