wav elen gth c onve SARB JEET r ter ECE- SING 11 N H ITTT R
ObjectivesConcept of wavelength converterVarious type of conversionClasses of wavelength converterApplicationsAdvantages and Disadvantages..
It refer to as wavelength conversion, shifting, translating of wavelength . Other name-VIFO (variable input-fixed output) Strategy used is nonlinearity of optical medium which can be either active or passive, resulting to different non linear effect. Concept
seminar OPTiCaL FiBer COmmUniCaTiOn - Since 1802WAVELENGTH CONVERTER AND OPTICAL NETWORKS The processor section may also CONVERSION contain an electronic regenerator Wavelength conversion is a circuit that reconstitutes the process by which the electrical signal from the received wavelength is changed without data thereby rectifying any errors altering the data carried by the induced by transmission through signal. The device that the fiber . performs this function is The electrical data is then usually called a wavelength converted back to an optical signal converter but it is also referred in an electrical-to-optical (E/O) to as a wavelength section by modulating an optical (or frequency) changer, shifter transmitter that emits a compliant or translator. Therefore the wavelength at the output port (i.e. input/output (I/O) ports converted wavelength, λconv). This should have capability of a method can be modular and hence variable input–fixed output flexible, but the transmission rate Converter and the majority of tends to be restricted due to the optical switching networks limitations of the O/E/O interfaces use this type of device
COHERENT WAVELENGTH CONVERTERS Depends on principle of 4 Wave Wixing (FWM) and Difference freq generation(DFG) in non linear optical medium. Interaction of two optical signals, input data and CW probe signal result to two new signal component . Property of phase conjugation in conversion help us to overcome noise problem.
Four wave mixing Arises from optical nonlinearity. Property of phase conjugation/spectral inversion in conversion help us to overcome noise problem. Converted signal ωconv = 2ωCW − ωin Satellite signal ωs = 2ωin − ωCW, result as cross talk effect Can be used for multiple wavelength conversion by sending more than one CW probe signal. This property is used in optical switching networks.
Difference frequency Generation(DFG) Arises from second order non linerity of optical medium. Produces single output signal which is determined from diff in freq of interacting optical signals. No satellite signal as side bands, so it is preferred over FWM, no cross talk happens. Realizing it practically is difficult due to complicated phase-matching of interacting waves.
Cross-modulation Optical control signal experiences the changes Wavelength produced due to intensity variation of intensity-modulated Converter input signal in active cavity. Definition- process of imposing the nonlinear response of medium onto control signal is cross modulation scheme. This scheme is dependent on : # property of nonlinear medium- optical gain & material absorption # modulation on optical Signal- XGM, XPM, XAM, DPM.
Cross-gain modulationwavelength converter Principle- intensity modulated data on one signal wavelength (pump signal),produces variation in carrier density within SOA medium—inverted gain modulation. Which imprint gain modulation onto continuous wave (CW) signal called probe signal. Probe signal have inverse copy of data and when wavelength of probe signal is diff from pump signal, wavelength conversion obtained. Thus data is shifted from pump signal wavelength to a probe signal wavelength. Its transfer function, it is result of slow gain recovery of SOA which gives gradual decrease in its response.
Cross-phase modulation wavelength converter Relies on dependency of refractive index on the carrier density in active region of the SOA. Signal beam modulates the gain of the SOA by depleting the carriers, when CW beam encounter the modulated gain and refractive, its phase is changed . PM-AM create an interferometer structure. Probe signal wavelength λ CW propagates through the optical filter acquiring the refractive-index- induced phase modulation in the active cavity of the SOA while the input signal at λ in is blocked by this optical filter.• Hence the CW probe signal combines with the phase-modulated probesignal in the PM–AM element when the interference is constructive.
Cross-phase modulation wavelength converter Mach–Zehnder interferometer (MZI) configuration is used in the lower path to increases the gain of the converted probe signal. Phase to amplitude modulation can be obtained when a relative phase difference is introduced between the interferometer paths because of different path lengths where probe signal is recombined to produce constructive interference.
Cross-phase modulation wavelength converter Frequency/wavelength chirp- It is deviation in the emission frequency with respect to time when a laser is driven by a time-varying current source (i.e. intensity-modulated digital signal). Since refractive index is related to frequency then a variation in the refractive index produces a variation in frequency at each instant. This chirp is commonly observed in the intensity-modulated converted probe signal affect of the pulses when the refractive index varies suddenly due to an instantaneous change in amplitude pulse . When frequency chirp shifts the optical frequency towards the shorter wavelength it is known as blue shift, and for longer wavelength is called red shift. The sign of the chirp is said to be positive when the leading edge of the pulse is red shifted in relation to the central wavelength and the trailing edge is blue shifted, and when the shifts are opposite to the foregoing then the sign of chirp will be negative.
•The relationship between the frequency chirp Δf and the phase of the converted signal φ is given by•Above eq.shows the influence of phase variations on thefrequency chirp, the phase of the converted probe signal isdependent upon the intensity-modulated signalpower. If Pin(t) is the input signal power then the phasevariation can be written as•term α represents the line width enhancement factor In the contextof the material properties of the nonlinear medium the α-parameterhas a strong dependence on the signal wavelength and may bedefined in terms of gain and refractive index variation aswhere λ is the signal wavelength, dnr/dn represents the differentialrefractive index and dg/dn is the differential gain which defines thechange in gain with respect to change in carrier density.
Interferometer configuration Nonlinear optical loop mirrors showing Segnatec interferometer in the insetDelay interferometric wavelength conversion Michelson interferometer
Basic principle of an XAM wavelength converter is that CW probe signal at wavelength λcw and the intensity-modulated input signal at wavelength λin are fed into the EAM and the converted output at signal wavelength λconv is obtained at the output of an optical filter. EAM possesses faster absorption characteristics in comparison with the slow gain recovery of an SOA, XAM-based wavelength converters are faster than wavelength converters based on SOA technology. Cross absorption modulation wavelength converter
APPLICATION 01 WINTER OPTICAL FIBER COMMUNICATION• In distributing the network control and Templatemanagement into smaller sub networks and allowsflexible wavelength assignments within the subnetwork.• Ultra fast wavelength conversion by incorporatingadditional fiber Bragg grating elements.• Used in 3R (optical regeneration), for wavelengthreallocation or reassignment.• Used in various optical switching and routingtechnique for avoiding any conflict amongwavelength present in the network.
http://www.optical-network.com/terminology.php?letter=all&id=4http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-23-11242www.ece.ucsb.edu/courses/ECE228/228B.../Lecture11_228B_S11.pdfBOOKS:GERD KEISERJOHN M SENIOR
Life is like taxi, which carriesdifferent people in ur life.. So be cool Template and tackle all of them Sarbjeet Singh 12/11/11
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