A story of sensors

Trinidad & Tobago Guardian

November 18, 2014

By Mark Lyndersay

Eric Fossum
Prof. Eric R. Fossum

Prof Eric R Fossum is probably the most important man in the world of modern photography, but he almost walked right past me without my knowing it. 

Lost on my way to the lecture he was scheduled to give last Monday, I spotted an old school friend, who also happened to be the chair of the Open Lectures Committee that brought Prof Fossum to T&T. 

In an uncharacteristic moment of mental agility, I deduced that the person ambling along beside him had to be the feature speaker.

As the professor gripped my hand firmly after introductions, he quietly said, “Thanks for coming to the lecture.”

“Huh,” I might have said if I were 40 years younger, “as if.”

Prof Fossum is the scientist who leveraged the groundbreaking charge-coupled device (CCD) technology that underpins almost all modern visual telecommunications to create a more energy-efficient and ultimately more scalable revision called complementary metal-oxide-semiconductor or CMOS technology.

Moore’s Law, the axiom that’s rather efficiently predicted the rate of technological progress (it doubles every year), has been kind to these light-gathering technologies. In 1971, it was possible to put 2.3 light-gathering sensors on a chip, now transistors are packing in up to 2.6 billion of them.

The learned professor quickly powered through the technical part of his presentation, a dense thing made of high-level physics and some folksy characterisations of his invention.

“Light is a wave,” he noted as a slide came up, “but light is sometimes also a particle.”

This was the sort of thing that always drove me a little loopy in science class and at this level, with discussions that reference “photon shot noise” and “the Poisson Process,” things were drifting firmly in the direction of hard science.

One sentence peeped through, however: a mention that scientists seem to be agreeing that we are approaching the limits of physics when it comes to pixel sizes.

Pixels, or picture elements, are the tiny light-sensitive sites packed onto a camera’s sensor that actually capture the light representing your photo and translate it into the electrical impulses that become the bits of an image.

Prof Fossum began his work on the technology that would become the CMOS sensor at NASA’s Jet Propulsion Laboratory, where he was charged with making digital-capture devices that were smaller, lighter and more energy efficient to fit into the smaller spacecraft that the space agency was building.

Galileo launched in 1989 with an 800 x 800 pixel sensor, but in 1992, the professor’s team developed Intrapixel Change Transfer, a method of reducing noise and amplifying signal.

This began the era of a camera system on a chip, where the chip itself carried the technologies needed to decode the light it was capturing.

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