We analyze and demonstrate a passive single-mode fiber depolarizer by using cascaded 2 x 2 couplers, recirculating delay lines, and a commercial laser diode. Design criteria and principles are discussed. We reduced the degree of polarization (DOP) to less than 20 dB by using ten cascaded couplers. The DOP can be reduced even further with more couplers. Experiments illustrate that this depolarizer is insensitive to the input polarization state and can eliminate polarization noise in a polarization-sensitive fiber-optic system.
A new type of all-single-mode fiber depolarizer, based upon a 2 x 2 coupler and a recirculating delay line and useable with a coherent light source, is proposed and demonstrated. The reduction in the degree of polarization is examined theoretically and experimentally. Design criteria and principles are discussed. With a narrow-band laser source, the degree of polarization was tuned between 99.8% and 1.15%. Experiments illustrate how this depolarizer can eliminate the effects of induced polarization fluctuation in a polarization-sensitive fiber-optic system. The experimental results support the theoretical model.
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