Ultrahigh thermal-efficient all-optical silicon photonic crystal nanobeam cavity modulator with TPA-induced thermo-optic effect.

We propose and experimentally demonstrate an on-chip all-optical silicon photonic crystal nanobeam cavity (PCNBC) modulator. With the advantages of the strong two-photon absorption (TPA)-induced thermo-optic (TO) effect, ultrahigh thermal-efficient tuning with π phase shift temperature difference ΔTπ of 0.77°C and power Pπ of 0.26 mW is implemented. Moreover, the all-optical modulation is carried out by a pulsed pump light with an average switching power of 0.11 mW. The response times for the rising and falling edges are 7.6 µs and 7.4 µs, respectively. Such a thermal-efficient modulator is poised to be the enabling device for large-scale integration optical signal control systems.

Compact non-volatile ferroelectric electrostatic doping optical memory based on the epsilon-near-zero effect.

With the booming development of optoelectronic hybrid integrated circuits, the footprint and power consumption of photonic devices have become the most constraining factors for development. To solve these problems, this paper proposes a compact, extremely low-energy and non-volatile optical readout memory based on ferroelectric electrostatic doping and the epsilon-near-zero (ENZ) effect. The writing/erasing state of an optical circuit is controlled by electrical pulses and can remain non-volatile. The device works on the principle that residual polarization charges of ferroelectric film, which is compatible with CMOS processes, are utilized to electrostatically dope indium tin oxide to achieve the ENZ state. Simulation results show that a significant modulation depth of 10.4 dB can be achieved for a device length of 60 µm with an energy consumption below 1 pJ.

Energy-efficient non-volatile ferroelectric based electrostatic doping multilevel optical readout memory.

Non-volatile multilevel optical memory is an urgent needed artificial component in neuromorphic computing. In this paper, based on ferroelectric based electrostatic doping (Fe-ED) and optical readout due to plasma dispersion effect, we propose an electrically programmable, multi-level non-volatile photonics memory cell, which can be fabricated by standard complementary-metal-oxide-semiconductor (CMOS) compatible processes. Hf0.5Zr0.5O2 (HZO) film is chosen as the ferroelectric ED layer and combines with polysilicon layers for an enhanced amplitude modulation between the carrier accumulation and the confined optical field. Insertion loss below 0.4 dB in erasing state and the maximum recording depth of 9.8 dB are obtained, meanwhile maintaining an extremely low dynamic energy consumption as 1.0-8.4 pJ/level. Those features make this memory a promising candidate for artificial optical synapse in neuromorphic photonics and parallel computing.

Lateral waveguide scanner integration on surface-emitting mid-infrared lasers.

In this paper, a novel, to the best of our knowledge, monolithic non-mechanical semiconductor laser scanner in the mid-infrared (MIR) spectrum is proposed. A deflector above the active region at the substrate side is used for coupling the vertical light into a lateral substrate waveguide, which creates a chain of coherent emitters such as optical phased arrays (OPAs) for beam steering. The numerical simulation reveals that GaSb-based surface-emitting interband cascade lasers (SE-ICLs) are an excellent platform for waveguide scanner integration. Due to the hundreds of micrometers of optical path difference and the narrow gap between each emitter, an extremely high angle tuning coefficient of 0.84°/nm covering the whole 28.6° steering range is obtained. This work theoretically verifies the feasibility of integrating an OPA scanner into the GaSb-based SE-ICLs, providing a practical solution to fabricate compact steerable MIR laser sources. Note that this substrate OPA concept has strong adaptation potential to extend to even longer wavelength devices such as InP and GaAs-based quantum cascade lasers.

Small divergence substrate emitting quantum cascade laser by subwavelength metallic grating.

Metallic periodic structure in subwavelength scale offers an exciting way to couple light into surface plasmons (SPs), thus manipulating the properties of near-field optics. We show that subwavelength metallic grating (SMG) defined on the substrate side of substrate emitting quantum cascade lasers enables far-field improvement in mid-infrared spectrum. The SMG is designed to tailor the interaction of SPs with single mode transverse magnetic light. The experiment results are in good agreement with the simulated model. A far-field full width at half maximum (FWHM) divergence angle of 3.9 ° in the direction perpendicular to the laser waveguide layers is obtained, improved by a factor of 8.5 compared with traditional surface emitting device.

Pigment Penetration Characterization of Colored Boundaries in Powder-Based Color 3D Printing.

Color 3D printing has widely affected our daily lives; therefore, its precise control is essential for aesthetics and performance. In this study, four unique test plates were printed using powder-based full-color 3D printing as an example; moreover, the corresponding pigment-penetration depth, chromaticity value and image-based metrics were measured to investigate the lateral pigment penetration characteristics and relative surface-color reproduction of each color patch, and to perform an objective analysis with specific microscopic images. The results show that the lateral pigment-penetration depth correlates with the number of printed layers on the designed 3D test plates, and the qualitative analysis of microscopic images can explain the change in chromaticity well. Meanwhile, there is an obvious linear correlation between the mean structural similarity, color-image difference and color difference for current color samples. Thus, our proposed approach has a good practicality for powder-based color 3D printing, and can provide new insight into predicting the color-presentation efficiency of color 3D-printed substrates by the abovementioned objective metrics.

Advanced Surface Color Quality Assessment in Paper-Based Full-Color 3D Printing.

Color 3D printing allows for 3D-printed parts to represent 3D objects more realistically, but its surface color quality evaluation lacks comprehensive objective verification considering printing materials. In this study, a unique test model was designed and printed using eco-friendly and vivid paper-based full-color 3D printing as an example. By measuring the chromaticity, roughness, glossiness, and whiteness properties of 3D-printed surfaces and by acquiring images of their main viewing surfaces, this work skillfully explores the correlation between the color representation of a paper-based 3D-printed coloring layer and its attached underneath blank layer. Quantitative analysis was performed using ΔE*ab, feature similarity index measure of color image (FSIMc), and improved color-image-difference (iCID) values. The experimental results show that a color difference on color-printed surfaces exhibits a high linear correlation trend with its FSIMc metric and iCID metric. The qualitative analysis of microscopic imaging and the quantitative analysis of the above three surface properties corroborate the prediction of the linear correlation between color difference and image-based metrics. This study can provide inspiration for the development of computational coloring materials for additive manufacturing.

3D Printing of Oil Paintings Based on Material Jetting and Its Reduction of Staircase Effect.

Material jetting is a high-precision and fast 3D printing technique for color 3D objects reproduction, but it also suffers from color accuracy and jagged issues. The UV inks jetting processes based on the polymer jetting principle have been studied from printing materials regarding the parameters in the default layer order, which is prone to staircase effects. In this work, utilizing the Mimaki UV inks jetting system with a variable layer thickness, a new framework to print a photogrammetry-based oil painting 3D model has been proposed with the tunable coloring layer sequence to improve the jagged challenge between adjacent layers. Based on contour tracking, a height-rendering image of the oil painting model is generated, which is further segmented and pasted to the corresponding slicing layers to control the overall printing sequence of coloring layers and white layers. The final results show that photogrammetric models of oil paintings can be printed vividly by UV-curable color polymers, and that the proposed reverse-sequence printing method can significantly improve the staircase effect based on visual assessment and color difference. Finally, the case of polymer-based oil painting 3D printing provides new insights for optimizing color 3D printing processes based on other substrates and print accuracy to improve the corresponding staircase effect.

The solvent and zinc source dual-induced synthesis of a two dimensional zeolitic imidazolate framework with a farfalle-shape and its crystal transformation to zeolitic imidazolate framework-8.

Exploring new zeolitic imidazolate frameworks (ZIFs) with specific topologies and pore structures is important for extending applications and improving performances. In this work, a new farfalle-shaped ZIF with an ordered hierarchical structure (named ZIF-F) was easily built with zinc acetate and 2-methylimidazole (MeIm) in an aqueous system at room temperature. The synthesis mechanism of ZIF-F is a dual-induction interaction of a solvent and zinc source based on the synthesis protocol of ZIF-8. The prepared ZIF-F is a 3-5 µm dispersible particle constructed from numerous nanoplates with the same building units as ZIF-8. ZIF-F has a rich 4 nm inter-particle spacing with a 0.1074 cm3 g-1 total pore volume and exhibits high thermo- and solvent stability. It is worth noting that crystal transformation could occur from ZIF-F to ZIF-8 in methanol via the dissolution-recrystallization route. Regarding the adsorption of Congo red (CR), ZIF-F exhibits better adsorption capacity (182.82 mg g-1) than ZIF-8 (149.25 mg g-1) with 6 times higher adsorption rate than that of ZIF-8 because of the positive effect of its larger pore size and hierarchical structure.

10-W pulsed operation of substrate emitting photonic-crystal quantum cascade laser with very small divergence.

High-power broad area substrate emitting photonic-crystal distributed feedback (DFB) quantum cascade lasers (QCLs) emitting around 4.73 µm is reported. Two-dimensional centered rectangular photonic-crystal (CRPC) grating is introduced to enhance optical coherence in large area device. Main lobe far-field radiation pattern with a very small divergence angle of about 0.65° × 0.31° is obtained. A record peak output power for vertical emitting QCLs exceeding 10 W is obtained with high reflectivity (HR) coating. Robust single longitudinal mode emission with a side mode suppression ratio (SMSR) of 30 dB is continuously tunable by the heat sink temperature up to 65°C.