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Category: Passive Optical Components

Introduction to Some Common Passive Components In Fiber Optic Network

Introduction to Some Common Passive Components In Fiber Optic Network

Overview
A passive optical network (PON) is a point-to-multipoint, fiber to the premises (FTTP) network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises. PON allows several customers to share the same connection, without any active components. The word “passive” here refers to those devices do not require electrical-to-optical or optical-to-electrical conversion during its operation. The common passive optical components include optical connectors, couplers/splitters, optical attenuators, isolators, circulators, filters, switches and OADM (optical add/drop multiplexer) etc. With the benefits of PON, it is now widely used by people as a promising solution for modern access telecommunication networks.

Common Passive Components
Optical connectors
Optical connectors, also called fiber optic connectors, is used for temporary or demountable joint connection of two pieces of optical fibers, cable or optical devices. There are many kinds of optical connector types which have been developed at different times, and for different purposes. The most commonly used connector types include ST, SC, FC, MTRJ and LC style connectors.

Fiber Optic Common Connector types

Couplers/splitters
Coupler is an optical device that combines light from different fibers while splitter is an optical device that separates light into different fibers. In facet, in most cases, there is no difference between a coupler and a splitter, the function of the part is the same. The functional difference is created by which end you use as the input vs. the output. Example: 1×2 coupler/splitter, if the input side is on that of the single leg, it will split the signal down the two legs (splitter). Alternatively, if the input is send on the two leg side, the signal will be combined down the single leg (coupler). There are mainly two kinds of splitters: one is the traditional fused type splitter known as FBT coupler (or FBT WDM optical splitter), and the other is the PLC splitter based on the PLC (Planar Lightwave Circuit) technology. FBT coupler cost lower than the PLC splitter while the PLC splitter has a compact size and suits for density applications. In addition, according to its package, there are tray type, stainless tube type and rackmount box type.

coupler&splitter

Optical attenuators
Optical attenuators are devices that reduce transmitted light power in ia controlled manner. It is generally used in preserving a receiver from reaching saturation, wavelength power balancing, equalizing node power in multifiber-distribution network or testing. Optical attenuators can be divided into four types. They respectively are plug-style attenuators (with moving parts), in-line attenuators (without moving parts), fixed attenuators and variable attenuators.

optical attenuator

Optical isolators
Optical isolators are devices that prevents the propagation of back‐reflected light. Optical isolators transmit light only in one direction. They are used to block light transmission toward the laser, which is important for controlling noise because lasers are sensitive to inadvertent feedback at the same wavelength. The working principle of an Optical Isolator is based on two types of devices which work according to the properties of polarized light: Polarizers & Faraday Rotators.

optical isolator

Optical circulators
Optical circulator is an unidirectional (non-reciprocal) divices directing an optical signal form one port to the next sequentially in only one direction at a time. Optical circulator operated the same principle (Faraday rotators) as an isolator excepet for multiple ports, typically three or four ports. It is an useful element to construct optical add/drop components.

optical circulator

Optical switches
Optical switch is a device used to dynamically control the physical connections between input ports and output ports. There are many kinds of optical switches according to their fabrication technology. The most common types of optical switches are opto-mechanical optical switch, MEMS (Micro-Electro-Mechanical Systems) optical switches and magneto-optic switches etc. They are mainly used in optical fiber loop, automatic measurement, optical fiber network remote monitoring, light path switching, system monitoring, laboratory research and development, transplanting multiplexing, optical path monitoring system with dynamic configuration, ring road protection switch test, optical fiber sensing system, optical device testing and research and so on.

1x4-switch

Passive Optical Components Solution
Fiberstore can offer you a low cost and high quality option for all the above products. You can choose the excellent passive optical components in our on-line store or asking for the custom service by contacting us. We promise to offer a perfect and full-range solution for your passive optical network projects.

Overview of FBG Sensor

Overview of FBG Sensor

Though the electrical sensors have been widely used for decades in many fields, their inherent limitations such as transmission loss and susceptibility to electromagnetic interference(noise) that still can’t satisfy people’s requirements in many applications. The combination of fiber optic technology and sensing technology is an excellent solution to meet the demands and now hanve moved form experimental research applications in the lab to broad usage and applicability in field applications. Fiber Bragg grating (FBG) is one of the most commonly used and broadly deployed optical sensors, and we will introduce it in the following.

What Is FBG Sensor
FBG sensor is a fiber optic sensor based on fiber bragg grating technology that allows to monitor many different physical parameters, especially temperature, strain, deformation, pressure and vibration. Due to its apparent advantages against to the traditional sensor, FBG sensor is required anytime in industrial environment. In addition, it is especially immunity to electromagnetic radiation, small dimensions, long lifetime and their passive character. What’s more, FBG sensor can be connected as a chain of measuring points and between points can be distance between several centimeters up to several kilometers.

FBG SENSOR

FBG SENSOR

Working Principle of FBG Sensor
FBG sensor is mainly according to the priciple of FBG. FBG is a passive and discrete optical component at a specific spot in an optical fiber. It is constructed by using holographic interference or a phase mask to expose a short length of photosensitive fiber to a periodic distribution of light intensity. The refractive index of the fiber is permanently altered according to the intensity of light it is exposed to. Fiber Bragg grating refers to the resulting periodic variation in the refractive index.

theory

When the surrounding environment of fiber bragg grating changes, such as temperature, stress, strain, or other physical. The core refractive index and resulting period will be changed in order to vary the wavelength of reflected light. By measuring changes in before and after changes in the wavelength of reflected light, we can get the physical changes quantity.

FBG sensor

Applications of FBG Sensor
FBG sensor can be applied in many fields. Some common applications such as following:

  • Civil engineering
  • Bridge monitoring
  • Structural health monitoring
  • Water level remote measurement
  • Strain monitoring of concrete beam
  • Process of matching active and passive fibers
  • Biomechanics and Rehabilitation Applications
Basic Knowledge of Optical Switch

Basic Knowledge of Optical Switch

What Is Optical Switch
The most direct understanding of optical switch is a device(mechanical, opto-mechanical, or electronic types) used to open or close an optical circuit. In a network, we usually require protection switching (to complete or break an optical path), where key attributes must operate reliably after a long period in one position, system monitoring, and diagnosis commonly feature these devises. An optical switch has one or more inputs ports and two or more output ports that we usually call 1xN or NxN optical switch.

optical switch

Types of Optical Switch
According to the differences of fabrication process and technologies, optical switch can be divided into mechanical switch, MEMS(Microelectromechanical System) switch and other switches. The first two types are the most widely used products in the market nowadays. In addition, thermo-optic switch, electro-optic switch and acousto-optic optical switch are also used in some specific applications. And today, we will mainly introduce the first two types here.

Opto-mechanical switch may be said as the oldest type of optical switch. But it is the most widely deployed at the time. Due to its working principle, it is relatively slow with switching times in the 10-100 ms range. Nevertheless, they can achieve excellent reliability, insertion loss, and crosstalk. In general, opto-mechanical optical switches collimate beam optics from each input and output fiber and move these collimated beams around inside the device so that allows the distance between the input and output fiber without deleterious effects and achieves lower optical loss.

1x4 Opto-Mechanical Fiber Optical Switch

Microelectromechanical systems (MEMS) optical switch has attracted wide attention because of their versatility. MEMS optical switch can be considered as a subcategory of opto-mechanical switches. But due to the difference of fabrication processes and its unique miniature nature, its characteristics, performance and reliability concerns are different with the opto-mechanical switch. The most obvious point is the opto-mechanical switch has more bulk compared to other alternatives, but the MEMS switch overcomes this.

1x4-switch

How Does Optical Switch Work
Optical switch is a technology that operates on fiber optic circuit to work similar to traditional electrical switches. The optical switch we mainly mentioned here is operated by mechanical means which physically move fiber or other bulk optic elements. For example, the opto-mechanical switch redirected an optical signal by moving fiber by means of a mechanical device are typically stepper motor driven. It move a mirror(prisms, or directional couplers) that directs the light from the input to the desired output.

optomechanical switch-working

Applications of Optical Switch
Optical switch is a key component in nowadays optical network. It is generally used for a variety of applications such as provisioning of light paths, protection switching and as the elements that allow high speed packet switched networks. Additionally, it is also very useful in optical fiber, components or systems testing and measurement, as well as applications in multi-point fiber sensor systems.

 remote network monitoring

Optical Switch Tutorial from FiberStore

Optical Switch Tutorial from FiberStore

What is an Optical Switch?

Optical Switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another in telecommunication. Away from telecom, an optical switch is the unit that actually switches light between fibers, and a photonic switch is one that does this by exploiting nonlinear material properties to steer light (i.e., to switch wavelengths or signals within a given fiber).

An optical switch may operate by mechanical means, such as physically shifting an optical fiber to drive one or more alternative fibers, or by electro-optic effects, magneto-optic effects, or other methods. Slow optical switches, such as those using moving fibers, may be used for alternate routing of an optical switch transmission path, such as routing around a fault. Fast optical switches, such as those using electro-optic or magneto-optic effects, may be used to perform logic operations; also included in this category are semiconductor optical amplifiers, which are optoelectronic devices that can be used as optical switches and be integrated with discrete or integrated microelectronic circuits.

(Reference: WIKIPEDIA)

Optical Switching Technology

Optical switching technology as an important foundation for all-optical communication network technology, its development and application will greatly affect the development direction of future optical communication networks. So, how does it work?

Optical signals are multiplexed in three ways, space division, time division, and WDM. The corresponding optical switching methods space division switching, time division switching and wave division switching to complete the three multiplexed channels.

Space Division SwitchingIt is the domain swap space on the optical signal, the basic functional components of the spatial light switch. Spatial light switch is the principle of optical switching components gate array switch can be in any of the multiple input multiple output fiber established path. It can constitute an empty spectroscopic switching unit, and other types of switches can also together constitute a time-division switching unit or wave stars. Empty spectral switches generally have both fiber-based and space-based space division switching is a division of swap space.

Time Division SwitchingThis multiplexed signal multiplexing method is a communication network, a channel is divided into a number of different time slots, each optical path signal distribution occupy different time slots, a baseband channel to fit the high-speed optical data stream transmission. Need to use time division switching time slot interchange. The time slot interchanger of the input signal is sequentially written to the optical buffer, and then read out in accordance with established order, thus achieving a one frame at any one time slot exchange to another time slot and outputs completed the timing exchange program. Usually bistable lasers can be used as an optical buffer, but it is only the bit output, and can not meet the demand of high-speed switching and large capacity. While the optical fiber delay line is a more time-division switching device, the time-division-multiplexed signal light input to the optical splitter, so that each of its output channels are only a light signal of the same timeslot, then these signals combined through different optical delay line, after a signal of the type of delay line to obtain a different time delay, the final combination fits before the signals are multiplexed with the original signal, thereby completing a time-division switching.

Wave Division SwitchingShips in WDM systems, the source and destination are required to transmit signals using the same wavelength, such as non-multiplexed so multiplexed in wavelength division multiplexing technology is widely used in the optical transmission system, each multiplex terminal using additional multiplexers, thus increasing system cost and complexity. In the WDM system, wave spectral exchange in the intermediate transmission nodes, to meet no additional devices to achieve wavelength division multiplexing system source and destination communicate with each other, and you can save system resources, improve resource utilization rate. Wave spectroscopic switching system first lightwave signal demultiplexer is divided into plural wave splitting is required to exchange the wavelength channels in each channel wavelength switching the last signal obtained after multiplexing composed of a dense wave division multiplexing signal from an optical output, which take advantage of the characteristics of the fiber-optic broadband, low-loss band multiplexing multiple optical signals, greatly improving the utilization of the Fiber Channel, to improve the communication system capacity.

 

There are also hybrid switching technologies which are used in large-scale communication network in a variety of the optical path switching technology a mixture of multi-level link connection. In large-scale networks need to be multi-channel signal splitter and then access different link, making the advantages of wavelength division multiplexing can not play, so using wavelength division multiplexing technology levels connecting link, and then space division switching technology used in all levels of link exchange to complete the interface between the link, finally destination and then wave of the exchange of technical output corresponding optical signals, signal combined final sub output. Mixed-use switching technology time mixed, air separation – after midnight – wavelength division mixed several minutes – hours of mixing, air separation – wavelength division.

All-Optical Network Switching Technology

To realize the all optical network switching, the first is to use the circuit switch based optical add-drop multiplexing (OADM) and OXC (optical cross connect) technology to achieve wavelength switching, and then further realization of optical packed switching.
Wavelength switching is based on wavelength in units of optical circuit switched domain, wavelength switching optical signals to provide end-to-end routing and wavelength assignment channel. Wavelength switching key is to use the corresponding network node equipment, optical add-drop multiplexing optical cross-connect. Optical add-drop multiplexing the working principle is based on all-optical network nodes drop and insert the required wavelength path. Its main constituent elements of the multiplexer reconciliation multiplexer, as well as optical switches and tunable harmonic, etc.. Optical add-drop multiplexing of the working principle and the synchronous digital hierarchy (SDH) multiplexer separate interpolation function is similar, but in the time domain, while the other is acting in the optical domain. The optical cross-connect and the synchronous digital system digital cross-connect (DXC) similar effect, but to achieve the cross-connection to the passage in the wavelength at which the optical network node.
Optical wavelength to exchange essentially took office contingent is not efficient optical switching, connection-oriented attribute it established wavelength channel re-distribution to achieve maximum utilization efficiency can not be achieved, even if the communication is idle. Optical packet switching can be implemented with a minimum switching granularity multiplexing of bandwidth resources, improve the communication efficiency of the optical network. Optical packet switching is generally light and transparent packet-switched (OTPS), optical burst switching (OBS) and optical label switching (OMPLS). The optical the transparent packet switching characteristics is the packet length is fixed, the use of synchronous switching manner, the need for all input packets are synchronized in time, thus increasing the technical difficulty and increase the use of cost. The transmission optical burst the use of a variable-length packet data transfer header control information and separated in time and space, to overcome the shortcomings of the synchronization time, but it is possible to generate the packet loss problem. Optical label switching is carried out to add a tag in the IP packet in the core network access re-packet, and the routing method according to the tag inside the core network.
Although optical switching communication occasion require a higher (generally more than 10Gbps) is more suitable for lower transmission costs and greater system capacity can be achieved; via digital transmission rate when the system requirements require a lower transmission rate (2.5Gbps or less), the connection configuration more flexible access may be more appropriate to use the old-fashioned way of photoelectric conversion. Therefore, the practical application of the current should be selected according to the application scenarios appropriate system deployment.
With the future communication network technology development and all-optical network, optical switching technology will be more innovative and more efficient ways for communication network photochemical contribute to become an important part of social development and people’s lives.

Types of Optical Switches

Optical switches can be divided into mechanical and non-mechanical ones according to the driving methods.

Mechanical optical switch relies on the movement of optical fiber or optical elements to convert the optical path, such as a mobile optical fiber type, moving the sleeve to move the lens (including mirrors, prisms and self-focusing lens) types. The biggest advantage of this kind of optical switch is a low insertion loss and low crosstalk. Its disadvantage is slow and easy to wear, easy to vibration, impact shocks.

Non-mechanical optical switch relies electro-optic, magneto-optic, thermo-optic and other effects to change the refractive index of the optical waveguide, the optical path changes, such as electro-optic switch, magneto-optic switch, and thermo-optic switch. This kind of optical switch has good repeatability, fast switching speed, high reliability, long life and other advantages, and small size, can be monolithically integrated. The disadvantage is that the insertion loss and crosstalk performance is not ideal, which should be improved.

Here are three common optical switches.
Opto-Mechanical Switch

Opto-mechanical switch is the oldest type of optical switch and the most widely deployed at the time. These devices achieve switching by moving fiber or other bulk optic elements by means of stepper motors or relay arms. This causes them to be relatively slow with switching times in the 10-100 ms range. They can achieve excellent reliability, insertion loss, and crosstalk. Usually, opto-mechanical optical switches collimate the optical beam from each input and output fiber and move these collimated beams around inside the device. This allows for low optical loss, and allows distance between the input and output fiber without deleterious effects. These devices have more bulk compared to other alternatives, although new micro-mechanical devices overcome this.

Thermo-Optic Switch

Thermo-optic switches are normally based on waveguides made in polymers or silica. For operation, they rely on the change of refractive index with temperature created by a resistive heater placed above the waveguide. Their slowness does not limit them in current applications.

Electro-Optic Switch

These are typically semiconductor-based, and their operation depends on the change of refractive index with electric field. This characteristic makes them intrinsically high-speed devices with low power consumption. However, neither the electro-optic nor thermo-optic optical switches can yet match the insertion loss, backreflection, and long-term stability of opto-mechanical optical switches. The latest technology incorporates all-optical switches that can cross-connect fibers without translating the signal into the electrical domain. This greatly increases switching speed, allowing today’s telcos and networks to increase data rates. However, this technology is only now in development, and deployed systems cost much more than systems that use traditional opto-mechanical switches.

Optical Switch Protection System for DWDM Network Security

Optical switch protection system for the security of communication network provides a set of economic, practical solutions, the formation of a non-blocking, high reliability, flexible, anti-disaster ability of the optical communication network. Optical switch protection system by the automatic switching and network management stations, you can achieve light switch protection, monitoring and the optical path of the optical power emergency dispatch three main functions.

DWDM system in the trunk and local fiber optic transmission network has a large number of applications. Due to the amount of traffic carried by focus on the importance of safety more and more attention in the event of full resistance will affect all business network hosted. The DWDM network security has always been the most important in the transmission maintenance work. However, DWDM protection technology by its own limitations, has problems such as not flexible, large investment, and the effect is not ideal. Then the optical switch protection technology comes to play a very important role in the DWDM network security.
The optical switch protection system switching control module is a set of optical switches, optical power monitoring, stable light source monitoring in one of the high level of integration modules. Optical power monitoring module and optical switch control module coordination, selection of splitting ratio of 97:3 is more appropriate on the trunk, the equivalent of approximately 0.2dB attenuation on the transmission line; optical switching module contains 1×2 or 2×2 optical switch, controlled by the switch between the main and backup light routing operation.
Real-time monitoring of the optical power monitoring module communication optical fiber optical power value reported to the main control module; analysis and comparison of the main control module, found that the change in value of the optical power exceeds a preset threshold switching immediately issued instructions to the optical switch module; optical switch module by the Directive instantly switching action has occurred. In order to achieve a switching operation.
The optical path automatically switch protective equipment involved in trunk transmission system did not affect the transmission characteristics. In fact, switching equipment involved in the optical switch and splitter only two passive optical devices.
One end of the switching unit is connected to the transceiver of the transmission system, the main fiber optic cable and the spare cable, respectively connected to two output terminals of the 2×2 optical switch. When the optical path occurs when the optical power is abnormal, the optical switch is automatically switched to the alternate route.
It is understood that the optical switch protection system has the following advantages. Fast switching speed, the optical switch switching speed ships 5ms, plus system analysis, the response time of a single-ended switching time of less than 20ms, the switching time of less than 50ms for the entire system, the basic switching operation can be done without interrupting the communication, to achieve business grade level of protection.
Switching, high reliability, implemented through the optical power monitoring, to avoid false alarm of the optical frame, ensure switched judgment is correct. The spare fiber routing monitoring, to ensure the validity of the switch, and continue to be monitored after switching optical path.
Emergency dispatch function, simply switching command issued from the program, you can deploy routing to facilitate the realization of the non-blocking cutover and line maintenance work. The switch device for a transmission system is transparent, i.e. the switching device does not require the type of transmission system can use either SDH or DWDM.
The optical switch protection DWDM is an economical and safe a line protection method, but the the light automatic protection system intervention to DWDM systems, there are many issues to consider. Splitter 97:3 spectral, optical switching device insertion loss is about 2 dB intervention light switching device, the system has an additional two-fiber jumper whose fiber insertion loss is estimated as 1 dB, so the whole switching device Interventional theoretically maximum will bring 3dB attenuation, and many cases of practical use only in 1.5-2.5dB.
Optical automatic switching system for the DWDM line protection is both safe and economical means of protection. The future, as the size of the network continues to expand, optical switch protection systems will play a more important role to meet the requirements of the assessment indicators, to improve the safety of operation of the transmission network.

 

FiberStore’s Optical Switch Solution

FiberStore’s optical switches are based on Opto-Mechanical technology with proven reliability and available as optical switch 1×1, 1×2, 2×2 Non-Latching, Latching, Single-mode, Multimode versions. Besides these high performance Opto-Mechanical switch solutions, if you want to buy the other types such as thermo-optic and electro-optic ones, please contact the sales for special Custom Service.

Available Configuration
1X1 Mechanical              1X2 Mechanical
1X4 Mechanical              1X8 Mechanical
1X16 Mechanical            2X2 Mechanical
2X2B Mechanical            2X2BA Mechanical
D1X2 Mechanical            D2X2 Mechanical
D2X2B Mechanical
Available Mode
Single-mode
Multimode
Available Control Model
Latching

Non-lantching

What does an Optical Attenuator do

What does an Optical Attenuator do

An optical attenuator is a device commonly used to lower the amount of power of an optical signal in a fiber optic communication system. In fiber optics, attenuation can also be called transmission loss. It’s the reduction in light signal intensity with regards to the distance traveled by the signal inside a transmission medium. Attenuation is an important element to limit the transmission of the digital signal driving considerable distances. Optical attenuator reduces this optical signal because it travels along a totally unoccupied space or perhaps an optical fiber.

Optical fiber attenuators may employ several principles when utilized in fiber optic communications. One common principle may be the gap loss principle. Attenuators by using this principle are responsive to the modal distribution ahead of the attenuator. Thus, they should be utilized at or close to the transmitting end. Otherwise, the attenuators could establish less loss than intended. This problem is avoided by attenuators which use absorptive or reflective principles.

You will find three basic types of optical attenuator: the fixed attenuator, step-wise attenuator and the continuously variable attenuator. Fixed attenuators reduce light signals by a specific amount of negligible or no reflection. Because signal reflection isn’t an issue, fixed attenuators are known for more accurate data transmission. Principal components associated with fixed attenuators include the flatness over a specified frequency, range, voltage standing wave ratio (VSWR), the quantity of attenuation, average and peak power-handling capability, performance over a specific temperature, size and height. Fixed attenuators are also often accustomed to enhance interstage matching in an electronic circuit. Thornton’s fixed attenuators can be found from 5 dB to 25 dB. Mini-Circuits’ fixed attenuators are packaged in rugged plug-in and connector models. They are available in both 50- and 76-ohm models which range from 1to 40 dB spanning DC to 1500 MHz.

In variable optical attenuators (VOA), resistors are replaced with solid state devices like the metal semiconductor field effect transistor (MESFETs) and PIN diodes. VOA attenuates light signal or beam inside a guarded manner. Thus producing an output optical beam with various attenuated intensity. The attenuator adjusts the ability ratio between your bright beam from the tool and the light beam entering the device over a changeable rate. VOA is usually used in fiber optic communication systems to manage optical power levels in order to prevent damages in optical receivers which may be due to irregular or fluctuating power levels. Price of commercial VOA varies depending on the manufacturing technology used.

Fiberstore claims that it is optical attenuator units produce precision amounts of attenuation, utilizing the added flexibility of adjustment. Fiberstore’s variable attenuators can be found in single mode and multi-mode versions. They have low insertion loss and back reflection. The attenuators will also be compact in dimensions and obtainable in multiple packaging options. These attenuators could be adjusted in milliseconds with a simple square wave bias between 0 and 10 volts.