Simulation and Experimental Study of SCM/WDM Optical · PDF file Introduction: TDM,WDM...

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Transcript of Simulation and Experimental Study of SCM/WDM Optical · PDF file Introduction: TDM,WDM...

  • Simulation and Experimental Study of SCM/WDM Optical

    Systems

    Renxiang Huang University of Kansas

    May 23, 2001

  • OutlineOutline

    ■■ Introduction to SCM technologyIntroduction to SCM technology ■■ Demand for more bandwidthDemand for more bandwidth

    ■■ TDM,WDM strategiesTDM,WDM strategies

    ■■ SCM and WDM combinationSCM and WDM combination

    ■■ Numerical simulation modelNumerical simulation model ■■ Goals and general requirementsGoals and general requirements

    ■■ Description of the simulation modelDescription of the simulation model ■ Transmitter ■ Optical fiber nonlinear model ■ Receiver

  • OutlineOutline

    ■ Simulation results ■ BPSK, 4-subcarrier each with 2.5Gb/s datarate, self-coherent

    detection ■ QPSK, 2-subcarrier each with 2x2.5Gb/s datarate, self-

    coherent detection ■ ASK, 4-subcarriers each with 2.5Gb/s datarate, direct

    detection using narrowband optical filter ■ Traditional NRZ modulated OC192 system

    ■ Experiment

    ■ Conclusions and future work

  • Introduction: Introduction: Demand for more BandwidthDemand for more Bandwidth

    ■ Faster Internet access ■ High speed data transmission ■ Video Conferencing ■ High resolution image transmission ■ Other new services

    ■■ More fiber everywhereMore fiber everywhere

    ■■ Higher data-rate each wavelength----------TDMHigher data-rate each wavelength----------TDM

    ■■ More wavelengths in the fiber--------------- WDMMore wavelengths in the fiber--------------- WDM

  • Introduction: TDM,WDM strategiesIntroduction: TDM,WDM strategies

    ■■ TDM strategyTDM strategy ■■ Simple modulation format: IMDD binary systemSimple modulation format: IMDD binary system

    ■■ Short bit length, more bits in unit timeShort bit length, more bits in unit time

    ■■ Electrical TDM and optical TDM, Electrical TDM and optical TDM, solitonsoliton

    ■■ Grooming may be a big problemGrooming may be a big problem

    ■■ Difficult in transmission through fiber: chromatic dispersion,Difficult in transmission through fiber: chromatic dispersion, PMD, fiber nonlinearityPMD, fiber nonlinearity

    ■■ Does not scale well beyond OC192Does not scale well beyond OC192

  • Introduction: TDM,WDM strategiesIntroduction: TDM,WDM strategies

    ■■ WDM strategyWDM strategy ■■ Multiple wavelengths in a single fiberMultiple wavelengths in a single fiber

    ■■ Better utilization of optical fiber transmission windowBetter utilization of optical fiber transmission window

    ■■ Lower Lower bitratebitrate & lower power per wavelength & lower power per wavelength

    ■■ From CWDM to DWDM: increase bandwidth efficiencyFrom CWDM to DWDM: increase bandwidth efficiency example:example:2.5Gb/s per-channel data rate and 50GHz channel spacing, the

    bandwidth efficiency is 0.05 bit/Hz.

    ■■ Technical difficulties: Technical difficulties: lightwavelightwave sources, optical filters, sources, optical filters, dispersion management, dispersion management, nonliearnonliear crosstalkcrosstalk, …., ….

  • Introduction: SCM/WDM and OSSBIntroduction: SCM/WDM and OSSB

    ■■ SCM leverages mature microwave technologySCM leverages mature microwave technology

    ■■ Two-step modulation: RF modulation at sub-carriers, opticalTwo-step modulation: RF modulation at sub-carriers, optical modulation at wavelengths.modulation at wavelengths.

    ■■ OSSB is preferred: less dispersion penalty, higher bandwidthOSSB is preferred: less dispersion penalty, higher bandwidth efficiencyefficiency

    fOf 3- f 2 - f 1 - f 4+f 3+f 2+f 1+f 4-

    a. O ptical DSB SCM

    b. O ptical SSB SCM

    fO f 4+f 3+f 2+f 1+

    op tic a l d e tec tion us ing filte r

  • Introduction: SCM/WDM and OSSBIntroduction: SCM/WDM and OSSB

    ■■ SCM/WDM combinationSCM/WDM combination ■■ Large number of channels, low channel speed, easy groomingLarge number of channels, low channel speed, easy grooming

    and scaling, lower dispersion penaltyand scaling, lower dispersion penalty

    ■■ Advanced modulation format, phase modulation possibleAdvanced modulation format, phase modulation possible

    ■■ NonliearityNonliearity-introduced distortion-introduced distortion

    b. W DM

    a. W DM/SCM

    f 4+f 3+f 2+f 1+

    1λ 2λ

    1λ 2λ

  • An exemplary setup of SCM/WDM systemAn exemplary setup of SCM/WDM system

    λm

    λ1

    f1

    Σ

    f2 ch.2

    fn ch.n

    .

    .

    Receiver

    ch.1

    O pt

    ic a

    l W D

    M M

    U X

    O pt

    ic a

    l W D

    M D

    M U

    XAdd/drop

    f1

    Σ

    f2 ch.2

    fn ch.n

    .

    .

    Receiver

    ch.1

    Transmitter f1

    Σ

    f2 ch.2

    fn ch.n

    .

    .

    λ1ch.1

    Transmitter f1

    Σ

    f2 ch.2

    fn ch.n

    .

    .

    λm

    ch.1

    50GHz

    λ1 λ2 λ3 λ4 λ

    5GHz

  • Numerical model for SCM/WDM systemsNumerical model for SCM/WDM systems

    ■■ Goals and general requirementsGoals and general requirements ■■ To be able to handle different types ofTo be able to handle different types of multi multi-wavelength-wavelength

    SCM/WDM systemsSCM/WDM systems

    ■■ Include both dispersion and fiber Include both dispersion and fiber nonlinearitynonlinearity

    ■■ To be able to handle a variety of modulation formats, OSSB,To be able to handle a variety of modulation formats, OSSB, ASK, BPSK, QPSK and binary IMDDASK, BPSK, QPSK and binary IMDD

    ■■ Combine Combine waveform waveform distortion and noise: distortion and noise: sensitivitysensitivity

  • Transmitter simulation model

    C hanne l 4 da ta 2 .488G b it/s

    C hanne l 4 R F osc illa to r

    (17 .5G Hz)

    C hanne l 1 da ta 2 .488G b it/s

    C hanne l 1 R F osc illa to r (3 .6 G Hz)

    channe l 3 (13G Hz)

    channe l 2 (8 .3G Hz)

    T ransmitter fiilte r

    T ransmitter filte r

    S C M T ra nsm itter B lock D ia gram

    RF mu ltip lexer

    M Z m odu la tor

    90degree phase shift

    B ias

    LD Power

    amplifie r W D M coup le r

    f ro m o ther laser sourses

    to f iber

  • ■ 27-1 PRBS ■ Random relative delay between different sub-carriers

    and wavelengths ■ 6-order Butterworth filter for band-limiting ■ 64 to 256 samples per bit depending on the required

    simulation bandwidth

    Baseband signal generation

  • Baseband signal generation

    2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0

    0

    5 0 0

    1 0 0 0

    1 5 0 0

    2 0 0 0

    2 5 0 0

    3 0 0 0

    3 5 0 0

    4 0 0 0 C h a n n e l N u m b e r = 1 C h a n n e l W a v e le n g t h = 1 5 5 0 n m N u m b e r o f s a m p l e s / b i t = 6 4

    (a)eyediagram of baseband signal after the electrical filter

    0 0 . 5 1 1 . 5 2 2 . 5 3 3 . 5 4 4 . 5 5

    x 1 0 4

    - 2 0 0 0

    - 1 0 0 0

    0

    1 0 0 0

    2 0 0 0

    3 0 0 0

    4 0 0 0

    I c h a n n e l T R A N S M I T F I L T E R O U T P U T P U L S E - - > I N T E N S I T Y a f t e r f i l t e r i n g

    P u

    ls e

    in

    t e

    n s

    it y

    (

    m w

    )

    T i m e ( p s )

    C h a n n e l N u m b e r = 1 B i t R a t e = 2 . 4 8 G b / s C h a n n e l W a v e l e n g t h = 1 5 5 0 n m C a r r i e r f r e q u e n c y = 2 . 6 G H z

    - 6 - 4 - 2 0 2 4 6 8 - 3 0

    - 2 5

    - 2 0

    - 1 5

    - 1 0

    - 5

    0

    5

    1 0

    •Signal eyediagram

    •Signal waveform

    •Baseband Spectrum

  • )sin()()cos()()( tnTtfyAtnTtfxAts csnccsnc ωω ∑∑ ∞

    ∞−

    ∞−

    −−−=

    cA peak signal value

    nx and ny information bits (0, 1 or -1)

    )(tf normalized baseband bit shape function

    cω subcarrier frequency ASK: BPSK: QPSK:

    0or 1=nx 1-or 1=nx 1-or 1=nx 0=ny 0=ny 1-or 1=ny

    If f(t) represents a rectangular bit shape , the PSD of the complex envelope of MPSK is

    ) )sin(

    ()( 2

    S

    S Sc

    fT

    fT TAfP

    π π

    = , where ST is the symbol time.

    The 3dB bandwidth of BPSK and QPSK are both 0.88R if they have the same symbol rate R. Each symbol in QPSK represents 2 bits, so the spectrum efficiency is doubled.

    Sub-carrier generation

  • 4-subcarrier BPSK composite signal4-subcarrier BPSK composite signal

    0 . 5 1 1 . 5 2 2 . 5 3 3 . 5 4 4 . 5 5

    x 1 0 4

    - 5 0 0 0

    - 4 0 0 0

    - 3 0 0 0

    - 2 0 0 0

    - 1 0 0 0

    0

    1 0 0 0

    2 0 0 0

    3 0 0 0

    4 0 0 0

    5 0 0 0

    T R A N S M I T F IL T E R O U T P U T P U L S E - - > IN T E N S IT Y a f t e r c o m b i n e r

    P u

    ls e

    in

    t e

    n s

    it y