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Abstract

We present the performance analysis and specifications of a portable auto-phoropter system that can be employed for fast refractive assessment of a large population. A customized Shack–Hartmann wavefront sensor is developed to accurately measure the defocus and astigmatism of the eye within ±10D and ±6D, respectively. Three fluidic lenses are designed to correct the vision in real time. A digital Snellen chart is integrated into the system to validate the accuracy of the measurement and the correction by means of achieving 20/20 vision. The refractive error of eight subjects (16 eyes) has been measured objectively (without patient’s feedback) using the proposed system and the results are compared with their clinical prescription through the Bland–Altman method. It is shown that the auto-phoropter takes less than 8 s to measure and correct the eye refractive error with an accuracy of ±0.25D.

Tunable spherical fluidic lenses are among the most essential components in adaptive optics. However, fabricating cylindrical tunable lenses has proven more challenging, mainly due to the difficulty in eliminating the defocus component. We demonstrate a parametric approach to minimize the defocus in cylindrical tunable fluidic lenses. We theoretically model and experimentally verify that a dog-bone-shaped tunable cylindrical fluidic lens exhibits almost pure cylindrical performance within the range of ${\pm{\rm 5D}}$ of astigmatism. We anticipate these results will facilitate the use of tunable cylindrical fluidic lenses in adaptive optics applications and particularly ophthalmic devices, where rapid and reliable wavefront correction is required.

Magneto-optical properties of tellurium-arsenic-selenium glass (${{\rm Te}_{20}}{{\rm As}_{30}}{{\rm Se}_{50}}$Te_20As_30Se_50) were measured and analyzed. A Verdet constant of 15.18 rad/T/m at 1950 nm with the figure of merit of more than 8.72 rad/T, which is the highest value reported in glass materials at this wavelength, was measured. Compared to other chalcogenide glasses, such as ${{\rm Ge}_{10}}{{\rm Se}_{90}}$Ge_10Se_90 and ${{\rm Ge}_{25}}{{\rm As}_{15}}{{\rm S}_{60}}$Ge_25As_15S_60, ${{\rm Te}_{20}}{{\rm As}_{30}}{{\rm Se}_{50}}$Te_20As_30Se_50 glass exhibits higher Verdet constants, broader mid-infrared transparency window, and longer infrared absorption edge, making it a very promising material to fabricate magneto-optical devices for mid-infrared applications.

We present the design, implementation and performance analysis of a compact multi-photon endoscope based on a piezo electric scanning tube. A miniature objective lens with a long working distance and a high numerical aperture (≈ 0.5) is designed to provide a diffraction limited spot size. Furthermore, a 1700 nm wavelength femtosecond fiber laser is used as an excitation source to overcome the scattering of biological tissues and reduce water absorption. Therefore, the novel optical system along with the unique wavelength allows us to increase the imaging depth. We demonstrate that the endoscope is capable of performing third and second harmonic generation (THG/SHG) and three-photon excitation fluorescence (3PEF) imaging over a large field of view (> 400 μm) with high lateral resolution (2.2 μm). The compact and lightweight probe design makes it suitable for minimally-invasive in-vivo imaging as a potential alternative to surgical biopsies.

A 10 W level 976 nm single-frequency linearly polarized laser source was demonstrated with a two-stage all-fiber amplifier configuration. The continuous-wave output power of 10.1 W was obtained from the second stage amplifier by using a 20/130 μm single-mode, polarization maintaining, 1.5 wt. % ytterbium-doped phosphate double-clad fiber. This all-fiber single-frequency laser source is very promising for watt-level deep ultraviolet laser generation via frequency quadrupling.

An all-fiber amplifier for a single-frequency blue laser was demonstrated for the first time, to the best of our knowledge. Over 150 mW continuous-wave single-transverse-mode blue laser output was obtained with a 10 m 1000 ppm thulium-doped fluoride fiber pumped by a 1125 nm fiber laser at a power of 2 W. The output power was limited due to the onset of the competitive lasing at 783 nm. Photodarkening and photo-curing of the thulium-doped fiber amplifier were also studied and analyzed.

Enormous performance gains have been made in fluoride-based fiber lasers operating around 3 μm due to advances in fiber fabrication and improvements in high-power pump diode technologies during the last decade. Pulsed fluoride fiber lasers capable of producing high-energy/high-peak power mid-infrared pulses are of significant interest for a variety of applications. Q-switched and mode-locked fiber lasers have been demonstrated with various techniques in recent years. In this paper, pulsed Er^3+- and Ho^3+-doped ZBLAN (ZrF_4-BaF_2-LaF_3-AlF_3-NaF) fiber lasers are reviewed, and our achievement of pulsed fiber laser sources at 3 μm is presented. Power/energy scaling of pulsed ZBLAN fiber lasers and their potential applications are discussed.

Single-frequency fiber lasers have drawn intense attention for their extensive applications from high-resolution spectroscopy and gravitational wave detection to materials processing due to the outstanding properties of low noise, narrow linewidth, and the resulting long coherence length. In this paper, the recent advances of single-frequency fiber oscillators and amplifiers are briefly reviewed in the broad wavelength region of 1–3 μm. Performance improvements in laser noise and linewidth are addressed with the newly developed physical mechanisms. The solution to achieving higher power/energy is also discussed, accompanied by the start-of-the-art results achieved to date.

We show both experimentally and theoretically a method to increase the stimulated Brillouin scattering (SBS) threshold and output power of narrow linewidth fiber Raman amplifiers. This method employs two or more fibers with varying concentrations of the Raman gain material dopant such as GeO_2 or P_2O_5 in silicate-based glasses. These fibers are then cascaded to form an amplifier gain stage, disrupting the buildup of SBS that normally occurs in single continuous fibers. The numerical model shown is applicable to arbitrary amplifier systems for gain stage optimization and increased power scaling. We give experimental results for phosphosilicate fibers that agree well with simulation predictions that support the numerical model used.

Optical fibres having a radially nonuniform acoustically antiguiding structure produced by codoping their core with alumina and germania have been fabricated and investigated. The influence of the shape of the antiguiding acoustic refractive index profile and fibre core diameter on the stimulated Brillouin scattering (SBS) threshold and spectrum in the fibres has been assessed. An increase in SBS threshold by 4.4 dB with respect to a germanosilicate fibre having the same mode field diameter has been demonstrated.

We report a high-power synchronously pumped femtosecond Raman fiber laser operating in the normal dispersion regime. The Raman laser is pumped by a picosecond Yb^3+-doped fiber laser. It produces highly chirped pulses with energy up to 18 nJ, average power of 0.76 W and 88% efficiency. The pulse duration is measured to be 147 fs after external compression. We observed two different regimes of operation of the laser: coherent and noise-like regime. Both regimes were experimentally characterized. Numerical simulations are in a good agreement with experimental results.

We present the design and operation of an all-fiber, synchronously pumped, bidirectional optical parametric oscillator (OPO) for precision sensing applications. The fiber-based OPO (FOPO) generates two frequency combs with identical repetition rates but different carrier offset frequencies. A narrow beatnote was observed with full-width at half-maximum (FWHM) linewidth of <10  Hz when the two frequency combs were overlapped on a photodetector. The all-fiber design removes the need for free-space alignment and adjustment. In addition, an external delay line to overlap the two pulse trains in time on the detector is not needed since our unique design provides automatic delay compensation. We expect the novel FOPO to find important applications in precision measurements including rotation sensing with ultra-large sensing area and sensitivity.

We report Q-switched pulse operation of holmium (Ho^3+)-doped ZrF_4-BaF_2-LaF_3-AlF_3-NaF (ZBLAN) at ∼1190  nm in an all-fiber ring laser by using a fiber-optic graphene saturable absorber, which was fabricated by depositing graphene onto the flat surface of a side-polished D-shaped fiber. Stable Q-switched operation was established at a pump power of 180 mW with a repetition rate of 24 kHz and pulse width of 5.7 μs. When the pump power was increased to 1125 mW, 0.44 μJ Q-switched pulses with a repetition rate of 111 kHz and a pulse width of 0.8 μs were generated.

Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

We propose and demonstrate a 5-cm-long monolithic dual-wavelength single-longitudinal mode distributed Bragg reflector (DBR) all-phosphate fiber laser. Strong UV-induced fiber Bragg gratings are directly written in highly Er/Yb codoped phosphate fiber. The separation between gratings is selected as 1 cm to only excite two longitudinal modes in the DBR cavity. By exploiting the spatial hole burning effect and the polarization hole burning effect, stable narrow-linewidth dual-wavelength lasing emission with 38 pm wavelength spacing and a total emitted power of 2.8 mW is obtained from this DBR fiber laser. A microwave signal at 4.58 GHz is generated by the heterodyne detection of the dual-wavelength laser.

In-band core-pumped Ho^3+-doped ZBLAN fiber lasers at the 1.2 μm region were investigated with different gain fiber lengths. A 2.4 W 1190 nm all-fiber laser with a slope efficiency of 42% was achieved by using a 10 cm long gain fiber pumped at a maximum available 1150 nm pump power of 5.9 W. A 1178 nm all-fiber laser was demonstrated with an output power of 350 mW and a slope efficiency of 6.5%. High Ho^3+ doping in ZBLAN is shown to be effective in producing single-frequency fiber lasers and short-length fiber amplifiers immune from stimulated Brillouin scattering.

We report a new characterization technique of Raman gain materials through inverse Raman scattering (IRS). The technique is applied to silica glass optical fiber and several liquids in liquid-core optical fiber (LCOF). We obtain good quantitative agreement with a conventional technique that estimates the gain coefficient from steady-state Raman scattering measurements. Our results demonstrate that IRS is a viable tool to characterize new materials for ultralow-power nonlinear optics and all-optical switching.

We demonstrate label-free multi-photon imaging of biological samples using a compact Er^3+-doped femtosecond fiber laser mode-locked by a single-walled carbon nanotube (CNT). These compact and low cost lasers have been developed by various groups but they have not been exploited for multiphoton microscopy. Here, it is shown that various multiphoton imaging modalities (e.g. second harmonic generation (SHG), third harmonic generation (THG), two-photon excitation fluorescence (TPEF), and three-photon excitation fluorescence (3PEF)) can be effectively performed on various biological samples using a compact handheld CNT mode-locked femtosecond fiber laser operating in the telecommunication window near 1560nm. We also show for the first time that chlorophyll fluorescence in plant leaves and diatoms can be observed using 1560nm laser excitation via three-photon absorption.

We propose and demonstrate a synchronously pumped fiber optical parametric oscillator (FOPO) operating in the normal dispersion regime. The FOPO generates chirped pulses at the output, allowing significant pulse energy scaling potential without pulse breaking. The output average power of the FOPO at 1600 nm was ∼60  mW (corresponding to 1.45 nJ pulse energy and ∼55% slope power conversion efficiency). The output pulses directly from the FOPO were highly chirped (∼3  ps duration), and they could be compressed outside of the cavity to 180 fs by using a standard optical fiber compressor. Detailed numerical simulation was also performed to understand the pulse evolution dynamics around the laser cavity. We believe that the proposed design concept is useful for scaling up the pulse energy in the FOPO using different pumping wavelengths.

We report a diode-pumped 2.78 μm Er^3+-doped ZBLAN fiber laser passively Q switched by a graphene saturable absorber, which was directly deposited onto a fiber dichroic mirror by the method of optically driven deposition. Stable Q-switched operation with a pulse duration of 2.9 μs and a pulse energy of 1.67 μJ was achieved in a 10 m long gain fiber. The pulse duration was reduced to 1 μs when the gain fiber length was shortened to 2 m. This Letter demonstrates that graphene is a promising and reliable saturable absorber for mid-infrared pulse generation at 3 μm.

A versatile and powerful new method has been developed that enables the lithographic fabrication of nano‐architectured ordered 2D metal and metal‐oxide electrodes. Optical band gap, electronic carrier concentrations and resistivity of these highly transparent electrodes can be tuned by simply changing the dimensions of the unit nanostructures. Fabrication, electrical and optical properties of indium tin oxide, indium zinc oxide and silver electrodes are discussed.

Ultrafast UV and deep UV (DUV) sources are useful for many industrial applications. We present our research on developing a compact and high power picosecond Yb-fiber source for UV light generation (down to ~ 257 nm wavelength) via single pass second and third harmonics frequency conversion processes. Currently, the laser system delivers 260 mW average power at 343 nm (using THG) and 310 mW at 257 nm (using SHG from 515 nm).

Ag/dielectric/Ag-type plasmonic thermal emitters (PTEs) following a hexagonal lattice were fabricated, and their plasmonic emission spectrums were characterized with Fourier transform infrared spectroscopy. Nanoamorphous carbon (NAC) is used as a dielectric layer. Doping NAC with various materials over a wide range of levels enables control of the resistivity of the composite films where MoSi_2 was selected as the dopant. Wavelength tuning in the range of 4–7μm is demonstrated by changing the conductivity of the composite films as well as the lattice periodicity of the hexagonal lattice. We also tested the mechanical stability of the PTEs under mechanical strains.

We have formulated composites of lead (II) tetrakis (4-cumylphenoxy) phthalocyanine (PbTCPc) doped into nematic liquid crystal (LC), 4^′-pentyl-4-biphenylcarbonitrile (5-CB), that has received a 90° twisted alignment and investigated the nonlinear transmission properties using both pulsed (Nd:YLF 524 nm, 5 ns) and cw (532 nm) lasers. In the nanosecond regime, this compound is a reverse saturable absorber performing similarly to low-concentration solutions of PbTCPc. Under cw conditions, we observe optically self-activated polarization switching with low threshold input energy. Our results suggest the potential for an all-optical switch working from the nanosecond time scale to cw.

We measured transient photoinduced birefringence (δn) in various azobenzene dye films by pumping with a nanosecond pulse at 532 nm and probing at 633 nm. The switch-on times for the photoinduced birefringence range from nanoseconds to milliseconds and are systematically related with the lowest optical transition energies for those films. Moreover, our results suggest that the transient photoinduced birefringence measurement is a convenient way to determine the relative energies of π-π^* and n-π^* states in azo-based materials.

Researchers at the University of Arizona’s College of Optical Sciences and Nitto Denko Technical Corp. have created a rewriteable holographic display that may one day enable 3D holographic film.

A systematic study on a compact, novel phase-locked multicore fiber laser device that is based on a truly all-fiber approach is presented. Supermode selection inside this monolithic fiber device is numerically analyzed, and multicore fiber lasers operating explicitly at the in-phase supermode are experimentally demonstrated.

Photorefractive polymers are suitable for real‐time holographic applications. Since the recording and readout of a hologram is carried out with laser beams with the same wavelength, the readout process partially erases the stored information, a problem common to all current photorefractive materials and referred to as destructive readout. In this paper we describe photorefractive polymers that are sensitized by two‐photon absorption. Holographic recording is achieved with high‐intensity writing beams and readout using low light intensity, but high power beams. Using this nonlinear recording scheme, non‐destructive readout was demonstrated.

Layer-by-layer, self-limiting chemisorptive siloxane self-assembly using Si3O2Cl8 as the precursor affords thin, conformal, relatively dense, largely pinhole-free dielectric films that can be deposited on oxide surfaces with sub-nanometer control of film thickness (8.3(1) Å/layer). Deposition chemistry, microstructure, and hole injection/work function modification properties of these (SiO2)x-like films on single-crystal Si(111) and polycrystalline indium tin oxide (ITO) substrates have been characterized by synchrotron specular X-ray reflectivity, cyclic voltammetry, X-ray and UV photoelectron spectroscopy, and atomic force microscopy. Chemisorption of these (SiO2)x films onto the ITO anodes of three-layer, vapor-deposited organic electroluminescent devices (ITO/(SiO2)x/TPD/Alq/Al) nearly triples the external quantum and luminous efficiencies. The efficiency enhancement is attributed to hole and electron injection fluence balance caused by modification of the effective voltage profile brought about by the assembly of well-ordered siloxane layers. Interestingly, as a function of increasing (SiO2)x layer thickness, device turn-on voltage first increases (x = 0 → 1), progressively decreases (x = 1 → 2 → 3), and then increases (x = 3 → 4). A theoretical model based upon computation at the ab initio level is proposed in which the self-assembled dielectric layers induce an additional, thickness-dependent “built-in” electric field across the organic transport layers, thereby simultaneously enhancing electron injection from the cathode (increasing luminescence efficiency) and decreasing the efficiency of hole injection (changing the turn-on voltage).

A bis(diarylamino)biphenyl-functionalised methacrylate has been synthesised and polymerised to give a hole-transport polymer; copolymerisation with a chalcone- or cinnamate-functionalised methacrylate affords photo-crosslinkable hole-transport polymers that become insoluble upon exposure to ultra-violet irradiation. Organic light-emitting diodes (OLEDs) were fabricated based on both crosslinked and non-crosslinked hole-transport polymers, and the performances of the devices were evaluated.

New hole transport polymers have been prepared through copolymerization of a fluorinated triphenyl diamine derivative and trimethoxyvinylsilane. The modification with trimethoxysilane groups has resulted in materials which can be cross-linked through hydrolysis and are capable of forming covalent chemical bonds to oxidic surfaces. Organic light-emitting diodes containing these polymers show decreased operating voltages and enhanced operational stability due to improved interfacial contact between the hole transport layer and the anode.

A series of soluble arylamine-based hole-transporting polymers with glass transition temperatures in the range of 130−150 °C have been synthesized. The synthetic methodology allows facile substitution of the aryl groups on the amine with electron-withdrawing and electron-donating moieties, which permits tuning of the redox potential of the polymer. These polymers have been used as hole-transport layers (HTLs) in two-layer light-emitting diodes ITO/HTL/Alq/Mg [ITO = indium tin oxide, Alq = tris(8-quinolinato)aluminum]. The maximum external quantum efficiency of the device increases if the redox potential of the HTL is increased to facilitate reduction of the positive charge carriers at the HTL/Alq interface. A fluorinated hole-transport polymer with a relatively large redox potential (390 mV vs ferrocenium/ferrocene) yielded the device with the highest external quantum efficiency of 1.25% photons/e^-. The device stability, however, follows the opposite trend. The device with the most electron-rich HTL exhibited the best performance after prolonged usage.