Slashdot Mirror

← Back to Stories (view on slashdot.org)

Graphene-Based Image Sensor To Enhance Low-Light Photography

Posted by timothy on from the bright-light-of-the-moon dept.

cylonlover writes "A team of scientists at Nanyang Technological University (NTU) in Singapore has developed a new image sensor from graphene that promises to improve the quality of images captured in low light conditions. In tests, it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy."

17 of 103 comments (clear)

  1. New type of "bio" imaging ? by Anonymous Coward · · Score: 4, Interesting

    There was this article on slashdot 4 years ago, http://science.slashdot.org/story/09/07/23/1819215/people-emit-visible-light.

    Summary:

    "The human body literally glows, emitting a visible light in extremely small quantities at levels that rise and fall with the day, scientists now reveal. Japanese researchers have shown that the body emits visible light, 1,000 times less intense than the levels to which our naked eyes are sensitive. In fact, virtually all living creatures emit very weak light, which is thought to be a byproduct of biochemical reactions involving free radicals."

    So humans emit light that is 1,000 times too weak to detect, but this new sensor is 1,000 more sensitive to light, what a coincident! I imagine this would have great applications in the health industry eg. passive health assessment. Or another use might be a better lie detector :)

    1. Re:New type of "bio" imaging ? by drinkypoo · · Score: 3, Insightful

      It might not be better than the human eye, which can detect single photons, but it might be better than the human eye plus the human brain, which tends to ignore such stimuli.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    2. Re:New type of "bio" imaging ? by beelsebob · · Score: 2

      FTFA

      In tests, it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy.

      Do you know something the article doesn't?

    3. Re:New type of "bio" imaging ? by femtobyte · · Score: 4, Informative

      ^^^ This. The Nature Communications article is very clear, right from the abstract, that this sensor is 1000x more sensitive than previous *graphene* sensors. *Nowhere* in the journal article is the performance compared directly against CCD/CMOS sensors, but it's trivial to tell (from the numbers given) that this sensor isn't remotely "competitive" in the visible light region. Fortunately, that's not the interesting use of the sensor --- the journal article does compare and cite advantages against other infrared sensing technologies. The researchers might have meant to say that these graphene sensors could be useful for cheap, low-power (but not high sensitivity) visible light applications --- not what the journalists have twisted this into.

  2. Real world graphene? by phizi0n · · Score: 3, Interesting

    Is there any readily available consumer products, or even industrial products, that use graphene? If not then how long do we have to keep hearing about how great graphene is before we can actually use it?

  3. 1000 times better? by thesupraman · · Score: 3, Informative

    They claim 1000 times better sensitivity than CMOS, which people seem to be swallowing hook line
    and sinker, however since there are plenty of current CMOS sensors with a Quantum Sensitiviy (QE)
    of 60% to 80% for visible light, how exactly will the convert 1000 times more efficiently than that?
    1000 times less loss would take them from 80% to 99.99%, that thats only actually 20% better...

    I would imagine they are measuring at an extreme wavelength that existing CMOS sensors do not target,
    hardly an advantage for the applications being discussed in the article (normal cameras).

    Even quite boring consumer cameras have a QE of 20% to 40%..

    1. Re: 1000 times better? by imgod2u · · Score: 3, Insightful

      Exposure is exponential as well. So a camera with 2x exposure goes from 80% QE to 90% QE for example. The next 2x will get you to 95.

      That may not seem like much but keep in mind that vision itself is logarithmic. So going from 98 to 99% QE gets you dramatically better results than, say 40% to 41%

    2. Re: 1000 times better? by Bender_ · · Score: 3, Informative

      Some people do not seem to understand the term "quantum efficiency" (QE).

      The quantum efficiciency measures the fraction of photons that are actually detected by the camera.
      An external quantum efficiency of 50% means that 50% of all incident photons are converted into electron-hole pairs and can be detected.
      There are, however, loss mechanisms that prevent all e-h pairs to be collected. But this is not off by a factor of 1000x from the theoretical limit.

      As already stated by the original poster. This figure is probebably for some other wavelengths, like far infrared, where silicon is "blind" due to its band gap.
      Since humans are very blind to this wavelengths as well, the relevance in the cameras is questionable.

    3. Re:1000 times better? by asvravi · · Score: 5, Informative

      First off, if we cut through the usual dismal quality of scientific reporting, what they made is a photodetector, not an image sensor. It detects single events rather than capture an image. The sensitivity of the detector is not the same as quantum efficiency. The sensitivity they mention here includes a "photogain" by virtue of the detector operating more or less as a light-controlled amplifier. It takes electrical input energy and simply amplifies it based on incident light. That can create a flow of many more electrons than incident photons. The same thing can possibly be also done by introducing a gain in the conventional image sensor electronics too, but having this photogain right inside the sensor should theoretically lead to better noise performance. So we would expect the paper to quantify the noise characteristics, but it is woefully sparse on the noise details - which leads me to suspect this is yet another "invention" that is never going to see the light of day.

    4. Re: 1000 times better? by thegarbz · · Score: 3, Informative

      This figure is probebably for some other wavelengths, like far infrared, where silicon is "blind" due to its band gap.
      Since humans are very blind to this wavelengths as well, the relevance in the cameras is questionable.

      From TFA: "The new sensor is able to detect broad spectrum light, from the visible to mid-infrared, with great sensitivity. This will make it ideal for use in all types of cameras, including infrared cameras, traffic safety cameras, satellite imaging, and more."

      Certainly doesn't sound too different to CMOS based applications, though they do mention mid-IR and most CMOS sensors drop off towards the end of the near-IR spectrum.

  4. quantum efficiency by stenvar · · Score: 2

    As I recall, quantum efficiency of current sensors is around 50%. I don't see how you can get "1000 time more sensitive".

    1. Re:quantum efficiency by BronsCon · · Score: 2, Informative

      That's 50% of visible light, as in 50% of the minimum level of light in the visible spectrum required to be seen by the naked eye. If this sensor can "see" light that is 1/500th the intensity required to be seen by the naked eye, whereas current sensors can only "see" light that is 2x the intensity required to be seen by the naked eye, then the new sensor is 1000x more sensitive. It's not rocket science; hell, it's not even physics or optical science, just plain ol' algebra.

      --
      APK quotes people (including myself) without context and should not be trusted. Just thought you should know.
    2. Re:quantum efficiency by femtobyte · · Score: 2

      All the reporting framing this as a sensor for "1000x better" low-visible-light photography is simply crap by lazy tech journalists who can't bother to read the actual journal article. This sensor is fairly lousy in the visible light region --- claimed sensitivity down to the nanowatt level, which is more light than usually falling on your camera pixels (unless you're pointing the lens directly at the sun).
      The 1000x improvement is relative to previous *graphene* detectors, and is a 1000x increase in the amplitude of the signal produced in response to light. Graphene sensors are interesting because of their very broad band response: from visible light to ~10um mid infrared. This technology can improve infrared optoelectronics, in bands useful for a variety of purposes (telecommunications, satellite remote sensing, higher temperature thermal imaging, etc.); however, "enhance low light photography" was just something pulled out of an ignorant tech writer's ass to make a headline (with no relation to the actual research).

    3. Re:quantum efficiency by femtobyte · · Score: 2

      The actual Nature Photonics article does talk about the noise floor, which is on order of 1 nanowatt of illumination. That corresponds to ~10^9 visible light photons per second --- easily 10^6 times worse than what your ordinary camera pixels are capable of. Oh, and you need cryogenic cooling to do that well. This graphene sensor is not great for visible light sensing --- what it can do (potentially) better than alternate technologies is sense light all the way from visible to 10um mid-infrared.

  5. The three orders of magnitude... by Mr.+Chow · · Score: 5, Informative

    According to the paper, "Through this scheme, we have demonstrated a high photoresponsivity of 8.61A/W, which are about three orders of magnitude higher than those in previous reports from pure monolayer graphene photodetectors.". So it is 1000x better than previous iterations of a particular variety of detector, not the detectors we actually use.

  6. Can someone explain? by excelsior_gr · · Score: 2

    Amateur photographer here. Does this mean that the camera will just be able to photograph at higher ISOs without noise (or rather, that you could use a lower ISO in darker situations), or that the sensor will be able to record a picture with a wider stop range? Digital cameras have a range of about 6-7 stops, whereas our eyes have a 16-stop range (according to Bryan Peterson). HDR can be used to remedy this, but, more often than not, the pictures seem much too blown, saturated and unnatural. Sony has an in-camera HDR function, that can be tweaked to keep the color explosion at bay, but it is not exactly it. Being able to take photos in bad light is sweet and all, but it would be much more interesting creatively to have a camera that can picture what I see, without having to set up a whole flash array for lighting up all the dark areas (and having to imagine and troubleshoot, if I have the time, the combination of a flash+natural light exposure).

    So photo-gurus, will this sensor cut it? Are there any products in the market that address the issue described above?

    1. Re:Can someone explain? by femtobyte · · Score: 3, Informative

      Despite the poorly written article, this sensor tech is very *insensitive* compared to what you currently have for visible light technology. It's a 1000x improvement compared to previous wide-band graphene detectors, which can sense light from the visible out to 10um mid infrared (your camera can't do that). So no, this won't help your camera photograph at higher ISOs. And current camera sensors are within spitting distance of the theoretical physical limits on low light performance: while they've improved tremendously over the past couple decades, the noisiness of low-light pictures with the best current generation sensors is close to what you'll always be stuck with --- its the result of there being a finite number of photons, with sqrt(N) counting statistics fluctuations, available for even a "perfect" camera to see.