Optical imaging is one of the latest sensor technologies used in touch screen interfaces. Optical imaging technology enables users to interact with the screen with a high degree of accuracy, clarity and convenience. Based on optical imaging technology, a wide range of products have come into being, such as the optical touch overlay, the optical touch module and the optical interactive white board.
The optical imaging technology detects the touch point with optical sensors that operate on the basis of the principles of optics. An optical sensor is a device that converts light rays into electronic signals. It measures the physical quantity of light and translates it into a form read by the instrument. Optical sensors come with a lot of advantages, such as no contact pressure, no external interference, high-speed transmission of signal, capability of remote control, etc., and are widely used for detecting and tracking the motion of target object. Optical overlays use cameras, which detect specifically Infrared Light (IR).
Infrared Light Sources.
Infrared (IR) is a portion of the light spectrum with longer wavelengths than those of visible light and is radiated strongly by hot objects, so objects with heat are especially visible in infrared wavelengths of light. In optical touch devices, a filter that removes visible light is installed so that the camera sensor detects only infrared light. IR LEDs are used in most multi-touch optical equipment, as they are efficient and effective at providing infrared light.
Through camera sensor an optical image is converted into electronic signal and high-quality camera sensors ensure the good performance of the optical touch device. Firstly, a bandpass filter is required on the (IR sensitive) camera in order to prevent the visible light, adding to the touch's accuracy and responsiveness. Secondly, higher resolution of a camera with more pixels improves the optical touch's precision. Thirdly, higher frame rate means more snapshots and data in a short time, which make the touch screen more responsive. 
How it works.
An optical touch product uses an array of infrared (IR) LEDs in its bezel. When an object, or a finger, or a hand, approaches the screen, the IR light sources are interrupted. Two (or more) small-sized sensors then detect the interruption and track the movement of the approaching objects.
The heart of the technology is a controller that receives signals from the cameras, compensates for IR light distortions and locates the position of the touching object with extreme accuracy.
Besides compensation for distortions, a systematic algorithm is adapted to help eliminate the impact of ambient light to add to the accuracy of the optical touch screen.
Comparisons with other touch screen technologies.
Optical imaging technology uses optical sensor to track the touch point, so the approaching object can be detected before it physically reaches the screen. This means zero or very little pressure is applied to the screen for a response.
Optical touch products based on optical imaging technology can detect multiple touch points (fingers/pen/cards, etc) at the same time and allow users to use more than one object to point, rotate and stretch. Multi-touch goes beyond the capabilities of traditional touch screen devices, bringing a brand new touching and viewing experience to users.
Any substrate possible
Any substrate is suitable for the sensor, including glass, acrylic and polyester. Technologies such as capacitive and Surface Acoustic Wave (SAW) can only use glass with ITO (Indium Tin Oxide) coating for sensor substrate.
Designed for large displays
Optical imaging technology can be tapped into displays of very large sizes, while capacitive, resistive and SAW can hardly support devices over 30'. Optical imaging is consistent at all sizes, which makes purchase of large-scale optical touch equipment very cost-effective.