22 Important Laser Source Terms

Laser Source

A laser source is an electronic instrument used to produce laser light for a variety of test situations. More specifically, a laser source is any one of a number of specialized devices that transmit highly amplified coherent radiation in one (or more) specific frequencies. A variety of laser sources exist, including distributed feedback lasers, Fabry-Perot lasers, fiber coupled lasers and tunable lasers.

Back Scattered Light

Back scatter refers to the reflection of waves or electromagnetic signals from the point at which they originated. Back scattering is used in fiber optic technology to detect optical faults. The amount of scattering is measured and attenuation is determined using the data collected during this test.


C-band refers to a specific section of the electromagnetic spectrum. This frequency contains microwave wavelengths, which are most commonly utilized in the field of telecommunications. It is most well known for its role as the original frequency allocated for satellite communications and, due to its lower frequency level, performs better under adverse conditions than a variety of other band frequencies.

Central Wavelength

Central wavelength, or CWL, refers to the point between two wavelengths, equidistant from each, wherein transmittance is half of the peak. The distance between the two wavelengths (the midpoint of which is the central wavelength) is termed as the FWHM, or full width at half maximum.


Concerning the interaction of waves, coherence refers to a state of constant stationary interference. Coherence can also be used to describe all correlative characteristics between the physical qualities of various waves. Two waves can be described as coherent if they exhibit the characteristic of a constant relative phase.

Dense Wavelength Division Multiplexing (DWDM)

Dense wavelength division multiplexing (abbreviated as DWDM) refers to a type of optical technology that is used to enhance and increase bandwidth over preexisting fiber optic lines. This technology is utilized via the simultaneous combination and transmission of multiple signals at different wavelengths over the same fiber.

Distributed Feedback Laser Source

A distributed feedback laser source (or DFB) is a highly coherent source that transmits laser light within a narrow spectral width. It is possible to tune the DFB laser to a particular range of wavelength.

Fabry-Perot Laser Source

A Fabry-Perot laser source is a single-wavelength electronic device that emits a beam of laser light for testing applications. It is used with an optical power meter to determine levels of insertion loss and optical return loss, along with Polarization Dependent Loss (PDL) measurements of various fiber components. It is resistant to back scattering and is optimally stabilized for use in long- and short-term applications.

Fiber To The x (FTTx)

"Fiber To The x" is a collective generic expression that refers to various fiber deployment techniques that are classified by the location at which the fiber ends. The "x" in the acronym is changed to another letter, depending on where the fiber ends in a given situation. In FTTC, or fiber to the curb or cabinet, for example, the fiber most commonly ends approximately 300 yards from the customer's location. In FTTH, or fiber to the home, the fiber terminates at the customer's home or business.

Fiber-Coupled Laser Source

A fiber-coupled laser source is a unit of electronic test instrumentation that produces concentrated light in the form of a laser beam. It is ideal for emitting laser light into a component in which a polarized light source is required and provides easy coupling of multi-mode fibers.

Insertion Loss

Insertion loss refers to the loss of a signal's measurable power when a filter (or similar device) is inserted into an optical fiber or transmission line. It is calculated by finding the ratio (measured in decibels) of signal voltage measured from source to load before a filter is inserted as compared to the amount of voltage measured from source to load after a filter is added.


The term L-band refers to four separate bands found in the electromagnetic spectrum and includes spans from 1 to 2 gigahertz. The L-band frequency is most commonly utilized in radar technology, fiber optics and satellite telecommunications.

Laser Diode

A laser diode is a small semiconductor device that, while similar to an LED in appearance and construction, produces coherent laser radiation rather than incoherent light (the type produced by an LED). Used in a broad range of products, laser diodes are most frequently used as vital components in fiber optics systems and telecommunications devices.


Mode hopping refers to an event in which a laser, while operating on a particular resonator mode, suddenly switches to another mode. The mode to which the laser switches quickly takes over all of the optical power being produced. Mode hopping is most frequently the result of external stimuli, including noise disturbances or sudden variances in temperature. A device that utilizes a mode-hop-free tuning range effectively prevents the phenomenon of mode hopping by coordinating the gain maximum and the resonator mode frequencies.


Monochromaticism refers to the level and purity of a laser light's electromagnetic radiation in terms of energy. A laser inherently possesses high monochromaticity, directionality and coherence (as opposed to other light sources). When all of the photons that a laser emits have the same energy (and, thereby, the same wavelength), this laser is deemed to be monochromatic and emits a single spectral color.

Multimode Fiber

Multimode fiber, usually utilized in communication over short distances, is a type of optical fiber that is manufactured to transmit multiple rays of light (also known as modes) simultaneously. Each mode is carried at a reflection angle slightly different than the ray adjacent to it. In order to accommodate multiple modes at the same time, multimode fiber has a larger core than single-mode fiber.

Optical Power Range

Optical power range refers to the full spectrum of power that can be measured within an optical signal. When used to test the average amount of amplitude in a fiber optic system, this range is measured with an optical power meter.

Single-Mode Fiber

Single-mode fiber, most commonly used in fiber optic communication over long distances, is a type of optical fiber that is designed to transmit a single ray of light (or mode) at one time. Characterized by its ability to transmit a ray of light with less modal dispersion than multimode fiber, single-mode fiber is capable of preserving the integrity and purity of a light pulse over more lengthy distances.

Spectral Linewidth

Spectral linewidth refers directly to the width of a spectral line within a given electromagnetic transmission. It is also defined as the spectrum of a particular frequency in an electronic system.

Sweep Functions

Sweep functions are among a number of adjustable and programmable features on a given electronic testing instrument. This function provides a return of constant amplitude when testing a component with linearly increasing frequency.

Tunable Laser Source

A tunable laser source is an adjustable electronic device that emits a laser beam for testing purposes. Its construction provides a high signal-to-spontaneous-emission ratio, making it especially useful in testing components in the C-band and L-band ranges. The more dynamic range means that the user is more easily able to characterize DWDM testing devices with higher channel isolation.

Wavelength Range

Wavelength range is the name given to the entire measurable spectrum of electromagnetic radiation. This range includes visible light (between 400 and 800 nm), ultraviolet radiation (lower than 400) and infrared radiation (above 800 nm).