The goal of the OPTRA Compact Beam Steering (CBS) program is to provide an alternative approach to
a gimbal based system for both scanning and pointing a laser beam. The fundamental technology of the
CBS is a pair of rotating wedges, or Risley Prisms. The advantages of this type of system are:
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compactness
relative insensitivity to vibration
low moment of inertia
independent rotational axes (no carried axes, no need for slip rings)
robustness
speed
When a prism pair is oriented as shown in (a), they both refract light in the same direction and act as a
single prism with twice the prism angle of either. In (b), each prism has been rotated about the optical
axis by the same angle, but in opposite directions. In this case the beam remains close to the plane
defined by the optic axis and the refracted beam shown in (a). In (c), each prism has been rotated by
90 and they combine to act as a parallel plate – with no net angular deviation. Thus, any point in a
circular field of regard can be achieved by adjusted the angle between the prisms to obtain the desired
deflection off-axis, and then rotating the pair to steer the beam in the desired direction.
A very attractive features of prism-pair assemblies is the ability to generate scan patterns by rotating the
prisms at different velocities to obtain spiral, rosette, and pinwheel scans
Sprial Scan
Rosette Scan
OPTRA has developed Risley Prism laser beam steering systems for applications in collision avoidance
LIDAR, Free-space optical communications, and Infrared Countermeasures satisfying a wide range of
customer specifications. Other systems under development are for applications in laser cutting and
trepanning.
Steering/Scanning
Wavelength range
Beam Diameter
Field of Regard (FOR)
Pointing Accuracy
Size
Weight
Infrared
Countermeasures
Steering
2.0 - 4.7 µm
3 mm
120 degrees
1 mrad
2.3 inch diameter
3.5 inch length
2.3 lb
Optical
Communications
Steering
1.54 – 1.57 µm
4 inch
120 degrees
0.7 mrad
10.8 inch diameter
8.7 inch length
55 lb
Optical
Avoidance
Scanning
1.540 -1.580 µm
1 inch
60 degrees
1 mrad
3.4 inch diameter
1.7 inch length
2.3 lb
Optical Avoidance
Infrared Countermeasures
Optical Communications