Structuration and Devices

From Nanofabrication to Nanophotonics

PI : Associate professor Ngoc Diep LAI

Among plenty of techniques proposed to realize photonic structures, direct laser writing (DLW) has been considered as an ideal one to create any desired submicrometric structure. We have recently proposed and demonstrated a simple and low-cost method called low one-photon absorption (LOPA) DLW, which benefits the advantages of both one-photon absorption (OPA) and two-photon absorption (TPA) techniques, allowing us to fabricate arbitrary 2D and 3D submicro-structures. The LOPA fabrication technique is based on the use of an excitation laser with the wavelength located near the edge of the absorption band of the photoresist used. With this low absorption, the light beam can propagate deeply inside the material. By using a microscope lens of high numerical aperture, the laser beam is focused into small region with a very high intensity, which compensates for the low absorption of the photoresist. By scanning the focusing spot, any sub-wavelength structure can be created via local photopolymerization process. 1D, 2D, and 3D arbitrary structures, with sizes as small as 100 nm, have been fabricated using SU8 photoresist and a continuous-wave laser at 532 nm-wavelength with only a few milliwatts. Figures 1(a) shows an example of fabricated 3D structures.
Recently, we have applied this same technique to produce other 2D and 3D magnetic and 3D plasmonic structures on demand (figure 1, c, d). These demonstrations open up many applications in different fields, from physics to chemistry and biology. Furthermore, we have recently demonstrated that by using this LOPA-based DLW, and with a double-step process, it is possible to address most kinds of nanoparticles (gold, quantum dot, KTP, etc.) and to precisely embed them into desired polymeric photonic structures. Figures 1(b) show different kinds of 2D structures containing a single quantum dot at structures center.

NanoFabrication Illustration
Figure1: Examples of submicrostructures realized by the LOPA-based direct laser writing method. (a) SEM image of a photonic crystal (woodpile type). (b) Polymeric SU8 structures (pillar and multi-rings) contain a single quantum dot at center. (c) SEM image of the magnetic microstructures obtained by a mixture of the magnetic nanoparticles in SU8. (d) Optical image of plasmonic structures (letter NANO and the one hundred US dollar bill) produced by LOPA DLW on a thin gold film.
    1. T. H. Au, J. Audibert, D. T. Trinh, D. B. Do, S. Buil, X. Quélin, J.-P. Hermier, and N. D. Lai, “Controllable movement of single-photon source in multifunctional magneto- photonic structures,” Scientific Reports 10, 4843 (2020).
    2. T. H. Au, S. Buil, X. Quélin, J.-P. Hermier, and N. D. Lai, “High Directional Radiation of Single Photon Emission in a Dielectric Antenna,” ACS Photonics 6, 3024–3031 (2019).
    3. D. T. T. Nguyen and N. D. Lai, “Deterministic Insertion of KTP Nanoparticles into Polymeric Structures for Efficient Second-Harmonic Generation,” Crystals 9, 365 (2019).
    4. F. Mao, A. Davis, Q. C. Tong, M. H. Luong, C. T. Nguyen, I. Ledoux-Rak, and N. D. Lai, “Direct Laser Writing of Gold Nanostructures: Application to Data Storage and Color Nanoprinting,” Plasmonics 13, 2285–2291 (2018).
    5. Q. C. Tong, M. H. Luong, J. Remmel, M. T. Do, D. T. T. Nguyen, and N. D. Lai, “Rapid direct laser writing of desired plasmonic nanostructures,” Opt. Lett. 42, 2382- 2385 (2017).
    6. T. H. Au, D. T. Trinh, Q. C. Tong, D. B. Do, D. P. Nguyen, M. H. Phan, and N. D. Lai, “Direct Laser Writing of Magneto-Photonic Sub-Microstructures for Prospective Appli- cations in Biomedical Engineering,” Nanomaterials 7, 105 (2017).
    7. Q. C. Tong, M. T. Do, M. H. Luong, B. Journet, I. Ledoux-Rak, and N. D. Lai, “Direct laser writing of polymeric nanostructures via optically induced local thermal effect,” Appl. Phys. Lett. 108, 183104 (2016).
    8. M. T. Do, D. T. T. Nguyen, H. M. Ngo, I. Ledoux-Rak, and N. D. Lai, “Controlled cou- pling of a single nanoparticle in polymeric microstructure by low one- photon absorption– based direct laser writing technique,” Nanotechnology 26, 105301(2015).
    9. M. T. Do, T. T. N. Nguyen, Q. Li, H. Benisty, I. Ledoux-Rak, and N. D. Lai, “Submicro- meter 3D structures fabrication enabled by one-photon absorption direct laser writing,” Opt. Express 21, 20964-20973 (2013).

Polymer-based photonic devices for biomedical and environmental applications

PI: C.T. Nguyen (PhD), participants: I. Ledoux-Rak (PR), N.D. Lai (Associated Prof)
The increasing demand for enhanced environment and health protection requires a rapid and specific detection of highly toxic elements in the environmental domain and of pathogenic species in the biomedical domain in order to provide adapted and optimized treatments. In this context, we have conceived and realized microresonator-based optofluidic sensors made of polymeric vertically coupled microresonators integrated with a polymeric microfluidic channel, which display remarkable performances in terms of detection limit, specificity and rapidity. These optofluidic devices are adapted to portable or transportable analysis instruments for in situ measurements in environmental studies or medicine (points of care). By fabricating different microresonators on the same substrate, each of them being functionalized by a recognition ligand specific to a given analyte molecule, it is possible to simultaneously detect several target species contained in the same solution. The optofluidic devices can be also associated to an electrochemical sensor on a common microfluidic platform in order to implement a multi-functional sensor delivering in parallel various measurements parameters on the same target molecules. This research topic displays a highly pluridisciplinary character involving, besides physics, integrated optics technology, chemistry, biology and scientific instrumentation.