Tag Archives: Optical isolators

What is Fiber Optic Isolator?

Fiber optic isolator is a passive component used for fiber optic communications. As a magneto-optic device, the purpose of optical isolator is to allow light to be transmitted in only one direction. This helps prevent laser source from unwanted feedback which will damage the laser source or arouse unexpected laser problems, such as mode hop, amplitude modulate, frequency shift and so on. Therefore, isolator is an useful and indispensable device to reduce these effects. In the following parts, fiber optic isolator’s construction, operating principle and classifications will be discussed.


Construction of Optical Isolator

Fiber optic isolator includes three main parts of an input polarizer, a Faraday rotator with magnet, and an output polarizer. Only linearly polarized light can pass through the input polarizer into the Faraday rotator. The function of the Faraday rotator is to rotate the input light by a certain angle before it reaches the output polarizer. This allows the light in the forward direction to pass unimpeded. However, the light in the reverse direction will not be able to pass the optical isolator and is either reflected or absorbed. These three components of optical isolator skillfully work together and ensure the normal transmission of light signals.

Operation of Optical Isolator

The operation of optical isolator is based on the Faraday effect which was discovered by Michael Faraday in 1842. Faraday effect refers to a phenomenon that the plane of polarized light rotates while transmitting through glass (or other materials) that is exposed to a magnetic field. The rotation direction depends on the direction of the magnetic field instead of the direction of light transmission.

According to different light directions, there are two types of operation modes. One is the forward mode and the other is the backward mode. The forward mode enables light enter into the input polarizer and become linearly polarized. When laser light reaches the Faraday rotator, the Faraday rotator rod will rotate by 45° polarization. Thus, the light finally leaves the output polarizer at 45° polarization. However in the backward mode, the light first enters into the output polarizer with a 45° polarization. Next, as it passes through the Faraday rotator, it continues to be rotated for anther 45° in the same direction. Then the light of 90° polarization becomes vertical to the input polarizer and can not leave the isolator. As a result, the light will be either reflected or absorbed.


Types of Optical Isolator
1) Polarized Optical Isolator

Polarized optical isolator employs the polarization axis to keep light transmit in one direction. It allows light to propagate forward freely, but disallows any light to travel back. Also, there are dependent and independent polarized optical isolators. The latter is more complicated and often used in EDFA optical amplifier.

2) Composite Optical Isolator

Composite optical isolator is actually a type of independent polarized optical isolator. It is used in EDFA optical amplifier which consists of many other components, such as erbium-doped fiber, wavelength-division multiplexer, pumping diode laser and so on. Since there are many other components in EDFA module, this type of isolator is named as composite optical isolator.

3) Magnetic Optical Isolator

Magnetic optical isolator is essentially the polarized optical isolator in another expression. It stresses the magnetic part of a Faraday rotator. The Faraday rotator is generally a rod made of a magnetic crystal under strong magnetic field with Faraday effect.


In summary, fiber optic isolator guarantees the stable function of laser transmitter and amplifiers by eliminating unnecessary lights. It also ensures a higher performance of light transmission. Using fiber optic isolator is no doubt a good choice for your network.

Introduction of Some Common Passive Components In Fiber Optic Network

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

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.


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.


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.