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.
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