Defense Tech Briefs - Infrared Data Link Using an MQW Modulator on a Retroreflector

Subscribe to Defense Tech Briefs

Home

Tech Briefs

Photonics

Infrared Data Link Using an MQW Modulator on a Retroreflector

Naval Research Laboratory, Washington, DC

Jun 01 2007

Page 2 of 2

The basic idea of a modulating retroreflector on the smaller platform is not new. What is new is the use of an MQW device as the light modulator. An MQW light modulator typically contains several hundred layers (each of the order of 10 nm thick) of semiconductor materials like those of laser diodes. Electrically, an MQW modulator resembles a positive/intrinsic/ negative diode; optically, the MQW modulator exhibits a sharp absorption feature at a wavelength determined by the constituent materials and the numbers and thickness of layers. When a moderate reverse bias potential (≈15 V) is applied, the absorption feature shifts to greater wavelengths and its magnitude decreases. Hence, if the device is designed to position the absorption feature near the laser wavelength, the laser power transmitted through the device can be modulated significantly by varying the reverse bias potential.

Of all semiconductor electro-optical modulators, only MQW modulators offer the combination of high switching speed, low power consumption, low weight, large area, wide field of view, high optical quality, functionality in the desired infrared wavelength range, and ruggedness required for an infrared data link of the type undergoing development. It has been estimated that because of the MQW modulator, the power consumption of the modulatingretroreflector- based data-transmission subsystem aboard the smaller platform can be an order of magnitude smaller than that of an equivalent radio-frequency data-transmission subsystem.

Figure 2. The Uninhabited Helicopter, about 1 m long, carried a data-communication subsystem that included the modulating reflector, which was mounted on the tail facing downward toward a ground station.

In a field test of this system, the modulating retroreflector, which had an aperture diameter of 0.5 cm, was mounted on the tail of the helicopter pointing downward (see Figure 2). The helicopter was flown at an altitude of 50 to 100 ft. (≈15 to ≈30 m) and a range 100 to 200 ft. (≈30 to ≈61 m) from the ground station. A pseudorandom bit stream at a rate of 400 Kb/s was transmitted from the helicopter to the ground station, using a modulator power of only 40 mW. However, it was estimated that the modulator and detector bandwidths and the strength of the return signal were sufficient to sustain a data rate of 3 Mb/s. It is planned to demonstrate even higher rates in future tests.

This work was done by W. S. Rabinovich, G. C. Gilbreath, Chris Bovais, Kerry Cochrell, H. R. Burris, Mena Ferraro, Michael Vilcheck, Rita Mahon, Kim Goins, Ilene Sokolsky, John Vasquez, Timothy Meehan, Robin Barbehenn, D. S. Katzer, and K. Ikossi Ansatasiou of the Naval Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Photonics category. NRL-0010

This Brief includes a Technical Support Package (TSP).

Infrared Data Link Using an MQW Modulator on a Retroreflector (reference NRL-0010) is currently available for download from the TSP library.

Prev: Optical-Fiber Infrasound Sensors
Next: Photonic-Crystal-Based Devices for Commercial Applications

<< Start < Prev 1 2 Next > End >>

Dedicated to helping you design better products in a digital world... your guide to the latest tools & techniques for digital prototyping, simulation, and analysis of the real-world performance of your ideas.

Visit the Digital Design Center