How copper wires and fibers connect to transmit data

1, Photoelectric signal conversion method

For a long time, people have been using copper wire for the transmission of sound and information. However, more and more recently, fiber-optic cabling has begun to be used. Because of the cost, it is not possible to switch all copper wire into optical fiber all of a sudden. But if you want to convert some of the cables into light signals, the most important thing is to convert the electrical signals into light signals and then convert the light signal into electrical signals.

Using two diodes to convert electrical and optical signals, a semiconductor element such as "diode" should be used. However, diodes that convert electrical signals into light signals and diodes that convert light signals to electrical signals must be of different types. That means two types of diodes are required to connect copper and fiber.

A "laser diode" is used to convert the electrical signals transmitted by copper wires into light signals. Laser diodes are made from semiconductors called gallium arsenide (GaAs), which produce light at specific wavelengths when pressurized.

When the digital signals such as "1" and "0" are transmitted by copper wire, the high voltage state and the low voltage state correspond to "1" and "0" respectively. When the transmitted signal voltage is applied to the laser diode to convert the light signal, the light will produce or disappear. If the luminescence state and the vanishing state are set to "1" and "0" respectively, the digital data can be transmitted through the optical fiber.

If the optical signal transmitted by the fiber is reduced to electrical signals, it is necessary to use "photosensitive diode". One of the properties of the diode is that it produces a current that is proportional to the intensity of the light after being illuminated. When the optical signal transmitted by optical fiber is passed through the photosensitive diode, it can be converted into electrical signal directly. ---computer science (http://bianceng.cn)

2, the fiber and the same axis together

With the technology of converting electrical signals and optical signals to one another, high speed networks can be built at low cost by efficient use of fiber and copper wire.

The CATV is one of the representatives. In order to send TV programs, the coaxial line made of copper wire will be connected with CATV television station. Recently, Internet connections have started and applications have been made to local telephones, with more speed, more channels, and two-way communication.

The coaxial axis is difficult to transmit high frequency electrical signals at long distances. So to increase the communication distance you must use a large number of amplifiers, and the cost will increase.

If optical fiber is used to replace coaxial axis, the communication speed of CATV network can be improved without excessive use of amplifier. But if you want to bring fiber into each user's home, the cost will rise.

Thus, a relay device is set up between the CATV station and the user's home, and the cable between the CATV station and the relay device is replaced with fiber. The diode's optical-electric converters (o/e) and electric-optical converters (E/O) are used in relay devices. The shorter area between the relay device and the user's home still uses the original coaxial cable in the structure.

As a result, the backbone section is able to support broadband transmission and multi-channel, and the part of the relay device to the user's home is not subject to any changes, so there is no additional cost.