Multifunctional Sensing Based on an Ultrathin Transferrable Microring Laser

On-Demand Picoliter-Level-Droplet Inkjet Printing for Micro Fabrication and Functional Applications

With the advent of Internet of Things (IoTs) and wearable devices, manufacturing requirements have shifted toward miniaturization, flexibility, environmentalization, and customization. Inkjet printing, as a non-contact picoliter-level droplet printing technology, can achieve material deposition at the microscopic level, helping to achieve high resolution and high precision patterned design. Meanwhile, inkjet printing has the advantages of simple process, high printing efficiency, mask-free digital printing, and direct pattern deposition, and is gradually emerging as a promising technology to meet such new requirements. However, there is a long way to go in constructing functional materials and emerging devices due to the uncommercialized ink materials, complicated film-forming process, and geometrically/functionally mismatched interface, limiting film quality and device applications. Herein, recent developments in working mechanisms, functional ink systems, droplet ejection and flight process, droplet drying process, as well as emerging multifunctional and intelligence applications including optics, electronics, sensors, and energy storage and conversion devices is reviewed. Finally, it is also highlight some of the critical challenges and research opportunities. The review is anticipated to provide a systematic comprehension and valuable insights for inkjet printing, thereby facilitating the advancement of their emerging applications.

Switchable whispering gallery mode lasing via phase transition

Combining phase-transition materials with optical microcavities may advance the applications of whispering-gallery mode (WGM) lasing in performance customization, sensing, and optical switching. In this study, switchable WGM lasing based on phase transition is reported. The device is designed by introducing the phase-transition hydrogel into the capillary microcavity. After approaching the phase-transition point in hydrogel, the number of WGM lasing modes decreases sharply with a significant blueshift in the wavelength. The phenomenon is caused by the increase in light scattering and decrease in effective refractive index of the device. Furthermore, single-mode lasing is obtained by manipulating the phase transition, which exhibits superior reversibility. This study may pave the way for designing and multifunctioning of novel WGM lasing in photonic devices.

Dynamic manipulation of WGM lasing by tailoring the coupling strength

Miniaturized lasing with dynamic manipulation is critical to the performance of compact and versatile photonic devices. However, it is still a challenge to manipulate the whispering gallery mode lasing modes dynamically. Here, we design the quasi-three-dimensional coupled cavity by a micromanipulation technique. The coupled cavity consists of two intersection polymer microfibers. The mode selection mechanism is demonstrated experimentally and theoretically in the coupled microfiber cavity. Dynamic manipulation from multiple modes to single-mode lasing is achieved by controlling the coupling strength, which can be quantitatively controlled by changing the coupling angle or the coupling distance. Our work provides a flexible alternative for the lasing mode modulation in the on-chip photonic integration.

Single-mode lasing in an AlGaInAs/InP dual-port square microresonator

Mode selection is crucial to achieving stable single-mode lasing in microlasers. Here, we demonstrate experimentally a dual-port square microresonator for single-mode lasing with a side-mode-suppression ratio (SMSR) exceeding 40 dB. By connecting waveguides at two opposite vertices, the quality factor for the antisymmetric mode (ASM) is much higher than that of the symmetric mode (SM), enabling single-mode lasing. Furthermore, far-field interference patterns similar to Young's two-slit interference are observed. This microlaser is capable of providing two optical sources simultaneously for optical signal processing in high-density integrated photonic circuits.

Electrically Tunable Polymer Whispering-Gallery-Mode Laser

Microlasers hold great promise for the development of photonics and optoelectronics. At present, tunable microcavity lasers, especially regarding in situ dynamic tuning, are still the focus of research. In this study, we combined a 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) piezoelectric crystal with a Poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) microring cavity to realize a high-quality, electrically tunable, whispering-gallery-mode (WGM) laser. The dependence of the laser properties on the diameter of the microrings, including the laser spectrum and quality (Q) value, was investigated. It was found that with an increase in microring diameter, the laser emission redshifted, and the Q value increased. In addition, the device effectively achieved a blueshift under an applied electric field, and the wavelength tuning range was 0.71 nm. This work provides a method for in situ dynamic spectral modulation of microcavity lasers, and is expected to provide inspiration for the application of integrated photonics technology.

Large-Area Biocompatible Random Laser for Wearable Applications

Recently, wearable sensor technology has drawn attention to many health-related appliances due to its varied existing optical, electrical, and mechanical applications. Similarly, we have designed a simple and cheap lift-off fabrication technique for the realization of large-area biocompatible random lasers to customize wearable sensors. A large-area random microcavity comprises a matrix element polymethyl methacrylate (PMMA) in which rhodamine B (RhB, which acts as a gain medium) and gold nanorods (Au NRs, which offer plasmonic feedback) are incorporated via a spin-coating technique. In regards to the respective random lasing device residing on a heterogenous film (area > 100 cm2), upon optical excitation, coherent random lasing with a narrow linewidth (~0.4 nm) at a low threshold (~23 μJ/cm2 per pulse) was successfully attained. Here, we maneuvered the mechanical flexibility of the device to modify the spacing between the feedback agents (Au NRs), which tuned the average wavelength from 612.6 to 624 nm under bending while being a recoverable process. Moreover, the flexible film can potentially be used on human skin such as the finger to serve as a motion and relative-humidity sensor. This work demonstrates a designable and simple method to fabricate a large-area biocompatible random laser for wearable sensing.