DWDM Dense Wavelength Division Multiplexing

Prerequisite

• Multiplexing
• Optical Fiber
• PCM
• PDH
• SDH
• Transmission Fundamental

WDM

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

Multiplexing is a process in which multiple signals are combined for transmission over a single medium.

Fiber Optic

• Lightweight
• 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.

DWDM Characteristics

• Cost effectiveness.
• Multi protocol support / Transparency : It is physical layer protocol, It supports all types of data packets.
• Scalability.
• Reliability.

Dispersion

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.