Electrical Engineering Dictionary - part 125

tion that contains the data element that will
be processed by the computer.

operating point

See

operating system

a set of programs that

manages the operations of a computer. It
oversees the interaction between the hard-
ware and the software and provides a set of
services to system users.

operating temperature

the ambient case

temperature to which a device or circuit is ex-
posed during operation under all supply bias
and RF signal conditions, at which it must
meet all specified requirements unless other-
wise called out. The operating temperature
range is the minimum to maximum operating
temperatures of the device.

operation

specification of one or a set

of computations on the specified source
operands placing the results in the specified
destination operands.

operational amplifier

a high-gain DC-

coupled amplifier with a differential input
and single-ended output. In nearly all am-
plifier applications, the op-amp is used with
negative feedback (“closed-loop”), so that
the closed-loop gain of the amplifier depends
primarily on the feedback network compo-
nents, and not on the op-amp itself. It is
widely used as a basic building block in elec-
tronic designs. Abbreviated as “op-amp.”

operational control

control or decision

making activity that requires, or in some in-
stances may require, a human operator (dis-
patcher) to approve — or modify — auto-
matically computed decisions before they are
actually implemented; such a situation is typ-
ical in production management, in control of
supply and environmental systems, at upper
layers of process control systems.

operational impedance

a representation

in which the impedance of a system is ex-
pressed as a function of the Heaviside op-

erator

p = d/dt or the Laplace operator

s = jω. In the modeling of synchronous
machines, the Park’s transformed stator flux
linkages per second are often expressed in
terms of impedances

(p), and X

(p),

termed the quadrature- and direct-axis opera-
tional impedances, respectively. Using these,
the dynamics of the rotor windings are rep-
resented within the operational impedances,
and therefore the rotor of a synchronous ma-
chine can be considered as either a distributed
or lumped parameter system.

operational space

See

external space

operational space control

See

Cartesian-

based control

operator

See

Canny operator

Laplacian

operator

Marr-Hildreth operator

morpho-

logical operator

Sobel operator

opposition effect

See

weak localization

of light

optical adder

an optical device capable

of performing the function of arithmetic ad-
dition using binary signals. It can be con-
structed using a series of cascaded full adders
where carry has to ripple through each full
adder from least significant bit to most sig-
nificant bit. It can also be constructed using
cascaded layers. Each layer consists of a se-
ries of half adders. Carry also has to ripple
through the cascaded layers. It is also known
as digital adder.

optical addition

adding operation using

light. Two incoherent light beams have in-
tensities

A and B, respectively. When two

beams are combined, i.e., illuminating the
same area, the resultant intensity is

A + B.

optical amplifier

amplifier of electromag-

netic waves at optical frequencies, usually by
the process of simulated emission or nonlin-
ear optics. See

laser amplifier

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optical beam

beam of electromagnetic

power at optical frequencies.

optical bistability

the property of certain

nonlinear optical system to possess two pos-
sible output states for a given input state. In
one typical example, the bistable optical de-
vice has the form of a third-order nonlinear
optical material placed inside of an optical
cavity, and the device can display two pos-
sible different transmitted intensities for cer-
tain values of the input intensity.

optical bus

an optical channel used for

transmitting a signal from a source to one or
more detectors. A bus allows only the same
interchange of information to take place at
different detectors. A source is connected to
many detectors.

optical cavity

resonant structure for main-

taining oscillation modes at optical frequen-
cies.

optical character recognition (OCR)

process in which optically scanned characters
are recognized automatically by machine. It
is widely utilized in document storage, pro-
cessing and management.

optical circulator

a four-ports optical de-

vice that can be used to monitor or sample
incident light (input port) as well as reflected
light (output port) with the two other unidi-
rectional coupling ports.

optical communications

communication

of information at optical carrier frequencies.
There are two general categories:

1. free-space, such as with lasers and op-

tical modulators, and

2. guided-wave, such as over optical fiber

and using guided lightwave devices.

optical computer

(1) a general purpose

digital computer that uses photons as an elec-
tronic computer uses electrons. The technol-
ogy is still immature. The nonlinear opera-
tions that must be performed by a processor

in computer are difficult to implement opti-
cally.

(2) an analog optical processor capable of

performing computations such as correlation,
image subtraction, edge enhancement, and
matrix-vector multiplication that are usually
performed by an electronic digital computer.
Such a computer is usually very specific and
inflexible, but well adapted to its tasks.

optical computing

the use of optics to

aid in any type of mathematical computation.
Categories of optical computing include.

1. analog processing such as using optical

Fourier transforms for spectral analysis and
correlation,

2. optical switching and interconnection

using nonlinear, e.g., bistable, optical de-
vices, and

3. use of optical devices in digital com-

puters.

optical demultiplexer

a device that di-

rects an input optical signal to an output port
depending on its wavelength.

optical disk

a disk on which data are

stored optically. Data are written by alter-
ing the reflectivity of the surface, and read
by measuring the surface reflection of a light
source. Storage is organized in the same way
as on a magnetic disk, but higher storage den-
sity can be achieved.

optical disk track

the region on a com-

pact disk in which pits or other features are lo-
cated to store digital data. CD-ROM pit sizes
are approximately 0.5 microns in width and
from 0.8 to 3.6 microns in length, depending
on the number of ones and zeros represented
by the length. The track-to-track spacing is
1.6 microns.

optical energy

energy of an electromag-

netic wave oscillating at optical frequencies.
See also

energy

electromagnet

optical expert system

an expert system

that utilizes optical devices for performing

2000 by CRC Press LLC

logic operations. An expert system mostly
requires logic gates to perform inferences.
In an optical expert system, not only discrete
optical logic gates are used, but the paral-
lelism and capability of performing matrix-
vector multiplication of optical processor are
exploited as well. Sequential reasoning in an
electronic expert system is replaced by paral-
lel reasoning in an optical expert system, so
its speed can be increased substantially. As
with the optical computer, it is still immature.

optical fiber

a single optical transmis-

sion fiber usually comprised of a cylindrical
core (5–100 mm diameter) in which the light
is guided of higher index of refraction sur-
rounded concentrically by a cladding (125–
250 mm diameter) with a lower index of re-
fraction. More properly defined as an optical
waveguide. Some optical fibers may have
multiple concentric cores and/or claddings.
Optical fibers made be of all glass, all plas-
tic, or a combination of glass core and plastic
cladding construction. Optical glass fibers
may be silica- or fluoride-based glass.

optical fiber signal distortion

a change in

the temporal shape of an optical signal trans-
mitted through an optical fiber caused by a
combination of wavelength effects (disper-
sion) and multimode and polarization effects.
The wavelength effects include material dis-
persion, profile dispersion, and waveguide
dispersion.

The multi-mode effects cause

distortion by the differential time delays be-
tween the various modes propagating in a
multimode fiber.

The polarization effect

causes distortion by the differential time de-
lay between the two polarizations of a single
mode.

optical flow

the 2-D field of apparent ve-

locities of pixels on an image plane; i.e., the
raw motion information arising from the dis-
placement of points in the visual (optical)
field. Let each image point

p have an inten-

sity

I and a velocity v = (v

, v

), which are

both functions of

p and time t, where the ve-

locity represents the image plane projection

of the point’s 3-dimensional velocity. Under
the assumption that the point’s intensity does
not change along its trajectory, it follows that

(∂I/∂x)v

+ (∂I/∂y)v

+ (∂I/∂z)v

+∂I/∂t = ∇I · v + ∂I/∂t = 0.

See also

aperture problem

optical flux

See

optical flow

optical Fourier transform

the imple-

mentation of the Fourier transform using
the transform properties of a lens, spatial
light modulators, such as acousto-optic mod-
ulators, to generate the optical input in-
formation, and photodetector arrays to de-
tect the optical field representing the Fourier
transform.

See also

Fourier transform

two-dimensional Fourier transform

optical full adder

an optical device form-

ing part of an adder and able to receive three
inputs, augend, addend, and carry from the
previous stage, and deliver two outputs, sum
and carry. Several logic gates are required to
provide the sum and the carry.

optical gain

increase in the amplitude of

an optical signal with propagation distance in
an optical amplifier.

optical guided-wave device

an optical de-

vice that transmits or modifies light while it
is confined in a thin-film optical waveguide.

optical half adder

an optical device form-

ing part of an adder and able to receive two
inputs, augend and addend, and deliver two
outputs, sum and carry. The sum is the XOR
function of two inputs, and the carry is the
AND function of two inputs. An optical half
adder consists of an optical XOR gate and an
optical AND gate. It is also known as one-
digit adder.

optical inference engine

See

optical

expert system

2000 by CRC Press LLC

optical integrated circuit

guided wave

optics on a single substrate. If also incor-
porating active and electrical devices, also
known as opto-electronic integrated circuit
(OEIC).

optical interconnect

an optical communi-

cation system in an electronic computer that
consists of three primary parts:

1. sources,

2. optical paths with switches or spatial

light modulators, and

3. detectors.

An optical signal from a source of an array

of sources is transmitted to a detector of an ar-
ray of detectors in optical interconnects. The
transmitted optical signal from the source is
converted from an electronic signal. The de-
tector in turn reverts the optical signal into
an electronic signal. The merits of optical
interconnects include large bandwidth, high
speed of light propagation (the velocity of
electric signals propagating in a wire depends
on the capacitance per unit length), no in-
terferences, high interconnection density and
parallelism, and dynamic reconfiguration.

optical invariant

a parameter that re-

mains constant throughout an optical system.
A consequence of the optical invariant is that
the product of numerical aperture and mag-
nification in the system is constant.

optical isolator

a unidirectional optical

device that only permits the transmission of
light in the forward direction. Any reflected
light from the output port is blocked by the
device from returning to the input port with
very high extinction ratio.

optical Kerr effect

See

Kerr effect

optical linear algebraic processor (OLAP)

an optical processor that performs specific

matrix algebraic operations as fundamental
building blocks for optical computation and
signal processing.

optical lithography

lithography method

that uses light to print a pattern in a photo-
sensitive material. Also called photolithog-
raphy.

optical logic

logic operations, usually bi-

nary, that are performed optically.

optical logic gate

an optical device for

performing Boolean logic operations. The
basic idea is that since a computer is built by
Boolean logic gates, if we can make optical
logic gates, then we can eventually build a
complete optical computer. Since light does
not affect light, it cannot directly perform
nonlinear operations represented by sixteen
Boolean logic gates. A thresholding device is
required if intensities of two input beams are
simply added in the logic gate. For example,
to perform AND operation, 00-0, 01-0, 10-0,
11-1, the threshold is set at 2. Only when both
beams have high intensities, the output is 1.
Otherwise, the output is 0. To perform OR
operation, 00-0, 01-1, 10-1, 11-1, the thresh-
old is set at 1. The gate can be constructed
by directing two input light beams onto the
same detector. After passing through an elec-
tronic thresholding device, the resulting elec-
tric signal from the detector shows the logic
output. To implement optical logic gate with-
out using electronic circuit, optical threshold-
ing devices such as MSLM or nonlinear optic
materials can be used.

optical logical etalon (OLE)

pulsed non-

linear Fabry–Perot etalon that requires two
wavelengths (

= signal, λ

= clock).

optical maser

early equivalent name for

laser.

optical matrix–matrix multiplication

operation performing matrix–matrix multi-
plication using optical devices. For two-by-
two matrices

A and B, the matrix–matrix

multiplication produces two-by-two matrix
C, whose elements are

= a

+ a

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