Learn to choose the right fiber in minutes
How to select a right optical fiber?
The basic requirement when selecting the optical fiber is that the optical power coupled into the optical fiber from the emitting light source should be large enough, and the distortion generated after the optical signal is transmitted through the optical fiber is minimal.
Low transmission attenuation
In a particular wavelength range, the attenuation must be small enough to allow the relay distance to be as long as possible while meeting the optical power required by the receiver. When designing the system, consider the insertion loss of connectors, connectors, and couplers, and the amount of headroom required for system operation. For this reason, the correct choice of operating wavelength and fiber type.
Low coupling loss
Coupling losses include light source coupling loss and detector coupling loss. When the core size and numerical aperture are large, the coupling loss of the light source can be reduced, but the detector coupling loss increases. In order to reduce the coupling loss with the detector, it is required that the core size and the numerical aperture be sufficiently small so that the outgoing light of the optical fiber completely falls on the receiving surface of the detector. In order to improve the response speed of the receiver and reduce the noise, the area of the detector is required to be small, so the method of increasing the photo-sensitive surface of the detector cannot be used to reduce the coupling loss. Fibers with a large core size and numerical aperture have a small transmission bandwidth and are suitable for systems using LEDs.
Low connection loss
Connection losses include loss of connectors and connectors. The core diameter tolerance, out-of-roundness, and core and cladding concentricity errors are as small as possible to obtain the minimum connection loss. To increase the geometrical accuracy of the optical fiber, it is necessary to increase the manufacturing cost. Increasing the size of the core and the numerical aperture can reduce the adverse effect of the geometrical tolerance on the connection loss, but it is inconsistent with the increase of the bandwidth and a comprehensive consideration must be taken for the compromise.
Dispersion and bandwidth
In order for the modulated optical signal to pass through the full length of the optical fiber with minimal distortion, the dispersion of the optical fiber is required to be sufficiently small. In order to reduce fiber dispersion, the refractive index distribution index and the zero dispersion wavelength must be strictly controlled. For a specific system, the fiber type and working wavelength should be selected correctly. For example, a long-distance, high-rate submarine cable system should use a G.654 fiber with a zero-pigment shift of 1.55 μm. The wavelength-division multiplexing system should choose a small dispersion system. However, the non-zero but G.655 fiber reduces the four-wave mixing but has an adverse effect. The DWDM system used in the metropolitan area network must be a full-wave fiber with an extremely wide wavelength range and a wide range of available wavelengths. Systems using LEDs must fully consider the effects of material dispersion and other factors. The table above shows the typical parameters of a zero-cable single-mode fiber for reference when selecting the fiber.
Learn about optical repeater transmission system in minutes
The transmission distance of any optical fiber communication system is limited by the factors such as optical fiber loss and dispersion. The optical fiber communication network system, like the telecommunication network, must add a regenerative relay station at a certain distance to complete the transmission of signals during long-distance long-distance transmission. The amplification and regeneration to ensure signal transmission quality. In optical fiber transmission links, in addition to using various active devices with different functions, the quality of optical passive devices has an impact on the performance of optical fiber networks.
Learn about types of Optical-electrical-optical repeater
Absorption and dispersion of the optical fiber result in attenuation of the optical signal and waveform distortion, and therefore, the quality of information transmission is reduced, the bit error rate is increased, and the communication distance is limited. In order to meet long-distance communication requirements, there are usually two methods for the relay transmission of optical signals: First, an optical-electric hybrid repeater used in the early days, and an optical-electrical-optical conversion method is adopted, and its structure is shown in the following figure. Attenuation and distortion of the optical signal will be received by the optical receiver, and converted to electrical signals for processing, and then modulate the optical transmitter light source, convert the optical signal to continue transmission; Another method is to use optical amplifier to light The signal is amplified directly and transmitted.
Optical-electrical-optical repeater structure
Early (and still widely used) optical fiber relays use optical-electrical-optical conversion. The structure of a typical digital optical repeater is shown in the figure below, mainly consisting of a photodetector, an electrical signal amplifier (a low noise preamplifier and a high gain main amplifier), an equalizer circuit, an automatic gain controller (AGC) circuit, and a decision Regeneration circuit, light modulation circuit and light source.
Light-electric-light conversion process
The photodetector is used to sense the received optical signal, convert it into an electrical pulse signal, and then through an electrical signal amplifier for amplification, regeneration decision processing, etc., to restore the same digital signal stream as the transmission end, and then pass The light modulator modulates the light source, converts it into an optical signal and enters the optical fiber to continue transmission. That is, each relay station processes the transmitted optical signal using an optical-electrical-optical conversion method.
Optical-electric-optical repeater functional modules
From the composition of the repeater, the main functional modules can be summarized as follows.
Balanced magnification. It means that the distorted weak electrical signal that is input is equalized, compensated, shaped and amplified to a certain extent to meet the signal processing requirements.
Timing extraction circuit. It refers to extracting the clock frequency from the input electric pulse signal sequence to obtain the timing pulse for use in circuits such as synchronous demodulation.
Decision regeneration circuit. It refers to regenerating the transmission distortion waveform to obtain the same electrical pulse sequence shape process as the transmission end.
The most important feature of this repeater is that it can shape and regenerate the pulse signal so that the distortion of the waveform will not be accumulated. The inadequacies are complex equipment, high costs, and inconvenient maintenance.
The optical-electrical-optical conversion repeater technology is relatively mature, but its disadvantage is that the equipment is complex and the cost is high, and it is also a bottleneck of the signal transmission link (the electric signal bandwidth is much narrower than the optical signal bandwidth). With the development of optical device technology, it has been developed to directly amplify and relay optical signals.
Prior to the advent of optical fiber amplifiers, repeaters of optical fiber communication systems used optical-electrical-optical conversion methods without exception. This resulted in the complexity of equipment in communication systems, which resulted in high costs and reduced capacity. As a result, the efficiency of the system was reduced. Increased network costs and other issues. Therefore, scientists have long been devoted to the study of all-optical relays, that is, direct optical amplification repeaters that do not require optical-electrical-optical conversion. The emergence of optical fiber amplifiers is an important milestone in the history of optical fiber communications. The development trend of optical fiber communication systems is to realize all-optical networks. Optical amplifiers are directly used to amplify optical signals. The amplification process is shown in the figure.
Optical amplifier type
An all-optical repeater, ie, an optical amplifier, is characterized by directly amplifying the optical signal and has a high degree of transparency to the signal pair format and rate (because the optical amplifier only amplifies the received signal, so it can support various bit rates and any The format of the signal) makes the system structure simple and flexible.
Optical amplifiers mainly include semiconductor optical amplifiers (SOAs) and fiber amplifiers. The title optical amplifier refers to an optical amplifier device made of a semiconductor material. If the reflection film at both ends of the semiconductor laser is removed, that is, a semiconductor traveling wave optical amplifier without feedback, it can amplify light of different wavelengths. Fiber amplifiers include two types: nonlinear fiber amplifiers and doped fiber amplifiers. The doped fiber amplifier is an optical amplifier developed in recent years. It utilizes a rare-earth metal ion doped (Er), neodymium (Nd), praseodymium (Pr), ytterbium (Tm), etc. doped with a rare- The ions are incorporated into the optical fiber, and the pump light source is externally applied to meet certain conditions to constitute an optical amplifier. Common doped fiber amplifiers (1.55 μm operating band), Erbium doped fiber amplifiers (1.3 μm working band), Erbium-doped fiber amplifiers (1.55 μm working band), etc.
Understand the handheld fiber optic microscope in minutes
What is a digital microscope?
A digital microscope is a variation of a traditional optical microscope that uses optics and a digital camera to output an image to a monitor, sometimes by means of software running on a computer. … Since the image is focussed on the digital circuit the entire system is designed for the monitor image.
The handheld fiber optic microscope
Reliability and performance of a fiber optic link largely depends on the quality of interconnects. Contaminated connectors can cause the mating surfaces to separate leading to high insertion loss and back-reflection. Furthermore, some dirt particles can even scratch or dig into the glass causing permanent damage to the end-face of the connector. Therefore, inspection of fiber optic connectors should be performed whenever a connection is to be made.
The handheld microscope specifically designed for fiber optic connector end face inspection.
3.5-inch TFT display
Up to 250x overall magnification
4x digital zoom
SD card storage up to 8G
Snapshot, video recording and playback
News for Wednesday 20 March, 2019