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Optics Letters

Zheng Gong, Xianwen Liu, Yuntao Xu, Mingrui Xu, Joshua B Surya, Juanjuan Lu, Alexander Bruch, Changling Zou, Hong X Tang
Chip-based soliton frequency combs have been demonstrated on various material platforms, offering broadband, mutually coherent, and equally spaced frequency lines desired for many applications. Lithium niobate (LN), possessing both second- and third-order optical nonlinearities, as well as integrability on insulating substrates, has emerged as a novel source for microcomb generation and controlling. Here we demonstrate mode-locked soliton microcombs generated around 2 μm in a high-Q z-cut LN microring resonator...
June 15, 2019: Optics Letters
Donggyu Kim, Alexander Keesling, Ahmed Omran, Harry Levine, Hannes Bernien, Markus Greiner, Mikhail D Lukin, Dirk R Englund
In this Letter, to the best of our knowledge, we report a new method to generate uniform large-scale optical focus arrays (LOFAs). By identifying and removing undesired phase rotation in the iterative Fourier transform algorithm (IFTA), our approach rapidly produces computer-generated holograms of highly uniform LOFAs. The new algorithm also shows a faster compensation of system-induced LOFA intensity inhomogeneity than the conventional IFTA. After only three adaptive correction steps, we demonstrate LOFAs consisting of O(103 ) optical foci with an intensity uniformity greater than 98%...
June 15, 2019: Optics Letters
Jun Guan, Adrian J Menssen, Xiang Liu, Jingyu Wang, Martin J Booth
Photonic integrated circuits (PICs) are important enabling technologies for the developments of areas such as quantum information processing (QIP). Coupled-mode integrated beam splitters (IBS) are widely used in many PICs, so direct and accurate testing of individual IBSs inside a PIC is increasingly desirable, as the development of PICs for QIP is scaled up. Here we demonstrate a solution for component-wise testing of coupled-mode IBSs without limitations on component location and PIC architectures. The method is based on the imaging of an individual IBS with a custom-built multifunctional adaptive optical microscope, combined with the calculation of its beam-splitting ratio through numerical modelling...
June 15, 2019: Optics Letters
A A Voronin, A M Zheltikov
Analysis of the complex refractive index of atmospheric air reveals remarkably broad and continuous regions of anomalous and near-zero group-velocity dispersion in the subterahertz (sub-THz) and millimeter-band atmospheric windows. One such broadband dispersion anomaly is shown to occur in the high-frequency wing of the 60-GHz band of molecular oxygen. Adjacent to this dispersion anomaly is a broadband atmospheric transparency region within which the group-velocity dispersion is unusually weak, enabling distortion-free long-distance transmission of broadband millimeter-wave field waveforms, as well as broadband remote sensing in the millimeter band...
June 15, 2019: Optics Letters
M S Pochechuev, A A Lanin, I V Kelmanson, D S Bilan, D A Kotova, A S Chebotarev, V Tarabykin, A B Fedotov, V V Belousov, A M Zheltikov
We demonstrate stain-free, high-contrast, subcellular-resolution imaging of astroglial cells using epi-detected third-harmonic generation (THG). The astrocyte-imaging capability of THG is verified by colocalizing THG images with fluorescence images of astrocytes expressing a genetically encodable fluorescent reporter. We show that THG imaging with an optimized point-spread function can reliably detect significant subcellular features of astrocytes, including cell nuclei, as well as the soma shape and boundaries...
June 15, 2019: Optics Letters
Chih-Hao Liu, Dmitry Nevozhay, Hongqiu Zhang, Susobhan Das, Alexander Schill, Manmohan Singh, Salavat Aglyamov, Konstantin V Sokolov, Kirill V Larin
Wave-based optical coherence elastography (OCE) is a rapidly emerging technique for elasticity assessment of tissues having high displacement sensitivity and simple implementation. However, most current noncontact wave excitation techniques are unable to target a specific tissue site in 3D and rely on transversal scanning of the imaging beam. Here, we demonstrate that dye-loaded perfluorocarbon nanoparticles (nanobombs) excited by a pulsed laser can produce localized axially propagating longitudinal shear waves while adhering to the laser safety limit...
June 15, 2019: Optics Letters
Miao Zhang, Zhijun Ren, Ping Yu
We report a technique to break the depth of field (DOF) limit in optical coherence tomography (OCT) using a finite energy Airy beam. The Airy beam is generated using a phase mask in a Fourier transform schematic and provides the DOF improvement due to its low diffraction. We compare Airy beam OCT with conventional Gaussian beam OCT using lateral resolution and sensitivity. Experimental data from the polystyrene beads in water as well as lemon tissue confirm the extension of DOF up to 10 mm in Airy beam OCT, while the DOF of Gaussian beam OCT is less than 3...
June 15, 2019: Optics Letters
Ting Zhao, Huifu Xiao, Yingtao Li, Jianhong Yang, Hao Jia, Guanghui Ren, Arnan Mitchell, Yonghui Tian
In this Letter, we first demonstrate periodically and independently tunable double Fano resonances (DFRs) using waveguide-coupled cavities consisting of two silicon microring resonators (MRRs) and a feedback-coupled waveguide. The proposed device is fabricated on the silicon-on-insulator substrate using the standard complementary metal-oxide-semiconductor fabrication process. The DFR can be tuned independently by changing the resonant wavelengths of two MRRs using the thermo-optic effect. The highest extinction ratio of the Fano resonances is measured to be as high as 29...
June 15, 2019: Optics Letters
Sucbei Moon, Yusi Miao, Zhongping Chen
We present a very simple method of constructing a polarization-sensitive optical coherence tomography (PS-OCT) system. An ordinary fiber-based swept-source OCT system was reconfigured for PS-OCT by adding a long section of polarization-maintaining fiber in the sample arm. Two polarization modes of a large group-delay difference formed spatially distinguished polarization channels. The depth-encoded information on the polarization states was retrieved by an amplitude-based analysis. We found that our method provides an economic scheme of PS-OCT...
June 15, 2019: Optics Letters
Shun Fujii, Shuya Tanaka, Mika Fuchida, Hikaru Amano, Yuka Hayama, Ryo Suzuki, Yasuhiro Kakinuma, Takasumi Tanabe
In this Letter, we report phase-matched four-wave mixing separated by over one octave in a dispersion-engineered crystalline microresonator. Experimental and numerical results presented here confirm that primary sidebands were generated with a frequency shift up to 140 THz, and that secondary sidebands formed a localized comb structure, known as a clustered comb in the vicinity of the primary sidebands. A theoretical analysis of the phase-matching condition validated our experimental observations, and our results agree well with numerical simulations...
June 15, 2019: Optics Letters
Esmerando Escoto, Rana Jafari, Rick Trebino, Günter Steinmeyer
When confronted with a pulse train whose intensity and/or phase versus time varies from pulse to pulse, multi-shot pulse-measurement techniques usually exhibit a coherent artifact (CA), which substantially complicates the interpretation of the measurement. In frequency-resolved optical gating (FROG), such instabilities are indicated by discrepancies between the measured and retrieved FROG traces. Here we consider the simultaneous retrieval of the CA and the average pulse characteristics from a single FROG trace in the limit of significant fluctuations...
June 15, 2019: Optics Letters
Mingzheng Lei, Zhennan Zheng, Chunqi Song, Yunping Bai, JinWang Qian, Shanguo Huang, Xinlu Gao
A photonic microwave frequency shift keying (FSK) signal generator is proposed and experimentally demonstrated based on an equivalent photonic switch (EPS). The EPS is constructed using a polarization-multiplexing dual-drive Mach-Zehnder modulator (PM-DMZM). By properly controlling the data sequences and RF signals applied to the PM-DMZM, microwave FSK signals with flexible frequency intervals can be obtained. The proposed FSK signal generator features the advantages of a simple structure, low loss, good stability, and great frequency tunability...
June 15, 2019: Optics Letters
M S Arjunan, Anirban Mondal, Amlan Das, K V Adarsh, Anbarasu Manivannan
Highly reproducible and precisely controlled gradual variation in optical reflectivity or electrical resistance between amorphous and crystalline phases of phase change (PC) material is a key requirement for multilevel programming. Here we report high-contrast multilevel set and reset operations through accumulative switching in growth-dominated AgInSbTe PC material using a nanosecond laser-based pump-probe technique. The precise tuning of fractions of crystallized or re-amorphized region is achieved by means of controlling the number of irradiated laser pulses enabling six stable multilevels with high-reflectivity contrast of 2% between any two states...
June 15, 2019: Optics Letters
Jonel F Binamira, Percival F Almoro
In conventional multiple-plane phase retrieval method, the wave propagations that proceed in the same ordered sequence could slow down convergence or lead to stagnation. In this Letter, a novel, to the best of our knowledge, algorithmic technique to accelerate phase retrieval using an unordered sequence of propagations is demonstrated experimentally. The main advantage of the technique is the significant increase in the change in amplitude, a key and essential element for a successful iterative phase retrieval...
June 15, 2019: Optics Letters
Erga Lifshitz, Uri Arieli, Shahar Katz, Iftach Nir, Assaf Levanon, Michael Mrejen, Haim Suchowski
The Fourier transform-infrared (FT-IR) spectrometer is a widely used high-resolution spectral characterization method in materials, chemicals, and more. However, the inverse relation between the spectral resolution and the interferometer's arm length yields a tradeoff between spectral resolution and spectrometer footprint. Here, we introduce a novel method to overcome this traditional FT-IR resolution limit. The enhanced high-resolution multi-scan compact FT-IR spectrometer we present achieves an effectively long interferogram by combining multiple short FT-IR scans...
June 15, 2019: Optics Letters
Paris Panagiotopoulos, Miroslav Kolesik, Sergei Tochitsky, Stephan W Koch, Jerome V Moloney
We identify a two-stage filamentation regime for high-power 10 μm multipicosecond pulses propagating in the atmosphere. The first low-intensity stage is mainly regularized by ionization through excitation induced dephasing, which can lead to strong pulse shortening downstream. This shortening in turn causes a significant reduction of the many-body induced plasma, which changes the dynamics drastically. As a result, a distinct second stage is predicted where peak intensities are clamped at 1 order of magnitude higher than in the first stage...
June 15, 2019: Optics Letters
Ye Ming Qing, Hui Feng Ma, Shang Yu, Tie Jun Cui
An angle-insensitive dual-functional resonator composed of a compound metallic grating is proposed and characterized numerically. The resonator exhibits different response characteristics for TE and TM polarization, thus enabling two functions, corresponding to a high-sensitivity sensor and a low Q-factor absorber. For TE polarization, the Q-factor, refractive index sensitivity, and figure of merit of the resonator can reach 283.4, 2577.6 nm/RIU, and 181.5  RIU-1 , respectively, due to the excitation of cavity mode resonance...
June 15, 2019: Optics Letters
M Paúr, B Stoklasa, D Koutný, J Řeháček, Z Hradil, J Grover, A Krzic, L L Sánchez-Soto
We show that, for optical systems whose point spread functions exhibit isolated zeros, the information one can gain about the separation between two incoherent point light sources does not scale quadratically with the separation (which is the distinctive dependence causing Rayleigh's curse) but only linearly. Moreover, the dominant contribution to the separation information comes from regions in the vicinity of these zeros. We experimentally confirm this idea, demonstrating significant superresolution using natural or artificially created spectral doublets...
June 15, 2019: Optics Letters
Matan Benyamin, Hadar Genish, Ran Califa, Ariel Schwartz, Zeev Zalevsky, Nisan Ozana
A novel method for non-contact and continuous detection of photoacoustic signals is presented and experimentally demonstrated. The approach is based on analysis of the contrast of time-varying speckle patterns, and suggests a more robust alternative in respect to interferometric and refractometric available solutions.
June 15, 2019: Optics Letters
Haojun Zhang, Daniel A Cohen, Philip Chan, Matthew S Wong, Shlomo Mehari, Daniel L Becerra, Shuji Nakamura, Steven P DenBaars
A novel approach to realize DFB gratings on GaN based laser diodes is presented and continuous-wave single longitudinal mode operation is achieved. The first order gratings were fabricated on the surface of indium tin oxide (ITO) on top of the laser ridge, which combines the benefits of simplified fabrication, easy scalability to wider ridges, and no regrowth or overgrowth. Under continuous-wave operation, the laser emits with a full FWHM of 5 pm, a SMSR of 29 dB and output power from a single facet as high as 80 mW...
June 15, 2019: Optics Letters
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