Fiber Optic Cables

Question 1

What are the 3 elements fiber is constructed from?

Answer 1

core- provides the transmission path
cladding- reflects signals back into the wavelength, can be made from glass or plastic.
buffer- protective plastic coating, can be tight or loose.

Question 2

How are fiber optic cables specified?

Answer 2

using the mode, composition(glass/plastic) and core/cladding size.
e.x. 8.3 micron core/125 micron, cladding, SMF glass.

Question 3

Tell me about SMF.

Answer 3

Single Mode Fiber.
small core of 8-10 microns and long wavelengths.
Uses a laser to generate a near infrared light signal 1310 or 1550 nm
Supports up to 100 Gbps
Runs many kilometers
2 grades of SMF: OS1- for indoor use, and OS2- for outdoor deployment.

Question 4

Tell me about MMF.

Answer 4

Multimode Fiber.
larger core of 62.5 or 50 microns and shorter wavelengths.
Transmits light using multiple waves of varying length 850 or 1300 nm
Less expensive than SMF
Doesn’t support as high signaling speeds or long distances, more suitable for LANs.

Question 5

Tell me about MMF OM categories.

Answer 5

Optical Multimode.
OM1- 62.5 micron, uses LED transmitters, mainly 1Gbps
OM2- 50 micron, uses LED transmitters, mainly 1 Gbps
OM3/OM4- 50 microns designed for use with 850 nm vertical -cavity surface-emitting lasers (VCSEL) also referred to as Laser Optimized MMF (LOMMF) meaning it supports higher modulation than the LED based optics.

Question 6

List popular Fiber optic connectors.

Answer 6

Straight Tip (ST): bayonet style connector, uses push and twist locking mechanism. Mainly used for MMF.

Subscriber Connector (SC): push pull design. Supports SMF and MM. Commonly used for Gigabit Ethernet.

Local Connector/Lucent Connector (LC): small form factor, tabbed push pull design. Widely used for Gigabit Ethernet and 10/40 GbE.

Question 7

What is a MPO?

Answer 7

Multi-Fiber push on.
A high density fiber connector that connects multiple fibers.
Allows for low footprint back bone or trunk cabling.
SMF and MMF variants
Mostly used to combine 10 Gbps or 25 Gbps lanes into a 40, 100, or 400 Gbps parallel optical link.
Has the same footprint as a duplex LC pair.

Question 8

What is WDM?

Answer 8

Wavelength Division Multiplexing.
A means of using one or two strands to provide multiple channels.
Uses different wavelengths so it can increase the capacity of fiber without needing additional strands.

Question 9

How does a duplex fiber channel work?

Answer 9

uses one transmit lane and one receive lane.
requires 2 strands.

Question 10

How does parallel fiber work?

Answer 10

Transmits data simultaneously across multiple fiber strands in a single cable.
Uses bundles of lanes working at 10 or 25 Gbps to achieve 40 or 100 Gbps links.
These channel links require between 8 and 20 strands.

Question 11

What is BiDi?

Answer 11

Bidirectional
BiDi supports transmit and receive signals over the same strand of fiber.
Uses slightly different/shifted wavelengths for transmitting(Tx) and receiving(Rx) over the same fiber strand.
E.x. 1310 nm for Tx and 1490 nm for Rx

Question 12

What is coarse wavelength division multiplexing and dense wavelength division multiplexing?

Answer 12

CWDM- technology for multiplexing up to 16 signal channels on a single fiber using different wavelengths.
DWDM- technology for multiplexing 20,40,80 or 160 signal channels on a single fiber using different wavelengths. Uses tighter wavelength spacing so it requires more precise lasers than CWDM.

Question 13

What is multiplexing?

Answer 13

combines multiple data signals into a single optical fiber, enabling higher data transmission capacity and efficiency.

Question 14

What is a PC and UPC connector?

Answer 14

Physical contact and UltraPhysicalContact.

Question 15

What does the TIA/EIA cabling standard require for fiber patch cord polarity?

Answer 15

An odd number of elements in the link, such as two patch cords and a permanent link.

Question 16

What are Polish Grades?