Category: Fiber Transceivers

As we know, in most cases, when a fiber is used or spliced, it is essential to prepare clean ends. Stripping, cleaving, polishing are the basic steps to ensure fiber ends clean and smooth. Since we have discussed fiber optic splicing and polishing in the last several weeks, we must know more about them. Cleaving, an essential step of making fiber ends clean, though it’s a simple mean, but it works surprisingly well, at least for standard glass fibers. Thus, I want to share something about the cleaving in this paper today.

Understanding Of Cleaving

Cleaving is one of the processes for termination or splicing. Simple to understand, it “cut” an optical fiber or makes it precisely broken, just like cutting glass plate. But it is different from the general concept “cut”, or perhaps, we may define it as a professional “cut technique” because fiber is cut by scoring or scratching the surface and applying stress so that the glass breaks in a smooth manner along the stress lines created by the scratch. With a properly well done cleaving, the fiber will cleave with a clean surface perpendicular to the length of the fiber, with no protruding glass on either end.

Cleaver – If you have more experiences in the cleaving and splicing, you must know that a right cleaver helps cut out costly mistakes. The working principle of cleaver is very easy to understand. It first holds the fiber under low tension, scores the surface at the proper location and then applies greater tension until the fiber breaks. Automatic cleavers now are widely used because they can produce consistent results, irrespective of the operator. It is easy to use and does not need training. Users just need to clamp the fiber into the cleaver and operate its controls. In addition, there are some cleavers less automated. This kind of cleavers are more dependent on operator technique and less predictable as they require operators to exert force manually for breaking the fiber.

Scribe – Except the cleaver, there is another tool for cleaving which is typically used to remove excess fiber from the end of a connector before polishing. Scribe is a simple hand tool with a hard, sharp tip (generally made of carbide or diamond), that is used to scratch the fiber manually (some scribes are with pen-style shapes). Then the operator pulls the fiber to break it. However, it is less predictable than a cleaver because both the scribing and breaking process are under manual control. Nonetheless, scribe can produce adequate results for polishing so that it is still used today.

Why Is Proper Cleaving So Important?

To get good fiber optic splices or terminations, especially when using the pre-polished connectors with internal splices, it is extremely important to cleave the fiber properly. As we know, fiber splicing requires mating two fiber ends. Any defect of the ends would impact the performance of fiber splicing. For example, if the fiber ends are not precisely cleaved, the ends will not mate properly. Or if the cleaved ends are at an angle, there will be a gap between the fibers that will cause loss in a mechanical splice or uneven fusion splicing. In addition, if there is a protrusion, or lip, on one of the fibers, the two fibers will not butt up against each other and if there are hackle or mist, the ends will reflect or diffuse light, also causing loss.

Warm Tips: A good cleaver is a little expensive but it’s easy to use and do not need much techniques and can help cut out costly mistakes. Of course, inexpensive cleaver provided in most termination kits is common used. If you decide to use such inexpensive cleaver, the point you may remember is that you must learn how to use it properly. Follow directions, but also do what comes naturally to you when using the device, as they are sensitive to individual technique.

As fiber cable network is built by drawing the long lines of physical cables, it is highly impossible to lay a continuous cable end-to-end. Then there comes the optical fiber pigtail, one of the cable assemblies, has a connector on one end and a length of exposed fiber on another end to melt together with fiber optic cable. By melting together the glass fiber cable, it can reach a minimum insertion loss.

Pigtails are terminated on one end with a connector, and typically the other side is spliced to OSP (Outside Plant Cable). They may be simplex: (single fiber), or multi-fiber up to 144 fibers. Pigtails do have male and female connectors in which male connectors will be used for direct plugging of an optical transceiver while the female connectors are mounted on a wall mount or patch panel. Fiber optical pigtails are usually used to realize the connection between patch panels in a Central Office or Head End and OSP cable. Often times they may also provide a connection to another splice point outside of the Head End or central office. The purpose of this is because various jacket materials may only be used a limited distance inside the building.

You may confused the purpose between fiber optic connector, fiber optic patch cord and fiber optic pigtail. Here we will figure it out.

Fiber optic connector is used for connecting fiber. Using one or two fiber optic connectors in one cable has two items with different assistance in fiber optical solutions.

Fiber optic patch cords(or called fiber jumpers) used as a connection from a patch panel to a network element. Fiber optic patch cords, thick protective layer, generally used in the connection between the optical transceiver and the terminal box.

Fiber Optic Pigtail called pigtail line, only one end of the connector, while the other end is a cable core decapitation. Welding and connecting to other fiber optic cable core, often appear in the fiber optic terminal box, used to connect fiber optic cable, etc.

Fiber optic cable can be terminated in a cross connect patch panel using both pigtail or field-installable connector fiber termination techniques. The pigtail approach requires that a splice be made and a splice tray be used in the patch panel. The pigtail approach provides the best quality connection and is usually the quickest.

Fiber pigtails are with premium grade connectors and with typical 0.9mm outer diameter cables. Simplex fiber pigtail and duplex fiber pigtails are available, with different cable color, cable diameter and jacket types optional. The most common is known as the fusion splice on pigtail, this is done easy in field with a multi-fiber trunk to break out the multi-fibers cable into its component for connection to the end equipment. And the 12 fiber or 6 fiber multi color pigtail are easy to install and provide a premium quality fiber optic connection. Fiber optic pigtails can be with various types of fiber optic terminations such as SC, FC, ST, LC, MU, MT-RJ, MTP, MPO, etc.

Pigtails offer low insertion loss and low back-reflection. They are especially designed for high count fiber fusion splicing. Pigtails are often bought in pairs to be connected to endpoints or other fiber runs with patch cables.

Optical amplifier is an important technology for optical communication networks. Without the need to first convert it to an electrical signal, the optical amplifiers are now used instead of repeaters. As we know, there are several types of optical amplifiers. Among them, the main amplifier technologies are Doped fiber amplifier (eg. EDFA), Semiconductor optical amplifier (SOA) and Fiber Raman amplifier. Today, we are going to study and compare different types of optical amplifiers in this paper.

Before the comparison of the different types of optical amplifiers, let’s take a closer look at fiber optic amplifier. In general, a repeater includes a receiver and transmitter combined in one package. The receiver converts the incoming optical energy into electrical energy. The electrical output of the receiver drives the electrical input of the transmitter. The optical output of the transmitter represents an amplified version of the optical input signal plus noise. Repeaters do not work for fiber-optic networks, where many transmitters send signals to many receivers at different bit rates and in different formats. However, unlike a repeater, an optical amplifier amplify optical signal directly without electric and electric optical transformation. In addition, an ideal optical amplifier could support multi-channel operation over as wide as possible a wavelength band, provide flat gain over a large dynamic gain range, have a high saturated output power, low noise, and effective transient suppression. Several benefits of optical amplifiers as the following:

Support any bit rate and signal format

Support the entire region of wavelengths

Increase the capacity of fiber-optic links by using WDM

Provide the capability of all-optical networks, not just point-to-point links

OK, after a brief introduction of the optical amplifiers, we formally begin today’s main topic. As we talk above, there are three main types of today’s amplifier technology. Each of them has their own working principle, features and applications. We will describe them one by one in the following paragraphs.

Doped fiber amplifier (The typical representative: EDFA)

Erbium-doped fiber amplifier (EDFA) is the most widely used fiber-optic amplifiers, mainly made of Erbium-doped fiber (EDF), pump light source, optical couplers, optical isolators, optical filters and other components. Among them, a trace impurity in the form of a trivalent erbium ion is inserted into the optical fiber’s silica core to alter its optical properties and permit signal amplification.

Working Principle

The working principle of the EDFA is to use the pump light sources, which most often has a wavelength around 980 nm and sometimes around 1450 nm, excites the erbium ions (Er3+) into the 4I13/2 state (in the case of 980-nm pumping via 4I11/2), from where they can amplify light in the 1.5-μm wavelength region via stimulated emission back to the ground-state manifold 4I15/2.

Semiconductor optical amplifier (SOA)

Semiconductor optical amplifier is one type of optical amplifier which use a semiconductor to provide the gain medium. They have a similar structure to Fabry–Perot laser diodes but with anti-reflection design elements at the end faces. Unlike other optical amplifiers SOAs are pumped electronically (i.e. directly via an applied current), and a separate pump laser is not required.

Fiber Raman amplifier (FRA)

Fiber Raman Amplifier (FRA) is also a relatively mature optical amplifier. In a FRA, the optical signal is amplified due to stimulated Raman scattering (SRS). In general, FRA can is divided into lumped type called LRA and distributed type called DRA. The fiber gain media of the former is generally within 10 km. In addition, it requires on higher pump power, generally in a few to a dozen watts that can produce 40 dB or even over gains. It is mainly used to amplify the optical signal band of which EDFA cannot satisfy. The fiber gain media of DRA is usually longer than LRA, generally for dozens of kilometers while pump source power is down to hundreds of megawatts. It is mainly used in DWDM communication system, auxiliarying EDFA to improve the performance of the system, inhibiting nonlinear effect, reducing the incidence of signal power, improving the signal to noise ratio and amplifing online.

As the quest for greater bandwidth continues and fibre optic connections within data centres and optic fibre networks increase, these challenges must be met by choosing the right type of connectivity. This is all driven by requirements for additional switching and routing, storage, virtualization, convergence, video-on-demand (VoD) and high performance cloud computing. All of these applications plus other bandwidth intensive applications increase the need for transmission speed and data volume over short distances.

Optic fibre 10G transmission systems are becoming more widely used and accepted and migration paths to 40G and 100G have been specified for optical fibre.

The IEEE 802.3ba 40G / 100G Ethernet standard provides guidance for 40G / 100G transmission with multimode fibre. OM3 and OM4 are the only multimode fibres included in the standard.

Parallel optics technology has become the transmission option of choice in many data centres and labs as it is able to support 10G, 40G, and 100G transmission. For parallel optics to work effectively, it requires the right choice of cable and connector.

Parallel optic interfaces differ from traditional fiber optic communication in that data is simultaneously transmitted and received over multiple optical fibres. In traditional (serial) optical communication, a transceiver on each end of the link contains one transmitter and one receiver. For example, on a duplex channel the transmitter on End A communicates with the receiver on End B and another optic fibre is connected between the transmitter on End B and the receiver on End A.

In parallel optical communication, the devices on either end of the link contain multiple transmitters and receivers, e.g. four transmitters on End A communicate with four receivers on End B. This spreads the data stream over the four optical fibres. This configuration would allow for the operation of a parallel optics transceiver which uses four 2.5 Gb/s transmitters to send one 10 Gb/s signal from A to B. In essence, parallel optical communication is using multiple paths to transmit a signal at a greater data rate than the individual electronics can support. This type of connectivity utilises a ribbon cable type design with all fibres aligned in a straight array, in either a 12 fibre or 24 fibre configuration.

In addition to the cable performance, the choice of physical connection interface is also important. Since parallel-optics technology requires data transmission across multiple fibres simultaneously, a multifibre connector is required. Factory terminated MPO / MTP connectors which have either 12 fibre or 24 fibre array, will support this solution. For example, a 10G system would utilise a single MPO / MTP (12 Fibre) connector between the 2 switches. Modules are placed on the end of the MPO connector to transition from a MPO connector to a 12 Fibre breakout LC duplex or SC duplex cable assembly. This enables connectivity to the switch. 40G and 100G systems require a slightly different configuration.

Utilising MPO / MTP connectivity has many benefits including:

High Density – multifibre connector and compact dimension of cable save space in costly data centre environments.

Reduces cable load in raised floors to existing active server/switch/storage equipment with LC Duplex interface (less cable OD, less connections.

Pre-connectorised solution, no splicing required on site.

Reliability -100% tested factory tested in a controlled environment

Latest active equipment by Cisco / IBM / HP /Sun Microsystems has the MPO-SFP connectivity interface for Gigabit Network transmission

Rapid Deployment – factory terminated modular system saves installation and reconfiguration time during moves, ads and changes.

Next Generation Network Proof – emerging high speed protocol are going to use MTP interface- your cabling infrastructure remains unchanged.

Difference between MPO and MTP connectors

From the outside there is very little noticeable difference between MPO and MTP connectors. Infact, they are completely compatible and inter-mateable. For example, an MTP trunk cable can plug into an MPO outlet and vice versa.

The main difference is in relation to its optical and mechanical performance. MTP is a registered trademark and design of UsConnec, and provides some advantages over a generic MPO connector. Since MPO / MTP optic fibre alignment is critical to ensure a precise connection there are some benefits in utilising the MTP connector. The MTP connector is a high performance MPO connector with multiple engineered product enhancements to improve optical and mechanical performance when compared to generic MPO connectors.

The MTP optic fibre connector has floating internal ferrule which allows two mated ferrules to maintain contact while under load. In addition, The MTP connector spring design maximizes ribbon clearance for twelve fibre and multifibre ribbon applications to prevent fibre damage.

Overall it provides a more reliable and precise connection.

In addition, it is also important when specifying an MPO/MTP system to ensure the correct polarity options and which cables and outlets have female or male pins.

In conclusion, three main factors must be considered are fiber optic cable type, fiber optic connector type and the switch port. In practical cabling, more should be considered. These three aspects are far from enough.

Wavelength-division multiplexing (WDM) is nothing new to us. It is a technology that multiplexes multiple optical signal on a single optical fiber by using different wavelengths of laser light. The multiple transmission paths involved in WDM network effectively relieve fiber exhaustion and extend link capacity, but they also make facility protection more essential than ever, because solid facility protection is the key to the availability of the link and the data being transmitted. This article introduces two methodologies that proven to be valid for optical link protection: electrical switching and optical switching.

Why Facility Protection is Essential to WDM Network?

With the explosion of information, the demand for extremely high-capacity data transmission began to soar. Enterprises and companies were asked to deliver greater volumes of traffic at much higher rates. Which spurs the need to store data in different facilities and to transport these data over different paths, so that if any network failure or downtime occurs, they can soon recover and keep the business running. In a properly protected WDM network, customers will have two or more sites that are connected to each other by diver paths, ensuring the availability and reliability of the network all the time. But fiber may break for many reasons including damage from the physical environment and human faults. Thus facility protection becomes vitally important.

Effective Facility Protection Methods for WDM Network

There are basically two methods for optical facility protection: one is electrical switching which adopts a cross connect to duplicate and select the working or protecting path, with two independent optics involved per each path and two Mux/Demux. And the other is optical switching, unlike electrical switching, it typically uses an optical switch to select the working or protected path.

Electrical Switching

In electrical switching, each service is simultaneously transmitted and received from two dark fibers. The signal from the device on the left side is transmitted to both working and protecting fiber, then it is delivered to the end device on the right side.

So how the cross connect duplicates the Tx signals and selects the working and protecting path (Rx) for the receiving signal? In fact, the Tx signal is sent through the cross connect and duplicated through both transponders. On the Rx direction, the cross connect switches the signal to the receiving optical power of the transponder.

Optical Switching

An optical switch is involved in this method to duplicate the data to the working and protecting fiber with an optical splitter, and selecting the operating fiber according to the optical power signals of all the services. One of the distinct differences between optical switching and electrical switching is that it simply offers no protection for the WDM optic.

Electrical Switching vs. Optical Switching: How to Choose?

When applied for optical facility protection, both methods have their benefits and drawbacks. For electrical switching, the WDM optic is better protected since it uses two uplink transponders per service – one for working and the other for protecting. Since protection is delivered per service, once a single service needs to be switched, the other service won’t be disturbed. Moreover, electrical switching is suited for any network topologies, and no power budget loss is associated with this method. However, electrical switching generally adopted more WDM optics and an additional Mux/Demux, hence fewer services are available through each unit, and it inevitably increases total costs.

While for optical switching which does not offer protection for WDM optic, more ports are available to transport services on each unit. Besides, no additional Mux/Demux is required in this method, so the overall cost of the solution can be decreased. The drawbacks of this method are that the optical switch lowers the optical power budget of the link. And optical switching is not suited for ring topologies for the fact that add and drop functionality is not available per wavelength.

Conclusion

Optical facility protection impacts the link availability, performance and reliability to a large extent. Your choice on facility protection method should always base on your specific needs, and taking power budget, network topology and cost into consideration. I hope this article would be helpful for you to make an informed decision.