About Optical hybrid cable (AOC) and all-optical transmission in HDMI optical fiber transmission–

       Since 2000, with the development of communication technology, optical module transmission technology has appeared in optical fiber communication. After 2002, digital transmission HDMI audio and video signal products have also appeared in the field of consumer electronics. In April 2002, seven companies including Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba jointly established the HDMI high-definition multimedia interface interface organization. HDMI transmission is divided into two parts: high-speed signal transmission and low-speed signal transmission: 1 - 12 4-pair cables with 12 feet transmit high-speed signals, using TMDS differential signal technology (TMDS (Time Minimized Differential Signal) invented by Silicon Image Company to minimize transmission differential signal transmission technology, TMDS is a differential signal mechanism, adopted It is a differential transmission method, which is the basic principle of HDMI technology. In optical fiber transmission HDMI: these 4 pairs of 12 TMDS cables are transmitted by 4 VCSEL+4 multimode optical fibers, which can easily solve the problem of high-speed transmission. In the HDMI low-speed transmission channel , 13-19 pins in HDMI have 7 electronic cables respectively responsible for: 5V power supply, HPD hot-swappable activation of CEC, internet, SDA, SCA, DDC channels. It is not so easy for these 7 electronic lines to use optical fiber transmission ,The most important display resolution is to read the DDC channel: it uses the command of the I2C interface on the HDMI source to read the E-EDID of the receiving end. I2C is the abbreviation of Inter-Integrated Circuit, which is a kind of Serial communication bus, using multi-master-slave architecture. The proposer of I2C is also one of the initiators of the HDMI organization: Philips Semiconductors.

The historical background of AOC optical hybrid cable science popularization

      HDMI cables are usually used to connect audio-visual equipment, TV sets, and monitors, so most of them are transmitted over short distances, usually only 3 meters long; what should users do if they need more than 3 meters? If you continue to use copper wire, the diameter of the copper wire will become larger, and it will be difficult to bend, and the cost will be high. Therefore, the best way is to use optical fiber. The HDMI AOC optical hybrid cable product is actually a technically compromised product. The original intention of the original development should be that all HDMI 19 cables are transmitted by optical fiber. This is the real optical fiber transmission HDMI, but because of the 7 It is difficult to encode and decode low-speed signals using VCSEL+multimode fiber for the first cable, so the developer simply transmits the 4 pairs of TMDS channels in the high-speed signal via VCSEL+multimode fiber, and the remaining 7 electronic wires are still directly connected by copper wires. It is found that after the high-speed signal is transmitted by optical fiber, the optical fiber HDMI AOC can be transmitted to a distance of 100 meters or even longer because the transmission distance of the TMDS signal is extended. Optical fiber HDMI AOC hybrid cable still adopts copper wire transmission for low-speed signal, the problem of high-speed signal is solved, but the problem of low-speed signal copper cable transmission is still not solved, so various compatibility problems are prone to appear in long-distance transmission. And all of this can completely solve this problem if the HDMI with all-optical technology solution is adopted. All-optical HDMI uses 6 optical fibers, 4 of which transmit high-speed TMDS channel signals, and 2 are used to transmit low-speed HDMI signals. An external 5V power supply is required at the RX display terminal as the excitation voltage for HPD hot-swap. After adopting the all-optical solution of HDMI, both the high-speed TMDS channel and the low-speed DDC channel are changed to optical fiber transmission, and the transmission distance is greatly improved.

Protocol Specification Support

      Although the fiber-optic hybrid cable has brought long-distance signal lossless transmission to a very high level, there is still a technology that completely solves the existence of copper wire as a transmission conductor, that is, pure optical fiber HDMI2.1 cable, HDMI2.1 pure optical active The optical cable (AOC) fully complies with the HDMI2.1 standard, and the signal transmission uses optical fiber without copper wires, and the optical fiber transmission is not subject to electromagnetic interference. The AOC transmission signal is uncompressed, with a maximum bandwidth of 48Gbps, which can perfectly transmit 8K ultra-high-definition images, and the longest transmission distance can reach 500m. Compared with traditional copper wires, this optical cable is longer, softer and lighter, with better signal quality and perfect electromagnetic compatibility characteristics. At the beginning of the year, the HDMI Association made a major update to the HDMI Cable certification test specification, and added a DMI Passive Adapter certification test plan. In the past, under the Ultra High Speed HDMI Cable test specification, in addition to supporting the HEAC function, the cable used to transmit HEAC still needs to be used. Only copper wires can be certified. If all optical fibers are used, evidence cannot be obtained. However, the HEAC function under the Premium High Speed HDMI Cable specification is optional support. After this specification is updated, it has become the first choice for the test solution of all-fiber AOC Cable at this stage. Pure optical fiber HDMI It has finally been officially recognized. Now it is said that HDMI optical fiber transmission is better than optical hybrid cable (AOC) and all-optical transmission. In fact, it mainly depends on cost performance and application market. Each has its own advantages.