Radiation-hardened Fiber

An optical fiber made with core and cladding materials that are designed to recover their intrinsic value of attenuation coefficient, within an acceptable time period, after exposure to a radiation pulse.



An instrument, distinct from a photometer, to measure power (Watts) of electromagnetic radiation.



The science of radiation measurement.


Raman Amplifier

An optical amplifier based on Raman scattering which generates many different wavelengths of light from a nominally single-wavelength source by means of lasing action or by the beating together of two frequencies. The optical signal can be amplified by collecting the Raman scattered light.


Random Jitter (RJ):

Random jitter is due to thermal noise and may be modeled as a Gaussian process. The peak-to-peak value of RJ is of a probabilistic nature, and thus any specific value requires an associated probability.

Random Jitter (RJ):

Rayleigh Scattering

The scattering of light that results from small inhomogeneities of material density or composition



Lines that represent the path taken by light.



A terminal device that includes a detector and signal processing electronics. It functions as an optical-to-electrical converter.


Receiver Overload

The maximum acceptable value of average received power for an acceptable BER or performance.


Receiver Sensitivity

The minimum acceptable value of received power needed to achieve an acceptable BER or performance. It takes into account power penalties caused by use of a transmitter with worst-case values of extinction ratio, jitter, pulse rise times and fall times, optical return loss, receiver connector degradations, and measurement tolerances. The receiver sensitivity does not include power penalties associated with dispersion, or backreflections from the optical path; these effects are specified separately in the allocation of maximum optical path penalty. Sensitivity usually takes into account worst-case operating and end-of-life (EOL) conditions.



Combination of an electron and a hole in a semiconductor that releases energy, leading to light emission.



The changing of direction of a lightwave in passing through a boundary between two dissimilar media, or in a graded-index medium where refractive index is a continuous function of position.


Refractive Index

A property of optical materials that relates to the speed of light in the material versus the speed of light in a vacuum.


Refractive Index Gradient

The description of the value of the refractive index as a function of distance from the optical axis along an optical fiber diameter. Also called refractive index profile.


Regenerative Repeater

A repeater, designed for digital transmission, in which digital signals are amplified, reshaped, retimed, and retransmitted.

Regenerative Repeater


Synonym for regenerative repeater.



A receiver and transmitter set designed to regenerate attenuated signals. Used to extend operating range.


Residual Loss

The loss of the attenuator at the minimum setting of the attenuator.



The ratio of a photodetector’s electrical output to its optical input in Amperes/Watt (A/W).


Return Path

A communications connection that carries signals from the subscriber back to the operator. The return path allows for interactive television and on-demand services, such as pay-per-view, video on demand, and interactive games.



Abbreviation for radio frequency. Any frequency within the electromagnetic spectrum normally associated with radio wave propagation.


RF Carrier

An AM technique wherein a carrier, with a frequency much higher than the encoded information, varies according to the amplitude of the information being encoded.



Abbreviation for radio frequency interference. Synonym for electromagnetic interference.



Abbreviation for red, green, and blue. The basic parallel component set in which a signal is used for each primary color, or the related equipment or interconnect formats or standards.


Ribbon Cables

Cables in which many fibers and/or copper wires are embedded in a plastic material in parallel, forming a flat ribbon-like structure.
(Photo courtesy of Force, Inc.)

Ribbon Cables


Abbreviation for relative intensity noise. Often used to quantify the noise characteristics of a laser.



A set of stations wherein information is passed sequentially between stations, each station in turn examining or copying the information, and finally returning it to the originating station.


Ring Network

A network topology in which terminals are connected in a point-to-point serial fashion in an unbroken circular configuration.

Ring Network

Rise Time

The time taken to make a transition from one state to another, usually measured between the 10% and 90% completion points of the transition. Alternatively the rise time may be specified at the 20% and 80% amplitudes. Shorter or faster rise times require more bandwidth in a transmission channel.

Rise Time


Abbreviation for root mean square. Technique used to measure AC voltages.



An ANSI recommended standard for video transmission used to evaluate the quality of a received picture quality. Different requirements exist for short-haul, medium-haul, and long-haul RS-250C. Each of these three levels is defined by the number of intermediate processing devices and the type of path (optical or electrical).



Abbreviation for request to send. In a communications network, a signal from a remote receiver to a transmitter for data to be sent to that receiver.



Abbreviation for return to zero. A common means of encoding data that has two information states called “zero” and “one” in which the signal returns to a rest state during a portion of the bit period.