Generation of an optical vortex with a segmented deformable mirror.

We present a method for the creation of optical vortices by using a deformable mirror. Optical vortices of integer and fractional charge were successfully generated at a wavelength of 633 nm and observed in the far field (2000 mm). The obtained intensity patterns proved to be in agreement with the theoretical predictions on integer and fractional charge optical vortices.

Mode purity comparison of optical vortices generated by a segmented deformable mirror and a static multilevel phase plate.

We present a mode purity comparison between optical vortices (OVs) generated by a static multilevel phase plate with 16 or 32 phase steps and a vortex generated with a segmented deformable mirror with 37 actuators. Computer simulations show the intensity and phase of the vortices generated with the two methods. The deformable mirror, by being reconfigurable, shows better mode purity for high charge OVs, while the static phase plate mode efficiency declines due to the fixed number phase quantization.

Vortex beam propagation through atmospheric turbulence and topological charge conservation.

The propagation of vortex beams through weak-to-strong atmospheric turbulence is simulated and analyzed. It is demonstrated that the topological charge of such a beam is a robust quantity that could be used as an information carrier in optical communications. The advantages and limitations of such an approach are discussed.

Performance of a compact adaptive-optics system.

The design of an adaptive-optics system for correction of a beam propagating through high-speed, unpredictable optical turbulence required the use of a robust controller rather than a conventional least-squares controller. We describe the 37-channel, 50-Hz adaptive-optical system and its performance (lambda/75 rms).

Indirect measurement of a laser communications bit-error-rate reduction with low-order adaptive optics.

In experimental measurements of the bit-error rate for a laser communication system, we show improved performance with the implementation of low-order (tip/tilt) adaptive optics in a free-space link. With simulated atmospheric tilt injected by a conventional piezoelectric tilt mirror, an adaptive optics system with a Xinetics tilt mirror was used in a closed loop. The laboratory experiment replicated a monostatic propagation with a cooperative wave front beacon at the receiver.

Bit-error rate for free-space adaptive optics laser communications.

An analysis of adaptive optics compensation for atmospheric-turbulence-induced scintillation is presented with the figure of merit being the laser communications bit-error rate. The formulation covers weak, moderate, and strong turbulence; on-off keying; and amplitude-shift keying, over horizontal propagation paths or on a ground-to-space uplink or downlink. The theory shows that under some circumstances the bit-error rate can be improved by a few orders of magnitude with the addition of adaptive optics to compensate for the scintillation.