Alternate-Phase Return-to-Zero (APRZ) is an optical

line code In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained c ...

. In APRZ the

field intensity In physics, field strength means the ''magnitude'' of a vector-valued field (e.g., in volts per meter, V/m, for an electric field ''E''). For example, an electromagnetic field results in both electric field strength and magnetic field strength. A ...

drops to zero between consecutive bits, and the

field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...

alternates between neighbouring bits, so that if the phase of the signal is, for example, 0 in even bits (bit number 2''n''), the phase in odd bit slots (bit number 2''n''+1) will be ''ΔΦ'', the phase alternation amplitude.

Special cases

Return-to-zero Return-to-zero (RZ or RTZ) describes a line code used in telecommunications signals in which the signal drops (returns) to zero between each pulse. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is s ...

can be seen as a special case of APRZ in which ''ΔΦ''=0, while

Carrier-Suppressed Return-to-Zero Carrier-Suppressed Return-to-Zero (CSRZ) is an optical line code. In CSRZ the field intensity drops to zero between consecutive bits ( RZ), and the field phase alternates by π radians between neighbouring bits, so that if the phase of the signal i ...

(CSRZ) can be viewed as a special case of APRZ in which ''ΔΦ''=π (and the duty cycle is 67%, at least in the standard form of CSRZ). APRZ can be used to generate specific optical modulation formats, for example, APRZ-

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, in which data is coded on the intensity of the signal using a binary scheme (light on=1, light off=0). APRZ is often used to designate APRZ-OOK.

Characteristics

The characteristic properties of an APRZ signal are those to have a spectrum similar to that of an RZ signal, except that frequency peaks at a spacing of ''B_R''/2 as opposed to ''B_R'' are observed (where ''B_R'' is the bit rate). Line codes Fiber-optic communications {{Telecom-stub