Endless polarization control systems for coherent optics

Abstract

In coherent optical systems or sensors, polarization matching between the superposed beams must be assured. The tracking range of automatic polarization control systems should be endless, i.e., any resets of finite range retarders, which transform the polarization, should cause no significant intensity losses. A variety of experimental systems including a computer as feedback controller are described in this paper. They include the minimum configuration of three fixed eigenmode retarders. i.e., the orientation of birefringence cannot be changed. These retarders are realized by fiber squeezers. Errortolerant systems which contain more than the minimum number of elements, however, are better suited to cope with time variant retarder transfer functions, etc. A fourth Rber squeezer allows the losses of a nonideal system to be kept to only 0.07 dB. Finally for the first time a closed loop system with two integrated optical retarders is described. These retarders have variable eigenmodes, i.e., adjustable birefringence orientation. An optimization procedure helps to idealize the device behavior. The system has less than 0.15 dB intensity losses, coupling and attenuation not Included.

Nonlinear polarizers based on four-wave mixing in high-birefringence optical fibers

“…Whenever optical signals from a telecommunication link are used in combination with polarization-sensitive components such as coherent receivers, optical switches, polarization demultiplexers, or sensors, it is thus necessary to stabilize the SOP at the fiber output. Conventional SOP control devices with relatively high polarization tracking speed are based on lithium-niobate electro-optical polarization transformers [2,3]. An entirely new class of fiber-based and potentially ultrafast SOP controllers has been introduced in recent years, based on third-order nonlinear polarization interactions among different waves within the optical fiber itself.…”

Fabrication of integrated-optic polarization controller using Z-propagating Ti-LiNbO/sub 3/ waveguides

“…While various reset schemes have been proposed [13], [15], a recent demonstration of a resetfree waveguide-type device consisting of a half-wave and two quater-wave plates using analog feedback [20] has solved the complications of reset schemes, making a remarkable progress toward the practicality of waveguide type polarization controllers.…”

“…It is this mode of operation that we have employed in our performance test described in Section 111-C. There is another mode of operation based on a similar device; in the "rotating wave plate" mode in which only MC is used, one simultaneously controls the propagation constant mismatch denoted as S above as well as K to create a desired polarization state [13], [15]. …”

Nonlinear optical fiber polarization tracking at 200 krad/s

“…In the presence of polarization-sensitive components at the end of the link such as coherent receivers, optical switches, polarization demultiplexers or sensors, the stabilization of the SOP at the fiber output requires endless or continuous polarization control devices with relatively high tracking speed. With conventional polarization controllers based on Lithium-Niobate electro-optical polarization transformers, polarization tracking speeds have risen from 0.1 rads/s [2] up to 59 krads/s [3]. A new class of all-fiber polarization controllers has been proposed in recent years, based on nonlinear polarization interactions, including so-called Brillouin and Raman polarizers, Refs.…”