Practical Optical Information for Modern Imaging Systems

Aliasing occurs when spatial information in the optical image exceeds what the discrete sensor sampling grid can represent correctly. The sampled result can contain false patterns, false detail, or moiré that were not present in the original scene.

No. Smaller pixels increase sampling density and raise the sensor's Nyquist frequency, which allows finer detail to be sampled correctly. Aliasing can still occur if meaningful spatial information remains above that higher sampling limit.

Nyquist frequency is half the sampling frequency. In an imaging sensor, it represents the highest ideal spatial frequency that can be represented without ambiguity by that sampling grid.

Lens MTF determines how much contrast is transferred at different spatial frequencies. If substantial image contrast reaches the sensor near or above Nyquist, those frequencies may contribute to aliasing.

An optical anti-aliasing filter modifies spatial information before the image reaches the sensor. Birefringent designs can create controlled image displacement that redistributes fine detail across neighboring sensor locations, reducing the strength of frequencies likely to alias.

The goal is not generic blur. A properly designed filter controls spatial redistribution so that objectionable aliasing is reduced while useful in-band image information is retained as much as practical.

Controlled optical displacement allows a designer to shape where image energy is placed before sampling. This provides more control over the resulting point-spread response than simply introducing uniform softening.

Polarization describes the orientation and phase relationship of the electric-field components of light. Optical elements can be used to select, rotate, or transform polarization depending on system requirements.

In linearly polarized light, the electric field oscillates along a fixed direction. In circular polarization, two orthogonal components have the appropriate relative amplitude and phase for the field direction to rotate as the light propagates.

A retardation element introduces a controlled phase difference between orthogonal polarization components. The resulting retardance depends on birefringence, thickness, wavelength, and orientation.

Birefringence is a difference in refractive behavior for different polarization components in an anisotropic material. It can produce beam displacement, phase retardation, and other polarization-dependent effects.

Optical behavior in a birefringent crystal depends on the relationship between light propagation, polarization, and the crystal's optical axes. Changing orientation can therefore change displacement, retardance, and polarization behavior.

Both materials possess useful optical anisotropy and birefringence. Material selection depends on wavelength, geometry, required optical behavior, environmental requirements, and manufacturing considerations.

Thickness can affect optical path length, retardance, beam displacement, and packaging. Wedge and parallelism can affect beam direction, interference effects, assembly geometry, and system performance.

Interferometry compares optical wavefronts to reveal small differences in optical path. Depending on the measurement configuration, it can be used to evaluate characteristics such as optical flatness or transmitted wavefront behavior.

Useful starting information can include the required optical function, wavelength, sensor model and pixel pitch, lens information, magnification, component dimensions, polarization requirements, available optical space, existing drawings, and representative images showing the problem.