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Optics Letters | Page 2

Xian Zhang, Xiao-Song Zhu, Yi-Wei Shi
A fiber optic surface plasmon resonance (SPR) sensor based on a silver-coated large-core suspended-core fiber was proposed. A dynamic chemical liquid phase deposition method was adopted to fabricate a set of proposed sensors with different silver layer thicknesses. A stable fully spiced all-fiber sensing system was established to evaluate the performance of the fabricated sensors. The results show that the proposed sensor with a thicker silver layer exhibits higher sensitivity and figure of merit. The performance of the proposed sensor is comparable to those of the conventional solid-core fiber and hollow fiber SPR sensors and much higher than that of the metal nanoparticle functionalized suspended-core fiber sensors...
September 15, 2019: Optics Letters
P Brůža, A Pétusseau, S Tisa, M Jermyn, L A Jarvis, D J Gladstone, B W Pogue
The emission of Cherenkov photons from human and animal tissue can be observed during clinical x-ray or particle beam irradiation. However, imaging this weak emission with the necessary single-photon sensitivity in the clinical room is challenging because of milliwatt-level ambient room lighting and the presence of stray high-energy radiation. In this Letter, we demonstrate, to the best of our knowledge, the first Cherenkov imaging with a time-gated quanta image sensor employing a large single-photon avalanche diode (SPAD) array...
September 15, 2019: Optics Letters
Yu-Hsuan Chuang, Yu-Zi Lin, Sunil Vyas, Yi-You Huang, J Andrew Yeh, Yuan Luo
A new approach for achieving isotropic differential phase contrast imaging by applying multi-wavelength asymmetric illumination is demonstrated. Multi-wavelength isotropic differential phase contrast scheme (MW-iDPC) can be implemented using an add-on module in any commercial inverted microscope. Isotropy of intensity transfer function is achieved using three axis measurements. The expression for MW-iDPC imaging is presented, and detailed mathematical analysis is performed for transfer function. By applying color leakage correction, image sensor responses can be calibrated...
September 15, 2019: Optics Letters
M B Pereira, G R Toniello, K S Souza, F Horowitz
The optical performance of very thin films has always been difficult to measure, and it has been a gray area due to interface and coating imperfections. Atomic layer deposition has produced pinhole-free, continuous, and extremely pure Titania films, with precise control at monolayer level, on native oxide/Si substrates, whose atomic force microscopy imaged nano-topology is approximately followed. For interface probing, the Abelès method is extended to the visible spectrum, and Cauchy dispersion curves are fitted to the refractive index experimental data, showing excellent compatibility with ellipsometric analysis...
September 15, 2019: Optics Letters
David Cardador Maza, Daniel Segura Garcia, Ioannis Deriziotis, Moisés Garín, Jordi Llorca, Angel Rodriguez
This study describes the detection of CO2 using macroporous silicon photonic crystals as thermal emitters. It demonstrates that the reduction of structural nonhomogeneities leads to an improvement of the photonic crystals' emission. Narrow emission bands (Q∼120) located within the R-branch of carbon dioxide were achieved. Measurements were made using a deuterated triglycine sulfate photodetector and the photonic crystals, heated to 400°C, as selective emitters. A gas cell with a CO2 concentration between 0 ppm and 10,000 ppm was installed in the center...
September 15, 2019: Optics Letters
N Carlon Zambon, P St-Jean, A Lemaître, A Harouri, L Le Gratiet, I Sagnes, S Ravets, A Amo, J Bloch
Light's orbital angular momentum (OAM) is an unbounded degree of freedom emerging in helical beams that appears very advantageous technologically. Using chiral microlasers, i.e., integrated devices that allow generating an emission carrying a net OAM, we demonstrate a regime of bistability involving two modes presenting distinct OAM (ℓ=0 and ℓ=2). Furthermore, thanks to an engineered spin-orbit coupling of light in these devices, these modes also exhibit distinct polarization patterns, i.e., circular and azimuthal polarizations...
September 15, 2019: Optics Letters
Xiaoqing Guo, Tingge Dai, Bei Chen, Hui Yu, Yuehai Wang, Jianyi Yang
A twin-Fano resonator based on a Mach-Zehnder interferometer (MZI) is demonstrated on a silicon-on-insulator platform. A dual-microring resonator replaces one of the couplers of the MZI to achieve twin-Fano resonance, which originates from the interference and coupling of modes in a dual-microring resonator. The slope can be tuned in a wide range from -84.2  dB/nm to 91.0 dB/nm by metal heaters integrated on one arm of the MZI, and the resonant wavelength remains fixed when the slope changes. The "X-type" spectrum is shown by self-alignment, which means manual alignment to form the X-type line is unnecessary after tuning dual-microrings because the X-type line can be produced easily by the difference in two correlated spectra rather than two independent spectra...
September 15, 2019: Optics Letters
Ya-Ping Li, Wei Chen, Fang-Xiang Wang, Zhen-Qiang Yin, Li Zhang, Hang Liu, Shuang Wang, De-Yong He, Zheng Zhou, Guang-Can Guo, Zheng-Fu Han
Quantum key distribution (QKD) can generate secure key bits between remote users employing the features of quantum physics. However, a shared reference frame is necessary for QKD systems in most scenarios. A reference-frame-independent (RFI) scheme can tolerate the reference frame drifting between legitimate remote users, which is significant in the operation of relative moving terminals such as satellites and aircraft. We design and experimentally demonstrate an RFI-BB84-QKD system by joint encoding with the polarization and orbital angular momentum states of the photons...
September 15, 2019: Optics Letters
Yubo Tang, Alex Kortum, Imran Vohra, Jennifer Carns, Sharmila Anandasabapathy, Rebecca Richards-Kortum
Line-scanning confocal microendoscopy offers video-rate cellular imaging of scattering tissue with relatively simple hardware, but its axial response is inferior to that of point-scanning systems. Based on Fourier optics theory, we designed differential confocal apertures with a simple subtraction technique to improve the line-scanning sectioning performance. Taking advantage of digital slit apertures on a digital light projector and a CMOS rolling shutter, we demonstrate real-time optical sectioning performance comparable to point scanning in a dual-camera microendoscope (<$6,000)...
September 15, 2019: Optics Letters
Guangyu Ren, Benle Dou, Youjie Hua, Feifei Huang, Yinyan Li, Junjie Zhang, Shiqing Xu
Lanthanide-doped optical functional glasses have received substantial attention in recent years owing to their excellent upconversion (UC) and infrared (IR) performance pumping when used in a semiconductor laser. In this study, the luminescence properties of Ho3+ ions were improved through the design of components used to modulate the microenvironment of the glass. To the best of our knowledge, this is a novel approach to enhancing the UC and IR emissions, and results in up to more than 130% improvement by regulating a tight network glass structure...
September 15, 2019: Optics Letters
Jiahao Zhang, Qianwen Ying, Zhichao Ruan
We investigate the time response of plasmonic spatial differentiators based on prism coupling configurations. We show that when the incident light is time-modulated, in addition to the spatial differentiation, the output field is also contributed by the signal derivative with respect to time. To reduce this impact, the incident pulse needs a steady time span, and the shortest steady time span is about 100 fs. We further show that the time modulation does not degrade the resolution of the spatial differentiation...
September 15, 2019: Optics Letters
Xinlu Gao, Shanguo Huang, Mingzheng Lei, Hao Zhang, Jinwang Qian, Yunping Bai, Zhennan Zheng
A chromatic dispersion (CD) immune microwave photonic phase shifter (MPPS) based on double-sideband (DSB) modulation is proposed and demonstrated. An optical spectrum processor introduces the phase shift to the MPPS. The DSB signals along two orthogonal polarizations are demodulated to two RF signals with both quadrature amplitude and phase items, transferring the CD-induced power fading to the phase item of the synthetic RF signals. Experimental results show that the RF signals over 14-25 GHz obtain random phase shift in 360° range without a power fading point (PFP) after passing through a dispersion compensation fiber with CD of -331  ps/nm...
September 15, 2019: Optics Letters
Bo Dong, Chenzhuo Li, Bing Pan
Video extensometer assesses mechanical properties of materials by measuring their length changes under different loadings with combined use of video recording and image processing. In this Letter, an ultrasensitive video extensometer implemented on a single-camera dual field-of-view (dual FOV) telecentric imaging system is proposed. The method integrates the idea of FOV separation and telecentric imaging, which can increase the strain resolution with an order of magnitude and enhance the strain accuracy significantly...
September 15, 2019: Optics Letters
Yingjie Liu, Shuai Wang, Yujie Wang, Wei Liu, Hucheng Xie, Yong Yao, Qinghai Song, Xinliang Zhang, Yu Yu, Ke Xu
An ultra-compact polarization splitter-rotator with a discretized subwavelength nanostructure is demonstrated on the silicon-on-insulator platform. The device has a length of only 7.92 μm. For TE0 -TE0 , a low insertion loss (<0.2  dB), low crosstalk (<-20  dB), and high extinction ratio (>40  dB) are achieved over a broad wavelength range from 1500 nm to 1600 nm. For TM0 -TE0 , the insertion loss is lower than 1 dB over 40 nm bandwidth (1530-1570 nm). The crosstalk is lower than -25  dB, and the extinction ratio is larger than 20 dB, from 1500 nm to 1600 nm...
September 15, 2019: Optics Letters
Jiachen Wang, Jinli Han, Jun He, Changrui Liao, Yiping Wang
An all-fiber mode-locked holmium-doped fiber laser operating in the noise-like pulse regime is reported. Employing a nonlinear amplifying loop mirror as the artificial saturable absorber, the laser generates pulses with energy up to 280 nJ, which is, to the best of our knowledge, the highest pulse energy ever achieved from mode-locked holmium-doped fiber lasers. We also discover a peculiar mode-locking operation mode using the laser. The peculiar mode falls into the category of a noise-like pulse, while it possesses a number of unique features (strong spikes in the optical spectrum, high temporal coherence, and chair-like pulse profile) that are not observed in previous research works regarding noise-like pulse lasers...
September 15, 2019: Optics Letters
Congcong Song, Xiuhuan Liu, Feng Liu, Meiling Zhang, Guijun Hu
We report on the fusion splice loss characteristics of each mode in few-mode fiber (FMF). The fusion fault loss characteristics of all modes of the six-mode step-index and graded-index fibers are measured, respectively. The high-order modes with high fault detection sensitivity are presented. The fault events with different loss amplitudes can be accurately characterized by high-order modes. On this basis, a fault detection and location method for FMF based on backscattered light of high-order modes is proposed and experimentally demonstrated...
September 15, 2019: Optics Letters
Shunshuo Cai, Álvaro González-Vila, Xuejun Zhang, Tuan Guo, Christophe Caucheteur
Surface plasmon resonance excitation with tilted fiber Bragg gratings has been typically studied using gold films to target biochemical sensing applications. However, surface plasmons can be excited on other metal coatings as well. In this work, plasmonic optical fiber grating platforms are developed using palladium films. Since the optical properties of this metal differ from the ones of gold, simulations are carried out to define the optimal thickness. Due to the phase transition of palladium in the presence of hydrogen, intensity changes in the optical transmission of the devices are produced...
September 15, 2019: Optics Letters
Jian Xu, Ang Wang, Yaping Dan
Multispectral analyzers based on nanostructured plasmonic spectral filters can potentially find a wide range of applications. However, spectral filters based on the widely reported microhole or ring arrays suffer from relatively wide filtering bands, resulting in a relatively low spectral resolution. In this work, we fabricate high-performance spectral filters based on vertically standing micropipes on a silver film. An infrared spectral microscope is used to investigate the properties of these micropipe spectral filters...
September 15, 2019: Optics Letters
Bok Young Kim, Yoshitomo Okawachi, Jae K Jang, Mengjie Yu, Xingchen Ji, Yun Zhao, Chaitanya Joshi, Michal Lipson, Alexander L Gaeta
We demonstrate an approach for automated Kerr comb generation in the normal group-velocity dispersion (GVD) regime. Using a coupled-ring geometry in silicon nitride, we precisely control the wavelength location and splitting strength of avoided mode crossings to generate low-noise frequency combs with pump-to-comb conversion efficiencies of up to 41%, which is the highest reported to date for normal-GVD Kerr combs. Our technique enables on-demand generation of a high-power comb source for applications such as wavelength-division multiplexing in optical communications...
September 15, 2019: Optics Letters
Yan-Jie Song, Ke Liu, Nan Zong, Wei Tu, Yong Bo, Da-Fu Cui, Qin-Jun Peng, Zu-Yan Xu
We report a compact, long nanosecond (ns) pulse duration stretched laser source by a multi-pass cavity (MPC). Based on the combination of the MPC and pump power, a high-power high beam quality 1064 nm Q-switched Nd:YAG laser with a pulse duration adjustable over the range of 160-1000 ns was obtained at a pulse repetition frequency of 10 kHz for the first time, to the best of our knowledge. At a typical pulse width of 560 ns, an average output power of 10.6 W was successfully achieved. The beam quality factor M2 was measured to be 1...
September 15, 2019: Optics Letters
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