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We present a design of a contact lens display, which features an array of collimated light-emitting diodes and a contact lens, for the augmented reality. By building the infrastructure directly on top of the eye, eye is allowed to move or rotate freely without the need of exit pupil expansion nor eye tracking. The resolution of light-emitting diodes is foveated to match with the density of cones on the retina. In this manner, the total number of pixels as well as the latency of image processing can be significantly reduced. Based on the simulation, the device performance is quantitatively analyzed. For the real image, modulation transfer functions is 0.669757 at 30 cycle/degree, contrast ratio is 5, and distortion is 10%. For the virtual image, the field of view is 82°, best angular resolution is 0.38', modulation transfer function is above 0.999999 at 30 cycle/degree, contrast ratio is 4988, and distortion is 6%.

The results of the precise measurement of the refractive index of stable germanium isotopes Ge72, Ge73, Ge74, and Ge76 single crystals with high enrichment and a germanium single-crystal Genat of natural isotopic composition with the Fourier-transform interference refractometry method from 1.94 to 20 μm with 0.1 cm−1 resolution and accuracy of 2×10−5 to 1×10−4 are shown. The content of 72 impurities measured by the mass spectrometric method was below 10−5–10−6 wt. %. Oxygen and carbon concentrations measured by IR spectroscopy in all crystals are within 5×1015 cm−3. All germanium crystals have a hole conductivity with specific electric resistivity of 45–50 Ohm×cm. The coefficients of the generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also given.

We design and fabricate a novel highly integrated all-fiber single mode-multimode-single mode long period grating (SMS-LPG) refractometer. The experiment and simulation results confirm that the powerful local refractive index modulation capability of the multimode fiber (MMF) simultaneously reduces the length of the LPG and achieves excellent refractive index sensitivity. The spectral characteristics and sensing responses of different duty cycles are investigated. The optimized SMS-LPG sample achieved a refractive index sensitivity of 427.01 nm/RIU. The miniature SMS-LPG refractometer is a new sensor for measuring the external refractive index.

We demonstrate a photonic integrated Mach-Zehnder interferometric sensor, utilizing a plasmonic stripe waveguide in the sensing branch and a photonic variable optical attenuator and a phase shifter in the reference arm to optimize the interferometer operation. The plasmonic sensor is used to detect changes in the refractive index of the surrounding medium exploiting the accumulated phase change of the propagating Surface-Plasmon-Polariton (SPP) mode that is fully exposed in an aqueous buffer solution. The variable optical attenuation stage is incorporated in the reference Si3N4 branch, as the means to counter-balance the optical losses introduced by the plasmonic branch and optimize interference at the sensor output. Bulk sensitivity values of 1930 nm/RIU were experimentally measured for a Mach Zehnder Interferometer (MZI) with a Free Spectral Range of 24.8 nm, along with extinction ratio of more than 35 dB, demonstrating the functional benefits of the co-integration of plasmonic and photonic waveguides.

Simultaneous measurements of refractive index, surface tension, and evaporation rate in pendant droplets have been conducted in water, ethanol, n-heptane, diesel, and Jet A fuel in a temperature range of 20°C-50°C at atmospheric pressure. The dispersion of the refractive indices has been determined by means of rainbow refractometry. The surface tensions have been measured based on the pendant droplet shape analysis. The Young-Laplace equation and the numerical model have been applied to precisely obtain surface tension from the balance between the droplet distortion of gravity and restoring the force of surface tension. The evaporation of the fuels has also been studied with pure droplets of a few millimeters in diameter in a temperature-controlled environment. The shadowgraph technique has been performed for the precise measurement of the droplet size change with a long-working-distance objective (10× magnification). The evaporation rate has been determined by the temporal rate of droplet diameter change extracted from the subsequent images. The experimental data in this work is compared with the previous work to validate the accuracy and estimate uncertainty. Furthermore, the simultaneous multi-property measurement of Jet A fuel (POSF 4658) has been conducted. These properties of the aviation fuel can be used in computation and modeling to further improve the knowledge of jet injection (atomization and evaporation) and practical combustion processes.

A bilayer asymmetric photonic crystal slab made of porous Si3N4/SiO2 is designed as a biosensor by considering the optical performance of this photonic crystal slab with a square lattice based on rigorous coupled-wave analysis theory and wavelength interrogation methods. The results show that this bilayer asymmetric photonic crystal can be used as a biosensor according to its excellent linearity relationship between the guided resonance peak shift and refractive index of aqueous solution with or without glycerol. The theoretical sensitivity value of the bilayer asymmetric photonic crystal biosensor is achieved as (S>286 nm/RIU) in the wavelength range from 1400 nm to 1600 nm. These results also indicate that the asymmetry bilayer structure has an important influence on its optical characteristic and sensitivity of the bilayer photonic crystal biosensor, and hence, it can be modified by changing the lattice constant and slab thickness. This research paper is very useful for understanding the application and design of biosensors based on porous structures.

The fiber geometry, fiber parameters and mode-guiding properties are crucial for realizing high-performance fiber-based sensors. In this work, we propose and demonstrate a few-mode fiber (FMF)-based surface plasmon resonance (SPR) biosensor. The FMF-SPR sensor was fabricated via side-polishing a few-mode fiber and coating a thin layer of gold film, on the basis of the optimization of fiber geometry, thickness of the gold film and mode selection, which were performed with the finite element method. The refractive index (RI) sensing performance of three such sensors with different residual fiber thicknesses were investigated. In the RI range from 1.333 to 1.404, the highest sensitivity up to 4903 nm/RIU and a figure of merit of 46.1 RIU-1 are achieved. For testing the bovine serum albumin (BSA) solution, an averaged BSA RI sensitivity of 6328 nm/RIU and an averaged BSA concentration sensitivity of 1.17 nm/(mg/ml) are realized. Benefiting from only a few modes supported in the FMF, a smaller line-width of the SPR spectrum is obtained, which further results in a higher figure of merit (FOM). Moreover, when combined with the superiority of the mode-multiplexing technology brought by the FMF, the FMF-SPR sensors may find applications in biochemical analysis with high performance and high throughputs.

In this paper, we demonstrate point-by-point inscription of eccentric fiber Bragg grating (EFBG) in conventional single-mode fiber (Corning SMF-28) with second-order Bragg resonances within the C-band using an IR femtosecond laser. Highly localized fiber Bragg gratings can be inscribed point-by-point with focused ultrashort pulses. EFBGs are localized close to the core-cladding interface, yielding strong cladding mode resonance couplings and high photoinduced birefringence. The inscription conditions to optimize the grating fabrication have been explored to achieve second-order resonances of good spectral quality. Potential applications of EFBG in refractometry sensing are further illustrated. Two interrogation techniques for EFBG in refractometry are reported and experimentally tested.

A high-sensitivity and label-free method for identifying a transgenic plant genome is highly desirable in plant biotechnology. Here, we present a terahertz (THz) metamaterial (MM)-based biosensor that comprises a planar array of gold split-ring (SR) resonators capable of sensing a considerable shift in the resonance frequency due to the change of the dielectric environment on the MM chip. The meta-sensor is employed to detect transgenic tomato genome DNAs by THz time-domain spectroscopy. The experimental results were confirmed by finite-element modeling through varying the thickness and dielectric constant of the DNA overlayer. Consequently, high-efficiency and label-free discrimination between the wild-type and transgenic genome DNA was achieved.

Conventional optical refractometry methods are often limited by a narrow measurement range, complex hardware, or relatively high cost. Here, we present a novel refractometry method to measure the bulk refractive index (RI) of materials (including solids and liquids) using lensless holographic on-chip imaging and autofocusing, which is simple, cost-effective, and has a large RI measurement range. As a proof of concept, two compact prototypes were built to measure the RIs of solid materials and liquids, respectively, and they were tested by measuring the RIs of a ZnSe plate and a microscopy immersion oil. Experimental results show that our devices have an average accuracy of ~3 × 10−4 RI unit (RIU) with an estimated precision of ~3 × 10−3 RIU for solids; and an average accuracy of ~1 × 10−4 RIU with an estimated precision of ~3 × 10−4 RIU for liquids. We believe that this cost-effective and portable RI measurement platform holds promise to be used in laboratory and industrial settings.

In most fiber-optic gas sensing applications where the interested refractive index (RI) is ~1.0, the sensitivities are greatly constrained by the large mismatch between the effective RI of the guided mode and the RI of the surrounding gaseous medium. This fundamental challenge necessitates the development of a promising fiber-optic sensing mechanism with the outstanding RI sensitivity to achieve reliable remote gas sensors. In this work, we report a highly sensitive gas refractometer based on a tapered optical microfiber modal interferometer working at the dispersion turning point (DTP). First, we theoretically analyze the essential conditions to achieve the DTP, the spectral characteristics, and the sensing performance at the DTP. Results show that nonadiabatic tapered optical microfibers with diameters of 1.8-2.4 µm possess the DTPs in the near-infrared range and the RI sensitivities can be improved significantly around the DTPs. Second, we experimentally verify the ultrahigh RI sensitivity around the DTP using a nonadiabatic tapered optical microfiber with a waist diameter of ~2 μm. The experimental observations match well with the simulation results and our proposed gas refractometer provides an exceptional sensitivity as high as −69984.3 ± 2363.3 nm/RIU. MOE (Min. of Education, S’pore) Published version

For the see-through and near-to-eye displays, light throughput and uniformity of luminance over the field of view are improved by employing an optical image guide with discretely depth-varying surface relief holographic gratings. In the design process, a newly developed mathematical model, in conjunction with rigorous coupled wave analysis of diffraction efficiency, eliminates massive and time consuming iteration of non-sequential ray tracing but rapidly identifies the depth-varying structure and optimum optical performance. The depth-varying grating based approach achieved a 1.37x improvement in light throughput compared to the conventional depth un-varying design, 315 cd/m2/lm, along with improved uniformity over the field of view of 35 (H) x 20 (V) degrees with an eye box size of 17 (H) x 14 (V) mm.

A comparative study of quantitative phase imaging techniques for refractometry of optical waveguides is presented. Three techniques were examined: a method based on the transport-of-intensity equation, quadri-wave lateral shearing interferometry and digital holographic microscopy. The refractive index profile of a SMF-28 optical fiber was thoroughly characterized and served as a gold standard to assess the accuracy and precision of the phase imaging methods. Optical waveguides were inscribed in an Eagle2000 glass chip using a femtosecond laser and used to evaluate the sensitivity limit of these phase imaging approaches. It is shown that all three techniques provide accurate, repeatable and sensitive refractive index measurements. Using these phase imaging methods, we report a comprehensive map of the photosensitivity to femtosecond pulses of Eagle2000 glass. Finally, the reported data suggests that the phase imaging techniques are suited to be used as precise and non-destructive refractive index shift measuring tools to study and control the inscription process of optical waveguides.

This study presents refractive index measurements of human and porcine adipose tissues and lipid droplet content in the visible and near-infrared. The coefficients of the Sellmeier formula were calculated for approximation of tissue dispersion. For the first time, to the best of our knowledge, the phase transition temperatures and temperature increments 𝑑𝑛/𝑑𝑇 of adipose tissue were quantified for a wide wavelength range from 480 to 1550 nm and from room temperature up to 50°C. For human abdominal adipose tissue, the refractive index increment averaged across all wavelengths is 𝑑𝑛/𝑑𝑇=−(3.54±0.15)×10−4°C−1, for porcine tissue 𝑑𝑛/𝑑𝑇=−7.92(0.74)×10−4°C−1, and for porcine lipid droplet 𝑑𝑛/𝑑𝑇=−6.01(0.29)×10−4°C−1. Data available in literature for refractive indices of adipose tissues measured by different techniques are summarized and compared with the received data.

The polar decomposition method for Mueller matrices proposed by Lu–Chipman has been demonstrated and validated for many applications. However, in some situations, e.g., when analyzing the Mueller matrix of birefringent turbid media with Mie-sized scatterers acquired in reflection geometry, the method may suffer from limitations due to the assumptions required by this method. Here we extend the Lu–Chipman method and show that it can provide more reasonable results for these situations. The method has been validated experimentally with turbid phantoms. Thus, this Letter may prove useful in tissue polarimetry.

We propose and experimentally verify an innovative label-free optical fiber biosensor based on a Mach-Zehnder interferometer for bovine serum albumin (BSA) concentration detection. The proposed fiber biosensor utilized a micro-cavity within a single-mode fiber to induce Mach-Zehnder interference. A remarkable feature of this biosensor is that external media can directly interact with the fiber core signal through microfluidic channels connected to the micro-cavity and sensor surface. The device was fabricated by means of femtosecond laser micromachining and chemical etching. A fiber interferometer of this type exhibits an ultrahigh refractive index sensitivity of −10,055 nm/RIU and a detection limit of 3.5 × 10−5 RIU. Different concentrations of BSA with an infinitesimally small refractive index difference can be clearly differentiated in situ by the interferential spectra of the structure. Experiments demonstrated the biosensor exhibited a BSA solution concentration sensitivity of −38.9 nm/(mg/mL) and a detection limit of 2.57 × 10−4 mg/mL, respectively. Moreover, this biosensor is a sub-microliter dose and ultrasensitive at the low concentrations detected in BSA, which make it a promising for biochemical applications such as DNA hybridization, cancer screenings, medicine examination and environmental engineering, etc.

The light scattering characteristic plays a very important role in optic imaging and diagnostic applications. For optical detection of the cell, cell scattering characteristics have an extremely vital role. In this paper, we use the finite-difference time-domain (FDTD) algorithm to simulate the propagation and scattering of light in biological cells. The two-dimensional scattering cell models were set up based on the FDTD algorithm. The cell models of normal cells and cancerous cells were established, and the shapes of organelles, such as mitochondria, were elliptical. Based on these models, three aspects of the scattering characteristics were studied. First, the radar cross section (RCS) distribution curves of the corresponding cell models were calculated, then corresponding relationships between the size and the refractive index of the nucleus and light scattering information were analyzed in the three periods of cell canceration. The values of RCS increase positively with the increase of the nucleo-cytoplasmic ratio in the cancerous process when the scattering angle ranges from 0° to 20°. Second, the effect of organelles in the scattering was analyzed. The peak value of the RCS of cells with mitochondria is higher than the cells without mitochondria when the scattering angle ranges from 20° to 180°. Third, we demonstrated that the influence of cell shape is important, and the impact was revealed by the two typical ideal cells: round cells and oval cells. When the scattering angle ranges from 0° to 80°, the peak values and the frequencies of the appearance of the peaks from the two models are roughly similar. It can be concluded that: (1) the size of the nuclei and the change of the refractive index of cells have a certain impact on light scattering information of the whole cell; (2) mitochondria and other small organelles contribute to the cell light scattering characteristics in the larger scattering angle area; and (3) the change of the cell shape significantly influences the value of scattering peak and the deviation of scattering peak position. The results of the numerical simulation will guide subsequent experiments and early diagnosis of cervical cancer.

Optical tweezers have been used to trap and manipulate microparticles within living animals. When the optical trap is constructed with an oil-immersion objective, it suffers from spherical aberration. There have been many investigations on the influence of spherical aberration when the particles are trapped in a water medium. However, the dependence of optical force on trapping depth is still ambiguous when the trapped particles are immersed in a high refractive index medium (such as biological tissue, refractive index solution) in experiments. In this paper, the microparticles are immersed in an aqueous solution of glycerol to mimic the cells within biological tissue. As the trapping laser is focused into the specimen, spherical aberration is introduced, degrading the optical trapping performance. It is similar to trapping in water; altering the effective tube length can also compensate for the spherical aberration of the optical trap in a high refractive index medium. Finally, the cells in living mice are trapped by the optical tweezers with the help of spherical aberration compensation.

The refractive index distribution of cells and tissues governs their interaction with light and can report on morphological modifications associated with disease. Through intensity-based measurements, refractive index information can be extracted only via scattering models that approximate light propagation. As a result, current knowledge of refractive index distributions across various tissues and cell types remains limited. Here we use quantitative phase imaging and the statistical dispersion relation (SDR) to extract information about the refractive index variance in a variety of specimens. Due to the phase-resolved measurement in three-dimensions, our approach yields refractive index results without prior knowledge about the tissue thickness. With the recent progress in quantitative phase imaging systems, we anticipate that using SDR will become routine in assessing tissue optical properties.

The whispering gallery mode (WGM) is generated by light propagating within a nonlinear micro-ring resonator, which is modeled and made by an InGaAsP/InP material, and called a Panda ring resonator. An imaging probe can also be formed by the micro-conjugate mirror function for the appropriate Panda ring parameter control. The 3D WGM probe can be generated and used for a 3D sensor head and imaging probe. The analytical details and simulation results are given, in which the simulation results are obtained by using the MATLAB and Optiwave programs. From the obtained results, such a design system can be configured to be a thin-film sensor system that can contact the sample surface for the required measurements The outputs of the system are in the form of a WGM beam, in which the 3D WGM probe is also available with the micro-conjugate mirror function. Such a 3D probe can penetrate into the blood vessel and content, from which the time delay among those probes can be detected and measured, and where finally the blood flow rate can be calculated and the blood content 3D image can also be seen and used for medical diagnosis. The tested results have shown that the blood flow rate of 0.72−1.11 μs−1, with the blood density of 1060 kgm−3, can be obtained.

A reflection-type phase-sensitive weak measurement for biosensing and chemical label-free sensing is presented. The phase difference between p and s polarizations in total internal reflection caused by biomolecular recognition is measured by weak value amplification. The system with p and s polarizations in a common path is stable and robust. The sensing process occurring on the silicon dioxide surface is achieved with a resolution of 3.6×10sup-6/suprefractive index units. The applicability is demonstrated by real-time monitoring biomolecular interaction of IgG and protein A.

The definition of the meter is based on the speed of light in a vacuum; however, most dimensional measurements, when performed using laser interferometry, are performed in air. A velocity of light compensation needs to be applied to the velocity of the laser light for accurate measurements of the speed of light to be approximated in a vacuum. Most practices use a weather-station method, whereby the ambient conditions are measured. Thereafter, the modified Edlén's equation is used, and corrections are calculated for the wavelength of the laser. The theoretical calculation is, however, only accurate to 3*10sup-8/supwithout taking into account the accuracy of the sensors. Thus, this work focuses on investigations into the velocity of light compensations, both to improve upon the accuracy of the Edlén equation method in everyday use, and to verify the accuracy of the current weather-station systems in use through comparison with the refractometer. A refractometer that allows for velocity of light compensation measurements was developed, tested, and verified. The system was designed to be simple and cost-effective for use in everyday dimensional measurements, but with high accuracy. Achieved results show that although simple in design, the refractometer is accurate to at least 1*10sup-8/sup, which meets our initial condition for design.

In this work, we report the development, construction, and the performance of two liquid refractometers that use a reflective diffraction grating immersed in a test liquid. The liquid is contained in a transparent glass cell with a rectangular cross section. The grating is oriented in such a way that the propagation directions of the incident beam and the beam diffracted by the lower part of the grating immersed in the liquid are perpendicular. In this configuration, the refractive index is determined by measuring the angle of the zeroth-order diffraction beam coming from the upper part of the grating, which is in contact with air. The diffractive refractometers (DR-1 and DR-2) have different angle measurement procedures and different light detection systems, and their advantages and drawbacks are pointed out. In the experiments, precisions of the order of 10sup-5/supand 10sup-4/supfor DR-1 and DR-2 are achieved, respectively. The performances of both systems are compared with the performance of a commercial Abbe refractometer in the measurement of sugar and NaCl aqueous solutions.

We propose and demonstrate a novel temperature-insensitive bio-sensor for accurate and quantitative detection of Escherichia coli (E. coli) bacteria in water. Surface sensitivity is maximized by operating the long-period fiber grating (LPFG) closest to its turnaround wavelength, and the temperature insensitivity is achieved by selectively exciting a pair of cladding modes with opposite dispersion characteristics. Our sensor shows a nominal temperature sensitivity of ∼1.25 pm/°C, which can be further reduced by properly adjusting the LPFG lengths, while maintaining a high refractive index sensitivity of 1929 nm/RIU. The overall length of the sensor is ∼3.6 cm, making it ideally suitable for bio-sensing applications. As an example, we also show the sensor's capability for reliable, quantitative detection of E. coli bacteria in water over a temperature fluctuation of room temperature to 40°C.

Dual-depth spectral-domain optical coherence tomography (SD-OCT) enables high-resolution in vivo whole-eye imaging. Two orthogonally polarized beams from a source are focused simultaneously on two axial positions of the anterior segment and the retina. For the detector arm, a 1×2 ultrafast optical switch sequentially delivers two spectral interference signals to a single spectrometer, which extends the in-air axial depth range up to 9.44 mm. An off-pivot complex conjugate removal technique doubles the depth range for all anterior segment imaging. The graphics-processing-unit-based parallel signal processing algorithm supports fast two- and three-dimensional image displays. The obtained high-resolution anterior and retinal images are measured biometrically. The dual-depth SD-OCT system has an axial resolution of ∼6.4 μm in air, and the sensitivity is 91.79 dB at 150 μm from the zero-delay line.

In this report we present studies on beetles of the Scarabaeidae family. The selected beetles show brilliant colors and in addition interesting polarization features. Mueller matrices of such beetles are of large interest to explore for biomimetics and for the understanding of the biological relevance of the observed polarization phenomena. Several species of the Scarabaeidae family have been studied by Hodgkinson, Goldstein and our group to mention some. Ellipticity, degree of polarization and other derived parameters have been reported and Arwin et al. also did optical modeling to determine structural parameters of the scutellum part of the exoskeleton of Cetonia aurata. Mueller matrices are very rich in information about the sample properties and can also be analyzed by addressing depolarization. Cloude showed that a depolarizing Mueller matrix can be represented by a sum of up to four non-depolarizing Mueller matrices weighted by the eigenvalues of the covariance matrix of the Mueller matrix. These eigenvalues are all positive for a physically realizable Mueller matrix and this, so called sum decomposition can be used to filter matrices and obtain a measure of experimental fidelity. The result of the decomposition can also be used to describe a Mueller matrix as a set of basic optical elements having direct physical meaning, such as polarizers and retarders. Pioneering work on decomposition of Mueller-matrix images, including studies of beetles, was performed by Ossikovski et al. We have also previously demonstrated this with Cloude as well as regression decomposition of Mueller matrix spectra and images measured at near-normal incidence on C. aurata. Using Cloude decomposition we found that the experimentally determined Mueller matrix of C. aurata decomposes into a set of a mirror and a circular polarizer. Those results were then the basis for a more stable regression decomposition where the result was confirmed. Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Vetenskapsradet (VR) [621-2011-4283]; Knut och Alice Wallenbergs Stiftelse [2004.0233]; Carl TryggersVid tiden för disputation förelåg publikationen endast som manuskript

A guided Bloch surface wave resonance (GBR) configuration is introduced for label-free biosensing. The GBR is realized by coupling the first-order diffraction of a subwavelength grating with the Bloch surface wave at the interface between a 1D photonic crystal slab and bio-solution. In addition to sustaining the Bloch surface mode, the photonic crystal provides the design freedom of simultaneously increasing the quality and decreasing the sideband transmissions of the resonance spectrum. The low sideband and high-quality features along with the large sensitivity rising from the strong overlap between the Bloch surface mode and the bio-solution make the GBR suitable for the design of biosensors. Biosensors with a high figure of merit are realized by the compact configurations.

Vortex beams are plagued by the intrinsic chromaticity of the physical phenomenon used to generate them. To the authors' best knowledge, attempts to generate them in a broad spectral range remain quite scarce and limited in their results. Crystal optics and especially conical diffraction (CD) (or refraction) intrinsically create achromatic vortices. The vortex is created by a wavelength-independent topological charge, embedded directly in the Fresnel equations. However, for biaxial crystals of low crystallographic symmetry, which includes all crystals used practically for CD, the dispersion of the binormal axis creates a chromaticity effect. In this Letter, we propose a new way to compensate this dispersion of the binormal axis of a biaxial crystal in order to generate white-light vortex beams by CD in a 250 nm spectral range, covering almost all the visible range. The advantages of the ability to use CD in a wide spectral range vastly exceed the sole generation of vortex beams.

A mid-infrared fiber optical parametric oscillator is proposed and designed based on a three-hole As(2)S(5) suspended-core fiber (SCF). The eigenmodes of the SCF are depicted and the pump condition for single-mode operation is analyzed. The zero-dispersion wavelength is shifted to 2 μm by tuning the core diameter of the SCF. Using the degenerate four-wave mixing coupled-wave equations, a tuning range of the idler wavelength from 2 to 5 μm and a maximum conversion efficiency of 19% are numerically predicted in a 0.1-m-long SCF pumped by a 2.7 W thulium-doped fiber laser.

We report on the first demonstration of a flexible optical waveguide interconnecting device made of a general purpose pressure-sensitive adhesive (PSA) tape embedding nanopatterned Al thin film diffractive grating couplers. The diffractive elements allow selected broadband light to be perpendicularly coupled/decoupled into/from a PSA tape waveguide in which they are integrated. Waveguide losses and coupling efficiency are evaluated. The versatility and low cost of the used materials make the presented configuration very promising for cost-effective, ready-to-use short-distance optical interconnections.

Brillouin spectroscopy has been used to characterize shear acoustic phonons in materials. However, conventional instruments had slow acquisition times over 10 min per 1 mW of input optical power, and they required two objective lenses to form a 90° scattering geometry necessary for polarization coupling by shear phonons. Here, we demonstrate a confocal Brillouin microscope capable of detecting both shear and longitudinal phonons with improved speeds and with a single objective lens. Brillouin scattering spectra were measured from polycarbonate, fused quartz, and borosilicate in 1-10 s at an optical power level of 10 mW. The elastic constants, phonon mean free path and the ratio of the Pockels coefficients were determined at microscopic resolution.

Coherent light scattering presents complex spatial patterns that depend on morphological and molecular features of biological cells. We present a numerical approach to establish realistic optical cell models for generating virtual cells and accurate simulation of diffraction images that are comparable to measured data of prostate cells. With a contourlet transform algorithm, it has been shown that the simulated images and extracted parameters can be used to distinguish virtual cells of different nuclear volumes and refractive indices against the orientation variation. These results demonstrate significance of the new approach for development of rapid cell assay methods through diffraction imaging.

We examine the performance of a tunable liquid crystal q-plate in a reflective geometry. When the device is tuned to a half-wave retardance, it operates as a q-plate with twice the value (2q) by adding a quarter-wave retarder between the mirror and the q-plate. However, when the device is tuned to a quarter-wave retardance, it acts as the original q-plate without the retarder. Experimental results are shown. Using an input tunable polarization state generator, the system allows the switchable production of all states on both the first- and second-order Poincaré spheres.

We demonstrate a compact, robust, and stable terahertz source based on a novel two section digital distributed feedback laser diode and plasmonic photomixer. Terahertz wave generation is achieved through difference frequency generation by pumping the plasmonic photomixer with two output optical beams of the two section digital distributed feedback laser diode. The laser is designed to offer an adjustable terahertz frequency difference between the emitted wavelengths by varying the applied currents to the laser sections. The plasmonic photomixer is comprised of an ultrafast photoconductor with plasmonic contact electrodes integrated with a logarithmic spiral antenna. We demonstrate terahertz wave generation with 0.15-3 THz frequency tunability, 2 MHz linewidth, and less than 5 MHz frequency stability over 1 minute, at useful power levels for practical imaging and sensing applications.

We report on a high-power, narrow spectral bandwidth 2.907 µm PPMgLN optical parametric oscillator (OPO) pumped by a 1.064 µm pulsed Nd:YAG MOPA laser source. Free-running operation of the OPO exhibits maximum average output power of 71.6 W at 2.907 µm with a slope efficiency of 26.7%. Broad 2.907 μm spectral bandwidth of the free-running OPO was suppressed from ~9 nm to less than 0.7 nm by using a VBG as one cavity mirror. The maximum average power was 51.7 W at 2907.55 nm for the spectrum-narrowed OPO, corresponding to a slope efficiency of 22.5%. Continuously tunable ranges of ~8 nm around 2.907 µm had been achieved via adjusting the temperatures of the VBG and PPMgLN accordingly.

In this study, a new flat-field concave grating miniature spectrometer is proposed with improved resolution across a wide spectral band. A mirror is added to a conventional concave grating spectrometer and placed near the existing detector array, allowing a wide spectral band to be divided into two adjacent subspectral bands. One of these bands is directly detected by the detector, and the other is indirectly analyzed by the same detector after being reflected by the mirror. These two subspectral bands share the same entrance slit, concave grating, and detector, which allows for a compact size, while maintaining an improved spectral resolution across the entire spectral band. The positions of the mirror and other parameters of the spectrometer are designed by a computer procedure and the optical design software ZEMAX. Simulation results show that the resolution of this kind of flat-field concave grating miniature spectrometer is better than 1.6 nm across a spectral band of 700 nm. Experiments based on three laser sources reveal that the measured resolutions are comparable to the simulated ones, with a maximum relative error between them of less than 19%.

We demonstrate the polarization mode selection and the dependence of coupling efficiency on polarization state of pump light for an optofluidic ring resonator (OFRR) laser. An optical fiber is chosen to serve as the ring resonator and surrounded by rhodamine 6G dye solution of lower refractive index as the fluidic gain medium. When the ring resonator is pumped by a linearly s-polarized laser, the emitted whispering gallery mode (WGM) lasing is of parallel polarization (TM mode), while p-polarized laser excitation generates a vertically polarized lasing emission (TE mode), both TM and TE mode lasing emission coexist simultaneously if the ring resonator is pumped by the s- and p-mixed polarized light. Further investigation reveals that the lasing intensity of the TM mode is approximately twice that of the TE mode for the same pump energy density, meaning an obvious difference of coupling efficiency on the polarization state of pump light; the experimental results of coupling efficiency are well explained by an induced dipole model.

Rayleigh anomalies (RAs) and surface plasmon polaritons (SPPs) on subwavelength metallic gratings play pivotal roles in many interesting phenomena such as extraordinary optical transmission. In this work, we present a theoretical analysis of the effect of finite metallic grating size on RA-SPP resonances based on the combination of rigorous coupled wave analysis and finite aperture diffraction. One-dimensional arrays of gold subwavelength gratings with different device sizes were fabricated and the optical transmission spectra were measured. As the grating size shrinks, the broadening of the RA-SPP resonances is predicted by the theoretical model. For the first order RA-SPP resonances, the results from this model are in good agreement with the spectra measured from the fabricated plasmonic gratings.

We analyze a method recently proposed to retrieve the size, refractive index, and concentration of particles in nonabsorbing nanofluids from measurements of the complex effective refractive index of two dilutions of the nanofluid [Opt. Lett.39, 559 (2014)]. The method uses simple formulas to retrieve the particles' parameters. First, we discuss precautions needed with the new method when inferring the refractive index of the particles from measurements of the imaginary part of the effective refractive index of two dilutions of the original nanofluid. Then we analyze the use of this methodology to obtain some average radius in the size of polydisperse suspensions and in the case of suspensions of weakly absorbing particles. We also perform an error analysis considering fixed errors in measurements and calculating the errors in the retrieved size, refractive index, and concentration of particles. Finally, we characterize experimentally nanofluids of polymeric particles fabricated of poly(methyl-methacrylate) (PMMA) and polystyrene (PS) for which we achieved an uncertainty of 5×10(-3) and 1×10(-2) in the determination of the particle refractive index, respectively, and a precision better than 3% in the determination of their radii.

We previously established that spectroscopic microscopy can quantify subdiffraction-scale refractive index (RI) fluctuations in a label-free dielectric medium with a smooth surface. However, to study more realistic samples, such as biological cells, the effect of rough surface should be considered. In this Letter, we first report an analytical theory to synthesize microscopic images of a rough surface, validate this theory by finite-difference time-domain (FDTD) solutions of Maxwell's equations, and characterize the spectral properties of light reflected from a rough surface. Then, we report a technique to quantify the RI fluctuations beneath a rough surface and demonstrate its efficacy on FDTD-synthesized spectroscopic microscopy images, as well as experimental data obtained from biological cells.

In general, Fourier transform lenses are considered as ideal in the design algorithms of diffractive optical elements (DOEs). However, the inherent aberrations of a real Fourier transform lens disturb the far field pattern. The difference between the generated pattern and the expected design will impact the system performance. Therefore, a method for modifying the Fourier spectrum of DOEs without introducing other optical elements to reduce the aberration effect of the Fourier transform lens is proposed. By applying this method, beam shaping performance is improved markedly for the optical system with a real Fourier transform lens. The experiments carried out with a commercial Fourier transform lens give evidence for this method. The method is capable of reducing the system complexity as well as improving its performance.

Optical vortices are associated with a spatial phase singularity. Such a beam with a vortex is valuable in optical microscopy, hyper-entanglement, and optical levitation. In these applications, vortex beams with a perfect circle shape and a large topological charge are highly desirable. But the generation of perfect vortices with high topological charges is challenging. We present a novel method to create perfect vortex beams with large topological charges using a digital micromirror device (DMD) through binary amplitude modulation and a narrow Gaussian approximation. The DMD with binary holograms encoding both the spatial amplitude and the phase could generate fast switchable, reconfigurable optical vortex beams with significantly high quality and fidelity. With either the binary Lee hologram or the superpixel binary encoding technique, we were able to generate the corresponding hologram with high fidelity and create a perfect vortex with topological charge as large as 90. The physical properties of the perfect vortex beam produced were characterized through measurements of propagation dynamics and the focusing fields. The measurements show good consistency with the theoretical simulation. The perfect vortex beam produced satisfies high-demand utilization in optical manipulation and control, momentum transfer, quantum computing, and biophotonics.

We propose an on-chip integrated differential optical microring refractive index sensing platform which leverages laminar flow conditions. Close spacing between a sensing and a reference resonator, and sharing the same microfluidic channel allows the two resonators to experience similar environmental disturbances, such as temperature fluctuations and fluidic-induced transients, achieving reliable and sensitive sensing performance. We obtain a noise floor of 80.0 MHz (0.3 pm) and a bulk refractive index sensitivity of 17.0 THz per refractive index unit (RIU) (64.2 nm/RIU), achieving a limit of detection of 1.4×10^(-5) RIU in a 30 min and an 8° C window.

In a recent study we reported on the gradient index (GRIN) lens Stokes polarimeter (GLP) [Opt. Lett.39, 2656 (2014)10.1364/OL.39.002656OPLEDP0146-9592]. With a simple architecture, this polarimeter can measure the state of polarization in a single shot. In this article, we present further studies for improving the performance of the GLP. Detailed discussions are presented on the optimization process of the GLP based on different choices of data from the CCD images. It is pointed out that many optimization techniques, although developed for other types of Stokes polarimeters, can also be applied to the GLP because the GRIN lens can traverse all possible retardance and fast axis modulations.

We have developed an interferometric optical microscope that provides three-dimensional refractive index map of a specimen by scanning the color of three illumination beams. Our design of the interferometer allows for simultaneous measurement of the scattered fields (both amplitude and phase) of such a complex input beam. By obviating the need for mechanical scanning of the illumination beam or detection objective lens; the proposed method can increase the speed of the optical tomography by orders of magnitude. We demonstrate our method using polystyrene beads of known refractive index value and live cells.

The radiative transport equation (RTE) is used widely to describe the propagation of multiply scattered light in disordered media. In this tutorial, we present two derivations of the RTE for scalar wave fields. The first derivation is based on diagrammatic perturbation theory, while the second stems from an asymptotic multiscale expansion. Although the two approaches are quite distinct mathematically, some common ground can be found and is discussed.

The iridescence of the blue feathers of the Formosan blue magpie (Urocissacaerulea) is not conspicuous when the viewing angle is less than 40°. The spongy medullary keratin inside the feather barbs is investigated by two-dimensional Fourier analysis of transmission electron microscopic images of various positions on a barb to explain this unique characteristic. The orientation of the quasi-ordered nanostructure varies depending on its position of the feather barb. The predicted reflectance increases with the distance of the nanostructures from the vertex of the feather barb, and this result agrees closely with measurements.

Metamaterials with hyperbolic dispersion based on metallic nanorod arrays provide a flexible platform for the design of bio- and chemical sensors and nonlinear devices, allowing the incorporation of functional materials into and onto the plasmonic metamaterial. Here, we have investigated, both analytically and numerically, the dependence of the optical response of these metamaterials on refractive index variations in commonly used experimental sensing configurations, including transmission, reflection, and total internal reflection. The strategy for maximising refractive index sensitivity for different configurations has been considered, taking into account contributions from the superstrate, embedding matrix, and the metal itself. It is shown that the sensitivity to the refractive index variations of the host medium is at least 2 orders of magnitude higher than to the ones originating from the superstrate. It is also shown that the refractive index sensitivity increases for higher-order unbound and leaky modes of the metamaterial sensor. The impact of the transducer's thickness was also analysed showing significant increase of the sensitivity for the thinner metamaterial layers (down to few 0.01 fraction of wavelength and, thus, requiring less analyte) as long as modes are supported by the structure. In certain configurations, both TE and TM-modes of the metamaterial transducer have comparable sensitivities. The results provide the basis for the design of new ultrasensitive chemical and biosensors outperforming both surface plasmon polaritons and localised surface plasmons based transducers.

A real-time microscopic profilometry system based on digital fringe projection and parallel programming has been developed and experimentally tested. Structured light patterns are projected onto an object through one pathway of a stereoscopic operation microscope. The patterns are deformed by the shape of the object and are then recorded with a high-speed CCD camera placed in the other pathway of the microscope. As the optical pathways of both arms are separated and reach the same object point at a relative angle, the recorded patterns allow the full-field object height variations to be calculated and the three-dimensional shape to be reconstructed by employing standard triangulation techniques. Applying proper hardware triggering, the projector-camera system is synchronized to capture up to 120 unique deformed line patterns per second. Using standard four-step phase-shifting profilometry techniques and applying graphics processing unit programming for fast phase wrapping, scaling, and visualization, we demonstrate the capability of the proposed system to generate 30 microscopic height maps per second. This allows the qualitative depth perception of the stereomicroscope operator to be enhanced by live quantitative height measurements with depth resolutions in the micrometer range. (C) 2015 Optical Society of America

A full-vectorial H-field formulation-based finite element approach is used to optimize a biosensor structure incorporating a horizontal slot waveguide. It is designed to detect DNA hybridization through the change of the effective index of the waveguide structure. The key parameters, such as normalized power confinement, power density, change in effective index, and sensitivity are presented by optimizing the device parameters of the slot waveguide. It is shown here that a 90.0 μm long compact Mach-Zehnder section can be designed with horizontal slot waveguide to detect DNA hybridization and for a ring resonator arrangement a sensitivity of 893.5 nm/RIU is obtained.