XENPAK Transceiver Modules Overview

by Fiber-MART.COM

Over the years of 10GbE’s existence, there have been numerous different form factors and optics types introduced. Although the newest SFP+ transceivers offer a much smaller form factor and the ability to offer 1G/10G combo ports on hardware for the first time, the oldest form factor XENPAK remains very popular as the install base is large.

fiber-mart XENPAKBecause of continued breakthroughs in component-level integration, it became possible to package a “transponder” in increasingly smaller packages. At the same time, a market need arose for systems with more than one 10 Gbps optical port on a single optical interface card and an interest to leverage the same “hot pluggability” feature that was available with the SFP modules that covered lower data rates. The density and pluggability issue was in particular true for 10GbE applications but also for SDH/SONET applications.

A new MSA became available, called the XENPAK-MSA, to address the above-mentioned market needs. XENPAK MSA was instigated by Agilent Technologies and Agere Systems, that defines a fiber-optic or wired transceiver module which conforms to the 10GbE standard of the IEEE 802.3 working group. The MSA group received input from both transceiver and equipment manufacturers during the definition process. XENPAK has been replaced by more compact devices providing the same functionality. The XENPAK MSA was publicly announced on March 12, 2001 and the first revision of the document was publicly released on May 7, 2001. The most recent revision of the MSA, Issue 3.0, was published on September 18, 2002. The result covered all physical media dependent (PMD) types defined by the IEEE at that time for 802.3ae 10GbE.

Although the XENPAK agreement received early support, its modules were thought to be overly large for high density applications. As of 2010, vendors generally changed to use XFP modules for longer distances, and Enhanced small form-factor pluggable transceivers, known as SFP+ modules, for higher densities. The newer modules have a purely serial interface, compared to the four “lane” XAUI interface used in XENPAK. Like the move from GBIC to SFP, the move from XENPAK to SFP+ seems inevitable. However, XENPAK modules are still needed in the market currently.

The XENPAK housing is equipped with two SC optical connectors, and its board attachment scheme requires a cut-out in a PCB with alignment to a mating PCB connector. Unlike the SFP pluggable device, the XENPAK package was intended to be fully EMI compliant; hence a cage or guidance system is not required. An industry standard 70-pin electrical connector provides the electrical interface. The input and output data signals are transmitted according to a new electrical interface specification, called XAUI, which was defined in IEEE 802.3ae. In short, the XAUI interface specification is based on four bidirectional lanes carrying 3.125 Gbps per channel. This setup simplified electrical trace management on the host PCB board relative to the 300-pin transponder, which required 16 parallel electrical channels per 10 Gbps optical signal. However, it also required that each trace carry a higher data rate. In order to simplify design and layout, additional overhead processing was added to the signal with which to correct for signal integrity challenges in the host PCB. The four 3.125 Gbps XAUI lanes give an aggregate bandwidth of 12.5 Gbps in order to transmit a 10.3125 Gbps optical signal.

While use in SDH/SONET applications was foreseen in principle, most versions are specifically aimed at 10GbE applications, where large volumes were expected.

Many tranceiver users faced difficulties applying XENPAK devices, mainly due to the module’s size, required board cut-out, and associated thermal issues. The market requested that an alternative smaller sized package be defined that would not require a board cut-out. Three solutions have been proposed: XGP, X2 and XPAK. The application area is the same as for XENPAK, 10GbE and Fibre Channel, but SDH/SONET applications are also foreseen.

The XGP concept has since been abandoned due to lack of agreement on a specification.

The two remaining and competing MSAs are the X2 and XPAK. These were developed around the middle of 2002, both using the same 70-pin electrical interface connector that was required for XENPAK. However, unlike the XENPAK, both the X2 modules and XPAK modules require a guiding/cage system. Both of the packages are of smaller size than XENPAK. The first parts available to the market were intended for 10GbE applications, and the input and output data signals are according to the XAUI specification as for XENPAK. Versions accommodating SDH/SONET STM-64/OC-192 applications are also foreseen, where the electrical interface would be addressed with four 2.5 Gbps data signals based ipon the OIF SFI4 Phase 2 based electrical interface specification.

Differences Between PLC Splitters and FBT Coupler

by Fiber-MART.COM

FBT Coupler and PLC splitter Tech

 

PLC Splitter

 

Planar Lightwave Circuit (PLC) splitter, PLC splitters are used to distribute or combine optical signals. It is based on planar lightwave circuit technology and provides a low cost light distribution solution with small form factor and high reliability. Planar lightwave circuit (PLC) splitter is a type of optical power management device that is fabricated using silica optical waveguide technology to distribute optical signals from Central Office (CO) to multiple premise locations.

 

FBT Coupler

 

Fused biconical taper,this is traditional technology to weld several fiber together from side of the fiber.

 

2. Comparison between FBT and PLC.

 

PLC splitter

 

SpliSplit Ratio (Max): 1*64 splits

Eveness: Can split light evenly

Size: Compact size

 

FBT coupler

 

Split Ratio: 1*8 splits

Eveness: Eveness is not very precise

Size: Big size for multi splits

 

TDL (Temperature Dependent loss)

 

Due to the manufacturing process and to the sensitivity of the fused region and of the splices integrated in the device, Fused coupler manufacturers have to specify also the TDL value. for a 1×2 Fused coupler, a typical value is +/10.15dB for a temperature range from -5 to +75 centigrade . At the first sight, it could look good, but we have here again to take into account the cascading effect. To make the comparison with 1×8 PLC splitter we have to multiply 0.15 by 3 (3 1×2 for each arm) to finally obtain 0.45dB.

 

PLC splitter works from -40 to 85 centigrade with a typical TDL of out +/- 0.25dB (-5 to 75 centigrade:+/-0.15dB)

 

Please note that this TDL effect is already included in the Max. insertion loss specifications available on data sheets.

 

PDL (Polarization dependent loss)

 

An lon-exchange PLC splitter shows a PDL much less than 0.2 dB independently from the split-ratio. A 1×2 fused coupler PDL ranges from 0.1 to 0.15dB.Also in this case, we have to cascade discrete 1*2 Fused coupler to obtain the desired split-ratio, Then also PDL will be increased.

 

A 1×8 fused coupler will show up to 0.45dB PDL, what is more than the double of a 1×8 PLC splitter.

 

Reliability

 

As previously explained, to fabricate  1×8 fused coupler, you need 7discrete 1×2 couplers and 6 splices. The risk of failure of a device, normally calculated by parameter called FIT(failure in time), is typically low for a single 1×2 fused coupler, but in the case of a 1×8 fuse fused coupler ,it has to be at lease multiplied by 7 and in addition to add the risk associated to the massive presence of splices in the circuits. As everybody knows, a splice is a potential failure point in a system to be minimized a s much as possible.At the contrary, a PLC splitter knows only 2 critical  points: input and output

 

People take advantage of fiber optic splitter that will send or simply combine optical signals in a good many products, which include FTTH solution, or anything else. Once in a while contain a challenge: Will certainly Make the most of PLC Splitter or FBT Coupler?

 

When you undertake compare, came across undertake compare meant for tools within the same exact split-ratio.

 

The figure 1 shows the insertion loss plot of a standard 1×8 PLC splitter from 1250 to 1650 nm. You can observe the maximum insertion loss including the water-peak in E band region(1360 to 1460 nm) and also the excellent uniformity out of this plot.

 

Typical value is 9.8dB for insertion loss and 0.5dB for uniformity.

 

A 1×2 fused coupler insertion loss plot is showed in the figure 2.if you analyze the operating wavelength range from 1250 to 1650 nm as for PLC splitter you will still find an overall good performance level. But that’s a single 1×2 fused coupler, so you are not comparing the same devices.

 

The 3rd plot represents the insertion loss spectral behavior for 1×8 fused coupler. To fabricate a 1×8 fused coupler device each arm have to be manufactured using 3 cascaded (spliced) 1×2 couplers. it means that the “worst” arm could show 10.8dB insertion loss max and the uniformity will be 3dB.

Fibre optic splicing introduction

Fibre optic splicing introduction

Rather than using optical fibre connectors, it is possible to splice two optical fibres together. An fibre optic splice is defined by the fact that it gives a permanent or relatively permanent connection between two fibre optic cables. That said, some manufacturers do offer fibre optic splices that can be disconnected, but nevertheless they are not intended for repeated connection and disconnection.

There are many occasions when fibre optic splices are needed. One of the most common occurs when a fibre optic cable that is available is not sufficiently long for the required run. In this case it is possible to splice together two cables to make a permanent connection. As fibre optic cables are generally only manufactured in lengths up to about 5 km, when lengths of 10 km are required, for example, then it is necessary to splice two lengths together.

Fibre optic splices can be undertaken in two ways:

• Mechanical splices
• Fusion splices

The mechanical splices are normally used when splices need to be made quickly and easily. To undertaken a mechanical fibre optic splice it is necessary to strip back the outer protective layer on the fibre optic cable, clean it and then perform a precision cleave or cut. When cleaving (cutting) the fibre optic cable it is necessary to obtain a very clean cut, and one in which the cut on the fibre is exactly at right angles to the axis of the fibre.

Once cut the ends of the fibres to be spliced are placed into a precision made sleeve. They are accurately aligned to maximise the level of light transmission and then they are clamped in place. A clear, index matching gel may sometimes be used to enhance the light transmission across the joint.

Mechanical fibre optic splices can take as little as five minutes to make, although the level of light loss is around ten percent. However this level of better than that which can be obtained using a connector.

Fusion splices form the other type of fibre optic splice that can be made. This type of connection is made by fusing or melting the two ends together. This type of splice uses an electric arc to weld two fibre optic cables together and it requires specialised equipment to perform the splice. The protective coating from the fibres to be spliced is removed from the ends of the fibres. The ends of the fibre optic cable are then cut, or to give the correct term they are cleaved with a precision cleaver to ensure that the cuts are exactly perpendicular. The next stage involves placing the two optical fibres into a holder in the fibre optic splicer. First the ends if the cable are inspected using a magnifying viewer. Then the ends of the fibre are automatically aligned within the fibre optic splicer. Then the area to be spliced is cleaned of any dust often by a process using small electrical sparks. Once complete the fibre optic splicer then uses a much larger spark to enable the temperature of the glass in the optical fibre to be raised above its melting point and thereby allowing the two ends to fuse together. The location spark and the energy it contains are very closely controlled so that the molten core and cladding do not mix to ensure that any light loss in the fbre optic splice is minimised.

Once the fibre optic splice has been made, an estimate of the loss is made by the fibre optic splicer. This is achieved by directing light through the cladding on one side and measuring the light leaking from the cladding on the other side of the splice.

The equipment that performs these splices provides computer controlled alignment of the optical fibres and it is able to achieve very low levels of loss, possibly a quarter of the levels of mechanical splices. However this comes at a process as fusion welders for fibre optic splices are very expensive.

Mechanical and fusion splices

The two types of fibre optic splices are used in different applications. The mechanical ones are used for applications where splices need to be made very quickly and where the expensive equipment for fusion splices may not be available. Some of the sleeves for mechanical fibre optic splices are advertised as allowing connection and disconnection. In this way a mechanical splice may be used in applications where the splice may be less permanent.

Fusion splices offer a lower level of loss and a high degree of permanence. However they require the use of the expensive fusion splicing equipment. In view of this they tend to be used more for the long high data rate lines that are installed that are unlikely to be changed once installed.