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Creating new experiences with
a high-transparency and
high-luminance display
“Transparent Screen Display”

Sony has been working on the development of a transparent screen display
with the intention of providing new video experiences that cannot be realized
with LCD, OLED, or other conventional flat displays. As an initial step,
a cylindrical transparent screen display was announced at SIGGRAPH
(Special Interest Group on Computer Graphics),
the international conference and exhibition. It is anticipated that this technology
will be used for applications such as next generation AI speakers to achieve
an unprecedented level of communication.

Researchers
Tomoharu Nakamura / Akira Tanaka /
Yuta Yoshimizu / Yuriko Imai
Display & Expression
Show video
Show video

Click here for the description of the video content.

This is an introduction video that shows the technology and prototype of the transparent screen realized by HOE (Holographic Optical Element).

Developing a Display That Provides New Video Experiences

Our project aims to develop a display that provides new video experiences. A display that can express a sense of presence to feel like “actually there”. In sci-fi movies, there are often scenes where a 3D hologram appears in an empty space and begins talking as if the person were there. We would like to make this a reality.

XR technology displays are anticipated to realize a strong sense of immersion and reality by integrating the real world with a virtual one. These displays generally fall into one of two categories. The first is a panoramic XR display that surrounds the viewer to immerse them in a virtual world. The second is a volumetric XR display. In this case, the viewers surround the object.

Our new transparent screen display was developed by pursuing the possibilities of new volumetric XR displays. XR displays may evoke HMD (Head Mounted Display), but we are aiming to realize a transparent display that makes viewers feel as if the object is sharing the same space, without the need to wear any special devices.

As the first step in this research, we developed a cylindrical display that makes it looks as if a 2D object is floating in front of you by using a screen that balances transparency and luminance.

Source: K. Nomoto, “Toward “KANDO” Creation with Immersive Visual Expression,” The 27th International Display Workshops (IDW ‘20), Vol. 27, 5-8 (2020).

A cylindrical transparent screen display. The dimensions are approximately 100 mm x 180 mm, with a maximum luminance of 1,000 cd/m2. It is assumed that it will be used indoors.

Core Technology of Transparent Screen Display
(Mechanism and Production Process of HOE Screens)

In developing transparent screen displays, a significant challenge is balancing transparency and luminance. These two properties are essentially in a trade-off relationship. The more transparent the screen, the darker the image becomes. The more luminous the screen, the hazier it becomes. We explored technical approaches for the optimal transparent screen to solve this trade-off. One promising method is HOE (Holographic Optical Element) a diffractive optical element that can add various optical functions to transparent film.

Laser beam is applied to a photosensitive photopolymer film. Two laser beams, an object beam (a diffusion beam) and a reference beam, are applied to form interference fringes. The material in the film changes according to where the laser beam in the interference fringes is strong or weak, thereby forming parts with high and low refractive indices. When an illumination light with the same wavelength and incident angle as a reference beam is applied to the film, a reproduction light that behaves the same as the object beam is generated when it passes through the film. On the other hand, lights with different properties will pass through the film.

This is based on the same principle as a 3D hologram picture. A hologram picture reproduces the image as if the object is there by illuminating the illumination light on the film that records the object light. Our HOE screen achieves a transparent screen by using diffusing light as the object light to be recorded.

Basic principle of HOE screens

HOE itself is an old technology on a research level. However, on a practical level, producing HOE screens with sufficient diffraction efficiency, transparency, and surface quality for display applications requires both delicate work and a wide range of knowledge. We started from the start-up of the manufacturing equipment and established the process of manufacturing the HOE screen by repeating simulations, experiments and evaluations. In addition to balancing transparency and luminance, another major challenge was screen size. The larger the screen size, the more uneven the surface tended to become, but we were eventually able to manufacture uniform and high-quality HOE screens through repeated trial and error.

Introduction to key manufacturing
/
evaluation equipment
for HOE screens

Laser exposure equipment: Creates interference fringes by applying two laser beams onto a photopolymer film. Our research know-how is utilized in the optical system as well as exposure conditions.

Goniophotometer: A sample is placed on a glass substrate and rotated while a light is applied. The sensor is used to measure the amount and direction of light distributed, thereby evaluating the light-distribution properties of HOEs.

Spectrometer: Measures the transmittance and diffraction efficiency of HOE screens by acquiring the optical spectrum.

Haze meter: Measures the degree of haze by illuminating a light onto transparent films.

Laser exposure equipment
Laser exposure equipment
Laser exposure equipment

Laser exposure equipment

Spectrometer
Spectrometer
Spectrometer

Spectrometer

The Originally Developed Cylindrical Projection System

As HOE screens are susceptible to external lights, realizing a practical transparent screen display required a structure that was less susceptible. We took advantage of Sony’s vast knowledge of display devices to devise an original cylindrical projection system.

Our unique cylindrical projection system, which consists of a set of lenses and a mirror, makes it possible to evenly display bright, high-definition images onto a cylindrical surface.

Light is projected upwards via a projection lens onto a mirror on the ceiling to form an image on the HOE screen inside the acrylic cylinder. The HOE screen is optimally designed and manufactured for the incident angle of the light. The flexibility of the design also allows for modifications of the angle of incident light, angle of diffracted light, and diffusion angles to maximize the luminance for viewing positions in different applications.

In addition, by using a laser that is narrower than the HOE diffraction spectral width (as opposed to a light source with a wide spectral width such as an LED), it is possible to diffuse the light more efficiently when projecting it onto the screen.

Thanks to all of the above, the light from the projector is strongly diffused as it matches the diffraction conditions of the HOE screen, while background and illumination lights do not match the conditions and pass through. Thus, a high-luminance image can be displayed on a transparent screen even in a bright environment, making the object look as if it is floating in the real world.

Structure of transparent screen display

T. Nakamura, T. Yano, K. Watanabe, Y. Ishii, H. Ono, I. Tambata, N. Furue and Y. Nakahata, “360-degree Transparent Holographic Screen Display,” ACM SIGGRAPH 2019 Emerging Technologies, Article No. 1 (2019).

Comparison of haze and brightness in HOE screen and conventional transparent screens
The photographs above show cylindrical displays with a HOE screen (a) and a conventional transparent screen (b), and the graph that compares the haze and relative luminance with a cylindrical display (c). The horizontal axis shows the haze, while the vertical axis shows relative luminance with a cylindrical display, clearly indicating that the HOE screen is superior in terms of both haze and luminance.

Challenges in View of a Wider Range of Applications

Following the announcement at SIGGRAPH, we received comments from both inside and outside the company on people’s expectations for transparent screen displays to be used as hardware for displaying characters. To be precise, we anticipate that if this technology is used to display characters for AI speakers, it will make the AI more personable, which may well lead to the establishment of new relations between humans and the digital world as well as humans and devices.

To further expand the range of applications of transparent screens, we are also currently developing flat-type transparent screen displays. The newest prototype achieved 3,000 cd/m² of luminance and over 85% transparency despite using a smaller projector, thereby realizing a high-luminance video display even in a bright environment. We also expect it will assist in promoting new types of communication such as data indication at retail checkouts and face-to-face consultations in the finance field as well as real-time caption displays for the hearing impaired.

One-Stop Development
from Device to Display

The fact that we had members from different technological backgrounds such as materials, devices, optics, mechanical engineering, electrical engineering, and software was a major asset in taking on the development of transparent displays. By handling the full prototyping process internally, we were able to develop devices with a focus on display, achieving a high degree of perfection that allows viewers to easily comprehend the product and its applications. We are determined to further accelerate development while imagining a world where transparent displays are commercialized in a diverse range of scenarios for better communication than ever before.

Researchers

Tomoharu Nakamura

Tokyo Laboratory 01

This project was born from a desire to create a new display with our own hands. If we propose an idea that we think is interesting and if it is approved as a project, engineers from different domains can participate, allowing us to proceed with the development as one team. Thanks to this environment, where taking on challenges is encouraged, we were able to continue with the development and realize our goals. It’s great to work with passionate people who are driven to push boundaries.

Akira Tanaka

Tokyo Laboratory 01

I was previously in charge of image sensor design. When I learned that there was a project to develop transparent screen displays, I volunteered to work on this theme. From the light sensing side to the light sending side. I am grateful for this flexible working environment, where people from different specialist fields are accepted and developed. I feel that Sony is a company where we can tackle multiple projects and really grow as engineers.

Yuta Yoshimizu

Tokyo Laboratory 01

At the Sony R&D Center, it is possible to pursue one’s own specialties and interests with many opportunities to take on new challenges. If something interests us, we have a variety of options to get involved, from transferring to a new project to taking on multiple projects at the same time. The freedom of this environment makes it both an easy and a rewarding place for researchers to work.

Yuriko Imai

Tokyo Laboratory 01

I decided to join Sony after seeing a demonstration of a cylindrical transparent screen display at an international conference while a student. Initially, I didn’t know much about display technology, but I took advantage of my specialty in wave optics to contribute to the development of HOE screens. I believe that if each member can bring their strengths to the table and contribute, we can achieve results as a team.

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