Understanding Fiber Cable: OM1 vs OM2 vs OM3 vs OM4

Understanding Fiber Cable: OM1 vs OM2 vs OM3 vs OM4

The transmission rate and bandwidth of multimode optical fibers

When the geometric size of the fiber (mainly the core diameter d1) is much larger than the wavelength of light (about 1 micron), there will be dozens or even hundreds of propagation modes in the fiber. Different propagation modes will have different propagation speeds and phases, so time delays will occur after long-distance transmission, resulting in wider optical pulses. This phenomenon is called modal dispersion of optical fiber, also known as intermodal dispersion.

There will be a bandwidth (channel bandwidth) parameter in the parameters of multimode fiber, the unit is MHz·km, and sometimes it is asked whether the transmission rate of multimode fiber reaches 200 Mbit/s? How to understand the relationship between the two?

Let’s first understand the bandwidth of multimode fiber.

Usually, the information capacity of multimode fiber is measured by the product of bandwidth and length. Why is the unit not MHz, but MHz·km? First of all, we must understand the characteristics of multimode fiber: the additional group delay, intermodal dispersion, material dispersion, waveguide dispersion, etc. in the process of transmitting optical waveguide signals in multimode optical fiber led to signal distortion. Among them, intermodal dispersion is the decisive factor for bandwidth. The material dispersion and waveguide dispersion are usually negligible in multimode fiber, but they significantly impact single-mode fiber.

The above-mentioned factors will cause that the transmission length of the optical waveguide signal is inversely proportional to the bandwidth when the signal is transmitted in the multimode fiber. Generally, the longer the transmission length, the lower the transmission bandwidth. The unit of MHz·km is to describe the capacity that multimode fiber can transmit within 1 KM (provided that the signal does not fail). Fiber length is an iconic physical parameter. Once the distance is determined, the fiber selection range can be narrowed according to the user’s current or future bandwidth requirements. Therefore, it is meaningless to simply say the actual bandwidth of the multimode fiber, and the length must be added to ensure that the signal does not fail, so the unit becomes MHz·KM. For example, if the bandwidth is 600 MHz·KM, its bandwidth is only 300 M at a place of 2 KM. For step-index multimode fiber, the influence of various factors makes its bandwidth-length product limited to 20MHz·KM; for gradient-index fiber, its bandwidth-length product can be as high as 2.5GHz·KM; and for single-mode fiber, due to factors such as small dispersion and narrow light source spectrum width, it can be considered that its transmission bandwidth is infinite. Studies have shown that for a short wavelength of 0.85 μm, if the root-mean-square spectral width of the light source is 20 nm, the total bandwidth of the fiber in the best case is only 1 GHz km; For 1.30 μm wavelength, if the profile index is well controlled, the highest bandwidth can exceed 10 GHz·km.

OPTIC CABLE

What are OM1 and OM2 Fiber Optic Cables?

Before we look at the two current standards for multi-mode fiber (OM3 and OM4), it’s important to investigate the origins of fiber optic cables. OM1 and OM2 were standard fare in the 1990s and 2000s, but today they are considered obsolete. They aren’t even listed in the ISO/IEC 11801 and TIA 568 wiring standards.

The reasons for their decline were simple: bandwidth and cable length. OM1 could support 10 Gbps, but only for 33 meters. It was commonly used for shorter 100 Mbps connections. OM2 was slightly better at 10 Gbps for 82 meters but was also only used for shorter runs up to 1 Gbps. Why even mention OM1 and OM2, then?

Because you still might see them out in the wild in older installations. The telltale sign is the cable jacket, the outer coating of a cable that protects the delicate fiber inside of it. OM1 and OM2 always have an orange jacket (versus aqua for OM3 and OM4). Older installations also might require you to change plans to maintain backward compatibility, so it’s worth knowing about OM1 and OM2.

What is OM3 Fiber Optic Cable?

OM3 fiber is very physically similar to OM2; however, OM3’s higher-quality core material allows for better light propagation characteristics throughout the length of the cable. This reduces the model dispersion. This is when different light patterns in the multi-mode fiber arrive at the other end of the cable at different times, reducing the effectiveness of the cable across a longer distance. The core material and more advanced manufacturing techniques required to produce it increase the price, however. On average, OM3 is about twice the price of OM2.

Advantages and Applications of OM3 Cables

OM3’s improvements allow for some distinct advantages over OM1 and OM2. OM3 cables can provide for up to 100 Gbps, a huge bandwidth boost over OM2. OM3 can also run 10 Gbps for 300 meters, an almost 4x improvement over OM2. At 100 Gbps, it is limited to 100 meters.

OM3 cables are found in applications where any combination of speed and distance are essential, including:

Campus networks: OM3 cables’ improved length allows them to connect buildings across a broader campus. With buildings too far apart for copper to reach, the max length of OM3 is essential.

Data centers: OM3 cables are commonly used in data centers where high bandwidth connections between servers and connections from servers to storage are paramount for application performance.

Large wifi deployments: Wifi access points spread across a large area, like a stadium or airport, would require the cable length to reach the spread out access points as well as increased bandwidth to handle large numbers of clients in dense areas.

In these and other applications, OM3 is critical for sufficient data transfer.

Multimode fiber

What is OM4 Fiber Optic Cable?

OM4 is another step up in performance from OM3. Further improvements in fiber core material and manufacturing allow for another big boost over OM3, but at another doubling in price, on average.

Advantages and Applications of OM4 Cables

OM4 cables provide greater bandwidth than OM3 cables, quadrupling the max speed to a blazing 400 Gbps. OM4 can also run up to 550 meters for 10 Gbps and 125 meters for 100 and 400 Gbps.

OM4 cables find applications in various scenarios:

Future-proofing: If it’s within your budget, OM4 is a great choice to install even if you don’t require the bandwidth it provides today. You’ll be ready for future requirements without an expensive reinstall.

Backbone Installations: OM4 cables are commonly used for backbone installations, feeding multiple locations or buildings from one trunk.
Anywhere OM3 can be used: Again, if it’s in your budget, OM4 can be used anywhere OM3 would be to provide even greater distance and higher bandwidth connectivity.

Different fiber

Comparison of parameters and specifications of OM1, OM2, OM3 and OM4 optical fibers

OM1 refers to 50 μm or 62.5 μm core diameter multimode fiber with a full injection bandwidth of 850/1300 nm and above 200/500 MHz·km;

OM2 refers to the 50 μm or 62.5 μm core diameter multimode optical fiber with a full injection bandwidth of 850/1300 nm and above 500/500 MHz·km;

OM3 is a 50 μm core diameter multimode fiber optimized by 850 nm laser. In 10 Gb/s Ethernet using 850 nm VCSEL, the fiber transmission distance can reach 300 m

OM4 is an upgraded version of OM3 multimode optical fiber, and the optical fiber transmission distance can reach 550 m.

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Source: AngNet FTTX