BASIC NETWORK TOPOLOGIES
1. Bus – Backplane
user 1user 2user 3. . . .
• Issues of contention for accessing the bus
user 1user 2user 3user 4user 5user 6user 7
• Individual passive optical tap is required for each node. • Similar to BUS Network in this regard.
• Approach becomes intolerable for large node networks.
3. STAR NETWORK
user user user user user user StarCoupler
• The signal from each signal is mixed in the star coupler and broadcast to all other users on the coupler. OPTICAL NETWORK TERMINOLOGY
• SONET/SDH- Synchronous Optical Network later called Synchronous Digital Hierarchy- This standard defines a synchronous frame structure for transmitting time division multiplexed signals. • OC-xx Optical Carrier; STM-xx Synchronous Transfer Module – each bit rate is a multiple of the lowest level OC-1 or STM-1 bit rate. SONET
FIBER OPTIC NETWORK LAYOUT
Long Haul NetworkWANMANLANLAN12MANLANLAN12
Long Haul Network – Provides signal transmission link between distant regions within a country, countries, and continents. (BUS) Wide Area Network – Connects significant portion of a country (hundreds of kilometers). (STAR) Metropolitan Area Network- Interconnects users in a city and its outlying regions. (RING) Local Area Network- Connects a small number of users in a region of a few kilometers. (RING) 4
(Stanford’s HORNET- Hybrid Opto-Electronic Ring Network)
Access PointλAccess PointλAccess PointλAccess PointλAccess Pointλ12345λDrop3PacketReceiverPacketSwitchTunableTransmitterλ1λΝλ1λΝPOPLANTo Long-HaulNetworkWirelessIP Cell • POP- Point of Presence – switches traffic between the ring and the carriers long-haul network. • Access Points- nodes for accessing and sending data to the ring. • WDM MAN – In this architecture Access Points are connected in a ring topology. Wavelength Division Multiplexing approach is used to route signals on the MAN. A rapid tunable (Δ>Δ 17
Fabry Perot Filter:
• A cavity of length L with intensity reflectivity R has an intensity transmittiance of ()()( ) 222114sinTincRIIRRδ−=−+ /2
• The transmittance is maximum whenever
• Therefore the frequency is maximum whenever
with θ the angle of the beam relative to the surface normal within the cavity. • The spacing between adjacent modes is therefore:
• The signal channel bandwidth can be defined as:
where N are the number of channels, Sch is the normalized channel spacing (Sch = Δνch/B, and B is the bit rate. • Typically Δνbw ~ B
FSRchbwchFNSSννΔ∴100 nm) can be achieved using acousto-optic filters. The only filter that can currently be used to select several wavelengths simultaneously. • Basic Operation: Assume that the input light is entirely TE polarized. At the output end of the device a polarizer is placed that selects only TM polarized light. The acousto optic (AO) device changes the polarization of a narrow spectral band of light from TE to TM. This light can then pass out of the device. 22 • An AO wave in an AO medium induces a periodic (period = Λa) change in the ordinary and extraordinary refractive indices (no, ne) of the medium. • If the refractive indices nTM and nTE of the TE and TM modes satisfy the Bragg condition then light couples from one polarization mode to the orthogonal state. 1TMTEannλλ=±Λ • An output polarizing BS can be used to filter out a narrow spectral band near λ that had its polarization changed. • If only one waveguide is used the device will be sensitive to the state of the input polarization. • However using two polarizing waveguide BSs in cascade as shown in the figure can be used to form a polarization insensitive device. Surface...