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Nanowires replace Newton’s glass prism

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A University of Cambridge team has designed a nanowire-based spectrometer that doesn’t require dispersive elements like a prism, therefore permitting greater miniaturisation than conventional systems

Artist's impression of single-nanowire spectrometer. Credit: Ella Maru Studio

Scientists have designed an optical spectrometer made from single nanowire that is small enough to be used in smartphones. The device, described in a paper published in Science in September, doesn’t require components such as prisms, which enables a further degree of miniaturisation than traditional optical systems.

According to the researchers from University of Cambridge, UK, the system is the smallest spectrometer ever designed. It could be used in potential applications such as assessing the freshness of foods, the quality of drugs, or even identifying counterfeit objects, all from a smartphone camera.

Today, the majority of spectrometers are based around principles similar to what Isaac Newton demonstrated with his prism in the 17th Century – the spatial separation of light into different spectral components. Such a basis fundamentally limits the size of spectrometers – they are usually bulky and complex, and challenging to shrink to sizes much smaller than a coin.

The Cambridge team, working with colleagues from the UK, China and Finland, used a nanowire whose material composition is varied along its length, enabling it to be responsive to different colours of light across the visible spectrum. Using techniques similar to those used for the manufacture of computer chips, they then created a series of light-responsive sections on this nanowire.

‘We engineered a nanowire that allows us to get rid of the dispersive elements, like a prism, producing a far simpler, ultra-miniaturised system than conventional spectrometers can allow,’ said first author Zongyin Yang from the Cambridge Graphene Centre. ‘The individual responses we get from the nanowire sections can then be directly fed into a computer algorithm to reconstruct the incident light spectrum.’

Tom Albrow-Owen, co-first author, added: ‘When you take a photograph, the information stored in pixels is generally limited to just three components – red, green, and blue,’ he said. ‘With our device, every pixel contains data points from across the visible spectrum, so we can acquire detailed information far beyond the colours which our eyes can perceive. This can tell us, for instance, about chemical processes occurring in the frame of the image.’

The team’s approach could allow unprecedented miniaturisation of spectroscopic devices, ‘to an extent that could see them incorporated directly into smartphones,’ noted Dr Tawfique Hasan, who led the study, ‘bringing powerful analytical technologies from the lab to the palm of our hands.’

One of the most promising potential uses of the nanowire could be in biology, to image single cells directly without the need for a microscope. And unlike other bioimaging techniques, the information obtained by the nanowire spectrometer contains a detailed analysis of the chemical fingerprint of each pixel.

The researchers hope that the platform they have created could lead to an entirely new generation of ultra-compact spectrometers working from the ultraviolet to the infrared range. Such technologies could be used for a wide range of consumer, research and industrial applications, including in lab-on-a-chip systems, biological implants, and smart wearable devices.
The Cambridge team has filed a patent on the technology, and hopes to see real-life applications within the next five years.

Latest commercial products

Sponsored - Edmund Optics

Edmund Optics is a world-class manufacturer of stock and custom optical prisms. The company produces more than 500,000 prisms per year from a wide variety of Schott, Ohara and CDGM substrates. Its factories utilise a full range of precision manufacturing equipment for grinding, polishing and fine-finishing, all supported by a comprehensive suite of metrology. These capabilities allow highly-skilled technicians to hit high precision specifications such as λ/20 irregularity, 0.5 arc-second angular tolerances and 10-5 surface quality.
World-class prism manufacturing facilities are complemented by a vast inventory of standard components that can be quickly modified for rapid prototyping. Where a fully custom prism is required, expert optical design and manufacturing engineers can help develop a solution. All prisms are available with a wide range of anti-reflective coatings on the entrance and exit faces, as well as metallic coatings for reflective surfaces if needed.

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Other prisms on the market today include the PrismMaster Flex from Trioptics, a versatile goniometer for optics manufacturing. The vertical configuration and modular product concept make it a productive yet flexible solution for production-related quality testing of prisms and plano-optical components.

The goniometer enables optimal adaptation to customers’ measurement requirements by means of three expansion stages. With an electronic autocollimator in a swivel arm, the PrismMaster Flex is well-suited for productive measurement of surface angles of manufactured prisms in comparison to a known reference prism. With measurement times under one second per sample, the system delivers rapid results.

In the PrismMaster Flex 1D, the position information of the swivel arm is captured so that absolute surface angles and tilt angles are also measurable. In the PrismMaster Flex 2D, the position information of the sample table is additionally captured, allowing for spatial angular relationships, wedge orientations and pyramidal angles to be measured.

Laser Components has experience in the manufacture and specialist coating of laser optics, including optical prisms. Its Isosceles Brewster prisms are used primarily in beam deflection and compensation of GVDs (group velocity dispersion) in femtosecond laser applications.

In such a setup the prism would be placed in the beam path such that the beam is incident on the leg face of the prism at the Brewster angle. In this instance, light that is polarised parallel to the surface is transmitted with negligible loss, and light that is polarised perpendicular to the surface is predominantly reflected. Isosceles Brewster prisms are typically supplied un-coated.

Laser Components manufactures Brewster prisms in fused silica, SF10 and Suprasil1 substrate material in a range of standard sizes. As with the majority of the company’s manufactured products, custom designs are available.

The PZX prism grinding machine from OptiPro is the latest solution for companies looking to enhance their prism manufacturing capabilities. The PZX is capable of machining prisms up to 6 inches thick with a maximum diameter of 10 inches for the longest diagonal. Powered by user-friendly G series software, operators can quickly set up jobs to machine all prisms surfaces in one cycle by specifying the angle and material removal for each surface. Compound angles can be machined with precision due to a rotating B-axis with -90 to 180 degrees of motion. In addition, dual spindles provide the ability to perform rough and fine grinding of prism surfaces in one cycle without the need to manually change tools.

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