OTDR FAQ, for all kinds of OTDR

by http://www.fiber-mart.com

 OTDR is short for Optical Time Domain Reflectormeter, The OTDR act likes RADAR, it injects a series pulse (laser) from the OTDR fiber interface and transmits over the optical fiber and detects the returning signal from the fiber back-scatter and reflecting from joints (including splicing, active connecting, etc), Based on the return signal, the OTDR generates trace and display on the screen. From the trace, the OTDR device is able to calculate fiber length, attenuation and joint loss for the optical fiber.
What is the basic function for the OTDR?
Measure the length for the optical fiber
Measure the optical fiber distance between two sites
Locate fault points and ruptures of the optical fiber
Showing the trace for the optical fiber
Measure the attenuation for the optical fiber cable
Measure the refection of the reflection events for the fiber cable
2>. What’s the basic feature that an OTDR should have?
There is distance, loss and reflection figure for each event
It should display the length and attenuation for the whole fiber cable
Large storage function for traces
Easy operation and with GUI interface.
RS232/USB/Network etc to upload data to a PC
PC analysis software to analyzing the stored data
Generate report for the tested traces
Back light for dark and night operation
Built-in VFL (Visual Fault Locator)
3>. How to select an OTDR?
Before you buy the OTDR, please evaluate your needs and the skill of the intended users first, ask yourself several questions:
Are you installing or maintaining fiber?
If Maintenance, is finding the location of the fault the main task?
If Installation, do you need measure more than loss and length? E.g. Connector quality, dispersion, Optical Return Loss?
If you get the answer, please visit link for more details about choose the right OTDR: How to choose the right OTDR?
4>. How many OTDR manufacturers in the market?
There are many manufactures like EXFO, JDSU, Fluke, FIBER-MART, Yokogawa, Anritsu, etc.
5>. What is the dynamic range
The dynamic range determines the total optical loss that the OTDR can analyze, and the total length of the fiber link can measure unit. The higher the dynamic range, the greater the distance the OTDR can analyze. The specification of the dynamic range must be carefully considered for two reasons as below.
OTDR manufacturers specify the dynamic range of ways (playing with specifications as pulse amplitude, signal-to-noise ratio, averaging time, etc.). It is therefore important to understand them thoroughly and avoid making comparisons unsuitable.
Having an insufficient dynamic range results in an inability to measure the full link length, affecting, in many cases, the precision of the link loss and connector losses and attenuation far end . A good method is to select an OTDR empirical whose dynamic range is 5 to 8dB higher than the maximum loss you will find.
6>. What is Event dead zone and attenuation dead zone
Event Dead Zone: Refers to the minimum necessary for consecutive reflection events can be “solved”, ie differentiated from each other. If a reflective event is within the dead zone event that precedes it, it cannot be detected or measured correctly. Industry standard values ranging from 1-5 m for this specification.
Attenuation Dead Zone: Refers to the minimum required distance after a reflective event, for the OTDR to measure a loss of reflective event or reflection. To measure and characterize small links or locate faults in cables and patch cords, it is best to have the attenuation dead zone as small as possible. Industry standard values ranging from 3 to 10 m for this specification.
7>. What is the pulse, and how to choose pulse width based on the fiber length
The key is to always use the shortest pulse width possible that will satisfy the trace quality and allow the user to see the end of the fiber. Short pulse widths are used for short fibers. Long PW’s are used on long fibers. If the trace quality exhibits excessive noise that cannot be removed by additional averages, select the next higher pulse width.
8>. What is OTDR resolution
The sampling resolution is defined as the minimum distance between two consecutive sampling points acquired by the instrument. This parameter is important because it defines the ultimate distance accuracy and ability OTDR troubleshooting. Depending on the selected pulse amplitude and the range of distance.
9>. Can I use SM OTDR to test MM fiber
It may use SM (Single Mode) OTDR to test MM (Multimode) fiber, but not accurate, the distance, cable loss, connector loss, return loss all may not right, because the laser inject from small core diameter fiber to large core diameter fiber, the laser cannot be fully injected, so the test result is not precise.
10>. What is OTDR Launch Cable, why do I need it.
An OTDR Launch Cable is able to allow the OTDR to measure the loss and reflection of the first connection in the link. However, it won’t eliminate the ‘dead zone’ after the first connection in the fiber link. We generally recommend 1km launch cable for the fiber network.
11>. What is tail cord and why do I need it.
A tail cord is a long distance patch cord connect to the end of the tested fiber link, it creates OTDR back scatter after the final connection in the fiber link under test, to measure the loss and reflection for the last connection in the network
12>. What is an “echo” or “ghost” event on an OTDR trace
An echo occurs when the OTDR receives unwanted multiple reflections. Large reflective events are more likely to cause multiple reflections due to large amounts of energy reflected back to the OTDR. Portions of the energy reflected multiple times result in echoes. These waveform artifacts look like real events; however they seldom have loss associated with them.
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Fujikura 22S cladding alignment fusion splicer

by http://www.fiber-mart.com

AFL has introduced the Fujikura 22S active cladding alignment fusion splicer. With this model’s moveable v-grooves, splicer errors due to dust and other contaminants are virtually eliminated, says the company. Removable sheath clamps allow the use of fiber holders, and the unit’s large monitor provides a crystal clear image, even in bright sunlight.
“Fujikura continues to improve upon fusion splicing technology by incorporating newer features that make splicing easier,” comments Greg Pickeral, product manager for AFL’s fusion splicing systems. “The Fujikura 22S incorporates many of the advanced features of our more expensive models yet retains the quality and reliability they are known for.”
The fully ruggedized Fujikura 22S chassis provides for shock, dust and moisture protection, while the model’s two camera observation system provides for accurate fiber alignment and loss estimation calculations. Additional features include a long-life battery that provides power for up to 200 splice cycles (including the application of the splice sleeve), and an electrode life which has been extended to 5,000 splices, minimizing downtime for replacement and stabilizations. The unit’s transit case and work tray provide multiple options for utilizing workspace.
Ideal for field splicing, the 22S maintains high quality in the most extreme environments. Software updates are available via the Internet allowing users to quickly update their software as new splice programs become available. The Fujikura 22S is also fully compatible with the company’s FUSEConnect line of fusion installable connectors.

Singlemode fiber and multimode fiber different and selection method(2)

The application of fiber optics is being gradually extended from the trunk or the computer room to the desktop and residential users, which means that more and more users who do not understand the characteristics of the fiber have come into contact with the fiber optic system. Therefore, when designing fiber link systems and selecting products, full consideration should be given to the current and future application requirements of the system, use of compatible systems and products, the greatest possible ease of maintenance and management, and adaptation to the ever-changing field conditions and user installation requirements.

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1. Can a fiber optic connector be terminated directly on a 250 μm fiber?  

 

Loose sleeve fiber optic cable contains bare fiber with an outer diameter of 250 μm, which is very small and fragile. It is unable to fix the fiber and is not enough to support the weight of the fiber optic connector and is very insecure. The connector is terminated directly on the fiber optic cable. At a minimum, a 900 μm tight jacket is required to wrap around the 250 μm fiber to protect the fiber and support the connector.

2. Can the FC connector be connected directly to the SC connector?

Yes, this is just a different connection method for two different types of connectors.
If you need to connect them, you must select a mixed adapter and use the FC/SC adapter to connect the FC connector and the SC connector at both ends. This method requires that the connectors should all be flat ground. If you absolutely need to connect APC connectors, you must use a second method to prevent damage.

The second method is to use a hybrid jumper and two connection adapters. Hybrid patch cords use different types of fiber connectors at both ends. These connectors will connect to the place where you need to connect. In this way, you can use a universal adapter to connect the system in the patch panel, but bring the system budget to budget. The increase in the number of connector pairs.

3. The fixed connection of optical fibers includes mechanical optical fiber connection and thermal welding. What are the selection principles for mechanical optical fiber connection and thermal welding?

Mechanical fiber optic connection, commonly known as fiber optic cold connection, refers to an optical fiber connection method in which a single or multi-fiber optical fiber is permanently connected through a simple connection tool and a mechanical connection technology without the need of a thermal fusion bonding machine. In general, mechanical splices should be used in place of thermal fusion when splices are made at a small number of cores dispersed at multiple locations.

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Mechanical fiber optic connection technology is often used in engineering practices such as line repairs and small-scale applications in special occasions. In recent years, with the large-scale deployment of fiber-to-the-desktop and fiber-to-the-home (FTTH), it has been recognized that mechanical fiber optic connection is an important means of fiber optic connection.

For fiber-to-the-desktop and fiber-to-the-home applications with a large number of users and geographically dispersed features, when the scale of the users reaches a certain level, the construction complexity and construction personnel and fusion splicer cannot meet the time requirements for users to open services. Because of the simple operation, short training cycle, and low equipment investment, the mechanical fiber connection method provides the most cost-effective solution for optical fiber connection for large-scale deployment of optical fibers. For example, in the high corridors, narrow spaces, insufficient lighting, inconvenient on-site power and other occasions, mechanical fiber optic connection provides a convenient, practical, fast and high-performance optical fiber continuation means for design, construction and maintenance personnel.

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 4. What is the difference between fiber optic splice enclosure requirements and fiber optic splice closures used in telecom operators’ outdoor lines in fiber-to-the-home systems?

First of all, in the fiber-to-the-home system, it is necessary to reserve the position of the optical splitter installation and termination, accommodation, and protection of the jumper to and from the optical splitter in the joint box according to actual needs. Because the actual situation is that the optical splitter may be located in the cable joint box, optical cable transfer box, wiring box, ODF and other facilities, and in which the optical cable termination and distribution.

Secondly, for residential quarters, the optical fiber cable splice box is installed in a buried manner. Therefore, the optical cable splice box has higher requirements for buried performance.

In addition, in the fiber-to-the-home project, it may be necessary to consider the entry and exit of a large number of small-core optical cables.

10G to 40G / 100G MPO Optical Link Testing Technology

by http://www.fiber-mart.com

Objective
Technology changes the life, informatization is the trend of the development of the world today. Networking, cloud computing, large data and other emerging network information technology innovation and application, and in mobile interconnection technology, the 3G network is maturing, 4G LTE network from the beginning of last year in the national pilot run, mobile interconnection speed will be a new step. In this era of information industrialization, we work and live in the city is also in the transformation of the Intelligent city, a variety of network applications are closely related to us. Whether it is the application of new technology or the construction of the Intelligent city, the application cannot be separated from the basic network. The construction of the basic network is based on the site, the active terminals, and interconnecting devices, as well as the basic interconnection channel-cabling system. Cabling system needs to be installed on the site, easy to be affected by environment, product quality, installation process and other factors, is the most important link to determine the quality of network transmission. The reliability of Cabling system depends not only on the quality supervision in the project but also on the final  field acceptance test.
The urgency of test technology development
At present, most of the small and medium-sized cabling projects still use 10 Gigabit as the backbone to achieving Gigabit to the desktop network architecture. However, with the rapid development of 3G / 4G and Internet services, bandwidth cannot meet the needs of applications. The main link uses 40G / 100G to become a large-scale wiring project, especially the inevitable trend of enterprise data center and Internet IDC data center project construction. According to IDC market report, after 2015, 40G / 100G will gradually become the mainstream port rate.
Since the IEEE released the 802.3ba 40G / 100G standard in June 2010, the 40G / 100G network has mainly been based on experimental networks and has fewer requirements for on-site testing. After more than two years of systematic research and development testing, the current 40G / 100G transmission technology is maturing, major manufacturers have introduced 40G / 100G switching routing equipment, carrier-class long-distance backbone link using single-mode optical fiber systems, and buildings and data centers The integrated cabling system is mainly based on multimode OM3 / OM4 optical fiber system transmitting over short distances. It adopts 12-pin MPO connector and four-channel / ten-channel pre-connected optical cable. Pre-connected optical cable greatly reduces installation time and labor costs, but how to quickly identify the polarity of the fiber, fast and accurate test of the link attenuation has become the primary problem of field testing.
Traditional optical fiber testing technology
First of all, let us first review the original Gigabit, 10 Gigabit optical fiber link test technology. In 2003, TIA-526-14-A multi-mode optical cable installation light intensity loss test standard formally defines the CPR (CoupledPowerRatio) optical coupling rate detection method, the light source is divided into five levels (as shown below), LED light source is level 1 Light source, VCSEL The vertical cavity surface emits a laser light source at a level between level 3 and level 4, and the FP laser light source corresponds to a level 5 light source. At the same time, the test limits of optical loss are further increased. The maximum loss value of 1000BASE-SX applied to OM1 optical fiber is 2.6dB. The maximum loss value of 10GBASE-SR applied to optical fiber OM3 is 2.6dB. This standard, as a common standard for optical fiber link testing, is not aimed at specific network applications. It emphasizes the normal state of optical signal transmission. It is recommended to use LED light sources to test multimode fiber links. This method can detect the worst fiber link Happening. The laser-optimized VCSEL light source is used to detect the link for a specific network application. For example, if the active device uses a VCSEL light source or the current network is to be upgraded to use a VCSEL light source, the measured fiber loss value is relatively close to the real loss in the network application value.
850NM CPR Categories
The TIA-526-14-A standard is referenced by several related test standards such as ANSI / TIA / EIA-568-B, ISO / IEC11801, ISO / IEC14763-3 and others. And ANSI / TIA / EIA568-B.1.7.1 and ISO / IEC14763-36.22 also specify the size and use of 50 / 62.5um multimode fiber spools. The reel is modeled as a mode filter by means of a coiled optical fiber to reduce the high mode generated by the light source in the optical cable and reduce the difference of test results caused by different light sources and improve the stability and repeatability of multimode optical fiber testing.
10G MPO multi-core fiber test solution
Compared with traditional dual-core fiber optic connectors such as LC, SC, and ST, MPO connectors can support at least 12-core optical fibers. The MPO connector is mainly used for pre-attached optical fiber cables. Because MPO optic fiber has 12 core channels, TIA-568-C.0-2009B.4 has analyzed the channel polarity in detail, for the duplex transmission, there are mainly three kinds of polarities A, B, C connections. All three methods are for a common goal —- to create an end to end optical transceiver channel, but the three ways cannot be compatible, respectively, using different polarity connectors and adapters. For the entire link compatibility and consistency, as far as possible to consider the use of the same polarity connectors and adapters, such as the use of the jumper polarity are AB, adapter types are KEYUP-KEYUP, or the polarity will cause different Confusion, easy to install error, resulting in link failure. Therefore, in the 10G Fiber Channel, the MPO main link polarity mainly adopts Class C (see below). The two ports are internally interoperable according to the corresponding numbers. The optical channels are connected in groups of two or more, such as 1- – 2, 2 — 1, forming a full-duplex transceiver channel. The left and right ends are converted into the LC interface through the MPO to LC module box and then connected to the device through the LC jumper. This situation is mainly used in the data center high-density cabling system.

Test Cables Don’t Last Forever

by http://www.fiber-mart.com

I frequently hear customers complain that although nothing has changed in their fiber optic cable assembly production process, the measured Insertion Loss (IL) and Return Loss (RL) values of their product aren’t as good as they once were. Is something wrong with the measurement equipment? Well, it’s possible but unlikely.

Obviously something has changed. If it’s not the measurement equipment, then it must be either the product or the measurement setup. Over time the production process can become a familiar, perhaps boring, routine. Operators may become less meticulous in cleaning, use polishing film longer than appropriate, or even take shortcuts. Eventually this takes a toll and yield suffers.

Let’s suppose you’ve eliminated this possibility with a clean sweep of procedures and a reset to rigorous production guidelines. Yet the problem persists. A “gold-standard” product is useful at this stage – a “known-good” example of the best of your previous production, carefully kept, with very good IL and RL values recorded. Using your current rigorous procedures, re-measure this gold-standard product. It should still look good. If it doesn’t, read on …

I have written that IL and RL tests on a product cannot be made in isolation. Remember, we are measuring connector loss, and the device under test (DUT) needs to be connected to a test cable (aka jumper cable, reference cable, or test lead). It’s important to note that the quality and condition of test cables have a direct bearing on the measured product’s IL and RL measurements.

Assess the quality and condition of test cables.

Firstly, ensure the test cable’s connectors are clean. Next, take a close look to ensure they are in good condition. Keep in mind that both connectors and coupling sleeves don’t last forever. They will degrade with use, and it’s not just scratches and pits. Sliding surfaces wear out. As the fit becomes loose, alignment will suffer.

How many matings can a test connector undergo before it should be replaced? It would be nice to have a definitive number to work with. However, it’s difficult to give a definite answer as it depends on the type and quality of the connectors and the skill of the operators.

Suppose replacing all the test cables and couplers restores your gold-standard product to the previous good measured values. This is useful information. Take a minute to determine approximately how many matings these particular test cables have undergone. What number did you arrive at? Now you know how many couplings are too many!

Identify a usage limit and determine a replacement schedule.

I propose you set usage limit at, say, half the above number. Weigh the ongoing cost of replacement and time required to replace test cables. How does this compare with the cost if you let products go to the failure stage?

A regime of frequent monitoring of the gold-standard device might help nail down the test cable usage limit. (Don’t do this too frequently, or your gold-standard cable will degrade.) This monitoring regime will help you create a reasonable replacement schedule.

Here’s a helpful tip: If you use the Viavi MAP/PCT system, it can track measurement jumper usage and warn if the cable exceeds a user-defined limit. If you use another test instrument, I encourage you to look into whether it can track usage and provide this type of warning as well.

Implement robust process controls.

Test cables do have a finite useful working life. And this lifespan will vary. For example, one improper mating or cleaning can potentially damage a test cable’s end-face enough to render it unusable.

Implementing robust process controls will go a long way to extend the test cable’s life and identify when it needs to be replaced. As discussed, I recommend:

  • Frequently inspecting test cable end-faces between matings
  • Adhering to good cleaning practices
  • Using a “known-good” cable for troubleshooting

Here’s another tip: Telcordia’s GR-326 specification provides excellent guidance on this topic. It is highly recommended that any cable assembly manufacturer procures a copy and, at minimum, adheres to the requirements of Section 8.0.

If you are seeing degraded IL/RL results with your fiber optic cable assemblies, I recommend you first establish rigorous production controls. Next, follow the guidelines in this article to implement procedures to assess the condition of test cables, track usage, and create a reasonable replacement schedule.

What is Visual Fault Locators(VFL)?

Visual fault locator is now one of the most commonly used fiber optic testing devices to trace optical fibers, check fiber continuity and find faults such as breaks, bad splices and tight, sharp bends in fiber optic cable.

Visual fault locator is now one of the most commonly used fiber optic testing devices to trace optical fibers, check fiber continuity and find faults such as breaks, bad splices and tight, sharp bends in fiber optic cable.

Visual Fault Locator, it could be regarded to be part of OTDR and the fiber fault locator is cheap. Fiber visual fault locator is a kind of device which is able to locate the breakpoint, bending or cracking of the fiber glass. It can also locate the fault of OTDR dead zone and make fiber identification from one end to the other end. Designed with a FC,SC,ST universal adapter, this fiber testing red light is used without any other type of additional adapters, it can locates fault up to 10km in fiber cable, with compact in size, light in weight, red laser output.

Visual Fiber Optic Fault Locator is used to check, locate and patch faults on singlemode and multimode optical fibers as well as other fiber optic components. The rugged and compact design of the visual fault locator is very suitable for daily use in all fiber optic applications such as in the field, in industrial environment as well as in the laboratory.

Many of the problems encountered in troubleshooting fiber optic networks are related to making proper connections. Since the light used in fiber optic systems is infrared (IR) light, which is beyond the range of the human eye, one cannot see it. In order to solve these problems, you need a visual fault locator. Visual fault locator(VFL) is a kind of device which is able to locate the breakpoint, bending or cracking of the fiber glass. It can also locate the fault of OTDR dead–zone and make fiber identification from one end to the other end.

Importance of Visual Fault Locator

The complex network integrated by optical fiber, connector and jumper makes you difficult to find the fault location. So the visual fault locator is an essential tool that quickly and easily locates problem areas in fiber cables. By pinpointing the exact location of fiber damage, technicians can diagnose, troubleshoot and fix the problem timely and efficiently. The VFL is also used for conducting continuous tests and performing fiber identification. With visual fault locator, you can easily isolate high losses and faults in optical fiber cables.

Working Principle

A powerful visible light from a red diode laser is injected into the fiber, so not only fibers  can be traced, but also high loss points can be made visible. Most applications center on short cables to connect to the fiber optic trunk cables, such as those used in premises cabling or telco central offices. The VFL works best on short cables, up to a few kilometers, thus, it covers the range where optical time-domain reflectometers (OTDRs) are not useful because of the dead zone of the OTDR.

Fiber visual fault locators include the pen type, the handheld type and portable visual fiber fault locator:

Pen type:

Pen Shape Visual Fault Locator

 

Handheld type:

handheld optical Visual Fault

Portable visual fiber fault locator:

Portable Visual Fault Locator

Comment

This basic tool is one that all installers, and maintenance personnel should have in their tool kit.  It is the most economical test tool for quickly verifying continuity, checking the validity of patch cables before or after installation, test and find breaks in LANs, verifying short lengths of installed fiber, or looking for cracked fiber in splice cases, bad connectors, tight crimps in fiber cable, backbone breaks or anywhere light continuity needs checking.

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