What is Dispersion in Optics?

In optics, dispersion refers to light that is separated by individual colors as it passes through an object. Rainbows are the most common example of this event. The rainbow forms when white light is separated into components of different wavelengths (or colors). Dispersion can result in signal degradation in many applications, especially over large distances.

Dispersion in Optical Fibers

There are three types of dispersion: modal, chromatic, and material.

Modal Dispersion

Modal dispersion refers to the path taken by a ray of light. Many transmitters emit multiple mode types. Some of the light rays travel through the fiber while others reflect off of the fiber core’s boundary, instead traveling along an indirect path on the waveguide. These constitute the two types of modes: high-order modes and low-order modes.

  • High-order modes enter the fiber at acute or obtuse angles, and take significantly longer to pass through fiber than low-order modes.
  • Low-order modes enter the fiber directly and pass through it more quickly.

Modal dispersion can be eliminated by using a single-mode fiber. These fibers only transmit one mode of light, so the signal won’t be spread through modal dispersion.

Chromatic Dispersion

Chromatic dispersion results from the emitter’s spectral width, which determines the number of wavelengths that are emitted—the smaller the spectral width, the fewer wavelengths. Longer wavelengths move faster than shorter ones, so they arrive at the end of the fiber quicker to spread out the signal. Chromatic dispersion may be decreased by narrowing the transmitter’s spectral width. A monochromatic emitter has just a single wavelength, so it does not contribute to chromatic dispersion.

Chromatic dispersion is important to researchers who design optical equipment, including cameras, optical microscopes, and telescopes. The system in such equipment must be carefully planned—which includes using a combination of lenses made of different materials with different indices of refraction—so that the chromatic aberrations are minimized, resulting in an optimal image.

Material Dispersion

Material dispersion occurs when the wavelength depends on the refractive index of the fiber core material. Material dispersion is a contributing factor to a number of phenomena, including:

  • Waveguide delay dispersion
  • Chromatic aberrations in lenses
  • Group delay distortion
  • Color separation in prisms
  • Multimode group delay spread
  • Differential mode delay

Metrology manufacturers rely on glass prisms to disperse light in precision equipment, such as spectrometers.

Glass Fabrication from Swift Glass

If you’d like to learn more about optical dispersion, you can pick up our free eBook, “Understanding the Optical Properties of Glass.” It provides an in-depth look at key properties that affect the optical performance of your glass material, including the refractive index, chromatic dispersion, and transmission/transmittance. Knowing this information is especially vital for engineers who work in industries in which the optical performance of glass is key to meeting application specifications.

Swift Glass is an ISO 9001:2015-certified and ITAR-registered company with nearly 100 years of experience in the industry. Custom glass fabrication is our specialty, and we are known for our company-wide commitment to providing quality solutions for original equipment manufacturers. We work with leading glass manufacturers—including Corning and Schott—and we stock a wide range of materials, allowing us to quickly respond to your needs. We have provided solutions for companies in the biomedical, industrial, optical, and aerospace industries.

If you are in need of glass fabrication services, be sure to contact our team to request a quote today.

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