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2D / 3D switching technology

A fundamental limitation of autostereoscopic displays is the reduction in effective resolution caused by the optical filter. For instance, a native 4K panel (3840 x 2160 pixels) is typically divided to produce a 3D effect combining two Full HD images (1920 x 1080 pixels each).

This resolution loss is often acceptable for objects and scenes. While sharper details are always desirable, the enhanced depth perception and immersive quality of the 3D effect generally outweigh the perceived reduction in sharpness.

Text, however, presents a significant challenge. Fine lines and small fonts (especially those under 3 pixels in size) are frequently not resolved correctly by lenticular or diffractive optical systems. Although increasing font size is a recommended practice for 3D application design, the inherent difficulty in rendering crisp, small text remains a major drawback. This limitation hinders the use of autostereoscopic displays for everyday tasks like reading emails, reviewing documents (PDF/Word), or web browsing.

A practical solution to this problem is 2D/3D switching technology. In its simplest form, this technology allows the display to operate in two modes:

  • A high-resolution 2D mode, where the optical filter is disabled, preserving the panel's native resolution (e.g., 4K).
  • An optically active 3D mode, which is engaged only when depth perception is required, sacrificing resolution for the stereoscopic effect.

Physics background: refractive index​

To understand the operating principle of this technology, we must review how light interacts with different materials. Light travels at varying speeds depending on the medium it passes through. In a vacuum, where nothing impedes its progress, light achieves its maximum speed of approximately 300,000 km/s. In a denser medium like water, however, its speed decreases—to approximately 225,000 km/s.

This change in velocity is critical. When light transitions from one medium to another (e.g., from air to water), its change in speed causes it to bend, a phenomenon known as refraction. This is why a straw placed in a glass of water appears bent or broken at the water's surface.

The degree to which a material slows down light is defined by its refractive index. If two adjacent materials have an identical refractive index, light passes between them without changing speed or direction, in other words, without any refraction occurring. In this case, the boundary between the materials becomes invisible, and the straw would appear straight.

This principle is the key to 2D/3D switching technology. The goal is to create a system where two optical materials can be made to have either matching or mismatching refractive indices on command.

This is achievable using liquid crystals. These materials are the foundation of LCD displays because their optical properties can be precisely controlled with an electric field. A liquid crystal can be switched between distinct molecular states (often called on and off states), each with a different refractive index. By aligning the refractive index of the liquid crystal layer with that of a neighboring lens material, the lenses can be effectively turned "off," allowing light to pass straight through for a high-resolution 2D image. Applying an electric field switches the liquid crystals to a state with a mismatched refractive index, activating the lenses to create the 3D effect.

2D / 3D switchable displays​

Therefore, a 2D/3D switchable display integrates a layer of liquid crystals within its optical filter (e.g., the lenticular lens layer).

In 2D Mode, an electric signal aligns the liquid crystals to a state where their refractive index matches that of the lens polymer. This renders the lenses optically inactive, as light passes through without refraction. The result is a clear, high-resolution image at the display's native resolution (e.g., 4K), effectively functioning as a standard 2D monitor with a slightly thicker glass substrate.

In 3D Mode, the applied electric field is changed, switching the liquid crystals to a state with a mismatched refractive index. This reactivates the lenses, as light now bends at the material boundaries to create the necessary refraction for stereoscopic vision. The "pen bends," and the display produces a glasses-free 3D effect, albeit at a lower effective resolution.