13. Wavelength-Division Multiplexing

TRUE

[TRUE or FALSE] It is easy to understand WDM.

TRUE

[TRUE or FALSE] WDM is just a variation of FDM.

low

FDM uses __-frequency electromagnetic waves.

high

WDM uses __-frequency electromagnetic waves.

prism

The colors are transmitted thru the air together and may mix, but they can be easily separated using a simple device like a _____.

optical coupler/optical amplifier

one of the components used in WDM.

optical fiber cable

kind of cable used in WDM

Fiber to the Home (FTTH) Passive Optical Networks

It uses a simple version of WDM to allow bidirectional communications over a single fiber to reduce costs.

different wavelengths

In FTTH passive optical networks, the signals downstream and upstream are at _____ to prevent interference.

1490nm and 1550nm

PON standards’ wavelength used for downstream?

1310nm

PON standards’ wavelength used for upstream?

FTTH Passive Optical Network

CWDM vs. DWDM

coarse WDM and dense WDM (CWDM and DWDM)

2 types of WDM (HINT: CD)

coarse WDM (CWDM)

It is defined by WDM systems with fewer than 8 active wavelengths per fiber.

8

CWDM is defined by WDM systems with fewer than __ active wavelengths per fiber.

CWDM

It is used for short-range communications, so it employs wide-range frequencies with wavelengths that are spread far apart.

wavelength drift

[CWDM] Standardized channel spacing permits room for _____ as lasers heat up and cool down during operation.

CWDM

It is a compact and cost-effective option when spectral efficiency is not an important requirement.

spectral efficiency

CWDM is a compact and cost-effective option when _______ is not an important requirement.

dense WDM (DWDM)

It is defined in terms of frequencies.

TRUE

[TRUE or FALSE] DWDM’s tighter wavelength spacing fits more channels onto a single fiber, but costs more to implement and operate.

DWDM

It is for systems with more than 8 active wavelengths per fiber.

DWDM

It dices spectrum finely, fitting 40-plus channels into the C-band frequency range.

40-plus

DWDM dices spectrum finely, fitting ____ channels into the C-band frequency range.

C-band

DWDM dices spectrum finely, fitting 40-plus channels into the ____ frequency range.

13nm

channel width: CWDM

1nm

channel width: DWDM

20nm

channel spacing: CWDM

0.8nm

channel spacing: DWDM

4-18

number of channels: CWDM

up to 160

number of channels: DWDM

CWDM

does not use an optical amplifier

DWDM

uses an optical amplifier

up to 120km

CWDM range

up to 500km

DWDM range

DWDM

It transmits multiple data signals using different wavelengths of light thru a single fiber.

incoming optical signals

In DWDM, _____ are assigned to specific frequencies within a designated frequency band.

increased

The capacity of fiber is ______ when these signals are multiplexed onto one fiber.

4-8 times

Transmission capabilities is ___ of TDM Systems with the help of Erbium doped optical amplifier.

Erbium doped optical amplifier

Transmission capabilities is 4-8 times of TDM Systems with the help of ______.

Erbium doped fiber amplifier (EDFA)

other term for Erbium doped optical amplifier

EDFA

It increases the optical signal and do not have to regenerate signal to boost its strength.

300km

DWDM lengthens the distances of transmission to more than ____ before regeneration.

• O band

• E-band

• S-band

• C-band

• L-band

• U-band

DWDM Bands (HINT: OESCLU)

O-band

original band, PON upstream

E-band

water peak band

S-band

PON downstream

C-band

lowest attenuation, original DWDM band, compatible with fiber amplifiers, CATV

L-band

low attenuation, expanded DWDM band

U-band

ultra-long wavelength

1260-1360nm

O-band wavelength

1360-1460nm

E-band wavelength

1460-1530nm

S-band wavelength

1530-1565nm

C-band wavelength

1565-1625nm

L-band wavelength

1625-1675nm

U-band wavelength

C-band, L-band

DWDM’s range starts from ___ until ____.

O-band, L-band

CWDM’s range starts from _____ until ____.

• unlimited transmission capacity

• scalability

• transparency

• dynamic provisioning

Why DWDM? (HINT: USTD)

independent

DWDM is a protocal and bit rate ______ hence, data signals such as ATM, SONET, and IP can be transmitted thru same stream regardless their speed difference.

optical layer

DWDM signals are never terminated within the _____ allows the independence of bit rate and protocols, allowing DWDM technology to be integrated with existing equipment in network.

TRUE

[TRUE or FALSE] DWDM has a flexibility to expand capacity within any portion of their networks.

Mike Flynn

“DWDM technology gives us the ability to expand out fiber network rapidly to meet growing demands of our customer,” said _____, group Prresident for ALLTEL’s comms operations.

ATM

DWDM coupled with ____ simplifies the network, reduce network costs and provide new services.

TRUE

[TRUE or FALSE] They can add current and new TDM systems to their existing technology to create a system with virtually endless capacity expansion.

DWDM system

• channel spacing

• signal direction: uni and bidirectional

• signal trace

optical transmission principles (HINT: CSS)

• ring topology vs. mesh topology

• single hop vs. multi-hop networks

network classificaitons (HINT: RS)

• transmitter

• link

• receiver

• optical add/drop multiplexers and optical cross connect components

DWDM components (HINT: TLRO)

transmitter

laser with precise stable wavelength

link

optical fiber that exhibits low loss and transmission performance in relevant wavelength spectra.

receiver

photo detectors and optical demultiplexers using thin film filters or diffractive elements

optical add/drop multiplexers and optical cross connect components

enables new signals to come in and existing signals to come out

TRUE

[TRUE or FALSE] Well-engineered DWDM systems offer component reliability, system availability, and system margin.

humidity

Although filters were often susceptible to ____, this is no longer the case.

• optical fiber doped with erbium

• amplifier

2 key elements of an optical amplifier (HINT: OA)

optimal system performance

Automatic adjustment of the optical amplifiers when channels are added or removed achieves ______.

1530-1565nm

Silica-based optical amplifiers with filters and Fluoride-based optical amplifiers perform equally well in this range.

TRUE

[TRUE or FALSE] The system wavelength and bit rate can be upgraded but planning for this is critical.

• attenuation

• rayleigh scattering

• attenuation due to absorption

• dispersion

transmission challenges (HINT: ARAD)

attenuation

This is caused by intrinsic factors (primarily scattering and absoprtion) and extrinsic factors (stress from the manufacturing process, the envi, and physical bending)

rayleigh scattering

An issue at shorter wavelengths.

attenuation due to absorption

An issue at longer wavelengths.

attenuation due to absorption

Includes: the intrinsic properties of the material, the impurities in the glass, and any atomic defects.

dimmer

In attenuation due to absorption, the impurities absorb the optical energy, causing the light to become _____.

dispersion

It is the spreading of light pulses as they travel down optical fiber.

distortion

Dispersion results in ____ of the signal, which limits the bandwidth of the fiber.

chromatic dispersion and polarization mode dispersion

2 General Types of Dispersion

linear

Chromatic dispersion is _____.

chromatic dispersion

It occurs because different wavelengths propagate at different speeds.

square of the bit rate

chromatic dispersion increases as the _______.

nonlinear

Polarization Mode Dispersion is ______.

Polarization Mode Dispersion (PMD)

It is caused by ovality of the fiber shape as a result of the manufacturing process or from external stressors.

ovality

Polarization Mode Dispersion (PMD) is caused by ___ of the fiber shape as a result of the manufacturing process or from external stressors.

DWDM

It is ready made for long-distance telecomms operators that use either point-to-point or ring topologies.

TRUE

[TRUE or FALSE] DWDM is used for building or expanding networks.

TRUE

[DWDM] Network wholesalers can lease capacity, rather than entire fibers. True or False?

transparency

The ______ of DWDM systems to various bit rates and protocols.

thin fiber

Applications of DWDM: utilize the existing ____.