Analysis of fiber optic couplers and fiber optic cables

An optocoupler (referred to as optocoupler) is a semiconductor optoelectronic device that encapsulates the light-emitting element and the photosensitive element in the same housing, and transmits electrical signals through the conversion of electricity → light → electricity in the middle. Photocouplers can be combined into many series of photocouplers by combining different types of light-emitting elements and photosensitive elements according to different requirements. At present, the most widely used photocoupler is a combination of light-emitting diodes and phototransistors.

The optocoupler uses the optical signal as the medium to realize the coupling and transmission of the electrical signal. The input and output are completely isolated electrically, and it has the characteristics of strong anti-interference performance. For the industrial application measurement and control system that includes both the weak current control part and the strong current control part, the use of optocoupler isolation can well realize the isolation of weak current and strong current, and achieve the purpose of anti-interference. However, the use of optocoupler isolation requires consideration of the following issues:

① When the optocoupler is directly used to isolate and transmit analog quantities, the nonlinear problem of the optocoupler should be considered;

② When the optocoupler is isolated to transmit digital quantities, the response speed of the optocoupler should be considered;

③ If the output has power requirements, the power interface design of the optocoupler must be considered.

According to the shielding, twisted pair can be divided into unshielded twisted pair (UTP: Unshielded Twisted Pair) and shielded twisted pair (STP: Shielded Twisted Pair).

fiber optic coupler

shielded twisted pair

According to the different shielding methods, shielded twisted pair is divided into two categories, namely STP (Shielded Twicted-Pair) and FTP (Foil Twisted-Pair). STP refers to a shielded twisted pair in which each line has its own shielding layer, while FTP is a shielded twisted pair with an overall shield. It should be noted that the shield only has a shielding device on the entire cable, and both ends are properly grounded. only works under the circumstances. Therefore, the entire system is required to be shielded devices, including cables, sockets, crystal heads and patch panels, etc. At the same time, the building needs to have a good grounding system.

The outer layer of the shielded twisted pair cable is wrapped with aluminum foil to reduce radiation, but it cannot completely eliminate radiation. Shielded twisted pair cables are relatively expensive and more difficult to install than unshielded twisted pair cables. Similar to coaxial cable, it must be equipped with special connectors that support shielding and corresponding installation techniques. But it has a higher transmission rate, up to 155Mbps within 100 meters.

Unshielded twisted pair

Unshielded twisted pair cable consists of multiple twisted pairs and a plastic sheath. The International Association of Electrical Industries defines five different quality levels for twisted pair cables.

Commonly used in computer networks are Category 3 and Category 5 and Category 5e and current Category 6 unshielded twisted pair cables. The third type of twisted pair is suitable for most computer local area networks, while the fifth and sixth types of twisted pair greatly improve the properties of the transmission medium by increasing the winding density and high-quality absolute image material.

According to electrical performance, twisted pair can be divided into: Category 1, Category 2, Category 3, Category 4, Category 5, Category 5e, Category 6, Category 6e, Category 7, a total of 9 twisted pair types. The larger the type number, the newer the version, the more advanced the technology, the wider the bandwidth, and of course the more expensive it is. The labeling method of these different types of twisted pair is as follows: if it is a standard type, it is marked by "catx". For example, the commonly used Category 5 cable is marked as "cat5" on the outer skin of the wire. Note that the letters are usually lowercase. , instead of uppercase. And if it is an improved version, it is marked by "xe". For example, the super 5 line is marked as "5e", and the letters are also lowercase, not uppercase.

Twisted pair technical standards are formulated by the American Telecommunications Industry Association (TIA), and its standard is EIA/TIA-568B, as follows.

Category 1 (Category 1) line

It is the most original unshielded twisted pair copper cable in the ANSI/EIA/TIA-568A standard, but it was originally developed not for computer network data communication, but for telephone voice communication.

Category 2 (Category 2) line

It is the first unshielded twisted pair cable that can be used for computer network data transmission in ANSI/EIA/TIA-568A and ISO Class 2/Class A standards, with a transmission frequency of 1MHz and a transmission rate of 4Mb/s. It is mainly used for old Token Network.

Category 3 (Category3) line

It is an unshielded twisted pair cable specially used for l0BASE-T Ethernet network in ANSI/EIA/TIA-568A and ISO Class 3/Class B standards. The transmission frequency is 16MHz and the transmission rate can reach l0Mb/s.

Category 4 (Category 4) line

It is an unshielded twisted pair cable for Token Ring networks in ANSI/EIA/TIA-568A and ISO Category 4/Class C standards, with a transmission frequency of 20MHz and a transmission rate of 16Mb/s. Mainly used for token-based LAN and 10BASE-T/100BASE-T.

Category 5 (Category 5) line

It is an unshielded twisted pair cable for running CDDI (CDDI is an FDDI network based on twisted pair copper wire) and Fast Ethernet in ANSI/EIA/TIA-568A and ISO Category 5/Class D standards, with a transmission frequency of 100MHz, The transmission rate reaches 100Mb/s.

Category excess 5 wire

It is an unshielded twisted pair cable used to run Fast Ethernet in ANSI/EIA/TIA-568B.1 and ISO Category 5/Class D standards. The transmission frequency is also 100MHz, and the transmission rate can also reach 100Mb/s. Compared with Category 5 cables, Category 5e has great improvements in the four main indicators of near-end crosstalk, total crosstalk, attenuation and signal-to-noise ratio.

Category 6 (Category 6) line

It is an unshielded twisted pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards. It is mainly used in Fast Ethernet and Gigabit Ethernet. Because its transmission frequency can reach 200 ~ 250MHz, which is twice the bandwidth of the super-category 5 line, and the maximum rate can reach 1000Mb/s, which meets the needs of Gigabit Ethernet.

Category excess 6 wire

It is an improved version of Category 6 cable. It is also an unshielded twisted pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards. It is mainly used in Gigabit networks. In terms of transmission frequency, it is the same as Category 6 line, which is 200-250MHz, and the maximum transmission rate can also reach 1 000Mb/s, but it has great improvement in crosstalk, attenuation and signal-to-noise ratio.

Category 7 (Category 7) line

It is the latest twisted pair in the ISO Category 7/F standard, mainly to adapt to the application and development of 10 Gigabit Ethernet technology. But it is no longer an unshielded twisted pair, but a shielded twisted pair, so its transmission frequency can reach at least 500MHz, which is more than twice that of Category 6 and Category 6e cables. Up to 10Gb/s.