Holographic technology has the extraordinary ability to replicate the two fundamental properties of light: intensity information and phase information. Intensity information is similar to what we perceive in standard photographs - it helps distinguish between the lighter and darker elements within an image. Conversely, phase information delves into the wave properties of light, pinpointing the exact location of a particular point within the wave. Holographic techniques emerge as the most natural choice for creating convincing three-dimensional images, because they can faithfully record and reproduce both of these properties.
Digital holographic microscopes use light sources that generate uniform wave patterns by splitting them into reference light and signal light. This ingenious process allows for the simultaneous acquisition of phase and intensity information from a light-emitting object by interference between these two light sources. This remarkable capability allows us to reconstruct the shapes of objects, whether they are micro or nano sized.
In the past, access to phase information was limited to relative distribution and couldn't be captured by standard cameras. However, the hologram principle has greatly improved our access to phase information, and a notable advantage of digital holographic microscopy is its ability to quantify and express phase information in constant numerical values.
Basic Principles of Digital Holographic Microscopy
The core principle of digital holographic microscopy is based on the concept of light interference. When light interacts, it produces interference patterns known as constructive and destructive interference. These patterns serve as critical clues to reconstruct objects in three dimensions by providing phase information about the light.
The process begins with data collection using a standard digital camera, and then involves reconstructing the original target object using diffraction principles. The interference pattern captured by the camera is fed into a computer algorithm that removes the interference pattern to reveal the shape of the original object.
Applications of Digital Holographic Microscopy
Like traditional microscopes, holographic microscopes are primarily used to visualize the three-dimensional structures of biological samples or the distribution of components within materials. However, the Realistic Media Research Laboratory of the Electronics and Telecommunications Research Institute (ETRI) Realistic Media Research Laboratory is pioneering the development of holographic microscopes tailored for semiconductor and display measurements.
In the past, 2D microscope technology was sufficient, but with recent advances in stacking technology, semiconductors and other storage devices now have complex 3D structures. As a result, the demand for depth measurement has skyrocketed, and in this context, the future of holographic microscopy technology appears promising.
With the emergence of OLED technology, the display market is embracing micro panels, and holographic microscopes are poised to contribute significantly to the rapid measurement of these compact panels.
Distinguishing Features: Comparison of conventional and holographic microscopes
Existing microscopes mainly adopt a transmissive structure so that illumination light sources pass through the sample. Therefore, it is excellent for observing intensity information that distinguishes the contrast of biological specimens.
In contrast, the ETRI Sensitive Media Research Laboratory's digital hologram microscope has a reflective structure. It is a technology that can derive phase information from light interference phenomena and quantitatively express this phase information quantitatively. It is an innovative technology that can observe nano-scale structures through reflected light data.
The Metaverse Era Envisioned with Digital Hologram Microscopes
At the heart of the metaverse is a high-resolution micro-display element (such as an OLED). The metaverse is very similar to AR and VR technologies, which require realistic, high-quality images.
To implement a realistic image, the key is to reduce the size of the display element and the circuitry that drives this technology. This is where holographic microscopy comes in. The hologram microscope improves the quality of high-resolution display elements as a tool for precise measurement.
Challenges in the Development of Digital Hologram Microscopy
Digital hologram microscopy faces several challenges in solving problems caused by the distortion of laser light sources and optical systems. In a laser light source with a constant wavelength characteristic, interference fringes (speckles) are formed like grains. These speckles, which appear as light and dark dots on the screen, are similar to noise and adversely affect image quality.
On the other hand, optical system distortion refers to abnormal phenomena such as distorted, overlapping images or blurred effects - collectively known as aberrations.
To mitigate speckle problems and optical system distortion, extensive measurements and data collection have been required. While it has been difficult to quantify these problems in the past, recent advances in deep learning-based technologies have made it easier to automatically remove or correct speckle and distortion. This concept is similar to the filter function of the camera.
