Avalanche Photodetectors (APD) make use of internal multiplication to achieve high-speed and high gain-bandwidth due to impact ionization. The result is the optimized series of high responsivity APD’s, Avalanche Photodiode detectors, exhibiting excellent sensitivity. Scientists at IBM have used nano-engineering techniques to make the world’s fastest “avalanche photodetector“. Such devices are used in telecommunications networks and the work is an important advance in the field of optical communications. The photodetector is made using germanium, which is compatible with silicon-chip-making technology and could therefore find use in next-generation high-performance computer systems.

Computer processors communicate with each other over millions of tiny copper wires. Scientists would ideally like to use light pulses instead of electrical signals because enormous amounts of information could then be sent between processors using much less power. Such architecture relies on the rapid conversion of optical pulses to electrical signals and back again – but current technologies for doing this tend to be slow, noisy and incompatible with silicon processing.

One promising solution is the avalanche photodetector, which converts relatively weak optical signals into robust electrical pulses. In such a device, an incoming light pulse strikes a semiconductor, freeing a few charge carriers. These carriers are accelerated by an electric field and in turn impact-ionize (or free) other charge carriers, and so on. This creates an avalanche of carriers that is then extracted as the amplified signal. However, this process occurs over a finite distance and time and is therefore subject to random fluctuations in numbers of carriers produced. This phenomenon is known as amplification noise and it degrades the performance of the photodetector.

Although it suffers from amplification noise, germanium is widely used in photodetectors because (unlike silicon) it can detect light in the infrared part of the electromagnetic spectrum – an important frequency range for optical communications. IBM have come up with a new way of removing noise from germanium-based photodectectors.

The device is the fastest of its kind, converting optical signals at 40 Gbps (40 billion bits per second) – about four times faster than the best conventional detectors. What is more, its small size means that it operates with just a 1.5 V power supply, compared with the 25 V of previous devices.

Intel is also working on this technology. Intel has collaborated with industry, academic, and government partners to develop a silicon-based avalanche photodetector (APD). APDs are light sensors that process optical communications to electrical signals. Intel’s avalanche photodetector has a gain-bandwidth product of 340GHz, the best result ever reported for an APD. Intel’s avalanche photodetector breakthrough represents the first time that a silicon photonic device beats an equivalent made from traditional optical materials. Avalanche photodetectors are optical devices that sense light and amplify signals. Intel’s silicon-based avalanche photodetector has the highest gain-bandwidth product ever seen (340 GHz). The gain-bandwidth product is a standard measure for APD performance that multiplies the device’s amplification capability (gain) by the fastest speed signal that can be detected (bandwidth). This means that Intel’s new APD device has the capability to detect signals at higher speeds and lower power levels than commercial APDs today. This breakthrough creates the possibility of using APDs for 40 Gbps optical communication links.