Lee M. Burberry

Quantum enhancement of a coherent ladar receiver using phase-sensitive amplification

We demonstrate a balanced-homodyne LADAR receiver employing a phase-sensitive amplifier (PSA) to raise the effective photon detection efficiency (PDE) to nearly 100%. Since typical LADAR receivers suffer from losses in the receive optical train that routinely limit overall PDE to less than 50% thus degrading SNR, PSA can provide significant improvement through amplification with noise figure near 0 dB. Receiver inefficiencies arise from sub-unity quantum efficiency, array fill factors, signal-local oscillator mixing efficiency (in coherent receivers), etc. The quantum-enhanced LADAR receiver described herein is employed in target discrimination scenarios as well as in imaging applications. We present results showing the improvement in detection performance achieved with a PSA, and discuss the performance advantage when compared to the use of a phase-insensitive amplifier, which cannot amplify noiselessly.

Acousto-optic deflector for free-space laser communications*

A technique is developed to steer the transmit laser beam for free-space laser communications (lasercom) using a 2-dimensional acousto-optic (AO) Bragg cell deflector. Important characteristics of the AO Bragg deflector include high angular resolution, fast switching speed, high electrical and optical efficiency, and high reliability with no moving parts. A demonstration transmitter terminal was developed to steer a laser over a range of 360 degree(s) X 36 degree(s). Several unique capabilities are provided by the AO deflector which are not possible with conventional steering mirrors. For example, multiple simultaneous beams can be independently steered anywhere within the total steering range. Also, the AO deflector can produce variable defocus (zoom) that increases the divergence of the beam to over 10 times the diffraction-limited beam width. A direct-digital- synthesizer (DDS) was developed to produce stable and fast switching frequencies for input to the AO deflector. All of the beam control and diagnostic functions for the demo transmitter are provided by a menu-driven PC486-33 computer program.

A High Speed, High Resolution, Laser Scanner Subsystem; Measurement Techniques

Techniques for testing laser scanning subsystems play an important role in their development. Testing determines how well the design was implemented, indicates whether all pertinent factors were taken into consideration during the design and error analysis, and most importantly, demonstrates system performance. This paper will discuss typical test methods for scanner subsystems designed and fabricated by the Optical Systems Department of Harris Government Communications Systems Division. Specifications for one Harris scanner are given in Table 1, and a method to test each parameter is discussed below.