Tag Archives: EDFA Optical Amplifier

Advanced Optical Components – Optical Isolator


Connectors and other types of optical devices on the output of the transmitter may cause reflection, absorption, or scattering of the optical signal. These effects on the light beam may cause light energy to be reflected back at the source and interfere with source operation. To reduce the effects of the interference, an Optical Isolator is used. Many laser-based transmitters and Optical Amplifiers use an optical isolator because the components that make up the optical circuit are not perfect.

The optical isolator comprises elements that will permit only forward transmission of the light; it does not allow for any return beams in the fiber transmission routes or in the optical amplifiers. There are a variety of optical isolator types, such as Polarized (dependent and independent), Composite, and Magnetic.

Polarized Optical Isolator

As mentioned, the Polarized Optical Isolator transmits light in one direction only. This is accomplished by using the polarization axis of the linearly polarized light. The incident light is transformed to linearly polarized light by traveling through the first polarizer. The light then goes through a Faraday rotator; this takes the linearly polarized light and rotates the polarization 45 degrees, then the light passes through the exit polarizer. The exit polarizer is oriented at the same 45 degrees relative to the first polarizer as the Faraday rotator is. With this technique, the light is passed through the second polarizer without any attenuation. This technique allows the light to propagate forward with no changes, but any light traveling backward is extinguished entirely.

The loss of backward-traveling light occurs because when the backward light passes through the second polarizer, it is shifted again by 45 degrees. The light then passes through the rotator and again is rotated by 45 degrees in the same direction as the initial tilt. So when the light reaches the first polarizer, it is polarized at 90 degrees. And when light is polarized by 90 degrees, it will be “shut out.” The figures below show the forward- and reverse-transmitted light in a dependent polarized optical isolator.

Forward-Transmitted Light through a Polarized Optical Isolator

Reverse-Transmitted Light through a Polarized Optical Isolator

It should be noted that these figures depict the dependent type of polarized optical isolator. There is also an independent polarized optical isolator. The independent device allows all polarized light to pass through, not just the light polarized in a specific direction. The principle of operation is roughly the same as the dependent type, just slightly more complicated. Tips: The Independent Optical Isolators are frequently used in EDFA Optical Amplifiers.

Composite Optical Isolator

In fact, Composite Optical Isolator is a type of polarization independent isolator used in the EDFA optical amplifier. The EDFA optical amplifier is comprised of Erbium-Doped Fiber, Wavelength-Division Multiplexer, Pumping Diode Laser, Polarization Independent Isolator, and other passive components. Because the polarization independent isolator is composited with the others components into a single EDFA module, it is called a Composite Optical Isolator.

Magnetic Optical Isolator

Magnetic Optical Isolator is another name for polarized optical isolator. The magnetic portion of any isolator is of great importance. As mentioned, there is a Faraday rotator in the optical isolators. The Faraday rotator is a rod composed of a magnetic crystal having a Faraday effect and operated in a very strong magnetic field. The Faraday rotator ensures that the polarized light is in the correctly polarized plane, thus ensuring that there will be no power loss. Here is a figure that shows a basic magnetic optical isolator.

Magnetic Optical Isolator

Optical isolators are used to ensure stabilization of laser transmitters and optical amplifiers as well as to maintain good transmission performance. Ultra speed and large capacity optical fiber trunk systems are expanding as a result of the development of optical amplifiers. In parallel, the demand for optical isolators is increasing. Demand is also expected to increase as LAN and other subscriber fiber optic networks expand. It is therefore imperative that optical isolators be further improved to achieve higher performance, smaller size, and lower price. Luckily, you can now find the best optical isolators solution in Fiberstore, a Manufacturer & Supplier of Fiber Optic Network Solutions focus on Professional Customization.

Optical Isolator in Standard Size Jacket Tube

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Technology Of Fiber Optic Amplifiers


In fiber optic communication, the visible-light or infrared (IR) beams carried by a fiber are attenuated as they travel through the material. Then there comes to the fiber optic amplifier which is used to compensate for the wakening of information during the transmission.

Amplifiers are inserted at specific places to boost optical signals in a system where the signals are weak. This boost allows the signals to be successfully transmitted through the remaining cable length. In large networks, a long series of optical fiber amplifiers are placed in a sequence along the entire network link.

Common fiber optical amplifiers include Erbium-Doped Fiber Amplifier (or EDFA Amplifier), Raman fiber amplifier, and silicon optical amplifier (SOA). Erbium doped fiber amplifier is the major type of the fiber amplifier used to boost the signal in the WDM fiber optic system, as we know it is WDM that increase the capacity of the fiber communications system and it is the erbium-doped fiber amplifier that makes WDM transmission possible. Fiber amplifiers are developed to support Dense Wavelength Division Multiplexing (DWDM) which is called DWDM EDFA amplifier and to expand to the other wavelength bands supported by fiber optics.

There are several different physical mechanisms that can be used to amplify a light signal, which correspond to the major types of optical amplifiers. In doped fibre amplifiers and bulk lasers, stimulated emission in the amplifier’s gain medium causes amplification of incoming light. In semiconductor optical amplifiers (SOAs), electron-hole recombination occurs. In Raman amplifiers, Raman scattering of incoming light with phonons in the lattice of the gain medium produces photons coherent with the incoming photons. Parametric amplifiers use parametric amplification.

When light is transmitted through matter, part of the light is scattered in random directions. A small part of the scattered light has frequencies removed from the frequency of the incident beam by quantities equal to the vibration frequencies of the material scattering system. Raman fiber optic amplifiers function within this small scattering range. If the initial beam is sufficiently intense and monochromatic, a threshold can be reached beyond which light at the Raman frequencies is amplified, builds up strongly, and generally exhibits the characteristics of stimulated emission. This is called the stimulated or coherent Raman effect.

EFDA fiber optic amplifier functions by adding erbium, rare earth ions, to the fiber core material as a dopant; typically in levels of a few hundred parts per million. The fiber is highly transparent at the erbium lasing wavelength of two to nine microns. When pumped by a laser diode, optical gain is created, and amplification occurs.

Silicon or semiconductor optical amplifier functions in a similar way to a basic laser. The structure is much the same, with two specially designed slabs of semiconductor material on top of each other, with another material in between them forming the “active layer”. An electrical current is set running through the device in order to excite electrons which can then fall back to the non-excited ground state and give out photons. Incoming optical signal stimulates emission of light at its own wavelength.

Fiber optic repeater also can re-amplify an attenuated signal but it can only function on a specific wavelength and is not suitable for WDM systems. That is the reason why optical fiber amplifier plays a much more important role in communication systems.