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Video optical transceiver application

2021-08-24

Video optical transceiver is a device that converts one to multiple analog video signals into optical signals through various encodings and transmits them through fiber optic media. As the process of converting video signals into optical signals involves two technologies: analog conversion and digital conversion, video optical transceiver is further divided into analog optical transceiver and digital optical transceiver. The principle of optical transceiver is to modulate signals onto light and transmit video through optical fibers.

The principle of optical transceiver is to modulate signals onto light and transmit data through optical fibers, usually using the following modulation methods:

Amplitude modulation or emphasis control system (AM): A fully analog system in which the brightness or intensity of the light emitting diode (LED) within the optical emission unit varies linearly with the input video amplitude. The amplitude modulated optical signal is sent to the optical receiving unit through optical fibers, which converts the signal into analog baseband video.

2 frequency modulation or pulse frequency modulation (FM): It is also an analog system, where the RF carrier adjusts the frequency linearly through the input video signal. The modulated carrier is used in the LED or laser transmitter of the optical emission unit, and the frequency modulated signal is sent to the optical receiving unit through fiber optics. The analog optical terminal converts the signal into digital baseband video.

1 Simulation

The analog optical transceiver adopts PFM modulation technology for real-time transmission of image signals, which has been widely used in previous years. The transmitting end will first perform PFM modulation on the analog video signal, followed by electro-optical conversion. After the optical signal is transmitted to the receiving end, it will undergo electro-optical conversion, and then undergo PFM demodulation to recover the video signal. Due to the use of PFM modulation technology, the transmission distance can easily reach around 30 km, and some products can reach a transmission distance of 80 km, or even hundreds of kilometers. Moreover, after transmission, the image signal has minimal distortion, high signal-to-noise ratio, and minimal nonlinear distortion. Through the use of Wavelength-division multiplexing technology, two-way transmission of image and data signals can also be realized on one optical fiber to meet the actual needs of monitoring projects. This analog optical transceiver also has some drawbacks:

Production debugging is relatively difficult;

It is difficult to achieve multi-channel image transmission with a single fiber, and the performance will decrease. The optical terminal can transmit 16 images, 1 audio, and 2 reverse 485 data on a single fiber;

C has poor anti-interference ability, is greatly affected by environmental factors, and has temperature drift;

Due to the use of analog modulation and demodulation technology, its stability is not high enough. With the increase of usage time or changes in environmental characteristics, the performance of the optical transceiver will also change, which brings some inconvenience to engineering use.

2 digits

Due to the significant advantages of digital technology compared to traditional analog technology in many aspects, just as digital technology has replaced analog technology in many fields, the digitization of optical transceiver has become the mainstream trend. There are two main technical methods for digital image optical transceivers: one is MPEG II image compression digital optical transceivers, and the other is non compression digital image optical transceivers. Image compression digital optical transceiver generally adopts MPEG II image compression technology, which can compress the moving image into N × The 2Mbps data stream is transmitted through standard telecommunications communication interfaces or directly through optical fibers. Due to the use of image compression technology, it can greatly reduce the signal transmission bandwidth. Compared to analog video optical transceiver, digital video optical transceiver has obvious advantages:

1. Long transmission distance: up to 80Km or even further (120Km);

2 supports video lossless regeneration relay, so multi-level transmission mode can be adopted;

3. Low environmental interference and high transmission quality;

The signal capacity supported by 4 can reach 16 channels or even more (32 channels, 64 channels, 128 channels)

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