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Things You Should Know Before Choosing an OTDR

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OTDR that is short for optical time domain reflectometry, is a fiber optic tester for the characterization of optical networks that support telecommunications. It can be used to measure loss, optical return loss (ORL) and optical distance on a fiber optic link. Besides, by providing pictorial trace signatures of the fibers under test, an OTDR can offer a graphical representation of the entire fiber optic link. However, there are so many OTDR brands in the market. Choosing the right OTDR for your application can be challenging. So this post is intended for giving some reminders when choosing an OTDR. Hope it may help you.
Why You Need an OTDR?
As we all know, fiber testing is an essential procedure to make sure that the network is optimized to deliver reliable and robust services without fault. So here are two reasons for why an OTDR is needed.
First, service providers and network operators want to insure that their investments into fiber networks are protected. Installers need to use OTDR performing bi-directional tests and providing accurate cable documentation to certify their work. Of course, OTDRs can be used for troubleshooting problems such as break locations due to dig-ups.
Second, premises fiber networks have tight loss budgets and less room for error. Therefore installers have to test the overall loss budget with a light source and power meter, which is a big task. While OTDR can easily pinpoint the causes for excess loss and verify that splices and connections are within appropriate tolerances, which saves lots of time. Besides, it is also the only way to know the exact location of a fault or a break.
What and Where Will You Test?
Before choosing a suitable OTDR, ask yourself the following two questions.
Loss, reflectance, splicing alignment and distance, which one are you going to test? Make sure the OTDR you choose can do what you want easily, quickly and accurately. If you need to make “live” test (like during a “hot cut”—splicing of fibers in a working cable), you need an OTDR that can do an active splice loss measurement in “real time”.
Where are you going to do testing? A good understanding of the applications of an OTDR will help you make the right choice for specific needs. For example, what kind of networks will you test? LAN (local area network), metro or long haul? What is the maximum distance you might have to test? 700 m, 25 km, 150 km?
What Should Be Focused on When Choosing an OTDR?
Many people may be familiar with OTDR but not know how to choose a real right one. Except for the quality that we must focus on, the following three factors also should be attached great importance to.
A Simplified and Task-focused User Interface
Maintaining fiber health is just as challenging and makes fast troubleshooting critical. Almost every OTDR on the market today is designed to cover carrier applications. As a result, many OTDR have very complex user interfaces which require the user to make sense numerous buttons and controls and navigate cumbersome multi-level menus. It’s bad for users improving operating efficiency. So a simplified and task-focused user interface test equipment is important.
Precision Fiber Channel Information
With the wide use of short patch fibers and various types of fiber connectors, details on network link—loss, connector and reflectance—are critical to ensuring performance. However, OTDR with an attenuation dead zone of more than 3m are no longer applicable for testing data center fiber. But when problems arise, an OTDR with precision fiber channel information can help users with various skill levels efficiently perform troubleshooting and accelerate network recovery.
Effective Planning and Documentation
As data centers grow and change, it’s challenging to ensure all fibers are installed with certificated quality. Therefore, integrated project management capabilities with cable-by-cable granularity can save time and planning effort. An OTDR with built-in project management capability that allows users plan day-to-day activities without using a personal computer or laptop.

 

QSFP28 100G Transceivers & DAC Guide

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

Telecom industry embraces the prosperity of 100G optics market in 2017. With such a bright future, fiber optic market attracts a wide attention, and many vendors want a piece of the pie. The 100G optics like the CFP, QSFP28 modules and cables are varied in different standards. QSFP28 100G, along with its compact size and reliable performances, gradually becomes the mainstream form factors of the 100G optics market. QSFP28 modules come in different standards (LR4, SR4, PSM4, CWDM4), and the QSFP28 AOC and DAC cables are also available for 100G systems. Which one is ideal for your 100G network? This article attached with the detailed information of all the 100G optics, will blew your mind.
QSFP28 DAC Inside Rack: <5 m
QSFP28 passive DAC cables are launched to decrease the cost of 100G systems, which provide a cost-effective I/O solution for 100GbE connectivity within 5 m. QSFP28 to QSFP28 DACs and QSFP28 to 4x SFP28 DACs are the two common types of the QSFP28 DAC cables. QSFP28 to QSFP28 direct attach cable is usually used inside racks with QSFP28 connectors terminated on each end. QSFP28 breakout DACs can achieve 25G to 100G transmission with a QSFP28 connector on one end and 4 SFP28 connectors on the other end. If your 100GbE deployment is within 5m intra racks, the QSFP28 DAC is ideal for you.
QSFP28 AOC: Up to 100 m
The QSFP28 AOC is a cost-efficient, four-channel optical transceiver that conforms to the QSFP28 multi-source agreement. It is capable of delivering 100-Gbps data rates over four lanes of 25 Gbps with a reach of up to 100 m, maximum. Just as the QSFP28 DAC, QSFP28 AOC cable also comes in two types—QSFP28 to QSFP28 AOC and QSFP28 to 4SFP28 AOC. The former one is best fit for 3-20 m, and QSFP28 breakout can support a link length of up to 100 m. The QSFP28 AOC supports InfiniBand EDR and 100 Gigabit Ethernet (100GBase-SR4) transmission speeds and is best for close-range, high-speed transmission in data center networks, such as between servers and server racks.
QSFP28 SR4 Close Range: 5-100 m
For 100GbE cabling with multimode fiber between switches, QSFP28 SR4 with 12-fiber OM4 MTP fiber cable is the perfect choice. It can support reaches up to 100 m over OM4. The 100Gbase-SR4 QSFP28 module achieves four lanes of 25G dual way transmission over eight fibers. QSFP28 SR4 module is compliant with 100GBASE-SR4 standard certificated by IEEE. It is the firstly published 100G standard to support short distance over multimode fibers. Many vendors offer the compatible QSFP28 SR4 optics with good quality and high reliability. fiber-mart.COM is one of the best that can provide the test-assured OEM optics with great customer feedback. All the products included in the below chart are provided at fiber-mart.COM.
QSFP PSM4 Between Switches: 100 m-500 m
For 100G connectivity, if the reaches are beyond 100m but less than 500m, you can use the QSFP PSM4. Unlike the QSFP28 SR4 optics (by IEEE), PSM4 standard is published by MSA. 100G PSM4 QSFP28 is designed to support a transmission distance up to 500 m over MPOI single-mode multi-fibers.
QSFP CWDM4 Mid-Reach: 500 m-2 km
Reaches less than 2 km are usually called mid-reaches. QSFP28 CWDM4 is the module designed to meet the mid-reach requirements. MSA published 100Gbase-CWDM4 standard for QSFP28 over single-mode up to 2 km over through duplex LC interface. It uses WDM technologies like 100Gbase-LR4. But the transmission distance is shorter and the cost is much lower.
QSFP28 LR4 Long Span: d10 km
For long distance transmission between two buildings, the IEEE standard 100Gbase-LR4 is being used in QSFP28 form factor which is known as QSFP-100G-LR4 module. Unlike QSFP-100G-SR4 modules, QSFP-100G-LR4 uses the WDM technologies for four 25G lanes transmission. The four 25G optical signals are being transmitted over four different wavelengths. It has a duplex LC interface for 100G dual-way transmission. 100Gbase-LR4 QSFP28 can support transmission up to 10 km over single-mode fiber. But one problem is that the cost of QSFP28 LR4 is very high now. What’s worse, you would need the EDFA to offiber-martet the link loss.

Four Basic Elements in a WDM System

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We know that fiber can carry more data over long distances than any other physical medium. That makes fiber a very precious material. And how to make the most use of your fiber plant becomes a question. So there comes Wavelength Division Multiplexing (WDM).
Why Should We Deploy WDM ?
WDM can multiply your fiber capacity by creating virtual fibers. The foundation of WDM lies in the ability to send different data types over fiber networks in the form of light. By allowing different light channels, each with a unique wavelength, to be sent simultaneously over an optical fiber network, a single virtual fiber network is created. Instead of using multiple fibers for each and every service, a single fiber can be shared for several services. In this way WDM increases the bandwidth and maximizes the usefulness of fiber. Since fiber rental or purchase accounts for a large share of networking costs, substantial costs can be saved through the application of WDM. Next I will introduce to you the basic four elements in the form of a WDM system.
The Core Technology of WDM System
Generally speaking, a WDM system consists of four elements, that are transceiver, multiplexer, patch cord and dark fiber. The following text will explain them to you respectively.
Fiber Optic Transceivers. Optical transceivers are wavelength-specific lasers that convert data signals from SAN or WAN to optical signals that can be transmitted into the fiber. Each data stream is converted into a signal with a light wavelength that is an unique color. Due to the physical properties of light, channels cannot interfere with each other. Therefore, all WDM wavelengths are independent. Creating virtual fiber channels in this way can reduce the number of fibers required. It also allows new channels to be connected as needed, without disrupting the existing traffic services.
Optical Multiplexers. The WDM multiplexer, sometimes referred to as the Mux, is the key to optimizing, or maximizing, the use of the fiber. The multiplexer is at the heart of the operation, gathering all the data streams together to be transported simultaneously over a single fiber. At the other end of the fiber the streams are demultiplexed and separated into different channels again.
Patch cord. The transceiver transmits the high-speed data protocols on narrow band wavelengths while the multiplexer is at the heart of the operation. The patch cable is the glue that joins these two key elements together. LC fiber patch cables are popular, which connect the output of the transceiver to the input on the multiplexer.
Dark fiber. A requisite for any WDM solution is access to a dark fiber network. The most common way of transporting optical traffic over an architecture is by using a fiber pair. One of the fibers is used for transmitting the data and the other is used for receiving the data. This allows the maximum amount of traffic to be transported. At times only a single fiber is available. Because different light colors travel on different wavelengths, a WDM system can be built regardless. One wavelength is used to send data and a second one to receive it.

Introduction to Semiconductor Optical Amplifier (SOA)

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Optical amplifier, with the introduction in 1990s, conquered the regenerator technology and opened doors to the WDM technology. It is mainly used to amplify an optical signal directly, without the need to first convert it to an electrical signal. There are many types of optical amplifiers, namely Raman amplifiers, erbium doped-fiber amplifiers (EDFAs), and semiconductor optical amplifier (SOA). This article will make a clearer introduction to SOA amplifier, and analyze its advantages and disadvantages.
The Basics of Semiconductor Optical Amplifier (SOA)
SOA optical amplifiers use the semiconductor as the gain medium, which are designed to be used in general applications to increase optical launch power to compensate for loss of other optical devices. Semiconductor optical amplifiers are often adopted in telecommunication systems in the form of fiber-pigtailed components, operating at signal wavelengths between 0.85 µm and 1.6 µm and generating gains of up to 30 dB. Semiconductor optical amplifier, available in 1310nm, 1400nm, 1500nm, 1600nm wavelength, can be used with singlemode or polarization maintaining fiber input/output.
Key Points of SOA Amplifier
1310 nm, 1400 nm, 1550 nm and 1610 nm wavelength selectable
High fiber-to-fiber gain of 20 dB
Up to 16 dBm output
1 MHz with 10 ns pulse width (optional)
PM Panda fiber input/output (optional)
Similar to lasers, but with non-reflecting ends and broad wavelength emission
Incoming optical signal stimulates emission of light at its own wavelength
Process continues through cavity to amplify signal
Working principle of SOA amplifier
The basic working principle of a SOA is the same as a semiconductor laser but without feedback. SOAs amplify incident light through simulated emission. When the light traveling through the active region, it causes these electrons to lose energy in the form of photons and get back to the ground state. Those stimulated photons have the same wavelength as the optical signal, thus amplifying the optical signal.
SOA Over EFDA in DWDM Networks
As the solution below, 120km Metro Networks by Using an SOA amplifier. You may wonder why not use EDFA in the above networks.
Theoretically, SOA optical amplifiers are not comparable with EDFA in the terms of performance. The noise figure of SOA optical amplifier is typically higher, the gain bandwidth can be similar, SOAs exhibit much stronger nonlinear distortions in the form of self-phase modulation and four-wave mixing. Yet, the semiconductor optical amplifier is of small size and electrical pumped, which is often less expensive than EDFA. Additionally, SOA can be run with a low power laser.
How to Choose SOA Optical Amplifier?
When selecting SOA amplifier, you have to check the every detailed parameter in the product data sheet. But, seriously, do you understand it? No, please read the following part.
The key parameters used to characterize a SOA amplifier are gain, gain bandwidth, saturation output power and noise.
Gain is the factor by which the input signal is amplified and is measured as the ratio of output power to input power (in dB). A higher gain results in higher output optical signal.
Gain bandwidth defines the range of bandwidth where the amplification functions. A wide gain bandwidth is desirable to amplify a wide range of signal wavelengths.
Saturation output power is the maximum output power attainable after amplification beyond which no amplification is reached. It is important that the SOA has a high power saturation level to remain in the linear working region and to have higher dynamic range.
Noise defines the undesired signal within the signal bandwidth which arises due to physical processing in the amplifier. A parameter called noise figure is used to measure the impact of noise which is typically around 5dB.

 

Why Third-party 40G QSFP+ Transceiver, Instead of OEM QSFP Module?

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For the data center or network upgrade, 40G network is a trending choice. Then where do you buy the 40G QSFP transceiver? Will you choose an OEM one or a third-party one? There are some differences between third-party 40G QSFP transceiver and OEM 40G QSFP transceiver, which will be shown below.
Features of OEM 40G QSFP Transceiver Modules
As we know, the OEM 40G QSFP transceiver from name brand like Cisco, Juniper and Brocade is widely used in data center and enterprise network. They all have some great features. The Cisco 40G QSFP transceiver offers a wide variety of high-density and low-power 40 Gigabit Ethernet connectivity options for data center, high-performance computing networks, enterprise core and distribution layers, and service provider applications. Here are some benefits of Cisco 40 Gbps transceiver:
Hot-swappable input/output device that plugs into a 40 Gigabit Ethernet Cisco QSFP port
Flexibility of interface choice (for different reach requirements and fiber types)
Interoperable with other IEEE-compliant 40GBASE interfaces where applicable
Certified and tested on Cisco QSFP 40G ports for superior performance, quality, and reliability
High-speed electrical interface compliant to IEEE 802.3ba
QSFP Form factor, 2-wire I2C communication interface and other low-speed electrical interface compliant to SFF 8436 and QSFP。
The Brocade 40 Gbps transceiver supports highly reliable operations in data center and is optimized for Brocade switching platforms. It undergoes strict qualification and certification testing.
Why Choose 3rd 40G QSFP Optical Transceivers Over OEM?
40G QSFP transceiver from Cisco and Brocade is reliable and with high-quality, but why so many third-party 40 Gbps transceiver occurred on the market? The answer seems simple, the transceiver market need it. With high-speed development of the optical communication industry, the demand for 40G QSFP transceiver is increasing. The third-party 40G QSFP with good compatibility and high stability is the perfect choice for some customers. Here are some amazing advantages of the third-party 40 Gbps transceiver:
Price advantage
Optics that you buy directly from name brand is expensive because it includes the costs of testing and validation, and the majority of what you pay for goes into their pocket as pure profit. While the third-party providers may not use the same testing procedures as the name brand, but most have nearly 100% success in compatibility. The third-party providers don’t mark up the 40G QSFP as much as the name brand, so they offer better price for the customer.
Quality and Reliability
The third-party 40Gbps transceiver is reliable as the original one if you buy from a reliable optics provider. Usually, the reliable third-party provider will offer warranty and support after you buy from them, because they are highly focused and specialize in the optical transceiver market.
More choice for 40G QSFP transceiver
The third-party optical transceiver is compatible for most name brand transceivers, so it will have more choice for your data center and enterprise networks.
For the 40 Gbps transceiver, fiber-mart.COM provides various of compatible brands for you, Cisco, Genetic, Juniper Networks, Arista Networks, Brocode, HPE, Dell, Intel, IBM, etc. All have passed the compatibility testing.

Decoding Grade A Connector in Fiber Optic Cables

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With the advances in fiber optic technology and transmission systems, reliable cabling systems are becoming even more important. Active optical equipment, which is often worth hundreds of thousands of dollars, is all connected into the network via the humble fiber optic patch cord or patch lead. The risk of network downtime due to unreliable cabling is one that should be avoided. Therefore, these types of networks, along with many other Data Center and high speed Commercial networks require reliable cabling infrastructure in order to maximize performance and to ensure long term reliability. Today’s article will introduce Grade A optical fiber cables.
What Are Grade A, Grade B, Grade C Fiber Optic Connector?
IEC standards dictate the connector performance requirement for each grade of fiber optic patch cord connector. These standards guide end users and manufacturers in ensuring compliance to best practices in optical fiber technology.
According to IEC 61753 and IEC 61300-3-34 Attenuation Random Testing Method, Grade C connectors have the following performance characteristics.
Attenuation: 0.25dB-0.50dB, for >97% of samples.
Return Loss: 35dB
According to IEC, Grade B connectors have the following performance characteristics
Attenuation: 0.12dB-0.25dB, for >97% of samples.
Return Loss: 45dB
Grade A connector performance (which is still yet to be officially ratified by IEC) has the following performance characteristics. Average Insertion loss of 0.07dB (randomly mated IEC Standard 61300-3-34)and a Maximum Insertion Loss of 0.15db max, for >97% of samples.
While the return loss using IEC 61300-3-6 Random Mated Method is >55dB (unmated–only angled connectors) and >60dB (mated), this performance level is generally available for LC, A/SC, SC and E2000 interfaces.
How are Grade A Connectors on Optical Fiber Patch Cords Identified?
Grade A fiber optic patch cords are identified with the letter ‘A’ printed on the connector side. The symbol is actually the letter ‘A’ enclosed within a triangle (“A”).
This identification marker is proof that you are using a high quality fiber optic patch cord. Grade A connectivity is also available for Optical fiber through adapters. The same rule applies for A grade fiber optic Adapters which also have the letter “A” clearly marked.
What Does a Fiber Optic Patch Cord Meet the Grade A Criteria?
Firstly a high quality Grade A fiber optic patch cord begins with using high quality zirconia ferrules and high quality optical fiber cable. However, the manufacturing and testing process must be first class.
In order to meet the stringent performance criteria of ‘A’ Grade connectors on patch cords, high quality manufacturing, inspection, testing and Quality Assurance (QA) procedures are required. Without the proper expertise in optical fiber technology, many other manufacturers are unable to meet these requirements.
To consistently achieve ‘A’ Grade performance, high accuracy testing using state of the art test equipment as well as constantly assessing testing methods are all required. Analysing and ensuring mechanical end face limits and that parameters are within range, ensures that Grade A connectivity is achieved.
Grade A connectors offer virtually the same IL performance as a fusion splice, with the added benefit of providing a physical contact which can be connected, disconnected and moved when required.
Conclusion
It is important to fully understand the benefits of using reliable, good quality optic fiber patch cords and connectivity. Good quality connectors with low Insertion Loss will meet large bandwidth and high speed requirements of the latest active optical equipment allowing large streams of data to be transmitted reliably over long distances. Grade A connectors on optical fiber patch cords are an example of the advances in this technology.