Definition

wavelength

Wavelength is the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal propagated in space or along a wire. In wireless systems, this length is usually specified in meters (m), centimeters (cm) or millimeters (mm). In the case of infrared (IR), visible light, ultraviolet (UV), and gamma radiation (γ), the wavelength is more often specified in nanometers (nm), which are units of 10-9 m, or angstroms (Å), which are units of 10-10 m.

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

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A sound wave is the pattern of disturbance caused by the movement of energy traveling through a medium, such as air, water or any other liquid or solid matter, as it propagates away from the source of the sound. A water wave is an example of a wave that involves a combination of longitudinal and transverse motions. An electromagnetic wave is created as a result of vibrations between an electric field and a magnetic field.

How wavelength is measured

Instruments such as optical spectrometers or optical spectrum analyzer can be used to detect wavelengths in the electromagnetic spectrum. Wavelengths are measured in kilometers (km), meters, millimeters, micrometers (μm) and even smaller denominations, including nanometers, picometers (pm) and femtometers (fm). The latter is used to measure shorter wavelengths on the electromagnetic spectrum, such as UV radiation, X-rays and gamma rays. Conversely, radio waves have much longer wavelengths, reaching anywhere from 1 mm to 100 km, depending on the frequency.

If f is the frequency of the signal as measured in megahertz (MHz) and the Greek letter lambda λ is the wavelength as measured in meters, then:

Wavelength measured
How a wavelength is measured

λ = 300/f

and, conversely:

f = 300/λ

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

Wavelength calculated
How to calculate wavelength

Wavelength formula

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

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

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 WDM (DWDM) 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 nm, 1,300 nm and 1,550 nm.

Waveforms

Waveform describes the shape or form of a wave signal. Wave is typically used to describe an acoustic signal or cyclical electromagnetic signal because each is similar to waves in a body of water.

There are four basic types of waveforms:

  1. Sine wave.The voltage increases and decreases in a steady curve. Sine waves can be found in sound waves, light waves and water waves. Additionally, the alternating current voltage provided in the public power grid is in the form of a sine wave.
  2. Square wave.The square wave represents a signal where voltage simply turns on, stays on for a while, turns off, stays off for a while and repeats. It's called a square wave because the graph of a square wave shows sharp, right-angle turns. Square waves are found in many electronic circuits.
  3. Triangle wave.In this wave, the voltage increases in a straight line until it reaches a peak value, and then it decreases in a straight line. If the voltage reaches zero and starts to rise again, the triangle wave is a form of direct current (DC). However, if the voltage crosses zero and goes negative before it starts to rise again, the triangle wave is a form of alternating current (AC).
  4. Sawtooth wave.The sawtooth wave is a hybrid of a triangle wave and a square wave. In most sawtooth waves, the voltage increases in a straight line until it reaches its peak voltage, and then the voltage drops instantly -- or almost instantly -- to zero and repeats immediately.

Relationship between frequency and wavelength

Wavelength and frequency of light are closely related: The higher the frequency, the shorter the wavelength, and the lower the frequency, the longer the wavelength. The energy of a wave is directly proportional to its frequency but inversely proportional to its wavelength. That means the greater the energy, the larger the frequency and the shorter the wavelength. Given the relationship between wavelength and frequency, short wavelengths are more energetic than long wavelengths.

Electromagnetic waves always travel at the same speed: 299,792 kilometers per second (kps). In the electromagnetic spectrum, there are numerous types of waves with different frequencies and wavelengths. However, they're all related by one equation: The frequency of any electromagnetic wave multiplied by its wavelength equals the speed of light.

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 (APs) 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 April 2020

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How did the development of dense wavelength-division multiplexing improve the use of wavelengths in long-distance fiber communications?
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nice article
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