Perovskite Lanthanum-Doped Barium Stannate: A Refractory Near-Zero-Index Material for High-Temperature Energy Harvesting Systems.

The recent interests in bridging intriguing optical phenomena and thermal energy management has led to the demonstration of controlling thermal radiation with epsilon-near-zero (ENZ) and the related near-zero-index (NZI) optical media. In particular, the manipulation of thermal emission using phononic ENZ and NZI materials has shown promise in mid-infrared radiative cooling systems operating under low-temperature environments (below 100 °C). However, the absence of NZI materials capable of withstanding high temperatures has limited the spectral extension of these advanced technologies to the near-infrared (NIR) regime.

Controlling of lattice strains for crack-free and strong ferroelectric barium titanate films by post-thermal treatment.

In this study, we experimentally demonstrate fabrication of ultra-smooth and crystalline barium titanate (BTO) films on magnesium oxide (MgO) substrates by engineering lattice strain and crystal structure via thermal treatment. We observe that oxygen-depleted deposition allows growth of highly strained BTO films on MgO substrates with crack-free surface. In addition, post-thermal treatment relaxes strain, resulting in an enhancement of ferroelectricity.

Lead-Sealed Stretchable Underwater Perovskite-Based Optoelectronics Self-Recovering Polymeric Nanomaterials.

To harness the full potential of halide perovskite based optoelectronics, biological safety, compatibility with flexible/stretchable platforms, and operational stability must be guaranteed. Despite substantial efforts, none has come close to providing a solution that encompasses all of these requirements. To address these issues, we devise a multifunctional encapsulation scheme utilizing hydrogen bond-based self-recovering polymeric nanomaterials as an alternative for conventional glass-based encapsulation.

Effects of ion clustering and excited state absorption on the performance of Ho-doped fiber lasers.

The effects of ion clustering and excited state absorption occurring in holmium-doped fiber lasers are investigated experimentally and theoretically. It is found that the slope efficiencies of holmium-doped fiber lasers are reduced by inhomogeneous upconversion associated with the clustering of Ho ions. Via theoretical analysis based upon Judd-Ofelt theory, it is also found that the effect of excited state absorption on the performance of Ho-doped fiber lasers is negligible, a fact indicating that ion clustering is the dominant cause of the lower-than-expected slope efficiencies observed in holmium-doped fiber lasers.

Long-distance transmission of broadband near-infrared light guided by a semi-disordered 2D array of metal nanoparticles.

Near-infrared (NIR) waveguides are a key component of planar photonic devices such as optical communication couplers, image sensors, and spectroscopes for chemical or biological molecules. Conventional NIR waveguides used for signal transmission include silicon-on-insulator (SOI) waveguides and channel/ridge-type metal micro-strips. However, these waveguides usually have limitations of either signal delay or signal loss in optically integrated devices.

All-fiber Tm-doped soliton laser oscillator with 6 nJ pulse energy based on evanescent field interaction with monoloayer graphene saturable absorber.

We demonstrate an all-fiber Tm-doped soliton laser with high power by using a monolayer graphene saturable absorber (SA). Large area, uniform monolayer graphene was transferred to the surface of the side-polished fiber (SPF) to realize an in-line graphene SA that operates around 2 μm wavelength. To increase the nonlinear interaction with graphene, we applied an over-cladding onto the SPF, where enhanced optical absorption at monolayer graphene was observed.

Brillouin optical correlation domain analysis with more than 1 million effective sensing points based on differential measurement.

Large increase of effective sensing points in Brillouin optical correlation domain analysis (BOCDA) is achieved by simultaneously applying double modulation and optical time gate based on differential measurement scheme. The noise substructure of Brillouin gain spectrum induced by the double modulation is effectively suppressed by the differential measurement, leading to 2,000 times enlargement of the measurement range. Distributed strain and temperature sensing along a 10.

Design of broadband multilayer dichroic coating for a high-efficiency solar energy harvesting system.

We report on the design and performance of a broadband dichroic coating for a solar energy conversion system. As a spectral beam splitter, the coating facilitates a hybrid system that combines a photovoltaic cell with a thermal collector. When positioned at a 45° angle with respect to incident light, the coating provides high reflectance in the 40-1100 nm and high transmission in the 1200-2000 nm ranges for a photovoltaic cell and a thermal collector, respectively.

Broadband supercontinuum generation using a hollow optical fiber filled with copper-ion-modified DNA.

We experimentally demonstrated supercontinuum generation through a hollow core photonic bandgap fiber (HC-PBGF) filled with DNA nanocrystals modified by copper ions in a solution. Both double-crossover nano DNA structure and copper-ion-modified structure provided a sufficiently high optical nonlinearity within a short length of hollow optical fiber. Adding a higher concentration of copper ion into the DNA nanocrystals, the bandwidth of supercontinuum output was monotonically increased.

Active control of all-fibre graphene devices with electrical gating.

Active manipulation of light in optical fibres has been extensively studied with great interest because of its compatibility with diverse fibre-optic systems. While graphene exhibits a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, electric control of all-fibre graphene devices remains still highly challenging. Here we report electrically manipulable in-line graphene devices by integrating graphene-based field effect transistors on a side-polished fibre.

A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi2Te3 topological insulator.

We experimentally demonstrate a femtosecond mode-locked, all-fiberized laser that operates in the 2 μm region and that incorporates a saturable absorber based on a bulk-structured bismuth telluride (Bi(2)Te(3)) topological insulator (TI). Our fiberized saturable absorber was prepared by depositing a mechanically exfoliated, ~30 μm-thick Bi(2)Te(3) TI layer on a side-polished optical fiber platform. The bulk crystalline structure of the prepared Bi(2)Te(3) layer was confirmed by Raman and X-ray photoelectron spectroscopy measurements.

Linearly configured BOCDA system using a differential measurement scheme.

We experimentally demonstrate a linearly configured Brillouin optical correlation domain analysis (BOCDA) system enhanced by a differential measurement scheme. On-off control of the pump phase modulation with an intentional loss at the end of a fiber under test is applied for the acquisition of a Brillouin gain spectrum. This application leads to a four-fold enhancement of the spatial resolution and doubling of the measurement range in comparison with the former system under the same modulation parameters.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber.

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated.

Differential measurement scheme for Brillouin optical correlation domain analysis.

We newly propose and experimentally demonstrate a differential measurement scheme for Brillouin optical correlation domain analysis, where the difference between Brillouin gain spectra constructed by a normal and a phase-modulated Brillouin pump waves are analyzed to measure local Brillouin frequencies in optical fibers. In experiments, a five-fold enhancement in the spatial resolution is obtained compared to an ordinary BOCDA system under the same modulation parameters, as a result of the improved dynamic range by the suppression of background noises.

Bidirectional measurement for Brillouin optical correlation domain analysis.

We propose and experimentally demonstrate a bidirectional measurement for Brillouin optical correlation domain analysis as a novel and simple way of the performance enhancement. Brillouin gain and loss spectra of two adjacent correlation peaks are simultaneously and independently analyzed by applying midpoint attenuation in a fiber under test, which doubles both the speed and the range of the distributed measurement.

In situ gas sensing using a remotely detectable probe with replaceable insert.

We demonstrate a spectroscopic gas sensor using an optical fiber probe with a replaceable insert. The probe consists of a hollow-core photonic bandgap fiber (HC-PBGF) with a core diameter of 10.9 μm and a glass tube where a 2-μm hollow core fiber (HCF) with a gold coated end facet can be inserted.

Variable-frequency lock-in detection for the suppression of beat noise in Brillouin optical correlation domain analysis.

We propose and experimentally demonstrate a novel lock-in detection method to avoid a beat noise in Brillouin optical correlation domain analysis (BOCDA) which appears in the sweep of the sensing position and deteriorates the measurement accuracy by distorting the acquired Brillouin gain spectrum. In our analysis, the origin of the beat noise is shown to be the fluctuation of the Brillouin gain induced by the chopping of the intensity-modulated pump wave, and the optimal relation between the modulation and the lock-in frequencies is developed as an effective solution to circumvent the beat noise.

Design of waveguide grating with ultrafast tunable index contrast.

A long-period waveguide grating (LPWG) with a tunable index contrast is proposed. The design features a simple configuration that consists of a two-mode waveguide formed on periodically poled lithium niobate with an angle with respect to its domain wall and a traveling-wave electrode. In the design, the electrical traveling wave introduces a periodic change in the refractive index of waveguide, which functions as a long-period waveguide grating that couples between symmetric and anti-symmetric core modes.

High-accuracy measurement of cladding noncircularity based on phase velocity difference between acoustic polarization modes.

A high-accuracy measurement method for the noncircularity (ellipticity) of silica glass fibers is demonstrated. This method makes use of the phase velocity difference between two eigen polarization modes of the lowest-order acoustic flexural wave in an optical fiber. The relationship between the acoustic phase velocity difference and the fiber ellipticity is formulated.

Fabrication of a highly efficient core-mode blocker using a femtosecond laser ablation technique.

We present a method for the fabrication of a highly efficient core-mode blocker based on a laser micromachining technique. The process for the fabrication is as follows. A micron-sized crater is made by irradiation of an ultra-short pulse laser on the end face of a single-mode fiber, and then a defect that acts as a core-mode blocker is formed by splicing the cratered fiber with a normal fiber.

Tunable photonic microwave notch filter using SOA-based single-longitudinal mode, dual-wavelength laser.

A novel photonic microwave notch filter with capability of frequency tuning is proposed and experimentally demonstrated. The scheme is based on a fiber Bragg grating (FBG)-based, single longitudinal mode, wavelength-spacing tunable dual-wavelength fiber laser and a dispersive fiber delay line. By using a symmetrical S-bending technique along the FBGs, the wavelength spacing of the laser can be tuned, which enables the microwave notch frequency tuning.

Tunable optical delays based on Brillouin dynamic grating in optical fibers.

We demonstrate a novel kind of tunable optical delays based on dynamic grating generated by Brillouin scattering in an optical fiber. An axial strain gradient is applied to a 15 m section of a polarizationmaintaining fiber, and the Brillouin reflection grating is generated position-selectively by controlling the optical frequencies of Brillouin pump waves. Tunable time delays of up to 132 ns are achieved with an 82 ns Gaussian pulse.

Tunable dispersion slope compensator using two uniform fiber Bragg gratings mounted on S-shape plate.

We propose and experimentally demonstrate a novel method for tunable dispersion slope compensation. We use two uniform fiber Bragg gratings (FBGs), a spatially designed S-bending stage and 4-port circulator. Two FBGs are mounted on each surface of a metal plate along the calculated quadratic curve.

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.

Control of hollow-core photonic bandgap fiber ellipticity by induced lateral tension.

We describe the fabrication of elliptical hollow-core photonic bandgap fibers (EC-PBGFs). It was shown that the aspect ratio of the hollow core can be controlled by tuning the negative pressure in the space between the intermediate preform cane and outer jacketing tube, and by placing this preform assembly off-center in the furnace, resulting in lateral tension during the final draw. Modal birefringences of fabricated PBGFs with different aspect ratio were measured using a Sagnac loop interferometer.