Single mode means the fiber enables one type of light mode to be propagated at a time. While multimode means the fiber can propagate multiple modes.
Here is a quick overview of fiber optic internet download speeds; Fiber optics: Up to 10 Gbps (a data transfer rate up to 10 billion bits per second) Cable connections: 25 – 300 Mbps (a data transfer rate up to 300 million bits per second).
For singlemode fiber, the loss is about 0.5 dB per km for 1310 nm sources, 0.4 dB per km for 1550 nm. (1.0 dB/km for premises/0.5 dB/km at either wavelength for outside plant max per EIA/TIA 568)This roughly translates into a loss of 0.1 dB per 600 (200m) feet for 1310 nm, 0.1 dB per 750 feet (250m) for 1300 nm.
Instead of a gel layer or sleeve to protect the fiber core, tight-buffered cables use a two-layer coating. One is plastic; the other is waterproof acrylate. The acrylate coating keeps moisture away from the cable as the gel-filled sleeves do for loose-tube cables.
These terms refer to the diameter in microns of a fiber optic cable's core and cladding. The first set of numbers - 9, 50 and 62.5 refer to the diameter of the fiber cable's core. The second set of numbers - 125 refer to the diameter of the outside of the fiber cable's cladding.
Single Mode fiber optic cable has a small diametral core that allows only one mode of light to propagate. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further.
Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km (100BASE-FX), 1 Gbit/s up to 1000 m, and 10 Gbit/s up to 550 m. Because of its high capacity and reliability, multi-mode optical fiber generally is used for backbone applications in buildings.
In fact, there are two types of these fibers: Low Water Peak (LWP) fibers, which lower the loss in the water peak E band of the spectrum; and Zero Water Peak (ZWP) fibers, which eliminate the loss in the water peak and further lower the loss across the entire spectrum.
Some types are single-mode, some types are multi-mode. Multi-mode cables can be found in OM1, OM2, OM3 and OM4 types. Each type has different properties. Like OM2, its core size is 50µm, but the cable is optimized for laser based equipment that uses fewer modes of light.
The maximum transmission distance of OM4 fiber is 400-550m (depending on module capability) while OM3 fiber can only be up to 300m. And thus, OM4 can tolerate a higher level of loss at distances between 200-300m as it is designed to operate at longer distances than OM3 fiber.
OM3 vs OM4 Distance
| 850 nm Ethernet Distance |
|---|
| Fiber Type | 1G | 40/100G |
| OM3 | 1 km | 100 m |
| OM4 | 1 km | 150 m |
Multimode graded index fiber in test cables should be 62.5/125 for OM1 cable plants or 50/125 for OM2, OM3, OM4 or OM5 fiber cable plants. There are no significant differences in types of 50/125 fiber so any type of this size fiber can be used to test any other type.
| Fiber Type | Color Code |
|---|
| Multimode (62.5/125) (OM1) | Orange | Slate |
| Multimode (100/140) | Orange | Green |
| Single-mode (OS1, OS1a, OS2) | Yellow | Yellow |
| Polarization Maintaining Single-mode | Blue | Undefined |
As noted before, single-mode patch cables can be used for 10G 10GBASE-LRM SFP+, 10GBASE-LR SFP+, 10GBASE-ER SFP+, 10GBASE-ZR SFP+, 10GBASE-CWDM SFP+, 10GBASE-DWDM SFP+ and SFP+ BiDi modules. Multimode fibers, especially the OM3 and OM4 cables, are supported for 10GBASE-SR SFP+ transceiver modules.
As with Singlemode SFPs, Multi-Mode SFPs are identified by the color of the Bale Clasp:
- Black color coded bale clasp designates a Multi-mode SFP.
- The color of the compatible fiber optic patch cord or pigtail is orange.
Coupling a multimode fiber to a single-mode fiber will cause about 20 dB loss. Connecting a 62.5 fiber to a 50 micron core fiber will cause 2 to 4 dB loss, depending on the type of source (laser or LED). In any case, it can be enough loss to prevent network equipment from working properly.
Like singlemode, multimode fiber provides high bandwidth at high speeds, but transmission is limited to shorter distances than singlemode. (In longer cable runs, the multiple paths of light in a multimode fiber tend to create signal distortion).
If the distance is less than a couple of miles, multimode fiber will work well and transmission system costs (transmitter and receiver) will be in the $500 to $800 range. If the distance to be covered is more than 3-5 miles, single mode fiber is the choice.
Designed for long-distance communication, a single mode fiber cable allows light signals to travel more than 10 miles, a much longer distance than multimode. Single mode fiber also accommodates much higher bandwidths than multimode. Even tiny dust particles or debris can cause issues with signal transmission.
There are three common core sizes: 9/125, 50/125, and 62.5/125. Each of those numbers stands for a measurement, and that measurement is in microns. I quickly drew a cross-section of a fiber cable to help explain all this. The red represents the core, and that's where you see your three measurements.
