Ye Pu

Endoscopic optical imaging using a single multimode fiber (MMF) has emerged as a promising approach for highly compact, minimally invasive, and high-resolution imaging. Unlike conventional fiber bundles, MMF-based endomicroscopes exploit the controlled excitation of multiple spatially overlapping modes in a single MMF. of core diameters of tens of micrometers. to deliver and collect light to form images with sub-micrometer resolution. Here, we introduce a fluorescence lifetime imaging microscopy (FLIM) modality to the MMF endomicroscope. We use amplitude modulation of a 405 nm single-mode light source at radio frequency (RF) and lock-in detection of autofluorescence to obtain intensity and lifetime images at sub-micrometer resolution. We experimentally demonstrate the capability of the ultrathin endomicroscope to perform label-free imaging in thick ex vivo murine submandibular gland tissue. With a temporal resolution of 0.03 ns, the FLIM images show distinguished structures of lifetime differences down to 0.5 ns. The combination of sub-micrometer fluorescence intensity and lifetime images in a minimally invasive endomicroscope opens new avenues for label-free cancer detection.

Flexible ultra-compact low-loss optical waveguides play a vital role in the development of soft photonics. The search for suitable materials and innovative fabrication techniques to achieve low loss long polymer optical waveguides and interconnects has proven to be challenging. In this paper, we demonstrate the fabrication of submicron optical waveguides in polydimethylsiloxane (PDMS) using divinylbenzene (DVB) as the photopolymerizable monomer through two-photon polymerization (2PP). We show that the commercial oxime ester photoinitiator Irgacure OXE02 is suitable for triggering the DVB photopolymerization, resulting in a stable and controllable fabrication process for the fabrication of defect-free, 5-cm long waveguides. We further explore a multi-track fabrication strategy to enlarge the waveguide core size up to ~3 μm for better light confinement and reduced cross-talk. In these waveguides, we measured a refractive index contrast on the order of 0.005 and a transmission loss of 0.1 dB/cm at 710 nm wavelength.

Compact, low loss flexible optical waveguides are crucial in optofluidic and microfluidic devices for a dense integration of optical functionalities. We demonstrate the fabrication of compact optical waveguides in polydimethylsiloxane through multiphoton laser direct writing using phenylacetylene as the photosensitive monomer. Our fabrication technique employs photo-induced radical chain polymerization initiated by the monomer molecule itself without a photoinitiator. Because of the dense π-electrons in phenylacetylene, we achieved a high refractive index contrast (Δn ≥ 0.06) between the waveguide core and the PDMS cladding. This allowed for efficient waveguiding with a core size of 1.3-µm with a measured loss of 0.03 dB/cm in the spectral band of 650-700 nm.

We demonstrate the fabrication of ultra-compact, low-loss optical waveguides in polydimethylsiloxane through multiphoton polymerization, without a photoinitiator, using laser direct writing. The transmission loss was measured 0.03 dB/cm in the 650-700 nm band.

We report the fabrication of compact flexible optical waveguides in polydimethylsiloxane through multiphoton direct laser writing, for the first time without a photoinitiator. A transmission loss of 0.03 dB/cm was measured in the 650–700 nm band.

We demonstrate three-dimensional imaging through a thin turbid medium using digital phase conjugation of the second harmonic signal emitted from a beacon nanoparticle. The digitally phase-conjugated focus scans the volume in the vicinity of its initial position through numerically manipulated phase patterns projected onto the spatial light modulator. Accurate three dimensional images of a fluorescent sample placed behind a turbid medium are obtained.

A nonlinear optical plasmonic core-shell nanocavity is demonstrated as an efficient, subwavelength coherent light source through second-harmonic generation. The nonlinear optical plasmonic nanocavity incorporates a noncentrosymmetric medium, which utilizes the entire mode volume for even-order nonlinear optical processes. In previous plasmonic nanocavities, enhancement of such processes was only possible at the interface but symmetry prohibited in the body. We measured an enhancement of over 500 times in the second-harmonic radiation power. Calculations show that an enhancement of over 3500 times is achievable.

DOI:https://doi.org/10.1103/PhysRevA.74.069902