What Is a USB Amplifier?
Optical fiber amplifier (Optical Fiber Ampler, abbreviated OFA) refers to a new type of all-optical amplifier used in optical fiber communication lines to achieve signal amplification [1] .
Fiber-optic signal amplifier
- Chinese name
- optical fiber amplifier
- Foreign name
- Optical Fiber Ampler
- Optical fiber amplifier (Optical Fiber Ampler, abbreviated OFA) refers to a new type of all-optical amplifier used in optical fiber communication lines to achieve signal amplification [1] .
- A transimpedance amplifier is a circuit structure commonly used in optoelectronic detection preamplifiers. It is a type of integrated op amp. It provides the operational amplifier-based current to the voltage conversion amplifier through the resistance gain and user-selected bandwidth.
Basic concept of fiber-optic transimpedance amplifier
- The transimpedance amplifier is a circuit structure commonly used in photodetection preamplification. There is no concept of gain-bandwidth product in the design of a transimpedance amplifier, and its bandwidth analysis often confuses designers. In order to study the derivation of the gain-bandwidth characteristics of the transimpedance amplifier in this kind of specific gain-bandwidth product, the relationship between the gain and bandwidth of the transimpedance amplifier was derived by using a single-pole approximation method, and simulation was performed using Multisim software to verify the conclusion Sex. It is pointed out that gain and bandwidth are still contradictory in transimpedance amplifiers.
- Optical fiber amplifier (Optical Fiber Ampler, OFA for short) refers to a new type of all-optical amplifier applied to optical fiber communication lines to achieve signal amplification. According to its position and role in the optical fiber line, it is generally divided into three types: relay amplification, pre-amplification and power amplification. Compared with the traditional semiconductor laser amplifier (SOA), OFA does not need to go through complicated processes such as photoelectric conversion, electro-optical conversion, and signal regeneration. It can directly amplify the signal, and has good "transparency", which is especially suitable for long distances. Optical communication relay amplification. It can be said that OFA has laid a technical foundation for the realization of all-optical communication [1] .
OFA Fiber Optic Transimpedance Amplifier OFA Classification
- Depending on the amplification mechanism, OFA can be divided into two major categories.
1 OFA Optical fiber transimpedance amplifier1 , rare earth doped OFA
- When making optical fibers, a special process is used to mix the rare-earth elements such as erbium, europium, or ytterbium ions into the core deposition of the optical fiber to produce the corresponding erbium-, erbium-, or erbium-doped optical fibers. The doped ions in the optical fiber transition to a metastable, highly excited state after being excited by the pump light, and are induced by the signal light to generate stimulated radiation to form a coherent amplification of the signal light. This OFA is essentially a special laser. Its working cavity is a section of rare-earth-doped fiber. The pump light source is generally a semiconductor laser.
- Current optical fiber communication systems operate in two low-loss windows: the 1.55 m band and the 1.31 m band. Selecting different doping elements can make the amplifier work in different windows.
- (1) Erbium-doped fiber amplifier (EDFA)
- EDFA operates in a 1.55 m window, which has a fiber loss coefficient of 1.31 m and a low window (only 0.2 dB / km). The commercial EDFA has low noise, good gain curve, large amplifier bandwidth, compatible with wavelength division multiplexing (WDM) system, high pumping efficiency, stable working performance, mature technology, and is favored in modern long-distance high-speed optical communication systems. At present, "erbium-doped fiber amplifier (EDFA) + dense wavelength division multiplexing (DWDM) + non-zero dispersion fiber (NZDF) + photon integration (PIC)" is becoming the main technical direction of international long-distance high-speed optical fiber communication lines.
- (2) Erbium-doped fiber amplifier (PDFA)
- PDFA works in the 1.31m band, and 90% of the installed optical fibers work in this window. PDFA is of great significance to the upgrade and expansion of existing optical communication lines. At present, PDFA with low noise and high gain has been developed, but its pumping efficiency is not high, the working performance is unstable, the gain is sensitive to temperature, and it is still some distance from practical use [1] .
2 OFA Fiber Optic Transimpedance Amplifier 2. Nonlinear OFA
- Non-linear OFA is a kind of laser amplifier that uses the non-linear effect of optical fiber to amplify signal light. When the optical power density in the fiber reaches a certain threshold, stimulated Raman scattering (SRS) or stimulated Brillouin scattering (SBS) will occur, forming a coherent amplification of the signal light. Nonlinear OFA can be divided into Raman fiber amplifier (SRA) and Brillouin fiber amplifier (BRA). The SRA developed so far has not yet been commercialized.
- The development of OFA began in the 1980s and made major breakthroughs in the early 1990s. In the design of modern optical communication systems, how to effectively increase the transmission distance of optical signals, reduce the number of relay stations, and reduce system costs has always been the goal of people's continuous exploration. OFA is a key device to solve this problem, and its development and improvement are still in the ascendant worldwide.
- With the development of dense wavelength division multiplexing (DWDM) technology and fiber amplification technology, including erbium-doped fiber amplifier (EDFA), distributed Raman fiber amplifier (DRFA), semiconductor amplifier (SOA) and optical time division multiplexing (OTDM), Widely used, optical fiber communication technology is continuously developing towards higher speed and larger capacity communication systems, while advanced optical fiber manufacturing technology can maintain stable and reliable transmission and sufficient margin, and can also meet the demand for large bandwidth of optical communication And reduce non-linear damage [1] .
The role of the optical fiber transimpedance amplifier
- Amplifying circuit is one of the circuits widely used in electronic technology. Its function is to amplify the weak input signal (voltage, current, power) to the value required by the load without distortion. Types of amplifier circuits: (1) voltage amplifier: the input signal is small, and requires a large output voltage without distortion, also known as small signal amplifier; (2) power amplifier: the input signal is large, and the amplifier needs to output sufficient power, Also called large signal amplifier. The role of the amplifier circuit: The amplifier circuit is one of the circuits widely used in electronic technology. Its role is to amplify the weak input signal (voltage, current, power) to the value required by the load without distortion.
Fiber transimpedance amplifier amplifier circuit types
- (1) Voltage amplifier: The input signal is small and requires a large output voltage without distortion, also known as small signal amplifier; (2) Power amplifier: The input signal is large and requires the amplifier to output sufficient power, also known as large signal Amplifier. Optical amplifiers do not need to convert optical signals to electrical signals, and then switch back to optical signals. This feature leads to two advantages of optical amplifiers over regenerators. First, the optical amplifier supports any bit rate and signal format because the optical amplifier simply amplifies the received signal. This property is usually described as the optical amplifier is transparent to any bit rate and signal format. Second, the optical amplifier not only supports single signal wavelength amplification-like a regenerator, but also supports optical signal amplification in a certain wavelength range. Moreover, only optical amplifiers can support time division multiplexing and wavelength division multiplexing networks with multiple bit rates, various modulation formats, and different wavelengths. In fact, only with the emergence of optical amplifiers, especially EDFA, WDM technology can really play an important role in fiber optic communications. EDFA is currently the most popular optical amplifier. Its appearance has brought the theory of wavelength division multiplexing and all-optical networks into reality.
The main types of fiber optic transimpedance amplifiers
- Two main types of optical amplifiers are in use: semiconductor optical amplifiers (SOA) and fiber optical amplifiers (FOA). Semiconductor optical amplifiers are essentially the active medium of semiconductor lasers. In other words, a semiconductor amplifier is a laser diode with little or no optical feedback.
The difference between fiber amplifier and semiconductor amplifier
- The active medium (or gain medium) of a fiber amplifier is a special fiber or transmission fiber, and is connected to a pump laser; when the signal light passes through this fiber, the signal light is amplified. Fiber amplifiers can be further divided into rare earth ion fiber amplifiers (Rare Earth Ion Doped Fiber Amplifier) and non-linear fiber amplifiers. Like semiconductor amplifiers, the working principle of rare-earth ion-doped fiber amplifiers is also stimulated radiation; while non-linear fiber amplifiers use the nonlinear effects of optical fibers to amplify optical signals. Practical fiber amplifiers include erbium-doped fiber amplifiers (EDFA) and fiber Raman fiber amplifiers (Raman Fiber Amplifier).
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Structure of fiber-optic transimpedance amplifier
- The positive end of the op amp in the figure is directly grounded. Dphoto is a photodiode for receiving signals. The feedback resistance Rf determines the size of the gain. Vbias is the reverse bias voltage. It can improve the corresponding linearity of the photocell and reduce the junction capacitance , Increase the circuit bandwidth. In order to study the frequency characteristics of the transimpedance amplifier, it is necessary to use the equivalent circuit model of the photocell Dphoto.
<!--[]--> Fiber Transimpedance Amplifier <!-[Edit this section]-> Characteristics of Transimpedance Amplifier
- Selectable conversion gain
- Selectable corner frequency
- Capacitive input source compensation
- Adjustable power settings
- Optional input reference voltage
Application of fiber-optic transimpedance amplifier
- A transimpedance amplifier is used to convert external current to voltage. Typical applications include sensor measurements using current outputs such as photodiodes. The conversion gain of TIA is in ohms, and its usable range is from 20 K to 1.0 M ohms. The output capacitance of a current output sensor such as a photodiode is usually large. This requires adding a parallel feedback capacitor to the transimpedance amplifier to ensure stability. The transimpedance amplifier has a programmable feedback capacitor that meets this need and provides bandwidth limitations to reduce wideband noise.