How to Define an AOC (Active Optical Cable) Product Specification
This article is a short guide to defining an AOC (Active Optical Cable) product specification.
When I write an AOC product spec, I usually split it into three main parts:
Application
Appearance
Function
Starting from these three topics makes spec discussions with customers or R&D engineers much more efficient.
1. Application. Application can be broken down into three parts:
Ask the customer for requirements. This is the fastest and clearest approach: have the customer state the product spec they need.
Ask the customer for the use case. If the customer cannot state a clear spec, ask them to describe the application scenario and help evaluate it.
Propose based on competitors' specs. Almost every product has similar offerings from competitors, so starting from the applications they target is also a good approach.
2. Appearance
Connector type: the connector form factor, e.g., USB-C, the hottest today, which supports reversible insertion, or QSFP, the most popular in data centers, which supports four-lane in/four-lane out data transfer.
Connector dimension: in consumer electronics, the overall size of the plug is scrutinized closely, since consumers generally prefer thin, light and compact products.
Cable diameter: thinner is generally better, because thinner cables are easier to route.
Cable color: some vendors specify a cable color. If not, composite cables are usually black, OM3 fiber is aqua, and OM4 fiber is aqua or violet.
3. Function
a. Storage environment. The conditions under which the product can be stored without damage. Without special requirements, this is typically 85 degC, RH 85%, the familiar "85/85".
b. Operating temperature. The conditions under which the product can be used without damage. There are usually three grades:
0~50 degC: consumer applications, such as PCs and phones
0~70 degC: industrial, such as servers
-5~85 degC: high-end industrial, for more demanding applications
c. Data rate per lane. The per-lane signal rate and signal format. To overcome high-frequency limits today, the choice between PAM4 and NRZ must be discussed. Besides the maximum bandwidth, the minimum-frequency requirement is often overlooked: some protocols first send a very low-frequency signal for handshaking at the start of communication. So the highest and lowest signal frequencies, as well as the signal format, must all be considered; they are key criteria for choosing the driver IC.
d. Length. AOC bandwidth is far higher than copper, but length is still limited. The longer the cable, the more these two factors matter:
The VCSEL's spectral distribution: a narrower spectral width (FWHM) is needed to overcome dispersion over longer distances
Choosing the right fiber for the length (OM1, OM2, OM3, OM4, OM5): the higher the number, the higher the unit price, but also the wider the bandwidth.
e. Power consumption. An AOC needs driver ICs for optical-electrical conversion, so it always draws power. Higher power generally supports higher bandwidth, but also generates more heat.
f. Eye diagram specification. The eye diagram is how an AOC's high-frequency performance is judged, and it is a key criterion for choosing the driver IC.
g. Transmission direction. USB, for example, is bidirectional, while HDMI is unidirectional. This is a key criterion for choosing the driver IC, VCSEL and PD.
h. Cable bending radius. Split into dynamic and static; a smaller bend radius means the cable tolerates tighter bending.
i. Mechanical. Mechanical characteristics such as vibration, flex and insertion/extraction force are usually defined per EIA 364, TIA-455, SFF and similar standards.
j. EEPROM. If needed, an MCU can be embedded in the product to read and write the EEPROM, enabling product information logging, signal tuning, status readout and more.
Based on my own experience, these are the main points to watch when negotiating specs with customers, R&D or contract manufacturers during AOC product development.
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