Apple is Rockley Photonics’ largest customer. So says Rockley in a document filed with the US Securities and Exchange Commission (SEC) as it prepares to be listed on the New York Stock Exchange (NYSE).
The Form S-4 document provides details of Rockley’s silicon photonics platform for consumer ‘wearables’ and medical devices, part of the emerging health and wellness market.
Andrew Rickman, Rockley Photonics’s CEO, discusses what the company has been working on and how a wearable device can determine a user’s health.
The first of several articles on silicon photonics-based biosensors for medical and other applications.
Andrew Rickman
Part 1: Consumer Wearables
Ever wondered what the shining green light is doing on the underside of your smartwatch?
The green LED probes the skin to measure various health parameters - biomarkers - of the wearer. Just what light can reveal about a user’s health is a topic that has preoccupied Rockley Photonics for several years.
Rockley is not solely interested in using the visible spectrum to probe the skin but also light at higher wavelengths. Using the infrared portion of the spectrum promises to reveal more about the watch wearer's health.
Rockley can also shed light on its own healthcare activities following the announcement of its merger with SC Health that will enable Rockley to be listed on the NYSE, valued at $1.2 billion.
SC Health is a Special Purpose Acquisitions Company or SPAC. Also known as a ‘blank cheque’ company, a SPAC is a publicly listed cash shell company that raises money to acquire an early-stage start-up before its listing.
For Andrew Rickman, who will remain as Rockley’s CEO, the latest development is consistent with his silicon photonics vision when he established Bookham Technologies in 1988.
He views silicon photonics as an enabling technology, a platform that can address multiple industries, the healthcare market being the most promising. As such, Rockley is no more a healthcare company than it is an optical transceiver or a LiDAR player, says Rickman.
SPAC path
Rockley is not commenting on the SC Health transaction except to say that start-ups aspire to go public or be acquired. “We are going public through this route,” says Rickman.
Rockley can’t say much about SC Health either. What Rickman will say is that shell companies are created by people with a particular industry background: “Clearly, there is a very big health dimension to Rockley, and SC Health is a health-oriented SPAC.”
Rockley’s silicon photonics platform is already being used for the optical transceiver market through a joint venture with Hengtong Optic-Electric. Rockley is also working with partners to develop co-packaged optics solutions, where its optics is packaged alongside a chip to enable optical input-output.
The company’s other interests include advanced optical computing, environmental sensing, vision systems/ LiDAR and spectroscopy, its approach for wearable and medical diagnostics devices.
The medical diagnostics market uses ‘invasive’ techniques where lab equipment analyses samples such as blood, saliva and urine. In contrast, the non-invasive health market was largely created with the advent of smartwatches, says Rickman. Here the light is used to probe under the skin where it is scattered. The reflected light is then analysed by the watch.
Rickman says that, unlike the established medical diagnostics market, knowledge and expertise for the newer non-invasive approach is limited: “It creates an opportunity for us to fill the gap.”
Rockley’s expertise ranges from the semiconductor process needed to make the sensor and the measurement and analysis of the data collected.
Medical diagnostics
Medical diagnostic equipment analysing a blood sample, for example, determines its many constituents. Specially designed biochemical ‘labels’ are used that attach to what is being detected. Such labels are fluorescent so that the degree of binding and hence the amount of tested-for material is determined by measuring the degree of fluorescence, says Rickman.
Silicon photonics start-ups are among firms developing alternative equipment that is “label-free” and does not require fluorescent labels. Such equipment still requires biochemistry for ‘receptors’ that trap the constituents being tested for. But here what is measured is refractive index changes of the light.
Label-free sensors use silicon photonics circuits that measure the refractive index. The circuits can be a waveguide and ring resonator or a Mach-Zehnder interferometer. Light shined through the circuit undergoes tiny changes in its refractive index caused by constituent-receptor bindings on the sensor’s surface. The circuits are tiny, meaning sensors can be integrated on-chip to measure multiple biomarkers.
Silicon photonics-based biosensors promise more compact diagnostic systems than those used in labs and hospitals. Such systems could be used in ambulances, intensive care units and at a doctor’s office. They can also deliver test results in 25 minutes or less, far quicker than sending samples to a lab and having to wait hours or a day for results.
“There are a lot of companies in this [biosesnor diagnostics] field,” says Rickman. “It is a field deserving close attention and is an exciting area.” However, Rockley’s focus is non-invasive wearables instead.
Wearables cannot match the diagnostic detail provided by invasive techniques, says Rickman. But non-invasive techniques have much scope for diagnostic improvement compared to existing smartwatches.
And while a blood test may provide far greater detail, it indicates only what is happening when a sample is taken. A wearable, in contrast, can continuously monitor the user. This creates new healthcare opportunities, say Rickman.
LEDs and lasers
The technique underpinning smartwatch monitoring has the long title of non-invasive diffuse reflective spectroscopy.
Light at different wavelengths penetrates the skin and is scattered by blood vessels and cells and the interstitial fluid in between. The reflected light is analysed using spectroscopy to glean medical insights.
The smartwatch uses a green LED since blood haemoglobin has a good light absorption at that wavelength. “Effectively, what is being measured is the expansion and contraction of the blood vessels,” says Rickman. “It is measuring the amount of light that is absorbed by the change of the volume of blood.”
It doesn’t stop there. Using a red LED and extending it into the infrared range, the blood oxygenation level is measured using the ratio of oxygenated (bright red) and unoxygenated (darker red) haemoglobin. “The ratio of the two wavelengths that you get back is proportional to the blood oxygen level,” says Rickman.
The visible range can also detect bilirubin, a yellow-orange bile pigment associated with jaundice.
“But that is pretty much it,” says Rickman. “All the other thousands of constituents, if they have absorption peaks, are swamped in the visual range by haemoglobin.”
What Rockley has done is extend the light’s spectral to measure absorption peaks that otherwise are dwarfed by water and haemoglobin.
“We are addressing the visible range and extending it into the infrared range, getting much more accuracy using laser technology compared to LEDs which opens up a whole range of things,” says Rickman.
To do this, Rockley has used its silicon photonics expertise to shrink a benchtop spectrometer to the size of a chip. Normally miniaturisation reduces performance. For a start, the size of the aperture that collects light is reduced, says Rickman. But Rockley claims its silicon photonics platform and its design improves greatly the signal-to-noise ratio compared to a benchtop spectrometer.
“We are talking orders of magnitude improvement over the best-in-class benchtop instruments,” says Rickman.
An important parameter associated with optical transceivers is the link budget, says Rockley, which means getting enough signal to the receiver to recover the data sent. This is defined as part of a standard and being compliant requires meeting the specification.
“Here [with spectroscopy], no one is determining the performance that must be met; there is no standard,” says Rickman, making it an area ripe for innovation.
Platform process
What a wearable spectrometer must deliver is a highly accurate wavelength registration and a deconvolving of what the spectrum comprises, says Rickman
Rockley says one aspect of its silicon photonics process is its use of relatively large waveguides: several microns wide compared to hundreds of nanometers.
It makes sense for companies to adapt CMOS processes for silicon photonics to create sub-micron waveguides, he says, but if the dimensions are smaller than the light’s wavelength, it becomes highly sensitive to the manufacturing process and polarisation while experiencing higher optical loss.
“With the larger waveguides, we get 20x better wavelength registration,” says Rickman. “That is the difference between being able to make the product, or not.”
Healthcare benefits
Rockley says its spectrometer-on-a-chip measures a range of biophysical and biochemical biomarkers. “It will go a lot further than watches today, a lot deeper but not as deep as a blood draw,” says Rickman.
The sensor can detect lactate, urea, glucose - ‘a tough one but a big one’ - and chemical biomarkers that are in a high proportion in blood, says Rickman
“The diseases that are predominant over life, each one has a handful of biomarkers,” says Rickman. “A non-invasive smartwatch can measure these, providing good indicators of the early onset of a disease.”
Detecting the onset of disease will enable more effective treatment, better patient outcomes and less costly healthcare. “The smartwatch doesn’t have to be conclusive,” says Rickman. It is not replacing a full analysis but it can be an early warning and lead to a better outcome.
Such continuous noninvasive monitoring will also help patients with chronic diseases, improving their treatment.
Rickman didn’t detail what probing with infrared light will enable but the filed S-4 Form says Rockley is exploring the early detection of key diseases. These include coronary arterial disease, diabetes, chronic kidney disease, Covid-19, asthma, hepatitis C, cirrhosis, Alzheimer’s, stroke, flu, sepsis and cancer.
Rickman says there is research looking at detecting early onset Covid-19 using a patient’s vital signs but this requires their presence at a clinic. The parameters monitored include blood sugar, blood pressure, hydration, blood oxygen level and heart rate.
Using the parameters combined with machine learning can determine if a patient will have a bad covid-19 experience or not. If the former, drastic treatment steps can be taken before the patient becomes ill.
Market opportunity
Rickman is excited at the scale of the wearable opportunity. In microelectronics, it is consumer applications that drive economies of scale. There may be millions of units of optical transceivers, he says, but that doesn't achieve ‘hyper-scale. “You want to be making tens of millions of units a week,” he says.
The press release announcing the stock market float referred to Rockley working with world-class partners. Asked about Apple and Samsung, leading makers of smartwatches, Rickman would only say that Rockley is targeting the wearable and medical device markets for customers.
However, the S-4 Form names Apple and other firms such as smartwatch maker Zepp Health, LifeSignals Group which makes wearable medical biosensors, and Withings France SA that makes watches and other healthcare devices. Meanwhile, healthcare company, Medtronic, is a strategic investor in Rockley.
Rockley is projecting revenues of $1.1 billion in 2024 if all goes to plan.
Career passion
Rickman has been interested in silicon photonics and sensing “since the beginning of time”.
He points out how, in the mid-80s, before he founded Bookham, Professor Richard Soref, a silicon photonics luminary, had provided a guide as to what could be done in silicon photonics. “I went on and had the privilege of working with Soref,” says Rickman.
When Rickman investigated the application areas for silicon photonics, he thought that Bell Labs had already solved the problems associated with optical communications so he focussed on sensors. Back then, it was tough to create a multidisciplinary team needed to exploit the biosensor opportunity.
Then, in the late 90s, the dotcom era started and it was clear that many problems remained in making optical-fibre componentry. Bookham dropped its sensor work and focussed exclusively on optical communications.
Rockley was formed in 2013 as a silicon photonics platform company. “It was a question of which of these applications, out of a massive menu that we collected over time, were going to take off in the timeframe of Rockley Photonics,” he says.
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