Mapping the design space of photonic topological states via deep learning.

Topological states in photonics offer novel prospects for guiding and manipulating photons and facilitate the development of modern optical components for a variety of applications. Over the past few years, photonic topology physics has evolved and unveiled various unconventional optical properties in these topological materials, such as silicon photonic crystals. However, the design of such topological states still poses a significant challenge. Conventional optimization schemes often fail to capture their complex high dimensional design space. In this manuscript, we develop a deep learning framework to map the design space of topological states in the photonic crystals. This framework overcomes the limitations of existing deep learning implementations. Specifically, it reconciles the dimension mismatch between the input (topological properties) and output (design parameters) vector spaces and the non-uniqueness that arises from one-to-many function mappings. We use a fully connected deep neural network (DNN) architecture for the forward model and a cyclic convolutional neural network (cCNN) for the inverse model. The inverse architecture contains the pre-trained forward model in tandem, thereby reducing the prediction error significantly.

Bilayer dispersion-flattened waveguides with four zero-dispersion wavelengths.

We propose a new type of bilayer dispersion-flattened waveguides that have four zero-dispersion wavelengths. Low and flat dispersion can be achieved by using two different material combinations, with a much smaller index contrast as compared to the previously proposed slot-assisted dispersion-flattened waveguides. Without using a nano-slot, dispersion becomes less sensitive to waveguide dimensions, which is highly desirable for high-yield device fabrication. Ultra-low dispersion, high nonlinearity, and fabrication-friendly design would make it promising for practical implementation of nonlinear photonic functions. The proposed waveguide configuration deepens our understanding of the dispersion flattening principle.

Mid-infrared spectrometer using opto-nanofluidic slot-waveguide for label-free on-chip chemical sensing.

A mid-infrared (mid-IR) spectrometer for label-free on-chip chemical sensing was developed using an engineered nanofluidic channel consisting of a Si-liquid-Si slot-structure. Utilizing the large refractive index contrast (Δn ∼ 2) between the liquid core of the waveguide and the Si cladding, a broadband mid-IR lightwave can be efficiently guided and confined within a nanofluidic capillary (≤100 nm wide). The optical-field enhancement, together with the direct interaction between the probe light and the analyte, increased the sensitivity for chemical detection by 50 times when compared to evanescent-wave sensing. This spectrometer distinguished several common organic liquids (e.g., n-bromohexane, toluene, isopropanol) accurately and could determine the ratio of chemical species (e.g., acetonitrile and ethanol) at low concentration (<5 µL/mL) in a mixture through spectral scanning over their characteristic absorption peaks in the mid-IR regime. The combination of CMOS-compatible planar mid-IR microphotonics, and a high-throughput nanofluidic sensor system, provides a unique platform for chemical detection.

Air-clad silicon pedestal structures for broadband mid-infrared microphotonics.

Toward mid-infrared (mid-IR) silicon microphotonic circuits, we demonstrate broadband on-chip silicon structures, such as: (i) straight and bent waveguides and (ii) beam splitters, utilizing an air-clad pedestal configuration which eliminates the need for typical mid-IR-lossy oxide cladding. We illustrate a sophisticated fabrication process that can create high-quality pedestal structures in crystalline silicon, while preserving its mid-IR transparency. A fundamental waveguide mode is observed between λ=2.5 µm and λ=3.7 µm, and an optical loss of 2.7 dB/cm is obtained at λ=3.7 µm. Our pedestal silicon structures show 50:50 mid-IR power splitting enabling the further development of mid-IR silicon microphotonics.

Post-fabrication trimming of athermal silicon waveguides.

We experimentally demonstrate the post-fabrication trimming of polymer-coated athermal silicon waveguides by exploiting the photosensitivity of As(2)S(3) chalcogenide glass to near-bandgap visible light. Our technique enables compensation of fabrication tolerances and modification of specific circuit functionalities after fabrication. Moreover, our athermal and trimmable waveguide technology is highly resilient to high optical power, and thus extremely appealing for nonlinear applications. Finally, it enables to fix the absolute wavelength and spectral response of silicon devices with extremely low dependence from temperature and power.

Demonstration of high-Q mid-infrared chalcogenide glass-on-silicon resonators.

We demonstrated high-index-contrast, waveguide-coupled As2Se3 chalcogenide glass resonators monolithically integrated on silicon fabricated using optical lithography and a lift-off process. The resonators exhibited a high intrinsic quality factor of 2×10(5) at 5.2 µm wavelength, which is among the highest values reported in on-chip mid-infrared (mid-IR) photonic devices. The resonator can serve as a key building block for mid-IR planar photonic circuits.

Photo-induced trimming of chalcogenide-assisted silicon waveguides.

A chalcogenide-assisted silicon waveguide is realized by depositing a thin layer of A(2)S(3) glass onto a conventional silicon on insulator optical waveguide. The photosensitivity of the chalcogenide is exploited to locally change the optical properties of the waveguide through exposure to visible light radiation. Waveguide trimming is experimentally demonstrated by permanently shifting the resonant wavelength of a microring resonator by 6.7 nm, corresponding to an effective index increase of 1.6·10(-2). Saturation effects, trimming range, velocity and temporal stability of the process are discussed in details. Results demonstrate that photo-induced treatments can be exploited for a post-fabrication compensation of fabrication tolerances, as well as to set and reconfigure the circuit response.

Engineering broadband and anisotropic photoluminescence emission from rare earth doped tellurite thin film photonic crystals.

Broadband and anisotropic light emission from rare-earth doped tellurite thin films is demonstrated using Er3+-TeO2 photonic crystals (PhCs). By adjusting the PhC parameters, photoluminescent light can be efficiently coupled into vertical surface emission or lateral waveguide propagation modes. Because of the flexibility of light projection direction, Er3+-TeO2 is a potential broadband light source for integration with three-dimensional photonic circuits and on-chip biochemical sensors.

Cellular Leiomyoma versus Endometrial Stromal Sarcoma: A Report of a Rare Case Presenting a Diagnostic Challenge on Intraoperative Frozen Section.

Endometrial stromal sarcomas (ESSs) account for approximately 0.2% of all uterine malignancies. Cellular leiomyoma (CL) often simulates low-grade ESS due to similar cytology. We report the case of a 34-year-old female with a mass per abdomen. Frozen sections showed a tumor with many thin- and thick-walled vessels along with hyaline material. A differential diagnosis of CL and endometrial stromal tumor was suggested. The index case was diagnostically challenging to pathologists. Paraffin sections supplemented by immunohistochemistry (smooth muscle actin, CD10, and beta-catenin) favored CL. Frozen section sometimes leads to over/underestimation of tumor in view of small sampling area of tumor.

Simulation of an erbium-doped chalcogenide micro-disk mid-infrared laser source.

The feasibility of mid-infrared (MIR) lasing in erbium-doped gallium lanthanum sulfide (GLS) micro-disks was examined. Lasing condition at 4.5 µm signal using 800 nm pump source was simulated using rate equations, mode propagation and transfer matrix formulation. Cavity quality (Q) factors of 1.48 × 10(4) and 1.53 × 10(6) were assumed at the pump and signal wavelengths, respectively, based on state-of-the-art chalcogenide micro-disk resonator parameters. With an 80 µm disk diameter and an active erbium concentration of 2.8 × 10(20) cm(-3), lasing was shown to be possible with a maximum slope efficiency of 1.26 × 10(-4) and associated pump threshold of 0.5 mW.

Photo-induced trimming of coupled ring-resonator filters and delay lines in As2S3 chalcogenide glass.

Selective exposure to visible light is used to permanently trim the resonant wavelengths of coupled ring-resonator filters and delay-lines realized on a chalcogenide As2S3 platform. Post-fabrication manipulation of the circuit parameters has proved an effective tool to compensate for technological tolerances, targeting demanding specifications in photonic integrated circuits with no need for always-on power-hungry actuators. The same approach opens a way to realize photonic integrated circuits that can be reconfigured after fabrication to fulfill specific applications.

Optical loss reduction in high-index-contrast chalcogenide glass waveguides via thermal reflow.

A thermal reflow technique is applied to high-index-contrast, sub-micron waveguides in As(2)S(3) chalcogenide glass to reduce the sidewall roughness and associated optical scattering loss. We show that the reflow process effectively decreases sidewall roughness of chalcogenide glass waveguides. A kinetic model is presented to quantitatively explain the sidewall roughness evolution during thermal reflow. Further, we develop a technique to calculate waveguide optical loss using the roughness evolution model, and predict the ultimate low loss limit in reflowed high-index-contrast glass waveguides. Up to 50% optical loss reduction after reflow treatment is experimentally observed, and the practical loss limiting factors are discussed.

Integrated chalcogenide waveguide resonators for mid-IR sensing: leveraging material properties to meet fabrication challenges.

In this paper, attributes of chalcogenide glass (ChG) based integrated devices are discussed in detail, including origins of optical loss and processing steps used to reduce their contributions to optical component performance. Specifically, efforts to reduce loss and tailor optical characteristics of planar devices utilizing solution-based glass processing and thermal reflow techniques are presented and their results quantified. Post-fabrication trimming techniques based on the intrinsic photosensitivity of the chalcogenide glass are exploited to compensate for fabrication imperfections of ring resonators. Process parameters and implications on enhancement of device fabrication flexibility are presented.

Cavity-enhanced multispectral photodetector using phase-tuned propagation: theory and design.

We propose and theoretically analyze what we believe to be a novel design of cavity-enhanced photodetectors capable of sensing multiple wavelengths simultaneously in a single pixel. The design is based on phase-tuned propagation of resonant modes in cascaded planar resonant cavities. We show that this concept can be generalized to detect multiple wavelength combinations covering the entire near to far infrared spectrum. Besides its multispectral detection capability, the design also features minimal spectral cross talk and significantly suppressed noise. The intrinsic design versatility and scalability, as well as process compatibility with planar microfabrication, suggest the design's wide application potential for telecommunications, infrared imaging, and biochemical sensing.

Resonant cavity-enhanced photosensitivity in As2S3 chalcogenide glass at 1550 nm telecommunication wavelength.

We report the first (to our knowledge) experimental observation of resonant cavity-enhanced photosensitivity in As(2)S(3) chalcogenide glass film at 1550 nm telecommunication wavelength. The measured photosensitivity threshold is <0.1 GW/cm(2), and a photoinduced refractive index increase as large as 0.016 is observed. The photosensitive process is athermal; further, we confirm the absence of two-photon absorption in As(2)S(3), suggesting that defect absorption accounts for the energy transfer from photons to glass network. Besides its potential application for reconfigurable photonics circuit, such photosensitivity is also an important design consideration for nonlinear optical devices using chalcogenide glasses.

Design of optical meta-structures with applications to beam engineering using deep learning.

Nanophotonics is a rapidly emerging field in which complex on-chip components are required to manipulate light waves. The design space of on-chip nanophotonic components, such as an optical meta surface which uses sub-wavelength meta-atoms, is often a high dimensional one. As such conventional optimization methods fail to capture the global optimum within the feasible search space. In this manuscript, we explore a Machine Learning (ML)-based method for the inverse design of the meta-optical structure. We present a data-driven approach for modeling a grating meta-structure which performs photonic beam engineering. On-chip planar photonic waveguide-based beam engineering offers the potential to efficiently manipulate photons to create excitation beams (Gaussian, focused and collimated) for lab-on-chip applications of Infrared, Raman and fluorescence spectroscopic analysis. Inverse modeling predicts meta surface design parameters based on a desired electromagnetic field outcome. Starting with the desired diffraction beam profile, we apply an inverse model to evaluate the optimal design parameters of the meta surface. Parameters such as the repetition period (in 2D axis), height and size of scatterers are calculated using a feedforward deep neural network (DNN) and convolutional neural network (CNN) architecture. A qualitative analysis of the trained neural network, working in tandem with the forward model, predicts the diffraction profile with a correlation coefficient as high as 0.996. The developed model allows us to rapidly estimate the desired design parameters, in contrast to conventional (gradient descent based or genetic optimization) time-intensive optimization approaches.

IAC standardized reporting of breast fine-needle aspiration cytology, Yokohama 2016: A critical appraisal over a 2 year period.

BACKGROUND: Breast cytology is a significant component of the "Triple approach" for pre-operative diagnosis of breast lumps, the other two being clinical assessment and radiological imaging. The role of Fine needle aspiration cytology (FNAC) as a first line investigation in diagnosing breast lesions is well documented, however histopathology is the gold standard. Cyto-histopathological correlation is of great relevance and also increases precision.AIMS \& OBJECTIVES:The present study was conducted with the aim to categorize breast lesions according to the latest standardized reporting system proposed by International academy of cytologists (IAC) in 2016. Evaluation of diagnostic accuracy, sensitivity and specificity of FNAC in diagnosing breast lesions and cyto-histopathological correlation was planned. MATERIALS AND METHODS: All FNAs of breast lesions over a period of 2 years were included in the study. The cases were grouped into five standardized categories proposed by the International academy of cytology: Category I (Insufficient material), Category II (Benign), Category III (Atypical, probably benign), Category IV (Suspicious, probably in situ or invasive) & Category V (Malignant) respectively. Specificity, sensitivity, diagnostic accuracy, negative and positive predictive value of FNAC were calculated and cyto-histopathological correlation assessed wherever possible. RESULTS: Out of 468 breast lesions reported on FNAC, the category wise distribution was - Category I, II, III, IV & V accounting for 23(4.9%), 342(73.07%), 7(1.5%), 11(2.35%) and 85(18.16%) respectively. Histopathology was performed in 331/468 cases with cyto histological concordance of 98.4% and a type agreement rate of 90.9%. The sensitivity, specificity, positive and negative predictive value and diagnostic accuracy was 98.90%, 99.16%, 97.82%, 99.58% and 99.09% respectively. CONCLUSION: FNAC is a simple, reliable, cost effective, first line diagnostic procedure for all breast lumps. In collaboration with physical examination and imaging studies (triple approach), FNAC is a highly sensitive diagnostic tool. Adopting a universally acceptable standardized reporting system for breast cytology can enhance the diagnostic accuracy of FNAC.

Femtosecond laser photo-response of Ge23Sb7S70 films.

Ternary chalcogenide glass films from identical parent bulk glasses were prepared by thermal evaporation (TE) and pulsed laser deposition (PLD) and subjected to 810-nm femtosecond laser exposure at both kHz and MHz repetition rates. The exposure-induced modification on the glass film's surface profile, refractive index, and structural properties were shown to be a function of laser irradiance, the number of laser pulses per focal spot, and repetition rate. Film response was shown to be related to deposition technique-related density and the number of glass bonds within the irradiated focal volume. The induced changes resulted from a reduction in glass network connectivity among GeS(4/2), GeS(4), S-S and S(3)Ge-S-GeS(3) units.

Hormones of pregnancy, alpha-feto protein, and reduction of breast cancer risk.

Parity profoundly reduces breast cancer (BC) risk later in life. It has been reasoned that hormones (either estradiol E2 or estriol E3), progesterone (P) or human chorionic gonadotropin (hCG) in the serum of pregnant women might lead to that reduction in risk. These agents have been shown to reduce BC incidence in nonpregnant rats. We investigated the hypothesis that exogenously added E2, E3, P, or hCG are not the proximal effectors of risk reduction, but that they elicit alpha-fetoprotein (alphaFP) from the nonpregnant liver, and that cFP is the proximal agent by which reduction of BC risk is obtained. Methylnitrosourea (MNU)-exposed animals were treated with saline, E3, E2 + P, E3 + P, hCG, or were allowed to experience pregnancy, and AFP levels were measured in the serum and subsequent tumor incidence was recorded. Human HepG2 liver cells in culture were treated with E3, E2 + P, P, or hCG and elicited AFP was measured in the media. The HepG2 culture media containing elicited AFP was assessed for its ability to inhibit proliferation of T47D cells when applied to these human BC cells in culture, and to inhibit the estrogen-induced phosphorylation of the estrogen receptor in T47D cells. For each condition in the prevention studies, hormone treatment reduced the incidence of BC to an extent similar to that reported by the original studies. In each condition, alphaFP levels in serum were elevated over that in control animals. In culture, treatment of human liver cells with E3, E2 + P, or hCG, but not P alone, led to increased levels of AFP in the media. Media containing hCG-elicited AFP inhibited the estrogen-stimulated proliferation of T47D cells in culture, and inhibited phosphorylation of the estrogen receptor, whereas, estrogens and hCG did not inhibit the growth of these tumor cells in culture. In conclusion, since the hormones of pregnancy elicit alphaFP from the liver, and alphaFP but not the hormones of pregnancy has direct antitumor properties, it is concluded that alphaFP is the proximal agent through which reduction in BC incidence is realized from the experience of pregnancy.

Fabrication and testing of planar chalcogenide waveguide integrated microfluidic sensor.

We have fabricated and tested, to the best of our knowledge, the first microfluidic device monolithically integrated with planar chalcogenide glass waveguides on a silicon substrate. High-quality Ge(23)Sb(7)S(70) glass films have been deposited onto oxide coated silicon wafers using thermal evaporation, and high-index-contrast channel waveguides have been defined using SF(6) plasma etching. Microfluidic channel patterning in photocurable resin (SU8) and channel sealing by a polydimethylsiloxane (PDMS) cover completed the device fabrication. The chalcogenide waveguides yield a transmission loss of 2.3 dB/cm at 1550 nm. We show in this letter that using this device, N-methylaniline can be detected using its well-defined absorption fingerprint of the N-H bond near 1496 nm. Our measurements indicate linear response of the sensor to varying N-methylaniline concentrations. From our experiments, a sensitivity of this sensor down to a N-methylaniline concentration 0.7 vol. % is expected. Given the low-cost fabrication process used, and robust device configuration, our integration scheme provides a promising device platform for chemical sensing applications.