Fiber Optics
15 free questions with worked answers, and 78 more in the full bank.
Free questions
While analyzing an OTDR trace of a newly installed 5km single-mode link, you see a sharp spike upwards followed by a drop in the trace level. What physical event does this signature represent?
3 marks · Medium
An OTDR trace shows an event at 4km that appears to be a "gainer" (the trace goes up, showing negative loss). What is the actual physical cause of a gainer in an OTDR trace?
4 marks · Hard
You are shooting an OTDR trace on a short 100m patch cord but cannot see the connector at the far end clearly due to the initial pulse width. What setting should you adjust?
1 mark · Easy
You perform a Tier 1 certification (OLTS) on a multi-mode fiber link. The measured loss is 2.5 dB, but the calculated loss budget is 1.8 dB. What is the immediate result?
3 marks · Medium
When measuring Optical Return Loss (ORL) on a single-mode video link, the meter reads 20 dB. The specification requires >45 dB. What does the 20 dB reading indicate?
4 marks · Hard
A technician scopes an SC/UPC connector and sees a large dark smudge directly over the core of the fiber. What is the correct next step?
1 mark · Easy
Under a fiber microscope, you observe permanent pitting and scratches crossing the 9-micron core of a single-mode LC connector, even after multiple wet/dry cleanings. What is the impact on performance?
3 marks · Medium
During a campus backbone installation, a contractor pulls a 24-strand outdoor loose-tube cable around a 90-degree conduit bend. The conduit diameter is 2 inches, and the cable diameter is 0.5 inches. The contractor bends the cable over a 4-inch radius. Why is this a problem?
3 marks · Medium
You are terminating a 12-strand distribution cable. According to the standard TIA-598 color code, what is the color of fiber #6?
1 mark · Easy
A crew is pulling a heavy armored OSP cable using a tugger. They exceed the maximum rated pulling tension of 600 lbs for a few seconds. Later, tests show high attenuation across all fibers. What physically happened inside the cable?
4 marks · Hard
A data center needs to upgrade a 100-meter server-to-switch link to 40GBASE-SR4. What type of fiber and wavelength should they select for the most cost-effective solution?
3 marks · Medium
A telecom provider is troubleshooting a 60km long-haul single-mode link. The link passes perfectly at 1310nm but shows 8 dB of excess loss at 1550nm. What is the most likely physical cause?
4 marks · Hard
A technician spliced two pigtails in a splice tray. The link passes the initial OTDR test. Two days later, the link drops. When the tech opens the tray, the link suddenly comes back up. What is the likely issue?
3 marks · Medium
You are designing a DWDM network using the ITU-T G.694.1 grid. The system uses a 100 GHz channel spacing. Approximately how much wavelength separation exists between adjacent channels?
4 marks · Hard
A technician accidentally patches a CWDM transceiver module transmitting at 1470nm into a DWDM multiplexer designed for the C-band. What will happen?
3 marks · Medium
More Fiber Optics questions (page 1 of 2)
Answers and explanations are in the full bank.
- Which standard category represents the highest performance laser-optimized multimode fiber suitable for 100Gbps over short distances? · 1 mark
- A mechanical splice is showing a loss of 1.5 dB on a single-mode link. The tech pulls it apart, cleans it, and puts it back together, but it still reads 1.5 dB. The fiber ends were cleaved at a perfect 90-degree angle. What is missing? · 4 marks
- You are installing an FTTH router. The provider explicitly requires an APC connector, but you patch an SC/UPC cable into the SC/APC port. What happens? · 3 marks
- Why is 850nm strictly used for multimode fiber, while 1310nm and 1550nm are used for single-mode fiber? · 1 mark
- A technician strips the 250-micron acrylate coating off a fiber to prepare it for fusion splicing. They immediately put it into the cleaver without doing anything else. The splice machine rejects the fiber due to poor cleave angles. What step was skipped? · 3 marks
- An OTDR trace on a 10km link shows a massive drop at 5km, but no reflectance spike. What is the most likely cause of this event? · 3 marks
- A technician is using a dead-zone box (launch ring) of 1000m to test a 500m fiber link. Why is the launch cable longer than the link being tested? · 4 marks
- During an OLTS test, the technician sets a reference by connecting the light source and power meter with a single reference cord. Then, they add a second cord to test the link. What is this referencing method called? · 3 marks
- You are tracing cables in an enterprise data center. You find a bright aqua-colored fiber optic jacket. What type of fiber does this jacket color universally denote? · 1 mark
- A 10G link over OS2 fiber works fine for weeks, then drops out randomly on hot days. The OTDR trace looks normal when tested in the morning. An inspection of the splice enclosure on the roof shows the splice trays are crammed full of slack loops. What is the diagnosis? · 4 marks
- A tech is pulling a loose-tube gel-filled cable into a building. Code dictates that unrated outside plant (OSP) cable can only run a certain distance inside a building before terminating or transitioning to an indoor-rated cable. What is this typical distance limit? · 3 marks
- According to ITU-T G.652.D, what specific improvement was made to standard single-mode fiber to support CWDM across the entire spectrum? · 3 marks
- What safety precaution is absolutely mandatory before viewing the end of an installed fiber optic cable with an optical microscope? · 1 mark
- A network engineer wants to run a 10Gbps signal and a 1Gbps signal over a single strand of fiber simultaneously using a BiDi (Bidirectional) transceiver system. How does a BiDi system separate the transmit and receive signals on one fiber? · 4 marks
- On an OTDR, what parameter determines the index of refraction (IoR) setting, and what happens if it is set incorrectly? · 3 marks
- During routine technical work, which statement about total internal reflection in optical fiber should guide the technician? · 3 marks
- During routine technical work, which statement about single-mode fiber should guide the technician? · 3 marks
- During routine technical work, which statement about multimode fiber should guide the technician? · 3 marks
- During routine technical work, which statement about the fiber cladding should guide the technician? · 3 marks
- During routine technical work, which statement about an 850 nm optical link should guide the technician? · 3 marks
- During routine technical work, which statement about the 1310 nm window should guide the technician? · 3 marks
- During routine technical work, which statement about an LC connector should guide the technician? · 3 marks
- During routine technical work, which statement about an SC connector should guide the technician? · 3 marks
- During routine technical work, which statement about an APC fiber connector should guide the technician? · 3 marks
- During routine technical work, which statement about an optical time-domain reflectometer should guide the technician? · 3 marks
- During routine technical work, which statement about an optical loss test set should guide the technician? · 3 marks
- During routine technical work, which statement about an OTDR launch cable should guide the technician? · 3 marks
- During routine technical work, which statement about an OTDR receive cable should guide the technician? · 3 marks
- During routine technical work, which statement about a macrobend should guide the technician? · 3 marks
- During routine technical work, which statement about a microbend should guide the technician? · 3 marks
- During routine technical work, which statement about a fusion splice should guide the technician? · 3 marks
- During routine technical work, which statement about a mechanical splice should guide the technician? · 3 marks
- During routine technical work, which statement about modal dispersion should guide the technician? · 3 marks
- During routine technical work, which statement about link-budget margin should guide the technician? · 3 marks
- A 24 km link at 0.25 dB/km has 6 connectors at 0.3 dB each and 9 splices at 0.1 dB each. What is the total loss? · 3 marks
- Light travels 74 km through fibre with refractive index 1.46. What is the one-way propagation delay? · 4 marks
- An amplifier raises optical power by a factor of 16. What is that gain in decibels? · 3 marks
- During a workshop assessment, the reported condition is: A previously stable fiber link now shows high loss immediately after a patch cord was reconnected. What should be done before replacing transceivers? · 1 mark
- During a workshop assessment, the reported condition is: An OTDR shows one reflective event near the beginning of a link and normal backscatter afterward. Which physical feature is the most likely source? · 3 marks
- During a workshop assessment, the reported condition is: Loss at 1550 nm rises much more than loss at 1310 nm after a cable was tied tightly around a support. What fault should be suspected? · 1 mark
- During a workshop assessment, the reported condition is: The first connector of a short link is hidden inside the OTDR's initial dead zone. What setup change will improve measurement? · 3 marks
- During a workshop assessment, the reported condition is: The far-end connector cannot be characterized because the OTDR trace ends at that connector. What should be added? · 1 mark
- During a workshop assessment, the reported condition is: Two technicians obtain different insertion-loss results because they used different reference procedures. What is the correct response? · 3 marks
- During a workshop assessment, the reported condition is: A 1310 nm single-mode link is tested only at 850 nm with a multimode source. Why is the result unsuitable? · 1 mark
- During a workshop assessment, the reported condition is: A multimode link passes with one source but fails with another because launch conditions differ. Which control improves repeatability? · 3 marks
- During a workshop assessment, the reported condition is: A green APC connector is forced into a blue UPC adapter. What problem can result? · 1 mark
- During a workshop assessment, the reported condition is: Received optical power is above the receiver's maximum input specification. What is the main risk? · 3 marks
- During a workshop assessment, the reported condition is: No optical power is measured at the far end, but the transmitter is enabled and emits at the expected level locally. What should be checked systematically? · 1 mark
- During a workshop assessment, the reported condition is: A link has acceptable insertion loss but fails an optical return-loss requirement. Which issue should receive attention? · 3 marks
- During a workshop assessment, the reported condition is: An OTDR event is nearly nonreflective and shows a small permanent loss at a documented splice location. What does it most likely represent? · 1 mark
- During a workshop assessment, the reported condition is: A splice appears as a gain when measured from one direction with an OTDR. What should the technician do? · 3 marks
- During a workshop assessment, the reported condition is: A new multimode channel has correct connector loss but inadequate bandwidth-distance performance. Which fiber property is most relevant? · 1 mark
- During a workshop assessment, the reported condition is: A duplex fiber link has light present on both transmit ports but neither receiver detects a signal. Which installation error is likely? · 3 marks
- During a workshop assessment, the reported condition is: A cable route requires a turn tighter than the manufacturer's minimum bend radius. What should the installer do? · 1 mark
- During a workshop assessment, the reported condition is: A technician is about to inspect an active fiber by looking directly into the connector. What is the correct safety action? · 3 marks
- During a workshop assessment, the reported condition is: A connector remains dirty after one cleaning cycle. What is the best next action? · 1 mark
- During a workshop assessment, the reported condition is: Calculated link loss leaves only 0.1 dB below the receiver sensitivity limit. How should this design be judged? · 3 marks
- A 8 km fiber has 0.19 dB/km attenuation, 0.3 dB total connector loss, and 0.1 dB total splice loss. What is the total link loss? · 1 mark
- Transmit power is -4.5 dBm and path loss is 2.7 dB. What receive power is expected? · 1 mark
- Which statement about fusion splicing is correct? · 1 mark