Researchers have created an innovative digital holographic microscope that operates using a smartphone, allowing for precise 3D measurements. This microscope, which is both affordable and highly portable, could extend the use of 3D measurement technology to many different applications, including education and onsite diagnostics in areas with limited resources.
Researchers have created an innovative digital holographic microscope that operates using a smartphone, allowing for precise 3D measurements. This microscope, which is both affordable and highly portable, could extend the use of 3D measurement technology to many different applications, including education and onsite diagnostics in areas with limited resources.
This type of holographic microscope digitally reconstructs holograms to reveal intricate 3D details about a sample, enabling accurate measurements of both its surface and internal structures. Traditionally, digital holographic microscopes rely on complex optical setups and a personal computer for processing, making them cumbersome for outdoor usage.
“Our digital holographic microscope employs a straightforward optical setup created with a 3D printer and a smartphone-based calculation system,” explained Yuki Nagahama, the lead researcher from Tokyo University of Agriculture and Technology. “This design makes it low-cost, portable, and suitable for various applications and environments.”
In the journal Applied Optics from the Optica Publishing Group, the researchers illustrated their smartphone-based digital holographic microscope’s capacity to capture, reconstruct, and display holograms nearly instantaneously. Users can even zoom in on the 3D reconstructed images by pinching the smartphone screen.
“Because our holographic microscope system can be produced at a low cost, it has the potential for significant medical applications, like diagnosing sickle cell disease in low-income countries,” stated Nagahama. “It can also serve for research in various field settings or enrich educational experiences by allowing students to study live organisms both in school and at home.”
Rapid smartphone-based reconstruction
Digital holographic microscopes operate by capturing the interference patterns formed between a reference beam and the light scattered from a specimen. This holographic data is then digitally reconstructed, providing 3D information that facilitates measuring the object’s features, including those hidden beneath the surface.
While smartphone-operated digital holographic microscopes have been introduced before, existing technologies either process holograms on separate devices or lack real-time reconstruction capabilities. This challenge often stems from the limited computing power and memory capacity of smartphones. To achieve quick reconstruction, the researchers implemented a technique called band-limited double-step Fresnel diffraction, which minimizes the number of data points to speed up image reconstruction from holograms.
“During my time as a student, I worked with portable digital holographic microscopes that initially utilized laptops for computing,” said Nagahama. “With the advent of smartphones, I wanted to explore their potential for broader applications and considered using them to tackle issues like artifact removal from observed images, guiding the development of this microscope.”
To enhance portability, the researchers designed a lightweight housing for the optical components using a 3D printer. They also created an Android application that reconstructs the holograms captured by the optical system.
The microscope produces a holographic image reconstruction on the image sensor of a USB camera integrated within the optical setup. The hologram can then be viewed on an Android smartphone, which performs real-time computational image reconstruction. Users can interact with the reconstructed hologram directly on the smartphone’s touchscreen.
Almost real-time reconstruction
The researchers tested their new microscopy system using a test object with a known pattern to verify if the microscope could accurately observe the pattern. They successfully analyzed the pattern on the test object and used the device to examine other samples, such as a cross-section of a pine needle.
The team demonstrated that using band-limited double-step Fresnel diffraction allowed for hologram reconstruction at a frame rate of up to 1.92 frames per second, enabling nearly real-time image display for stationary objects.
Going forward, they plan to utilize deep learning techniques to further enhance the image quality produced by the smartphone-based microscope. Typically, digital holographic microscopes generate unintended secondary images during reconstruction, and the researchers are investigating how deep learning could help eliminate these extraneous images.
