Category Archives: Fiber Testers & Tools

DWDM MUX/DEMUX Insertion Loss Test

During the selection of a DWDM MUX/DEMUX, the insertion loss should always be considered. Generally, a report including the insertion loss value of each port on the DWDM MUX/DEMUX, is usually attached with the product. These values are tested by professional testers. This post will illustrate how to test the insertion loss of DWDM MUX/DEMUX by using an easy-to-get optical power meter.

DWDM MUX insertion loss test

Products Required for Insertion Loss Test

We will use Cisco Catalyst 4948E switch and Cisco compatible DWDM SFP+ modules as light source to test the insertion loss of a 40-CH DWDM MUX/DEMUX provided by FS.COM. This DWDM MUX/DEMUX has a typical insertion loss of 3.0 dB. Channel 25 port and Channel 60 port will be tested. The products and tools required are listed as following:

DWDM MUX/DEMUX Insertion Loss Test Steps

First, install the 80km C25 DWDM SFP+ module in the SFP+ port of Cisco Catalyst 4948E. Second, connect the Tx port of the SFP+ module to the Rx port of Channel 25 port with a length of LC-LC simplex single-mode patch cable. Then, connect the TX port of the COM port to the optical power meter with a length of LC-SC simplex single mode patch cable.

optical interface cleaning

Please note to clean all the optical interfaces before connecting to ensure the accuracy of the testing result. The connection is shown in the following picture.

DWDM insertion loss test

Press the λ button to select the wavelength of 1550nm. Then, we will get the optical power value (2.68dB) of the signal from C25 80km DWDM SFP+ module. Light loss occurs when the optical signal pass LC-LC simplex SMF patch cable (Loss1), CH25 port, LC-SC simplex SMF patch cable (Loss2) and COM port (Loss 3) as shown in the above picture.

We get a simple formula here:

Input power – Insertion Loss (CH25) – Loss1-Loss2 -Loss3 = 2.68dB (REF value)

If we want to get the insertion loss value of Channel 25, the formula will be:

Insertion Loss (CH25) = Input power – Loss1 -Loss2 -Loss3 – 2.68dB (REF value)

We can set the 2.68dB as the reference value. And if we can test the optical power value of the channel 25 SFP+ after it experienced these three loss points, the difference value will be the insertion loss of the channel 25 channel port.

DWDM insertion loss test

As the com port could be regarded as an adapter, we will use an adapter to connect the LC-SC and LC-LC patch cables together. Then, connect them to the optical power meter as shown in the above picture, we can get the difference value which is 3.58dB. This value is the insertion loss of the Channel 25 port on this 40Ch DWDM MUX/DEMUX. This value might not be very accurate value, but it is close to it.

DWDM MUX/DEMUX Insertion Loss Testing Video

 

We have taken a video about how to test the 40CH DWDM MUX/DEMUX insertion loss with optical power meter. You can get more details in this video. All the products and tools in this video are provided by FS.COM. Kindly contact sales@fs.com or visit FS.COM for more if you are interested.

Overcome OTDR Dead Zone With Launch Fiber

OTDR is a popular fiber optic testing tool which can be used to test the fiber loss, and locate the faults in fiber optic links. However, the OTDR dead zone will affect the testing result and the application of OTDR. To overcome OTDR dead zone during fiber optic testing, launch fiber is being added between OTDR and optical fiber link under test. OTDR launch fiber comes in different types of packages. OTDR launch box and OTDR launch fiber ring are the most commonly used launch fibers.

Why Can Launch Fiber Overcome OTDR Dead Zone?

OTDR insert pulses of light into fiber optic link and measure the back reflection caused by fiber faults to locate the faults. If a long fiber link is required to be tested, a lot of optical power should be inserted into the optical fiber to make sure that the light can be seen at the other end. If powerful optical pulses are inserted into optical fiber, pulse width of the launched optical signal will be increased, which will cause the dead zone at a length of fiber and affect the testing result of OTDR. This dead zone might be hundreds or thousands meters long.

OTDR launch box

To minimize the affection of the OTDR dead zone during fiber optic testing. A length of long enough optical fiber is being added between the OTDR and the fiber under test. In this way, the OTDR dead zone will happen in this additional optical fiber. The launch fiber is actually a length of optical fiber which is long enough to cover the OTDR dead zone to increase the testing accuracy. Launch fiber is usually terminated with a connector on each end to connect the OTDR with the fiber link under test.

launch fiber

OTDR Test With Launch Fiber

OTDR launch fiber mainly has two designs, one is fiber ring design and the other is box design, separately known as launch fiber ring and OTDR launch box or OTDR dead zone box. The using of them is generally the same. Here offer two situations about how to use OTDR launch fiber.

OTDR testing with launch fiber

In some cables, launch cable is being used to cover the dead zone at the beginning of the fiber link. In these cases, OTDR launch fiber or OTDR launch box is deployed between the OTDR and the near end connection as shown in the above picture. This allows the accurate measurement of the fiber loss at the near end connection.

OTDR and launch fiber

In some cases, the fiber loss at the far end connection should also be tested. Then, the launch fiber can be installed added at the far end connection to work as a receive cable, as shown in the above picture.

Please note that the launch fiber you used for testing should have the same fiber types (OS2, OM1, OM2, OM3, OM4) as the optical fiber under test.

Conclusion

Using launch fiber to overcome OTDR dead zone is the choice in most cases, especially for long optical fiber testing. Let the OTDR dead zone occur in the launch cable to ensure the accurate testing result. Launch fiber is suggested to be added at the beginning and the end of the fiber optic link, if the light loss of the whole fiber link is required. If you want to need more specific details about OTDR launch box, kindly visit another article: Why Do You Need OTDR Launch Box

How to Use Optical Power Meter

To ensure the signal transmission quality in fiber optic network, optical power should be well controlled. Optical power should not be too high or too low. And it should be within the scope of the device’s requirement. To achieve accurate measurement, optical power meter is usually used to test the optical power. It is easy to use and can be really helpful during fiber optic network installation and maintenance.

Buttons on Optical Power Meter

The functions and operation of optical power meters provided by the market are similar. Generally there are four buttons on the optical power meter: power button, dBm/w button, REF button and λ button. The functions of these buttons are listed in the following:

  • Power button: turn the power meter on or off;
  • dBm/w button: shift between linear (mW) mode and logarithmic (dBm) mode;
  • REF button: press this button to set the current measured power as the referent point;
  • λ button: select the calibrated wavelength. The most commonly used wavelengths are 850nm, 980nm, 1310nm, and 1550nm.

Here takes an example of a typical handheld optical power meter (FOPM-104) which is designed by FS.COM as shown in the following picture.optical power meter

Adapter Type of Optical Power Meter

To use the optical power meter, a length of fiber optic patch cable is usually required to connect the optical power meter interface and the interface of devices requiring test. For instance, if the interface on the optical power meter is FC, the device for testing has a LC interface. Then a length of FC-LC fiber patch cable is needed. Some of the optical power meters have only one fixed optical interface. Some can provide replaceable optical adapter to fit different patch cables. The above mentioned FOPM-104 handheld optical power meter provides three type adapters: SC, FC and ST (as shown in the following picture).optical power meter adapter

For testing of fiber optic interface like LC, SC, ST and FC, this above power meter is enough. Some optical power meter might have two optical interfaces for common connectors. However, interface like MTP/MPO, optical power meter with special interface should be used. The following picture shows a MTP optical power meter provided by FS.COM, which can be used to test devices or components with MTP interfaces like 40G SR4 QSFP+ transceiver.MTP optical power meter

Optical Power Measurement Using Optical Power Meter

The using the optical power meter is simple. The following video will take the example of 10G-LR SFP+ Cisco compatible module to illustrate how to use an optical power meter for testing. This cisco compatible transceiver will be inserted in Cisco Nexus 9396PX switch. A length of single-mode LC-FC fiber patch cable is required. This is because 10G-LR SFP+ transceiver is a single-mode transceiver working on wavelength of 1310nm. After the optical power meter is connected to the module. Turn on the power button and press λ button to select 1310nm wavelength. At first the power value will change rapidly, then it slows down until still. The final power value will be shown on the screen.

Kindly visit Optical Power Meter page or contact sales@fs.com for more details.

Related Article: DWDM MUX/DEMUX Insertion Loss Test

Causes of Mechanical Splice Termination Failures

FTTH (fiber to the home) has become increasingly popular in optical communication industry. Fiber optic termination, as one of the topics which have never been out of fashion in this field, has naturally become a focus of FTTH network deployment, especially the indoor termination. In FTTH network, mechanical splice connectors are usually used in FTTH indoor termination with the advantages of flexibility, fast-installation and cost-effective. Currently manufactures can provide various types of mechanical splice connectors of high quality which have low insertion loss and high performance. However, no matter how excellent the mechanical splicing technology is, there are still fiber optic termination failures and bad fiber optic termination due to improper operation. To avoid it, this post is to offer the causes of mechanical splice termination failures.

The Basic of Mechanical splicing

Before finding the cause of mechanical splice failure, the basic of mechanical splicing should be introduced. To finish a mechanical splice, the buffer coatings of fiber optic should be removed mechanically with sharp blades or calibrated stripping tools. In any type of mechanical stripping, the key is to avoid nicking the fiber. Then the fibers will be cleaved. Two fiber ends are then held closely in retaining and aligning a mechanical splice connector with some index matching gel between them. The gel are used to form a continuous optical path between fibers and reduce reflecting losses.

mechanical splicing

Causes of Mechanical Splice Termination Failures

Mechanical splice connector is sensitive to many factors. There are also a large number of factors to cause failures. However, most of the factors are located at the end face of fiber optic. The following is to describe them in details.

Contamination

When facing mechanical splice failures, there would be no argument that contamination is the first thing to think about. There are many ways that contamination can be carried into the fiber termination splices. Generally, there are the following possible causes of splice contamination:

  • Using a dirty cleave tool: as the fiber should be cleave before inserted in the connector, a fiber optic cleaves would be used. If a dirty cleave is used, the contamination would be attached on the end face of the fiber optic and be embedded in the connector. Thus, do remember to clean the surfaces thoroughly with alcohol wipes;
  • Wiping the fiber after cleaving;
  • Setting the connector or fiber down on a dusty surface;
  • Heavy airborne dust environment;
  • Glass fragments from insertion broken fibers, or applying excessive force;
  • Polluted index matching gel.

comtamination

Please note that once the contamination is carried inside the mechanical splice connector, especially with the index matching gel, there would be little possibility to clean them out, which means the connector may be scrapped.

Glass Fragmentation

Improper operation like overexertion when inserting the fiber optic into the mechanical splice connector might break the fiber optic and produce glass fragmentation which will cause air gap and optical failure. Or if a broken fiber if inserted, there will also be optical failure. If the glass fragments are embedded in the connector, they cannot be cleaned out and the connector would be scrapped. Thus, be gentle and carefully when splicing the fiber ends.

glass-fragmentation

Bad Cleave

Cleaving the fiber optic is an important step during fiber optic mechanical splicing. The quality of the cleave can decide the quality of the optical splice transmission to some degree. It is not easy to inspect the cleave quality in the field. There are several possibilities there might cause the bad cleaves:

  • Dull or chipped cleave tool blade
  • The bent tongue on the cleave tool concentrated too much bend stress on the fiber
  • Bending the fiber too much or too tight of a radius
  • Applying no tension or insufficient tension to the fiber while cleaving.

bad cleave

Excessive Fiber Gap

Fiber gap is another factor that might cause the fiber optic termination failure. The fiber optic transmission is very sensitive to the gap between two fiber ends in the mechanical splice connector. Improper operations that might cause the excessive fiber gap are listed as following:

  • Cleaving the fiber without enough lengths;
  • The fiber is not fully inserted, or pulled back during termination;
  • The fiber was not held steady during termination and was pushed back into the fan-out tubing when terminating outdoor cable.

These faults can be corrected one time.

fiber gap

Excessive Cleave Angle

During fiber cleaving, cleave angle can be produced easily and is difficult to be inspected in field. These angles are typically ranging from 1 to 3 degree. Even with precision tool, there might still be cleave angle ranging from 0.5 to 1 degree. The angle is generally produced by bent tongue, fiber bending or insufficient fiber tension.

cleave-angle

However the cleave angles can be corrected by fine tuning with a VFL (visual fault locator). Rotating the fiber while using a VFL and terminate the connector at the position (as shown in the following picture).

VFL-tuning-fiber

Conclusion

Fiber optic mechanical splicing gives quick and high quality result at a low price for fiber optic termination. Choosing the right fiber optic mechanical splice connector and fiber optic cleaver of high quality is not enough. Acknowledge the possible causes to fiber optic termination failures and use the right tools with skills can reduce the risk of termination failure effectively.

Source: http://www.fs.com/blog/causes-of-mechanical-splice-termination-failures.html

Drop Cable and Its Termination in FTTH

FTTH (fiber to the home) networks are installed in many areas covering indoor section, outdoor section, as well as the transition in between. To fulfill the cabling requirements from different areas, different types of fiber optic cables are well developed. Drop cable as an important part of FTTH network forms the final external link between the subscriber and the feeder cable. This blog post will focus on this special outdoor fiber optic cable.

The Basic of FTTH Drop Cable

Drop cables, as previously mentioned, are located on the subscriber end to connect the terminal of a distribution cable to a subscriber’s premises. They are typicality small diameter, low fiber count cables with limited unsupported span lengths, which can be installed aerially, underground or buried. As it is used in outdoor, drop cable shall have a minimum pull strength of 1335 Newtons according to the industry standard. Drop cables are available in many different types. The following part introduces three most commonly used drop cables divided according to the cable structure.

Flat Type Drop Cable, also known as flat drop cable, with a flat out-looking, usually consists of a polyethylene jacket, several fibers and two dielectric strength members to give high crush resistance. Drop cable usually contains one or two fibers, however, drop cable with fiber counts up to 12 or more is also available now. The following picture shows the cross section of a flat drop cable with 2 fibers.

flat drop cable

Figure-8 Aerial Drop Cable is self-supporting cable, with the cable fixed to a steel wire, designed for easy and economical aerial installation for outdoor applications. This type of drop cable is fixed to a steel wire as showed in the following picture. Typical fiber counts of figure-8 Drop Cable are 2 to 48. Tensile load is typically 6000 Newtons.

Figure-8 Aerial Drop Cable

Round Drop Cable usually contains a single bend-insensitive fiber buffered and surrounded by dielectric strength members and an outer jacket, which can provide durability and reliability in the drop segment of the network. The following shows the cross section of a round drop cable with one tight buffered optical fiber.

round drop cable

Drop Cable Connectivity Method: Splice or Connector?

It’s necessary to choose a right architecture for FTTH network from overall. However, drop cable as the final connection from the fiber optic network to customer premises also plays an important role. Thus, finding a flexible, efficient and economical drop cable connectivity method becomes a crucial part of broadband service. Whether to use a fiber optic connector, which can be easily mated and un-mated by hand or a splice, which is a permanent joint? The following will offer the answer and the solutions for your applications.

It is known that splice, which eliminates the possibility of the connection point becoming damaged or dirty with a permanent joint, has better optical performance than fiber optic connector. However, splice lack of operational flexibility compared with fiber optic connector. Fiber optic connector can provide an access point for networking testing which cannot be provided by splicing. Both methods have their own pros and cons.

Generally, splice is recommended for drop cables in the places where no future fiber rearrangement is necessary, like a greenfield, new construction application where the service provider can easily install all of the drop cables. Fiber optic connector is appropriate for applications which flexibility is required, like ONTs which have a connector interface.

Choosing the Right Splice Method

For splice, there are two methods, one is fusion splicing, the other is mechanical splicing. Fusion splicers have been proved to provide a high quality splice with low insertion loss and reflection. However, the initial capital expenditures, maintenance costs and slow installation speed of fusion splicing hinder its status as the preferred solution in many cases. Mechanical splicing are widely used in FTTH drop cable installation in countries, as a mechanical splice can be finished in the field by hand using simple hand tools and cheap mechanical splicer (showed in the following picture) within 2 minutes. It’s a commonly used method in many places, like China, Japan and Korea. However, in US mechanical splicing is not popular.

FTTH Drop Cable Mechanical Splicer

Choosing the Right Connector

For fiber optic connector, there are two types connector for drop cable connection. Field terminated connector, which contains fuse-on connector and mechanical connector, and pre-terminated drop cable, which is factory terminated with connector on the end of drop cable.

Fuse-on connector uses the same technology as fusion splicing to provide the high optical connection performance. However, it requires expensive equipment and highly trained technician, and more time like fusion splicing. Mechanical connector could be a replacement of fuse-on connector (showed in the following picture), if the conditions do not fit the mentioned ones. It could be a time-save and cost-save solution for drop cable termination.

fuse-on connector

If you have no limits in cost and want high performance termination in a time-save way, pre-terminated drop cable could be your choice. Many factories can provide you customized drop cables in various fiber types, fiber optic connector and lengths.

Conclusion

Customer demand for higher bandwidth will continue to drive the development of FTTH as well as its key component like drop cable. Choosing the right drop cable and drop cable termination method is as important as choosing the right network architecture in FTTH.

Source: http://www.fs.com/blog/drop-cable-and-its-termination-in-ftth.html