Intelligent Photonic Multi-Sensor Solutions

With the Internet of Things (IoT) quickly rising in front of us, it would be easy to get caught in the trap of thinking that both the trajectory and applications will be somewhat predictable. While hindsight is 20/20, the future can be a little trickier to envision. We can likely all agree that when we saw the first brick-sized wireless telephone, it wasn’t hard to tap our creative problem solving to conclude that subsequent generations were going to get smaller, cheaper and generally “better”. But few people could have envisioned the “smartphone,” let alone Apple’s first edition iPhone. Fewer still looked from that first brick to an age of sensor-driven, cloud-connected apps in the palms of our hands.

Small Data Drives Big Data

The IoT will be built upon some basic functional blocks. High level connectedness (i.e. “the internet”) is obvious, as are “the things” (smartphones, toasters, TVs, lights, thermostats). The cloud and big data are also fairly well recognized. But where does the data come from?

One obvious answer is from our activities and behavior, led by the mobile devices we are carrying with us. Traffic reporting apps, such as Google or Waze, make use of our data every day. Our “likes” on everything from a local eatery to geo-political opinion, especially when cross-referenced with our location record, creates a vast behavioral database that everyone from friends to retail coupon pushers can capitalize on. The last and somewhat unsung heroes of the IoT revolution will be the sensors. Beyond GPS, the missing link in the big data pie is a broad, but granular, understanding of what’s going on in the spaces we occupy. Sensors will bring awareness to the Internet of Things, and lighting is a natural host for the awareness.

Phase I: A Platform is Born

Our built environments have some very common ingredients, including walls, windows, furnishings, HVAC systems and lighting. Due to the combination of its “hardwired” electrical nature, and its ubiquity across our microspaces, lighting is well suited to be a primary system through which we can host many of the sensor systems that will create this “Internet of Awareness” for the IoT (Figure 1).

While the concept of connected lighting doesn’t sound particularly innovative, the reality is that very few of today’s lighting installations can really be called “connected”. A modern building management system (BMS) may be able to command banks of lights on or off on a preset schedule, track the overall trend of occupancy sensor triggers in a series of spaces, and maybe even infer the amount of energy usage/savings that those events trigger, but things pretty much stop there. In reality, prior to the start of the solid state (or LED) lighting revolution, there really wasn’t much to control beyond on and off.

Recent photonically-integrated chip level solutions (Figure 2) are enhancing both the capabilities and connectedness of our lighting, providing a preview of the coming tsunami of sensor driven awareness that will not only deliver information on lighting levels and energy usage, but a raft of building-level data that will encompass everything from air quality and space utilization to the wearable-transmitted vital signs of users in those spaces.

The whole point of the Internet of Awareness is sensing, so any system architecture decisions will naturally start by answering the question of what we intend to sense. The architecture example we use assumes the objective to be a smart lighting system, with the core functions including integrated occupancy and ambient light sensing controlled by a smart lighting manager. Lighting needs control, it needs sensors, and it provides the basic payback model for other sensing to ride on. For a commercial space, a system integrator expands the sensing to include such things as temperature, humidity, CO/CO₂, motion and presence. Some of these sensor additions, such as direction of travel information available from a pixelated presence sensor, will provide information useful to the lighting system, while others, such as CO/CO₂ sensing, are pass-through information that will be delivered back to the response to BMS.

To facilitate sensor extensibility when architecting an IoT sensor hub (Figure 3), industry standard platforms should be considered. In the example above, I²C has been chosen for core expansion. Simple UART-based connectivity, such as RS-485, can also be employed. The need for distributed intelligence must also be considered, and will be driven by the frequency and volume of the sensor data being captured. Whether you look at it as ‘sensors, with intelligence thrown in at no extra charge’, or vice versa, the simplest approach for widely distributed sensing will be a single dedicated controller which includes one or more integrated sensors. With the addition of basic wired or wireless connectivity, an IoT star is born!

The convenience of lighting as the initial sensor platform is undeniable. An existing system lighting is in place now, it’s in a convenient physical location to both provide it with power and to enable useful granularity in the data that comes from the sensed environment, and there is a convenient benefit in the form of integrated sensing and control to provide a payback in the form of basic energy savings.

Phase II: Extend the Platform to New Applications

While the approach above describes one completely new concept, namely IoT-connected smart lighting serving as the extensible sensor hub of our built spaces, there is an alternate branch of the family tree that may be less obvious – the creation of a cross-application intelligent photonics platform. The basic intelligent flow found in the smart lighting manager – sense, interpret, control, communicate – coupled with sensor expansion and analog/digital inputs and outputs, can enable a wide variety of photonic-based applications.

There is an incredible amount of information in the light, and a wide array of bandwidths to choose from. The smart lighting manager used in the initial illustration is equipped with nanophotonic tri-stimulus XYZ interference filters that respond to the visible spectrum as the human eye does (Figure 4).

However, in order to normalize the filter responses across temperature and a variety of light sources (including IR influences in daylight or incandescent sources), a total of six filters are employed to provide data on X, Y, Z, IR, dark and clear channels. While the initial application addresses the IoT smart lighting opportunity, the architecture is effectively an intelligent 6-channel spectrometer platform. The use of nano-photonic interference filters, which are laid onto the intelligent sensor platform in a standard CMOS process, enables relatively rapid filter design and implementation across a wide spectrum spanning from deep and near UV through visible to near IR (600 to 1000nm – Figure 5). In addition, the control-oriented architecture of the platform enables the onboard intelligence to be tapped for quick configuration to specific applications, while additionally delivering both decision making as well as photonic source control to support active sensing architectures (Figure 6).

Some applications in visible and near- IR include food quality assessment, chemical product safety (detecting urea or melamine in milk, for example), authentication, signal detection and medical/SpO₂. Mid-IR applications include bio-sensing such as glucose monitoring, fat/cholesterol detection, and alcohol. Longwave IR (PIR) integration would require some distinct material design, but would allow sensing to extend into fire/safety as well as presence detection and people counting.

In all cases, the ability to sense, interpret and communicate the result becomes critically import to address the wide range of potential applications that exist farther over the horizon. Support for additional sensors, as provided in the examples here by the I²C bus, even creates the opportunity for hybrid systems that might bring together photonics and such diverse elements as MEMS, RFID, temperature/humidity and/or time of flight sensor systems.

In speaking to one of the original committee members of the TCP/IP protocol, they pointed out that while they never conceived that cameras would be connected to the network, they did envision that there would be things they couldn’t envision. A photonics platform approach must similarly account for that which cannot yet be accounted for. We might not know what the app is, but we do know we need to support it.

This article was written by Tom Griffiths, Marketing Manager – Sensor Driven Lighting, ams AG (Raleigh, NC). For more information, contact Mr. Griffiths at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit http://info.hotims.com/55589-201  .

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