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PubMed Journal Database | Optics express RSS

02:01 EDT 19th July 2019 | BioPortfolio

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Showing PubMed Articles 1–25 of 1,300+ from Optics express

A high dynamic range optical detector for measuring single photons and bright light.

Detecting light is fundamental to all optical experiments and applications. At the single photon level, the quantized nature of light requires specialised detectors, which typically saturate when more than one photon is incident. Here, we report on a massively-multiplexed single-photon detector, which exploits the saturation regime of a single click detector to exhibit a dynamic range of 123 dB, enabling measurement from optical energies as low as 10 photons per pulse to ∼ 2.5 × 10photons per pulse. This...

30 GHz heterogeneously integrated capacitive InP-on-Si Mach-Zehnder modulators.

We demonstrate high-bandwidth O-band Mach-Zehnder modulators with indium phosphide-on-silicon (InP-on-Si) capacitive phase shifters that are compatible with heterogeneous laser fabrication processes. An electro-optic conversion efficiency of 1.3 V⋅cm and a 3 dB bandwidth of up to 30 GHz was observed for a phase modulator length of 250 μm at a 0 V bias. Open eye patterns were observed at up to 25 Gb/s.

C-band PAM-4 signal transmission using soft-output MLSE and LDPC code.

We propose a DSP scheme with soft-output maximum likelihood sequence equalizer (sMLSE) and low-overhead (8.51%) low density parity check (LDPC) code for C-band PAM-4 transmission. In order to apply LDPC code in conjunction with MLSE, the conventional hard-output MLSE is modified to have a soft-output value by using the Max-log BCJR algorithm. The feasibility of this approach is experimentally investigated in a 56 Gb/s C-band PAM-4 system. In order to investigate the advantages of the proposed scheme, we com...

Generation and probing of 3D helical lattices with tunable helix pitch and interface.

We propose a method for generation of tunable three-dimensional (3D) helical lattices with varying helix pitch. In order to change only the lattice helix pitch, a periodically varying phase along the propagation direction is added to the central beam - one of the interference beams for lattice construction. The phase periodicity determines the helix pitch, which can be reconfigured at ease. Furthermore, a helical lattice structure with an interface (domain wall) is also achieved by changing the phase struct...

Theoretical simulation on exciplex pumped Rb vapor laser.

Considering spectrally resolved absorption and temperature distribution, a physical model is established to describe the laser kinetic and thermodynamic processes of an exciplex pumped Rb vapor laser. A comparison with Carroll's model is made. Influences of pump intensity, temperature, reflectivity of output coupler, and number density of Kr on the performance of CW Rb-Kr XPAL with uniform temperature distribution are calculated and analyzed. Besides, with the heat accumulation considered, the temperature d...

Real-time experimental demonstration of DSP-enabled soft-ROADMs with multi-level flexible add/drop functions for cloud access networks.

Making use of digital filtering, drop RF signal-driven intensity modulation and passive optical coupling, DSP-enabled flexible ROADMs, termed soft-ROADMs, are experimentally demonstrated in real-time, which are free from both optical filters and O-E-O conversions and are inherently transparent to major network design characteristics. In a 4-channel IMDD optical network node incorporating FPGA-based orthogonal digital filter multiplexing, fully real-time soft-ROADM dynamic add and drop operations at both sub...

Dual-band vortex beam generation with different OAM modes using single-layer metasurface.

Recently, considerable attention has been focused on orbital angular momentum (OAM) vortex wave, owing to its prospect of increasing communication capacity. Here, a single-layer metasurface is proposed to realize vortex beams with different OAM modes and polarizations carried at two distinctive bands. Both the resonant and geometric (Pancharatnam-Berry) phase cells are adopted to construct this metasurface for generating the desired phase profile, and each type of phase modulation cell can independently con...

High beam quality and high peak power Yb:YAG/Cr:YAG microchip laser.

The prospect for developing a passively Q-switched Yb:YAG/Cr:YAG monolithic microchip laser that operates at cryogenic temperature is theoretically analyzed. It is concluded that such a system has the potential to deliver laser pulses with improved energy and increased peak power in comparison with composite Yb:YAG/Cr:YAG or Nd:YAG/Cr:YAG devices that are operated at room temperature. Consequently, a cryogenically cooled Yb:YAG/Cr:YAG system is built and the emission performances are investigated. Laser pul...

2/3 octave Si/SiO infrared dispersive mirrors open new horizons in ultrafast multilayer optics.

Dispersive mirrors operating in a broadband infrared spectral range are reported for the first time. The mirrors are based on Si/SiO thin-film materials. The coatings exhibit reflectance exceeding 99.6% in the spectral range from 2 to 3.2 µm and provide a group delay dispersion of -100 fs and -200 fs in this range. The fabricated mirrors are expected to be key elements of Cr:ZnS/Cr:ZnSe femtosecond lasers and amplifiers. The mirrors open a new avenue in the development of ultrafast dispersive optics operat...

Characterization of microresonator-geometry-deformation for cavity optomechanics.

We have studied the effect of geometry deformation on the mechanical frequencies and quality factors for different modes in the Whispering Gallery Mode (WGM) microresonators, that is unavoidable in the practical fabrication. The subsidence of the sphere and a more general condition with fewer symmetries and complex deformation of eccentricity, subsidence, and offset are first modeled in this paper, which could tune the mechanical frequency in a much wider spectral range than the pillar-diameter-induced pert...

Inter-core crosstalk in weakly coupled MCFs with arbitrary core layout and the effect of bending and twisting on the coupling coefficient.

We investigate the bending and twisting-induced longitudinal variation of the inter-core coupling coefficient (ICCC) and its effect on inter-core crosstalk (ICXT) in weakly coupled multi-core fibers (MCFs) with an arbitrary core layout. An analytical discrete changes model (DCM) for ICXT field propagation under those conditions is proposed for the first time, providing very fast and rather accurate mean ICXT power estimates. The analytical mean ICXT power estimates are validated through numerical simulation...

Integer and fractional electromagnetically induced Talbot effects in a ladder-type coherent atomic system.

Both integer and fractional electromagnetically induced Talbot effects are experimentally investigated in a coherent rubidium 5S - 5P - 5D ladder-type system. By launching a probe laser into a periodically modulated lattice constructed by two crossed coupling fields with a small angle inside the rubidium vapor, a high-resolution diffraction pattern is obtained. The diffraction pattern is reproduced completely at detection positions of an integer multiple of twice the Talbot lengths. Meanwhile, the fractiona...

Design method for compact, achromatic, high-performance, solid catadioptric system (SoCatS), from visible to IR.

Maresse described a classical solid catadioptric system (SoCatS) for a lens comprising a solid body and a single-focal Maksutov type construction, characterized by two refractive and two reflective surfaces. Due to ray propagation through the solid block twice, the design is feasible at a single wavelength, otherwise suffering on chromatic aberration induced by dispersion. We design a SoCatS for a telescope and describe a class of solutions to reduce and control chromatic and some spherical aberration in th...

High spectral purity electromagnetically induced transparency-based microwave optoelectronic oscillator with a quasi-cylindrical microcavity.

High spectral purity microwave oscillators are widely exploited in science and military areas including communication, radar, and navigation. Here, we theoretically analyze and experimentally observe the application of tunable electromagnetically induced transparency (EIT) effect generated within a single quasi-cylindrical microresonator (QCMR) to a high spectral purity microwave optoelectronic oscillator (OEO). Stable single-frequency microwave oscillation with phase noise of -123 dBc/Hz at 10 kHz offset f...

Experimental quantification of the free-carrier effect in silicon waveguides at extended wavelengths.

We examine the electro-optic effect at wavelengths ranging from 1.31 to 2.02 μm for: (1) an Electronic Variable Optical Attenuator (EVOA); and (2) a Micro-Ring Resonator (MRR). For the EVOA, simulations were performed to ascertain the relationship between free-carrier concentration and optical attenuation, and are in agreement with our observation of an increase in attenuation with increasing wavelength. MRRs were fabricated for use around wavelengths of 2 μm to explore the sensitivity of operation to bus...

Programmable pulse shaping for time-gated amplifiers.

We experimentally demonstrate a novel use of a spatial light modulator (SLM) for shaping ultrashort pulses in time-gated amplification systems. We show that spectral aberrations because of the device's pixelated nature can be avoided by introducing a group delay offset to the pulse via the SLM, followed by a time-gated amplification. Because of phase wrapping, a large delay offset yields a nearly-periodic grating-like phase function (or a phase grating). We show that, in this regime, the phase grating perio...

X-ray zoom lens allows for energy scans in X-ray microscopy.

We introduce a new design and development of a compound refractive X-ray zoom lens for energy scans in X-ray microscopy. Energy scans are, in principle, equivalent to radial scans in the reciprocal space for X-ray diffraction. Thanks to the absence of sample or detector motions, energy scans are better suited for microscopy, which requires high stability. In addition, close to the absorption edge of an element, energy scans can yield chemical information when coupled with resonant effects in full field diff...

Highly efficient thulium-doped high-power laser fibers fabricated by MCVD.

We report a hybrid process by combining both vapor-phase and solution-doping techniques of rare-earth doped preform fabrication in conjunction with the MCVD technique, in order to fabricate highly efficient Tm-doped laser fibers. The proposed fabrication route takes advantage of co-doping silica with high alumina content through the vapor-phase doping process, which is otherwise difficult to achieve using conventional solution doping technique. In addition, by employing the solution doping method, high-puri...

Wideband sub-THz half-wave plate using 3D-printed low-index metagratings with superwavelength lattice.

High-index dielectric metasurfaces are rarely reported around 0.1-0.3 THz, as an extremely large etching depth is needed according to the millimeter-scale wavelength. In this work, we propose an easy solution to sub-THz wideband polarization control by utilizing 3D-printed low-index (n~1.5) metagratings. The metagrating with subwavelength lattice is shown as a very efficient half-wave plate (net polarization conversion of 87%) at 0.14 THz but showing noisy spectrum. The design with superwavelength lattice o...

Ultraprecision machining of microlens arrays with integrated on-machine surface metrology.

Microlens arrays (MLAs) are increasingly applied in high-end photonics and imaging systems. Advanced diamond turning machining with tool servo technique is a superior method of fabricating micro-structured arrays with sub-micrometer form accuracy and nanometer surface finish. This paper proposes an innovative framework for ultraprecision machining of MLA. The established metrology-integrated machining platform consists of a 3-axis ultraprecision turning machine and a nanometric interferometric probe. On-mac...

Achromatic complex holograms for laser mode conversion.

While conventional complex phase masks are chromatic, we present an achromatic holographic phase mask capable of performing optical beam transformations in a spectral range exceeding 1000 nm. The system consists of a holographic phase mask fabricated by encoding the desired phase profiles into volume Bragg gratings, inserted in between two surface gratings. This device automatically adjusts each spectral component diffracted by the surface grating to the Bragg angle of the volume Bragg grating and equalizes...

Deep learning wavefront sensing.

We present a new class of wavefront sensors by extending their design space based on machine learning. This approach simplifies both the optical hardware and image processing in wavefront sensing. We experimentally demonstrated a variety of image-based wavefront sensing architectures that can directly estimate Zernike coefficients of aberrated wavefronts from a single intensity image by using a convolutional neural network. We also demonstrated that the proposed deep learning wavefront sensor can be trained...

High-sensitivity refractive index and temperature sensor based on cascaded dual-wavelength fiber laser and SNHNS interferometer.

A novel differential intensity-measurement high-sensitivity refractive index (RI) sensor based on cascaded dual-wavelength fiber laser and single-mode-no-core-hollow-core-no-core-single-mode (SNHNS) structure is proposed and demonstrated. The sensing unit consists of one uniform fiber Bragg grating (FBG) and an SNHNS structure as all-fiber interferometer filter. The dual-wavelength fiber laser has a ring cavity composed of two FBGs with central wavelengths of 1550.10nm and 1553.61nm. Through monitoring the ...

Effect of pad elastic modulus on polishing-induced subsurface damages distribution and laser-induced damage performance of fused silica optics.

The plastic subsurface damages distribution and their influence on the laser induced damage performance of fused silica optics polished with different pads are investigated. The elastic interaction model, plastic indentation model and wear relationships are combined together to theoretically characterize the plastic subsurface damages distribution in different polishing processes, which shows consistent results with experiments. It reveals that most of the polishing-induced subsurface damages are plastic da...

Two-dimensional hexagonal boron nitride nanosheet as the planar-alignment agent in a liquid crystal-based electro-optic device.

The planar-alignment agent in an electro-optic liquid crystal (LC) device plays an essential role for the LC's electro-optical characteristics. Rubbed polyimide (PI) layers are conventionally used as the planar-alignment agent in traditional liquid crystal displays (LCDs). Here we experimentally demonstrate that the 2D hexagonal boron nitride (h-BN) nanosheet can serve as the planar-alignment agent in an LC cell. This h-BN has higher chemical stability and more optical transparency than the PI layer. Two h-...


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