Optics for 5G

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Prism technology that’s now a major part of optical communications is finding its way into next-generation lidar systems

Engineers from optoelectronics firm Finisar in Sydney, Australia, have been awarded the Australian Prime Minister’s $250,000 Prize for Innovation for developing and commercialising light-bending switches. The technology uses prisms and a liquid-crystal-on-silicon (LCoS) chip that improve the capacity, reliability and speed of the internet.

Dr Simon Poole, Andrew Bartos, Dr Glenn Baxter and Dr Steven Frisken, inventors of the technology, were honoured with the award from the Australian government. The four engineers commercialised the optical switch through the company Engana, which is now part of Finisar.

The switch is based on three components: a prism that’s able to divide the light into different wavelengths; an LCoS chip that can steer the light into different optical fibres; and the algorithms that manage the device.

The prisms are used to split light into more than 100 wavelengths, which are then switched from one optical fibre to another, enabling them to handle 10 terabits of information per second, or one million simultaneous high-definition streaming videos.

Finisar’s Flexgrid wavelength selectable switches are used by the world’s major telecommunication companies for high-speed internet and mobile phone access. The switches allow optical fibres – once only used for the inflexible long-haul conduits joining cities and countries – to handle more data, as well as making them more efficient and reliable.

The device has made fibre optic communication cheaper to use over short connections, and has enabled internet traffic to grow in volume and drop in price. By carrying many signals at the same time and switching rapidly between fibres, the switches have transformed point-to-point optical fibres into adaptable mesh networks. Their ability to be controlled by software also lets network managers reroute traffic when a network fault occurs.

In 2001, the speed and volume of internet traffic was limited, because of problems with both capacity and reliability of communication infrastructure, according to Poole.

‘Large companies were spending billions of dollars looking for solutions,’ he said. ‘The four of us had all worked in optics, and we were looking for something to contribute to after the dot-com collapse.’

‘We could see that there was huge scope for optics in the network, as a lot of other people could,’ added Bartos. ‘But we could see that the networks were too inefficient, too inflexible. So we took a contrarian view. We looked for something completely different, something unorthodox, and we came up with this idea.’

The initial inspiration for the switch came from a data projector that was available at the time, which used something called liquid crystal on silicon (LCoS). ‘This technology was great for projecting images on to a screen, and I thought I could see a way that we could use it to project different colours of light into different fibres,’ Frisken said. ‘That set us on the path to creating an optical wavelength switch.’

Finisar, which has 230 employees at its Sydney base, recently introduced a product that not only switches light in networks, but also measures signal quality. In the future, the firm aims to boost the capacity of its devices further to meet the demands of 5G and the Internet of Things.

Prisms for lidar

The four engineers’ innovations and mentoring are now seeding a new generation of optics-based companies, including Cylite, which is developing eye care diagnostics, Terra15 for geophysical sensing, and Baraja for autonomous vehicles.

Baraja has built a new class of lidar system for autonomous vehicles that, it claims, addresses issues regarding performance and scalability. The new lidar technology, dubbed Spectrum-Scan, pairs prism-like optics with a wavelength-tuneable laser to deliver high performance and long-range capability.

Baraja’s technology uses off-the-shelf components, such as the optical-grade silica-glass found in smartphone cameras, and telecom-grade lasers, enabling it to be mass-produced.

Current lidar solutions scan the road using physically rotating lasers, or by using moving mirrors to steer the light using microelectromechanical systems (MEMS). According to Baraja, these moving parts have unresolved reliability problems in vehicles, because of constant vibration and shock.

These legacy scanning methods inject cost, reliability and performance issues, and contribute to the unwieldy appearance and vehicle integration difficulties of existing lidar solutions, according to the company.

‘We are confident that we have built a high-performance lidar system, one that addresses many of the challenges facing the autonomous vehicle industry today,’ said Cibby Pulikkaseril, Baraja co-founder and CTO. ‘Automakers and tech companies want to put fleets of safe and reliable autonomous vehicles on the road. Spectrum-Scan lidar will help them get there faster.’

While headquartered in Sydney, Baraja also has offices in San Francisco and China. The company is currently expanding throughout Asia and Europe. Baraja is backed by funding from Sequoia China, Blackbird and other investors.

‘When Baraja came to us with its unique approach to lidar, we immediately saw how differentiated its approach was,’ said Steven Ji, partner at Sequoia China. ‘After seeing its technology in action, we could see how well it addressed the limitations of other products. Baraja’s technology will be critical to the entire autonomous vehicle industry.’

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Commercial products

Featured product: 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.

www.edmundoptics.eu/capabilities/optical-coatings

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Other commercial products

Suppliers of prisms include Alkor Technologies, A. Optical, Berliner Glas, Edmund Optics, Esco Optics, Optimax, Thorlabs and Zygo. Alkor Technologies’ prisms are made from optical glass, fused silica, BaF2, CaF2, silicon, germanium and ZnSe. Angle tolerances can be as low as two arc seconds and sizes between 2mm and 200mm.

Berliner Glas’s prism systems offer 20µm optical path length difference or λ/10 of wavefront accuracy, while Esco Optics’ right-angle prisms, equilateral prisms and laser prisms have a surface quality better than laser grade, 10-5, or λ/20.

Optimax grinds and polishes prisms from various optical materials for UV, visible and IR applications. In addition, Optimax can offer a wide variety of coating options including BBAR, V-coat and mirror coatings.

Available in sizes ranging from 3mm to 60mm, Thorlabs’ right-angle prisms can be used to deviate a light path by 90° or 180°, depending on which surface is used as the input for the light source. These prisms are fabricated from N-BK7, UV fused silica, CaF2, or ZnSe. Thorlabs’ N-BK7 prisms are available uncoated or with one of its three standard broadband antireflection coatings.

Finally, Zygo’s Optics business segment is able to supply prisms with sub arc-second angle tolerances, very flat surfaces and excellent transmitted wavefront characteristics. In addition, Zygo offers a broad range of coating options, including polarising films, antireflective coatings, and coatings to improve reflectance for prisms.

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