A study recently completed by Israel's Soreq Nuclear Research Center has proved that 3D laser printing can directly manufacture high-quality and complex polymer optical devices at the end of optical fibers. The details of this micro optical device are smaller than the diameter of a hair filament, and it can provide a very compact and inexpensive way to customize light beams for various applications.
Shlomi Lightman, head of the research team of Israel's Soreq Nuclear Research Center in Israel, said: "Communication technology, the Internet and many other applications are based on optical fibers. When light comes out of optical fibers, it is usually transmitted to the next location using large optical elements. Our approach minimizes the scale and cost of this process by integrating the cabling process into the fiber itself."
In addition, it is worth noting that the whole fabrication process of micro optical devices took less than 5 minutes. The cost of such optical fiber and micro optical device is less than 100 dollars, which is about one tenth of the cost of standard microscope objective lens with similar functions.
Shlomi Lightman said: "The ability to generate Bessel beam directly from optical fiber can be used for particle operation or fiber integrated stimulated emission loss (STED) microscope, which is a technology to generate super resolution images. Our manufacturing method can also upgrade cheap lenses to higher quality intelligent lenses by printing intelligent small structures on the lenses."
In order to manufacture this tiny optical device, researchers used a 3D direct laser printing manufacturing technology. It uses a femtosecond pulsed laser beam to generate two-photon absorption in photosensitive optical materials, and then only the small volume with two-photon absorption becomes a solid, which provides a method for creating high-resolution 3D elements.
Although this 3D direct laser printing has been used for some time, it is difficult to obtain the correct proportion and alignment when manufacturing such small optical devices at the fiber tip. Therefore, the researchers created an optical measurement system to analyze the performance of the beam formed by the manufactured equipment. The laser beam diffraction is very low, and the laser power is close to 10 MW/cm2, but the fabricated micro optical devices are not damaged.
Shlomi Lightman pointed out: "Before starting the manufacturing process, we overcame this obstacle by conducting highly accurate 2D and 3D simulations. In addition, we must carefully consider how to integrate optical elements with each other and then align them with the fiber core."
After careful planning based on simulation, the researchers used a commercial 3D direct laser writing system and a photosensitive polymer with high optical quality to print an optical device 110 microns high and 60 microns in diameter at one end of a single-mode fiber. The device comprises a parabolic lens for collimating light and a spiral axial lens for twisting light. This turns the light coming out of the fiber into a distorted Bessel beam.
In order to analyze the quality of the fabricated optical devices, researchers have established an optical measurement system to capture the shape beam propagating from the modified optical fiber. They observed very low diffraction in the beam, which means it can be used in applications such as STED microscopy and particle manipulation.
They also found that the laser power could reach nearly 10 MW/cm2 before destroying the fabricated micro optical devices. This shows that although the device is made of polymer, which is more vulnerable to high power thermal damage than glass, it can still be used to generate relatively high laser power.
Now, researchers have proved that using this direct 3D laser printing method can create accurate multi-element micro optical elements. Recently, they are experimenting with mixed photosensitive materials, which contain a low proportion of polymers. It is reported that compared with polymer materials, these materials can produce optical devices with higher quality, longer shelf life and better resistance to high-power lasers.
Source: OFweek
