What Is a Corner Cube?
Corner Cubes are devices that retroreflect incident light back in the direction of incidence.
The reflected image is inverted. Unlike mirrors, which are retroreflective only at an angle of incidence of 0°, Corner Cubes’ retroreflectivity is effective even at large angles of incidence. This feature is frequently used for difficult optical-axis adjustment tasks or to reduce working time.
Corner Cube has three reflective surfaces. In general, the maximum allowable angle of incidence at which the phenomenon of total reflection of light can be obtained is theoretically limited to 5.7°.
Uses of Corner Cube
Corner Cubes are used as reflectors for laser-based length measuring machines. They were developed to measure the distance between the Moon and the Earth, and were placed on the lunar surface when the Apollo spacecraft landed on the Moon.
There are many things around us that use the same property. The red reflector on the back of a bicycle or the reflectors (orange or colorless) on the road or on the side of the road are made up of many very small reflectors. Recently, smaller sealed versions are also available, allowing Corner Cubes to be used in a wide variety of locations.
Corner Cubes mounted on vehicles and roads are often made of plastic, and highly accurate Corner Cubes can be used for surveying. Many cubes are made of glass, and their length can be measured from the time they return to the laser beam.
Corner Cube Principle
The three faces of a Corner Cube are placed in an orthogonal relationship to each other. The three planes are xy-plane, yz-plane, and zx-plane, respectively. For example, when light is reflected from the xy-plane, only the z-component of the 3-dimensional vector component indicating the direction of light travels has its sign reversed, while the x- and y-components remain unchanged. Similarly, the sign of the x component is reversed in the yz-plane and the sign of the y component is reversed in the zx-plane.
Due to this property, rays of light that are reflected sequentially in the three planes and whose incoming direction vector is [a, b, c] are [-a, -b, -c] when inverted. In other words, it returns light in the direction it came from. There are a total of six possible combinations of the order in which the incident light is inverted, determined by the position of the incident rays, resulting in the sign of all components being inverted regardless of the order in which they are reflected.
Types of Corner Cubes
Devices that reflect microwaves emitted from a radar in the direction of the radar antenna are called radar corner reflectors. Three conductive metal sheets or screens are pasted together at 90° to reflect incoming radio waves from the front in a parallel manner. However, the reflective surface must be larger than the incident wavelength to function.
Reversal mirrors are made by applying the Corner Cube principle. A reversal mirror is two mirrors combined at right angles. In a reversal mirror, the left and right sides of the image are reversed, but in a reversal mirror, the left and right sides are kept the same.
Corner Cube Structure
There are two types of Corner Cubes: hollow and prismatic. Both have the same basic structure that uses reflections on three surfaces.
Due to the “optical path difference” caused by the relative speeds of the observation station and the satellite, a slightly shifted orthogonality is more effective than a reflector with an exact orthogonality. Many of the reflectors actually used on satellites have their orthogonality intentionally shifted.
Corner Cube Reflector, Cube corners, and Corner reflector are other names for Corner Cube. Corner Cube Prisms and Corner Cube Mirrors are also called Corner Cube Prisms or Corner Cube Mirrors, depending on the reflection principle.