Visible light chip rules the waves
Measurements are essential to the production process in many industries. Take the food industry, for example, in which pathogens and other substances that do not belong in food must be identified and removed in time to avoid possible food scandals. Or consider farming, for which light, air, water and fertiliser must be combined in the correct proportions to produce an optimal harvest. Just think of the possibilities if a sensor technology could be developed that is not only extremely compact but can also perform various complex measurements simultaneously and real-time and on-site.
Many sensors make use of light. Because light and matter is a beautiful combination; certainly when it comes to organic matter. Current equipment makes use of expensive lasers and analytical software. This equipment is often very large and consists of bulky components, lots of lasers, glass fibre, prisms and microscope lenses. The development of integrated optics has made chip technology possible based on light, which is accompanied by substantial cost reductions and introduction into arrays and matrix sensors.
From infrared to visible light solutions
Nowadays there are three main platforms available to produce standardized solutions for integrated chips, being Silicon Photonics (Si), Indium Phosphide (InP) and TriPleX™. All three platforms are applicable for infrared (IR) light, which is logical as the traditional applications can be found in telecom and data communications. Contrary to Si and InP, the TriPleX platform is also applicable for visible light. Especially for sensing applications, this is very beneficial as IR based sensors have been suitable for only a single application and difficult to manufacture, due to their expensive and still frequently used large components. Also for applications such as microscopy, people prefer to work with visible light and this means that almost all applications developed in this field are also based on visible light. An additional advantage of visible light sources is that they are very high-quality light sources, which cost virtually nothing and are very small, making them ideally applicable to, for instance, a disposable design. LioniX, based in Twente, the Netherlands, designs, develops and manufactures customised ‘visible light’ chips. Chip designs are either completely tailored to customers’ needs or are based on standard elements in a design library.
Multi Project Wafer (MPW) runs
The latter option offers each customer the possibility to design their own chips and to participate in one of the company’s Multi Project Wafer (MPW) runs. All customers, therefore, use the same structure; only the functionality differs. This considerably reduces the price per run for each client. LioniX provides design-to-manufacturing expertise and ‘horizontal integration’, by partnering with foundries, suppliers of complementary technologies and R&D institutes. The LioniX brand of integrated optics technology is called TriPleX™ and allows for medium and high index-contrast waveguides with low channel attenuation, especially for visible light. The high index-contrast and broad wavelength range make the technology extremely suitable for a variety of applications, ranging from telecoms to sensing. This technology has since become a worldwide standard.
Micro ring resonator
The company has also developed a micro ring resonator: a microscopically small, flat disc in which visible light is trapped. Even though the light is trapped in the ring, this remains in contact with the outside world and the light is able to engage in sensor activity, both in liquids and in air. It is possible to place various rings on a single surface, creating a multi-sensor. The typical diameter is 50-100 micrometres, which means that hundreds of rings can fit on a chip only one square millimetre in size. These rings can be controlled and read by the same detector, using one light source, which is very interesting for a whole range of sensor applications. Sensor applications are not only important for our food safety; the medical world is also interested in taking measurements using multiple parameters. Blood, saliva, faeces: taken together, these measurements help to form a complete picture of a patient’s condition. This, in turn, supports a better and quicker diagnosis and analysis. Current measuring equipment is often expensive, large and complex. If we want to switch to equipment capable of taking synchronised measurements, which is inexpensive to read and even disposable, photonic integrated chips are the solution. The advantages of visible light pave the way for designing this disposable, miniaturised chip.
Building a neural network of rings
A sensor must be sensitive to multiple external influences. Each ring therefore receives a special coating which is sensitive to a single application. Platform technology makes other specific measurements possible by using multiple rings. And all of this takes place on a surface area of just one square millimetre. Because the light intensity inside the ring is enormously high, extremely sensitive measurements are possible. No light is lost and the ring resonator is also, therefore, extremely energy efficient. The goal is to develop a very inexpensive chip that is extremely effective and capable of measuring more, and more complex, data simultaneously and in a much shorter time. Moreover, in practice, measurements are always sensitive to ‘cross reactions’: taking a single measurement which produces only a single reaction is actually impossible. By equipping multiple rings to perform multiple applications, a kind of neural network is created from which researchers, doctors or farmers are able to extract much more information. By combining rings, each of which produces a small amount of information, a complete picture can be formed.
It is time to invest in PIC
There’s no longer any turning back, according to LioniX. The trend that has begun will only accelerate because there are now three optical platforms available with standardised basic building blocks. This means that many more users can begin experimentation simultaneously at much lower cost and this should result in an enormous acceleration in the field of integrated photonic circuitry. LioniX expects that during the next 10 years much of the devices used nowadays, will be replaced by devices that incorporate PIC. Innovation therefore is no longer optional; if you wish to continue being an application builder or machine developer 10 years from now, it is time to invest in these components of the future, which are better, cheaper and suitable for a wider range of applications.