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Photonics integration on silicon for sensing, imaging and communication


Photonics is in use all around us. Optical sensors, for example, analyse organic and inorganic substances from gaseous, liquid and solid samples. Optical instruments are used in microscopy, spectroscopy and medical imaging. And the combination of low-loss optical fibres and fast optoelectronics enables global connectivity with ever-increasing data rates. But now it's time to follow the success of microelectronics by integrating photonics on small chips.

From discrete components to integrated circuits

Microelectronic technology has already enabled the integration of electronic systems and circuits on small silicon chips for decades, and with a continuously increasing level of integration density. At the same time, the main trend in optics and optoelectronics - together known as photonics - has been to assemble discrete devices that are based on a large variety of materials and technology platforms. This tends to make photonic systems bulky and expensive. The latest achievements by VTT and others in rapidly growing silicon photonics technology now enable integration of optics and optoelectronics on small Si chips.


Industrial collaboration

Medlumics is a good example of fruitful collaboration between VTT and a fabless company that wants to exploit silicon photonics. According to their CEO Eduardo Margallo, "VTT’s low-loss photonic platform is helping us improve our medical virtual biopsy products by miniaturizing all the optics into a tiny chip, thus reducing the size and cost of what are otherwise complex systems. We have found a strong commitment to quality procedures and reliable fabrication, which has been fundamental for our success in moving towards a commercial product."

Another example of close collaboration with the industry is VLC Photonics, a company providing optical chip design and characterisation services. VLC is familiar with all relevant photonics integration platforms, offering its expertise to other companies that search to exploit all the advantages of custom optical integrated circuits. "Photonic integration allows to miniaturize complete optical systems into a chip, increasing reliability and performance, while reducing cost, size and weight. VTT's integration platform also extends silicon photonics capabilities into new applications not currently supported by other major platforms," says Iñigo Artundo, their CEO, and continues: "We hope to build together with VTT an attractive platform for users from all fields, allowing for an easy and affordable design support and low-cost and solid chip fabrication"

Technological breakthroughs

The idea of optical waveguide circuits on silicon is not new, but one that has not been easy to realise in practice and in a commercially viable way. Silicon itself is only transparent at infrared wavelengths (>1.2 µm), where efficient generation of light from Si is impossible. Fast modulators and photodetectors also used to be difficult to integrate monolithically on silicon. In passive waveguide circuits the high refractive index (~3.5) of Si allows tight confinement of light into silicon waveguides, but conventional Si waveguides need to have submicron dimensions to ensure the single-mode operation that is crucial for many applications. Many research groups have recently demonstrated very dense photonics integration and even very fast modulators and photodetectors using Si waveguides of 220 nm thickness, but these suffer from relatively high propagation losses (~2 dB/cm), large polarisation dependency, narrow wavelength range (~30 nm) and difficult input/output coupling.

VTT was recently able to demonstrate very dense photonics integration with Si waveguides 3 and 4 µm thick. These waveguides have a special cross-section that offers single-mode operation, low losses (0.1 dB/cm), ultra-wide wavelength range (from 1.2 µm to >3 µm) and efficient coupling to optical fibres (>90%). One breakthrough was to reduce the bending radius of these waveguides by three orders of magnitude to just a few µm. This allows dense integration of complicated optical systems on tiny Si chips (<1 cm2). VTT has also developed a unique technology for the hybrid integration of light sources and other optoelectronics on these Si chips, and the development of fast monolithically integrated modulators and photodetectors is now also under way. Short and long term R&D is carried out in several EU projects (RAPIDO, BiopsyPen and RAMPLAS) and in close collaboration with the industry.

Easy access to state-of-the-art technology

As a member of the ePIXfab consortium, VTT now reduces the barrier faced by small companies in particular in harnessing the power of silicon photonics. In multi-project wafer (MPW) runs, the development and prototyping costs are shared between multiple MPW users. VTT's first MPW run was launched in 2013, with the fabrication costs starting from just EUR 6,000 per user. Both Medlumics and VLC photonics participated in this run. Companies can also explore VTT's silicon photonics technology with the support of the recently launched ACTPHAST project. Introduction to all silicon photonics technologies (including VTT's) and hands-on design exercises are provided by ePIXfab in one-week training programmes.

Watch the video: ACTPHAST - photonics innovation accelerator for European companies

See the latest message about Industry 4.0 and photonics as a key enabling technology for this transformation. The new movie also includes testimonials from ACTPHAST supported companies.