FIBER OPTICS

Increase in Bitrate-Distance Product

Agrawal-Fiber Optic Communications

Progress In Lightwave Communication Technology

Agrawal-Fiber Optic Communications

Waveguide Basics• Light is guided by a medium with a higher refractive index (Core) surrounded by

that with a lower one (Cladding)• Step-index• Numeric aperture (NA) = sine of the largest acceptance angle

• Typically, NA=0.15 for single mode fiber (SMF) and 0.3 for multimode fiber (MMF).

' 2 21 2 1sin( ) 2mNA n n n

1

21

n

nn

Optical Fiber

• Some Typical Dimension :– Single Mode Fiber (SMF): 8 μm core– MultiMode Fiber (MMF) : 50, 62.5, 85, 100, 200

μm core• Index profile:

– Step vs. Graded vs. multi-step…

Graded index

8 8

Optical Loss

Agrawal-Fiber Optic Communications

Dispersion• Different components of transmitted signal travel at different

velocities in the fiber and arrive at different times at the receiver– Modal dispersion: different modal components of a pulse travel

at different velocities– Chromatic dispersion: different spectral components of a pulse

travel at different velocities• Material dispersion: due to -dependence in doped silica (or

any other core material)• Waveguide dispersion: due to waveguide design

– Polarization dispersion: different polarization components of a pulse travel at different velocities

Multimode Fiber Limitation: Modal Dispersion

Multimode Fiber Limitation: Modal Dispersion

Modal Dispersion is critical in MMF.