As light sources, digital sensors, and coating chamber technologies continue to improve, optical filters will naturally evolve and continue to advance. Optical filters are critical for some of the most demanding applications in automation, energy, medical imaging, security, and multi-element optical systems.
These advancements require developments on new substrates such as flexible thin film polymers and IR grade materials including silicon and germanium, or with new chemicals and compounds that yield high transmission and high blocking filters in the UV and IR spectrums. Advancements in coating chamber technology have resulted in higher precision filters yielding bandwidths of <1nm with tolerances of <1%, which truly pushes the limits of top of the line spectrophotometers. With each advancement, tolerances and specifications have been further optimized to better represent a precision substrate with improved surface quality, surface flatness, parallelism, and transmitted wavefront.
New materials, sub-nanometer specifications, deep UV to far IR spectral coverage, and various improved tolerances will continue the advancement of optics and photonics in nearly every consumer and scientific application.
The largest diameter filters that Edmund Optics® can produce are 300mm. Tolerances and uniformity become a concern on substrates this large due to sputtering and coating limitations.
Common filter substrate materials include fused silica, N-BK7, and float glasses. Recently a trend towards fluoride materials, IR crystalline materials like silicon and germanium, and polymers and plastics has emerged.
The first step is to determine what type of filter is required for the application. The basic types of filters are shortpass, longpass, bandpass, dichroic, notch, and neutral density. Each type of filter has unique characteristics that lend better to one application or another. The second step is to determine what wavelengths are required, as filters are defined by what part of the spectrum they pass or do not pass. For instance, an UV Cut-Off (or Longpass) filter is designed to pass both the visible and IR portions of the spectrum, but block (or "cut") the UV portions of the spectrum.