Verbeter OTDR meetresultaten
De meetresultaten worden verbeterd door het gebruik van een Launch koffer waarin zich een pre launch fiber bevindt. Bijvoorbeeld de Merconet ANS5, ANS6, ANS7, ANS8, ANS9, ANT0, ANT1, ANT2, ANT3, ANT4, ANT5 en ANT6.
Omdat er zeer weinig licht terugkomt van de gereflecteerde puls van een OTDR, moet het ontvanger circuit zeer gevoelig zijn. Dit betekent dat grote reflecties (meer dan 1 procent van het uitgangssignaal) de ontvanger in de OTDR verzadigen. En/of volledig oversturen hierdoor heeft de ontvanger ook enige tijd nodig om te herstellen voordat een nieuwe meting gedaan kan worden.
De meest voorkomende plaats waar je dit ziet is de aansluiting op de OTDR zelf. De reflectie veroorzaakt een overbelasting gelijk aan 50 meter tot 1 kilometer fiber. Dit is afhankelijk van het OTDR ontwerp, golflengte en de omvang van de reflectie. Het wordt meestal de "dead end zone" genoemd. Om dit te voorkomen wordt een launch box gebruikt ook wel genoemd pulse suppresser. Het verplaatst het meetpunt waardoor de OTDR tijd heeft om te herstellen.
Voorbeeld Verzadiging
In de pop-up wordt getoond dat door het verleggen van het meet moment met een launch, de Trace nu te meten is.
OTDR launch pulse and launch cable
Wanneer het begin van de fiber niet te meten is door oversturing dient er een launch box gebruikt te worden. Hierdoor stelt de OTDR zich beter in, en de conditie van de het begin van de fiber en connector kan nu gemeten worden. Om zo universeel mogelijk te zijn is 1000 meter een goede standaard. Ook voor aansluitingen welke niet speciaal gepolijst zijn verbeterd het de meet resultaten.
OTDR Test with 1 Launch box
De meest voorkomende is de dead zone aan het begin van de fiber.
OTDR Test with 2 Launch boxes
2 Launch boxen worden in gezet indien de far end connector niet goed gemeten wordt.
De fiber in de launch box moet altijd gelijk zijn aan de te meten fiber. Standaard zijn leverbaar de 500 en 1000 meter launch boxen voor OS1, OS2, OM1, OM2, OM3, OM4 de Merconet ANS5, ANS6, ANS7, ANS8, ANS9, ANT0, ANT1, ANT2, ANT3, ANT4, ANT5 en ANT6.
Voor meer informatie zie onze cursus:
CU85 Glasvezel cursus
MM MultiMode 850 en 1300nm
SM SingleMode 1310/1490/1550/1625
CWDM gebruikt de gehele frequentie band van 1270 tot 1675 met 17 kanalen op:
1270/1290/1310/1330/1350/1370/1390/1410/1430/1450/1470/1490/1510/1530/1550/1570/1590nm DWDM gebruikt de gehele frequentie band van 1270 tot 1675 met 6 kanalen:
- O-band 1260-1360nm
- E-band 1360-1460nm
- S-band 1460-1530nm
- C-band 1530-1565nm
- L-band 1562-1625nm
- U-band 1625-1675nm
Optical fiber standards
Both SM (singlemode) and MM (multimode) fibers are divided into many types and categories that comply with established standards and factory specifications. The specifications of various types and categories of the fibers are contained in the standards set by international organizations. In addition, there are numerous factory standards/specifications used on local markets.
Terminology and classification
An organization responsible for international standardization in the field of fiber-optic communications is IEC (International Electrotechnical Commission Technical Committee 86) (IEC TC86) that has defined the following series of types:
- Multimode fibers, e.g. A1a, A1b, A1d..., further divided into groups (e.g. A1a.1...),
- Single-mode fibers, e.g. B1, B4, B6...
However, more popular markings are based on shorts of the fiber kinds:
- OM - Optical Multimode
- OS - Optical Singlemode
The examples are: OM1, OM2, OM3, OM4, OM5, OS1, OS2. The specifications defining specific transmission parameters of the fibers will be presented later in the text.
OS1 Indoor cable (tight buffered) ISO/IEC-11801, ITU-T G.652A/B/C/D, TIA-492CAAA, EN 50173-1.
OS2 Indoor and Outdoor cable (tight buffered and loose tube) ISO/IEC 11801, ITU-T G.652C/D, TIA-492CAAB, EN 50173-1.
The OM markings have been widely adopted, in contrast to OS ones. In the case of single-mode optical fibers the more common names are those used by another international organization, the ITU (International Telecommunication Union), specifically by the department dedicated to standardizing telecommunications solutions (ITU-T).
ITU-T recommendations are are widely known and used.
"Transmission media and optical systems characteristics" are covered by G.600-G.699 series, optical fibers are described in the G.650-G659 range. Each recommendation is for a specific type of fiber.
Selected standards and recommendations
Below there is a summary of selected standards for fiber optics.
ISO/IEC standards:
- IEC 60793 parameters of optical fibers and and cables:
- IEC 60793-2-10 - applicable to multimode optical fiber types A1a, A1b, and A1d
- IEC 60793-2-50 - applicable to single-mode 9/125 optical fiber types B1.1, B1.2, B1.3, B2, B4, B5
- IEC 60794-2 - requirements for indoor cables
- IEC 60794-3 - requirements for outdoor cables
- ISO/IEC 11801 - specifies general-purpose telecommunication cabling systems (structured cabling), including several classes of optical fiber interconnections (OM1 - OM4, with specified minimum modal bandwidth at 850 nm, and OS1, with attenuation max 1 dB/km)
The table below presents a simplified summary of multimode fiber types defined by IEC standards
| Type | Core diameter [µm] | Min modal bandwidth [MHz • km] |
| | | OFL* | EMB** |
| | | 850 nm | 1300 nm | 850 nm |
| OM1 | 50 or 62.5 | 200 | 500 | - |
| OM2 | 50 | 500 | 500 | - |
| OM3 | 50 | 1500 | 500 | 2000 |
| OM4 | 50 | 3500 | 500 | 4700 |
OFL* - OverFilled Launch - standardized fiber bandwidth measurement method where the source launches light uniformly into all modes of the multimode fiber (LED source).
EMB** - Effective Modal Bandwidth - effective modal bandwidth of center/offset launch (laser source illuminating a small portion of the fiber core).
OM1 enables 10 Gbps data rate over very short distances (up to 33 meters), while OM4 allows for transmission of a 100 Gbps data stream over a distance up to 150 m.
ITU-T recommendations:
- ITU-T G.650.1 and G.650.2 - definitions and test methods for linear, deterministic attributes of single-mode fibers and cables
- ITU-T G.651.1 - characteristics of a 50/125 µm multimode graded index optical fiber cable
- ITU-T G.652 - characteristics of a single-mode optical fiber and cable (9/125 μm, four versions: A, B, C, D)
- ITU-T G.653 - characteristics of a dispersion-shifted single-mode optical fiber and cable (DS-SMF)
- ITU-T G.654 - characteristics of cut-off shifted single-mode optical fiber and cable (CS-SMF)
- ITU-T G.655 - characteristics of non-zero dispersion-shifted single-mode optical fiber and cable (NZDS-SMF)
- ITU-T G.656 - characteristics of a fiber and cable with Non-Zero Dispersion for Wideband Optical Transport
- ITU-T G.657 - characteristics of a bending loss insensitive single mode optical fiber and cable for the access network
ITU-T recommendations are much more restrictive (or precise) than the transmission performance categories defined by the IEC (OS1 and OS2). For example, the specifications required by OS2 are fulfilled by G.652.C fiber, which means that G.652D fiber has even better parameters.
Single-mode fibers most useful for typical applications are those compliant with the following standards:
G.652 - defines 4 versions (A, B, C, D). The G.652.C and G652.D variants feature a reduced water peak (ZWP - Zero Water Peak), which allows them to be used in the wavelength region between 1310 nm and 1550 nm supporting Coarse Wavelength Division Multiplexed (CWDM) transmission. G.652.D is Standard Single Mode Fiber (SSMF) dedicated for 10 Gbps and 40 Gbps systems (thanks to reduced polarization mode dispersion - PMD). Currently, it is the most popular optical fiber.
G.655 - defines an optical fiber with performance specified at 1550 nm and 1625 nm with a non-zero chromatic dispersion slope in these wavelength regions. This kind of optical fiber can support long-haul systems using Dense Wavelength Division Multiplexed (DWDM) transmission in 1530 nm to 1625 nm wavelength window.
G.656 - optical fiber dedicated for use in broadband systems using both DWDM and CWDM, intended to operate in 1460 nm to 1625 wavelength window.
G.657 - defines optical fibers that produce lower levels of attenuation caused by bends. The minimum bending radius has been reduced to 15-5 mm (depending on version). G.657A fiber is compatible with G.652 fibers, G.657.B versions do not provide 100% compatibility with the other fibers, however have unique mechanical characteristics suitable for the most demanding installations.
How to compare all of the existing standards and recommendations?
ITU-T (International Telecommunication Union) recommendations are based on IEC (International Electrotechnical Commission) standards, however there may be slight differences in some versions.
And the TIA (Telecommunications Industry Association)
Some comparisons:
Multimode fibers:
OM1 - 62,5/125 – IEC60793-2-10 A1b – TIA 492-AAAA
OM2 - 50/125 – IEC60793-2-10 A1a.1 – G.651.1 – TIA 492-AAAB
OM3 - 50/125 – IEC60793-2-10 A1a.2 – G.651.1 – TIA 492-AAAC
OM4 - 50/125 – IEC60793-2-10 A1a.3 – TIA 492-AAAD
Singlemode fibers:
G.652A, B – 9/125 – IEC60793-2-50 B1.1
G.652C, D – 9/125 – IEC60793-2-50 B1.3
G.655 – 9/125 – IEC60793-2-50 B4
G.657A – 9/125 – IEC60793-2-50 B6_a1
G.657B – 9/125 – IEC60793-2-50 B6_a2
Parameters of selected single-mode fibers
| Fiber type | G.652.C | G.652.D | G.655 | G.657.A (1) |
| Attribute | Detail | Value |
| Mode field diameter | Wavelength | 1310 nm | 1310 nm | 1550 nm | 1310 nm |
| | Range of nominal values | 8.6-9.5 μm | 8.6-9.5 μm | 7-11 μm | 8.6-9.5 μm |
| | Tolerance | ±0.6 μm | ±0.6 μm | ±0.7 μm | ±0.4 μm |
| Cladding diameter | Nominal | 125.0 μm | 125.0 μm | 125.0 μm | 125.0 μm |
| | Tolerance | ±0.1 μm | ±0.1 μm | ±0.1 μm | ±0.7 μm |
| Core concentricity error | Maximum | 0.6 μm | 0.6 μm | 0.8 μm | 0.5 μm |
| Cladding noncircularity | Maximum | 1.0% | 1.0% | 1.0% | 1.0% |
| Cable cut-off wavelength | Maximum | 1260 nm | 1260 nm | 1450 nm | 1260 nm |
| Macrobend loss | Radius | 30 mm | 30 mm | 30 mm | 10 mm |
| | Number of turns | 100 | 100 | 100 | 1 |
| | Maximum at 1550 nm | 0.1dB | 0.1dB | 0.1dB | 0.75 dB |
| | Maximum at 1625 nm | - | - | - | 1.5 dB |
| Proof stress | Minimum | 0.69 GPa | 0.69 GPa | 0.69 GPa | 0.69 GPa |
| Chromatic dispersion coefficient | λ0min | 1300 nm | 1300 nm | - | 1300 nm |
| | λ0max | 1324 nm | 1324 nm | - | 1324 nm |
| | S0max | 0.092ps/nm2• km | 0.092ps/nm2• km | - | 0.092ps/nm2• km |
| Attenuation coefficient* | Maximum at 1310-1625 nm | 0.4 dB/km | 0.4 dB/km | - | 0.4 dB/km |
| | Maximum at 1383±3 nm | 0.4 dB/km | 0.4 dB/km | 0.4 dB/km | - |
| | Maximum at 1550 nm | 0.3 dB/km | 0.3 dB/km | 0.35 dB/km | 0.3 dB/km |
| | Maximum at 1625 nm | - | - | 0.4 dB/km | - |
| PMD coefficient | M | 20 sections | 20 sections | 20 sections | 20 sections |
| | Q | 0.01% | 0.01% | 0.01% | 0.01% |
| | Maximum PMDQ | 0.5 ps/√km | 0.20 ps/√km | 0.20 ps/√km | 0.20 ps/√km |
* Attenuation coefficient should be measured only for longer sections of fibers (shouldn't be measured using e.g. patch cords).
