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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Optical bistability on a thin-film Faraday rotator

Masao Hirano

Published Sep 30, 1994• 0 citations
Publisher

Abstract

We proposed an all-optical bistable unit made of a Faraday medium and investigated theoretically its unique characteristics. Optical bistability in our proposed unit was experimantally confirmed. In this paper, using a 830 nm wavelength laser diode and a thin garnet film rotator as a Fabry-Perot resonator, optical bistability is confirmed again. Bistable characteristics, threshold incident power, on-off power ratio, and dynamic characteristics, are examined to attain controllability with the external magnetic field. In our proposed unit's construction, an all-optical sensing device (a magnetic field sensor) is proposed and evaluated for application to the OB operation.

DOI
10.1117/12.187990

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We proposed an all-optical bistable unit made of a Faraday medium and investigated theoretically its unique characteristics. Optical bistability in our proposed unit was experimantally confirmed. In this paper, using a 830 nm wavelength laser diode and a thin garnet film rotator as a Fabry-Perot resonator, optical bistability is confirmed again. Bistable characteristics, threshold incident power, on-off power ratio, and dynamic characteristics, are examined to attain controllability with the external magnetic field. In our proposed unit's construction, an all-optical sensing device (a magnetic field sensor) is proposed and evaluated for application to the OB operation.
Abstract An optical bistable device can be useful not only for optical memory but also for optical sensing by using its binary signal process characteristics. In this case, if a nonlinear Faraday medium is used in the optical bistable device, some interesting features can be obtained as already shown by the present author. Those unique characteristics are that, by controlling the polarization direction by an external magnetic field, a multiple interference can also be controlled not only by the phase associated with an optical path variation but also the polarization direction. This paper describes a theoretical analysis of the fluctuation of transmission and reflection as a function of an absorption in a medium besides the incident intensity reduction and discusses the bistability characteristics and the threshold values against the parameters. It is shown that the control of the bistable function, the realization of a low threshold value, and the increase of a discontinuous power variation ratio (= optical intensity ratio between on and off in the binary signal process) at the threshold value are accomplished as the result of the introduction of the external magnetic field control method. Therefore, it can be concluded that a Faraday medium is very useful for an optical bistable device.
We have proposed and discussed that an introduction of the Faraday medium to the optical bistable devices brings new and good characteristics on the application to optical sensing. In this paper, characteristics of the optical bistability are analyzed theoretically for the optical bistable operation with the Faraday effect, the threshold power, and several parameter dependences of the characteristic. Consequently, by controlling them with an external magnetic field which is an operatable factor, the optical bistability shows much usefulness and effectiveness by the following points: the controllability of the bistable operation, the reduction in the threshold power, and the enlargement in the discontinuous power variation ratio.
We investigated the optical and magnetic properties of a transparent magnetic garnet with a particular focus on its applications to atomic physics experiments. The garnet film used in this study was a magnetically soft material that was originally designed for a Faraday rotator at optical communication wavelengths in the near infrared region. The film had a thickness of 2.1 μm and a small optical loss at a wavelength of λ=780 nm resonant with Rb atoms. The Faraday effect was also small and, thus, barely affected the polarization of light at λ=780 nm. In contrast, large Faraday rotation angles at shorter wavelengths enabled us to visualize magnetic domains, which were perpendicularly magnetized in alternate directions with a period of 3.6 μm. We confirmed the generation of an evanescent wave on the garnet film, which can be used for the optical observation and manipulation of atoms on the surface of the film. Finally, we demonstrated a magnetic mirror for laser-cooled Rb atoms using the garnet film.
In this paper, a thin film of oil red O coated by partial dielectric mirrors (PRFORO) operating as an optical bistable device is proposed. The equation of the output-input intensity relation considering nonlinear absorption inside PRFORO is derived and the optical bistability (OB) of PRFORO is shown. Additionally, the influence of the nonlinear refractive, absorptive coefficients of oil red O (ORO), reflective coefficient of mirrors, and the thickness of thin film on the OB is numerically investigated and discussed. As a result, the threshold switching power is lower than 19 mW; the minimum power of output up-state is larger than 40 µW for the optimal PRFORO designed with an ORO concentration larger than 0.1 mM; the thickness of the thin film is longer than 0.1 mm; and the reflective coefficient of mirrors is lower than 93%. The proposed model is suitable for all-optical switches, optical images, and signal processing.