TDK

A new laser display module is in development now for augmented reality (AR) glasses that steers images straight to the back of users’ retinas. Lightweight and slim, this new module is already sparking expectations that it will help AR grow into a mass-market technology.

One of the issues impeding the wider adoption of AR is that the glasses have been so heavy and cumbersome that the market has not accepted these iterations for regular use.

The second issue with current AR technology is that it has not yet truly combined real-world information with virtual information. Currently, your focus needs to switch and select either virtual information on glass, or real-world information through glass forcing your eyes to change focal depth which is not real “augmented reality” at all.

TDK has overcome these issues by successfully developing a very compact size Full-Color Laser Module (FCLM), which is exponentially smaller and lighter than current systems. The new FCLM module is based on Hard Disk Drive (HDD) head technology, making truly lightweight and streamlined AR glasses feasible.

 Perhaps more significant is that this new FCLM technology makes authentic AR possible by creating “focus-free glass” using Direct Retinal Projection (DRP). DRP renders clear and focused images directly on the eye’s retina, eliminating the need to adjust the eye’s focus between the real-world environment and the AR glass surface. In addition, DRP technology allows the virtual AR image to be seen clearly even if the user has imperfect eyesight. It is effective, comfortable, and unobtrusive, and ultimately enables a true, authentic augmented reality experience.

VR vs. AR

The definitions for VR and AR remain stubbornly indistinct around the edges, but VR generally applies to immersive experiences that are the entirely virtual world, while AR refers to experiences that blend virtual information with the real world. In AR, the user typically wears glasses that afford a full view of the real world but still allow for some method of presenting a virtual overlay. For AR, users typically need to recognize the virtual world and the real world simultaneously.

An example use case for AR glasses is factory workers using AR to see an overlay of real-time monitoring data while doing inspections. Consumers can use AR glasses to see how a room will look with a different color of paint or with new furniture. To achieve more seamless visual integration with normal sight, AR requires much more difficult projection technology than VR.

Ultrasmall Full-Color Laser Module (FCLM)

Some current AR rigs mount a very small screen in the user’s field of vision. The use of a screen, no matter how small, makes them inherently bulky. The other existing type of AR projects images onto single or dual waveguides which optically connect to lenses. This method enables much more compact glasses than the aforementioned screen method. However, there remains the critical issue of the large light source which significantly impacts any size or weight reduction efforts.

As the light source for projection, the full-color laser is best in terms of wide color range and good scalability at higher resolution thanks to the laser beam scanning projection technology. But to realize full color, we need the three primary colors of laser diodes (red, green, and blue), with very precise alignment for full-color projection. 

This design requires space for passive optical components like multiple half-mirrors and lenses, as well as precise assembly and alignment of spatial optics that complicate the production process. These complexities are why current full-color laser light source modules are so bulky.

The goal has been to develop a display technology that uses neither lenses nor mirrors so that the resulting module could be smaller. NTT (Nippon Telegraph and Telephone) Corporation, which specializes in advanced optical telecommunications technologies, recently created just that. NTT’s Planar Lightwave Circuit (PLC) Technology incorporates the red, blue, and green lasers and can be optically coupled in a single solid device chip. This is a much more sophisticated way to realize full-color projection.

For effective use in AR, the last critical issue is precisely coupling the red, green, and blue beams to a PLC device. Since the PLC waveguide input port size is only 1.5 μm, the three laser diodes need to be aligned and bonded very precisely to realize accurate optical coupling. An incredibly precise assembly technology and process.

“As the leading developer and manufacturer of hard disk drive (HDD) heads, TDK successfully developed very precise and efficient optical assembly technology that can be used in largevolume production”

For such a difficult assembly, we looked at TDK’s unique expertise in other related precision manufacturing challenges to arrive at a solution. As the leading developer and manufacturer of hard disk drive (HDD) heads, TDK successfully developed very precise and efficient optical assembly technology that can be used in largevolume production. This optical assembly method allows the x, y, and z-axis positions of the laser diodes to be precisely adjusted relative to the PLC by turning on the beams and monitoring laser light output through the PLC so that laser output power is maximized. Then the laser diode and PLC are quickly docked. This unique precision HDD head manufacturing technology can be effectively applied at scale, delivering a new and promising path forward in the development of AR glasses.

FCLM specs

The resulting display FCLM is roughly one-tenth the size of a typical space-optics module, measuring only 8mm x 5.5mm x 2.7mm, and its weight is 0.35g. The construction of the module also enables images to be displayed in full-color depth – approximately 16.2 million colors. Compared to conventional AR platforms, FCLM is 10X smaller and 10X lighter, making the wide adoption of more effective and comfortable AR glasses possible.

AR glasses using FCLM and

DRP Using the FCLM, a completely new type of AR glasses has been created. In these new glasses, the laser beam emitted from the FCLM is scanned by a MEMS mirror, then the laser beam is directly projected onto the eye’s retina. This is called direct retinal projection (DRP). To date, QD Laser, Inc. has been the only company in the world to bring DRP glasses to the commercial market. However, their current product uses a conventional large-size full-color laser that is too bulky to build into the glasses themselves. This design requires that the large laser module be carried at the waist, severely restricting use cases.

With the ultra-small FCLM, TDK and QD Laser collaborated to integrate the module into the temple of the glasses, enabling the world’s first AR glasses using DRP. The biggest feature of these new AR glasses is that you can see virtual world projections simultaneously with real-world images without adjusting your focus. Even if your eyes are focused at a distance, you can recognize the information presented by the AR glasses. This is the “real AR” which has never been achieved in AR glasses. With no switching of optical focus our attention between real and virtual worlds, this technology opens exciting new opportunities for the application of AR glasses in daily life.

What is next. Implementing a real or authentic visual AR experience has proven a very difficult technological challenge that has never been realized until now. With this new ultra-small FCLM and the incorporation of DRP, these difficulties have been overcome, paving the way for new implementations and broad adoption of AR technology.

About the authors Hideaki Fukuzawa received the Ph.D. degrees in electrical engineering from Tohoku University, Japan in 2004. Since 1995, he has been with Corporate R&D Center in Toshiba Corporation, and main research items are magnetic and spintronic devices, such as HDD head and highly sensitive sensor in charge of optical devices and system for AR/VR glasses and beyond 5G optical communications, as well as spintronic devices for new applications.

Tsuyoshi Komaki joined TDK Corporation in 1991. He was a member of the Development Department of the Recording Media Division, where he was involved for the development and mass production of optical discs. He is mainly responsible for the development of organic materials for CD-R, DVD and Blu-ray Disc. Since 2018, he has been part of Tech & IP and oversees the development of laser modules for AR/VR glasses.