There are very different kinds of optical modulators:
Acousto-optic modulators are based on the acousto-optic effect. They are used for switching or continuously adjusting the amplitude of a laser beam, for shifting its optical frequency, or its spatial direction.
Electro-optic modulators exploit the electro-optic effect in a Pockels cell. They can be used for modifying the polarization, phase or power of a beam, or for pulse picking in the context of ultrashort pulse amplifiers.
Electroabsorption modulators are intensity modulators, used e.g. for data transmitters in optical fiber communications.
Interferometric modulators, e.g. Mach–Zehnder modulators, are often realized in photonic integrated circuits for optical data transmission.
Fiber-optic modulators can exploit various physical principles. They can be true fiber devices, or contain fiber pig-tailed bulk components.
Liquid crystal modulators are suitable for, e.g., optical displays and pulse shapers. They can serve as spatial light modulators, i.e. with a spatially varying transmission, e.g. for displays.
Chopper wheels can periodically switch the optical power of a light beam, as required for certain optical measurements (e.g. those using a lock-in amplifier).
Micromechanical modulators (which are microelectromechanical systems = MEMS), e.g. silicon-based light valves and two-dimensional mirror arrays, are particularly useful for projection displays.
Bulk-optical modulators, e.g. of the electro-optic type, can be used with large beam areas, and handle correspondingly large optical powers. On the other hand, there are fiber-coupled modulators, often realized as a waveguide modulator with fiber pigtails, which can easily be integrated into fiber-optic systems. [Enc11]
A condition of high input current that causes pulse width distortion at the output of the transimpedance amplifier (TIA).
Refers to the average power of an optical carrier. If the optical power is gated on and off, the optical power is defined as the average power during the burst, not including turn-on and turn-off transitions. Optical power measurements are averaged sufficiently to assure that any changes to content that is modulated onto the laser does not affect the measurement.
Optical Pump Laser
A shorter wavelength laser used to pump a length of fiber with energy to provide amplification at one or more longer wavelengths. See also EDFA. [Fib111]
Optical Return Loss (ORL)
The ratio (expressed in dB) of optical power reflected by a component or an assembly to the optical power incident on a component port when that component or assembly is introduced into a link or system. [Fib111]
Optical Rise Time
The time interval for the rising edge of an optical pulse to transition from 10% to 90% of the pulse amplitude. Alternatively, values of 20% and 80% may be used. [Fib111]
Pulse Waveform Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/o
Optical Signal-to-Noise-Ratio (OSNR)
The optical equivalent of SNR. [Fib111]
The electromagnetic spectrum within the wavelength region extending from the vacuum ultraviolet at 40 nm to the far infrared at 1 mm. [Arr11]
Optical Spectrum Analyzer (OSA)
A device that allows the details of a region of an optical spectrum to be resolved. Commonly used to diagnose DWDM systems. [Fib111]
Optical Time Domain Reflectometer (OTDR)
A fault detector that measures distance to a reflection surface by measuring the time it takes for a lightwave pulse to reflect from the surface. Reflection inter-face surfaces include the ends of cables and breaks in fiber. The reflectometer is capable of launching a pulse into a transmission medium and measuring the time required for its reflection to return by back-scattering or end reflection, thus indicating the continuity, crack, fracture, break or other features of the medium. [Arr11]
A device that accepts an electrical signal as its input, processes this signal, and uses it to modulate an opto-electronic device, such as an LED or an injection laser diode, to produce an optical signal capable of being transmitted via an optical transmission medium. [ITS96]
Excerpt from ANSI/SCTE 87-1 2008,
“Graphic Symbols For Cable Systems Part 1: HFC Symbols”
Another name for optical fiber. [Fib111]
The range of materials and devices that generate light (lasers and light-emitting devices), amplify light (optical amplifiers), detect light (photodiodes), and control light (electro-optic circuits). Each of these functions requires electrical energy to operate and depends on electronic devices to sense and control this energy. [Arr11]
The time that it takes a satellite to complete one circumnavigation of its orbit. [Sat07]
Organizationally Unique Identifier (OUI)
A 3-octet Institute of Electrical and Electronic Engineers (IEEE) assigned identifier that OUI can be used to generate universal local area network (LAN) media access control (MAC) addresses and Protocol Identifiers per ANSI/IEEE Std 802 for use in Local and Metropolitan Area Network applications.
"O"ring seals are found at joints on the connector to prevent moisture migration into the connector, cable, and mating equipment. [Arr11]
This part of the connector holds the clamp nut "O"ring in place, and controls the amount of compression on the "O"ring. The "O" ring carrier eliminates inconsistencies of over-com-pressing, causing damage to the cable, and under-compressing, allowing moisture migration. [Arr11]
A waveguide, generally a three-point device that allows simultaneous reception of vertically and horizontally polarized signals. The input port is typically a circular waveguide. The two output ports are rectangular waveguides. [Arr11]
Optical Spectrum Analyzer
A circuit generating an alternating current wave at some specific frequency. [Arr11]
Open Systems Interconnection
Open System Interface
Optical Signal-to-Noise Ratio
Operation Systems Support
Over-The-Air Reception Devices
Optical Time Domain Reflectometer; an instrument that locates faults in optical fibers or infers attenuation by backscattered light measurements. [Fib111]
Optical Time Domain Reflectometer Operation, http://www.althosbooks.com/fiopba.html
Office of Telecommunications Policy
Organizationally Unique Identifier
Out-of-Band Channel (OOB)
An out-of-band channel is the combination of the forward and reverse out-of-band communications channels. The OOB channel provides an IP-based communication channel between the network and the digital set-top converter.
The portion of the cable RF range that is used to deliver system or service information to a receiver. Its frequency range is generally 70-130 MHz.
The portion of the cable RF range that is used to deliver data from the home receiver to the headend. Its frequency range is 5-40 MHz.
The useful power or signal delivered by a circuit or device. [Arr11]
The signal amplitude, usually expressed in decibel millivolts, at the output port of an active or passive device. [Arr11]
Outside Plant (OSP)
In telephony, all cables, conduits, ducts, poles, towers, repeaters, repeater huts, and other equipment located between a demarcation point in a switching facility and a demarcation point in another switching facility or customer premises. [Fib111]
Outside Plant Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/o
A company that overbuilds an incumbent telecommunications operator and offers customers a competitive alternative, generally with highly advanced fiber-optic networks. See also CLEC.
A case where a TV station’s Predicted Grade B Contour is overlapped by the Predicted Grade B Contour of a television station located in a different market.
Open Video Systems
picoamp; one trillionth of an Amp or 10-12 Amps. [Fib111]
Private Automatic Branch Exchange. See PBX. [Fib111]
A series of bits containing data and control information, including source and destination node addresses, formatted for transmission from one node to another.
Packet Identifier (PID)
A unique integer value used to identify elementary streams of a program in a single- or multi-program MPEG-2 stream.
Packet Internet Grouper (PING)
It is an Internet utility that verifies the connection between your computer and another IP address by sending packets to the address and checking for a response.
A digital loop on which all information (signaling and user content) is encoded in packets.
Packetized Elementary Streams (PES)
An MPEG stream is composed of one or more elementary streams (ES), each containing audio, video or data. ES's can be grouped into Program Streams, which are formed by breaking ES's into chunks, the PES's, and interleaving them.
Packet-switched Network (PSN)
A PSN transports information by breaking up the bit stream into addressable digital “packets” that are transmitted independently and then reassembled in the correct sequence at the destination. Because these networks allow “sharing” of communications links, they are more efficient than circuit-switched networks.
The process of routing and transferring data by means of addressed packets so that a channel is occupied during the transmission of the packet only and upon completion of the transmission the channel is made available for the transfer of other traffic. [Fib111]
A passive attenuation device used to reduce a signal's amplitude. [Arr11]
A partial or complete failure of interlace in which the scanning lines of alternate fields do not fall exactly between one another but tend to fall (in pairs) one on top of the other.
PAL stands for Phase Alternate Line. PAL is the standard broadcast protocol for televisions outside of North America and much of Japan. PAL is comprised of a 625 line 50-interlaced fields per second format that is used to reduce artifacts on screen (left over pixels that form objects that interfere with the picture). Phase Alternate Line is so-called because of how the chrominance signal is phase reversed on every other line, in between the spaces on an interlacing signal. [Glo07]
Peak to Average Power Ratio; a comparison of the peak power detected over a period of sample time to the average power level that occurs over the same time period. [Alt09] Also referred to as Crest Factor. [Wik118]
Peak-to-Average Ratio; often used interchangeably with peak to average power ratio (PAPR), or crest factor [Wik118]
The geometric shape that has the property of reflecting the signals parallel to its axis to one point, the focal point. [Arr11]
An antenna with a geometric shape that has the property of reflecting received signals parallel to its axis to a focal point and into a folded dipole or feedhorn. [Arr11]
A term used in binary communication systems to indicate whether a number of 1’s in a transmission is even or odd. If the number of 1’s is even, the parity is said to be even; if the number of 1’s is odd, the parity is said to be odd. [Fib111]
Parity Diagrams courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/p
A grant that is smaller than the corresponding bandwidth request from the CM.
Packet and Access Shelf Interface
The region of usable frequency in electronics or wavelength in optics. [Fib111]
Passive Branching Device
A device which divides an optical input into two or more optical outputs. [Fib111]
Passive Branching Device Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/p
A component that requires no external source of power for it to function.
A circuit or network not using active devices such as tubes or transistors. A component of the broadband system which is not supplied with activating power; a device basically static in operation, that is, it is not capable of amplification or oscillation, and requires no power for its intended function. Examples include splitters, directional couplers, taps and attenuators. [Arr11]
A sequence of characters used to prevent unauthorized access to a computer or its files. It is entered along with its corresponding user ID, which are then compared against a list of authorized users before access is granted.
Actual signal attenuation from point of transmission to point of reception. [Arr11]
Pathological Test Code
A special test pattern used with DTV and HDTV signals to create the longest strings of zeros and ones over the serial link. This requires the serial transport link to handle much lower frequency components than is typical in a normal data link. [Fib111]
A graph type plot of receive or transmit signal characteristics by an antenna over a geographic zone or area. [Arr11]
Cable programming services for which subscribers pay an additional fee above the basic cable service charge. Also called Premium Cable.
Pay Cable Unit
Each premium service to which a household subscribes is counted as one unit.
Movies, sports, and made-for-cable specials that are available to the cable customer for a charge in addition to the basic fee.
Payload Header Suppression
The suppression of the header in a payload packet, e.g., the suppression of the Ethernet header in forwarded packets.
Payload Service Class Table (PSC)
A MIB table that maps RTP Payload Type to a Service Class Name.
Payload Unit Start Indicator (PUSI)
A flag in an MPEG header. A value of 1 indicates the presence of a pointer field as the first byte of the payload.
An event that has an associated viewing cost, and which may be purchased separately from any package or subscription. The ordered events could include movies, special events, such as sporting, or adult programming. The event could be purchased by either impulse PPV by using a television remote (this application requires a continuous land line phone based connection), or over the phone PPV (this application may have additional costs for processing). [Fib111]
Private Branch Exchange; a subscriber-owned telecommunications exchange that usually includes access to public switched networks. [Fib111]
Physical Contact; refers to an optical connector that allows the fiber ends to physically touch. Used to minimize back reflection and insertion loss. [Fib111]
Printed Circuit Board; also referred to as PWB (printed writing board). [Fib111]
Peripheral Component Interface
Pulse Code Modulation
Personal Communication Network
Private Cable Operator
Personal Communications Service
Plastic Clad Silica [Fib111]
Protocol Data Unit
The maximum instantaneous value of a varying current or voltage. Also called crest. [Arr11]
Peak Power Output
The output power averaged over that cycle of an electromagnetic wave having the maximum peak value that can occur under any combination of signals transmitted. [Fib111]
In optical emitters, the spectral line having the greatest output power. Also called peak emission wavelength. [Fib111]
Entities within the same layer.
Ratio of the number of cable customers to the total number of households passed by the system.
Per Hop Behavior (PHB)
In the IETF Differentiated Services (DiffServ) approach to quality of service differentiation, the treatment by a network router or switch of a group of network traffic flows for the “hop” to the next router switch. Packets “marked” or “tagged” with a common service classification in the packet header are aggregated into flow “bundles” which are treated the same, e.g., have the same priority or the same risk of being discarded in the event of network congestion.
The ratio, expressed as a percentage, of the amplitude of the synchronizing signal to the peak-to-peak amplitude of the picture signal between blanking and reference white level.
The minimum technical criteria that must be met by cable television systems, consistent with standard set by the FCC or the local ordinance.
The point in an elliptical satellite orbit which is closest to the surface of the earth. [Sat07]
Perigee Kick Motor (PKM)
Rocket motor fired to inject a satellite into a geostationary transfer orbit from a low earth orbit especially that of a STS or Shuttle-based orbit of 300 to 500 miles altitude. [Sat07]
Direct response advertising for which the cable network or system running the commercial is paid based on the number of responses received rather than the air time used.
Peripheral Component Interface (PCI)
An interface standard for connecting hardware expansion cards to a computer. The typical PCI connection is a slot, or edge-card connector, on the computer's motherboard allowing devices such as network cards, graphics cards or drive controllers to be connected to the computer. Some PCI devices are integrated onto the motherboard, especially in the case of “brand-name” computers. PCI has eclipsed ISA as the interface of choice due to its higher transfer rate, ease of configuration and improved Plug-and-Play ability.
Permanent Virtual Circuit (PVC)
A point-to-point connection between two specific locations on an ATM, Frame Relay, of X.25 network. PVCs are pre-defined by the ATM, Frame Relay, or X.25 network administrator. See also SVC.
Personal Communications Service (PCS)
Digital networks deployed in cellular; like configuration at 1.8GHz to 2.2GHz.
Personal Video Recorder (PVR)
a consumer device which uses a hard disk drive to record television programs based on the user's preferences. Also provides pause of live television feature. Or a set of equipment that allows a user to timeshift television without removable media.
Packetized Elementary Streams
Program Elementary Stream
Pulse-frequency Modulation; also referred to as square wave FM. [Fib111]
A relative quantity describing the time relationship between or among waves having identical frequency. The complete wave cycle is divided into 360 equal parts, called degrees of phase. Also, the location of a position on a waveform of an alternating quality, in relation to the start of a cycle. Measured in degrees, with 360°corresponding to one complete cycle. [Arr11]
The imaginary part of the axial propagation constant for a particular mode, usually expressed in radians per unit length. See also attenuation. [Fib111]
When the output of an amplifier fluctuates in phase, even though the input does not, the circuit introduces phase distortion into the signal.
Phase variations arising in a channel and caused by incidental frequency modulation of signals transmitted over the channel. This occurs when the carrier supply frequencies in a frequency-division-multiplexed carrier system are not perfectly constant.
The control of as oscillator such that its output signal maintains a constant phase angle relative to a second, reference signal. [Arr11]
When the information is impressed on a radio frequency signal by varying its phase angle.
An optical modulator which can be used to control the optical phase of a laser beam. Frequently used types of phase modulators are electro-optic modulators based on Pockels cells, and liquid crystal modulators, but it is also possible to exploit thermally induced refractive index changes or length changes of an optical fiber, or induce length changes by stretching. Various kinds of phase modulators are used within the area of integrated optics, where the modulated light propagates in waveguides. Important properties of phase modulators are:
the amount of phase modulation which can be achieved (determining the possible modulation index and relative power in optical sidebands)
the required drive voltage
the modulation bandwidth (range of modulation frequencies), which can e.g. be many gigahertz for electro-optic modulators, and far less for devices based on thermal effects or using liquid crystal materials
the optical bandwidth in which the device can be used
the device aperture, limiting the beam radius of the modulated beam
the outer dimensions of the device
For different types of phase modulators, such properties vary in huge ranges. Therefore, different kinds of phase modulators are appropriate for different applications.