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Substation Year 3 lvl 3 > Optical Fiber > Flashcards

Optical Fiber Flashcards

(84 cards)

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1
Q

What is an optical fiber?

A

A hair-thin strand of ultrapure glass or plastic that transmits light signals using total internal reflection.

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2
Q

What are the main parts of an optical fiber?

A

Core, cladding, coating (buffer), and jacket.

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3
Q

What is the core in an optical fiber?

A

The central part where light is transmitted.

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4
Q

What is the cladding in an optical fiber?

A

A layer that surrounds the core and reflects light back into the core using total internal reflection.

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5
Q

What is the coating or buffer used for in optical fibers?

A

To protect the fiber from moisture and physical damage.

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6
Q

What is total internal reflection?

A

The phenomenon where light reflects entirely within the core when it hits the cladding at a certain angle, keeping the light confined.

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7
Q

What defines the Numerical Aperture (NA) of a fiber?

A

The angle at which light can enter the fiber and still be totally internally reflected.

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8
Q

What materials are typically used for the core and cladding?

A

Ultrapure glass or plastic, often with different refractive indices to ensure internal reflection.

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9
Q

What is the purpose of the jacket in a fiber optic cable?

A

To provide additional protection and strength to the cable.

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10
Q

What is the function of the buffer layer in fiber optics?

A

It protects the fiber during installation and is stripped off during splicing or termination.

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11
Q

What are the two basic types of optical fiber?

A

Multimode and single-mode fibers.

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12
Q

What do the numbers in fiber specs like 50/125 or 62.5/125 represent?

A

The core and cladding diameters in microns (e.g., 50 µm core and 125 µm cladding).

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13
Q

What is step-index multimode fiber?

A

A type of multimode fiber with a uniform core and distinct cladding that causes high attenuation due to modal dispersion.

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14
Q

Why is step-index multimode fiber rarely used today?

A

Because it has high attenuation and dispersion, making it inefficient.

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15
Q

What is graded-index multimode fiber?

A

A multimode fiber where the core’s refractive index gradually decreases outward to reduce modal dispersion and increase bandwidth.

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16
Q

What are common sizes for graded-index multimode fiber?

A

50/125 and 62.5/125 microns.

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17
Q

What standard fiber is 62.5/125 µm known as?

A

OM1 standard fiber.

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18
Q

What are OM2 and OM3 fibers optimized for?

A

OM2 is optimized for general multimode use; OM3 is optimized for 850 nm VCSEL lasers and higher bandwidths.

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19
Q

Why was 50/125 fiber revived after the 1980s?

A

It offers higher bandwidth and works well with laser sources for gigabit LANs and longer distances.

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20
Q

What wavelength lasers are commonly used with multimode fiber?

A

850 nm and 1300 nm (VCSELs and FP lasers).

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21
Q

What is the typical core diameter of single-mode fiber?

A

8 to 10 microns.

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22
Q

What is the cladding diameter of single-mode fiber?

A

125 microns.

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23
Q

How does the core size of single-mode fiber compare to multimode?

A

Much smaller; single-mode core is ~9 µm, multimode core is ~50–62.5 µm.

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24
Q

What is the main advantage of single-mode fiber?

A

It allows light to travel in a single ray (mode), enabling virtually infinite bandwidth and longer distances.

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25
What wavelengths are used with single-mode fiber?
Typically 1,300 nm and 1,550 nm.
26
What is POF and its use?
Plastic Optical Fiber, used for short-distance consumer applications like audio/TV.
27
What is PCS and HCS fiber?
Plastic Clad Silica and Hard Clad Silica; step-index designs with small cores and thin plastic cladding.
28
What are bend-insensitive fibers used for?
Patch cords and tight enclosures.
29
What are erbium-doped fibers used for?
Long-distance signal regeneration in amplifiers.
30
What happens if single-mode and multimode fibers are mixed?
Severe signal loss, up to 20 dB, especially when going from multimode to single-mode.
31
What is a typical loss when mixing 62.5/125 and 50/125 fiber?
Up to 3 dB loss due to mismatched core sizes.
32
What is attenuation in optical fiber?
The loss of optical power per unit length, measured in decibels per kilometer (dB/km).
33
What causes attenuation in optical fibers?
Absorption and scattering of light.
34
What is the primary absorber that contributes to attenuation?
Hydroxide ions (OH⁺) in the glass.
35
What is scattering in optical fibers?
Light bouncing off atoms in the fiber, especially when traveling at shorter wavelengths.
36
Why does scattering decrease at longer wavelengths?
Because scattering is inversely proportional to the fourth power of the wavelength.
37
Which wavelengths are most commonly used in fiber optics?
850 nm, 1,300 nm, and 1,550 nm.
38
At which wavelength does light experience the lowest attenuation?
1,550 nm.
39
What is shown in Figure 5-6 (Attenuation graph)?
Light attenuation varies with wavelength, with absorption peaks and scattering illustrated.
40
What are fiber 'windows'?
Wavelength ranges (850, 1300, and 1550 nm) where fiber transmits with minimal attenuation.
41
What determines the attenuation coefficient of a fiber?
The amount of power lost per kilometer due to absorption and scattering.
42
What is dispersion in fiber optics?
The spreading of light pulses over time as they travel through the fiber.
43
Why is dispersion a problem?
It causes signal distortion and limits the bandwidth and transmission distance.
44
What is modal dispersion?
Occurs in multimode fibers when different modes (light paths) arrive at different times.
45
How does graded-index fiber reduce modal dispersion?
By gradually changing the refractive index in the core to equalize path times.
46
What is chromatic dispersion?
Occurs when different wavelengths of light travel at different speeds through the fiber.
47
Which fibers experience chromatic dispersion?
All fibers, but it significantly affects single-mode fibers at long distances.
48
How can chromatic dispersion be reduced?
Using lasers with a narrow spectral width or dispersion-shifted fibers.
49
What is polarization mode dispersion (PMD)?
A type of dispersion in single-mode fiber due to slight imperfections causing different polarizations to travel at different speeds.
50
What limits multimode fiber bandwidth?
Primarily modal and chromatic dispersion.
51
What limits single-mode fiber bandwidth?
Mostly chromatic and polarization mode dispersion.
52
Why is fiber bandwidth higher at shorter distances?
Because dispersion hasn’t had enough distance to spread the signal significantly.
53
What is the purpose of fiber optic cable construction?
To protect the optical fiber from environmental and mechanical damage.
54
What are the basic components of a fiber optic cable?
Optical fiber, strength members, and outer jacket.
55
What are strength members in fiber optic cables?
Materials (like aramid yarn/Kevlar) that provide tensile strength and prevent fiber breakage.
56
What is the role of the cable jacket?
To protect against physical and environmental factors like moisture, abrasion, and chemicals.
57
What are common types of cable jackets?
PVC, LSZH (Low Smoke Zero Halogen), PE (Polyethylene), and plenum-rated jackets.
58
What is a tight-buffered cable?
A cable where each fiber has its own protective buffer and is easy to handle and terminate.
59
Where are tight-buffered cables commonly used?
Indoors and in premise networks.
60
What is a loose-tube cable?
A cable where fibers are placed in a gel- or water-blocking-filled tube, providing protection in harsh environments.
61
Where are loose-tube cables typically used?
Outdoors in campus or long-distance applications.
62
What is a breakout cable?
A cable with individually jacketed fibers within an outer jacket; used where fibers need to be separated.
63
What is a distribution cable?
A cable with tight-buffered fibers bundled together, used when space is limited.
64
What are fiber optic cable ratings based on?
Flammability and smoke characteristics required by building codes.
65
What is a plenum-rated cable?
A cable suitable for air-handling spaces with low-smoke, fire-resistant properties.
66
What is a riser-rated cable?
A cable used in vertical shafts (risers); less stringent fire requirements than plenum.
67
What is a general-purpose cable?
A cable used in areas where plenum or riser rating is not required.
68
What does OFNP stand for?
Optical Fiber Nonconductive Plenum — highest fire rating for plenum spaces.
69
What does OFNR stand for?
Optical Fiber Nonconductive Riser — used in riser shafts.
70
What is OFNG cable?
General-purpose optical fiber cable.
71
Why are cables gel-filled or water-blocked?
To prevent moisture from entering and damaging the fibers.
72
What are armored cables?
Cables with metal or Kevlar reinforcement to protect against rodents and crushing.
73
Where is PE (Polyethylene) jacket typically used?
Outdoor environments due to moisture resistance.
74
What is LSZH cable used for?
Indoor spaces where low smoke and non-toxic emissions are essential during fire.
75
What is the maximum pulling tension for fiber optic cables typically?
About 600 pounds for outside plant cables, and 100 to 200 pounds for indoor cables.
76
How should fiber optic cables be pulled during installation?
Using pulling grips attached to the strength members, not the fiber itself.
77
What happens if you exceed pulling tension limits?
It can break the fiber or damage the cable’s internal structure.
78
What is bend radius?
The minimum radius you can safely bend a fiber optic cable without damaging it.
79
What is the typical bend radius during installation?
20 times the cable’s outside diameter.
80
What is the minimum bend radius after installation?
10 times the cable’s outside diameter.
81
Why is bend radius important in fiber optics?
Bending a cable too tightly can cause excessive signal loss or breakage.
82
What should be avoided during fiber optic installation?
Crushing, kinking, twisting, and bending the cable too tightly.
83
How should fiber optic cables be stored or coiled?
In large coils that respect the minimum bend radius.
84
What is the role of conduit in fiber installation?
To protect the cable from external damage during and after installation.

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