EE 230: Optical Fiber Communication Lecture 14

From the movieWarriors of the Net

Optical Time Division Multiplexing

OTDM Routing Network

Multiplexing

• Frequency-division multiplexing (FDM) for electrical signals

• Code-division multiplexing (CDM) for electrical signals

• Wavelength-division multiplexing (WDM) for optical signals

• Time-division multiplexing (TDM) for both types

Modulation

• Amplitude modulation

• Frequency modulation

• Phase modulation

Simple to implement

• amplitude modulation

• pulse amplitude modulation

• amplitude shift keying

Economize bandwidth

• quadrature amplitude modulation

• single sideband modulation

• vestigial sideband modulation

Economize power

• double sideband modulation

• double sideband carrier-suppressed modulation

These are easy to modulate but difficult to demodulate

Noise resistant

• phase modulation

• frequency modulation

• pulse position modulation

• pulse code modulation (widely used)

• amplitude shift keying

• frequency shift keying

Pulse Formats

Optical Bit and Packet Interleaving

OTDM Bit Interleaved Multiplexer

Packet Interleaved Multiplexer

Demultiplexing

• OTDM and soliton systems require RZ format• Nonlinear devices required to demultiplex• n EO modulators required for 2n channels• Sagnac interferometer (NOLM) uses XPM• FWM devices use clock signal as pump,

generate new wavelength for “1” bits

Synchronizer

OTDM Bit Interleaved Demultiplexer

Packet Interleaved Demultiplexer

Nonlinear Optical Loop Mirror-NOLM

Solitons

Comparison of Soliton Transmission to other Technologies

Effective area of single-mode fiber

for 1.2<V<2.405,

otherwise

Aeff=w2

62/3

879.2619.165.0

VVa

w

Va

w

ln

1

Peak power for a soliton

where is the pulse width in time and n2 is the nonlinear index of refraction

22

2

3775.0

cn

ADP eff

Example: Corning SMF-28 fiber

• nCO=1.4504, nCL=1.4447, a=4.1 m, =1550 nm. NA=?

• NA=0.13. k=?• k=2/=4.05x106 m-1. V=?• V=2.16. w/a=?• w/a=1.19. w=?

• w=4.87 m. Aeff=?

• Aeff=7.46x10-11 m2

Example, continued

• D=19 ps/km-nm, n2=3.18x10-20 m2/W, =20 ps. P=?

• D=1.9x10-5 s/m2

3=3.72x10-18 m3

2=4x10-22 s2=9.87

• P=0.108W=108 mW—pretty high!