Piotr Wasylczyk

Light‐Fueled Microscopic Walkers

The first microscopic artificial walker equipped with liquid-crystalline elastomer muscle is reported. The walker is fabricated by direct laser writing, is smaller than any known living terrestrial creatures, and is capable of several autonomous locomotions on different surfaces.

High‐Resolution 3D Direct Laser Writing for Liquid‐Crystalline Elastomer Microstructures

The paper describes 3D structures made of liquid-crystalline elastomer (LCE) - rings, woodpiles, etc. - fabricated by two-photon absorption direct laser writing with sub-micrometer resolution while maintaining the desired molecular orientation. These results lay the foundations for creating 3D, micrometer-sized, light-controlled LCE structures.

Alignment engineering in liquid crystalline elastomers: Free-form microstructures with multiple functionalities

We report a method to fabricate polymer microstructures with local control over the molecular orientation. Alignment control is achieved on molecular level in a structure of arbitrary form that can be from 1 to 100 μm in size, by fixing the local boundary conditions with micro-grating patterns. The method makes use of two-photon polymerization (Direct Laser Writing) and is demonstrated specifically in liquid-crystalline elastomers. This concept allows for the realization of free-form polymeric structures with multiple functionalities which are not possible to realize with existing techniques and which can be locally controlled by light in the micrometer scale.

Transmission phase gratings fabricated with direct laser writing as color filters in the visible

Simple diffraction structures having the form of a regular grid of pillars can generate a significant range of hues in white light transmission due to color-dependent diffraction into higher orders. We present the fabrication of such submicrometer scale structures by three dimensional laser two-photon photolithography, results of their optical properties measurements and compare the latter with numerical simulations.

Microstructured gradient-index antireflective coating fabricated on a fiber tip with direct laser writing

We present a simple broadband gradient-index antireflective coating, fabricated directly on a single mode telecom fiber tip. A regular array of hemi-ellipsoidal protrusions significantly reduce the Fresnel reflection from the glass-air interface. The parameters of the structure were optimized with numerical simulation for the best performance at and around 1550 nm and the coating was fabricated with Direct Laser Writing. The measured reflectance decreased by a factor of 30 at 1550 nm and was below 0.28% for the 100 nm spectral band around the central wavelength. Compared to quarter wavelength antireflective coatings the demonstrated approach offers significantly reduced technological challenges, in particular processing of a single optical material with low sensitivity to imperfections in the fabrication process.

Light Robots: Bridging the Gap between Microrobotics and Photomechanics in Soft Materials

For decades, roboticists have focused their efforts on rigid systems that enable programmable, automated action, and sophisticated control with maximal movement precision and speed. Meanwhile, material scientists have sought compounds and fabrication strategies to devise polymeric actuators that are small, soft, adaptive, and stimuli-responsive. Merging these two fields has given birth to a new class of devices-soft microrobots that, by combining concepts from microrobotics and stimuli-responsive materials research, provide several advantages in a miniature form: external, remotely controllable power supply, adaptive motion, and human-friendly interaction, with device design and action often inspired by biological systems. Herein, recent progress in soft microrobotics is highlighted based on light-responsive liquid-crystal elastomers and polymer networks, focusing on photomobile devices such as walkers, swimmers, and mechanical oscillators, which may ultimately lead to flying microrobots. Finally, self-regulated actuation is proposed as a new pathway toward fully autonomous, intelligent light robots of the future.

Highly asymmetric near infrared light transmission in an all-dielectric grating-on-mirror photonic structure.

We demonstrate a photonic structure, composed of a dielectric quarter-wavelength stack topped with a transmission phase grating, designed to exhibit a significant asymmetry in the near infrared light transmission for waves propagating in opposite directions. The asymmetry, defined as the difference between the intensity transmission coefficients, reaches 0.72 ± 0.06 for a single wavelength and exceeds 0.2 over a spectral range spanning from 700 to 850 nm for one incident polarization and 750-800 nm for both polarizations. The experimental results are consistent with the numerical model of light propagation in the structure.

Witnessing the pulse birth—transient dynamics in a passively mode-locked femtosecond laser

High temporal resolution measurements of the output of an Yb:KYW femtosecond laser, recorded immediately after opening the laser cavity, give an insight into the transient laser dynamics. The evolution of the light intensity measured with linear and nonlinear detectors, together with the time-resolved laser spectrum were measured and the process of the mode-locking onset was investigated. A phenomenological model of the laser dynamics has been developed that reproduces the experimental results.

Tunable Semiconductor Double-Chirped Mirror With High Negative Dispersion

We have developed a tunable semiconductor double-chirped mirror with high negative dispersion grown by molecular beam epitaxy. The simplified numerical plane-wave reflection transfer method was applied to design the dispersive mirror structure. The multilayer stack was grown of AlAs/GaAs materials and capped by an SiNx antireflective layer. The group delay dispersion as well as reflectivity characteristic were continuously tunable across the mirror surface from 1080 to 1000 nm. Within this range, the negative value of the dispersion changed from -3850±100 fs2 over the 6 nm band around 1080 nm to -2200±100 fs2 over 13 nm around 1000 nm with the reflectivity from the range of 99.0÷99.2%. The mirror performance was tested in a diode-pumped femtosecond Yb:KYW oscillator.

Polarization-dependent diffraction in all-dielectric, twisted-band structures

We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 μm have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.