A G657A1 patch cord is a single-mode cord made on ITU-T G.657.A1 bend-insensitive fibre, which is specified to keep loss low in bends down to a 10 mm radius. It is compatible with G.652.D fibre, so it can be mated or spliced with existing networks. It suits dense racks, cable managers and wall outlets. Radix Fibrotech makes these cords to order in Pune.
G.657 categories A1, A2, B2 and B3 in plain terms
A G657A1 patch cord (written G.657.A1 in the standard) uses single-mode fibre that meets ITU-T Recommendation G.657, category A1. G.657 covers bend-insensitive single-mode fibre in two families, A and B. Each category is defined by the smallest bend radius at which the fibre must still meet the standard's macrobend loss limits. The A categories also meet the G.652.D requirements. The B families allow a wider range of core geometry in return for tighter bending, so they are not required to be compatible with G.652. The single-mode fibre optic cable guide covers the wider fibre standards.
| Category | Minimum bend radius in G.657 | Relation to G.652.D | Typical use |
|---|---|---|---|
| A1 | 10 mm | Compatible | Racks, panels and general patching where some routing space remains |
| A2 | 7.5 mm | Compatible | Crowded cabinets, wall outlets, access drops |
| B2 | 7.5 mm | Not required to be compatible | Short in-building runs |
| B3 | 5 mm | Not required to be compatible | Very tight in-building routing over short lengths |
These are the radius figures named for each category. The standard also sets the number of turns, the wavelengths and the maximum loss for each, and those details differ between categories and editions. For any limit beyond the radius, follow the fibre maker's datasheet and the current edition of the Recommendation.
G.657.A1 patch cord vs G.652.D cord
A1 fibre also meets the G.652.D limits, so a G.657.A1 cord can replace a G.652.D cord without changing the link. The connectors, the polish and the operating wavelengths of 1310 and 1550 nm are the same. The cord mates with existing G.652.D cables and adapters, and a pigtail or cord on A1 fibre can be spliced to G.652.D fibre in the usual way. The fibre pigtail guide describes how pigtails are joined.
The difference is bend behaviour. On a straight run, you will see no change in loss. The benefit appears where a cord is looped tightly behind a patch panel, around a cable manager finger or inside an outlet box. A G.652.D cord in the same place can lose noticeably more, and the loss rises with wavelength.
Jacket colour does not tell you which fibre is inside. A yellow single-mode cord can be G.652.D or G.657, so ask for the category on the jacket legend and the label. Do not assume that any cord sold as single-mode is bend-insensitive.
Tight racks, cable managers and wall outlets
High-density racks and cable managers
A 1U panel with 48 LC ports needs thin cords and tight loops. Vertical managers, rings and fingers give cords a short radius, and a rear door closing on slack makes it shorter. G.657.A1 fibre tolerates these loops with low added loss. The practical limit is then the cord jacket and the connector boot, not the glass.
Wall outlets, ONTs and cabinets
The space behind a wall outlet is small and the cord usually leaves at a right angle. Installers coil slack into the box. G.657.A1 suits these drops, and G.657.A2 gives more margin where the box is very shallow. The SC to SC patch cord page covers the SC cords used in these places.
Why long wavelengths matter
Bend loss increases with wavelength, so 1550 nm and longer wavelengths are where a poor bend shows first. A cord that tests well at 1310 nm may read high at 1550 nm if it is bent too tightly. Test single-mode cords at both wavelengths.
What bend-insensitive fibre does not fix
Bend-insensitive fibre reduces macrobend loss, which is loss from a visible curve. It does not remove other faults:
- Crush and pinch. A cord trapped under a door or a tray lid can lose light through microbends, or break.
- Pulling tension. Cords hung from their connectors by their own weight put strain on the boot and the fibre.
- Kinks. A sharp kink in the jacket is a mechanical fault whatever the fibre.
- Dirty end faces. Contamination causes more loss than most bends do, and bend-insensitive fibre has no effect on it.
The radius in the G.657 table applies to the bare fibre under the standard's test conditions. A jacketed cord has its own minimum bend radius, set by the cord maker and normally larger than the fibre figure. Follow the cord rating when routing, and use the fibre figure only to understand how much margin the glass has.
Choosing A1, A2 or B3 for a cord
| Situation | Suggested category | Check before ordering |
|---|---|---|
| Rack and panel patching with at least 10 mm of bend radius available | A1 | Whether the project specification names a category |
| Crowded managers, outlets or cabinets where radius may fall below 10 mm | A2 | The loss per turn at 1550 nm on the fibre datasheet |
| Very short in-building run with a radius near 5 mm | B3 | How the fibre mates with the plant it joins, since B categories are not required to be G.652 compatible |
| Project documents name G.657.A1 or A2 | Exactly the named category | That the jacket legend and label show the category |
Radix quotes cords on G.652.D, G.657.A1 and G.657.A2 fibre. If you need B2 or B3 fibre, say so in the quote and attach the fibre maker's datasheet. Where documents name one category, supply that category and avoid silent substitution, even with a fibre that is compatible, since the specification may be checked against the label.
What to send us for a quote
List each configuration on its own line, with:
- fibre category: G.657.A1, G.657.A2 or another named category, or G.652.D
- fibre maker datasheet, if the project names one
- connector and polish at end A and end B
- simplex or duplex
- jacket, fire rating and outer diameter
- length and tolerance
- where the cord will be routed, with the tightest bend expected
- maximum insertion loss and minimum return loss, if the project sets them
- label text, jacket legend and test report format
- quantity for that line
Send the list through the request a quote page. The full set of connector pairs and options is on the single-mode patch cords page.
Marking and documents for bend-insensitive cords
A bend-insensitive cord and a standard cord look alike, so marking does the work. Radix builds to your drawing and bill of materials, which includes the jacket legend and the label. Ask for the fibre category, such as G.657.A1, in the legend, with the connector and polish on the label.
For acceptance, ask for the loss report in the format the project needs, tied to cord serial numbers. If the specification refers to a fibre maker's datasheet, send it with the quote, so the fibre can be matched to it.
Questions buyers ask
What does G657A1 mean on a patch cord?
It means the cord is made with single-mode fibre meeting category A1 of ITU-T Recommendation G.657, a bend-insensitive grade specified for a 10 mm bend radius. It is written G.657.A1 in the standard and often G657A1 in catalogues and searches.
Can a G.657.A1 patch cord be used with G.652.D fibre?
Yes. A1 fibre also meets the G.652.D limits, so it mates with G.652.D cables and adapters and splices to G.652.D fibre. The cord can replace a standard single-mode cord without changing the link design.
Is G.657.A1 the same as bend-insensitive fibre?
A1 is one grade of bend-insensitive fibre. G.657 also defines A2, B2 and B3, which are specified for tighter radii. When a document says bend-insensitive, ask which category it needs.
When should I choose G.657.A2 instead of A1?
Choose A2 when the cord will be bent tighter than about 10 mm, such as in shallow outlet boxes, crowded cabinets or very dense managers. In ordinary rack patching with room to route, A1 is normally enough unless the project names A2.
Does a G.657.A1 cord need different connectors?
No. The connector types, ferrule sizes and polishes are the same as on a G.652.D cord, so LC, SC, FC, ST and MPO ends are all available. The fibre is the only change, and it is invisible except on the label and legend.
What bend radius can I use on the finished cord?
Use the minimum bend radius published for the cord, which depends on its jacket and construction and is normally larger than the fibre figure in G.657. Ask for the cord rating in the quote when routing is tight.