Author: Fiber-MART.COM

An Optical Time Domain Reflectometer (OTDR) is an optical measurement instrument designed to detect faults, splices and bends in optical fiber cables.  It functions by launching pulses of light into the optical fiber and measuring the back reflections created by the faults, splices, and bends.  It can identify the exact location of the fault by measuring the round trip time from the launch to the detection of the reflected returning pulse.  The time is determined by the speed of light in the glass core of the optical fiber.

With so many factors affecting the launch and detection process, problems such as unreliable traces of measurements are likely to be seen especially when only a little amount of light comes back to the OTDR for analysis.  This occurs when trying to look at a very long length optical fiber.  If you are trying to look at a very long optical fiber, it is necessary to launch a lot of power to see the end.  When a lot of optical power is launched, the pulse width of the launched optical signal is increased.  The large pulse width decreases the resolution of the measurement and can be as much as several hundred meters.  Faults near to the launch end are then masked because of the hundreds of meters between the launch pulse and the receiver being able to see the reflected pulse.  If there is a fault near the launch point, it can also create large reflections that saturate and overload the receiver.  This length of fiber is sometimes called the Dead Zone because the faults are masked in the length close to the OTDR.  The receiver requires an amount of time to recover from saturation.  Depending on the OTDR design, wavelength, and magnitude, the OTDR may take up to 500 meters or more to fully recover.

Most OTDR manuals suggest the use of launch fibers to resolve these issues.  Launch fibers place the necessary length of fiber between the OTDR and the actual fiber being measured providing time for the receiver to settle and also for the pulse width dependent resolution to be overcome.  When launch fibers are used, faults close to the end of the fiber being measured can be seen by the OTDR.  They do not interfere with the actual fiber being measured and thus are very secure and proven as a technique for identifying faults in the total length of fiber from the first interface to the last.

An OTDR launch fiber, often available on a small spool or within a “launch box”, is used to create the proper conditions for testing another similar optical fiber for faults.  This method avoids undesirable variations in loss and distance measurements.  A launch fiber will help to overcome the blind spot or Dead Zone of an OTDR brought about by high launch power or faults near the launch end of the fiber.  In summary, an OTDR launch fiber provides both the time and distance required for the OTDR to effectively look at and measure the characteristics of the entire length of fiber being tested, especially the length closest to the OTDR.

Polarization maintaining fused coupler is covering a wide range of optical devices that may have been used or not, includes optical splitters, optical combiners, and couplers. The couplers are operating in different applications that require other than specific connections. The fused coupler is used to split optical signals between two fibers into one and they are constructed by fusing & tapering the fibers together. This method is used for creating a simple and rugged method of splitting. Polarization maintaining fused coupler is built using unique fusing technique and polarization maintains fiber.

What is the main use of PM fused couplers?

The PM fused coupler is the type of component that is allowing the redistribution of optical signals. The device is able to distribute the other optical signals from one fiber among two or more fibers. The coupler is having the ability to combine the optical signals from two or more fibers into a single fiber.  The input signal is not directly transmitted from one fiber to another, but divided among the output ports.

The operating wavelength of fused PM Splitter is up to ±20 nm for 1550 nm region devices. If you are looking for a fused coupler for operations within the standard bandwidth or splitter, it is best to order a standard center wavelength. There are companies manufacturing the polarization maintaining fused coupler. The manufactures uses unique fusing techniques and PM fiber to build couplers. They have the features of excess loss, small size and high polarization extinction ratio.

The PM fused coupler is split into high power linearly polarized light into multiple paths without perturbing the line. It is also used as the power tap to monitor signal power in a PM fiber system without disturbing the linear SOP of light propagating in the PM fiber.

Listed below are the features of PM fused coupler –

Available for slow or fast axis operation

Compact in-line package

High extinction ratio

Low insertion loss

High stability and reliability

The fused coupler is used in applications like fiber optic instruments, fiber amplifiers, fiber sensors, coherent detecting, and research. Optical couplers are important devices in optical communication and there are various types of optical couplers with different transmission characteristics. Fused PM splitters have a wide variety of options with the standard configuration of 1×2, 2×2, 1×3 (monolithic) and 1×4 (compact cascaded). The couplers are configured and built in-line with the industry requirement.

The optical couplers are fused fiber branching devices that split the portion of light allowing optical monitoring. The devices are used extensively in amplifier power control and in transmission equipment for monitoring the performance. The polarization dependent loss coupler is offering low levels of sensitivity to polarization and enables effective management of optical networks. The couplers are available in a wide range of split ratios, lengths and packaging. The Polarization maintaining fused coupler can be bought online for its best usage.

A fused coupler is consisting of two, parallel fibers that can be stretched, twisted, and fused together. The length of the coupling region determines the coupling from one fiber to the other. The Polarization maintaining fused coupler is used to add additional functionality to the network such as network status monitoring. It is the most cost-effective way to minimize the loss and maximize the wavelength isolation. Polarization maintaining fiber coupler is capable of combining two or more inputs into a single output and also divides a single input into two or more outputs.

fiber-mart.com is the most unique fusing technique that builds the 980/1030/1064nm polarization maintaining fused coupler (PMC). The ratio can be selected according to the requirement and the businesses can benefit a lot buying the fused coupler online.  It features low excess loss, small size and high polarization extinction ratio. The polarization maintaining fused coupler is widely used for optical sensors and amplifiers. A unique fusing technique is used for building the polarization maintaining fused coupler.

How does a fused fiber coupler work?

A fused coupler is consisting of two, parallel optical fibers which are close to each other due to twisting, fusing, and stretching. The length of coupling region determines the coupling ratio from one fiber to the other. Light is launched into the coupling ratio during the manufacturing process and the output power from each output port is carefully monitored. After the achievement of the desired coupling ratio, the fully automated process stops. The process is known as Fused Biconical Taper (FBT) process.

These are the features of Polarization maintaining fused coupler

It incorporates Low Insertion Loss

It has high extinction ratio

Available in compact In-Line Package

It enables high stability and reliability

It maintains good uniformity with high directivity

Wide variety of wavelengths 780 nm-2005 nm

It is used for fiber optic instruments and fiber sensors

It is also used in research works and enables coherent detection

Polarization maintaining fiber coupler is capable of combining two or more inputs into a single output and also divides a single input into two or more outputs. Make sure that you have the fused coupler for your business or job at the best price and specifications. The coupler are developed using fusing technique and polarization maintaining fiber.

More than a dozen types of fiber optic connectors have been developed by various manufacturers since 1980s. Although the mechanical design varies a lot among different connector types, the most common elements in a fiber connector can be summarized in the following picture. The example shown is a SC connector which was developed by NTT (Nippon Telegraph and Telephone) of Japan.

1. The fiber ferrule.

SC Connector Fiber Ferrule

SC connector is built around a long cylindrical 2.5mm diameter ferrule, made of ceramic (zirconia) or metal (stainless alloy). A 124~127um diameter high precision hole is drilled in the center of the ferrule, where stripped bare fiber is inserted through and usually bonded by epoxy or adhesive. The end of the fiber is at the end of the ferrule, where it typically is polished smooth.

2. The connector sub-assembly body.

The ferrule is then assembled in the SC sub-assembly body which has mechanisms to hold the cable and fiber in place. The end of the ferrule protrudes out of the sub-assembly body to mate with another SC connector inside a mating sleeve (also called adapter or coupler).

3. The connector housing

Connector sub-assembly body is then assembled together with the connector housing. Connector housing provides the mechanism for snapping into a mating sleeve (adapter) and hold the connector in place.

4. The fiber cable

Fiber cable and strength member (aramid yarn or Kevlar) are crimped onto the connector sub-assembly body with a crimp eyelet. This provides the strength for mechanical handing of the connector without putting stress on the fiber itself.

5. The stress relief boot.

Stress relief boot covers the joint between connector body and fiber cable and protects fiber cable from mechanical damage. Stress relief boot designs are different for 900um tight buffered fiber and 1.6mm~3mm fiber cable.

A systems analysis continues to be completed to consider dynamical transient effects in the physical layer of an Optical WDM Network. The physical layer dynamics include effects on different time scales. Dynamics from the transmission signal impulses possess a scale of picoseconds. The timing recovery loops in the receivers be employed in the nanoseconds time scale. Optical packet switching in the future networks will have microsecond time scale. Growth and development of such optical networks is yet continuing. Most of the advanced development work in optical WDM networks is presently focused on circuit switching networks, where lightpath change events (for example wavelength add/drop or cross-connect configuration changes) happen on the time scale of seconds.

It is focused on the dynamics from the average transmission power associated with the gain dynamics in Optical Line Amplifiers (OLA). These dynamics may be triggered by the circuit switching events and have millisecond time scale primarily defined by the Amplified Spontaneous Emission (ASE) kinetics in Erbium-Doped Fiber Amplifiers (EDFAs). The transmission power dynamics will also be influenced by other active components of optical network, for example automatically tunable 100GHz DWDM, spectral power equalizers, or other light processing components. When it comes to these dynamics, a typical power of the lightpath transmission signal is recognized as. High bandwidth modulation from the signal, which actually consists of separate information carrying pulses, is mostly ignored.

14_nodes Ring WDMRing WDM networks implementing communication between two fixed points are very well established technology, in particular, for carrying SONET over the WDM. Such simple networks with fixed WDM lighpaths happen to be analyzed in many detail. Fairly detailed first principle models for transmission power dynamics exist for such networks. These models are implemented in industrial software allowing engineering design calculations and dynamical simulation of these networks. Such models could possibly have very high fidelity, but their setup, tuning (model parameter identification) and exhaustive simulations covering a variety of transmission regimes are potentially very labor intensive. Adding description of new network components to such model could need a major effort.

14_nodes Mesh WDMThe problems with detailed first principle models is going to be greatly exacerbated for future Mesh WDM networks. The near future core optical networks will be transparent to wavelength signals on a physical layer. In such network, each wavelength signal travels through the optical core between electronic IP routers around the optical network edge using the information contents unchanged. The signal power is attenuated in the passive network elements and boosted by the optical amplifiers. The lightpaths is going to be dynamically provisioned by Optical Cross-Connects (OXCs), routers, or switches independently on the underlying protocol for data transmission. Such network is basically a circuit switched network. It might experience complex transient processes of the average transmission power for every wavelength signal at the event of the lightpath add, drop, or re-routing. A mix of the signal propagation delay and channel cross-coupling might result in the transmission power disturbances propagating across the network in closed loops and causing stamina oscillations. Such oscillations were observed experimentally. Additionally, the transmission power and amplifier gain transients could be excited by changes in the average signal power because of the network traffic burstliness. If for some period of time the wavelength channel bandwidth is not fully utilized, this could result in a loss of the average power (average temporal density of the transmitted information pulses).

First circuit switched optical networks are already being designed and deployed. Fraxel treatments develops rapidly for metro area and long term networks. Engineering design of circuit switched networks is complicated because performance has to be guaranteed for all possible combinations of the lightpaths. Further, as such networks develop and grow, they potentially need to combine heterogenous equipment from a variety of vendors. A system integrator (e.g., Fiber-mart.com) of such network might be different from subsystems or component manufacturer. This creates a necessity of developing adequate means of transmission power dynamics calculations which are suitable for the circuit switched network business. Ideally, these methods should be modular, independent on the network complexity, and use specifications on the component/subsystem level.

Fiber-mart.com has technical approach to systems analysis that’s to linearize the nonlinear system around a fixed regime, describe the nonlinearity like a model uncertainty, and apply robust analysis that guarantees stability and gratifaction conditions within the presence of the uncertainty. For a user of the approach, there is no need to understand the derivation and system analysis technicalities. The obtained results are very simple and relate performance to basic specifications of the network components. These specifications are somewhat not the same as those widely used in the industry, but could be defined from simple experimentation using the components and subsystems. The obtained specification requirements may be used in growth and development of optical amplifiers, equalizers, optical attenuators, other transmission signal conditioning devices, OADM Modules, OXCs, and any other optical network devices and subsystems influencing the transmission power.

With the continuous progress of science and technology, the Internet has gradually gone into the homes of the ordinary people, and the speed of broadband has increasingly become the topic of people in the entertainment and work often, from narrowband dial-up to broadband Internet, and then the fiber access Internet, broadband network, the rapid pace of PON technology gradually come to the front. Currently, there are two quite compelling PON standard has been officially released, which are GPON standard developed by the ITU / FSAN and EPON standard developed by IEEE 802.3ah working group. PON technology has been no doubt the ultimate solution for the future FTTH era. EPON and GPON who will the dominant FTTH tide has become a new hot debate. What’s the difference between EPON and GPON?

GPON and EPON Differences

Perhaps the most dramatic distinction between the two protocols is a marked difference in architectural approach. GPON provides three Layer 2 networks: ATM for voice, Ethernet for data, and proprietary encapsulation for voice. EPON, on the other hand, employs a single Layer 2 network that uses IP to carry data, voice, and video.

A multiprotocol transport solution supports the GPON structure (Figure 1). Using ATM technology, virtual circuits are provisioned for different types of services sent from a central office location primarily to business end users. This type of transport provides high-quality service, but involves significant overhead because virtual circuits need to be provisioned for each type of service. Additionally, GPON equipment requires multiple protocol conversions, segmentation and reassembly (SAR), virtual channel (VC) termination and point-to-point protocol (PPP).

EPON provides seamless connectivity for any type of IP-based or other “packetized” “communications” (Figure 2). Since Ethernet devices are ubiquitous from the home network all the way through to regional, national and worldwide backbone networks, implementation of EPONs can be highly cost-effective. Furthermore, based on continuing advances in the transfer rate of Ethernet-based transport — now up to 10 Gigabit Ethernet — EPON service levels for customers are scalable from T1 (1.5 Mbit/s) up through 1 Gbit/s.

Upstream Bandwidth

Subtracting the various system run overhead from the total bandwidth of the system uplink transmission is the upstream available bandwidth. It has a great relationship with the number of the ONU contained in the system, DBA (Dynamic Bandwidth Allocation) algorithm polling cycle, the type of bearer services, as well as the various business proportion. EPON and GPON are broadband access technology, hosted business IP data services. Below we will calculate the uplink the beared pure IP services available bandwidth of EPON and GPON that contain 32 ONUs, fiber optic coupler,the case of polling period 750s.

EPON

EPON upstream rate is 1.25 Gbit/s. Because the 8B/10B line coding, each 10bit are 8bit valid data, so its effective upstream transmission bandwidth is 1 Gbit/s. EPON upstream overhead of running the system and its proportion of the total bandwidth are as following:

1. Used for the the burst reception of physical layer overhead: about 3.5%;

2. Ethernet frame encapsulation overhead: about 7.4%;

3. MPCP (Multi-Point Control Protocol) and OAM operation and management of maintenance protocol overhead: about 2.9%;

4. DBA algorithm resulting in the remaining time slots (that is not sufficient to transfer a complete Ethernet frame time slot) wasted: about 0.6%;

5. EPON upstream total overhead is all of the above about 144 Mbit/s, the available bandwidth is about 856 Mbit/s.

GPON

GPON supports a variety of rate levels, has asymmetric rate that downlink is 2.5Gbps or 1.25Gbps, the upgoing is 1.25Gbps or 622 Mbps. NRZ encoding the uplink total bandwidth for 1.244 Gbit/s, GPON upstream overhead of running the system as following:

1. The proportion of its total bandwidth is used for the the burst reception of physical layer overhead: about 2.0%;

2. GEM (GPON encapsulation method) frame and the Ethernet frame encapsulation overhead: about 5.8%;

3. The PLOAM (physical layer operation, management and maintenance) protocol overhead: about 2.1%;

4. Remaining slots of the DBA algorithm introduced the additional encapsulation overhead: about 0.8%.

5. GPON upstream total overhead is all of the above about 133 Mbit/s, the available bandwidth about 1111 Mbit/s.