45 Mbps cat's eye modulating retro-reflector link over 7 Km

Abstract

Modulating retro-reflectors (MRR) allow free space optical links with no need for pointing, tracking or a laser on one end of the link. They work by coupling a passive optical retro-reflector with an optical modulator. The most common kind of MRR uses a corner cube retro-reflector. These devices must have a modulator whose active area is as large as the area of the corner cube. This limits the ability to close longer range high speed links because the large aperture need to return sufficient light implies a large modulator capacitance. To overcome this limitation we developed the concept of a cat's eye MRR. Cat's eye MRRs place the modulator in the focal plane of a lens system designed to passively retro-reflect light. Because the light focuses onto the modulator, a small, low capacitance, modulator can be used with a large optical aperture. However, the position of the focal spot varies with the angle of incidence so an array of modulators must be placed in the focal plane, In addition, to avoid having to drive all the modulator pixels, an angle of arrival sensor must be used. We discuss several cat's eye MRR systems with near diffraction limited performance and bandwidths of 45 Mbps. We also discuss a link to a cat's eye MRR over a 7 Km range.

Novel non-mechanical fine tracking module for retroreflective free space optics

“…Using GPS information, a gimbal provided coarse pointing putting the aircraft into the FOV (Field of View) of the fine steering mirrors, which then optically tracked the UAV. 45Mbps at 7km marine link from ship to shore have also been reported using the same system architecture [5].…”

“…It employs a MRR (Modulator Retro-Reflector) to reflect back and modulate a CW (Continuous Wave) interrogating beam launched from the BS. Data can be encoded using either LC (Liquid Crystal) optical shutter or MQW (Multiple Quantum Well) modulators, which offer data rates of tens of Mbps [2]. The interrogator beam could also be modulated in order to implement an uplink channel (BS to the UAV) [3].…”

Discuss Performance of Corner-Cube Prism for Modulating Retro-Reflector Terminal in Free-Space Laser Communication

“…978-1--0911-1/12/$31.00 ©2012 IEEE Corner-cube prism modulating retro-reflector optical communications terminal is different from the classic way of communication structure , as figure (1) shown above [6]. so the link factor in the equation should be adjusted, corner-cube prism is signal transmitter as while is signal receiver.…”

Modulating Retro-Reflector Devices and Current Link Performance at the Naval Research Laboratory

“…Below are details of two experiments using CERs. 1) 45 Mbls 7 km linkfrom boat to shore A 1.6 cm diameter flat focal plane CER MRR was used in a FSO link from a laser interrogator on a cliff 30 meters above Chesapeake Bay to the cat's eye on a boat on the bay [15]. The laser interrogator consisted of a 5 Watt laser, a 65 MHz photodetector with -40 dBm sensitivity, a pointing and tracking system, and a bistatic aperture with a 15 cm receiver aperture and a 13 cm transmit aperture.…”