What Is The Difference Between Singlemode SFP and Multimode SFP

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There are two types of SFP transceivers, Single-mode SFP and Multi-mode SFP, both work with a different kind of optical fiber. The Single-mode (also known as Mono-mode) fibers are used with Single-mode SFP transceivers, whereas Multi-mode optical fibers are used with Multi-mode SFP transceivers. Let’s discuss the difference between both and what should we take care of when using them.

What are Single-mode SFP transceivers?

The Single-mode fiber (SMF) has much close-fitted receptions for optics used. The core of this type of fiber is much smaller (around 9 µm) and the transmitted laser wavelength is narrower. This allows Single-mode fiber the ability for much higher bandwidth and for much longer distances in transmission. Single-mode SFP transceivers work mostly in 1310nm and 1550nm wavelength and are typically used in longer transmission distances, reaching 2km to 160km. Two Single-mode fibers are used for the transmission, one for transmitting and the other one for receiving the optical signal from the SFP. There are also Single-mode Bidi SFPs with Simplex connection available which are used in pairs, if 1310 nm is transmitted and 1550 nm is receiving wavelength at one end, then the other SFP must be transmitting at 1550 nm and receiving at 1310 nm. With Bidi SFPs this is made possible via WDM technique, which allows transmitting and receiving over only one single fiber.

What are Multi-mode SFP transceivers?

The Multi-mode fiber (MMF) has a much bigger core (50µm) and typically uses a longer wavelength of light. Due to this, the optics used with Multi-mode fiber have a greater ability to accept light from the laser. The optics used with Multi-mode fiber are cheaper compared to the ones used with Single-mode fiber. The common Multi-mode SFPs operate over 850 nm wavelength and are only used for short distance transmissions from usually about 100m to 550m. Although Multi-mode fiber is not capable to carry signals for a longer distance, in combination with multi-mode transceivers it is the cheapest solution for short distances.

Since these both types of fibers, Single-mode and Multi-mode are not compatible with each other. One of the main reasons for an incompatibility can be the choosing of a wrong wavelength and thus a wrong laser source, what leads to the fact that the fiber has the wrong core size and thus a data transmission does not come to pass.

While selecting the right SFP module, we must check the transmission distance and wavelength we want to use. This will help us to select the accurate SFP modules more efficiently. Furthermore, the costs for transceiver modules which keep adding up over time will be a problem for many users. To save even more, we can choose BlueOptics transceiver modules, containing compatible types of SFP, SFP+, XFP, QSFP and QSFP28 modules, which are a lot cheaper than artificially overpriced originals, which use the same components. BlueOptics offers fiber optic transceiver modules for any brand, such as Cisco, HPE, Juniper, Brocade, etc. which are all 100% compatible!

 

The development of optical transceivers and their future

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Nowadays, when we look at the product- and funcionalityrange of optical transceivers , we owe it to a long technical development.
Since the beginning, all transceiver specifications are defined under non-proprietary standards of the Multisource Agreement (MSA) of the SFF Committee. This allows intercomptability of products from different manufacturers.
At the beginning of the development of optical modules, only modules that had to be soldered into the hardware existed. These transceivers came in the 1×9 SFF format and were first used in 1999.
The maintenance of these modules was extremely time-consuming, a better solution was needed.
From now on, the development of optical modules split into two areas. In fixed and removable (hot-pluggable) optics.
In 2000, the first interchangeable module has been developed : The GBIC (gigabit interface converter) transceiver. It has a duplex SC connector and can be used at distances of up to 160KM.
This technological development offered many obvious advantages: In addition to simplifying maintenance, a network for the “pay as you grow” principle has now been established. By pluggable modules the user was easily able to subsequently increase the bandwidth on a network. The introduction of the GBIC modules by many large network manufacturers started the large spreading of this transceiver.
Unfortunately the GBIC module still had one major drawback: The size. The port density and thus the overall network performance declined significantly. Furthermore, for operators of large networks, such as Telecommunications providers, it was not necessary to upgrade the ports later on. In 2001, the actual fixed optics have appeared on the market: 2×5 SFF and 2×10 SFF. These transceivers are substantially smaller than the GBIC. This was now possible by the newly introduced LC duplex connectors and the resulting smaller PCBs (Printed Circuit Boards ) are possible and among other things. SFF optics are currently also still widespread very far. Today they are used, besides the building wiring, in most EPON ONU hardware and have been obtained strongly in importance by the proliferation of EPON networks again.
But in LAN and MAN networks only replaceable modules are used since the introduction of GBICs.
In the year 2002, the form factor SFP (Small form-factor pluggable) was put on the market. This contained a lot of advantages over the GBIC. It has an LC Duplex connector so that the entire design of the transceiver has been reduced to about a half of the GBIC module. This also accounted for the resulting disadvantages of dwindling port density and overall performance. All network manufacturers use SFP modules for entry-level devices or floor distributors till now on.
With the increasing demand for bandwidth an important step in the development of optical data transmission was made. In the year 2005, the first XENPAK modules were developed. These transceivers provide transmission rates up to 10 Gigabits. The Transmission works with an XAUI interface over 4 channels á 3.125 Gigabit. Thereby the bandwidth of the networks could be increased significantly. Ultimately the disadvantages of the technique predominated. High production costs, a too great design, which again led to lower port density, and the relatively high power consumption of up to 10W per port, could not cover the needs of the customers.
As the successor, in the year 2006, the X2 transceiver was published. Like the XENPAK transceiver, the X2 module has an electrical interface. The differences were minimal, but the next decisive step should not be long in coming.
In the year 2007  the first XFP transceiver was published. This offered significant advantages in the 10 Gigabit networking. The transmission is no more realized with four, but only through one serial channel. By that the PCBs could be significantly reduced, so the LC duplex connector could also be used with the XFP. These modules are only slightly larger than an SFP module, which finally brought an increase in port density 10 Gigabit networks. Furthermore, the power consumption, similar to an SFP, is only up to 3.5W.
The final stage of development in the 10 Gigabit transmission form is the SFP+ transceiver. This offers other minor improvements over XFP modules. The power consumption and the size could be further reduced. SFP+ is now the standard form factor for 10 Gigabit networks with all major network equipment.
In 2011, the first QSFP modules came on the market. This allowed a transmission of 40 Gigabit with a hot-pluggable module for the first time. The speed is achieved by four internal 10 Gigabit CWDM channels. The modules are slightly larger than a XFP transceiver and have a tab in the length of the module to be able to remove it from the hardware. QSFP transceivers also have a MPO/MTP connector.
Today there are two variants of these modules. The QSFP-SR , with a range of up to 150 meters on OM4 fibers, as well as the QSFP-LR, with a range of up to 10KM over OS2 fibers. The standards for QSFP-ER , with a range of 40KM, already exist. The BlueOptics will launch this QSFP -ER transceiver in the fourth quarter of 2014 as one of the first manufacturers worldwide.

Can I reduce my network costs by using Cisco compatible transceivers and cables?

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Network equippers such as the Cisco Company are designed to bind their customers and move them to purchase only Cisco distributed hardware. In this case, the buyer is urged that only official Cisco components will work. In fact, some hardware (such as the Cisco Catalyst series) refuses to work with optical Transceivers, Direct Attach Cables or Active Optical Cables from third-party vendors without entering previously undocumented commands.
However, the possibility exists. For this reason, worldwide pluggable compatible products are deployed in Cisco hardware – the price saving compared to original products is enormous.
Especially large network operators with numerous ports can increase the scalability and significantly reduce costs by using Cisco compatible optical Transceivers, Direct Attach cables or Active Optical Cables.
Industrial Standards
For the user, the most important factor is the functionality of the products without any restrictions and, of course, a favorable price. As with all electronic components, different Cisco compatible optical Transceivers, Direct Attach Cables und Active Optical Cables also show significant differences concerning the installed components and the software programming. With the meanwhile large number of suppliers and differing prices on the market it is sometimes difficult to keep the overview. So what do you have to pay attention to?
In addition to compliance with generally applicable industrial standards, the required products must also be conform to the respective MSA (Multi Source Agreement) standards in order to ensure interoperability with the available fiber optic ports of the used hardware. In addition, the dimensions for an exact fit of the pluggable components are standardized in the MSA.
Optical Transceivers
Optical Transceivers (such as QSFP28, QSFP, SFP28, SFP+, XFP, etc.), should also be equipped with high-precision lasers that have a long lifetime and do not become “blind” after a short period of use in the network. Well-known brand manufacturers of quality lasers are Avago, Lumentum or Oclaro.
Another point is the use of ICs on printed circuit boards (PCBs). Here, there are also brand components of American companies such as Maxim Integrated, Netlogic, Mindpseed or Analog Devices. Manufacturers who rely on B-ware save a few more points, the follow-up costs due to maintenance work or even network losses because of the modules quickly exceed these small additional savings. The best compatible transceivers in the market reach lifetimes of up to 10 years by the use of brand lasers and ICs and are thereby qualitatively on the same level as the original Transceivers from Cisco.
Active Optical Cables
In the case of Active Optical Cables in addition to the transceiver connector (QSFP28, QSFP, etc.) the used fiber is also a decisive factor in the price formation of the product. On the one hand, different fiber categories can be selected (OM2, OM3, OM4). Depending on the bandwidth and link length you have to make right choice for your own requirements. Brand manufacturers such as Corning, Fujikura and YoFC offer high-quality fibers for interference-free transmissions.
Direct Attach Cables
Direct Attach Cables (for example with QSFP28, QSFP or SFP+ connection) are also available on the market in various qualities. High-quality components are components of well-known cable manufacturers such as Belden, TE Connectivity and Amphenol, which can be found in different wire diameters. In order to avoid CRC errors and ensure a consistently good connection in its network, the used cable must harmonize with the used hardware. Some switches, for example, require active cables with signal amplification, while others can be used with cheaper passive versions that only conduct the signals 1:1.
Compatibility of OEM products
In order for the products to work in the Cisco used hardware, they must be programmed accordingly in order to communicate with the hardware. As Cisco is the world’s largest manufacturer of network products, it has a very broad portfolio, and many different systems have emerged over time. For each individual system, the transceiver or cable used must be adapted accordingly to provide 100% functionality. Of course, there are many interoperabilities among the Cisco systems, which means that compatible products can also be used in different Cisco hardware without additional customization. Here it is important to have a manufacturer with the appropriate know-how, who can handle the compatibility mechanisms and offer long warranty periods.

What interconnection solutions are available for QSFP28?

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The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver. The data rates are from 4×1 Gb/s for QSFP and 4×10 Gbit/s for QSFP+  and to the highest rate of 4×28 Gbit/s known as QSFP28[3] used for 100 Gbit/s links.

The QSFP28 standard is designed to carry 100 Gigabit Ethernet, EDR InfiniBand or 32G Fibre Channel. This transceiver type is also used with direct-attach breakout cables to adapt a single 100GbE port to four independent 25 gigabit ethernet ports (QSFP28-to-4x-SFP28). Sometimes this transceiver type is also referred to as “QSFP100” or “100G QSFP”  for sake of simplicity.

QSFP28 transceiver not only have the same physical size as the QSFP+ used for 40G traffic, but the lowest power consumption among those that are capable of handling 100G traffic.

Basically, there are two types of transceivers: QSFP28-SR4 and QSFP28-LR4.

QSFP28-SR4 transceivers is specially designed to support connections of up to 100 meters over multimode fiber. This approach is similar to using AOC cables, but here it is possible to use structured cabling. They use more expensive non-standard MPO (multi push-on/pull-off cable) connectors which cancel out some of the cost savings of the transceiver.

QSFP28-LR4 versions support connections up to 10km over single-mode fiber. They use standard LC connectors and the existing structured LC cabling.

QSFP28 Cable Assemblies

QSFP28 cable (DAC or AOC cables) is the more convenient, low-cost method of connecting 100G equipment. Using cable assemblies removes many of the problems associated with dirty connectors. DAC is suitable for applications within 15m and AOC up to 70m. AOC cable assemblies provide similar performance to discrete transceivers and fiber cables.

Active Direct Attach Copper Cable

Active copper cables are designed in the same cable type as the passive one, but they contain low power circuitry in the connector to boost the signal and are driven from the port without additional power requirements. The active version provides a low cost alternative to optical transceivers, and are generally used for end of row or middle of row data center architectures for interconnect distances of up to 15 meters.

The main difference between active DAC and passive DAC is that there is a driving chip in the design of active DAC.

Active Optical Cable

Active optical cable (AOC) incorporates active electrical and optical components. It can achieve longer distance than the copper assemblies. In general, active optical cable can reach more than 100m via multimode fiber. Compared to direct attach copper cable, AOC (eg. Cisco SFP-10G-AOC10M) weighs less and can support longer transmission distance. It is immune to electromagnetic energy since the optical fiber is dielectric (not able to conduct electric current). And it is an alternative to optical transceivers and it can eliminate the separable interface between transceiver module and optical cable. However, it costs more than copper cable. 100GbE QSFP28 AOC is composed of an OM4 multimode cable connecting two QSFP28 connectors on each end. Using the same port as transceiver optics, direct attach cables can support Ethernet, Infiniband and Fibre Channel but with independent protocols. In general, direct attach cable assemblies are divided into three families—direct attach passive copper cable, direct attach active copper cable and active optical cable (AOC).

Advantages of Active Optical Cables

The AOC assemblies provide the lowest total cost solution for data centers by having the key advantages as following:

  • Low weight for high port count architectures;
  • Small bend radius for easy installations;
  • Low power consumption enabling a greener environment.

For the 100G longer distance, the CFP and CFP2 offer DWDM Coherent technology and enable multi-channel long distance connectivity of more than 1000km. One thing we can’t miss is that the CFP is too big to be used in an Ethernet switch in volume.

Fan-out cable or breakout cable is considered as one of the the latest enabling technologies to help increase port densities and lower costs. Taking one (large bandwidth) physical interface and breaking it out into several (smaller bandwidth) interfaces, it has been highly recommended to be used in network migration. Breakout cables are also possible on most 100GbE QSFP+ ports where each of the 4 optical lines are broken out to 4 individual 25GbE or 10GbE interfaces. This solution requires either the deployment of a breakout cable that has 4 physical 25G / 10G endpoints, or the use of a breakout mux where an SR4 optic with MPO / MTP cable is deployed.

What is a tunable DWDM Transceiver and how does it work?

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We may ask why the tunable transceiver is available only for DWDM systems. That is happening because the frequency separation in CWDM systems is too wide in compared with the narrow band gap of DWDM systems. Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities (and cost) of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565 nm (C band), or 1570–1610 nm (L band).
Wavelength-converting transponders served originally to translate the transmit wavelength of a client-layer signal into one of the DWDM system’s internal wavelengths in the 1,550 nm band. Wavelength converting transponders rapidly took on the additional function of signal regeneration. Signal regeneration in transponders quickly evolved through 1R to 2R to 3R and into overhead-monitoring multi-bitrate 3R regenerators.
Around 88 different channels can be set with intervals of 0.4nm, which is the 50 GHz band. These optics usually start from channel 16 up to 61 but this depends on the manufacturer of the Router/Switch and which channels it supports.The wavelength is tuned by changing the filter wavelength.Tuning these optics can be done by us and some intelligent networking devices can do it for you. The transceivers can be used in various types of equipment such as switches, routers and servers from different vendors. These transponders are the spare batch for a given optical transmission system, they can replace a faulty fixed-wavelength transponder being tuned on their frequency by the embedded software and with an external operating software with either a laptop or API application.
Wavelength tunable optical transceivers are becoming important as components that enable ROADM  functionality in next-generation networks. These transceivers have the characteristic that their wavelengths can be switched between different DWDM channels while in use in the network. Channel switching capability has resulted in a reduction in the number of components and cost in today’s DWDM systems.
Form factor:
Tunable XFP transceivers
Small Form Factor 10Gb/s XFP transceiver complies with the XFP Multi-Source Agreement (MSA) Specification. It supports amplified DWDM 10Gb/s SONET/SDH, 10 Gigabit Ethernet, and 10 Gigabit Fibre Channel applications over 40km of fiber without dispersion compensation. These transceivers are capable of speeds of 10Gbit/s and have up to 80Km reach in a combination of optical components and optical fiber attenuation.Digital diagnostics functions are available via a 2-wire serial interface, as specified in the XFP MSA.
The SFP+ tunable transceiver
This form factor allows network equipment manufacturers to reduce the size and power consumption for 10G connections while supporting the network operators rapidly increasing capacity needs driven by data-heavy network applications.
Tunable SFP+ module is a high performance tunable pluggable transceiver for use in the C-band window covering 1528 nm to 1566 nm. The module supports data rates from 9.95 Gb/s to 11.3 Gb/s and is provided in an SFP+, MSA compliant package. The reach may be up to 80 km link lengths on 9 μm singlemode fiber.
One important feature of tunable transponders is the hot-swappable functionality which allows a quick restoration for a faulty fixed transceiver.
The next step is to develop a higher-performance tunable transceiver to satisfy the 100G systems. As the core of tunable transceivers, tunable laser requires higher power, a wider tuning range, and lower power consumption. In addition, the package of the next generation tunable transceivers must be more and more compact to meet the aggregation switches.
Advantages summary
Flexible network management. A tunable SFP+ transceiver will be remotely configured for a specific wavelength to support bandwidth changes as needed in Enterprise or Metro networks.
Reduced network inventory. One tunable SFP+ transceiver will support more than 80 different wavelengths. It will allow network operators to hold one tunable device code as opposed to 80+ fixed wavelength transceivers.
Reduced power consumption. It will provide a significant reduction in electrical power dissipation compared to other tunable solutions.
Compact and high-density form factor. The new tunable SFP+ transceiver will be about the size of a pack of gum, saving valuable real estate in data centers.
Increased network capacity. The tunable SFP+ will double the number of channels supported in this compact transceiver form factor. Upgrading to 50 GHz channel spacing doubles the capacity potential in Enterprise and Metro networks.

The Main Application of Optical Switch

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Optical switches are an integral part in fiber optic transmission systems and contribute to the development of the “all-optical” network. An optical switch is simply a switch which accepts a photonic signal at one of its ports and send it out through another port based on the routing decision made.
There are two basic types of optical switches – the O-E-O (Optical to Electrical to Optical) and the O-O-O, or all-optical switch. Each has its place in fiber optic systems with their unique features and capabilities.
The OEO switch is a technology already used in networks today. The problem with this technology is that may not be able to keep up with the speed of optical transmission in the future. OEO switches are also bit rate and protocol dependant, which means that protocols must be used and bits from the transmitted frames must still be processed (unlike with OOO switches). They have the ability to process header information, and are able to make routing decisions based on this. The OOO switch holds the promise of the future AON -All Optical Networks,, but it is still an emerging technology and cannot adequately function without the intelligence that OEO switches currently hold.
Protocols and Standards
OEO switches are already being used within the confines of SONET Synchronous Optical Networks or SDH.- synchronous Digital Hierarchy.  SONET and SDH are multiplexing protocol standards which were setup to support the very fast data rates required in optical networks.
Optical switching networks makes use of Dense Wave Division Multiplexing (DWDM). This is a multiplexing technique where multiple signals can be shared on a single optical fiber, with each signal sharing a different wavelength (ie. a different spectrum of light). DWDM systems today carry up to 160 different signals on a single fiber. This greatly enhances bandwidth of networks today. Optical networks use the standard protocol of traditional networks, such as IP and Ethernet.
The Optical switch will soon be operating within a network architecture known as GMPLS (Generalised MPLS).
Applications
Prime applications are optical protection, test systems, and remotely reconfigurable add-drop multiplexers.
NxM Matrix Switch – This switch uses standard telecom optical SFP (Small Form Pluggable) transceivers on the inputs to convert the incoming optical signal to its native electrical digital data stream. Similar optical transceivers are used on each of the corresponding outputs to convert the switched electrical data stream back to an optical signal for further transmission. The switch matrix is electrical and includes other functions such as reclocking and retiming to help clean up the signal and return it to its original condition, discounting any conversion-related anomalies.
Passive protection switching for service restoration following a disruption, such as a fiber cut. At the transmit location the signal is split into two redundant signals and sent over two diverse optical paths. This switch design accepts these two optical signals from the same transmitter via the different fiber paths and will monitor the optical activity on each fiber. One path is set as the primary optical path and will automatically switch to the redundant fiber path if this primary path were to be interrupted or if the signal level falls below a pre-determined optical threshold.
One common application for switches is in Remote Fiber Test Systems (RFTSs) that can monitor and locate a fault on a fiber transmission line.
An emerging application of optical switches is optical cross-connection. Optical cross-connects utilize optical switching fabrics to establish an interconnection between multiple optical inputs and outputs. Optical Cross Connects are similar of electronic routers which forward data using switches. An OXC may contain a whole series of Optical Switches.
Types of Optical Switches MEMS
The Micro Electrical Mechanical System (MEMS) was the first all optical device to be developed into a physically feasible product and is now the most common wavelength switching technique without initial electronic conversion. These devices are normally miniscule mechanisms made from silicon, with many moving mirrors ranging from a few hundred micrometers to a few millimeters. These mirrors exist on a silicon wafer and are packed as an array. The switch works by deflecting light waves from one port to another through these mirrors.
Liquid Crystal Switches
The Liquid Crystal Switch makes uses of the polarisation effects of light in liquid crystals (similar to the type used for laptop screens) to switch light. The advantages of the liquid crystal switch lies in its low power consumption..
Bubbled Switch
A bubble based switch, named the Photonic Switching Platform has been developed by Agilent Technologies Inc, using technology similar to that which is used in inkjet printers. This switch is capable of using 32×32 switches without the moving parts of MEMS.
Thermo-Optic Switches
These switches are normally small in scalability, from 1×2 to 6×6 switches. There are two main types of switches: digital optical switches (DOS) and interferometric switches. The DOS works by changing the refractive index of light. Using a 1×2 Y switch, light travels through both arms of the switch. One of the arms is heated and the light will be blocked in the switch.