| 摘要 |
PURPOSE: To reduce the effect of polarization dependent hole burning in an optical transmission system using an optical fiber amplifier. CONSTITUTION: Polarization modulation is realized by using two cascade connected polarization modulators. The modulator is composed of two cascade connected rotary wavelength plates and the two wavelength plates are composed of a half wavelength plate rotated at a first fixed angular velocity and a 1/4 wavelength plate rotated at a second angular velocity different from the first angular velocity following it. In another embodiment, the modulator is composed of the cascade of two adjustable phase retarders with the fixed direction of a relative angle 45 deg. and both of the phase retarders modulate input optical signals and generate cyclic phase shift between -πand +π. Further, in order to reduce the effect of polarization dependent loss, an SOP modulation frequency is selected so as to be the multiple of an information signal clock.
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