In an optical source or detector, the ratio of the number of output quanta to the number of input quanta.
Note: Input and output quanta need not both be photons.

Noise attributable to the discrete and probabilistic nature of physical phenomena and their interactions.
Note 1: Quantum noise represents the fundamental limit of the achievable signal-to-noise ratio of an optical communication system. This limit is never achieved in practice. [After FAA]
Note 2: Examples of quantum noise are photon noise in an optical signal and shot noise in an electrical… (Read More →)

Synonym quantum-noise-limited operation.

Operation wherein the minimum detectable signal is limited by quantum noise. Synonym quantum-limited operation.

A video format defined in ITU-T Recommendation H.261 that is characterized by 176 luminance pixels on each of 144 lines, with half as many chrominance pixels in each direction.
Note: QCIF has one-fourth as many pixels as the full common intermediate format.

A clock containing a quartz oscillator that determines the accuracy and precision of the clock.

An oscillator in which a quartz crystal is used to stabilize the frequency.
Note: The piezoelectric property of the quartz crystal results in a nearly constant output frequency, which is dependent upon the crystal size, shape, and excitation.

A digital signal that has been converted to a form suitable for transmission over a specified analog channel.
Note: The specification of the analog channel should include frequency range, bandwidth, signal-to-noise ratio, and envelope delay distortion. When quasi-analog form of signaling is used to convey message traffic over dial-up telephone systems, it is often referred to as voice-data. A modem… (Read More →)

Transmission in which a special-purpose modulator is used to convert digital signals into an analog form suitable for transmission over an analog voice-grade circuit.
Note: A complementary demodulator is used to recover the digital signal at the other end of the circuit. See modem.

A limited case of the nonassociated mode of signaling in which the path taken by a message through the signaling network is predetermined and fixed at a given point in time. [T1.226-1992]