Introduction of Optical Amplifier
With the rapid development of the optic communication networks, longer transmission lengths are required. Optical amplifier can satisfy the requirements of optical communication networks. An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be considered as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. This post is going to help you get a better understanding of optical amplifier.
Working Principles of Optical Amplifier
A basic optical communication link contains a transmitter and receiver, with an optical fiber cable connecting them. Although signals transmitting in optical fiber suffer far less attenuation than in other mediums, such as copper, there is still a limitation about 100 km on the distance the signals can travel before becoming too noisy to be detected.
Optical amplifiers are widely used in fiber optic data links. Figure 1 shows three ways in which optical amplifiers can be used to strengthen the performance of optical data links. A booster amplifier is used to increase the optical output of an optical transmitter just before the signal enters an optical fiber. The optical signal is attenuated as it travels in the optical fiber. An inline amplifier is utilized to restore (regenerate) the optical signal to its original power level. An optical pre-amplifier is operated at the end of the optical fiber link in order to increase the sensitivity of an optical receiver.
Figure 1. Optical amplifiers in fiber optic communication links
Features of Optical Amplifier
- Ratio of output power to input power
- Gain as a fuction of input power
- Range of wavelengths over which the amplifier is effective
- Maxmum output power, beyond which no amplification is reached
- undesired signal due to physical processing in amplifier
Optical fiber, made by a special process, in the fiber core layer deposition,incorporated with minimal concentration of rare earth elements, such as erbium, praseodymium or rubidium plasma, can produce corresponding erbium-doped, mixed with praseodymium or rubidium optical fiber. Fiber doping ions after motivated by the pump in the transition to the stability of the high excited state, under the induction signal light, stimulated radiation is produced, form a coherent amplification of the signal light.This OFA is essentially a special laser, its working cavity is a rare earth doped fiber particles, pump generally adopts the semiconductor laser light source.
The current optical fiber communication system operates in two low loss window: 1.55 mu m band and 1.31 mu m band. Select a different doping elements, can make the amplifier working in different window.
Erbium-doped Optical Fiber Amplifier (EDFA)
The erbium doped fiber amplifier is composed of an erbium doped fiber and a pumped light source, as shown in Figure 2. Erbium-doped fiber is the incorporation of the appropriate concentration of erbium ions in the silica fiber in the core ( Er3+), the role of the pump source is provided to the erbium ion energy, it would be from a low energy level, "pumped" to a higher energy level, it has optical gain function. When there is no pump function and the energy state of the Er3 + ions known as the ground state; after the pump energy absorption,Er3+ will be in a higher energy state, namely the transition from the ground state to an excited state. Since the lifetime of the high energy state is very short, the excited state of the Er3+ is rapidly over to the excited state, and the lifetime of the excited state is much longer, which is called the metastable state. When the Er3+ return from the transition of metastable excited state to ground state, the extra energy into fluorescence radiation, the wavelength of light radiation is determined by the metastable and energy level difference of base stations. In the 1550nm band, under the constant action of the pumping source, the metastable excited state of Er3+ is accumulated, and the number of the ions can exceed the number of ions in the ground state. When the number of particles in the high-energy state exceeds the number of particles, the inversion state of the particle number is reached.Only in this state can there be light amplification.Such as the photon energy of incident light signal is equal to the energy difference between the ground state and metastable, namely the light wavelength and the wavelength of the radiation of light are the same, it will also cause by the absorption of ground state and metastable leaps and metastable - the launch of the ground state transition, transition to absorb light energy absorption, launch transition energy, the size of the absorption and emission light energy from the ground state and metastable is proportional to the particle density.Because of the inversion of the number of particles, the total effect is that the emission of the light exceeds the absorbed light, which makes the incident light enhanced and the optical amplification is obtained.
Usage Tips
Troubleshooting
Fiber amplifier, the panel displays and the actual output is synchronized, if panel display is normal, then optical amplifier output is normal, if the amplifier power down or not when testing in this case,there are several possibilities:
- PM not allowed, domestic power meter can only test the equipment of smaller output , can not test EDFA of higher output, the power meter of testing optical amplifier must be imported, can't use the inaccurate instrument as the standard.
- The output port of flange is damaged, the possibility is small.
- Improper use, plug when machine is working, burn the output fiber tip of amplifier, cause the amplifier output power down, as this happens, just re-welded to the optical amplifier output connector.
- The pigtail of users is of poor quality,the core is too long, abrade the output connector of amplifier after inserting pigtail, the phenomenon is that the first test is good, the second time power is declined after inserted into test again, the solution to this problem is as long as to re-welding optical amplifier output connector.
- The wavelength of light source is wrong, if the wavelength of 1550 nm light transmitter has a deviation, can cause amplifier output power is not enough, also can cause small panel displays.
- Smaller light power of input optical amplifier, if it's lower than the standard values may lead to smaller light power, and panel display will be smaller.
Notes
- Do not point the fiber output to the human body, especially the eyes, so as to avoid damage.
- Do not route connections in an energized state, so as to avoid improper operation of output pigtail end face burns.
- As the output power of the product is large, please pay attention to the workshop temperature of the machine, keep good ventilation
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