Cross-phase modulation (XPM) is a
nonlinear optical
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typica ...
effect where one wavelength of light can affect the phase of another wavelength of light through the optical
Kerr effect
The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index chang ...
. When the optical power from a wavelength impacts the
refractive index, the impact of the new refractive index on another wavelength is known as XPM.
Applications of XPM
Cross-phase modulation can be used as a technique for adding information to a
light stream by modifying the
phase of a
coherent optical beam with another beam through interactions in an appropriate
nonlinear medium. This technique is applied to
fiber optic communications. If both beams have the same wavelength, then this type of cross-phase modulation is degenerate.
[
]
XPM is among the most commonly used techniques for
quantum nondemolition measurement Quantum nondemolition (QND) measurement is a special type of measurement of a quantum system in which the uncertainty of the measured observable does not increase from its measured value during the subsequent normal evolution of the system. This ne ...
s.
Other advantageous applications of XPM include:
*Nonlinear optical
Pulse Compression of
ultrashort pulses
*
Passive mode-locking
*
Ultrafast optical switching An optical transistor, also known as an optical switch or a light valve, is a device that switches or amplifies optical signals. Light occurring on an optical transistor's input changes the intensity of light emitted from the transistor's output ...
*
Demultiplexing
In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
of
OTDM channels
*Wavelength conversion of
WDM channels
*Measurement of nonlinear optical properties of the media (non-linear index n
2 (
Kerr nonlinearity
The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index chang ...
) and nonlinear response relaxation time)
Disadvantages of XPM
XPM in DWDM applications
In
dense wavelength-division multiplexing (DWDM) applications with
intensity modulation In optical communications, intensity modulation (IM) is a form of modulation in which the optical power output of a source is varied in accordance with some characteristic of the modulating signal. The envelope of the modulated optical signal is an ...
and direct detection (IM-DD), the effect of XPM is a two step process:
First the signal is phase modulated by the copropagating second signal. In a second step dispersion leads to a transformation of the phase modulation into a power variation. Additionally, the dispersion results in a walk-off between the channels and thereby reduces the effect of XPM.
*XPM leads to interchannel crosstalk in WDM systems
*It can produce amplitude and timing jitter
See also
*
Self-phase modulation — SPM
*
Four wave mixing — FWM
*
Stimulated Raman scattering — SRS
*
Cross-polarized wave generation
Cross-polarized wave (XPW) generation is a nonlinear optical process that can be classified in the group of frequency degenerate (four-wave mixing) processes. It can take place only in media with anisotropy of third-order nonlinearity. As a resul ...
— XPW
References
External links
Cross-phase modulation (RP Photonics, Encyclopedia of Laser Physics and Technology)
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Nonlinear optics
Fiber optics