Feature: Power management
Cutting laser power with a low noise InGaAs avalanche photodiode
By Ben White, Co-Founder and CEO, Phlux Technology W
hen working with transmit- receive systems, the transmitter frequently dominates the
bill of materials, board area and power budget, and the same applies to infrared (IR) links as it does to RF links. In IR designs, improving the front-
end receiver sensitivity helps push the operating range further out or allows to dial back laser power for the same range, making it a constant balancing act between these two levers during system design. When building a time-of-flight or
distance measurement setup, LiDAR, laser range finder or benchtop optical tester, typically short, high power pulses are fired from a laser diode to then capture the returned light with one or more IR sensors at the receiver input. Here it is less about the absolute transmit power than about how effectively the detector pulls a tiny, reflected signal out of the noise, because
16 April 2026
www.electronicsworld.co.uk
that determines whether a distant or low reflectivity target can be seen without oversizing the laser. To reach the required sensitivity in
the IR band, designers frequently turn to avalanche photodiodes (APDs) as detector of choice. Inside each APD, a carefully engineered semiconductor layer converts incoming photons into electrical current by generating electron-hole pairs, and the device structure steers these charge carriers to opposite electrodes under an applied electric field. As the reversebias voltage is increased,
the APD enters its avalanche region, where the internal field becomes strong enough for the carriers to pick up enough energy to then ionize additional atoms and create more carriers. Tis internal multiplication produces current gain directly inside the sensor, thus a handful of photons produce a measurable output pulse. In optimised devices, a single photon can be enough to trigger a detectable event.
Choosing the right material for the APD Te APD’s usable wavelength range is set primarily by the semiconductor material of the device. If made of silicon, the target peak response is around 900nm, allowing internal avalanche gains from about 50 to about 1,000. If the APD’s material is germanium or indium gallium arsenide (InGaAs), the sensitivity is then pushed to longer wavelengths, roughly 1000-1700nm. With these materials, the avalanche gains are more modest (10-40), because higher gain brings a significant noise penalty in compound semiconductors, with InGaAs generally providing a lower noise option than pure germanium for the same range. InGaAs APDs also cost more than Si
devices, because they use a compound semiconductor process. Given those constraints, it’s best to choose an InGaAs APD when operating wavelength really matters. When designing with Si APDs, we are working near 905nm, close to the
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