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.

Industrialization of PLC splitter chip technology

Fiber optic communication network has become the cornerstone of today’s world of information transfer. With the further development of the network and market demand for communication bandwidth increases, the entire communication network to the part between the user’s last ten km and last km, the network part is also being optical fiber. FTTH becomes an important direction of the development of fiber optic communication network.

FTTH mainly uses PON network technology, which requires a large number of low-cost optical splitters and other optical passive. Optical splitter device is an integral part of FTTH, and with the promotion of FTTH, there would be a great market demand. The traditional preparation of optical splitter technology is fiber fused biconical taper (FBT) technology. Its characteristics are mature and simple technology. The disadvantage is that the assigned ones too large, and the device size is too large, which causedthe decrease in yield and the rising cost of single channel, shunt reactive stars uniformity will deteriorate. FBT technology based fiber optic splitter preparation techniques have been unable to adapt to the market demand.

As you can see from the perspective of development of optical devices, PLC technology has become a mainstream technology for large-scale preparation of high-performance and low-cost optical splitter. It is the use of PLC technology, to produce the optical splitter chip, coupled with the optical fiber array package, complete the preparation of the optical splitter. Its features are: small size of the device, the cost is relatively low, splitter good uniformity, at the same time, the technical threshold is relatively high, especially for production of more than large ones optical splitter, suitable for mass production. It can ensure that the light emitting device miniaturization, low cost and high performance. Analysis of PLC technology, you can see that the glass-based PLC technology has great advantages in terms of equipment investment, production costs, the optimal choice of production required for fiber-to-the-home, low-cost optical devices such as optical splitter.

International, PLC technology has been widely used in the miniaturization, high-performance optical device fabrication and production, in particular, the optical splitter chip. In China, however, the reality is that we have become a PLC encapsulation big country, but is limited to the optical splitter and optical device fabrication device coupled packaging and downstream industry chain, no one PLC chip Health line, PLC core device chip entirely dependent on imports. Which there is a problem that the core preparation technique of the PLC device lies in the outward, this has resulted in major cost control of the device is limited in the chip at the same time, which also led to the lack of technical support further to the high-end integrated chip development, severe hinder the development of our country in the PLC application.

PLC splitter chip manufacturing process PECVD (plasma enhanced chemical vapor deposition) and FHD (flame hydrolysis deposition) and ion exchange. The former two with the substrate material is a silicon-based silica, and the latter with the substrate material is glass. AWG (arrayed waveguide grating) chip production, Silica optical waveguide splitter chips can be produced on silica on silicon waveguide or glass waveguide. Production by ion exchange glass waveguide PLC chip domestic number of colleges and universities have been conducting research and development, technical appraisal sample has been reached the international advanced level of similar products. The breakthrough of the results from the glass material, preparation equipment, process conditions designed to chip a full range of core technology to master the the buried low loss and low polarization characteristics PLC chip core preparation techniques.

Characteristics of the technology investment, equipment operation and low maintenance costs, simple process conditions, the production of optical passive low transmission loss and polarization characteristics with matching coupling of the fiber loss, environmental stability, and manufacturing costs low, very suitable in need of the PLC production line, can be used for producing low-cost fiber-to-the-home integrated optical splitter chip. Further pilot research and development, to solve adapted to the production of core technology, will be able to achieve your PLC splitter chip mass production.

In fact, in addition to the production of optical splitter chip, glass-based PLC technology R & D production environment with a wide range of other potential applications, for example, can be applied to detect the required light sensor.

Source: FiberStore

Fiber Optic Transmission

Optical fiber may be the medium of choice for high capacity digital transmission systems and speed local area network. Besides these applications, optical fiber is also used to transmit microwave signals for cable tv, cellular radio, WLAN and microwave antenna remoting. To deliver microwave over optical fiber, the microwave signal is converted into optical form in the input from the fiber and at the creation of the fiber, it’s converted back to electrical signal. The benefit of fiber transmission of microwave is reduced losses in accordance with metallic media (e.g. copper coaxial cable). This leads to longer transmission distance without signal amplification or utilization of repeaters.

There are two approaches to optical signal modulation and recovery. The very first type is IMDD (Intensity Modulation Direct Detection) and also the second type is Coherent Detection. In IMDD, the optical source intensity is modulated through the microwave signal and also the resulting intensity modulated signal passes through the optical fiber to a photodiode where the modulation microwave signal is converted to electrical domain. In Coherent Detection, the optical source is modulated in intensity, frequency or phase by the microwave signal. The modulated signal goes through the optical fiber towards the receiver where it is mixed with the creation of a local oscillator (LO) laser. The combined signal is converted to electrical domain using a photodiode. This produces an electric signal dedicated to the main difference frequency between the optical source and the LO laser (i.e. intermediate frequency). This signal is further processed to recuperate the analog microwave signal.

RFoG (Radio Frequency over Glass) is the cable operators’ implementation of microwave transmission over optical fiber where the coax portion of the HFC (Hybrid Fiber Coax) is substituted with a single fiber, passive optical network architecture (PON). RFoG allows cable operators to deploy fiber connectivity to customer premises (FTTP) while keeping its existing HFC and DOCSIS infrastructure. Such as the HFC architecture, video controllers and knowledge networking services are fed through a CMTS/edge router.

These electrical signals are then converted to optical and transported via a 1550 nm wavelength via a wavelength division multiplexer (WDM) and a passive optical splitter to a R-ONU (RFoG Optical Network Unit) located at the customer premises. R-ONUs terminate the fiber connection and convert the traffic to RF for delivery over the in-home network. Video traffic could be fed over coax to a set-top box, while voice and knowledge traffic could be delivered to an embedded multimedia terminal adapter (eMTA), The return path for voice, data, and video visitors are on the 1310 nm or 1590 nm wavelength to some return path receiver, which converts the optical signal to RF and feeds it back into the CMTS and video controller.

The benefit of radio-over-fiber technologies are that it centralizes the majority of the transceiver functionality by transmitting the microwave signals within their modulated format over fiber. This reduces the number of access suggests antennas with amplifiers and frequency converters. In-building passive picocell for GSM or UMTS is implemented using radio-over-fiber. Wireless base stations are located in a central communications room as well as their outputs/inputs fed through RF multiplexers to lasers/photodiodes contained within the optical transceiver hub. The modulated optical signals are linked to/from the remote antenna units (AUs) within the building using single-mode optical fiber. The bottom station utilizes a combined detector/optical modulator, that is directly coupled to the antenna, to ensure that no electrical amplification or any other processing is needed.

Source: http://www.fiberstore.com/

PLC Splitter Production and Packaging

With the recovery of optical fiber communication industry and the development of FTTX, the spring of fiber optic splitter market is coming.

There are two types of optical splitter, which are Fused fiber splitter and PLC splitter. PLC splitter is a hot research today, with a good prospect of application. PLC splitter package, however, is the difficulty in manufacturing.

The PLC splitter Package refers to the planar waveguide splitter on the light guide path (waveguide) with the fiber in the fiber array aligned one by one, and then stick with specific adhesive (such as epoxy glue) together with the technology. Wherein the alignment accuracy of the PLC splitter and an optical fiber array is the key technology. PLC splitter package involves a six-dimensional optical fiber array and optical waveguides in close alignment difficult. When the manual, the drawback is the low efficiency, poor reproducibility, human factors and is difficult to achieve large-scale production.

PLC splitter Production
PLC splitter using semiconductor technology (lithography, etching, developing technology) production. Multi-channel optical fiber array and the optical waveguide array is located on the upper surface of the chip, branching function is integrated on-chip is a chip on the splitter 1,1; Then, the ends of the chip, respectively coupling the input terminal and an output terminal package.

Compared with Fused Splitter, PLC splitter has these advantages: (1) loss wavelength is not sensitive to light, to meet the different wavelengths of the transmission needs. (2) spectroscopic uniform signal can be uniformly allocated to the user. (3) compact structure, small size, can be installed directly in the various existing junction box, without leaving a lot of space for installation. (4) only a single device shunt channel can achieve much more than 32 channels. (5) The multi-channel, low cost, stars ones more and more obvious cost advantages.

At the same time, the main drawback of the PLC splitter: (1) device fabrication process complexity, high technical threshold, the chip by several foreign companies to monopolize the domestic bulk package produced by very few companies. (2) relative to the higher cost of Fused Splitter more at a disadvantage, especially in the low channel splitter.

PLC splitter Packaging Technology
PLC splitter package process includes coupling alignment and bonding operations. Coupling of the PLC splitter chip and the optical fiber array is aligned with both manual and automated, and they depend on the hardware with the six-dimensional precision trimming frame, the light source, power meter, microscopic observation system, while the most commonly used are self-aligned , it is through the optical power feedback closed-loop control is formed, and therefore high coupling efficiency docking accuracy and docking.

PLC splitter has 8 channels and each channel must be accurately aligned to ensure that the relative position between the respective channels due to the manufacturing process of the waveguide chip and an optical fiber array (FA), so only the PLC splitter and the first channel of the FA and 8-channel simultaneous alignment can ensure that other channel aligned, thus reducing the complexity of the package. The most important in the packaging operation at the technical difficulty is the highest coupling alignment operation, it comprises two steps First Harmonic precise alignment. First tune the purpose is to enable the waveguide to light through; the purpose of precise alignment is precise positioning of the completion of the preferred optical power of the coupling point, and it is realized by the program to search the maximum optical power.