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 typic ...
effect where one wavelength of light can affect the phase of another wavelength of light through the optical
Kerr effect. When the optical power from a wavelength impacts the
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
, 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
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
stream by modifying the
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 ...
of a
coherent
Coherence, coherency, or coherent may refer to the following:
Physics
* Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference
* Coherence (units of measurement), a deri ...
optical beam with another beam through interactions in an appropriate
nonlinear
In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many othe ...
medium. This technique is applied to
fiber optic communications
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is pr ...
. 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 measurements.
Other advantageous applications of XPM include:
*Nonlinear optical
Pulse Compression Pulse compression is a signal processing technique commonly used by radar, sonar and echography to increase the range resolution as well as the signal to noise ratio. This is achieved by modulating the transmitted pulse and then correlating th ...
of
ultrashort pulses
*
Passive mode-locking
*
Ultrafast
In optics, an ultrashort pulse, also known as an ultrafast event, is an electromagnetic pulse whose time duration is of the order of a picosecond (10−12 second) or less. Such pulses have a broadband optical spectrum, and can be created by mo ...
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 wh ...
*
Demultiplexing of
OTDM channels
*Wavelength conversion of
WDM channels
*Measurement of nonlinear optical properties of the media (non-linear index n
2 (
Kerr nonlinearity) and nonlinear response relaxation time)
Disadvantages of XPM
XPM in DWDM applications
In
dense wavelength-division multiplexing (DWDM) applications with
intensity modulation 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 Self-phase modulation (SPM) is a nonlinear optical effect of light–matter interaction.
An ultrashort pulse of light, when travelling in a medium, will induce a varying refractive index of the medium due to the optical Kerr effect. This variatio ...
— SPM
*
Four wave mixing Four-wave mixing (FWM) is an intermodulation phenomenon in nonlinear optics, whereby interactions between two or three wavelengths produce two or one new wavelengths. It is similar to the third-order intercept point in electrical systems. Four-wave ...
— FWM
*
Stimulated Raman scattering
Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a ...
— SRS
*
Cross-polarized wave generation — XPW
References
External links
Cross-phase modulation (RP Photonics, Encyclopedia of Laser Physics and Technology)
{{optics-stub
Nonlinear optics
Fiber optics