Wavelength division Multiplexing (WDM) technique increase the capacity of signal carrying medium. WDM technique assign different frequency / wavelength value to every incoming signal. These signals are multiplexed on a single sharing medium. SONET/SDH use TDM technique and transmit data in the form of a single wavelength but DWDM transmit different wavelength for every signal.
Multiplexing is a process in which multiple signals are combined for transmission over a single medium.
- High data rate
- Secure communication
- No interference
- Less Expensive (Lower attenuation mean few repeaters)
Result : Fiber Optic Everywhere
Why not SDH/SONET ???
- Due to some Electronic issues.
- Due to Dispersion problem.
- Do to Optical detection circuitry.
- Transmission over 10 G is more affected by Dispersion.
- High transmission power required for high bit rate transmission.
- Polarization Mode dispersion affects the limits of a light pulse travel without degradation.
- Cost effectiveness.
- Multi protocol support / Transparency : It is physical layer protocol, It supports all types of data packets.
It is the broadening of light pulses. It is a very critical factor limiting the signal transmission. Excessive spreading/broadening cause bits to “overflow” their time slots and overlap adjacent bits. It causes inter symbol interference.
- CD = Chromatic Dispersion.
- PMD = Polarization Mode Dispersion.
CWDM and DWDM
WDM is the technique of data transmission by splitting and combining the multiple wavelengths of light.
- Coarse WDM.
- Dense WDM.
are two products of WDM but with different characteristics.They are differ in
- Number of Channels.
- Channel Spacing( 20 nm in CWDM and less than 1 nm in DWDM).
- Power. (DWDM require more power than CWDM).
- Cost. (DWDM 4 to 5 time expensive).
- Signal Amplification.
- Data Transmission. (DWDM can transmit longer distance).
EDFA – Erbium Doped Fiber Amplifier
- It is a fiber amplifier or Light amplifier.
- They preserve the wavelength of optical signal.
- Can amplify multiple channels simultaneously.
- Fiber Amplifier are 50% cheaper than regenerator.
- No need of optoelectronic conversion process.
A process in which re generators are used to amplify the single optical signal at one time. A photo detector is used to convert light signal into electrical signal for amplification.