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How to Grade Fibre Patch Leads
As we know, fibre patch lead is a cable with connector(s) on either end. So when to grade the fibre patch leads, the right way is to make it clear how to grade the connectors and cable.
Connector
Let’s begin with the connector. There are two aspects that should be noted well about the connector.
The first one is end-face quality. The polishing process during producing fibre patch leads is the key to good performance. According to IEC-61300-3-35, the polished end-face of a connector is divided into measurement regions defined as follows.
| Zone | Diameter for single-mode | Diameter for multimode |
| A: Core | 0 um to 25 um | 0 um to 65 um |
| B: Cladding | 25um to 120 um | 65um to 120 um |
| C: Adhesive | 120 um to 130 um | 120 um to 130 um |
| D: Contact | 130 um to 250 um | 130 um to 250 um |
There are 3 different level requirements for single-mode defined as below.
| Requirement for PC polished connector, single-mode fibre, RL ≥ 45dB | ||
| Zone name | Scratches | Defects |
| A: Core | None | None |
| B: Cladding | No limit ≤ 3um
None > 3um |
No limit < 2um
5 from 2um to 5um None > 5um |
| C: Adhesive | No limit | No limit |
| D: Contact | No limit | None≥10um |
| Requirement for PC polished connector, single-mode fibre, RL ≥ 26dB | ||
| Zone name | Scratches | Defects |
| A: Core | 2 ≤ 3um
None > 3um |
2 ≤ 3um
None > 3um |
| B: Cladding | No limit ≤ 3um
3 > 3um |
No limit < 2um
5 from 2um to 5um None > 5um |
| C: Adhesive | No limit | No limit |
| D: Contact | No limit | None≥10um |
| Requirement for APC polished connector, single-mode fibre | ||
| Zone name | Scratches | Defects |
| A: Core | ≤ 4
|
None |
| B: Cladding | No limit | No limit < 2um
5 from 2um to 5um None > 5um |
| C: Adhesive | No limit | No limit |
| D: Contact | No limit | None≥10um |
The second one is IL(insertion loss), RL(return loss). the quality of polishing will affect the IL&RL.
These parameters stand for the optical performance when mated with other connectors. According to IEC-61755-1, there are four grades to identify the optical performance of interface for single-mode fibre.
| Attenuation grade | Attenuation(>97%) | Mean |
| A | Reserved | Reserved |
| B | ≤0.25 | ≤0.12 |
| C | ≤0.50 | ≤0.25 |
| D | ≤1.0 | ≤0.50 |
| Return loss grade | Return loss(mated) | Notes |
| 1 | ≥60dB | ≥55dB in unmated condition(APC only) |
| 2 | ≥45dB | |
| 3 | ≥35dB | |
| 4 | ≥26dB |
Cable
When coming to the cable, especially fibre patch leads used in indoor applications. Most of the time, we are caring about the fire rate. There are three fire rates that widely used in applications.
OFNP, OFNR, OFN.
OFNP (Optical Fiber, Nonconductive, Plenum)
OFNP (optical fibre, nonconductive, plenum) is used in plenum applications. It is used between a ceiling and the floor above it, where space is reserved for the circulation of air. It has the highest rated fire retardant hence it emits little smoke during combustion. The non-conductive element within OFNP means it contains no electrically conductive components.
OFNR (Optical Fiber, Nonconductive, Riser)
OFNR (optical fibre, nonconductive, riser) is used in riser applications. It is used in vertical zone or space, such as the pathways that pass through floors inside a building, prevent fire from spreading from floors to floors within the building.
OFNR (Optical Fiber, Nonconductive)
Abbreviation for optical fibre nonconductive. OFN is the designation given by the National Fire Protection Association (NFPA) to interior Fiber optic cables that contain no electrically conductive component, and which are not certified for use in Plenum or Riser applications.
