Wavelength division multiplexing (WDM) is a technique that multiplexes multiple optical carrier signals onto a single optical fiber by using different wavelengths of light. Each wavelength can carry vast amounts of digital or analog information. In WDM, information signals from multiple sources modulate lasers operating at different wavelengths. The different wavelength signals enter the fiber at the same time through the same medium but take different transmission paths and arrive at the receiver end at slightly different times. WDM has advantages like enhanced capacity, full duplex transmission with a single fiber, and simpler more reliable components compared to electronic counterparts. However, the signals cannot be placed too close in wavelength spectrum to avoid interference.

1. 1Jia GENEROSA
Wavelength Division Multiplexing
• Is a technique which multiplexes several optical carrier signals onto a single optical fiber by using different wavelengths of light
• WDM is coupling light of two or more discrete wavelengths into and out of an optical fiber. Each wavelength is capable of
carrying vast amounts of information in either analog or digital form.
FREQUENCY DIVISION MULTIPLEXING WAVELENGTH DIVISION MULTIPLEXING
Operates in the MHz and GHz range Operates in the THz range
Signals propagate at the same time and follow the same
transmission path
Information signals from multiple sources modulate lasers
operating at different wavelength. Different wavelengths of light
enter the fiber at the same time and travel through the same
medium. However, they do not take the same path down the
fiber. Since each wavelength takes a different transmission path.
They each arrive at the receive end at slightly different times.
Types of absorption/ attenuation
1. Ion Resonance
2. Ultraviolet
3. Infrared
WAVELENGTH DIVISION MULTIPLEXING
Advantages Disadvantages
• Enhanced capacity
• Full Duplex transmission is possible with a single fiber.
• Components are simpler; more reliable and often less costly
than electronic counterparts.
• Easier to reconfigure (Add or Remove Chanels).
• Information can be analog (voice, video, FDM) or digital
(TDM).
• Signals cannot be placed so close in the wavelength
spectrum that they interfere with each other.
• Efficiency depends on system design parameters (optical
technique used to combine and separate signals).
TELEPHONY

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CWDM vs. DWDM
Coarse Wavelength Division Multiplexing
• Multiplex few onto a single fiber
Dense Wavelength Division Multiplexing
• Multiplex many onto a single fiber.
• Spacing between adjacent frequency is less than 200 GHz.
Example 1.] At 1550 nm and 100 GHz frequency separation, the wavelength separation is approximately 0.8 nm. Three adjacent
wavelengths each separated by 100 GHz correspond to 1550 nm, 1549.2 nm and 1548.4 nm.
Components
1. Wavelength-Division Multiplexers and Demultiplexers
a. Multiplexer or Combiners
✓ Combine signals with different wavelengths in a way that allows them to pass through a single optical fiber
without interfering with one another.
b. Demultiplexers or Splitters
✓
2. Wavelength Division Data Drop
✓ Similar to demultiplexers or multiplexers except they are located at intermediate points in the system.
✓ Devices that separate a wavelength from a fiber cable.
3. Wavelength Division Routers
✓ Directs signals of a particular wavelength to a specific destination while not separating all the wavelengths
present in the cable.
4. Wavelength Division Couplers
a. Diffraction Grating Prism
✓ Wavelength are separated by refracting them at different angles.
b. Dichrofilter

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✓ A mirror with a surface that has been coated with a material that permits light of only one wavelength to
pass through while refracting all other wavelengths
Diffraction Grating vs. Prism
Dichroic Mirror
SONET (Synchronous Optical Network)
✓ Technology similar to conventional TDM except SONET was developed to be used with optical fiber.
DESIGNATION FORMATION VOICE CHANNELS OUTPUT BIT RATE
OC-1 28 DS-1 672 57.84 Mbps
OC-48 48 OC-1 32,256 2.48332 Gbps
As many as 16 OC-48 (516,096 voice channels) can be combined using WDM.