# Wavelength Selective Couplers and Splitters

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Wavelength Selective Couplers (or Splitters) are used to either combine or split light of different wavelengths with minimal loss. Light of two different wavelengths on different input fibers can be merged (combined) onto the same output fiber. In the reverse direction light of two different wavelengths on the same fiber can be split so that one wavelength goes to one output fiber and the other wavelength is output onto the other output fiber. The process can be performed with very little loss.

As the coupling length is wavelength dependent, the shifting of power between the two parallel waveguides will take place at different places along the coupler for different wavelengths. All we need to do is choose the coupling length carefully and we can arrange for loss free wavelength combining or splitting. These functions are shown in the figure below. The graph of power transfer shows how power input on one of the fibers shifts back and forth between the two waveguides. The period of the shift is different for the two different wavelengths. Thus in the left-hand section of the diagram (combining wavelengths) there will be a place down the coupler where all of the light is in only one waveguide. If we make the coupler exactly this length then the signals have been combined. On the right-hand side of the diagram the reverse process is shown where two different wavelengths arrive on the same input fiber. At a particular point down the coupler the wavelengths will be in different waveguides so if we make this the coupling length then we have separated the wavelengths exactly. In fact both the processes described above are performed in the same coupler—the process is Bi-Directional (BiDi). Thus the coupler on the left can operate in the opposite direction and become a splitter and the splitter on the right can operate in the opposite direction and become a coupler (combiner). Note that each coupler or splitter must be designed for the particular wavelengths to be used.

Commercial devices of this kind are commonly available and are very efficient. The quoted insertion loss is usually between 1.2 and 1.5 dB and the channel separation is quoted as better than 40 dB. “Wavelength flattened” couplers or splitters of this kind operate over quite a wide band of wavelengths. That is a given device may allow input over a range of wavelengths in the 1310 nm band up to 50 nm wide and a range of wavelengths in the 1550 nm band also up to 50 nm wide.

Power Input to an EDFA

On the left-hand side of the figure we see an example of coupling two different wavelengths into the same output fiber. At the input of an EDFA you want to mix the (low level) incoming signal light with (high level) light from the pump. Typically the signal light will be around 1550 nm and the pump will be 980 nm. In this case it is possible to choose a coupling length such that 100% of the signal light and 100% of the pump light leaves on the same fiber. A major advantage of this is that there is very little loss of signal power in this process.

Splitting Wavelengths for CWDM Systems

On the right-hand side of the figure we show an example of CWDM demultiplexing. A mixed wavelength stream with one signal in each of the 1300 and 1550 nm bands is separated into its two component wavelengths. A CWDM system like this might be used in a system for distributing CATV and advanced VOD services to people in their homes. One signal stream might be carried at 1310 nm and the other at 1550 nm. A resonant coupler is shown here operating as a splitter separating the two wavelengths. Note that an identical splitter could also be used to combine the two wavelengths with very little loss.

Adding the Management Channel in DWDM Systems

In DWDM systems where many channels are carried in the 1550 nm band there is often a requirement to carry an additional relatively slow rate channel for management purposes. A convenient way to do this is to send the management information in the 1310 nm band and the mixed DWDM stream in the 1550 band. Wavelength selective couplers are commonly used for this purpose. A management signal (a single wavelength) in the 1310 band is coupled onto a fiber carrying many wavelengths between 1540 nm and 1560 nm. Another similar device (wavelength selective splitter) is used to separate the signals at the other end of the link.

# FBG Sensor Multiplexing Techniques On WDM System

Fiber Bragg Grating (FBG) is a simple and low-cost filter built into the core of a wavelength-specific fiber cable. FBGs are used as inline optical filters to block certain wavelengths, or as wavelength-specific reflectors.

In many applications a large number of sensors need to be used to achieve a distributed measurement of the parameters. In particular, using sensors in smart structures is of interest where sensor arrays are bonded or embedded into the materials to monitor the health of the structure. FBG sensors have a distinct advantage over other sensors because they are simple, intrinsic sensing elements that can be written into a fiber, and many sensors can be interrogated through a single fiber.

The most straightforward multiplexing technique for FBG sensors is wavelength division multiplexing (WDM), utilizing the wavelength-encording feature of an FBG-based sensor. The WDM technique is based on spectral splicing of an available source specturm. Each FBG sensor can be encoded with a unique wavelength along a single fiber. Since we are operating in the wavelength domain, the physical spacing between FBG sensors can be as short as desired to give accurate distributed information of measurands.

A parallel topology is used to allow simultaneous interrogation of all the sensors in WDM, as shown in Figure 4.15. A1 x N fiber optic splitter is used to divide the optical reflection into N channels, In each channel a matched fiber grating detects the wavelength shift from a specific FBG sensor.

In the parallel scheme each filter receives less than 1/2N of optical power as a result of using 1 x N fiber splitter and fiber coupler. More FBG sensors lead to a larger power penalty. An improved scheme using a serial matched FBG array is reported by Brady et al, as shown in Figure 4.15(b). This scheme is claimed to allow the optical power to be used more efficently than in the parallel topology. As can be seen, however, a large power penalty still exists through the use of the reflection of matched fiber gratings. A revised verison of the serial scheme is proposed, in which the transmisson of the matched FBG is used to monitor the wavelength shift from the corresponding sensing FBG. This reduces the power penalty of 6 dB.

# GEPON Splitter Of Passive Optical Components

With the growing demand of broadband, Passive Optical Network (PON) is the most promising NGN (Next Generation Networking) technology to meet the demand currently. GEPON(Gigabit Ethernet Passive Optical Network) use WDM technology and it is with 1Gbps bandwidth and up to 20km working distance, which is a perfect combination of Ethernet technology and passive optical network technology.

GEPON Technology:

The GEPON (Gigabit Ethernet Passive Optical Network) system is composed of the Optical Line Terminal (OLT), Optical Distribution Network (ODN) and Optical Network Unit (ONU).The ODN consists of only passive elements splitters, fibre connector and fiber optics. PON means passive optic network, EPON is integrated with Ethernet technologies, and GEPON is a Gigabit EPON. GEPON system is designed for telecommunication use. This series of products features high integration, flexible application, easy management, as well as providing QoS function. The fiber network speed can reach up to 1.25GB/s and each EPON OLT (Optical Line Terminal) system can distribute into 32 remote ONU (Optical Network Unit) to build up the fiber passive network by a max 32 way optical splitter with the advantage of big capacity of data transmission, high security, flexibility of buildup network, mainly applies for FTTH (Fiber To The Home) projects, which can access to IP telephone, Broadband data and IPTV.

GEPON is a perfect combination of Ethernet technology and passive optical network technology. It eliminate the usage of active fiber optic components between OLT and ONU, this will greatly cut the cost and make the network easier to maintain. GEPON use WDM technology and it is with 1Gbps bandwidth and up to 20km working distance.

Optical Splitter Work In GEPON Network:

Passive Fiber Optic Splitters For GEPON Network,the Optical Splitter, also named beam splitter, is based on a quartz substrate of integrated waveguide optical power distribution device, the same as coaxial cable transmission system, The optical network system also needs to be an optical signal coupled to the branch distribution, which requires the fiber optic splitter, Is one of the most important passive devices in the optical fiber link, is optical fiber tandem device with many input terminals and many output terminals, Especially applicable to a passive optical network (EPON, GPON, BPON, FTTX, FTTH etc.) to connect the MDF and the terminal equipment and to achieve the branching of the optical signal.

GEPON splitter based on planar lightwave circuit technology and precision aligning process can divide a single/dual optical input(s) into multiple optical outputs uniformly, and offer superior optical performance, high stability and high reliability to meet various application requirements. Our standard modules with GEPON Splitter have “ABS-type” & “Rack-type”. We can also have the customized dimension. If you need the customized service,pls contact us for detail conditions for customization. Our customization includes branding FiberStore or OEM,modifying physical size and appearance and re-designing per customer requirements.

FiberStore provides some kinds of passive optical components,available components include couplers, planar splitters and wavelength division multiplexers (WDMs).We not oly provide the optical components,but also suppply the cheap fiber optic cable.

# Noun Explanation of Several Common Optical Passive Devices

Noun Explanation of Several Common Optical Passive Devices

1) What is the PON?

PON is the English abbreviation of Passive Optical Network. Because of its large transmission capacity, low maintenance cost and fiber dosage saving, PON has now become the main optical access technology in the world, and is widely used mainly by the fiber to the home (FTTH) network construction. PON is mainly comprised of OLT, optical splitter and ONU. According to the agreement, PON can be divided into EPON, GPON, WDM-PON and so on.

2) What is the optical passive device?

Optical passive device is a kind of optical components which does not rely on any outside optical or electrical energy, and can do some optical functions by their own, such as coupler, filter and so on. Its working principle complies with the physical and geometrical optics theory, while laser transceiver device based on photoelectric energy conversion is called active devices.

3) How is the optical passive device classified?

Optical passive devices can be classified according to their production process and functions. According to the different production process, optical passive devices can be divided into fiber optical passive devices and integrated optical passive devices. According to the different functions, they can be divided into optical connection devices, optical attenuator, optical splitter, optical wavelength distribution devices, optical isolation devices, optical switch, optical modem devices and so on.

4) What is the main technical indicators to evaluate optical passive devices?

The main technical indicators to evaluate optical passive devices are: insertion loss, return loss, bandwidth, with ups and downs, power allocation error, the wavelength isolation, channel isolation, channel width, extinction ratio, switching speed, speed and so on. Different devices have different requirements of technical indicators, but most of the optical passive devices need the requirements of low insertion loss, high reflection loss, and wide working bandwidth.

5) What is the PLC?

PLC is the English abbreviation of Planar Lightwave Circuit, namely the planar optical waveguide. The optical passive device and traditional vertical difference, PLC devices are used by semiconductor fabrication, which can integrate the optical components with different functions into one chip. PLC is the basic technology of photoelectric device integration, modularization, miniaturization. The devices those are used PLC technology include: optical splitter, arrayed waveguide grating (AWG), variable optical attenuator (VOA), variable optical attenuation combiner (VMUX), reconfigurable optical add-drop multiplexer (ROADM) and so on.

6) What are the advantages of PLC splitter compared to FBT optical splitter?
Compared with the traditional device FBT splitter used of FBT(Fused Biconical Taper) processing, PLC splitter has wide work wavelength channel loss, good uniformity, small volume, wide working temperature range, high reliability, is currently the preferred connection of OLT and ONU and the realization of optical signal power distribution PON the access network.

7) What is the difference between Full-band PLC splitter and three FBT window splitter?

Due to the working principle and the limit of process, traditional FBT splitter can generally meet the transfer at most three different wavelength, which is called the three window splitter. While the loss of PLC splitter is very low in a very wide wavelength range (1260-1650nm), so in addition to meet the three a window outside the commonly used, PLC splitter can also be used for transmission and management more work wavelength. So PLC splitter is called full-band splitter. The wavelength requirements of EPON and GPON standards were 13101490 and 1550nm, the next generation PON standard (such as WDM-PON) will require more work wavelength. The use of PLC optical branch devices can better adapt to the needs of future network upgrade and development.

# Common Passive Fiber Optical Splitters

Fiber optical splitter, also named fiber optic coupler or beam splitter, is a device that can distribute the optical signal (or power) from one fiber among two or more fibers. Fiber optic splitter is different from WDM(Wavelength Division Multiplexing) technology. WDM can divide the different wavelength fiber optic light into different channels, but fiber optic splitter divide the light power and send it to different channels.

Work Theory Of Optical Splitters

The Optical Splitters “split” the input optical signal received by it between two optical outputs, simultaneously, in a pre-specified ratio 90:10 or 80:20. The most common type of fiber-optic splitter splits the output evenly, with half the signal going to one leg of the output and half going to the other. It is possible to get splitters that use a different split ratio, putting a larger amount of the signal to one side of the splitter than the other. Splitters are identified with a number that represents the signal division, such as 50/50 if the split is even, or 80/20 if 80% of the signal goes to one side and only 20% to the other.

Some types of the fiber-optic splitter are actually able to work in either direction. This means that if the device is installed in one way, it acts as a splitter and divides the incoming signal into two parts, sending out two separate outputs. If it is installed in reverse, it acts as a coupler, taking two incoming signals and combing them into a single output. Not every fiber-optic splitter can be used this way, but those that can are labeled as reversible or as coupler/splitters.

Attenuation Of Fiber Optic Splitter

An interesting fact is that attenuation of light through an optical splitter is symmetrical. It is identical in both directions. Whether a splitter is combining light in the upstream direction or dividing light in the downstream direction, it still introduces the same attenuation to an optical input signal (a little more than 3 dB for each 1:2 split). Fiber optic splitters attenuate the signal much more than a fiber optic connector or splice because the input signal is divided among the output ports. For example, with a 1 X 2 fiber optic coupler, each output is less than one-half the power of the input signal (over a 3 dB loss).

Passive And Active Splitters

Fiber optic splitters can be divided into active and passive devices. The difference between active and passive couplers is that a passive coupler redistributes the optical signal without optical-to-electrical conversion. Active couplers are electronic devices that split or combine the signal electrically and use fiber optic detectors and sources for input and output.

Passive splitters play an important position in Fiber to the Home (FTTH) networks by permitting a single PON (Passive Optical Network) network interface to be shared amongst many subscribers. Splitters include no electronics and use no power. They’re the community parts that put the passive in Passive Optical Network and are available in a wide range of break up ratios, including 1:8, 1:16, and 1:32.

Optical splitters are available in configurations from 1×2 to 1×64, such as 1:8, 1:16, and 1:32. There are two basic technologies for building passive optical network splitters: Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC). FBT Coupler is the older technology and generally introduces more loss than the newer PLC Splitter.

# Summarize Optical Splitters From Fiberstore

Optical Splitters Introduction:

The Fiber Optic Splitter, also named beam splitter, is with multiple input and multiple output end fiber tandem devices, M * N is commonly used to represent a divider with M input and N output.,with coaxial cable transmission system, network system also needs to be light signal is coupled, branch, distribution, and the optical divider is needed for implementation.

Two Kinds Of Fiber Splitters:

Fiber optic splitters are important passive components used in fiber optic communications. Nowadays two kinds of fiber splitters are popular used, one is the traditional fused type fiber optic splitter, which features competitive prices, the other is PLC (planar lightwave circuit) fiber optic splitter ,which is compact size and suit for density applications. Both of these two types fiber splitters has its advantages to suit for different requirement.

Fused Biconic Tapered (FBT) fiber optic splitters are mature technology types, it is low cost and easy to make, but fused fiber optic splitters optical loss are sensitive to wavelength and this is big disadvantages. PLC fiber optic splitters are small size and wide working wavelength, they are more reliable, suitable to use in passive optical network fiber optic splitting, we supply the PLC Splitters including 1*N PLC splitter module and 2*N PLC splitter module .The common configurations are 1×4, 1×8, 1×16, 1×32 and 1×64 PLC Splitters;but 2×4, 2×8, 2×16, 2×32 configurations are also available.

The Theory For Optical Fiber Splitters:

Fiber optic splitter is a device that split the fiber optic light into several parts by a certain ratio.Fiber optic splitters enable a signal on an optical fiber to be distributed among two or more fibers. Since splitters contain no electronics nor require power, they are an integral component and widely used in most fiber optic networks. For example, a 1X4 LC type equal splitting ratio fiber optic splitter can split the fiber optic light signal into four equal 25% parts and sent to the 4 different channels, LC is the connector type on the splitters. Fiber optic splitter key parameters include the optical loss, splitting ratio, isolation, PDL, etc.The diagram below shows how light in a single input fiber can split between four individual fibers (1×4):

Fiber Optic Splitter Features:

• Single Mode, multimode, and PM fiber types
• Multiple port configurations
• Various splitting ratios, 50:50 to 1:99
• Tube type or Box type
• PC, UPC, and APC fiber optic connectors
• Available with FC, SC, ST, LC, and MU terminations