Imaging fiber-optic speckle enables low-cost, attometer-precision wavelength meter

The St Andrews researchers think this breakthrough could revolutionize the future of fiber-optic communications.

Content Dam Lfw En Articles 2019 03 Imaging Fiber Optic Speckle Enables Low Cost Attometer Precision Wavelength Meter Leftcolumn Article Thumbnailimage File

IMAGE: This low-cost wavelength meter is highly accurate and uses just a length of optical fiber and a camera that images the speckle pattern emerging from the fiber. (Image credit: University of St Andrews)

A team of researchers from the University of St Andrews (St Andrews, Scotland) has achieved a breakthrough in the measurement of lasers that they say could revolutionize the future of fiber-optic communications. They also say the wavelength meter (or wavemeter) will boost optical and quantum sensing technology, enhance the performance of next-generation sensors, and expand the information-carrying capacity of fiber-optic networks.

Led by professor Kishan Dholakia from the School of Physics and Astronomy, the team passed laser light through a short length of optical fiber, which scrambles the light into a grainy pattern known as 'speckle'. As described in Optics Letters, the shape of the speckle pattern changes with the wavelength of the laser and can be recorded on a digital camera.

The team used the speckle pattern to measure the wavelength at a precision of an attometer. This is around one thousandth of the size of an individual electron and 100 times more precise than previously demonstrated. For context, the measurement of such small changes in the laser wavelength is the equivalent to measuring the length of a football pitch with an accuracy equivalent to the size of one atom.

Wavemeters are used in many areas of science to identify the wavelength of light. All atoms and molecules absorb light at very precise laser wavelengths, so the ability to identify and manipulate wavelength at high resolution is important in diverse fields ranging from cooling of individual atoms to temperatures colder than the depths of outer space, to the identification of biological and chemical samples. The ability to distinguish between different wavelengths of light also allows more information to be sent through fiber-optic communications networks by encoding different data channels with different wavelengths.

Conventional wavemeters analyze changes in wavelength using delicate, high-precision optical components. The cheapest instruments used in most everyday research cost tens of thousands of dollars. In contrast, the St Andrews wavemeter consists of only a 20 cm length of optical fiber and a camera. In the future it may be made even smaller.

Dholakia explains, "The principle of the wavemeter can be easily demonstrated at home. If you shine a laser pointer on a rough surface like a painted wall, or through a semi-transparent material like frosted sellotape, the laser gets scrambled into the grainy speckle pattern. If you move the laser, or change any of its properties, the exact pattern you see will change dramatically. It's this sensitivity to change that makes speckle a good choice for measuring wavelength."

In the future, the team hopes to demonstrate the use of quantum technology applications in space and on Earth, as well as to measure light scattering for biomedical studies in a new, inexpensive way.

SOURCE: University of St Andrews;

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