Shulou(Shulou.com)11/24 Report--

As the replenishment station of vehicle energy, the gas station determines how far we can go.

Similarly, if the optical signal can be transmitted over a long distance in the optical transmission network, the "gas station" is also very important. Optical amplifiers play the role of gas stations in the optical transmission network. The emergence and development of optical amplifier has overcome the biggest obstacle of high-speed and long-distance transmission-optical power limitation, which is an important milestone in the history of optical communication.

What is an optical amplifier? an optical amplifier is a kind of active device that amplifies the optical signal directly without going through the optical-electro-optical conversion. The function of optical amplifier is to enhance the attenuated optical signal and prolong the transmission distance. Compared with the regenerator needs optical-electro-optical conversion to amplify the signal, and can only amplify a single wavelength, the optical amplifier amplifies the optical signal directly to achieve all-optical transmission, and can achieve all-channel optical signal amplification at the same time.

Optical amplifier is divided into semiconductor optical amplifier and optical fiber amplifier. Semiconductor optical amplifier, as its name implies, is an amplifier made of semiconductor material. Because of its large coupling loss and high noise with optical fiber, it has been rarely used, so we focus on optical fiber amplifier. Optical fiber amplifier is divided into rare earth doped fiber amplifier and nonlinear optical amplifier. Rare earth-doped fiber amplifier is composed of rare earth elements in the fiber core, the most commonly used is erbium-doped fiber amplifier. Nonlinear optical amplifier is an amplifier made of the nonlinear effect of optical fiber, and the most commonly used one is Raman amplifier.

Then we take erbium-doped fiber amplifier and Raman amplifier as representatives to understand the working principle, characteristics and applications of fiber amplifier.

Erbium-doped fiber amplifier EDFA (Erbium Doped Fiber Application Amplifier, erbium-doped fiber amplifier) is a kind of erbium-doped fiber core. The basic components of EDFA include pump laser, coupler, erbium-doped fiber and optical isolator.

Pump laser: pump light is generated and the working wavelength is 980 nm or 1480 nm.

Coupler: input light signal and pump photosynthesis are input into erbium-doped fiber.

Erbium-doped fiber: under the excitation of pump light, the optical signal transmitted in it can be amplified.

Optical isolator: prevent the reflected light from affecting the stability of the optical amplifier and ensure that the optical signal can only be transmitted in the forward direction.

So how on earth is the signal amplified? Let's find the answer in erbium-doped fiber.

When erbium ions in N1 ground state (low energy state) in erbium-doped fiber are stimulated by pump light from pump laser, the absorbed pump light energy changes from N1 ground state to N3 high energy state.

Due to the instability of N3 high energy state, erbium ion will spontaneously become N2 metastable (relatively stable).

The erbium ion in N2 metastable state is stimulated by 1550 nm optical signal, and the stimulated radiation returns to N1 ground state. In this process, erbium ion releases energy, which is converted into the optical power of optical signal, so that the optical signal can be amplified.

Note: in addition to returning to the N1 ground state through the stimulated radiation mentioned above, the N2 metastable erbium ions will also spontaneously transition to the N1 ground state, resulting in spontaneous emission noise and affecting the signal-to-noise ratio of the system.

From the above amplification process, we can see that the erbium-doped fiber amplifier has the following four characteristics:

According to the position and function of erbium-doped fiber amplifier in the system, there are three application modes: OBA, OLA and OPA.

Raman fiber amplifier Raman amplifier consists of pump laser and coupler, which have the same function as erbium-doped fiber amplifier. It should be noted that the amplification process of the optical signal of the Raman amplifier is completed in the transmission fiber, which is different from the EDFA amplifier. According to the relationship between pump light transmission direction and optical signal transmission direction, Raman amplifier is divided into forward Raman amplifier and backward Raman amplifier.

So how does the Raman amplifier amplify the signal?

Based on stimulated Raman scattering, the Raman amplifier uses the transmission fiber as the gain medium to amplify the signal light by transferring the strong pump power to the signal light.

The basic principle of stimulated Raman scattering is that if a weak signal light and a strong pump light are transmitted in the same optical fiber at the same time, and the wavelength of the weak signal light is within the Raman gain bandwidth of the strong pump light, the energy of the strong pump light is coupled into the oscillation mode of the optical fiber silicon material through the stimulated Raman scattering, and then emitted at a longer wavelength, which is the wavelength of the signal light, so that the weak signal light can be amplified. Gain Raman gain.

Raman amplifiers have the following four characteristics:

How is the Raman amplifier applied in the transmission system? The forward Raman amplifier is applied to the transmitter, and the backward Raman amplifier is applied to the receiver.

Erbium-doped fiber amplifier VS Raman fiber amplifier the difference between erbium-doped fiber amplifier and Raman amplifier is shown in the following table.

Because erbium-doped fiber amplifier and Raman amplifier have their own advantages and disadvantages, erbium-doped fiber amplifier and Raman amplifier are generally used together, which can not only obtain higher gain, but also effectively reduce the total noise of the system and improve the signal-to-noise ratio of the system. to extend the transmission distance.

All right, that's all for the introduction of the optical amplifier.

In this era of more and more frequent information exchange, optical amplifiers, as gas stations in the transmission network, are the energy supplements on the way of information transmission, ensuring that our information can be delivered smoothly to the destination, whether the destination is on the other side of the mountain or the sea.

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc)

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