1. Field of the Invention
The present invention relates to a polarization conversion mechanism, more particularly to a polarization conversion mechanism and method for use in a display device and/or touch screen display.
2. Description of the Prior Art
A touch screen of a display device or mobile device is generally coated with a linear polarizer or a circular polarizer (linear polarizing layer+a quarter-wave plate) in order to be viewable under the strong environment light and to reduce the interference of the reflection light reflecting therefrom. At present one way of implementing is providing a quarter-wave plate and/or a linear polarizing layer adhesively on an external surface of the touch screen.
According to polarization theory, when a light beam passes through a wave phase delay plate, the phase difference (δ) is calculated from the formula
                    2        ⁢        π            λ        ⁢    nd    ,wherein n denotes the refraction index of the phase delay plate; d denotes the thickness of the phase delay plate; λ denotes wavelength of the passing light beam. When δ=π, the passing light beam is said to be linearly polarized light; when
      δ    =          π      2        ,the light is circularly polarized light and the remaining is called the elliptically polarized light. When
  nd  =            1      4        ⁢    λ  is an odd number, the phase difference (δ) is said to be conformed to
      δ    =          π      2        ,where the phase delay plate is called the quarter-wave plate. Under this condition, the linearly polarized light passing through the quarter-wave plate converts into the circularly polarized light. In the formula Δn=ne−no of the crystal layer, in case n is replaced by Δn and when
            Δ      ⁢                          ⁢      nd        =                  1        4            ⁢      λ        ,the phase delay plate is the quarter-wave plate, where ne and no are commonly used to denote optical index and refractive index respectively in the art. From above explanation, it is noted that the visible light (the natural light) consists of wavelength (λ) with 400 nm to 700 nm passing through the quarter-wave plate, wherein when a single wavelength is conformed with the condition
      (          δ      =              π        2              )    ,the visible light converts into circularly polarized light, the remaining wavelengths are substantially equivalent to the circularly polarized light or the elliptically polarized light. Moreover, when the elliptically polarized light passes through the linear polarizer, the light passage rate varies owing to the changed polarization angle of the elliptically polarized light with respect to the linear polarizer.
Due to the advance in optic technology, modern sunglasses of today are provided with a linear polarizer in order to withstand or reduce the glare of a sunny day outdoor. When the polarization direction (emitted light direction) of the linear polarizer in the sunglasses of a wearer is perpendicular to the polarization direction of a display device, the wearer cannot see the image displayed over the screen. When there is an angle formed between the two polarizations, a portion of the incident light cannot pass through the linear polarizer, thereby reducing the visibility of the image displayed over the screen. In order to overcome this disadvantage, the wave phase delay plate has been developed and is disposed over the linear polarizer so as to retard and hence prolonging the light passage through the display screen, and emitting the reflective light in form of circularly polarized light and elliptically polarized light. Since the circularly polarized light and elliptically polarized light have a relatively large passage rate relative to the linear polarizer, the problem of being unable to view the image displayed over the screen encountered in the prior art can be avoided.
In other words, the technique of absorbing the incident light is replaced by installing the linear polarizer or circular polarizer in the sunglasses so that the wearer of the sunglasses can see the image displayed over the screen of the display device. However, utilizing a polarizer (a linear polarizer+a quarter-wave plate or a quarter-wave plate+a linear polarizer) in the touch screen reduces the reflection of the incident light and the reflective light emitted from the touch screen is in form of the linearly polarized light and circularly polarized light. Under this condition, the overall thickness of the display device or mobile device is increased in addition to the expense of the polarizer.
Another way of utilizing a linear polarizer is installing the same in medium size touch display together with a wave phase delay plate so that the reflection of the incident light passes sequentially through the linear polarizer and the wave phase delay plate in term of circularly polarized light and elliptically polarized light. Since the reflection direction of the two polarized light is opposite to the hitting direction of the incident light owing to the colliding interface within the touch display and the rotational direction of the reflection, the reflection light refracts with respect to the linear polarizer after passing through the wave phase delay plate. In case the polarization direction is perpendicular with the linear polarizer, the polarized light cannot pass through the linear polarizer, thereby reducing the amount of the reflection light and hence interference between the incident and reflection light. In other words, viewing ability of the touch display under the strong environment light is increased.
Presently, a linear polarizer is usually installed on an exterior of a touch screen of a touch display together with a wave phase delay plate in order to convert the incident light as the circularly polarized light. Alternately, two wave phase delay plates are installed on the exterior and interior of the linear polarizer so as to convert the reflection light in form of circularly polarized light so as to reduce the reflection interference with the touch screen. However, the more the linear polarizer and the wave phase delay plate, the more the thickness of the touch screen becomes, thereby incurring extra expense and simultaneously reducing the utility rate of the light beam.
Therefore, it is an urgent business for the manufacturers to find or develop a polarization conversion mechanism for use in a display device and/or touch screen display, where the polarization conversion mechanism can increase the phase delay effect with the use of wave phase delay characteristics, in which a quarter-wave plate or film can be eliminated so that the linearly polarized light emits out as circularly and elliptically polarized light. The polarized plate provided accordingly has simple structure and reduces the overall thickness of the touch screen display.