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Optics Letters

Heba Shawki, Hussein Kotb, Diaa Khalil
In this work, we demonstrate a broadband tunable single-longitudinal-mode (SLM) random laser based on Rayleigh backscattering in a standard single-mode fiber. The wide tuning range of this SLM fiber laser over 1500-1570 nm is demonstrated with a linewidth of 4.5-30 kHz. The tuning is achieved using a tunable bandpass Fabry-Perot filter, and a semiconductor optical amplifier is used as the wide-bandwidth gain medium. The laser is able to operate in the S + C + L band.
August 15, 2017: Optics Letters
Sebastian A Schulz, Jeremy Upham, Liam O'Faolain, Robert W Boyd
Slow light photonic crystal waveguides tightly compress propagating light and increase interaction times, showing immense potential for all-optical delay and enhanced light-matter interactions. Yet, their practical application has largely been limited to moderate group index values (<100), due to a lack of waveguides that reliably demonstrate slower light. This limitation persists because nearly all such research has focused on a single photonic crystal lattice type: the triangular lattice. Here, we present waveguides based on the kagome lattice that demonstrate an intrinsically high group index and exhibit slow and stopped light...
August 15, 2017: Optics Letters
Yuzhang Liang, Zhiyong Yu, Ningjuan Ruan, Qian Sun, Ting Xu
A freestanding, multilayered fishnet metamaterial is reported to experimentally exhibit a negative refractive index in the green-light spectral range. The realization of a negative refractive index at such a high frequency range mainly originates from low-loss magnetic resonance and interactions between the neighboring functional layers. Based on a good agreement between the numerically simulated and experimentally measured transmittance and reflectance spectra, a single negative refractive index of -0.76 with a figure-of-merit of 0...
August 15, 2017: Optics Letters
Tianjun Liao, Xin Zhang, Xiaohang Chen, Bihong Lin, Jincan Chen
The negative illumination thermoradiative solar cell (NITSC) consisting of a concentrator, an absorber, and a thermoradiative cell (TRC) is established, where the radiation and reflection losses from the absorber to the environment and the radiation loss from the TRC to the environment are taken into consideration. The power output and overall efficiency of the NITSC are analytically derived. The operating temperature of the TRC is determined through the thermal equilibrium equations, and the efficiency of the NITSC is calculated through the optimization of the output voltage of the TRC and the concentrating factor for a given value of the bandgap...
August 15, 2017: Optics Letters
Grégoire M Smolik, Hans Peter Herzig
We propose a novel method for the design of binary two-level diffractive optical elements that provide an efficient diffractive function while reducing the reflectivity of a high-index interface. The structure can be fabricated with a single patterning step and is particularly useful for the mid-infrared spectral range. The concept is based on zero-order transmission gratings using subwavelength microstructures. To demonstrate the concept a Dammann grating has been realized in silicon and characterized in the mid-infrared by scanning the far-field intensity distribution...
August 15, 2017: Optics Letters
S Longhi
An arbitrarily shaped optical potential on a discrete photonic lattice, which transversely drifts at a speed greater than the maximum speed allowed by the light cone of the lattice band, becomes reflectionless. Such an intriguing result, which arises from the discrete translational symmetry of the lattice, is peculiar to discretized light and does not have any counterpart for light scattering in continuous optical media. A drifting non-Hermitian optical potential of the Kramers-Kronig type also is an invisible potential, i...
August 15, 2017: Optics Letters
Orad Reshef, Enno Giese, M Zahirul Alam, Israel De Leon, Jeremy Upham, Robert W Boyd
We show that standard approximations in nonlinear optics are violated for situations involving a small value of the linear refractive index. Consequently, the conventional equation for the intensity-dependent refractive index, n(I)=n0+n2I, becomes inapplicable in epsilon-near-zero and low-index media, even in the presence of only third-order effects. For the particular case of indium tin oxide, we find that the χ((3)), χ((5)), and χ((7)) contributions to refraction eclipse the linear term; thus, the nonlinear response can no longer be interpreted as a perturbation in these materials...
August 15, 2017: Optics Letters
Denis S Kharenko, Innokentiy S Zhdanov, Anastasia E Bednyakova, Evgeniy V Podivilov, Mikhail P Fedoruk, Alexander Apolonski, Sergei K Turitsyn, Sergey A Babin
A high-energy (0.93 nJ) all-fiber erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity, built of commercially available fibers and components, combines polarization maintaining (PM) and non-PM parts providing stable generation of highly chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165 fs. The results of the numerical simulation agree well with the experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons...
August 15, 2017: Optics Letters
Thomas Begou, Julien Lumeau
We present a systematic study of a stress coefficient of dielectric materials (SiO2, Nb2O5, and HfO2). In particular, we show a thickness dependence of the stress coefficient on layer thickness, which shows that the determination of this coefficient is complex and requires careful analysis. We then apply the different models of the stress coefficient to multilayer structures and show that stress-induced deformation can be precisely predicted in final components with a few percent accuracy.
August 15, 2017: Optics Letters
Qiu Wang, Yun Zhu, Yixin Zhang
We present a new beam wander model valid in all irradiance fluctuation regions by using extended Rytov theory with large-scale and small-scale filters. Comparing the calculated results of our wander model and commonly used models with the experimental data obtained in the case of different propagation distances, the waist radius of a beam wave, the outer scale of turbulence and turbulence strength, our new theory gives better agreement with the experimental results than others do.
August 15, 2017: Optics Letters
Ki-Chul Kwon, Young-Tae Lim, Chang-Won Shin, Munkh-Uchral Erdenebat, Jae-Moon Hwang, Nam Kim
We propose and implement an integral imaging microscope with extended depth-of-field (DoF) using a bifocal holographic micro lens array (MLA). The properties of the two MLAs are switched via peristrophic multiplexing, where different properties of the MLA are recorded onto the single holographic optical element (HOE). The recorded MLA properties are perpendicular to each other: after the first mode is recorded, the HOE is rotated by 90° clockwise, and the second mode is recorded. The experimental results confirm that the DoF of the integral imaging microscopy system is extended successfully by using the bifocal MLA...
August 15, 2017: Optics Letters
Thomas Zacharias, Barak Hadad, Alon Bahabad, Yaniv Eliezer
We demonstrate experimentally the generation of an optical beam having an axial focusing that is narrower than the Fourier limit. The beam is constructed from a superposition of Bessel beams with different longitudinal wave vectors, realizing a super-oscillatory axial intensity distribution. Such beams can be useful for microscopy and for optical particle manipulation.
August 15, 2017: Optics Letters
Alice Odier, Anne Durécu, Jean-Michel Melkonian, Laurent Lombard, Michel Lefebvre, Pierre Bourdon
Coherent beam combining by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters. However, a fast phase modulator operating at the frequency-converted wavelength, a non-standard component, would be necessary. Fortunately, nonlinear conversion processes rely on a phase-matching condition allowing for indirect phase control using standard phase modulators. In this Letter, coherent combining of second-harmonic generators is demonstrated in both birefringent and quasi-phase-matching schemes in CW regime...
August 15, 2017: Optics Letters
M Sumetsky
An elongated bottle microresonator with nanoscale parabolic effective radius variation can possess a series of dense equally spaced optical eigenfrequencies whose separation can match the eigenfrequency of its axially symmetric acoustic mode. It is shown that this acoustic mode can parametrically excite optical modes and give rise to a highly equidistant and moderately broadband optical frequency comb with the teeth spacing independent of the input laser power and the amplitude of mechanical vibrations.
August 15, 2017: Optics Letters
Selim Elhadj, Jae Hyuck Yoo
A laser damage test method based on damage size analysis (DSA) is described that simplifies the derivation of the lifetime optical damage threshold of film materials critical in the design of devices used in high-repetition-rate, high-power laser systems. The DSA method presented here is solely based on imaging to measure the damage site size produced from exposure to a known Gaussian-shaped beam with a fixed, systematically selected fluence well above the ablation threshold. The method locates the damage boundary produced from repeated exposures, using images with a high contrast, and maps it to the beam profile to extract a lifetime laser damage fluence threshold value...
August 15, 2017: Optics Letters
Kaicheng Liang, Osman O Ahsen, Zhao Wang, Hsiang-Chieh Lee, Wenxuan Liang, Benjamin M Potsaid, Tsung-Han Tsai, Michael G Giacomelli, Vijaysekhar Jayaraman, Hiroshi Mashimo, Xingde Li, James G Fujimoto
Endoscopic optical coherence tomography (OCT) instruments are mostly side viewing and rely on at least one proximal scan, thus limiting accuracy of volumetric imaging and en face visualization. Previous forward-viewing OCT devices had limited axial scan speeds. We report a forward-viewing fiber scanning 3D-OCT probe with 900 μm field of view and 5 μm transverse resolution, imaging at 1 MHz axial scan rate in the human gastrointestinal tract. The probe is 3.3 mm diameter and 20 mm rigid length, thus enabling passage through the endoscopic channel...
August 15, 2017: Optics Letters
Dae Hee Kim, Young Ho Yun, Ki-Nam Joo
In this Letter, we propose a novel type of spectroscopic ellipsometer, named spatially phase-retarded spectroscopic ellipsometry (SPARSE), based on the spatial polarization distribution opposed to the temporal polarization changes. SPARSE can collect all information necessary to characterize film structures with a single image acquisition, and it has the benefit of real-time measurements. For the verification, feasible experiments with single film-layered certificated reference materials and multi-layered film specimens were carried out...
August 15, 2017: Optics Letters
Masaki Tokurakawa, Eisuke Fujita, Christian Kränkel
We demonstrate a Kerr-lens mode-locked Tm(3+):Sc2O3 single-crystal laser in-band pumped by an Er(3+):Yb(3+) fiber master oscillator power amplifier at 1611 nm. Pulses as short as 166 fs with an average output power of 440 mW are obtained. The spectral bandwidth and center wavelength are 29.3 and 2124 nm, respectively. At a longer pulse duration of 298 fs, we obtain 1 W of average output power. The repetition rate is 95 MHz, and the conversion efficiency against the absorbed pump power is as high as 47%...
August 15, 2017: Optics Letters
Joseph S Suelzer, Thomas B Simpson, Preetpaul Devgan, Nicholas G Usechak
We experimentally demonstrate the generation of microwave signals with linewidths below 3 Hz and a tuning range over 35 GHz from a semiconductor laser subject to optical injection and opto-electronic feedback. The feedback loop uses neither a microwave spectral filter nor an amplifier to achieve a reduction in the microwave linewidth of six orders of magnitude. Two microwave frequencies, 25.4 and 45.9 GHz, are chosen to highlight single-sideband phase measurements of -105 and -95  dBc/Hz at a 10-kHz offset, respectively...
August 15, 2017: Optics Letters
Peicheng Liao, Changjing Bao, Arne Kordts, Maxim Karpov, Martin H P Pfeiffer, Lin Zhang, Yinwen Cao, Ahmed Almaiman, Amirhossein Mohajerin-Ariaei, Moshe Tur, Martin M Fejer, Tobias J Kippenberg, Alan E Willner
We experimentally demonstrate pump-linewidth-tolerant wavelength multicasting using microresonator-based soliton Kerr frequency combs. When Kerr comb lines serve as coherent pumps in a periodically poled lithium niobate waveguide, the linewidth of the multicast signal almost remains that of the original signal at different linewidths of Kerr combs, ranging from 100 kHz to 1 MHz. However, in conventional multicasting where free-running (FR) pumps are used, the linewidth of the converted signal significantly increases...
August 15, 2017: Optics Letters
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