A Guide to Filters and Splitters

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Choosing the right optical filter is like choosing the best sunglasses for your eyes. Too dark, and it may be too difficult to see; too light, and they are less effective at blocking the sun. With levels of UV (ultraviolet) light protection, and polarized vs. non-polarized lens, each will affect your vision differently, letting through a certain amount or particular types of light.

Optical filters work similarly, but instead of filtering sunshine, they filter laser light. Very specific spectrums of that laser. These lasers originate from integrated onboard optics or pluggable transceivers.

Optical filters play a key role in fiber optics, and as usual, they are offered in a plethora of acronyms: DWDM, CWDM, FWDM, MUX / DEMUX, OADM.

For example, the wavelength selectivity needed for an Optical Add-Drop Module (OADM) fine tunes the light by selectively adding and dropping optical channels. And since OADM can be for low-loss/low-cost passive devices, it doesn&#;t require any power, making it scalable, reliable and cost-effective.

The filters for WDM (Wavelength-Division Multiplexing) combine multiple signals for multiplexing and demultiplexing with each laser modulated for a pair of signals. There are also CWDM (Course Wavelength-Division Multiplexing) and DWDM (Dense Wavelength-Division Multiplexing) to throw in the mix.

You can see how the type of filter or filters you need depends on the wavelengths you&#;re working with. The transceiver wavelengths must match the filter ports to pass through the filter.

Since the CWDM filter&#;s purpose is to separate one signal from a group of signals, the wavelengths of light corresponding to the CWDM channel filter is allowed to pass while all others are reflected.

A single DWDM channel uses a filter to transmit and reflect other DWDM channels. In high-speed optical networks, DWDM filters have multiplex and de-multiplex wavelength signals that are evenly spaced from to nm.

It is important to note we are focusing on the C-Band (or conventional band) in the - nm wavelength range &#; not the L-Band (long &#;&#;nm) or S-Band (short &#;&#;nm). However, there are significant developments in the O-Band DWDM (- nm), sometimes referred to as LAN-DWDM, look for future announcement from us.

Filters pass the wavelengths of light that do not need to be dropped, and reflect through the wavelength(s) that are needed.

The three most common filter types for C-Band DWDM are: Thin Film filters (TFF), Flat-Top and Gaussian filters. They each have their own specific use cases depending on a myriad of variables including transceiver modulation, channel count, filter configuration and your system topology. Contact us to set up a call to see what fits your network best.

Yes, that&#;s a lot of information, which means there is a lot to consider when choosing the proper filter for your fiber optics.

A fiber optic splitter, on the other hand, takes the signal and &#; BOOM! &#; splits it. It can also be called an optical splitter or optical TAP.

Why would you want to split the signal of a fiber optic cable? To send the light into multiple directions, basically distributing the beam for multiple inputs and outputs. They&#;ve been important in passive optical networks for, as an example, a single PON interface to be shared among many subscribers.

In general, optical splitters have been widely used in PON networks. FTTH is one of the common application scenarios, and typical architectures are Optical Line Terminal (OLT) located in the central office (or head-end), to the Optical Network Unit (ONU) situated at the user end.

Of course, if the signal is split, the optical power output of the wavelengths is reduced by the number of splits. If you broadcast with Mbps, and split it 4 ways, you&#;ll be able to share Mbps at the end of each split. This is commonly referred to as a broadcast network.

There are &#;1xN&#; splitters &#; where the &#;N&#; is the number of splits, like 1x2, or 1x8. This is the split-ratio. There are also 2xN splitters. This allows two inputs into the split network, such as GPON and XGS-PON into the same split network.

So, it gets more complicated if you have, say, 2 signals going in and then split it to 64 endpoints. Because networks have greatly increased to serve more subscribers, this kind of scenario is not unusual. With the rapid growth of FTTx (FTTB, FTTH, etc.) there is a requirement for a higher split-ratio.

This, like everything in the networking world, has both advantages and disadvantages. Fiber optic splitters with higher split-ratios can share the optics, electronics, fiber and new install costs. Also, larger splits allow more flexibility and fiber management at the head end is simpler.

However, higher split-ratio splitters increases the endpoints sharing the same bandwidth from the OLT. PON Networks with longer distances and high-loss fiber cannot stand high split-ratios due to necessary optical power budgets.

Figure 1

The other disadvantage of high split-ratio is when you split a network with additional OLTs such as splitting a 1x64 into (two) 1x32&#;s, then you have to move an extreme number of fibers to accomplish this, impacting customers. So be mindful how many times you split the bandwidth from an OLT. And if you like cream in your coffee, or your peanut butter with jelly, we have coexistence modules that add both filters and splitters in the same device. This allows you to run DWDM services over the top of PON services on the same single fiber.

Figure 2 

Figure 3 &#; Drop and Continue WDM

While filters and splitters do different things, they can be used together to give you the results you want. But as you&#;ve seen, there are a lot of options and variations to choose from, so you need to determine what is required for your network beforehand so it can work at its most optimal.

Feel free to contact an account manager at Approved Networks to connect you with one of our solution experts for any of your fiber optic requirements.

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1. Basic Structural Differences Between Single-Mode and Multi-Mode Fibers

Differences in Outer Jacket Color

 

Easily distinguish between single-mode and multi-mode fibers with the secret of outer jacket color differences. According to the TIA-598C standard, it&#;s clear at a glance: a yellow outer jacket clearly identifies OS1/OS2 single-mode fibers, while the OM series multi-mode fibers are represented by orange for OM1/OM2, aqua for OM3/OM4, and the latest OM5 multi-mode fibers use a lime green outer jacket. This color coding makes fiber identification both intuitive and efficient.

Figure 1: Comparison of Outer Jacket Colors for Single-Mode and Multi-Mode Fibers

Core Diameter Differences

The significant differences in core structure between single-mode fiber (SMF) and multi-mode fiber (MMF) mainly lie in the core diameter. SMF, with its extremely thin 9-micron core diameter, focuses on the precise transmission of a single mode of light, particularly excelling at nm, nm, and WDM wavelengths with low dispersion and high bandwidth performance. In contrast, MMF has a wider core diameter, typically 50/62.5 microns, capable of carrying multiple modes of light transmission. However, this also introduces complexities in the transmission process, such as limited bandwidth, increased dispersion, and higher attenuation. Therefore, when selecting optical fibers, it is crucial to carefully consider the actual application scenarios and balance the characteristics of both types to choose the most suitable option.

Figure 2: Comparison of Core Diameters Between Single-Mode and Multi-Mode Fibers

Light Source Differences

Figure 3: Comparison of Light Sources Used in Single-Mode and Multi-Mode Optical Fibers

2. Differences in Transmission Distance Between Single-Mode and Multi-Mode Optical Fibers

Single-mode optical fibers are renowned for their superior long-distance transmission capabilities, whereas multi-mode optical fibers excel in short-distance communication. When supporting various Ethernet speeds, the two types of fibers demonstrate different transmission distance advantages. The following is an overview of specific data to help you visually understand the performance of each fiber type in different scenarios.

Fiber optic types Base/1Gb(SX)
Ethernet Base/1Gb(LX)
Ethernet 10Gb
Ethernet 40Gb
Ethernet 100Gb
Ethernet 0S1/0S2 Single-mode fiber
(nm) 5Km 20Km 40Km 40Km 80Km OM1 Multimode fiber
(850nm) 275m 550m 33m / / OM2 Multimode fiber
(850nm) 550m 550m 82m / / OM3 Multimode fiber
(850nm) 550m 550m 300m 100m 100m OM4 Multimode fiber
(850nm) 550m 550m 550m 150m 150m OM5 Multimode fiber
(850nm) / / 550m 440m 150m

Table 1: Comparison of Transmission Distances Between Single-Mode and Multi-Mode Optical Fibers

Despite the significantly superior transmission distances of single-mode optical fibers at 1G and 10G speeds compared to multi-mode optical fibers, they have not completely replaced multi-mode fibers in the specific domain of data centers. This is because, for the short-distance transmission needs commonly found in data centers, the performance difference between single-mode and multi-mode fibers is minimal. However, multi-mode fibers have a distinct advantage in terms of lower cost. This is especially true for OM3 and OM4 grade multi-mode fibers, which not only meet current high-speed network demands but also show strong support capabilities for future higher speeds. Therefore, even in the era of high-speed networks, multi-mode fibers maintain strong market demand and remain an important choice in data center construction.

3. Cost Differences Between Single-Mode and Multi-Mode Optical Fibers

When constructing a fiber optic transmission system, the multi-mode fiber solution demonstrates significant cost advantages. Specifically, a multi-mode transmission system, including optical modules and fiber patch cords, has an overall cost ranging from approximately 3,300 to 5,300 yuan. In contrast, the cost of a single-mode system exceeds 6,700 yuan, resulting in a price difference of several thousand yuan between the two. Therefore, choosing multi-mode fiber not only allows for superior transmission performance but also effectively reduces the cost of system setup, achieving both performance and economic optimization.

 

 

4. Frequently Asked Questions About Single-Mode and Multi-Mode Optical Fibers

 

&#;. Can single-mode and multi-mode optical fibers be mixed and used together?

Due to the fundamental differences in transmission modes, directly connecting single-mode and multi-mode optical fibers will result in significant link loss and reduced line stability. However, this obstacle can be easily overcome by using special single-mode to multi-mode conversion patch cords (also known as mode converters), allowing seamless connectivity between single-mode and multi-mode links while ensuring efficient and stable data transmission.

 

&#;. Can multi-mode optical modules be used with single-mode optical fibers?

It is not advisable to directly use multi-mode optical modules with single-mode optical fibers. The smaller core diameter of single-mode fibers and the relatively larger light divergence angle of multi-mode optical modules result in rapid signal attenuation during transmission, potentially causing the signal to disappear completely before reaching its destination, severely impacting communication quality.

 

&#;. Can single-mode optical modules be used with multi-mode optical fibers?

While multi-mode optical fibers are not directly compatible with single-mode optical modules, the stable operation of single-mode modules such as BASE-LX on multi-mode fibers can be achieved with the help of fiber transceivers and other conversion devices. This conversion solution resolves the connectivity issues between single-mode and multi-mode optical modules, ensuring efficient data communication.

 

&#;. How to choose between single-mode and multi-mode optical fibers?

When choosing between single-mode and multi-mode optical fibers, it is crucial to balance transmission distance and cost according to the specific application scenario. For short-distance transmissions up to 550 meters, multi-mode optical fibers are preferred for their lower cost and higher efficiency. For transmission distances extending beyond several kilometers, single-mode optical fibers demonstrate clear advantages with their stable transmission performance and longer reach.

 

Single-mode and multi-mode optical fibers each have their strengths and are favored in different application domains. Single-mode optical fibers, with their superior performance, dominate the construction of metropolitan area networks and passive optical networks (PON). On the other hand, multi-mode optical fibers, known for their cost-effectiveness and flexibility, shine in enterprise networks and data center environments. When making a decision, the key is to accurately understand the actual cabling needs and scenario characteristics to ensure the chosen fiber type perfectly matches, thereby promoting efficient and stable network operation.

With its unparalleled high-speed transmission capability and massive capacity advantage, fiber optics stands out as a shining star in the communications industry. In the world of fiber optics, single-mode and multi-mode fibers serve as two major pillars. They not only differ significantly in geometric structure but also exhibit distinct transmission performance characteristics, which directly impact the breadth and efficiency of their practical applications. This article aims to deeply explore and elaborate on the core differences between these two types of fibers and their application scenarios, providing readers with a precise guide for fiber selection to ensure your network architecture is both efficient and robust.The significant differences in core structure between single-mode fiber (SMF) and multi-mode fiber (MMF) mainly lie in the core diameter. SMF, with its extremely thin 9-micron core diameter, focuses on the precise transmission of a single mode of light, particularly excelling at nm, nm, and WDM wavelengths with low dispersion and high bandwidth performance. In contrast, MMF has a wider core diameter, typically 50/62.5 microns, capable of carrying multiple modes of light transmission. However, this also introduces complexities in the transmission process, such as limited bandwidth, increased dispersion, and higher attenuation. Therefore, when selecting optical fibers, it is crucial to carefully consider the actual application scenarios and balance the characteristics of both types to choose the most suitable option.Figure 3: Comparison of Light Sources Used in Single-Mode and Multi-Mode Optical FibersSingle-mode optical fibers are renowned for their superior long-distance transmission capabilities, whereas multi-mode optical fibers excel in short-distance communication. When supporting various Ethernet speeds, the two types of fibers demonstrate different transmission distance advantages. The following is an overview of specific data to help you visually understand the performance of each fiber type in different scenarios.Despite the significantly superior transmission distances of single-mode optical fibers at 1G and 10G speeds compared to multi-mode optical fibers, they have not completely replaced multi-mode fibers in the specific domain of data centers. This is because, for the short-distance transmission needs commonly found in data centers, the performance difference between single-mode and multi-mode fibers is minimal. However, multi-mode fibers have a distinct advantage in terms of lower cost. This is especially true for OM3 and OM4 grade multi-mode fibers, which not only meet current high-speed network demands but also show strong support capabilities for future higher speeds. Therefore, even in the era of high-speed networks, multi-mode fibers maintain strong market demand and remain an important choice in data center construction.Single-mode and multi-mode optical fibers each have their strengths and are favored in different application domains. Single-mode optical fibers, with their superior performance, dominate the construction of metropolitan area networks and passive optical networks (PON). On the other hand, multi-mode optical fibers, known for their cost-effectiveness and flexibility, shine in enterprise networks and data center environments. When making a decision, the key is to accurately understand the actual cabling needs and scenario characteristics to ensure the chosen fiber type perfectly matches, thereby promoting efficient and stable network operation.

If you want to learn more, please visit our website FWDM module.