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Abstract

A tunable laser includes a laser medium (24), a resonant cavity (27, 28), at least one Faraday rotation element (26), and a polarization sensitive attenuator (25). Waves of laser energy produced by the laser medium resonate in the resonant cavity between a 100% reflective surface (27) and a partially transmitting mirror surface (28). The waves pass through the attenuator (25) and are linearly polarized. The linearly polarized waves pass through the Faraday rotation element (26) and the polarization sensitive attenuator (25) on each pass through the resonant cavity. The Faraday rotation element includes a permanent magnet (54) and a trim coil (56) for generating both fixed and variable components of a magnetic field. The polarized wave is rotated by an amount proportional to the intensity of the total magnetic field and the wavelength of the polarized wave. The polarization sensitive attenuator allows only waves of a prescribed polarization angle to pass therethrough without attenuation. Only unattenuated waves continue to resonate within the resonant cavity. In one embodiment, the Faraday rotation element and the laser medium are combined in a single element. The laser is tuned by varying the current applied to the trim coil, thereby adjusting the amount of rotation imparted to the polarized wave, which amount of rotation determines the particular wavelength that is allowed to resonate within the resonant cavity without attenuation.

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