Wired Broadband and Related Industry Glossary of Terms with Acronyms As of 13 June 2011 Compiled By: Conrad L. Young, Director, Broadband Technical Strategy



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Differential Quadrature Phase Shift Keying [Sat07]
DER

Dynamic Extinction Ratio, ERRF; measured by applying an RF electrical signal at the RF input port of an optical intensity modulator, the DC bias voltage being tuned so as to set the modulator at the desired operating point (this operating point may be positive or negative quadrature, minimum, maximum or any other point of the transfer function depending on the application). ERRF is application dependent. For digital applications, the RF electrical signal is generated by a PRBS generator, the output optical signal is monitored by a high speed network analyzer. An eye diagram is displayed and the ratio between the high and low levels is recorded as the ERRF. [Jer04]

DES
Data Encryption Standard

Descrambler
An electronic circuit that restores a scrambled video signal to its standard form.

Destructive Interference



Any interference that decreases the desired signal. For example, two light waves that are equal in amplitude and frequency, and out of phase by 180°, will negate one another. [Fib111]

Destructive Interference Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/d


Detect

To rectify a modulated carrier wave and thereby recover the original modulating wave. [Arr11]
Detector
The photodiode in optical receivers.

Detent Tuning

Tuning into a channel by selecting a preset resistance. [Cha07]
Deutsch 1000

Deutsch 1000 was the first commercially successful fiber optic connector. It was a "pin vise" holding a stripped fiber. The nose piece is spring loaded and was pushed back when the connector was inserted into a mating adapter. The fiber stuck out into a drop of index matching fluid on a plastic lens. This solution was state of the art in the late 70s, yielding about 3 dB loss. Many users remember it as the connector on the front panel of the original Tektronix optical time domain reflectometer (OTDR). [Fib05]

Photograph of Deutsch 1000 Optical Connector courtesy of Fiber Optics Association, http://www.thefoa.org/tech/connID.htm




Deviation

The modulation level of an FM signal determined by the amount of frequency shift from the frequency of the main carrier. [Sat07]
DFAST
Dynamic Feedback Arrangement Scrambling Technique

DFB

Distributed Feedback [Arr11]
DFB Laser

A distributed feedback laser (DFB) is a type of laser diode, quantum cascade laser or optical fibre laser where the active region of the device is periodically structured as a diffraction grating. The structure builds a one dimensional interference grating (Bragg scattering) and the grating provides optical feedback for the laser. DFB laser diodes do not use two discrete mirrors to form the optical cavity (as they are used in conventional laser designs). The grating acts as the wavelength selective element for at least one of the mirrors and provides the feedback, reflecting light back into the cavity to form the resonator. The grating is constructed so as to reflect only a narrow band of wavelengths, and thus produce a single longitudinal lasing mode. This is in contrast to a Fabry-Perot Laser, where the facets of the chip form the two mirrors and provide the feedback. In that case, the mirrors are broadband and either the laser functions at multiple longitudinal modes simultaneously or easily jumps between longitudinal modes. Altering the temperature of the device causes the pitch of the grating to change due to the dependence of refractive index on temperature. This dependence is caused by a change in the semiconductor laser's bandgap with temperature and thermal expansion. A change in the refractive index alters the wavelength selection of the grating structure and thus the wavelength of the laser output, producing a wavelength tunable laser or TDL (Tunable Diode Laser). The tuning range is usually of the order of 6 nm for a ~50 K (90 °F) change in temperature, while the linewidth of a DFB laser is a few megahertz. Altering of the current powering the laser will also tune the device, as a current change causes a temperature change inside the device. Integrated DFB lasers are often used in optical communication applications, such as DWDM where a tunable laser signal is desired as well as in sensing where extreme narrow line width is required, or in gas sensing applications, where the signal of the absorbing gas is detected while wavelength tuning the DFB laser. DFB lasers are a cost effective alternative, whenever wavelength selection or tuning is required. [Wik116]

Schematic drawing of Quantum Wire (QWR) DFB Laser courtesy of Mutsuo Ogura, http://staff.aist.go.jp/ogura-m/QWR_laser/finitelength_qwr_DFB_laser/finitelength_qwr_DFB_laser_e3.htm



Photograph of DFB Laser courtesy of NEC (California Eastern Labs), www.cel.com




DHCP
Dynamic Host Configuration Protocol

Dial-up


Data communication established by a circuit-switched connection over a telephone network. Generally associated with less than broadband speeds (56 kbps or less).

Diameter-mismatch Loss


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