| Full titles | IEC 61753-1: Fibre optic interconnecting devices and passive components. Performance standard. Part 1: General and guidance. IEC 61755-1: Fibre optic interconnecting devices and passive components. Connector optical interfaces for single-mode fibres. Part 1: Optical interfaces for dispersion unshifted fibres. General and guidance |
| Publisher | IEC, subcommittee SC 86B |
| IEC 61753-1 edition | Edition 2.0 (2018-08), corrigendum 2019, Amendment 1 (2020-06). Consolidated as Edition 2.1. Stability date 2027. Edition 3 is in preparation (draft circulated for comment in 2026) |
| IEC 61755-1 edition | Edition 2.0 (2022-09). Replaced Edition 1.0 (2005) |
| Multimode equivalent | IEC 63267-1 Edition 1.0 (2023-05), for 50 µm enhanced macrobend loss multimode fibre |
| Related standards | IEC 61754 series, IEC 61300 series, IEC 60793-2-50, IEC 60793-2-10, IEC 62005 |
How these standards fit together
IEC publishes several families of standards for fibre connectors and passive components. Each answers a different question.
| Series | What it defines |
|---|---|
| IEC 61754 | Mechanical connector interface. Ensures compliant products mate and de-mate |
| IEC 61755 (single-mode) and IEC 63267 (multimode) | Optical interface. Geometric, dimensional and material requirements so randomly mated connectors meet a known attenuation and return loss grade |
| IEC 61753 | Performance standards. Sets of tests and severities for a given service environment, run once to prove a design |
| IEC 61300 | Basic test and measurement procedures used by the other series |
| IEC 62005 and reliability technical reports | Guidance on assessing performance over time |
IEC 61753-1 states that products from different suppliers with the same classification are only interchangeable when they also meet the interface standards. It also states that meeting a performance standard is not a guarantee of lifetime performance or reliability.
IEC 61753-1: operating service environments
IEC 61753-1 gives guidance for drafting performance standards for all passive fibre optic products. It defines the tests and severities that make up each performance category, or operating service environment. Test details are in normative Annex A. Tests are taken from the IEC 61300 series. Annex B sets the numbering of the product performance standards that follow it.
| Category | Environment | Product groups with tables in Annex A |
|---|---|---|
| C | Indoor controlled | Connectors, passive components, splices, fibre management systems, wall outlets, boxes, ODF modules, closures |
| OP | Outdoor protected | Connectors, field mountable connectors, passive components, splices, fibre management systems |
| OP+ | Extended outdoor protected | As OP |
| I | Industrial | Connectors and passive optical components |
| E | Extreme | Connectors and passive optical components |
| A | Outdoor aerial | Hardened connectors, street cabinets, boxes and closures |
| G | Outdoor ground | Hardened connectors and closures |
| S | Outdoor subterranean | Hardened connectors and closures |
Categories C, OP, OP+ and I also have an HD version. HD stands for heat dissipation. It applies where passive optical components share a housing with active electronics, and adds temperature ranges for that case.
Changes in Edition 2 (2018)
- Categories U and O were replaced by OP and OP+. OP+ contains the OP tests plus four other tests, with no mandatory sequence.
- Category I (Industrial) was added.
- The height of category A changed from 3 m to ground level. Category G now runs from 1 m below ground to 3 m above ground.
- Tests were added for wall outlets, wall or pole mounted boxes, mechanical splices, fusion splice protectors, ODF modules, street cabinets, field mountable connectors and hardened connectors.
- Mating durability for connectors in categories C, OP, OP+ and I was reduced to 200 cycles for cylindrical ferrules and 50 cycles for rectangular ferrules.
- The change in attenuation criterion for connectors became a plus or minus deviation from the starting value, rather than peak to peak.
IEC 61755 and IEC 63267: optical interface grades
IEC 61755-1 covers connection interfaces for dispersion unshifted single-mode fibre to IEC 60793-2-50, class B. It defines standardised optical connection grades. The grades are based on random mated connections between two connector populations, taking account of fibre mode field diameter mismatch and core offsets. IEC 63267-1 does the same for 50 µm enhanced macrobend loss multimode fibre (A1-OM2b to A1-OM5b), at 850 nm only.
| Part | Single-mode (IEC 61755) | Multimode (IEC 63267) |
|---|---|---|
| Part 1 | General and guidance. Defines the grades. Ed. 2.0, 2022 | General and guidance. Defines the grades. Ed. 1.0, 2023 |
| Part 2 | Fibre-to-fibre connection parameters. 2-1 non-angled PC, 2-2 angled (APC). Ed. 2.0, 2022 | 2-1 non-angled PC, 50 µm. Ed. 1.0, 2024 |
| Part 3 | Ferrule and material parameters. 3-1 non-angled and 3-2 angled (8°) 2,5 mm and 1,25 mm zirconia ferrules. Ed. 2.0, 2024 | IEC 63267-3-1 (zirconia ferrules) in preparation |
How the grades work
- There are two separate grades: an attenuation grade identified by a letter, and a return loss (RL) grade identified by a number.
- IEC 61755-1 gives single-mode random mated attenuation grades and return loss grades at 1310 nm. IEC 63267-1 gives multimode attenuation grades and return loss grades at 850 nm.
- Multimode grades use an encircled flux compliant launch condition. Angular core offset is treated as insignificant for multimode.
- Edition 2 of IEC 61755-3-1 and IEC 61755-3-2 (2024) added Grade B and Grade C interface requirements. Both parts define two variants that remain intermateable within a given grade.
- Grades describe randomly mated pairs. IEC 61755-3-1 and -3-2 include an informative annex on the expected attenuation when mated to a reference connector plug, which is a different condition.
Return loss levels named in the visual inspection tables
Each value is the return loss level used to set the end face visual requirements in that part. The grade definitions themselves are in IEC 61755-1 and IEC 63267-1.
| Interface | RL grade | Return loss |
|---|---|---|
| Single-mode PC (IEC 61755-2-1) | Grade 2 | ≥ 45 dB |
| Single-mode PC (IEC 61755-2-1) | Grade 3 | ≥ 35 dB |
| Single-mode PC (IEC 61755-2-1) | Grade 4 | ≥ 26 dB |
| Single-mode APC 8° (IEC 61755-2-2) | Not stated in table title | ≥ 60 dB |
| Multimode PC (IEC 63267-2-1) | Grade 2 | ≥ 20 dB |
These parts also give visual end face requirements for each RL grade, using IEC 61300-3-35 inspection.
Link between the two
IEC 61755-1 relates ferrule materials to the IEC 61753-1 categories. Zirconia ferrules can be used in all environmental categories. The thermoset epoxy polymer specified for some rectangular ferrules is limited to category C. IEC 61755-3-1 and -3-2 state that zirconia ferrules made to them suit all operating service environments in IEC 61753-1.
What it means in practice
- On a connector or component datasheet, look for the IEC 61753-1 category, for example C for indoor controlled locations or OP for outdoor protected locations.
- Look for both an attenuation grade and an RL grade, and the standard they come from. A grade without its standard reference is hard to compare.
- Check whether a loss figure is a random mate figure or a figure measured against a reference connector. They are not the same.
- For APC single-mode connectors, expect return loss to be specified much higher than for PC connectors.
Related reading: Fibre optic connectors explained: LC vs SC and UPC vs APC · Fibre insertion loss and return loss explained.