Optical rib/ridge waveguides are one of the most versatile and hence widely used optical waveguide structures in integrated photonics for different applications. One of the intrinsic features of such waveguide is that single mode condition can be achieved with certain configurations even the overall cross section area of the waveguide is large. For many years, a set of conventional criteria for the single mode condition has been accepted and used without sufficient validation and justification. To the best of my knowledge,  a systematic analysis and validation of the single mode condition for optical rib/ridge waveguides has never been attempted. The situation is somewhat acute for silicon optical waveguide in which the index contrast between the core and the cladding is large. In this presentation, the single mode conditions for optical rib/ridge waveguides are revisited through an analysis applying the full vector mode-matching method. New criteria for the “true-single-mode” (i.e., only HE₁₁ mode exists) and the “quasi-single-mode” (i.e., both HE₁₁ and EH₁₁ modes are permitted) conditions are derived exactly for silicon-on-insulator rib/ridge waveguides with different rib heights. It is observed that strong true single mode condition can be achieved for a wide range of practical design parameters. On the other hand, the quasi and the true single mode conditions start to converge when the rib height increases and/or the index contrast deceases beyond certain values when the semi-vector or scalar approximation is valid. Comparisons with the existing schemes indicate that the conventional criteria widely used in literature are valid only when the rib height is large and/or the index contrast is small in which the true and the quasi single mode conditions are nearly degenerate.

To date, a variety of mobile devices have emerged as healthcare tools. In particular, when they are integrated with advanced optical imaging techniques such as multispectral imaging and analysis, it would be very useful for early diagnosis of malignant and non-malignant skin diseases as well as quantitative monitoring of prognosis of the diseases after their treatment at home. Thus, we here demonstrate smartphone-based multispectral imaging and analysis for mobile diagnosis of various skin diseases. We first underlie how to develop smartphone-based multispectral imaging systems. We also investigate their potentials for mobile diagnosis of various skin diseases including acne, seborrheic dermatitis, psoriasis, and etc. In particular, we highlight that the smartphone-based multispectral imaging and analysis allows us to quantitatively monitor acne regions during their treatments with benzoyl peroxide and also to discriminate between seborrheic dermatitis and psoriasis occurred on the scalp with high sensitivity and specificity at ubiquitous environments. Furthermore, we discuss its potentials for mobile healthcare such as recommendation of personalized cosmetics.

Sub-MHz microwave photonic bandpass filter using backward scattering in an ultrahigh-Q microcavity is proposed and experimentally demonstrated. The bandpass transmission spectrum with a Q factor of ~10⁸ and high-order modes effectively suppressed is realized based on the backward scattering in a single ultrahigh-Q microcavity. Compared to reported works on microwave photonic bandpass filter, the bandwidth in this work is lowered over an order of magnitude.

Recently, polydimethylsiloxane (PDMS) based microfluidic channels have been integrated with standing surface acoustic wave (SSAW) devices for various applications like the cell or particle manipulation [1]. The SSAW is formed by direct interference of two or more surface acoustic waves which are generated by the interdigital transducers pairs [2-4]. The suspended cells/particles in the SSAW field experience acoustic radiation forces and are pushed to the pressure node or anti-node [5]. However, we use a straight single-phase unidirectional transducer (SSPUT) to generate surface acoustic wave (SAW) which can pattern cells in fluid. When the SAW is applied, the red blood cells are driven by the acoustic radiation force and patterned into the parallel lines, which indicates that a SSAW field is formed in the PDMS microchannel.

As shown in Figure 1, the SSPUT (Cr/Au, 50nm/300nm) is fabricated on a 128° Y-cut, X-propagating lithium niobate (LiNbO₃) substrate by the lift-off process. The PDMS micro-channel fabricated using the standard soft lithography technique is bonded on the LiNbO₃ substrate. The SSPUT has 20 pairs of electrodes whose widths and spacing gaps are 0.09 mm respectively. As shown in Figure 2, the S11 parameter of the device is measured using a vector network analyzer to determine the resonant frequency which represents the energy transmission capacity of the device. During the experiment, a voltage signal generated by an arbitrary signal generator is applied on the SSPUT to generate SAW. As shown in Figure 3, the red blood cells are suspended evenly in the microchannel when the SAW is off. After exposure to the 10.74 MHz SAW at 10Vpp, most of the red blood cells are patterned into two parallel lines within the channel and few are pushed to the sidewall. This similar phenomenon is more clearly observed at the 19.80MHz SAW and 20.99MHz as shown in Figure 4.

The aforementioned studies show that the interference of two SAWs forms a SSAW field in the microchannel which is placed between two parallel interdigital transducers. However, only a SSPUT is used to generate SAW in our study and the red blood cells are patterned in parallel lines when the SAW is on. It indicates that a SSAW field is formed in the microchannel. Most of the SAW is absorbed in the fluid and few SAW at the fluid/channel interface will reach the PDMS/air interface and bounce back again. Thus, the reflection of SAW at the PDMS/air interface is neglected. The SAW attenuation length on the substrate surface is greater than the channel width, so the SAW can reflect at the boundary between the fluid/ channel interface and the fluid/ substrate interface. The reflected and incident waves interfere to form a SSAW field. The cells are aggregated along the PDMS channel wall when the SSAW is applied because of the small contrast of acoustic impedance at the interface of fluid/ channel [6].

Recent research on medical implants has asked for more reliable and biocompatible hermetic packaging techniques with integrated circuits (IC). Besides, high-density multi-channel IC interconnects also become a major requirement to realize high-resolution application on electrical stimulation and recording. Previously proposed packaging methods are mostly based on wire bonding technique to bond pads on chip to pads on biocompatible ceramics substrate individually. However, the real medical implant product that are currently in use or under development still lack the high-density packaging techniques which limit the further development of application [1-3].

The development of film package in implantable electronic medical device is one of the major solution. Rodger et al [4] introduced a biocompatible interconnect film packaging method based on parylene film, which is already a huge achievement of high-density packaging techniques. Also, Rodger have demonstrated the parylene flex and high-density multi-channel retinal IC chip have a strong bonding to survive during surgical manipulation. Unfortunately, water penetration problem of parylene C film still exists in the in vivo corrosive body fluid environment that could not meet the requirement of long-term implantation in humans. Thus, A desired medical implants of lifetime 10 years are mostly depends on the packaging design protection on the device.

Thin film encapsulation has been studied on flexible OLED packaging using incompatible three layers MgF₂/ZnS film, which has a good water vapor and oxygen barrier capability that could substantial improvement in lifetime [5]. In this work, we built an ideal packaging design by introducing multiple biocompatible organic/inorganic film together on PI substrate. The water penetration route of multiple film will significantly enhanced due to the multiple films design. The fabrication and functional validation of the well designed multiple film are based on PI substrate of 1 µm organic parylene C (PA) and 50 nm inorganic aluminum oxide (Al₂O₃) film, which are five layers PA/Al₂O₃/PA/Al₂O₃/PA design structure (Fig. 1). PA and Al₂O₃ film are deposited using advanced chemical vapor deposition (CVD) and atomic layer deposition (ALD) technology, respectively. Specifically, the films packaging sample and the He leakage test sample are shown on fig.2a and fig.2b, respectively. The He leakage test pressure is 1×10^-10 Pa·m³/s, meeting FDA 10 year in vivo implantation standard. Furthermore, the in vivo biological compatibility results of cell relative growth rate (RGR) also demonstrate highly biocompatible level (0 level) in cell L929 (Fig. 3). 

In conclusion, the state-of-the-art multiple organic/inorganic film packaging has been successfully demonstrated as a useful package design. Thus, synergistic organic/inorganic packaging by “multiple PA and Al₂O₃ film” provides a promising film package design that ensures highly biocompatible and long-term implantable for medical implants market. Next, we will use this film packaging design in our 1024 high-density retinal product to achieve long time reliable implantation in vivo.

As the advantages of larger sampling throughout, simpler sampling preparation and cheaper instrument and reagent cost, immune-sensor is considered as a preferred screening tool for the determination of small molecular organic pollutants. In this study, an evanescent wave multi-channel biosensor for the detection of micro-pollutants in water environment was developed to detect typical micro-pollutants such as 2,4-dichlorophenoxyacetic acid (2,4-D), microcystin-LR (MC-LR), EDCs and antibiotics. Bio-sensors have shown good detection performances with low detecting limit, high frequency, sensitive and can meet the requirements for the detection of drinking water quality. The performances of the evanescent wave multi-channel biosensor was validated with respect to that of conventional high-performance liquid chromatography, and the correlation between methods agreed well (R² = 0.9762). Based on this bio-sensor an automated online optical bio-sensing system was developed. This system has successfully been applied to long-term, continuous determination and early warning for micro-pollutants. Thus, the bio-sensor system paves the way for a vital routine online analysis that satisfies the high demand for ensuring the safety of drinking water sources and water environment eco-system.

The impact on environment and on health of different pollutants, especially chemical pollutants, is becoming critical due to their drastic consequences on our main vital resource: water. In recent years, extensive efforts of fundamental research and developing practical processes have been devoted to the polluted water treatment. The semiconductor based photocatalytic process has shown a great potential as an environmental friendly and sustainable treatment technology due to its low-cost, and its ability to decompose the wide spectrum of contaminants in wastewater at room temperature without residual deposits that may require further post-treatment. With high surface/volume ratio, the nanostructured semiconductor shows enhanced photocatalytic efficiency in advancing water and wastewater treatment. Among the photocatalytic materials, ZnO nanostructure is a promising candidate for their easy-controllable synthesis, chemical and thermal stability. On the other hand, its further integration in a microfluidic system can overcome the main limitation of low speed mass transfer during the photo-degradation process of polluted water due to the shorter diffusion length within confined micro-chambers. Here we show a high efficiency microfluidic system decorated inside by ZnO nanostructures leading to a high throughput micro-reactor for water purification.

In dense wavelength division multiplexing (DWDM) systems, the dense signals should be broken into two groups with large channel spacing firstly in the demultiplexing process. Therefore, the cost of the whole system can be reduced without upgrading the existing filter. The key device to realize this function of DWDM system is interleaver. In this paper, basing on the analysis of the working principle of micro-ring resonator filters and Mach-Zehnder (M-Z) interferometer, the effects of essential parameter changes on the output waveforms (amplitude and phase property) have been deeply discussed. On the basis of the phase properties of micro-ring resonator filters, we proposed a nested ring resonator (NRR) which has a unique phase characteristic. Through our research, we found that the clever combination of NRR and M-Z interferomert can achieve wideband filtering. In this paper, we proposed a new bandpass filter and an interleaver that consists of MZI side-coupled with a NRR.

The output function of the nested ring resonator coupled to M-Z interferometer has been deduced. The output of the NRR coupled to M-Z interferometer is simulated using the output function, The influence of key parameters on the bandwidth, center wavelength, ultra-narrow bandwidth, passband flatness, sidelobe depression and bandwidth ratio of the filter has been analyzed in this paper.

Single-cell analysis (SCA) has revolutionized approaches to understanding complex biological systems, especially on the role of cellular heterogeneity in tissue development, health, and disease. Despite its recognized impact in basic biological sciences and clinical diagnosis/prognosis from its early successes, further progress of SCA remains hampered by its fundamental challenge in obtaining measurement with high information content on a large number of independent cells at high throughput.  This unmet capability to provide comprehensive catalogue of single-cells holds the key to further our understanding on tissue development and diseases, such as on the role of stem/progenitor cells in cancer and degenerative disorders.

 Optical imaging is regarded as one of the most effective tools to visualize living cells with high spatiotemporal resolution. However, its full adoption for high-throughput SCA has been hampered by the intrinsic speed limit imposed by the prevalent image capture strategies, which involve the laser scanning technologies, (e.g. galvanometric mirrors), and/or the image sensors (e.g. charge-coupled device (CCD) and complementary metal-oxide-semiconductor (CMOS)). The laser scanning speed is fundamentally limited by the mechanical inertia of the mirrors whereas the image capture rate of CCD or CMOS is ultimately limited by the required image sensitivity, i.e. scaling the frame rate inevitably compromises the detected signal intensity. Notably, this speed-versus-sensitivity trade-off of the image sensor explains why the throughput of flow cytometry has to be scaled down from 100,000 cells/sec to 1,000 cells/sec when the imaging capability is incorporated [1].

 To address these challenges, we adopt two related techniques to enable single-cell imaging with the unprecedented combination of imaging resolution and speed. Sharing a common concept of all-optical laser-scanning by ultrafast spatiotemporal encoding of laser pulses, these techniques, time-stretch imaging [2-6] and free-space angular-chirp-enhanced delay (FACED) imaging [7] enable ultrahigh-throughput single-cell imaging with multiple image contrasts (e.g. quantitative phase and fluorescence imaging) at a line-scan rate beyond 10’s MHz (i.e. an imaging throughput up to ~100,000 cells/sec). Moreover, they also enable quantification of intrinsic biophysical markers of individual cells – a largely unexploited class of single-cell signatures that is known to be correlated with the overwhelmingly investigated biochemical markers. All in all, these ultrafast single-cell imaging platforms could find new potentials in automated (deep) learning complex biological processes from such an enormous size of image data (from molecular signatures to biophysical phenotypes), especially to unveil the unknown heterogeneity between different single cells and to detect (and even quantify) rare aberrant cells. 

References:

1. Andy K. S. Lau, Ho Cheung Shum, Kenneth K. Y. Wong and Kevin K. Tsia "Optofluidic time-stretch imaging – an emerging tool for high-throughput imaging flow cytometry ," Lab on a Chip, 10.1039/C5LC01458A (2016).
2. T. W. Wong, et. al., “Asymmetric-detection time-stretch optical microscopy (ATOM) for ultrafast high-contrast cellular imaging in flow,” Sci. Rep. 4, 3656 (2014).
3. Goda, et al., “High-throughput single-microparticle imaging flow analyzer,” Proc. Natl Acad. Sci. USA 109, 11630 (2012). 
4. L. Chen, et. al., Deep learning in lable-free cell classification, Sci. Rep., 6, 21471 (2016).
5. Anson H. L. Tang, P. Yeung, Godfrey C. F. Chan, Barbara P. Chan, Kenneth K. Y. Wong, and Kevin K. Tsia, "Time-stretch microscopy on a DVD for high-throughput imaging cell-based assay," Biomed. Opt. Express 8, 640-652 (2017).
6. Queenie T. K. Lai al., "High-throughput time-stretch imaging flow cytometry for multi-class classification of phytoplankton," Opt. Express 24, 28170-28184 (2016).
7. Jianglai Wu, al., "Ultrafast Laser-Scanning Time-Stretch Imaging at Visible Wavelengths," Light: Sci.& Appl. 6, e16196 (2017).

Biological surfaces provide endless inspiration for design and fabrication of smart materials. It has recently been revealed to have become a hot research area in the materials science world[1].The capture silk of the cribellate spider Uloborus walckenaerius collects water
through a combination of multiple gradients in a periodic spindle-knot structure after rebuilding. Inspired by the roles of micro- and nanostructures (MNs) in the water collecting ability of spider silk[2], a series of bioinspired gradient fibers has been designed by integrating fabrication methods and technologies such as dip-coating,Rayleigh instability break-up droplets, phase separation, strategies of combining electrospinning and electrospraying, and web-assembly. Through such fabrications,“spindle-knot/joint” structures can be tailored to demonstrate the mechanism of multiple gradients (e.g., roughness, smooth, temperature-respond, photo-triggering,
etc.,) in driving tiny water drops. A water capturing ability can be developed by the combination of “slope” and “curvature” effects on spindle-knots on bioinspired fiber. The heterostructured fibers have been fabricated by electrohydrodynamic strategies,are intelligently responding to environmental humidity. A temperature-responsive fiber can realize the directional transport of droplet effectively. The multi-geometric gradient fiber achieves the droplet target transport in a long range along asdesigned bioinspired gradient fiber[1-2].
In contrast, biological surfaces such as plant leaves and butterfly wings with gradient structure features display the effect of water repellency. Smart bioinspired surfaces can be fabricated by combining machining, electrospinning, soft lithography, and nanotechnology. The gradient surfaces exhibit robust transport and controlling of droplets[3-4]. These bioinspired gradient surfaces would be promising applications into anti-icing,liquid transport, anti-fogging/self-cleaning, water harvesting, etc.
References
1. Y. Zheng. Pan Stanford Publishing. USA, ISBN 9789814463607. 0-216 (2015).
2. Y. Zheng, et al., Nature 463, 640 (2010).
3. M. Zhang,et al. Adv. Mater. 27, 5057 (2015).