Chromophoric cerium oxide nanoparticle-loaded sucking disk-type strip sensor for optical measurement of glucose in tear fluid.

BACKGROUND: Noninvasive monitoring of tear glucose levels can be convenient for patients to manage their diabetes mellitus. However, there are issues with monitoring tear glucose levels, such as the invasiveness of some methods, the miniaturization, inaccuracy, or the high cost of wearable devices. To overcome the issues, we newly designed a sucking disk-type (SD) strip biosensor that can quickly suck tear fluid and contains cerium oxide nanoparticle (CNP) that causes a unique color change according to the glucose level of the tear without complicated electronic components. METHODS: The SD strip biosensor composed of three distinct parts (tip, channel, and reaction chamber) was designed to contain the sensing paper, onto which tear fluid can be collected and delivered. The sensing paper treated with CNP/APTS (aminopropyltriethoxysilane) /GOx (glucose oxidase) was characterized. Then we carried out the reliability of the SD strip biosensor in the diabetic rabbit animals. We quantitatively analyzed the color values of the SD strip biosensor through the colorimetric analysis algorithm. RESULTS: We contacted the inferior palpebral conjunctiva (IPC) of a diabetic rabbit eye using an SD strip biosensor to collect tears without eye irritation and successfully verified the performance and quantitative efficacy of the sensor. An image processing algorithm that can optimize measurement accuracy is developed for accurate color change measurement of SD strip biosensors. The validation tests show a good correlation between glucose concentrations measured in the tear and blood. CONCLUSION: Our findings demonstrate that the CNP-embedded SD strip biosensor and the associated image processing can simply monitor tear glucose to manage diabetes mellitus.

Relative Humidity Sensors Based on Microfiber Knot Resonators-A Review.

Recent research and development progress of relative humidity sensors using microfiber knot resonators (MKRs) are reviewed by considering the physical parameters of the MKR and coating materials sensitive to improve the relative humidity sensitivity. The fabrication method of the MKR based on silica or polymer is briefly described. The many advantages of the MKR such as strong evanescent field, a high Q-factor, compact size, and high sensitivity can provide a great diversity of sensing applications. The relative humidity sensitivity of the MKR is enhanced by concerning the physical parameters of the MKR, including the waist or knot diameter, sensitive materials, and Vernier effect. Many techniques for depositing the sensitive materials on the MKR surface are discussed. The adsorption effects of water vapor molecules on variations in the resonant wavelength and the transmission output of the MKR are described regarding the materials sensitive to relative humidity. The sensing performance of the MKR-based relative humidity sensors is discussed, including sensitivity, resolution, and response time.

Fiber-bundle illumination: realizing high-degree time-multiplexed multifocal multiphoton microscopy with simplicity.

High-degree time-multiplexed multifocal multiphoton microscopy was expected to provide a facile path to scanningless optical-sectioning and the fast imaging of dynamic three-dimensional biological systems. However, physical constraints on typical time multiplexing devices, arising from diffraction in the free-space propagation of light waves, lead to significant manufacturing difficulties and have prevented the experimental realization of high-degree time multiplexing. To resolve this issue, we have developed a novel method using optical fiber bundles of various lengths to confine the diffraction of propagating light waves and to create a time multiplexing effect. Through this method, we experimentally demonstrate the highest degree of time multiplexing ever achieved in multifocal multiphoton microscopy (~50 times larger than conventional approaches), and hence the potential of using simply-manufactured devices for scanningless optical sectioning of biological systems.

Three-dimensional visualization system for ophthalmic microscopes using visible light and near-infrared illumination.

In this paper, we describe a three-dimensional visualization system for ophthalmic microscopes that is aimed at microsurgery without the eyepieces. A three-dimensional visualization system for ophthalmic microscopes using the mixed illumination, which consists of visible light and near-infrared illumination, is established in order to acquire more exact information of object and reduce the amount of light irradiated to the patients, and its usage in microsurgery without eyepieces is herein described. A custom-designed stereoscopic three-dimensional display which is manufactured for the convenience of the surgeons during the long-time surgery, is connected directly to the camera of the ophthalmic microscope in order to eliminate the discomfort of eyepieces to the surgeon and signal delay between the camera, mounted on the microscope, and display device for surgeon. The main features of the established system are the signal delay-free for surgeon and the low level of illumination for patient. In particular, it could significantly reduce the amount of light irradiated on a patient's eye via NIR illumination. Upon comparison with the conventional system during clinical ophthalmology trials, this system is confirmed to require almost the same operation time and reduced discomfort and eyestrain during long periods of observation.

Investigation of Temperature Sensitivity of a Polymer-Overlaid Microfiber Mach-Zehnder Interferometer.

The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical microfiber with a strong evanescent field into the MZI, a low index polymer with high thermal characteristics is deposited on the surface of the microfibers to realize a polymer-overlaid microfiber MZI. It was found that the thermal expansion factor in the proposed MZI plays an important role in the temperature sensitivity of the FSR. The temperature sensitivity of the polymer-overlaid microfiber MZI is improved, which is measured to be -8.29 nm/°C at 25 °C. The optical transmission spectrum of the polymer-overlaid microfiber MZI is converted to the spatial frequency spectrum via fast Fourier transform. The temperature sensitivity of the spatial frequency in the proposed polymer-overlaid MZI is estimated to be 18.31 pm-1 °C-1, which is 17 times higher than that of the microfiber MZI without polymer coating (1.04 pm-1 °C-1).

Investigation on Periodically Surface-Corrugated Long-Period Gratings Inscribed on Photonic Crystal Fibers.

Transmission characteristics of periodically surface-corrugated long-period gratings (LPGs) inscribed on photonic crystal fibers (PCFs) using a wet-etching technique were experimentally investigated. A conventional wet method was implemented to periodically engrave the silica cladding region of the PCFs resulting in the periodic surface corrugation in the PCF. After applying the external strain to the PCF with the periodic surface micro-ridges, periodic modulation of refractive index based on the photoelastic effect is induced resulting in the formation of the PCF-based LPG. Increasing the applied strain successfully improves the extinction ratio of the resonant peak of the PCF-based LPG without the resonant wavelength shift. We also measured the transmission characteristics of the PCF-based LPG with variations in temperature and ambient index.

In-line interferometer based on intermodal coupling of a multicore fiber.

An in-line interferometer based on the intermodal coupling of a multicore fiber (MCF) is proposed and experimentally demonstrated. The in-line interferometer is fabricated by adiabatically tapering the MCF. The intermodal coupling of the in-line interferometer is strongly affected by the waist diameter of the MCF, which changes the evanescent field and the pitch size. The effect of the waist diameters of the MCF on the intermodal coupling in the in-line interferometer is theoretically and experimentally investigated. The transmission oscillations of the multiple core modes resulting from the intermodal coupling and interference substantially become stronger as the waist diameter decreases. The extinction ratio and the oscillation periodicity of the transmissions oscillations are changed by the waist diameter.

Influence of the waist diameters on transmission characteristics and strain sensitivity of microtapered long-period fiber gratings.

Transmission characteristics of microtapered long-period fiber gratings (MTLPGs) and their strain and temperature sensitivities with variations in the waist diameters are investigated theoretically and experimentally. Transmission characteristics of MTLPGs strongly depend on the waist diameter of the tapered optical fiber (TOF) because of the modification of the effective index difference between the core and the cladding modes. Based on the photoelastic effect, the resonant wavelengths of MTLPGs with variations in strain shift to shorter wavelengths. The strain sensitivity of the MTLPG with a waist diameter of 25 µm is improved by a factor of 20 compared with that of a 125 µm long-period fiber grating. The temperature sensitivities of MTLPGs are also enhanced by reducing the waist diameter of the TOF.

Long distance fiber Bragg grating strain sensor interrogation using a high speed Raman-based Fourier domain mode-locked fiber laser with recycled residual Raman pump.

We propose a novel fiber Bragg grating (FBG) sensor interrogation using a Raman-based Fourier-domain mode locking (FDML) fiber laser for a high speed and long distance measurement. A residual Raman pump after the generation of the Raman-based FDML fiber laser is recycled for secondary signal amplification in a 2-m erbium-doped fiber (EDF) to further enhance the output power. The chromatic dispersion is precisely controlled to suppress the phase noise in the FDML laser cavity, resulting in the improvement of an R-number of 1.43 mm/dB. After recycling residual pump, we achieve the 40-km round trip transmission of the sensing probe signal with a high scan rate of 30.8 kHz. With 205-mW residual pump power, the bandwidth and the maximum gain are measured to be more than 50 nm, 10.3 dB at 1550 nm, respectively. The sensitivity of the proposed Raman-based FDML fiber laser to strain is also measured, which are 0.81 pm/µstrain in the spectral domain and 0.19 ns/µstrain in the time domain, respectively.

Imprinted bidirectional waveguide platform for large-core optical transceiver.

We introduce a new configuration for large-core optical transceiver platforms based on asymmetric three-dimensional multimode Y junctions. We developed a simply structured bidirectional waveguide platform without using a wavelength division multiplexing filter or angled mirror. This structure was designed with two different size waveguides by using the three-dimensional ray-tracing method. This structure transmitted nearly 100% power in each direction, upstream and downstream. This simple and cost-effective structure was fabricated by the imprint process using a metallic master fabricated by an ultraprecision machining method. The experimental results show that this structure is suitable for bidirectional communications in large-core optical transceivers at 155 Mbits/s.

Substrate geometry-dependent nonlinear absorption of carbon nanotubes deposited onto D-shaped optical fibers.

The effect of single-wall carbon nanotubes (SWNTs) on nonlinear optical absorption of D-shaped fibers with versatile the remaining length of the cladding region and the interaction length are investigated. The optical absorption based on SWNTs is induced by the energy bandgap in SWNTs. The bandgap energy depends on the tube diameter of SWNTs. After fabricating versatile D-shaped fiber, SWNTs are deposited on the polished surface of D-shaped fibers. The cladding region of single mode fibers is removed by a side-polishing technique and the D-shaped fiber is obtained. In the D-shaped fiber, the cladding region is thin enough to induce the evanescent field coupling of core mode to the other modes of the SWNT-overlay. The nonlinear absorption based on the SWNTs-overlay is changed by the remaining length of cladding region and the interaction length because the coupling strength of evanescent field strongly depends on the different remaining lengths of the cladding region and the interaction lengths as well.

Temperature and strain discrimination based on a temperature-insensitive birefringent interferometer incorporating an erbium-doped fiber.

A simple configuration for simultaneous measurement of temperature and strain exploiting a temperature-insensitive birefringent interferometer based on a photonic crystal fiber incorporating an erbium-doped fiber (EDF) is investigated. The transmission peak power of the birefringent interferometer incorporating the EDF is changed by the temperature variation because the amplified spontaneous emission of the EDF strongly depends on temperature. The applied strain changes the peak wavelength of the birefringent interferometer connecting with the EDF, which can make it possible to discriminate concurrent sensitivities like temperature and strain. The temperature and strain sensitivities were -0.04 dB/ degrees C and 1.3 pm/microepsilon, respectively.

Sensitive DNA biosensor based on a long-period grating formed on the side-polished fiber surface.

We demonstrate a sensitive DNA biosensor based on a long period grating (LPG) formed by a photolithograph process on the surface of a side-polished fiber. The biomolecules of the biosensor were immobilized on the silica surface between LPG patterns. The resonance wavelength was red-shifted after the binding of the poly-L-lysine, probe ssDNA and target ssDNA to the sensor surface. The overall wavelength shift after the successful DNA hybridization was 1.82 nm. The proposed LPG-based DNA biosensor is approximately 2.5 times more sensitive than the previously reported fiber grating-based DNA biosensors.

Strain and temperature sensitivities of an elliptical hollow-core photonic bandgap fiber based on Sagnac interferometer.

We fabricated an elliptical hollow-core photonic bandgap fiber (EC-PBGF) by controlling lateral tension in the hollow core region during the fiber drawing process. The absolute value of group modal birefringence becomes relatively high near the bandgap boundaries. We also experimentally measured the strain and temperature sensitivities of the fabricated EC-PBGF-based Sagnac loop interferometer. The strain and temperature sensitivities were very much dependent upon the wavelength. Moreover this PBGF-based interferometer can be a good sensor of physical parameters such as strain and temperature.

Voltage-tuned multiwavelength Raman ring laser with high tunability based on a single fiber Bragg grating.

A practical scheme for a tunable multiwavelength Raman fiber ring laser based on a single fiber Bragg grating with a voltage-controllable coil heater is investigated. The number of phase-shifted regions within a single fiber grating determines the number of reflection peaks and the number of lasing wavelengths in the multiwavelength Raman fiber ring laser. A stable multiwavelength Raman fiber ring laser with low output peak-power fluctuation of less than 0.5 dB at room temperature is achieved. A multiwavelength Raman fiber ring laser with a high extinction ratio of more than 50 dB is realized. High flatness is obtained for three lasing peaks, and the lasing peak-power difference is measured to be less than 0.2 dB. A voltage-controllable coil heater with heating elements is used to effectively control three lasing wavelengths in the multiwavelength output, and the tunability of each lasing wavelength is measured to be 0.11 nm/V.

Switchable multiwavelength erbium doped fiber laser based on a nonlinear optical loop mirror incorporating multiple fiber Bragg gratings.

We propose and experimentally demonstrate a switchable multiwavelength erbium doped fiber laser based on a highly nonlinear dispersion shifted fiber and multiple fiber Bragg gratings. A nonlinear optical loop mirror based on a highly nonlinear dispersion shifted fiber is implemented in the ring laser cavity to stabilize the multiwavelength output at room temperature. Multiple fiber Bragg gratings with the wavelength spacing of 0.8 nm are connected with an arrayed waveguide grating to establish a multichannel filter. The high quality of the multiwavelength output with a high extinction ratio of ~60 dB and high output flatness of ~0.5 dB is realized. The nonlinear polarization rotation based on the nonlinear optical loop mirror can provide the switching performance of the proposed multiwavelength fiber laser. The lasing wavelength can be switched individually by controlling the polarization controller and the cavity loss.

Fast-interleaving of dual-wavelength fiber ring laser using switchable fiber Bragg gratings.

We propose a novel lasing wavelength-switchable fiber ring laser based on the gain competition between two nearby band-pass wavelengths in a homogeneously broadened erbium-doped fiber gain. The cascaded two band-pass filters are demonstrated with fiber Sagnac loop interferometers including fiber Bragg gratings and polarization controllers. The fast electro-optic interleaving operation of dual-wavelength lasing outputs can be achieved by modulating the polarization state of one band-pass filter.

Simultaneous independent measurement of strain and temperature based on long-period fiber gratings inscribed in holey fibers depending on air-hole size.

We propose and experimentally demonstrate a simple and flexible scheme for the simultaneous measurement of strain and temperature using long-period fiber gratings (LPFGs) based on versatile holey fibers (HFs) with different air-hole sizes. The strongly resonant LPFGs (as much as approximately 24 dB) can be successfully achieved. The LPFGs inscribed in the HFs have similar temperature sensitivities regardless of air-hole size because of the same material composition. The strain sensitivities of the LPFGs, however, are different, since holey fibers have different cross-sectional areas depending on the air-hole size. The strain sensitivities of the HF-based LPFGs are enhanced by a factor larger than 2 as the air-hole size increases.

Fully reconfigurable photonic microwave transversal filter based on digital micromirror device and continuous-wave, incoherent supercontinuum source.

The combined use of a programmable, digital micromirror device (DMD) and an ultrabroadband, cw, incoherent supercontinuum (SC) source is experimentally demonstrated to fully explore various aspects on the reconfiguration of a microwave filter transfer function by creating a range of multiwavelength optical filter shapes. Owing to both the unique characteristic of the DMD that an arbitrary optical filter shape can be readily produced and the ultrabroad bandwidth of the cw SC source that is 3 times larger than that of Er-amplified spontaneous emission, a multiwavelength optical beam pattern can be generated with a large number of wavelength filter taps apodized by an arbitrary amplitude window. Therefore various types of high-quality microwave filter can be readily achieved through the spectrum slicing-based photonic microwave transversal filter scheme. The experimental demonstration is performed in three aspects: the tuning of a filter resonance bandwidth at a fixed resonance frequency, filter resonance frequency tuning at a fixed resonance frequency, and flexible microwave filter shape reconstruction.

Multiple-element photonic microwave true-time-delay beamforming incorporating a tunable chirped fiber Bragg grating with symmetrical bending technique.

We experimentally demonstrate a novel scheme for a multiple-element photonic microwave true-time-delay device with high tunability based on a tunable chirped fiber Bragg grating without center wavelength shift. We achieve the different true time delay by controlling the grating period of a chirped fiber Bragg grating based on the symmetrical bending technique as a multiwavelength signal source is applied to carry microwave signals. The proposed method does not require the complex structure of systems, wavelength tuning, and synchronization of optical devices such as tunable bandpass filters and optical input signals. We achieve the tunabilty of the time delay for a microwave signal carried over an optical signal in a range from 1 to 230 ps.