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Fiber Amplifiers
Frequently Asked Questions
In their simplest form, fiber amplifiers are made of a pump source (typically a fiber-coupled diode laser) and a doped optical fiber which is the gain medium. Fiber amplifiers are often thought of as lasers without the laser cavity or feedback.
The light injected from a pump source into the fiber amplifier passes through the doped fiber medium. The injected light induces stimulated emission in the doped glass fiber causing the generation of additional coherent photons. Given the unique geometry of the amplifier characteristics with small diameter and large lengths, they exhibit significant conversion efficiencies often reaching 40GB in amplification gain.
Despite their unique optical cavity offering clean amplification, fiber amplifier also can exhibit optical noise in the amplified signal. This is often related to the injected seed. Small fluctuation and imperfections in the pump source can get amplified and become more noticeable in the amplified signal. Spontaneous emission that is always present in the gain medium along with the stimulated emission can also add to the optical noise.
The main two types of fiber optical amplifiers are the fiber Raman amplifier and the Erbium-doped fiber amplifier (EDFA). Raman fiber amplifiers take advantage of Raman scattering in optical fibers to produce stimulated emission while Erbium-doped fiber amplifiers rely on the emission produced by the ion dopants in the core of the optical fiber.
Erbium-doped fiber amplifiers are widely used in long-haul optical communications. Their output wavelength at 1.5um conveniently matches the transmission peak for most optical fibers used in telecommunication applications. Their output wavelength and clean output beam profile, ensures that the optical signal does not decay and thus information is not lost due to the long propagation distances.
The polarization of input can witness changes after propagation through an optical fiber due to birefringence. Therefore, the polarization state is not necessarily maintained by an optical amplifier.
Yes, optical amplifiers can amplify the signal of pulsed lasers as well as CW lasers.
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