How To Convert Optical Signals Into Electrical Signals In The Photoelectric Conversion Process?

- Jul 18, 2020-

The photoelectric converter is a device similar to the baseband MODEM (digital modem). The difference from the baseband MODEM is that it is connected to the optical fiber dedicated line, which is an optical signal. Gigabit optical fiber transceiver (also known as photoelectric converter) is a fast Ethernet with a data transmission rate of 1Gbps. It still uses CSMA/CD access control mechanism and is compatible with existing Ethernet. With the support of the wiring system , Can smoothly upgrade the original fast Ethernet and can fully protect the original investment of users. At present, Gigabit network technology has become the preferred technology for new construction and transformation, and the performance requirements of the integrated wiring system have also increased. Principle: According to Shannon's theorem, the relationship between channel bandwidth and channel capacity is: C=Wlog2(1+S/N) (bps)…………………….. (1) where C is the channel capacity , W is the channel width, N is the noise power, S is the signal power, and S/N is the signal-to-noise ratio. It can be seen from (1) that the channel capacity can be improved by increasing the channel bandwidth and signal-to-noise ratio. The currently available twisted pairs supporting high-speed network applications are cat5, super cat5, and cat6, with their maximum bandwidths of 100MHZ, 100MHZ and 200MHZ. Because the Gigabit Ethernet twisted-pair cabling standard 802.3ab is based on the use of 4 pairs of cat5UTP, the bandwidth of Category 5 UTP is 1/100MHZ. Therefore, only from the perspective of bandwidth, the choice of Category 5 twisted pair can meet the requirements of Gigabit network applications. Consider again from the perspective of signal-to-noise ratio. Gigabit networks need to simultaneously use four pairs of UTP cables for high-speed parallel data transmission. Signal and noise are related to the following characteristic parameters of the cable respectively. These parameters are: Attenuation: refers to the attenuation of signal transmission along the link. Return Loss (RL): The reflection of the transmitted signal power due to the deviation of the characteristic impedance of the cable and the impedance of the link connector from the standard value. Near-end crosstalk loss (NEXT): Similar to noise, it is an interference signal transmitted from an adjacent pair of lines. This kind of crosstalk signal is due to the coupling of adjacent winding pairs in UTP through capacitance or inductance. Adjacent pair comprehensive crosstalk (Powersum): refers to the sum of the crosstalk between the other three pairs of working signals on the other three pairs of wires in an environment where four UTP pairs are used to transmit data at the same time. Suppose the transmitted signal is T, and the above four characteristic parameters are represented by A, R, NE, and P respectively, then: Singal(f)=f1(T, A)……………….…..(2) Noise(f) )=f2(R, NE, P).……………….. (3) Equations (2) and (3) represent the received signal and noise, respectively. The parameters A, R, NE, and P in the two equations are all Function of frequency f. Therefore, the following two formulas for calculating the signal-to-noise ratio are obtained: From these two formulas, it is known that to improve the signal-to-noise ratio, it is necessary to select UTP with excellent parameters such as A, R, N, P to increase S and reduce N. The higher the category of UTP, the more margins of the above parameters from the limit value specified by the standard, and the better its performance. Since some parameters of cat5UTP are greatly affected by construction quality or environment, and often fail to meet the requirements of wiring standards, the above-mentioned shortcomings of cat5UTP are improved by the super-category 5 UTP. Therefore, super cat5 and cat6UTP can meet the signal-to-noise requirements. Since the performance of cat6UTP is worried about super cat5, and cat6UTP can also meet the higher speed network applications in the future, therefore, Cat6UTP and its supporting connectors and plug-ins should be preferred under the current circumstances. This also increases the performance requirements of the integrated wiring system.

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