A Brief Understanding of AOC Active Optical Cables

In the era of big data, there are more and more high-density and high-broadband applications. At this time, passive optical cables or copper-based cable systems are less useful than before. In order to ensure the stability and flexible application of transmission, users urgently need a new type of product as the main transmission medium for high-performance computing and data centers. Under this circumstance, active optical cables have emerged.

1. The advantages of AOC active optical cables

Compared with traditional cables, active optical cables have many advantages such as high transmission rate, long transmission distance, low energy consumption, and convenient use. With the huge advantage of optical transmission, they are ideal for data center, electronic consumption and other fields.

As the trend of "replacement of copper cables with optical fiber cables" is irreversible, the future will be the era of "all-optical networks", and the technology of active optical cables will be seen every corner of the high-speed interconnection market.

2. The structure and signal transmission mode of AOC active optical cables

AOC active optical cable uses a length of optical fiber cable to connect two optical transceivers. With the help of an external power supply, the signal transmission is carried out by method of electrical-optical-electrical conversion, that is, the electrical signal is converted into an optical signal in transceiver A, and the optical signal is transmitted to transceiver B through the middle fiber optical cable, and then in transceiver B the optical signal is converted into an electrical signal.

3. The characteristics of AOC active optical cables

AOC active optical cable has such characteristics as low power consumption, small size, light weight and strong heat dissipation. Compared with copper cables, its transmission distance (up to 100~300m) is longer with better transmission performance. Compared with optical transceivers, the active optical cable does not have the problem of interface contamination, which greatly improves the stability and reliability of the system, reducing the management cost of the computer room.

4. The transmission principle of AOC active optical cables

Let's take QSFP+ AOC as an example. Both ends of the cable (end A and end B) are QSFP optical transceivers. In transceiver A, the data input Din is an electrical signal, and through the E-O converter, the electrical signal is converted into the optical signal of specific wavelength. At last, the optical signal is input into the optical cable after modulation and coupling; after the optical signal reaches the transceiver B through the optical cable, the O-E Converter detects the optical signal and then amplifies it. In the end, Dout outputs the corresponding electrical signal. The transmission of both ends is symmetrical.

Parallel optical interconnection is realized by parallel optical transceivers and ribbon optical cables. Parallel optical transceiver is based on VCSEL array and PIN array, with a wavelength of 850nm, suitable for multimode fiber 50/125um and 62.5/125um. In terms of packaging, the electrical interface adopts a standard Meg Array connector, and the optical interface uses a standard MTP/MPO ribbon optical cable. At present, the more common parallel optical transceivers include 4-way transceiver integrated and 12-way transceiver separated.

5. Active optical cable can be divided into three functional parts: light emitting part, light receiving part, and control circuit

(1) The light emitting part includes: VSCEL laser, monitor diode, drive and control circuit, etc.

The light emitting is the conversion of digital electrical signals into optical signals for transmission through optical fibers. It mainly includes signal modulation, static operating point adjustment and automatic power control and other sub-circuits， which has the functions of emission prohibition and monitoring output.

(2) The light receiving part includes: photodiode (PIN), transimpedance amplifier (TIA) and auxiliary circuit.

The light receiving is to convert the weak optical signal in the optical fiber into an electrical signal, and the transimpedance amplifier (TIA) outputs an amplitude limiting electrical signal with a non-light alarm function.

6. The application of AOC active optical cable products

(1) Used for connection between racks

AOC active optical cable is an ideal cable for the connection between data center racks and racks with the best length within 5~30m in general. High-speed cable DAC can be selected for short-distance connection within 5m, and optical transceiver + optical fiber wire jumper combination can be selected for long-distance connection over 30m.

(2) Used for connection between switches and between switches and servers

The 40G QSFP+ to 4*SFP+ active optical cable can connect two switches. It can also connect the switch on the top of the 10G rack and the server with a 10G network card in the rack to realize 10G network transmission.