Fiber recirculating delay-line tunable depolarizer

Abstract

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.

Depolarization bandwidth of fiber optic passive depolarizers

“…1 can be used to evaluate whether a passive depolarizer such as the recirculating delay lines, 11,12 could replace an active device in a system which encompasses optical amplifiers. The depolarizer can, for instance, be used in conjunction with an intensity modulator which is polarization independent, 15,16 so as to avoid the dispersion introduced by the delay lines.…”

“…Several devices implementing this technique have been described in the literature. [11][12][13][14] These devices are often referred to as passive depolarizers, since the polarization changes are obtained by exploiting the random phase changes ͑lack of coherence͒ of the light source. Thus, the output SOP is in turn random and depolarization is obtained when the light is averaged over a time interval usually assumed to be infinite, but which in practice must be large compared to 1/⌬, where ⌬ is the fullwidth-half-maximum ͑FWHM͒ source spectral width.…”

“…The averaging time is not an issue for devices such as the Lyot depolarizer, which require a wide-bandwidth source. On the other hand, a passive depolarizer such as the recirculating delay line 11,12 is practical when used with narrowlinewidth sources. This is one of its advantages.…”

A compact single-mode fiber ring depolarizer

“…In 1993, Dale R. Lutz proposed a passive fiber ring depolarizer made of polarization-maintaining fiber [5], which required polarization axis alignment. Later in 1998, Paisheng Shen proposed a depolarizer structure made of single-mode fiber ring [6], but with a polarization controller inserted in the fiber ring, which makes the device not feasible in practical uses. In this paper, we design a single-mode fiber ring depolarizer without any extra polarization control components requirement in the fiber ring, so that the device can be made compact and much facile in uses.…”

Dispersion-shifted fiber polarization scrambler based on Faraday effect

“…It is important to remark that, strictly speaking, light is not depolarized, so, its instantaneous DOP will always be near the unity. The technique used here to minimize the differs from other previous works [7], [8], which actually depolarize the light by introducing a differential group delay between the orthogonal modes greater than the coherence length. Our device simply makes the light SOP to change very fast, so light appears to be depolarized if the measure time is longer than the scrambling period.…”