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Optical Device Guide
Optical Device Guide

Various Optical Amplifiers (EDFA, FRA, and SOA)


What Is an Optical Amplifier?

The transmission loss of the light passing through optical fiber is the very small value of less than 0.2 dB per km with a light wavelength in the 1,550 nm band. However, when the length of the optical fiber is a distance as long as 10 km or 100 km, that transmission loss cannot be ignored. When the light (signal) propagating a long-distance optical fiber becomes extremely weak, it is necessary to amplify the light using an optical amplifier.

An optical amplifier amplifies light as it is without converting the optical signal to an electrical signal, and is an extremely important device that supports the long-distance optical communication networks of today. The major types of optical amplifiers include an EDFA, FRA, and SOA.


Difference between an OFA and SOA

There are 2 types of optical amplifiers; an OFA (Optical Fiber Amplifier) and SOA (Semiconductor Optical Amplifier). There are 2 further types of OFAs; an EDFA (Erbium-Doped Fiber Amplifier) and an FRA (Fiber Raman Amplifier).

Optical amplifiers OFA (Optical Fiber Amplifier) EDFA (Erbium Doped Fiber Amplifier)
FRA (Fiber Raman Amplifier)
SOA (Semiconductor Optical Amplifier)
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EDFA (Erbium Doped Fiber Amplifier)

As mentioned above, an EDFA is 1 type of OFA and is an optical amplifier with erbium ions added to the core of the optical fiber. It features high gain and low noise, is polarization independent, and can amplify optical signals in the 1.55 μm band or 1.58 μm band.

It was previously necessary to use an optical repeater to temporarily convert attenuated light into an electrical signal, electrically amplify and regenerate the waveform, then convert back to light and resend. In the 1990s, the debut of EDFAs enabled signals to be amplified as light.

Example EDFA Configuration

Irradiating a coupling module with light at 1.48 µm enables the light to be internally stored as energy, and light in the 1.55 µm band causes optical amplification when it propagates, and obtains a gain of 20 to 30 dB.

Example EDFA Configuration
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FRA (Fiber Raman Amplifier)

An FRA is a type of OFA. It causes stimulated emission based on SRS when strong excitation light enters the optical fiber. The light is then amplified in a wavelength range about 100 nm longer than the excitation light wavelength. It has a wide amplification wavelength region, and can be freely set by the wavelength of the excitation light.

FRA optical power and gain
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SOA (Semiconductor Optical Amplifier)

As suggested by the name, an SOA is a semiconductor element. By performing antireflective processing on the cleavage plane of a semiconductor laser and eliminating the resonator structure, light can enter from outside the semiconductor and amplify light via stimulated emission.

An SOA can be made in a compact size and its lower running costs compared to an EDFA mean it more economically efficient. Up until recent years, the input light of an SOA was highly polarization dependent, but research into low polarization dependency has proceeded in recent years. Furthermore, EDFAs are being replaced by SOAs at data centers, and their use is expected to expand in future optical communication.

SOA schematic

Anritsu SOA (Semiconductor Optical Amplifiers) >


Example SOA Applications

The SOA is used for embedding in 100G CFP/CFP2 ER4. Light sources for optical communication in the 1.3 μm band is used for 40 km transmission among data centers, and between mobile phone base stations and data centers. However, SOAs are required as pre-amplifiers to counter attenuation in the communication light when performing long-distance transmission. SOAs are embedded in 100 G CFP/CFP2 ER4 transceivers, and are now playing an important role in the market.

Example SOA Applications

Anritsu SOA (Semiconductor Optical Amplifiers) >

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