Printable optical microcavity (Ongoing)

This topic is about how to print optical microcavities using printing technology. The optical microcavity has a micro size about the diameter of the hair (several μm to several hundred μm), and has various shapes based on circles such as microdisks, microrings, and microtoroids (doughnuts). Since optical microcavitys show extremely high optical confinement effect and high Q factor at specific frequencies, related research such as optical frequency combs and integrated laser light sources is being actively conducted worldwide. Especially in the medical and biotechnology fields, this optical microcavity is attractive because it has the ability to detect about one virus in principle. In short, the optical cavity is a promising next-generation platform for creating innovative analytical methods such as ultra-sensitive sensing of biological samples.

In the fabrication of optical microcavities made of materials such as polymers, silica (glass), and silicon, the same way as highly optimized semiconductor processes is generally used such as lithography and etching. This is excellent in that it can be reproducibly manufactured in large quantities and large-scale integrated chips by a subtractive approach (cutting from the material), but it requires treatment with heat and acid. Therefore, the optical microcavity must be prepared in a highly equipped facility such as a semiconductor factory, and the materials that can be used are limited. Therefore, there are many hurdles for widespread industrial application in consideration of cost and practical use only with the current manufacturing method.

In this topic, the research on a completely new fabricating technology (inkjet printing method) for microdisk typed optical microcavities is conducting. The inkjet printing method is a technology for printing optical microcavities with the same technology as commercially available inkjet printers, and is an additive approach (placement of materials). The fabricating process is simple and easy, only (1) printing the clad layer and core disk layer, and (2) wet etching of the clad layer. In addition, the fabricating process can be performed at room temperature and atmospheric pressure, and on-demand and on-site fabricating is also possible. The microdisk optical cavity laser produced by the inkjet printing method forms a special propagation mode called Whispering Gallery Mode (WGM), which traps light around the disk and generates laser light. And the spectrum of the laser light is comb-shaped at equal intervals.

In previous achivements, there is a world record value (22% lower threshold than before) in the threshold of laser oscillation, which is a basic performance characteristic. This achievement was presented in the Nature Group's Scientific Reports, and was awarded the 40th Laser Society of Japan Encouragement Award. In addition, it received a great deal of attention from the industrial magazine and several newspaper reports. There is also remarkable achievements in subsequent developmental research, and in 2020, a paper published in the Applied Optics of the Optical Society of America (OSA) on the advanced process of the inkjet printing method was selected as "Editors' Pick". Additionally, in 2021, the research on the printable organic microdisk optical cavity laser biosensing application was published in OSA's Optical Materials Express with the official News Release of the society and made the cover of the top page of the official website. This has an impact as a basic research that will lead to the easy implementation of quantitative antigen-antibody tests from the production of microdisks as sensors to the tests at room temperature. In addition, it was featured and noticed by many domestic and foreign media such as EulekAlert!, and DoveMed.

Currently, an organic topological optical cavity that extends the function of the organic microdisk optical cavity to an integrated light source of optical vortex is developing as an ongoing project.

Degradation-recoverable solid-state polymer laser (Complete)

A dye-circulating solid-state laser, which is a completely new type of organic solid-state laser that can solve the problem of short operating lifetime in the research field on organic lasers was developed. This is the world's first device to confirm the self-repair of output using a completely new concept optical functional medium that allows laser dyes to diffuse and move in a solid polymer medium, and the degradation problem for using organic fluorescent molecules in solids has been dramatically improved, and one stone has been thrown at the most important issue of extending the life of the field. These achievements have been published in various academic journals and international conferences, including Optics Express. This research was carried out as a research fellow DC2 of the Japan Society for the Promotion of Science.

Mode-locked Yb:YAG ceramic laser (Complete)

A femtosecond pulsed laser using Yb:YAG ceramic was developed and showed the world's first light source using the same material, which has a higher scaling effect than before. Femtosecond lasers are important technologies are indispensable to improve living standards of humankind for astronomy, frequency standards, elucidation of ultra-high-speed phenomena, basic and applied physics such as communication, industries such as ultra-fine processing, medical treatment such as LASIK. As the latest news that clearly shows this, it is fresh in memory that the 2018 Nobel Prize in Physics was presented to research results on laser technology such as amplification of femtosecond pulsed lasers. Achievements on Yb:YAG ceramic femtosecond laser were presented in academic journals including the Optics Express, international conferences, and invited talk. In addition, it was featured in the international industrial magazine “Laser Focus World” and received the IEEE Fukuoka Branch Student Research Encouragement Award in 2010.