Theory of a tunable fiber ring depolarizer theory.

The depolarizing properties of a fiber ring structure have been analyzed, and the analytical solution to the device optimization has been found. The result proves that a tunable fiber ring depolarizer can completely depolarize light for any input state of polarization.

Passive single-mode fiber depolarizer.

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.

Fiber recirculating delay-line tunable depolarizer.

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.

Single-mode fiber coupling efficiency with graded-index rod lenses.

Losses are calculated for the single-mode graded-index- (GRIN-) lens coupler. The main advantage of this coupling system is large separation between fibers with small power loss. The excess loss of the GRIN-lens coupler is due primarily to the misalignments of the GRIN lenses and is most sensitive to angular tilt rather than lateral offset or end separation. The excess loss is calculated from the overlap of two differently sized or misaligned Gaussian beams. Experimental results show that this method is adequate for predicting losses that are due to misalignments of the GRIN lenses.

Fiber coupling using graded-index rod lenses.

The graded-index rod lens (GRIN lens) is useful in coupling between multimode optical fibers. Applications include connectors, switches, multiplexers, and branch couplers. In these devices, one GRIN lens collimates light from an input fiber, and a second lens collects the light and focuses it on an output fiber. This paper presents analyses of power losses in these devices resulting from lateral and angular misalignments and from the spacing between the lenses. It is found that the GRIN lens coupling system is very sensitive to angular alignment but is more tolerant of lateral errors and lens spacing.

Scanned beam holography.

The stability time for making a hologram with a cw gas laser is reduced by using a method called scanned beam holography. This new technique reduces the time during which extreme mechanical stability must be maintained in a holographic system. An experiment showing a reduction in stability time by a factor of sixteen illustrates the procedure. In some cases the stability times can be reduced sufficiently such that the conventional stable platform can be eliminated. Thus, objects which cannot be mounted on a stable platform can be used for holography.