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New design could make augmented reality glasses more power-efficient and practical for everyday wear.

Researchers at the University of Rochester have designed and demonstrated a new optical component that could significantly enhance the brightness and image quality of augmented reality (AR) glasses. The advance brings AR glasses a step closer to becoming as commonplace and useful as today’s smartphones.

“Many of today’s AR headsets are bulky and have a short battery life with displays that are dim and hard to see, especially outdoors,” says research team leader Nickolas Vamivakas, the Marie C. Wilson and Joseph C. Wilson Professor of Optical Physics with URochester’s Institute of Optics. “By creating a much more efficient input port for the display, our work could help make AR glasses much brighter and more power-efficient, moving them from being a niche gadget to something as light and comfortable as a regular pair of eyeglasses.”

In the journal Optical Materials Express, the researchers describe how they replaced a single waveguide in-coupler—the input port where the image enters the glass—with one featuring three specialized zones, each made of a metasurface material, to achieve improved performance.

“We report the first experimental proof that this complex, multi-zone design works in the real world,” says Vamivakas. “While our focus is on AR, this high-efficiency, angle-selective light coupling technology could also be used in other compact optical systems, such as head-up displays for automotive or aerospace applications or in advanced optical sensors.”

Metasurface-powered AR

In augmented reality glasses, the waveguide in-coupler injects images from a micro-display into the lenses so that virtual content appears overlaid with the real world. However, the in-couplers used in today’s AR glasses tend to reduce image brightness and clarity.

To overcome these problems, the researchers used metasurface technology to create an in-coupler with three specialized zones. Metasurfaces are ultra-thin materials patterned with features thousands of times smaller than a human hair, enabling them to bend, focus or filter light in ways conventional lenses cannot.

“Metasurfaces offer greater design and manufacturing flexibility than traditional optics,” says Vamivakas. “This work to improve the in-coupler, a primary source of light loss, is part of a larger project aimed at using metasurfaces to design the entire waveguide system, including the input port, output port and all the optics that guide the light in between.”

For the new in-coupler, the researchers designed metasurface patterns that efficiently catch incoming light and dramatically reduce how much light leaks back out. The metasurfaces also preserve the shape of the incoming light, which is essential for maintaining high image quality.

This research builds on earlier theoretical work by the investigators that showed a multi-zone in-coupler offered the best efficiency and image quality. Vamivakas says that advances in metasurface gratings enabled the design flexibility to create three precisely tailored zones while state-of-the-art fabrication methods—including electron-beam lithography and atomic layer deposition—provided the precision needed to build the complex, high-aspect-ratio nanostructures.

“This paper is the first to bridge the gap from that idealized theory to a practical, real-world component,” says Vamivakas. “We also developed an optimization process that accounts for realistic factors like material loss and non-ideal efficiency sums, which the theory alone did not.”

Three-zone performance test

To demonstrate the new in-coupler, the researchers fabricated and tested each of the three metasurface zones individually using a custom-built optical setup. They then tested the fully assembled three-zone device as a complete system using a similar setup to measure the total coupling efficiency across the entire horizontal field of view from -10 degrees to 10 degrees.

The measurements showed strong agreement with simulations across most of the field of view. The average measured efficiency across the field was 30 percent, which closely matched the simulated average of 31 percent. The one exception was at the very edge of the field of view, at -10 degrees, where the measured efficiency was 17 percent compared to the simulated 25.3 percent. The researchers attribute this to the design’s high angular sensitivity at that exact angle as well as potential minor fabrication imperfections.

The researchers are now working to apply the new metasurface design and optimization framework to other components of the waveguide to demonstrate a complete, high-efficiency metasurface-based system. Once this is accomplished, they plan to expand the design from a single color (green) to full-color (RGB) operation and then refine the design to improve fabrication tolerance and minimize the efficiency drop at the edge of the field of view.

The researchers point out that for this technology to be practical enough for commercialization, it will be necessary to demonstrate a fully integrated prototype that pairs the in-coupler with a real micro-display engine and an out-coupler. A robust, high-throughput manufacturing process must also be developed to replicate the complex nanostructures at a low cost.

Knee and epidural infiltrations are among the most common rheumatological procedures. Due to the shortage of rheumatologists in Cameroon (Sub-Saharan Africa), GPs play a vital role in treating patients with rheumatic diseases. However, before recommending this routine practice to GPs, it is necessary to assess their knowledge and practices, which was the aim of our study. There is little data available on this subject in sub-Saharan Africa, despite the recognized importance of GPs in the management of many rheumatic diseases [14]. Our study found that infiltration practices among GPs in Cameroon were performed in 23.2% of cases for the knee and 8.5% for the epidural. Knowledge and practice scores for these procedures are average and are linked to certain factors related to undergraduate and postgraduate training.

We found that GPs performed 23.2% of knee infiltrations and 8.5% of epidural infiltrations. The use of knee and epidural infiltrations by GPs varies according to geographical context. In high-income countries such as France, studies indicate that 15 to 30% of cases of knee osteoarthritis are managed with infiltrations by GPs, while epidurals predominantly remain the responsibility of specialists [15]. Key determinants include access to ultrasound guidance, which reduces failure rates for knee infiltrations, and ongoing training [15, 16]. Conversely, in sub-Saharan Africa, where rheumatologists are scarce, GPs perform these procedures more frequently despite the risks [17, 18]. This is also due to a lack of accessible therapeutic alternatives, such as surgery, competent physiotherapy, and the limited technical resources available [18]. Certain patient-related factors may also influence the use of infiltrations, notably obesity, as reported by Bello et al. [18].

We reported average scores for knowledge of knee and epidural infiltration, as well as for practice. There is a lack of literature on GPs’ knowledge of infiltration. This includes indications and absolute contraindications, such as active joint infection, anticoagulation and unbalanced diabetes, as well as the management of side effects, such as post-corticoid hypertensive flare-ups. A French study reported that only 40% of GPs were familiar with contraindications [15]. Factors influencing this poor level of knowledge and practice included gender; undergraduate rheumatology training of less than four weeks; having been in practice for less than three years; and never having attended a workshop or training course on infiltration. These data are consistent with literature. Liddell et al., in a study of 251 GPs in the United Kingdom, found that gender (male), experience (more than 10 years), specialized training (interest in rheumatology or orthopedics), and those practicing in rural areas were significant determinants of performing intra-articular injections, particularly in the knee, shoulder, and elbows [19]. In Germany, Spruit et al. found that 81% of GPs surveyed felt competent in performing musculoskeletal injections, particularly due to a lack of confidence in injection procedures, a lack of practical training, and little confidence in the diagnosis and therapeutic benefits of these procedures. They also reported a high referral rate after the procedure [20]. In a study of 204 GPs in Ireland, Farrell et al. found that 72% performed intra-articular injections, particularly in the knee and shoulder, with barriers such as their skills and medico-legal concerns [21]. Moore et al., in an interview with primary care physicians, found that barriers included a lack of confidence and discomfort with these procedures, the risk of side effects, incertitude regarding evidence and guidelines, and technical uncertainties [22].

Specialized training (e.g. workshops, echoguidance), access to contextualized recommendations, and clinical experience can significantly improve GPs’ knowledge and skills in rheumatology procedures [15, 16, 23]. Improving the training of GPs would likely reduce patient waiting times for these procedures and decrease the rate of referrals after the procedure [19]. Conversely, poor knowledge is associated with professional isolation, a lack of interaction with rheumatologists, and a scarcity of continuing training courses adapted to the local context, particularly in sub-Saharan Africa [17, 24]. It should also be noted that logistical constraints in Sub-Saharan Africa lead to non-standardized practices and higher rates of complications [18].

In order to improve the current situation in Cameroon, a number of important lessons need to be learned. With regard to training, we should advocate improving exposure to rheumatology during undergraduate internships and developing short training modules on rheumatology procedures (including punctures and infiltrations), as well as simplified protocols for GPs to use [25]. Telemedicine should be used to mentor young GPs, especially in rural areas [18]. Finally, reinforce practical teaching during undergraduate courses and encourage postgraduate training in rheumatology procedures.

Interpretation of the data from this study must take into account a number of limitations. Firstly, there is the common bias in data collection associated with online studies. Nevertheless, this is an important means of obtaining data for this type of study. Another limitation is the small sample size, as 80% of the 500 GPs trained annually in Cameroon leave the country, making them ineligible for the study. Additionally, this study focused on young GPs with no more than 5 years’ experience, due to the harmonization of undergraduate training programs in Cameroon 12 years ago, with the first cohort graduating 5 years ago. Nevertheless, this study enables us to establish the current situation and identify the key determinants on which it will be crucial to act. These data are consistent with those reported in the literature. Further studies are needed to assess teaching methods related to these procedures for undergraduate students and to evaluate the impact of workshops and courses on the current level of knowledge and practice of postgraduate GPs.