Real-time video transfer using multiple quantum-well retromodulators

Abstract

This paper is an update in the progress of the development of NRL's Multiple Quantum Well retromodulators for compact, low power communications. We report results for data-in-flight on a small, unmanned aerial vehicle at up to 5 Mbps, in preparation for real-time video transfer using an array of devices. This data was taken at Chesapeake Bay Detachment. We also report transference of color video using wavelet compression at 15 and 30 frames per second, at 4 to 6 Mbps in lab, at eye safe intensity levels. The unit is a cornercube modulator using a 980 nm shutter. A five-element array was used for the data-in-flight. First results of our 1550 nm devices are also presented as is progress in a "Cats Eye Retromodulator". IntroductionDue to its promise of wide bandwidth, freedom from frequency allocations issues, comparatively small communications terminals, and low power requirements, free space optical communications has emerged in recent years as an attractive alternative to the conventional Radio Frequency (RF) approach.There are many applications, where reducing the parasitic payload requirements for the onboard communications system would be advantageous and the Naval Research Laboratory (NRL) has been developing multiple quantum well (MQW) retroreflectors for just this purpose. [1,2] In this paper, we report progress in the implementation of the wide aperture MQW modulating retroreflector (MRR) for video and multiple Mega-bit-per-second (Mbps) data transfer for compact, lightweight, low power optical data transfer.The device couples an electro-absorptive narrow band tunable shutter with a standard optical corner cube. It is lightweight (on the order of ounces), low power (milliwatts), compact (centimeter-level diameters), and radiation-hard. [3] When coupled with a sensor and drive electronics, the package can serve as the communications payload for a remotely located platform.The payload is interrogated by a laser and modulated by the shutter.The modulated retroreflected light is received and demodulated at the transmit/receive location. This technique is especially suited to asymmetric links where the communications payload located remotely can be quite small -the size of a quarter for a single device and the size of a fist for an array. This asymmetry is enabled by the rangeto-the-fourth loss inherent in the use of retroreflected links. That is, the received power in the far field is proportional to:.where P laser is the transmit power, D retro is the diameter of the retroreflector, D rec is the receiver diameter, T atm is the transmission coefficient of the atmosphere, T cl is the transmission coefficient of clouds, θ div is the divergence of the transmit beam, and R is the range. The onus of the link consequently falls on the power of the transmitter, the size of the receive telescope and the quality of the In previous work, we reported data-in-flight on a micro-UAV of 400 kbps and 910 kbps at ranges on the order of 35 meters. [4] In this effort, psuedo random codes varying from 300 kbps through 5 ...

Progress in high-speed communication at the NRL Chesapeake Bay lasercomm testbed

“…This facility is utilized for field-testing of optical components such as modulators and erbium doped fiber amplifiers (EDFA) developed and built at NRL along with commercially available components 1 . In addition to conventional lasercomm, the facility at CBD is used in communication links with a modulated retroreflector 2,3 . These links include ground to UAV and shore to ship links transferring real-time video and other data.…”

The atmospheric neutral density experiment (ANDE) and modulating retroreflector in space (MODRAS): combined flight experiments for the space test program

“…This technique provides a compact, low power (150 mW per device), lightweight (less than an ounce per device) two-way optical communication platform. The NRL corner-cube devices can support up to 12 Mbps and has been demonstrated to support real-time video at 30 fps using wavelet compression 13 . The devices can made to operate with a 10 nm bandwidth at 850 nm, 980nm, 1.06 nm, or 1550 microns.…”