Abstract
We examine theoretically the role of thermodynamic spin fluctuations in optical guided waves propagating on a ferromagnetic film and undergoing Faraday rot ation. Using the equipartition theorem, we obtain the noise equivalent power (NEP) for these thermally excited magnetostatic spin waves, as a function of film thickness and applied magnetic field. These considerations place limiting sizes and modulation sensitivities on optical signal processing devices that are based on the Faraday effect. For example, if 1 mW of optical guided wave power propagates in a 1-μm film, then 46 pW of optical power are mode converted by these thermal spin waves and appear as optical noise. The NEP for all thermal spin waves in a 1-μm Bi-doped yttrium iron garnet film deposited on a gadolinium gallium garnet substrate is 30 nW and drops by a factor of two for a 10-μm film.
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