Single Mode LC APC Fiber Cable Adapters Lookback Fiber Optic
Testing
LC Loopback Cable&Module
Fiber Optic Loopback modules are also called optical loopback
adapters.They are designed for testing, engineering and the burnin
stage of boards or other equipment. Optical loopback adapters
provide system test engineers a simple but effective way of testing
the transmission capability and the receiver sensitivity of network
equipment.
Fiber Optic Loopback is provide a media of return patch for a fiber
optic signal. Typically it is used for fiber optic testing
applications or network restorations.
When used in testing applications, loopback signals are used for
diagnosing problems. The best practice is to send a loopback test
to network equipment, one at a time for isolating the problem.
Fiber optic loopbacks are designed in a compact footprint. They are
compliant with fast Ethernet, fiber channel, ATM and Gigabit
Ethernet.
Mini LC loopback is suit for 0.9mm cable and 0.25mm fiber.
Connector’s Standard
LC: TIA/EIA, FOCIS10, GR-326 EIA/TIA-604-10, IEC61754-20 and JIS
C5973.
Loopback Module Specification
| Items | BIF Single mode Fiber-G657B3 | BIF Multimode fiber- 50/125 or 62.5/125 |
| Insertion Loss(Typical) | 0.2dB | 0.2dB |
| Insertion Loss(Max) | 0.3dB | 0.7dB |
| Return loss | UPC>50dB,APC>60dB | >35dB |
| Operating& Storage temperature range | -40°C to +75°C |
| Repeat Ability | < 0.5dB (500 Cycle Passed) |
Loopback Cable Specification
| Items | BIF Single mode fiber- 9/125 G657 A1 | BIF Multimode fiber- 50/125 or 62.5/125 |
| Insertion loss(typical) | 0.2dB | 0.2dB |
| Insertion loss(Max) | 0.3dB | 0.3dB |
| Return loss | UPC>50dB; APC>60dB | >35dB |
| Operating& Storage temperature range | -40°C to +75°C |
| Repeat Ability | < 0.5dB (500 Cycle Passed) |
Application in Data Center
Collocated with 10G or 40G or 100G LC/UPC interface transceivers
Which to Choose for a Specific Transceiver?
Considering the common features of the transceiver and the
loopback, we should think about the connector type, polish type,
and cable type when selecting a loopback for the transceiver. The
selection guide for some mostly used transceiver modules is
summarized in the following tables.
Table 1: Loopback choices for 10G SFP+ transceivers
| Model | Interface type | Cable Type | Suited Loopback |
| 10GBASE-USR | LC Duplex (PC) | MMF | LC/UPC Duplex Multimode Fiber Loopback |
| 10GBASE-SR | LC Duplex (UPC) | MMF |
| 10GBASE-LR | LC Duplex (UPC) | MMF |
| 10GBASE-ER | LC Duplex (UPC) | SMF | LC/UPC Duplex Single-mode Fiber Loopback |
| 10GBASE-ZR | LC Duplex (PC) | SMF |
Table 2: Loopback choices for 40G QSFP+ transceivers
| Model | Interface type | Cable Type | Suited Loopback |
| 40GBASE-CSR4 | MTP/MPO (UPC) | MMF | 8/12 Fibers MTP/UPC Multimode Fiber Loopback |
| 40GBASE-SR4 | MTP/MPO (UPC) | MMF |
| 40GBASE-PLRL4 | MTP/MPO (APC) | SMF | 8/12 Fibers MTP/APC Single-mode Fiber Loopback |
| 40GBASE-PLR4 | MTP/MPO (APC) | SMF |
| 40GBASE-LR4 | LC Duplex (PC) | SMF | LC/UPC Duplex Single-mode Fiber Loopback |
| 40GBASE-LR4L | LC Duplex (UPC) | SMF |
| 40GBASE-ER4 | LC Duplex (UPC) | SMF |
| 40GBASE-LX4 | LC Duplex (UPC) | MMF/SMF | LC/UPC Duplex Multimode/Single-mode Fiber Loopback |
Table 3: Loopback choices for 100G QSFP28 transceivers
| Model | Interface type | Cable Type | Suited Loopback |
| 100GBASE-SR4 | MTP/MPO (UPC) | MMF | 8/12 Fibers MTP/UPC Multimode Fiber Loopback |
| 100GBASE-PSM4 | MTP/MPO (APC) | SMF | 8/12 Fibers MTP/APC Single-mode Fiber Loopback |
| 100GBASE-LR4 | LC Duplex (UPC) | SMF | LC/UPC Duplex Single-mode Fiber Loopback |
Table 4: Loopback choices for CFP transceivers
| Model | Interface type | Cable Type | Suited Loopback |
| 40GBASE-SR4 CFP | MPO/MTP (UPC) | MMF | 8/12 Fibers MTP/UPC Multimode Fiber Loopback |
| 40GBASE-LR4 CFP | SC Duplex (UPC) | SMF | SC/UPC Duplex Single-mode Fiber Loopback |
| 40GBASE-FR CFP | SC Duplex (UPC) | SMF |
| 100GBASE-LR4 CFP | SC Duplex(PC/UPC) | SMF |
| 100GBASE-ER4 CFP | SC Duplex(PC/UPC) | SMF |
| 100GBASE-SR4 CFP | MPO/MTP (UPC) | MMF | 24 Fibers MTP/UPC Multimode Fiber Loopback |
Conclusion
This post discusses specific fiber loopback choices for some most
commonly used fiber optic transceivers. For other transceiver
modules that are not mentioned in this post, we can also know how
to choose a suitable loopback for it by getting details about its
interface type, physical contact and cable type.
