A wavelength is a measure of distance between two identical peaks or crests -- high points -- or between two identical troughs -- low points -- in a wave.

Wavelengths represent a repeating pattern of traveling energy, such as light or sound. Their distinctive formations play an important role in distinguishing one type of energy from another. They are used by a variety of scientists and technology professionals -- from aerospace engineers to enterprise network administrators -- to identify different forms of energy.

The distance between repetitions in the waves indicates a type of wavelength on the electromagnetic radiation spectrum, which includes radio waves in the audio range and waves in the visible light range.

Relationship between frequency and wavelength

Wavelength is inversely related to frequency, which refers to the number of wave cycles per second. The higher the frequency of a signal, the shorter the wavelength.

If you think about wavelengths as the distance between two crests, frequency represents how many waves occur in a given timeframe. The following graphic illustrates an example of wavelength:

Imagine that you've been asked to recite the first five letters of the alphabet in 30 seconds, but you must use the whole 30 seconds to complete the exercise. You'll have to say each letter very slowly -- low frequency -- and leave a gap of time between each letter -- long wavelength. Now imagine you have to recite those same five letters in just three seconds. You're going to say those letters a lot faster -- high frequency -- with little to no gap between them -- short wavelength.

It is important to note, however, that light travels at the same speed no matter the length or frequency of the waves. Therefore, the above exercise is meant only to demonstrate the relationship between frequency and wavelength.

How wavelength is measured

Wavelengths are measured in kilometers, meters, millimeters, micrometers and even smaller denominations, including nanometers, picometers and femtometers. The latter is used to measure shorter wavelengths on the electromagnetic spectrum, such as ultraviolet radiation, X-rays and gamma rays. Conversely, radio waves have much longer wavelengths, reaching anywhere from one millimeter to 100 kilometers, depending on the frequency.

Instruments such as optical spectrometers or optical spectrum analyzers can be used to detect wavelengths in the electromagnetic spectrum.

Wavelength illustrated

Wavelength formula

A wavelength can be calculated by dividing the velocity of a wave by its frequency. This is often expressed as the following equation:

wavelength formula

The Greek letter lambda (λ) represents wavelength, expressed in meters. The v is wave velocity, calculated as meters per second. And the f stands for frequency, which is measured in hertz.

Wave division multiplexing

In the 1990s, fiber optic cable's ability to carry data was significantly increased with the development of wavelength division multiplexing (WDM). This technique was introduced by AT&T's Bell Labs, which established a way to split a beam of light into different wavelengths that could travel through the fiber independently of one another.

WDM, along with dense wavelength division multiplexing and other methods, permits a single optical fiber to transmit multiple signals at the same time. As a result, capacity can be added to existing optical networks, also called photonic networks.

The three most common wavelengths in fiber optics are 850 nanometers (nm), 1,300 nm and 1,550 nm.

In the 1990s, the ability to use fiber optic cable to carry data was significantly increased with the development of WDM. AT&T's Bell Labs originally developed the capability to split a beam of light into different wavelengths that could travel through the fiber at the same time. This created the ability to transmit multiple channels within a single optical fiber.

Wavelengths in wireless networks

Although frequencies are more commonly discussed in wireless networking, wavelengths are also an important factor in Wi-Fi networks. Wi-Fi operates at five frequencies, all in the gigahertz range: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz and 5.9 GHz. Higher frequencies have shorter wavelengths, and signals with shorter wavelengths have more trouble penetrating obstacles like walls and floors.

As a result, wireless access points that operate at higher frequencies -- with shorter wavelengths -- often consume more power to transmit data at similar speeds and distances achieved by devices that operate at lower frequencies -- with longer wavelengths.

This was last updated in November 2018

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How did the development of dense wavelength-division multiplexing improve the use of wavelengths in long-distance fiber communications?
nice article
What's your most reliable tool for analyzing wavelengths and frequencies?


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