Optics and Wave

Jan. 23, 2018

• LAN: 10Base2, 10BaseT, 100BaseT, Gigabit Ethernet (1Gb/s, 10Gb/s). Currently, 10 Gb/s channels in a fiber and very soon 40 Gb/s channels in a fiber.
• WAN: T1 line (1.544 Mb/s)
High speed undersea optical fiber cables (thousands of km long, transmitting in 40Gb/s)
Notes: Merit is in speed times distance product.
• Established optical network: Based on time division multiplex (TDM) called Synchronous Optical Network (SONET). Their speeds are limited by electronics switching time to 40Gb/s.
• Three options for upgrade:
1. Increase speed per channel.
2. Increase number of fibers.
3. Increase number of channels in a fiber.
Based on promising wavelength division multiplexing (WDM). Provide upgrade for existing "dark fibers" by adding carriers with different wavelengths.
Avoid limitation of electronics switching.
• Feasibility of WDM: low loss and low dispersion in glass fiber for 1.3-1.6μm , almost ideal optical amp. that can integrated with fibers, integrated optical filters, integrated solid state lasers and photodetectors, possibility of constructing all-optical components, such as multiplexer, demultiplexer, add-drop multiplexer (ADM) and optical cross-multiplexer (OXC).

These components enable the development of transparent (all-optical) networks that eliminate electrical-optical (E-O) and optical-electrical (O-E) conversions in opaque links for popular WDM bands: S-band (short) -- 1460 to 1530 nm, C-band (conventional) -- 1530 to 1565 nm and L-band (long) -- 1565 to 1625 nm.
The last two components (ADM & OXC) is required for the implementation of packet switched network where the bandwidth of each channel can be adjusted dynamically, e.g. Ethernet. This is in contrast to the fixed channel bandwidth of a circuit switched network.

• New network applications: metropolitan area networks (MAN), fiber to the home (FTTH), Storage area network (SAN).
• Maxwell equations: (Read Sec. 7.2-7.6 of EE361 Text book)

eh

by×e=b/t=μh/t

he

by×h==d/t=εe/t
Wave equation2e=2e/up2t2 whereup=1/με , permittivityε=εoεr , and permeabilityμ=μoμr
Refractive indexn=εr andup=c/n ifμr=1 wherec=1/μoεo is speed of light in air.
• Equations in phasor form (time harmonic):

×H=jωD

,×E=jωB ,
Wave equation2E=k2E ;k=ω/up is wave number.
Recall thatνλ=up (ν=ω/2π is freq,λ is wavelength in the medium, wavelength in airλo=λn )


Last Modified: January 22, 2018
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