Tag Archives: OLT

How to Ensure a High Quality PLC Splitter?

PLC (Planar Lightwave Circuit) splitter is an important component in PON (passive optical network) where a single optical input is split into multiple outputs. This makes it possible to deploy a Point to Multi Point physical fibre network with a single OLT (optical line terminal) port serving multiple ONTs (optical network terminal). The most common split ratios are 1:N or 2:N. N represents the output ports, usually as 2, 4, 8, 16, etc. The optical input power is distributed uniformly across all output ports. The PLC splitter shares the cost and bandwidth of the OLT and reduces fibre lines. This article will tell about how to keep a high quality PLC splitter from manufacturing to testing sides.


Key Manufacturing Steps of PLC Splitter

PLC splitter is composed by many miniature parts. Among them, there are three main components: fibre array for the input and output, and the chip. These three main components decide whether the PLC splitter is of good quality or not. Let’s see the key manufacturing steps of a PLC splitter.

Step1. Components Preparation

The PLC circuit chip is designed and embedded on a piece of glass wafer. Each end of the glass wafer is polished to ensure high precision flat surface and high purity. The V-grooves are grinded into a glass substrate. A single fibre or multiple ribbon fibre is assembled onto the glass substrate. This assembly is polished.

Step2. Alignment

After preparing the three components, it’s time for alignment. The input and output fibre array is set on a goniometer stage to align with the chip. Physical alignment between the fibre arrays and the chip is monitored through the power level output from the fibre array. Epoxy is then applied to the fibre array and the chip to affix their positions.

Step3. Cure

The assembly will be placed in a UV chamber to be fully cured at a controlled temperature.

Step4. Packaging

The bare aligned splitter is assembled into a metal housing where fibre boots are set on both ends of the assembly. A temperature cycling test will be done for a final screening to ensure the final product condition.

Step5. Testing

Optical testing items include insertion loss, uniformity and polarization dependent loss. This testing is to ensure the splitter compliant to the optical parameters in GR-1209 CORE specification.

Testing Standards of PLC Splitter

Then how to determine the quality of a PLC splitter? The GR-1209 standards provides comprehensive optical performance criteria. The following will introduce these specifications such as optical bandpass, insertion loss, return loss, uniformity and directivity.

Optical Bandpass

In a PON system, the downstream transmission uses 1490nm wavelength and 1310nm wavelength for the upstream transmission. Besides, the requirement for RF video overlay and network testing/maintenance should also be considered. The transmission wavelength for RF video is 1550 nm. And the wavelengths for networking testing and maintenance are 1550 nm and 1625 nm. So the standard opterating wavelength for a PON splitter is determined as 1260~1650 nm which covers most of the optical bands.

Insertion Loss

The optical splitter has the largest attenuation in a PON system. The insertion loss transfers from the input port to the output port. In order to conserve the power of a PON system, the insertion loss should be reduced to the least. There are formulas to calculate the maximum insertion loss of an optical splitter in a PON system according to the GR-1209 standard: 0.8 + 3.4 log2N (for 1xN optical splitter) and 1.0 + 3.4 log2N. To decide if the insertion loss is in the qualified range, you need to choose one formula to calculate.

Return Loss

Optical return loss is part of the power transferred from one input port back to the same input port or from an output port back to the same output port. A high return loss will influence the data transmission quality. So it’s important to minimize the noise to keep the PON system power for a better transmission.


Uniformity means the maximum insertion loss value between one input port and any two output ports or between two input ports and one output port. This can ensure that the transmission power at each splitter output port is the same in a PON system to simplify the network design.


Directivity is the part of power transferred from one input port to another input port or from an output port to another output port. For a 2xN optical splitter, when light injects into one of the input ports, light doesn’t only propagate out of the output ports. Some of the light propagates back through the second input port. And when the light injects into one of the output ports, light propagates back through the other output ports. In a bidirectional transmission system such as a PON, directivity is useful to reduce signal crosstalk. A high directivity value will increase the insertion loss due to the optical power loss.


FS.COM provides a variety of PLC splitters including 1×2, 1×4, 1×8, 1×16, 1×32, 1×64; 2×2, 2×4, 2×8, 2×16, 2×32, 2×64 in various package options, which offer cost-effective solutions for your applications. To ensure high performance, we have set a quality assurance program for PLC splitter. We always care every detail both in manufacture and testing. For detailed information, please contact us via sales@fs.com.

Brief Introduction of Fibre Optic Splitter

Fibre optic splitters are quite important in today’s optical network. Splitters can help users maximize the functionality of optical network circuits. A fibre optical splitter is a passive optical device that can split, or separate, an incident light beam into two or more light beams. These beams may or may not have the same optical power as the original beam. The outputs of a splitter can have various degrees of throughput. And that is very useful to decide whether the splitter is used for network monitoring or for a loss budget in a passive optical network (PON) architecture when designing optical networks. This article will give brief introduction of fibre optical splitter.

There are two kinds of the most commonly used fibre optical splitters. And they are planar lightwave circuit (PLC) and fused biconical taper (FBT). PLC splitters (as shown in the following picture), from the name, it’s easy to find out that PLC splitter is based on planar lightwave circuit technology. It uses an optical splitter chip to divide the incoming signal into multiple outputs. It consists of three layers including a substrate, the waveguide, and the lid. The waveguide layer accepts the incoming optical signal and passes it to the outputs. FBT splitter is fused with a heat source similar to a fusion splice. Fibres are aligned in a group to create a specific location and length and will be fused with heat to meet the desired parameters such as insertion loss. Fused fibres are put in a V-shaped groove and fixed in a silica tube with a mix of epoxy and silica powder to get the proper heat.


Fibre Optical Split Ratios

Fibre optical splitters vary in numbers of inputs and outputs. The split ratios are based on the network use of fibre optical splitters. In a PON architecture, it uses splitters to split a single fibre into multiple fibres to feed as many as 64 end users. A typical split ratio in PON application is 1:32, or one in coming fibre split into 32 outputs.

Large split ratios like 1:32 or 1:64 are often found in some kind of housing. That’s because with so many fibres related to these splitters, a platform should be used to manage the splitter modules, patch modules, patch cables, etc. Most often a high-density fibre bay is required so that the splitters can be all placed in a distribution site or a PON enclosure. The PON cabinet plays a significant role in today’s applications since the space is so limited. When it comes to a high-density frame with varying split ratios and large number of patch cords, the distribution frame is critical for a good cable management.

Cost Saving in FTTx/PON Applications

As the city grows and subscribers increase, the network architect must deal with multiple distribution points and backhaul. To meet so many subscribers’ requirements, the flexibility in head-end locations, distribution points and split ratios becomes more significant. To network service provider, saving capital and operational costs is important.

On one side, fibre optical splitters can save fibre cost by reducing the fibre usage and that’s why they are so important in FTTx/PON networks. Using a single fibre to feed as many as 64 end users significantly reduces the fibre quantity. On the other side, the long-term operation costs can’t be ignored either in optical network splitter applications. That’s one of PON’s advantages. For example, it can decrease the power consumption.

Another way to save cost is to ease maintenance and increase the flexibility for smaller split ratios, which lead to more bandwidth per subscriber. For example, a service provider would likely need to split the optical terminal line (OLT) with a 1:2 splitter, and adjust the split ratios from there based on delivery to residential (1:32). These multiple split ratios can create flexibility in the network as long as the utilization of transport electronics such as OLT is concerned. Loss budget can be greatly influenced by the use of multiple splitters.


From the above content, to run a network architecture, the network success and cost should be paid attention. And fibre optical splitter is such a good device to increase the efficiency of optical infrastructure and save the capital and future operational cost.

EPON — An Ideal Optical Access Network Solution

In recent years, the telecommunications backbone has experienced huge growth. The tremendous growth of Internet traffic has far surpassed the network capacity. The “last mile” still remains the bottle neck between high-capacity local area networks and the backbone network. So a new technology for optical access network, which is simple, scalable but not expensive, is needed. And that is Ethernet passive optical network (EPON).

EPON Definition

EPON, unlike other PON technologies which are based on the ATM standard, is based on the Ethernet standard. This lets you utilise the economies-of-scale of Ethernet, and provides simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at the customer premises and at the central office. As with other Gigabit Ethernet media, it is well-suited to carry packetized traffic, which is dominant at the access layer, as well as time-sensitive voice and video traffic.

EPON Network

An EPON network includes two parts: an optical line terminal (OLT) and an optical network unit (ONU).

The OLT resides in the central office (CO). This could typically be an Ethernet switch or Media Converter platform. OLT is mainly designed for controlling the information float across the optical distribution network (ODN). OLT has two float directions: upstream (getting an distributing different type of data and voice traffic from users) and downstream (getting data, voice and video traffic from metro network or from a long-haul network and sending it to all ONU modules on the ODN.

The ONU resides at or near the customer premise, in a building, or on the curb outside. It uses optical fibre for connecting to the PON on the one side, while interfacing with customers on the other side.

EPON Upstream and Downstream Traffic

In an EPON, the process of transmitting data downstream from the OLT to multiple ONU is fundamentally different from transmitting data upstream from multiple ONUs to the OLT.

In the downstream direction (from network to user), Ethernet frames transmitted by OLT pass through a 1:N (N represents the number of subscribers each fibre can serve) passive splitter and reach each ONU. Splitting ratios are usually between 4 and 64. At the splitter, the traffic is divided into separate signals, each carrying all of the ONU–specific packets. When the data reaches the ONU, it accepts the packets that are intended for it and discards the packets that are intended for other ONUs.


In the upstream direction (from user to network ), due to the directional properties of a passive combiner (optical splitter), data frames from any ONU will only reach the OLT, not other ONUs. Frames in EPON from different ONUs transmitted simultaneously may collide. Thus, ONUs need to share the trunk fibre channel capacity and resources.


EPON Advantages

First, EPON uses a point-to-multipoint topology instead of point–to-point in the outside plant. Thus it saves much of the cost of running fibre from every customer to the CO, installing active electronics at both ends of each fibre and managing all of the fibre connections at the CO. And EPON also eliminates active electronic components, such as regenerators and amplifiers, and replaces them with passive optical couplers that are less-expensive, simpler, and longer lived than active ones. As to the cost of expensive electronic components and lasers in the OLT, it will be shared over many subscribers not paid by each subscriber.

Second, EPON offers high bandwidth to subscriber. The traffic rates of 1Gbps in downstream and return traffic of 800 Mbps have been achieved already. Compared with point–to-point technology, EPON is specially made to address the unique demands of the access work. So more bandwidth can be got by each subscriber.

At last, the main advantage of EPON is that it can eliminate complex and expensive asynchronous transfer mode (ATM) and SONET elements and simplify the networks dramatically. Traditional telecom networks use a complex and multilayered architecture. While this architecture requires a router network to carry IP traffic, ATM switches to create virtual circuits, add/drop multiplexers (ADM) and digital cross-connects to manage SONET rings, and point-to-point DWDM optical links.


EPON is suitable for Fibre-to-the-Home/Building/Business applications, including voice, data and video services. EPON is a shared network but with much higher bandwidth. It’s a highly attractive access solution for service providers to extend fibre into the last mile because of low cost and good performance, resulting from their nature as passive networks, point-to-multipoint architecture, and native Ethernet protocol.

A Guide for PON

Nowadays, there is a growing popularity of Video-on-Demand (VoD), VoIP and increased IPTV deployment. Providers aim to offering fibre-to-the-home (FTTH), (fibre-to-the-building) FTTB and fibre-to-the-curb (FTTC) solutions through advancing passive optical network (PON) technology. The term “PON” may confuse you for its complexity and extensiveness. Details are as followed.

PON is a single, shared optical fibre that uses inexpensive optical splitters to divide the single fibre into separate strands. It can build up a point-to-point topology supporting 1Gbps transmission to home and business typically within 20km. PON system is called “passive” because that there are no active electronics within the access network. It uses optical splitters to separate and collect signals rather than electrically powered switching equipment.

PON consists of an Optical Line Terminal (OLT) connected to multiple Optical Network Units (ONUs) via an Optical Distribution Network (ODN).

OLT: it is a device at the service provider’s central office, performing conversion between the electrical signals used by the service provider’s equipment and the fibre optic signals used by the passive optical network and coordinating the multiplexing between the conversion devices on the other end of that network.

ODN: it is used for distributing signals to users in a telecommunications network by optical fibre. ODN has been made up entirely of passive optical components particularly singlemode optical fibres and optical splitters.

ONUs: they are devices near end users, delivering traffic-load information provided by OLTs to each end user.PON System

PON system has achieved significant deployment in today’s FTTx networks especially in FTTH networks as the development of Gigabit passive optical network (GPON) and Ethernet passive optical network (EPON). Nowadays, GPON and EPON are the mostly widely used types of PON for their low cost, high bandwidth, great flexibility and easy management, etc.

GPON: it is defined by ITU-T recommendation series G.984.1 through G.984.6. It can transport not only Ethernet, but also ATM and TDM (PSTN, ISDN, E1 and E3) traffic. It supports services like carrying video and delivering video on single fibre distribution, allowing low-consuming transmission, more efficient maintenance, cabling and overall performance.

EPON: it is defined by the Ethernet standard rather than by the ATM standard, making you utilise the economies-of-scale of Ethernet. It can provide simple and easy-to-manage connectivity to Ethernet-based, IP equipment both at the customer premises and at the central office. It is perfect for voice and video traffic solution as with other Gigabit Ethernet media.GPON and EPON

 For more information about OLTs, Optical Splitters and ONUs, please visit FS.COM.