Bandwidth doubles every two years.
- Long Haul Systems:
o connect major cities
o 16 – 160 wavelength DWDM (Dense Wavelength Division Multiplexing)
- Metro Access Networks
- Passive Optical Networks (PON)
o Fibre to the Premises (FTTP), Fibre to the Home (FTTH)
- Radio over Fibre (RoF) Systems
o Fibre wireless, RF photonic systems
o Millimetre-wave wireless networks
Wavelength Diving Multiplexing (WDM)
There are two main types of WDM (Wavelength Division Multiplexing) systems:
- Dense Wavelength Division Multiplexing (DWDM)
- Coarse Wavelength Division Multiplexing (CWDM)
DWDM is used for main networks. It is very expensive.
CWDM is used for Metro and Access Networks. It can be constructed at low cost. Optical add/drop Multiplexers (OADM) and Reconfigurable Optical add/drop Multiplexers (ROADM). CWDM is used to implement FTTP networks.
Passive Optical Networks
Passive optical networks can be classified into two main types:
- Time Division Multiplexing PON (TDM-PON)
- Wavelength Division Multiplexing PON (WDM-PON)
In TDM-PON 1/N of bit rate is available to N users. Passive splitter is used. Splitter attenuation limits the number of users. Different wavelengths are used for downstream and upstream signals.
Splitter loss equals to:
Where: N = Number of users.
WDM-PON uses arrayed waveguide grating (AWG) splitter. This network provides large capacity, high security, privacy and upgrade flexibility.
WDM/TDM hybrid PONs systems are also used.
Long reach WDM-PONs that used bidirectional amplifiers are being researched right now. Those simplified networks are useful to accommodate growing number of users.
Wavelengths can be reused to optimise use of available capacity with the use of wavelength converters.
Other types of optical networks include:
- Broadband (BPON),
- Ethernet PON (EPON),
- Gigabit PON (GPON),
- Gigabit Ethernet PON (GE-PON)
BPON is made to work in the frequencies in the range of 155 Mb/s to 622 Mb/s.
EPON is designed to work at a frequency of 1.25 Gb/s.
GPON is made to work at 2.5 Gb/s, over a length of 20 km, maximum 64 splits. It is used in USA and Australia.
GE-PON is used in Asia (Korea and Japan).
Radio Over Fiber
Radio over fiber (RoF) systems are used for delivery of broadband wireless services. Optical fiber characteristics such as: wide bandwidth, low transmission loss and protocol transparency are very useful. Radio signals allow mobility and easy access. RoF transmits analog signals between control station, central office and base stations.
Applications of RoF include fiber distributed 60 GHz mm-wave (millimetre-wave) broadband wireless access networks (BWANs). Spectral space has been assigned worldwide to 60 GHz communication systems.
RoF performance is dependent on optical modulation method, signal fading (caused by chromatic dispersion) and fiber nonlinearities (caused by high optical power levels). Signal fading is the main problem. Variation in phase shifts occurs between optical carrier and two sidebands.