Fiber Optic Association Certified Fiber
Optic Technician (CFOT) Examination
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A Instant Download Pdf
Question 1
What is the primary function of the core in an optical fiber?
A. To protect the fiber from mechanical stress
B. To reflect light back toward the source
C. To provide a low-refractive-index cladding layer
D. To guide light through total internal reflection
Answer: D – To guide light through total internal reflection. The core is the
central region of the fiber where light propagates. Its higher refractive index
relative to the cladding enables total internal reflection, which confines light
within the core over long distances.
Question 2
Which wavelength is most commonly used for single-mode fiber transmission in
metropolitan networks?
A. 850 nm
B. 1310 nm
C. 1550 nm
D. 1625 nm
,Answer: B – 1310 nm. While 1550 nm is used for long-haul, 1310 nm is the
dominant wavelength for metropolitan and access single-mode applications due
to lower dispersion and compatibility with standard SMF-28 fiber. 850 nm is
used for multimode, and 1625 nm is for monitoring or legacy systems.
Question 3
What numerical aperture (NA) value typically indicates a fiber with a larger light-
gathering ability?
A. 0.10
B. 0.22
C. 0.50
D. 1.00
Answer: B – 0.22. Typical multimode fibers have NA around 0.20–0.29, with 0.22
being common. Higher NA means greater acceptance angle but also higher
modal dispersion. 0.10 is typical for single-mode, 0.50 is unusually high for
communications fiber, and 1.00 is physically impossible for silica glass.
Question 4
In fiber optics, what does the term "attenuation" refer to?
A. The spreading of pulses over time
B. The reduction of optical power as light travels through the fiber
C. The change in wavelength due to nonlinear effects
D. The bending loss caused by sharp curves
Answer: B – The reduction of optical power as light travels through the fiber.
Attenuation is measured in dB/km and includes absorption, scattering, and
connector/splice losses. It does not describe pulse spreading (dispersion),
wavelength shifting, or bending alone, though bending contributes to
attenuation.
,Question 5
Which type of dispersion is caused by different wavelengths traveling at different
speeds in the fiber?
A. Modal dispersion
B. Chromatic dispersion
C. Polarization mode dispersion
D. Nonlinear dispersion
Answer: B – Chromatic dispersion. This arises because the refractive index of
silica varies with wavelength, so different spectral components of a pulse arrive
at different times. Modal dispersion is specific to multimode fibers. PMD is due
to birefringence, and nonlinear dispersion is a separate effect.
Question 6
What is the approximate core diameter of a standard single-mode fiber per ITU-T
G.652?
A. 8–10 µm
B. 50 µm
C. 62.5 µm
D. 125 µm
Answer: A – 8–10 µm. Standard single-mode fiber has a core of about 8–10 µm,
with cladding of 125 µm. 50 µm and 62.5 µm are multimode core sizes. 125 µm
is the cladding diameter, not the core.
Question 7
Which connector type is most commonly used for duplex single-mode
connections in data centers today?
A. ST
B. SC
C. LC
D. MTP/MPO
, Answer: C – LC. The LC connector (Lucent Connector) with its 1.25 mm ferrule is
the predominant choice for high-density single-mode duplex applications. SC is
still used but larger. ST is legacy. MTP/MPO is for multi-fiber arrays.
Question 8
What safety class is a typical 1550 nm laser used in telecom outside plant if it
emits >50 mW?
A. Class 1
B. Class 1M
C. Class 3B
D. Class 4
Answer: D – Class 4. Lasers above 50 mW at any wavelength are generally Class
4, posing fire and skin hazard risks in addition to eye damage. Class 3B is 5–50
mW. Class 1 and 1M are safe under normal operation.
Question 9
Which of the following is the correct formula for calculating optical power loss in
decibels?
A. Loss (dB) = 10 × log10(Pout / Pin)
B. Loss (dB) = 10 × log10(Pin / Pout)
C. Loss (dB) = 20 × log10(Pout / Pin)
D. Loss (dB) = 20 × log10(Pin / Pout)
Answer: B – Loss (dB) = 10 × log10(Pin / Pout). Since loss is a positive value when
Pin > Pout, this formula yields positive dB. Option A would give negative values.
The factor 20 is used for voltage or current ratios, not optical power.
Question 10
What is the primary cause of Rayleigh scattering in optical fibers?
A. Imperfections in the core-cladding boundary
Optic Technician (CFOT) Examination
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A Instant Download Pdf
Question 1
What is the primary function of the core in an optical fiber?
A. To protect the fiber from mechanical stress
B. To reflect light back toward the source
C. To provide a low-refractive-index cladding layer
D. To guide light through total internal reflection
Answer: D – To guide light through total internal reflection. The core is the
central region of the fiber where light propagates. Its higher refractive index
relative to the cladding enables total internal reflection, which confines light
within the core over long distances.
Question 2
Which wavelength is most commonly used for single-mode fiber transmission in
metropolitan networks?
A. 850 nm
B. 1310 nm
C. 1550 nm
D. 1625 nm
,Answer: B – 1310 nm. While 1550 nm is used for long-haul, 1310 nm is the
dominant wavelength for metropolitan and access single-mode applications due
to lower dispersion and compatibility with standard SMF-28 fiber. 850 nm is
used for multimode, and 1625 nm is for monitoring or legacy systems.
Question 3
What numerical aperture (NA) value typically indicates a fiber with a larger light-
gathering ability?
A. 0.10
B. 0.22
C. 0.50
D. 1.00
Answer: B – 0.22. Typical multimode fibers have NA around 0.20–0.29, with 0.22
being common. Higher NA means greater acceptance angle but also higher
modal dispersion. 0.10 is typical for single-mode, 0.50 is unusually high for
communications fiber, and 1.00 is physically impossible for silica glass.
Question 4
In fiber optics, what does the term "attenuation" refer to?
A. The spreading of pulses over time
B. The reduction of optical power as light travels through the fiber
C. The change in wavelength due to nonlinear effects
D. The bending loss caused by sharp curves
Answer: B – The reduction of optical power as light travels through the fiber.
Attenuation is measured in dB/km and includes absorption, scattering, and
connector/splice losses. It does not describe pulse spreading (dispersion),
wavelength shifting, or bending alone, though bending contributes to
attenuation.
,Question 5
Which type of dispersion is caused by different wavelengths traveling at different
speeds in the fiber?
A. Modal dispersion
B. Chromatic dispersion
C. Polarization mode dispersion
D. Nonlinear dispersion
Answer: B – Chromatic dispersion. This arises because the refractive index of
silica varies with wavelength, so different spectral components of a pulse arrive
at different times. Modal dispersion is specific to multimode fibers. PMD is due
to birefringence, and nonlinear dispersion is a separate effect.
Question 6
What is the approximate core diameter of a standard single-mode fiber per ITU-T
G.652?
A. 8–10 µm
B. 50 µm
C. 62.5 µm
D. 125 µm
Answer: A – 8–10 µm. Standard single-mode fiber has a core of about 8–10 µm,
with cladding of 125 µm. 50 µm and 62.5 µm are multimode core sizes. 125 µm
is the cladding diameter, not the core.
Question 7
Which connector type is most commonly used for duplex single-mode
connections in data centers today?
A. ST
B. SC
C. LC
D. MTP/MPO
, Answer: C – LC. The LC connector (Lucent Connector) with its 1.25 mm ferrule is
the predominant choice for high-density single-mode duplex applications. SC is
still used but larger. ST is legacy. MTP/MPO is for multi-fiber arrays.
Question 8
What safety class is a typical 1550 nm laser used in telecom outside plant if it
emits >50 mW?
A. Class 1
B. Class 1M
C. Class 3B
D. Class 4
Answer: D – Class 4. Lasers above 50 mW at any wavelength are generally Class
4, posing fire and skin hazard risks in addition to eye damage. Class 3B is 5–50
mW. Class 1 and 1M are safe under normal operation.
Question 9
Which of the following is the correct formula for calculating optical power loss in
decibels?
A. Loss (dB) = 10 × log10(Pout / Pin)
B. Loss (dB) = 10 × log10(Pin / Pout)
C. Loss (dB) = 20 × log10(Pout / Pin)
D. Loss (dB) = 20 × log10(Pin / Pout)
Answer: B – Loss (dB) = 10 × log10(Pin / Pout). Since loss is a positive value when
Pin > Pout, this formula yields positive dB. Option A would give negative values.
The factor 20 is used for voltage or current ratios, not optical power.
Question 10
What is the primary cause of Rayleigh scattering in optical fibers?
A. Imperfections in the core-cladding boundary
