Reviewed by Danielle Ellis, B.Sc.Sep 12 2024
According to a study published in Applied Optics, researchers from Tokyo University of Agriculture and Technology have created a new smartphone-based digital holographic microscope that allows for precise 3D measurements. The extremely portable and low-cost microscope has the potential to expand the use of 3D measuring capabilities to a wider variety of applications, including educational and point-of-care diagnostics in resource-limited situations.
Researchers developed a smartphone-based digital holographic microscope that can capture, reconstruct and display holograms in almost real-time. The researchers used the microscope to acquire cross-sectional images of a Nymphaea plant stem (left) and a pine needle (right). Image Credit: Yuki Nagahama, Tokyo University of Agriculture and Technology
Holographic microscopes use digital reconstruction to retrieve comprehensive 3D information from a sample, allowing for exact measurements of its surface and interior structures. However, modern digital holographic microscopes often require expensive optical equipment and a personal computer for computations, making them impractical to move or use outside.
Our digital holographic microscope uses a simple optical system created with a 3D printer and a calculation system based on a smartphone. This makes it inexpensive, portable and useful for a variety of applications and settings.
Yuki Nagahama, Research Team Leader, Tokyo University of Agriculture and Technology
In the Optica Publishing Group journal Applied Optics, the researchers show the smartphone-based digital holographic microscope's capacity to collect, rebuild, and display holograms in near real-time. Users may even zoom close on the reconstructed hologram image using a pinch motion on their smartphone screen.
Nagahama added, “Since our holographic microscope system can be built inexpensively, it could potentially be useful for medical applications, such as diagnosing sickle cell disease in developing countries. It could also be used for research in various field environments or in education by allowing students to observe living organisms at school and at home.”
Fast Smartphone-Based Reconstruction
Digital holographic microscopes capture the interference pattern of a reference beam and light scattered from the sample. The hologram is then digitally recreated, resulting in 3D data that can be used to measure the sample's properties, including those beneath the surface.
Although smartphone-based digital holography microscopes have previously been created, current solutions either rebuild the holograms on a separate device or do not provide real-time reconstruction. This constraint stems from the limited computational and memory capabilities of most cell phones.
To accomplish quick reconstruction on a smartphone, the researchers calculated the diffraction patterns using a technique known as band-limited double-step Fresnel diffraction. This approach decreases the quantity of data points, resulting in quicker computer image reconstruction from holograms.
“When I was a student, I worked on portable digital holographic microscopes, which initially used laptops as the computing system. With the rise of smartphones, I began exploring their potential as computing systems for broader applications and considered leveraging them for tasks like removing artifacts from observed images, which ultimately shaped the development of this microscope,” added Nagahama.
The researchers used a 3D printer to make a lightweight housing for the optical system that would aid in portability. To reconstruct the holograms that the optical system had captured, they also created an Android-based application.
The researchers used a 3D printer to manufacture a lightweight enclosure for the optical system, which aids mobility. They also created an Android-based software to rebuild the holograms captured by the optical device.
The microscope creates a reconstructed image of the hologram using the image sensor of a USB camera integrated into the optical system. This hologram can be seen with an Android smartphone, which offers real-time computational image reconstruction. The reconstructed hologram is then presented on the smartphone, allowing users to interact with it via the touchscreen.
Near Real-time Reconstruction
The researchers tested their novel microscopy system by utilizing a prepared item with a known pattern and then determining if the pattern could be reliably detected with the microscope. They were able to see the pattern on the test target successfully and utilized the microscope to examine various samples, including a cross-section of a pine needle.
The researchers demonstrated that by utilizing band-limited double-step Fresnel diffraction, holograms can be recreated at a rate of up to 1.92 frames per second. This allows images to be presented in near real time when monitoring stationary objects.
They then want to utilize deep learning to enhance the quality of images produced by the microscope that runs on a smartphone. In the process of reconstructing holograms, digital holographic microscopes frequently produce second unexpected images. Currently, researchers are investigating the potential of deep learning to eliminate these unwanted images.
Journal Reference:
Nagahama, Y., (2024) Interactive zoom display in a smartphone-based digital holographic microscope for 3D imaging. Applied Optics. doi.org/10.1364/AO.532972