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Accepted papers to appear in an upcoming issue

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Plasmon-enhanced waveguide for dispersion compensation in mid-infrared quantum cascade laser frequency combs

Yves Bidaux, Ilia Sergachev, Wolf Wuester, Richard Maulini, Tobias Gresch, Alfredo Bismuto, Stéphane Blaser, Antoine Muller, and Jérôme Faist

Doc ID: 287673 Received 02 Mar 2017; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We demonstrate dispersion compensation in mid-infrared quantum cascade laser frequency combs emitting at 7.8 μm using the coupling of a dielectric waveguide to a plasmonic resonance in the top cladding layer of the latter. Devices with group velocity dispersion as low as -40 fs2/mm were fabricated and nar- row beatnotes with a FWHM linewidth below 1 kHz were measured on the whole operation range. The optical output power reaches 275 mW and the optical spectrum spans 60 cm−1. The multi-heterodyne beat- ing spectrum of two devices was measured and spans 46 cm−1, demonstrating the potential of dispersion engineered waveguides for the fabrication of highly stable and reliable quantum cascade laser frequency combs with high output power across the mid-infrared.

Characterization of Ge1-x-ySiySnx/Ge1-xSnx multiple quantum well structure grown by sputtering epitaxy

Jun Zheng, Suyuan Wang, Hui Cong, Colleen Shang, zhi Liu, Chunlai Xue, Chuanbo Li, Yuhua Zuo, Buwen Cheng, James Harris, and Qiming Wang

Doc ID: 288008 Received 06 Mar 2017; Accepted 24 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: A high-quality Ge0.88Si0.08Sn0.04/Ge0.94Sn0.06 multiple quantum well (MQW) structure was grown on a Ge (001) substrate by sputtering epitaxy. The MQW structure was characterized by high-resolution X-ray diffraction and transmission electron microscopy. A surface-illuminated Ge0.88Si0.08Sn0.04/Ge0.94Sn0.06 MQW pin photodetectors were fabricated, with cut-off wavelength up to 2140 nm. The analysis of transitions from spectral response was fitted well with the theoretical calculations. Results suggest that sputtering epitaxy is a promising method for preparing high-quality low-dimensional Sn-based group IV materials and that Ge1-x-ySiySnx/Ge1-xSnx MQWs have potential applications in the development of efficient Si-based photonic devices.

High-speed wavelength-swept source at 2.0 µm and its application in imaging through scattering medium

Sisi Tan, lingxiao yang, Xiaoming Wei, can li, Nan Chen, Kevin Tsia, and Kenneth Kin-Yip Wong

Doc ID: 285054 Received 18 Jan 2017; Accepted 23 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: We report a high-speed wavelength-swept source operating at 2.0 µm through advanced time-stretch technology. It sweeps over 30 nm at a speed of 3.3×10⁹ nm/s and a repetition rate of ~19 MHz. To the best of our knowledge, this is the first time that MHz stable swept source has been implemented at such a long wavelength. A wide bandwidth is enabled by a simple mode-locked fiber laser that covers a wavelength range of ~60 nm. The all-optical wavelength sweeping is realized by a chirped fiber Bragg grating (CFBG), which shows a superior temporal stability and power efficiency, compared with those commonly-used dispersive fibers, particularly in the 2.0-µm wavelength window. To showcase its specialties, here we employ it to perform high-speed spectrally-encoded microscopy (i.e., time-stretch imaging) through scattering media at a line-scan rate of up to ~19 MHz. Better image quality is achieved comparing with conventional imaging window at 1.0 µm. It is believed that the potential applications of this new high-speed swept source will benefit the transient diagnosis that requires deep penetration, such as optical coherence tomography (OCT).

Laser-induced birefringence measurements by quantitative polarized phase microscopy

Thomas Doualle, alexandre ollé, philippe cormont, Serge Monneret, and Laurent Gallais

Doc ID: 287472 Received 24 Feb 2017; Accepted 23 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: A technique that provides quantitative and spatially resolved retardance measurement is studied for application to laser-induced modification in transparent materials. The method is based on the measurement of optical path differences between two wavefronts carrying different polarizations, measured by a wavefront sensor placed in the image plane of a microscope.We have applied the technique to the investigation of stress distribution induced by CO2 laser processing of fused silica samples. By comparing retardance measurements to the results of thermomechanical simulationswe demonstrate quantitative agreement between experiments and simulations. The technique provides an efficient and simple way to measure retardance less than 1nm with a diffraction limited spatial resolutionin transparent samples.

Bandwidth adaptable silicon photonic differentiator employing slow light effect

Siqi Yan, Ziwei Chen, Lars Frandsen, Yunhong Ding, Feng Zhou, Jianji Dong, and Xinliang Zhang

Doc ID: 286178 Received 07 Feb 2017; Accepted 22 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: A photonic differentiator (DIFF) plays a crucial role in photonic circuits (PICs). Despite the fact that a DIFF having terahertz-bandwidth has been reported, the practical bandwidth limits to being a band-pass response. In this study, we propose the concept of a bandwidth adaptable DIFF, which exploits the slow light effect in a photonic crystal waveguide (PhCW) to overcome the inherent bandwidth limitation of current photonic DIFFs. We fabricated a PhCW Mach-Zehnder Interferometer (PhCW-MZI) on the silicon-on-isolator (SOI) material platform to validate our concept. Input Gaussian pulses with full-width half-maximums (FWHM) ranging from 2.7 ps to 81.4 ps are accurately differentiated using our PhCW-MZI. Our all-passive scheme circumvents the bandwidth bottlenecks of previously reported photonic DIFFs and can greatly broaden the application area of photonic DIFFs.

Continuous variable quantum key distribution with a real local oscillator using simultaneous pilot signals

Sebastian Kleis, Max Rückmann, and Christian Schaeffer

Doc ID: 283072 Received 19 Jan 2017; Accepted 21 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: In this article we propose a novel implementation of continuous variable quantum key distribution (CV-QKD) that operates with a real local oscillator (LO) placed at the receiver site. In addition, pulsing of the continuous wave laser sources is not required, leading to an extraordinary practical and secure setup. It is suitable for arbitrary schemes based on modulated coherent states and heterodyne detection. The shown results include transmission experiments as well as an excess noise analysis applying a discrete 8-state phase-modulation. Achievable key rates under collective attacks are estimated. The results demonstrate the high potential of the approach to achieve high secret key rates at relatively low effort and cost.

High frequency continuous birefringence oscillationsin spin-polarized vertical-cavity surface-emitting lasers

Maria Torre, Hadi Susanto, Nianqiang Li, kevin Shires, Matias Salvide, Ian Henning, Michael Adams, and Antonio Hurtado

Doc ID: 284816 Received 23 Jan 2017; Accepted 21 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: Sustained, large amplitude and tuneable birefringenceinducedoscillations are obtained in a spin-Vertical CavitySurface Emitting Laser (spin-VCSEL). Experimentalevidence is provided using a spin-VCSEL operating at1300 nm, under continuous wave optical pumping andat room temperature. Numerical and stability analysesare performed to interpret the experiments and to identifythe combined effects of pump ellipticity, spin relaxationrate and cavity birefringence. Importantly, the frequencyof the induced oscillations is determined by thedevice’s birefringence rate which can be tuned to largevalues (up to hundreds of GHz). This opens the pathfor ultrafast spin-lasers operating at record frequenciesexceeding those possible in traditional semiconductorlasers and with ample expected impact in disparate disciplines(e.g. datacomms, spectroscopy).

A frequency stabilized diode laser with variable linewidth at a wavelength of 404.7nm

Benjamin Rein and Thomas Walther

Doc ID: 286960 Received 17 Feb 2017; Accepted 21 Mar 2017; Posted 21 Mar 2017  View: PDF

Abstract: We report on a frequency stabilized laser system with a variable linewidth at a wavelength of 404.7 nm used as an incoherent repump on the 6^{3} P_0 \leftrightarrow 7^{3}S_1 transition in mercury. By directly modulating the laser diode current with Gaussian white noise, the laser linewidth can be broadened up to 68 MHz. A Doppler-free DAVLL spectroscopy provides an error signal suitable for frequency stabilization even for the broadened laser. Without the need of an acousto-optic modulator for the linewidth tuning or lock-in technique for frequency stabilization, this laser system provides an inexpensive approach for an incoherent and highly efficient repumper in atomic experiments.

Interlinked add-drop filter with amplitude modulation routing fiber-optic microring to lithium niobate microwaveguide

Suxu Zhou, Jiangli Dong, Donghui He, Yuan Wang, Wentao Qiu, JianHui Yu, Heyuan Guan, wenguo zhu, Yongchun Zhong, Yunhan Luo, Jun Zhang, Zhe Chen, and Huihui Lu

Doc ID: 285969 Received 03 Feb 2017; Accepted 20 Mar 2017; Posted 21 Mar 2017  View: PDF

Abstract: We propose and experimentally demonstrate a new electro-optically controllable add-drop filter based on light coupling between a microfiber knot ring (MKR) and lithium niobate (LN) microwaveguide. In our design, the MKR works as a resonator and routes the resonant light into the LN microwaveguide. The LN microwaveguide, as an excellent intermediary between electronics and optics, is a robust platform that not only enables stable support and manipulation of the MKR, but also provides amplitude tunability taking advantage of its electro-optic property. Two add-drop filters with different diameters of the MKR, 1.12 mm and 560 μm, respectively, are studied, and a maximum amplitude tunability of ~0.139 dB/V is obtained. The results show that this design can be a solution to interconnect microstructured optical fiber with microstructured on-chip device, and provide an effective method to realize the active on-chip integration of the conventional fiber system

All-polarization maintaining, stretched-pulse Tm-doped fiber laser, mode-locked by graphene saturable absorber

Jaroslaw Sotor, Jakub Boguslawski, Tadeusz Martynkien, Pawel Mergo, Aleksandra Krajewska, Aleksandra Przewolka, Wlodek Strupinski, and Grzegorz Sobon

Doc ID: 286086 Received 03 Feb 2017; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: In this letter, we demonstrate an all-polarization maintaining (PM), stretched-pulse Tm-doped fiber laser generating ~200 fs pulses centered at 1945 nm. As a saturable absorber (SA) a graphene/Poly(methyl methacrylate) (PMMA) composite was used. This is, to the best of our knowledge, the first demonstration of stretched-pulse operation of a graphene-based fiber laser at 2 μm.

Mode-locked laser with pulse interleavers in monolithic photonic integrated circuit for millimeter wave and terahertz carrier generation

Mu-Chieh Lo, Robinson Guzman, Carlos Gordon, and Guillermo Carpintero

Doc ID: 282898 Received 20 Dec 2016; Accepted 19 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: In this paper we present photonic based mmW and THz frequency synthesizers developed through an InP-based generic photonic integration technology platform. This approach allows the monolithic integration of a Mode-Locked Laser (MLL) and two stages of pulse interleaver to multiply the repetition rate frequency. The core MLL is a multiple colliding pulse mode-locked laser that generates a pulse train signal of 80 GHz repetition rate. Cascading pulse interleaver structures that double the repetition rate, based on optical delay line-assisted Mach-Zehnder interferometers (MZI) we demonstrate the achievement of 160 GHz and 320 GHz. It is in agreement with the optical frequency combs with 25 dB SMSR and the pulse with 0.8 ps FWHM.

Diamond Ring Fiber for Evanescent Field Exposure

Wee Lit Ng, Wei Ru Wong, Ghafour Amouzad Mahdiraji, Rifat Ahmmed Aoni, Din Chai Tee, and Faisal Rafiq Mahamd Adikan

Doc ID: 287392 Received 24 Feb 2017; Accepted 18 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Diamond Ring Fiber (DRF) is proposed to allow high percentage of evanescent field exposure while maintaining low confinement loss. It provides a long and protected medium for light-matter interaction and large cavities to ease the infiltration of sensing elements. DRFs with different waveguide parameters have been analyzed theoretically and fabricated using stack-and-draw fiber drawing technique. Mode analysis has been performed experimentally on the fabricated fibers while the confinement loss and the percentage of evanescent field exposure are examined by simulation. DRF allows evanescent field exposure as high as 39.56% with negligible confinement loss at a wavelength of 1550nm.

From parabolic-trough to metasurface-concentrator: assessing focusing in the wave-optics limit

Liyi Hsu, Matthieu Dupre, Abdoulaye Ndao, and Boubacar Kante

Doc ID: 283777 Received 28 Dec 2016; Accepted 16 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: Metasurfaces are promising tools towards novel designs for flat optics applications. As such their quality and tolerance to fabrication imperfections need to be evaluated with specific tools. However, most such tools rely on the geometrical optics approximation and are not straightforwardly applicable to metasurfaces. In this Letter, we introduce and evaluate, for metasurfaces, parameters such as the intercept factor and the slope error usually defined for solar concentrators in the realm of ray-optics. After proposing definitions valid in physical optics, we put forward an approach to calculate them. As examples, we design three different concentrators based on three specific unit cells and assess them numerically. The concept allows for the comparison of the efficiency of the metasurfaces, their sensitivities to fabrication imperfections and will be critical for practical systems.

Ultra-long propagation of the surface plasmon polariton wave within ultra-wide bandwidth via phase sensitive optical parametric amplification

Mohammad Izadi and Rahman Nouroozi

Doc ID: 290283 Received 08 Mar 2017; Accepted 16 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: The propagation length enhancement of the surface plasmon polariton (SPP) waves could lead to their practical applications. This letter proposes the numerically verified phase sensitive nonlinear χ(2)-based optical parametric amplification (OPA) for ultra long propagation of the SPP wave within an ultra wide bandwidth. The strong nonlinear interaction between SPP mode and hybrid guided mode which limits the length enhancement, is mitigated in a silver coated linearly chirped periodically poled lithium niobate (PPLN) planar waveguide via slowly phase matched OPA. Obtained results indicate ultra long propagation length for the SPP mode of about 4 cm when a 135 MW/cm pump intensity is launched. The acceptance bandwidth of the amplified SPP shows its dependency to the pump intensity; for a pump intensity range between 70 to 135 MW/cm, the acceptance bandwidth is still ultra wide varying from 28 to 18 nm, respectively.

Coherent mode decomposition using mixed Wigner functions of Hermite-Gaussian beams

Takashi Tanaka

Doc ID: 285318 Received 23 Jan 2017; Accepted 16 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: A new method of coherent mode decomposition (CMD) is proposed, which is based on a Wigner-function representation of Hermite-Gaussian beams. In contrast to the well-known method using the cross spectral density (CSD), it directly determines the mode functions and their weights without solving the eigenvalue problem. This facilitates the CMD of partially-coherent light whose Wigner functions (and thus CSDs) are not separable, in which case the conventional CMD requires to solve an eigenvalue problem with a large matrix and thus is numerically formidable. An example is shown regarding the CMD of synchrotron radiation, one of the most important applications of the proposed method.

Tilted fiber Bragg gratings in multicore optical fibers for optical sensing

David Barrera, Javier Madrigal, and Salvador Sales

Doc ID: 285530 Received 24 Jan 2017; Accepted 15 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: We have inscribed a tilted fiber Bragg grating (TFBG) in selected cores of a multicore optical fiber. The presence of the TFBG permits to couple light from the incident guided mode to the cladding modes and to the neighbor cores and this interaction can be used for optical sensing. We have considered to measure different magnitudes: strain, curvature magnitude and direction and external refractive index. The curvature results show a linear dependence of the maximum crosstalk with the curvature magnitude with a sensitivity of 2.5dB/m-1 as the curvature magnitude increases and at the same time a wavelength shift of 70pm/m 1. Changes in the external refractive index gradually vanishes the cladding modes resonances and the crosstalk between the different cores obtaining a reduction of the 90% of the optical spectra integral area for refractive indexes between 1.398 to 1.474.

High Efficiency Femtosecond Raman Solitons Generation with Tunable Wavelength beyond 2μm

JIAQI LUO, Biao Sun, Junhua Ji, Eng Leong Tan, and Xia Yu

Doc ID: 286011 Received 01 Feb 2017; Accepted 15 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: We report an efficient Raman soliton laser system by optimizing the chirp of input pulses. The highest efficiency of energy transferred to Raman soliton is up to 97% over the tunable range from 1.98 to 2.31 μm. The pulse width of these tunable Raman solitons remains below 200 fs. The efficiency and the wavelength range are mainly limited by the background loss of silica fiber.

Direct Wide-angle Measurement of Photonic Band- structure in a Three-dimensional Photonic Crystal using Infrared Fourier Imaging Spectroscopy

lifeng chen, Martin Lopez Garcia, Mike Taverne, Xu Zheng, Ying-Lung Ho, and John Rarity

Doc ID: 287546 Received 01 Mar 2017; Accepted 15 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We propose a method to directly visualize the photonic band-structure of micron size photonic crystals using wide angle spectroscopy. By extending Fourier Imaging Spectroscopy sensitivity into the infrared range we have obtained accurate measurements of the band-structures along the high-symmetry directions (X-W-K-L-U) of polymeric three-dimensional rod-connected diamond photonic crystals. Our implementation also allows us to record single-wavelength reflectance far field patterns showing a very good agreement with simulations of the same designs. This technique is suitable for the characterization of photonic structures working in the infrared and in particular, to obtain band-structure information of complete photonic band gap materials.

Low index contrast imaging fibers

James Stone, Harry Wood, Kerrianne Harrington, and Tim Birks

Doc ID: 284462 Received 10 Jan 2017; Accepted 15 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: We present high resolution imaging fibers made from low-cost commercially available fiber preforms manufactured for the telecommunications industry. Our fabrication method involves multi-stacking arrays of different sized cores in order to suppress core-to-core cross-talk whilst building up a large array of cores. One of the fibers, based on a square arrays of cores, has comparable imaging performance to commercial imaging fibers but without the need for exceptionally high refractive index contrasts, and will enable the development of economically-viable single-use disposable imaging fibers.

The study of spinel LiTi2O4 superconductors via near-infrared reflection experiments

Yanmin Zhang, Wen Xu, Lan Ding, Xia Chen, jie zhang, Changneng Liang, Hongying Mei, Yanli Jia, Kui Jin, Chen Guan, Tiandi Chen, and Sasa Zhang

Doc ID: 285505 Received 26 Jan 2017; Accepted 14 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: We present an optical study on high-quality and single phase LiTi2O4 (LTO) superconductor thin films grown on MgAl2O4 substrates by pulsed laser deposition. The near-infrared (NIR) reflectivity is measured for samples with (001) and (111) lattice orientations. The temperature induced metal-superconductor transition can be observed and the superconducting transition temperature can be measured for both samples. We find that the NIR reflection experiment can reflect rightly the basic features of LTO superconductor thin films. Furthermore, the results obtained from this simple optical measurement suggest that the photo-induced electronic localization effect can be present in LTO thin films in metallic state. Such information cannot be obtained directly from conventional transport and magneto-transport measurements. These interesting and important findings demonstrate that the NIR reflection experiment is a powerful optical technique for contactless characterization and investigation of superconductor materials.

Digital micro-mirror device based common-path quantitative phase imaging

Cheng Zheng, Renjie Zhou, Cuifang Kuang, Guangyuan Zhao, Zahid Yaqoob, and Peter So

Doc ID: 286653 Received 16 Feb 2017; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: We propose a novel common-path quantitative phase imaging (QPI) method based on a digital micro-mirror device (DMD). The DMD is placed in a plane conjugate to the objective back aperture plane for the purpose of generating two plane waves that illuminate the sample. A pinhole is used in the detection arm to filter one of the beams after sample to create a reference beam. Additionally, a transmission-type liquid crystal device (LCD), placed at the objective back-aperture plane, eliminates the specular reflection noise arising from all the “off” state DMD micromirrors, which is common in all DMD-based illuminations. We have demonstrated high sensitivity QPI, which has a measured spatial and temporal noise of 4.92 nm and 2.16 nm, respectively. Experiments with calibrated polystyrene beads illustrate the desired phase measurement accuracy. In addition, we have measured the dynamic height maps of red blood cell (RBC) membrane fluctuations, showing the efficacy of the proposed system for live cell imaging. Most importantly, the DMD grants the system convenience in varying the interference fringe period on the camera to easily satisfy the pixel sampling conditions. This feature also alleviates the pinhole alignment complexity. We envision that the proposed DMD-based common-path QPI system will allow for system miniaturization and automation for a broader adaption.

Robust, low-noise, polarization-maintaining mode-locked Er-fiber laser with a planar lightwave circuit (PLC) device as a multi-functional element

Chur Kim, Dohyeon Kwon, Dohyun Kim, Sun Young Choi, Sang Jun Cha, Ki Sun Choi, Dong-Il Yeom, Fabian Rotermund, and Jungwon Kim

Doc ID: 286824 Received 21 Feb 2017; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: We demonstrate a new planar lightwave circuit (PLC)-based device, integrated with 980/1550 wavelength division multiplexer (WDM), evanescent-field-interaction-based SA and output tap coupler, that can be employed as a multi-functional element in mode-locked fiber lasers. Using this multi-functional PLC device, we demonstrate a simple, robust, low-noise, and polarization-maintaining mode-locked Er-fiber laser. The measured full-width at half-maximum (FWHM) bandwidth is 6 nm centered at 1555 nm, corresponding to 217-fs transform-limited pulse duration. The measured RIN and timing jitter are 0.22% [10 Hz – 10 MHz] and 6.6 fs [10 kHz - 10 MHz], respectively. Our result shows that non-gain section of mode-locked fiber lasers can be easily implemented as a single PLC chip that can be manufactured by wafer-scale fabrication process. The use of PLC processes in mode-locked lasers has a potential for higher manufacturability of low-cost and robust fiber and waveguide lasers.

Selective reflection from Rb layer with thickness below λ/12 and applications

Aram Papoyan, Armen Sargsyan, Ifan Hughes, Charles Adams, and David Sarkisyan

Doc ID: 287268 Received 22 Feb 2017; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: We have studied the peculiarities of selective reflection from Rb vapor cell with thickness L < 70 nm, which is over an order of magnitude smaller than the resonant wavelength for Rb atomic D₁ line λ = 795 nm. A huge (~240 MHz) red shift and spectral broadening of reflection signal is recorded for L = 40 nm caused by the atom-surface interaction. Also completely frequency resolved hyperfine Paschen-Back splitting of atomic transitions to four components for ⁸⁷Rb and six components for ⁸⁵Rb is recorded in strong magnetic field (B > 2 kG).

Linearly chirped tapered fiber Bragg grating based Fabry-Perot cavity and its application in simultaneous strain and temperature measurement

Konrad Markowski, Kazimierz Jędrzejewski, Michał Marzęcki, and Tomasz Osuch

Doc ID: 287336 Received 23 Feb 2017; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: A novel concept of a Fabry-Perot cavity composed of two linearly chirped fiber Bragg gratings written in a thermally-fused fiber taper is presented. Both chirped gratings are written in counter-directional chirp configuration, where chirps resulting from the optical fiber taper profile and linearly increasing grating periods cancel each other out, forming a high quality F-P resonator. A new strain sensing mechanism is proposed in the presented structure, which is based on strain induced detuning of the F-P resonator. Due to the different strain and temperature responses of the cavity, it can be used for the simultaneous measurement of these physical quantities, or it can be used as a temperature independent strain sensor.

Linewidth enhancement factor measurement based on FM-modulated optical injection: application to rare-earth doped active medium

Aurélien Thorette, Marco Romanelli, and Marc Vallet

Doc ID: 283232 Received 23 Dec 2016; Accepted 14 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: A new method for measuring the linewidth enhancement factor of a laser is proposed. It is based on frequency-modulated optical injection, combined with dual-frequency laser operation. The linewidth enhancement factor α is deduced from the experimental data using a theoretical analysis based on a standard rate equation model. As the intracavity power is kept constant, the method allows to free the process from the thermal effects that are usually present in AM/FM techniques. Measurement of α=0.28±0.04 in a diode-pumped Nd:YAG laser demonstrates that the method is well-suited for characterizing small values of α.

Controlled inhibition of spiking dynamics in VCSELs for neuromorphic photonics: theory and experiments

Joshua Robertson, Tao Deng, Julien Javaloyes, and Antonio Hurtado

Doc ID: 285531 Received 27 Jan 2017; Accepted 14 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: We report experimentally and on theory on the controllable inhibition of spiking regimes in a 1300 nm Vertical Cavity Surface Emitting Laser (VCSEL). Reproducible suppression of spiking dynamics is demonstrated at fast operation speeds (up to sub-ns rates) and with total control on the temporal duration of the spiking inhibition windows. This work opens new paths towards photonic inhibitory neuronal models for use in future neuromorphic photonic information processing systems and which are able to operate at speeds up to 8 orders of magnitude faster than biological neurons.

Ultra-broadband mid-wave-IR upconversion detection

Ajanta Barh, Christian Pedersen, and Peter Tidemand-Lichtenberg

Doc ID: 285809 Received 27 Jan 2017; Accepted 14 Mar 2017; Posted 20 Mar 2017  View: PDF

Abstract: In this letter, we demonstrate efficient room temperature detection of ultra-broad-band mid-wave-infrared (MWIR) light with almost flat response over more than 1200 nm, exploiting an efficient nonlinear up-conversion technique. Black-body radiation from a hot soldering iron rod is used as the IR test source. Placing a 20 mm long periodically poled lithium niobate (PPLN) crystal in a compact intra-cavity set-up (> 20 Watt CW pump at 1064 nm), MWIR wavelengths ranging from 3.6 to 4.85 µm is up-converted to near-infrared (NIR) wavelengths (820 to 870 nm). The NIR light is detected using a standard low-noise silicon-based camera/grating spectrometer. The proposed technique allows high conversion efficiency over wider band-width, without any need for shorter crystal length. Different analytical predictions and numerical simulations are performed a priori to support the experimental demonstrations.

High-speed stimulated hyperspectral Raman imaging using rapid acousto-optic delay lines

Mohammed Al Alshaykh, Chien-Sheng Liao, Oscar Sandoval, Gregory Gitzinger, Nicolas Forget, Daniel Leaird, Ji-Xin Cheng, and Andrew Weiner

Doc ID: 285619 Received 07 Feb 2017; Accepted 14 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: Stimulated Raman scattering (SRS) is a powerful, label-free imaging technique that holds significant potential for medical imaging. To allow chemical specificity andminimize spectral distortion in the imaging of live species, a high-speed multiplex SRS imaging platform is needed. By combining a spectral focusing excitation technique with a rapid acousto-optic delay line, we demonstrate a hyperspectral SRS imaging platform capable of measuring a spectral window of ~200 cm-1 within 12.8 μs with a scan rate of 30 KHz. We present hyperspectral images of a mixture of two different microsphere polymers as well as live fungal cells mixedwith human blood.

Single-mode unidirectional microcavity laser

Zhen-Nan Tian, Feng Yu, Yan-Hao Yu, Jun-Jie Xu, Qi-Dai Chen, and Hong-Bo Sun

Doc ID: 286216 Received 07 Feb 2017; Accepted 14 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: In this letter, we report a suspended whispering gallery mode microdisk with a hole pierced through its surface. The novel disk is made up of Rhodamine B-doped resin, which is fabricated by femtosecond laser direct writing technology. The pierced microcavity achieves highly directional emission of single-mode lasing with a far field divergence angle of about 10°, and its high-Q factor exceeds 2.6 × 10³. The excellent properties are confirmed by numerical simulation based on Finite-Difference Time-Domain method. The effect of the pierced hole on the microcavity performance is discussed in detail. The method is easy to implement and has a guiding significance for improving the characteristics of existing microcavity by simple modification.

In vivo photoacoustic imaging of vasculature with a low-cost miniature light emitting diode excitation

Xianjin Dai, hao yang, and Huabei Jiang

Doc ID: 286166 Received 07 Feb 2017; Accepted 13 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: In this Letter, we present a low-cost high-power miniature light emitting diode (LED)-based photoacoustic imaging system capable of in vivo mapping vasculature networks in biological tissue. Overdriving with 200-ns pulses and operating at a repetition rate of 40 kHz, a 1.2-W 405-nm LED with a radiation area of 1000µm x 1000µm and a whole size of 3.5mm x 3.5mm was used to excite photoacoustic signals in tissue. Phantoms including black stripes, lead and hair, were used to validate the system. In vivo imaging of the vasculature of mouse ear shows that LED-based photoacoustic imaging (LED-PAI) could have great potential for label-free biomedical imaging applications where the use of bulky and expensive pulsed lasers is impractical.

Cavity-induced phase noise suppression in Fabry-Perot modulator-based optical frequency comb

Joonyoung Kim, David Richardson, and Radan Slavik

Doc ID: 286136 Received 03 Feb 2017; Accepted 13 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: We investigate for the first time, both theoretically and experimentally, how the phase noise of the RF drive signal affects the phase noise of the individual tones of a Fabry-Perot (F-P) modulator-based optical frequency comb. We observe that the expected deleterious effect of the RF drive signal phase noise on the comb output is partially suppressed due to the filtering characteristics of the F-P cavity. We found that the cavity-induced phase noise suppression is strongest for high-order comb tones, e.g., reaching up to 40 dB for the 100th comb tone at high offset frequencies. The phase noise suppression becomes even stronger for low RF-drive powers, or when the seed laser does not resonate in the F-P cavity. For both cases we observe up to 10dB increase in phase noise suppression. We also evaluate the timing jitter improvement obtained thanks to the cavity-induced phase noise reduction. The timing jitter (integrated from 2.5 MHz to 2.5 GHz) decreased by a factor of 7 for the beat signal obtained between two comb tones that are 100 tones apart (in comparison with the timing jitter obtained in a cavity-less comb generator).

Lasing in organic mixed-crystal thin films with cavities composed of naturally formed cracks

Masaaki Mantoku, Masao Ichida, Ikurou Umezu, Akira Sugimura, and Tamao Aoki-Matsumoto

Doc ID: 287808 Received 03 Mar 2017; Accepted 13 Mar 2017; Posted 21 Mar 2017  View: PDF

Abstract: This study investigates the possibility that a crack pair which is naturally formed in the course of sample preparation functions as a laser cavity. Lasing with longitudinal mode structures has been reported in mixed-crystal thin films composed of fluorene and anthracene without artificial cavity structure. In the present study, it was shown that lasing is observed only when an excitation spot covers parallel pairs of cracks. The longitudinal mode intervals of the stimulated emission spectra for several crack pairs were found to be proportional to the inverse of the crack spacing. Furthermore, the interval for the artificially fabricated metal cavity followed the same linear relation. These results indicate that the crack pairs can function as laser cavities.

A design of ultracompact polarimeters based on dielectric metasurfaces

Shuwen Wei, Zhen Yu Yang, and Ming Zhao

Doc ID: 287130 Received 21 Feb 2017; Accepted 13 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: The state of polarization (SOP) is the key characteristic of light waves; its evaluation is typically based on measurements of the Stokes parameters. But conventional approaches often have bulky and complex optical system with long acquisition time. In this work, an ultracompact polarimeter based on dielectric metasurfaces is proposed. The pixel of the proposed metasuface has six areas; each area acts as not only a polarization separator but also a flat focusing lens. It can acquire a certain polarization component of the incident light and focus the component on the receiver. Therefore, the Stokes parameters of the incident light can be immediately determined through the data from the receiver, fully describing its SOP. The incident light waves with different SOPs are simulated to demonstrate that the reconstructed Stokes parameters are in good agreement with the original ones.

Determining topological charge of an optical beam using a wedged optical flat

Behzad Khajavi and Enrique Galvez

Doc ID: 284650 Received 12 Jan 2017; Accepted 13 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: The topological charge of a beam carrying an optical vortex is an important parameter that specifies the amount of orbital angular momentum carried by the beam and the order of the beam mode. We present an experimental method to determine the sign and magnitude of the topological charge using a wedged optical flat as a lateral shearing interferometer. When the wavefront of the beam is planar, the fringe pattern generated by the shearing interferometer consists of two conjoined forks that unambiguously identify the topological charge of the beam. We also investigated the changes in the pattern when the wedged flat is rotated.

Dynamics of an optically bound structure made of particles of unequal sizes

Vitezslav Karasek, Martin Siler, Oto Brzobohaty, and Pavel Zemanek

Doc ID: 285905 Received 01 Feb 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: The theoretical study based on the coupled dipoles model focuses on the dynamics of two optically bound dielectric spheres of unequal sizes confined in counter-propagating incoherent Bessel beams. We analyzed relative motion of the particles with respect to each other and defined conditions where they form stable optically bound structure (OBS). We also investigated motion of the center of mass of the OBS and found that its direction depends on the particle separation in the structure. Except optical interaction between objects we also considered a hydrodynamic coupling in order to obtain more precise results for moving OBS.

Pseudo actinometry for the measurement of reactive species density

Minwook Kang, Yunhyeok Ko, Il-yong Jang, Junhwa Jung, and Jae Hahn

Doc ID: 286458 Received 21 Feb 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: To compensate for the effect of plasma parameters in the signal of optical emission spectroscopy, we should normalize the emission intensity from the species against that of an inert gas (i.e., the actinometer). In many plasma processes in the semiconductor industry, plasma etching without using a neutral gas for the actinometer has become popular to achieve better critical dimension uniformity. We propose “pseudo actinometry” for normalization in the absence of an inert gas in the process plasma. Based on the theory of optical actinometry, we define a correction factor as the ratio of the emission intensity to the number density of the inert gas. As we reduced the density of the inert gas, we experimentally determined the correction factor by taking its convergence when the concentration of the inert gas was zero. As proof of concept, we applied pseudo actinometry to measure the density distribution of atomic chlorine in a photomask etching process without an inert gas. By comparing the distributions of chlorine radicals and the etch rate as measured by an ellipsometer, we calculated the correlation coefficient between the distributions. The correlation coefficient rapidly decreased to 0.65 when we used the correction factor determined at a flow rate for the inert gas of 20 standard cubic centimeters per minute at STP. By using pseudo actinometry, we successfully determined the distribution of chlorine radicals with a correlation coefficient of 0.98 in a plasma etching process without an inert gas.

Femtosecond semiconductor laser system withresonator-internal dispersion adaptation

Rouven Pilny, Benjamin Döpke, Jan C Balzer, Carsten Brenner, Andreas Klehr, Andrea Knigge, Guenther Traenkle, and Martin Hofmann

Doc ID: 285371 Received 03 Feb 2017; Accepted 13 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: We present a femtosecond laser diode system that is capableof autonomously adjusting itself to compensatefor the external dispersion in an arbitrary application.The laser system contains a spatial light modulator insidethe cavity which is controlled by an evolutionaryalgorithm in order to allow for phase and amplitudeshaping of the laser emission. The cavity internal dispersioncontrol is shown to be much more efficient thanan external control with a pulse shaper.

Ultrasensitive micro-scale parity-time-symmetric ring laser gyroscope

jinhan ren, Hossein Hodaei, Gal Harari, Absar Hassan, Weng Chow, Mohammad Soltani, Demetrios Christodoulides, and Mercedeh Khajavikhan

Doc ID: 287042 Received 20 Feb 2017; Accepted 11 Mar 2017; Posted 23 Mar 2017  View: PDF

Abstract: We propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non-Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed (√Ω)- thus enhancing the sensitivity to low angular rotations by orders of magnitudes. In addition, at its maximum sensitivity limit, the measurable spectral splitting is independent of the radius of the rings involved. Our work paves the way towards a new class of ultrasensitive miniature ring laser gyroscopes on chip.

Broadband single-mode single-polarization passive fully-aperiodic large-pitch fibers

Rémi du Jeu, Romain Dauliat, dia darwich, Aurélien Benoit, Raphael Jamier, Kay Schuster, and Philippe Roy

Doc ID: 285897 Received 17 Feb 2017; Accepted 11 Mar 2017; Posted 16 Mar 2017  View: PDF

Abstract: Two evolutions of fully-aperiodic large-pitch fiber designs employing few stress-applying parts are presented. The induced elasto-optic stress discriminates the two orthogonal polarization modes (LP01x and LP01y) of the fundamental mode, selectively delocalizing one of them into the cladding via a suitable coupling to one or several cladding modes. This ensures the propagation of a single linear polarization mode. For the largest core dimensions, the applied stress can however strongly influence the intensity distributions of core modes and a tailored design process must thwart this. The polarization properties are investigated experimentally with core scalability over a large spectral bandwidth into passive structures, leading to the evidencing of a single-mode single-polarization over a large span from 1µm to 1.6µm with a core dimension of 80µm and notably at 1400nm for a core dimension of 140µm. The polarization extinction ratio is also determined.

Controlling Interface States in 1D Photonic Crystals by tuning Bulk Geometric Phases

Wensheng Gao, Meng Xiao, Bao-jie Chen, Edwin Pun, Che Ting Chan, and Wing Yim Tam

Doc ID: 287737 Received 02 Mar 2017; Accepted 11 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: There is no known simple rule that assures the existence of interface states in photonic crystals. We show here that one can control the existence or absence of interface states in 1D photonic crystals through engineering the bulk geometrical phase such that interface states can be guaranteed in some or all photonic bandgaps. We verify experimentally the interface state design paradigm in 1D multilayered photonic crystals fabricated by electron beam vapor deposition. We obtain the geometrical phases by measuring the reflection phases at the bandgaps of the photonic crystals and achieve good agreement with the theory. Our approach could provide a platform for generating photonic crystal interface state for various applications.

F/Yb-codoped sol-gel silica glasses: toward tailoring the refractive index for the achievement of high power fiber lasers

HICHAM EL HAMZAOUI, Geraud Bouwmans, Andy Cassez, Laurent Bigot, Bruno Capoen, Mohamed Bouazaoui, Olivier Vanvincq, and Marc Douay

Doc ID: 285602 Received 25 Jan 2017; Accepted 10 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: Accurate control of both the doping distribution inside the fiber core and the low refractive index (RI) contrast between the fiber core and cladding materials is essential for the development of high power fiber lasers based on the use of single mode Large Mode Area (LMA) optical fibers. Herein, sol-gel monolithic F/Yb3+-codoped silica glasses were prepared from porous large silica xerogels doped with ytterbium salt solution, which have been subjected to fluorination with hexafluoroethane gas, before subsequent sintering. The fluorine content inside the doped glass has been tailored by adjusting the fluorination duration. Space homogeneity of fluorine and ytterbium concentrations in the cylindrical preforms has been checked by chemical analysis and Raman spectroscopy. Moreover, the glass with the lowest fluorine content has been successfully integrated as a core material in a microstructured optical fiber made using the stack-and-draw method. This fiber was tested in an all-fibered cavity laser architecture to evaluate potential lasing performances of the F/Yb3+-codoped silica glass. It presents a maximum efficiency of 70.4 %, achieved at 1031 nm from a 1.16 m-length fiber. These results confirm the potentialities of the obtained F/Yb3+-codoped glasses for the fabrication of LMA optical fiber lasers.

Compact interferometric module for full-field interferometric phase microscopy with low spatial coherence illumination

Amit Nativ and Natan Shaked

Doc ID: 285624 Received 25 Jan 2017; Accepted 09 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: We propose a compact and external off-axis interferometric module that can achieve interference with low spatial coherence illumination over the entire field of view. The interferometer is easy to align, stable, and can be connected to the output of an existing microscope illuminated with low spatial coherence light source, thus allowing quantitative phase imaging with low degree of spatial noise. We demonstrate the imaging and the interference properties of the proposed interferometric module and use it for quantitative phase imaging of reflective samples.

Split in phase singularities of an optical vortex by diffraction through a simple circular aperture

Yoshitaka Taira and Shukui Zhang

Doc ID: 284332 Received 27 Jan 2017; Accepted 09 Mar 2017; Posted 09 Mar 2017  View: PDF

Abstract: Diffraction patterns of an optical vortex through several shaped apertures reveal its topological charge. In this letter, we theoretically and experimentally show that diffraction of a Laguerre Gaussian beam through a circular aperture at an off-axis position can be used to determine the magnitude and sign of the topological charge. To our knowledge, this is the first time that a simple circular aperture has been used to detect orbital angular momentum of an incident optical vortex.

A compressive-sensing Fourier-transform on-chip spectrometer

Hugh Podmore, Alan Scott, Pavel Cheben, Aitor Velasco, Jens Schmid, Martin Vachon, and Regina Lee

Doc ID: 286360 Received 09 Feb 2017; Accepted 09 Mar 2017; Posted 09 Mar 2017  View: PDF

Abstract: We demonstrate compressive-sensing (CS) spectroscopy in a planar-waveguide Fourier-transform spectrometer device. The spectrometer is implemented as an array of Mach-Zehnder interferometers (MZIs) integrated on a photonic chip. The signal from a set of MZIs comprises an undersampled discrete Fourier interferogram, which we invert using l1-norm minimization to retrieve a sparse input spectrum. To implement this technique we use a subwavelength-engineered spatial heterodyne Fourier-transform spectrometer on a chip comprising 32 independent MZIs. We demonstrate the retrieval of three sparse input signals by collecting data from restricted sets (8 and 14) of MZIs and applying common compressive-sensing reconstruction techniques to this data. We show that this retrieval maintains the full resolution and bandwidth of the original device despite a sampling factor as low as ¼th of a conventional (non-compressive) design.

Partially coherent sources with circular coherence

Massimo Santarsiero, Rosario Martinez-Herrero, David Maluenda Niubó, Carlos de Sande, Gemma Piquero, and Franco Gori

Doc ID: 287006 Received 20 Feb 2017; Accepted 09 Mar 2017; Posted 17 Mar 2017  View: PDF

Abstract: A new class of partially coherent light sources is introduced. At the source plane, they exhibit perfect coherence along any annulus that is concentric to the source center. Between two points at different distances from the center, coherence can be partial or even vanishing. Such sources can be synthesized by using a generalized form of van Cittert-Zernike theorem where axial sources are used. Beam radiated by this type of sources are analyzed at the source plane and upon free propagation for some simple cases.

The Borrmann effect in photonic crystals

Vladimir Novikov and Tatyana Murzina

Doc ID: 287084 Received 21 Feb 2017; Accepted 08 Mar 2017; Posted 09 Mar 2017  View: PDF

Abstract: We present the experimental observation of the optical Borrmann effect in 1D porous silica based photonic crystals (PhC) composed of several hundreds of dielectric layers with different porosity. Two mechanisms of the effect are demonstrated, which involve the optical losses associated with the light scattering and absorption in nanoporous layers. Absorption is introduced by a small amount of silicon in partially annealed porous silicon PhC. We show that the PhC transmittance increases substantially under the Bragg diffraction condition, which is a manifestation of the Borrmann effect. The observed effects along with their polarization sensitivity are confirmed by numerical calculations.

Pupil segmentation adaptive optics for in vivo fluorescence retinal imaging

Daniel Wahl, Christine Huang, Stefano Bonora, Yifan Jian, and Marinko Sarunic

Doc ID: 283535 Received 05 Jan 2017; Accepted 08 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: Adaptive Optics (AO) for Scanning Laser Ophthalmoscopy (SLO) enables high resolution retinal imaging that can be used for pre-clinical research of diseases causing vision loss. Optical wavefront aberrations that decrease the quality of images can be corrected with a deformable optical element to improve the resolution. Pupil Segmentation Adaptive Optics (PS-AO) is an approach to sensorless AO that acquires images within sub-regions across the imaging pupil to measure the wavefront slopes at the corresponding locations of the beam. We present PS-AO as an approach to correct ocular aberrations that is quick and robust to motion for pre-clinical in vivo imaging. We demonstrated an improvement in resolution using PS-AO for in vivo fluorescence retinal imaging in mice using a MEMS-based segmented deformable mirror.

A 1 kW, 200 mJ picosecond thin-disk laser system

Thomas Nubbemeyer, Martin Kaumanns, Moritz Ueffing, Martin Gorjan, Ayman Alismail, Hanieh Fattahi, Jonathan Brons, Oleg Pronin, Helena Barros, Zsuzsanna Major, Thomas Metzger, Dirk Sutter, and Ferenc Krausz

Doc ID: 283086 Received 22 Dec 2016; Accepted 08 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: We report on a laser system based on thin-disk technology and chirped pulse amplification, providing output pulse energies of 200 mJ at 5 kHz repetition rate. The amplifier contains a ring-type cavity and two thin Yb:YAG disks, each pumped by diode laser systems providing up to 3.5 kW power at 969 nm wavelength. The average output power of more than 1 kW is delivered in an excellent output beam characterized by M² = 1.1 The output pulses are compressed to 1.1 ps at full power with a pair of dielectric gratings.

A 2-MHz multi-wavelength pulsed laser for functional photoacoustic microscopy

Liang Yizhi, Long Jin, Bai-Ou Guan, and Lidai Wang

Doc ID: 284049 Received 09 Jan 2017; Accepted 08 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: Fast functional photoacoustic microscopy requires multi-wavelength pulsed laser sources with high pulse repetition rates, short wavelength switching time and sufficient pulse energies. Here, we report the development of a stimulated-Raman-scattering based multi-wavelength pulsed laser source for fast functional photoacoustic imaging. The new laser source is pumped with a 532-nm 1-MHz pulsed laser. The 532-nm laser pulse is split into two beams: one pumps a 5-m optical fiber to excite a 558-nm wavelength via stimulated Raman scattering; the other one goes through a 50-m optical fiber to delay the 532-nm pulse by 220 ns. The two beams are combined and coupled into an optical fiber for photoacoustic excitation. As a result, the new laser source can generate 2 million pulses per second, switch wavelengths in 220 ns, and provide hundreds of nano-Joules pulse energy for each wavelength. Using this laser source, we demonstrate optical-resolution photoacoustic imaging of microvascular structures and oxygen saturation in the mouse ear. The ultrashort wavelength switching time enables oxygen saturation imaging of flowing single red blood cells, which is valuable for high-resolution functional imaging.

Creation of longitudinally polarized photonic nanojet via engineered microsphere

Mengxue Wu, Rui Chen, Jinzhong Ling, Zaichun Chen, Xudong Chen, Rong Ji, and Minghui Hong

Doc ID: 286609 Received 15 Feb 2017; Accepted 08 Mar 2017; Posted 14 Mar 2017  View: PDF

Abstract: Dielectric microspheres exhibit the ability to focus incident beam to a sub-wavelength spot with strong localized field intensity. In this paper, a high beam quality of longitudinally polarized electromagnetic component is created by decorating the surface of the microsphere with engineered structures. By changing the design of the engineered microspheres, relative contribution of the longitudinal and radial components of a radially polarized incident beam to the photonic nanojet can be modified efficiently, leading to a sharp spot size which exceeds the optical diffraction limit. More importantly, a high conversion efficiency of 0.89 is achieved. At a wavelength of 633 nm, a focal spot of 266 nm (0.42 λ) is achieved numerically by illuminating the engineered microsphere with a focusing beam at a numerical aperture of 0.7.

FIR thermometer methodology of eliminating the “decoupling” effect of a thermally coupled pair

feng qin, Hua Zhao, Moyang Lv, Wei Cai, Zhiguo Zhang, and wenwu cao

Doc ID: 286309 Received 08 Feb 2017; Accepted 07 Mar 2017; Posted 08 Mar 2017  View: PDF

Abstract: By separating the thermal population and nonradiative relaxation population, the fluorescence intensity ratio (FIR) of a thermally coupled pairs of rare earth ions is discussed. For a coupled pair, if the ratio of the thermal population in the upper level to the total population of the lower level abides by the Boltzmann distribution law, the universal FIR would be modulated by the proportion of the total population to the thermal population in the upper level. By defining the reciprocal of the proportion as the thermal population degree (η), ηFIR is verified to follow the pure Boltzmann law. By considering the fluorescent transient process, it is determined that the η values are obtainable from the weights of the fluorescent dynamic components of the upper level, and a method to calculate η is presented.

Quasi-needle-like focus synthesized by optical coherence tomography

Wen Bao, Zhihua Ding, Jianrong Qiu, shen yi, Peng Li, and Zhiyan Chen

Doc ID: 286970 Received 17 Feb 2017; Accepted 07 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: It is known that lateral resolution and depth of focus in an optical imaging system are coupled and a compromise between them has to be made. In this Letter, we propose to resolve the trade-off between lateral resolution and depth of focus by synthetic effective point spread function in optical-path-length domain. A quasi-needle-like focus is synthesized by optical coherence tomography. We demonstrate that the synthesized quasi-needle-like focus provides a four-fold extension of conventional depth of focus, while maintaining a high lateral resolution of 2.5 µm over a depth range of approximately 240 µm. The focal range can be further extended with more optical-path-length coded beams for synthesis involved.

Radially- and azimuthally- polarized nanosecond Yb-doped fiber MOPA system incoporating temporal shaping

Di Lin, Neda Baktash, Martin Berendt, Martynas Beresna, Peter Kazansky, W. Clarkson, Shaif-ul Alam, and David Richardson

Doc ID: 284648 Received 12 Jan 2017; Accepted 07 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: We report an Yb-doped fiber master-oscillator power-amplifier (MOPA) system with the capability of selectively generating doughnut-shaped radially- and azimuthally-polarized beams with user-defined temporal pulse shapes. The desired output polarization was generated with the aid of a nanograting spatially variant half-waveplate (S-waveplate). The latter was used to convert the linearly-polarized fundamental (LP01) mode output from the pre-amplification stages to a doughnut-shaped radially-polarized beam prior to the power amplifier stage. A maximum output pulse energy of ~860 µJ was achieved for ~100 nanosecond pulses at 25 kHz with user defined pulse shape for both radial and azimuthal polarization states. The polarization purity and beam propagation factor (M2) were measured to be >12dB and 2.2 respectively.

Dual-channel recording based on null reconstruction effect of orthogonal linear polarization holography

Jinliang Zang, Guoguo Kang, Peng Li, Ying Liu, fan lan, Yifan Hong, Yong Huang, Xiaodi Tan, Anan Wu, Tsutomu Shimura, and Kazuo kuroda

Doc ID: 285110 Received 18 Jan 2017; Accepted 05 Mar 2017; Posted 06 Mar 2017  View: PDF

Abstract: We report on dual-channel recording within polarization holography written by orthogonal linear polarization waves. Null reconstruction effect (NRE) of linear polarization holography was experimentally achieved at large cross-angle of inside the polarization-sensitive media. Based on the NRE, two polarization encoded holograms were recorded in dual-channel recording system with negligible inter-channel crosstalk. The two polarization multiplexed holograms could then be sequentially or simultaneously readout by shifting the polarization state of reference wave with the best signal-to-noise(SNR) of 18:1 obtained within experiment.

Optical concatenation of a large number of beads with a single-beam optical tweezer

Remy Avila, Joaquín Ascencio-Rodríguez, DANIEL TAPIA-MERINO, Oscar Rodriguez Herrera, and Arturo González-Suárez

Doc ID: 286053 Received 03 Feb 2017; Accepted 03 Mar 2017; Posted 06 Mar 2017  View: PDF

Abstract: Optical tweezers consist of the spatial confinement of microscopic dielectric particles by the action of forces produced by the change in momentum of the photons of a highly focused laser beam that are deviated by the particle. In experiments that use a single laser beam it is common to capture not only one but a few particles in the optical trap. However, to our knowledge, the formation of a long chain of beads optically confined with a single laser beam has never been reported. In this work, up to 73 silica spheres immersed in water are seen concatenated along the propagation direction of a 976 nm wavelength gaussian laser of 300 mW of power. This long chain of beads is obtained when the laser is focussed through an oil-immersion DIN microscope objective with 100× magnification and a numerical aperture of 1.25. When performing the same experiment using an infinity-corrected UplanFLN 100× objective with numerical aperture of 1.3, the maximum number of concatenated beads is only 14. Our results suggest that the mechanisms responsible of the observed phenomena involve successive refocusing of the laser beam by each trapped sphere, optically induced dipole coupling (commonly referred to as optical binding) and aberrations generated by the DIN microscope objective.

Asymptotically stable compensation of soliton self-frequency shift

Sabrina Pickartz, Uwe Bandelow, and Shalva Amiranashvili

Doc ID: 285553 Received 25 Jan 2017; Accepted 02 Mar 2017; Posted 02 Mar 2017  View: PDF

Abstract: We report on the stable cancellation of the soliton self-frequency shift (SSFS) in nonlinear optical fibers. A soliton, which scatters a group velocity matched pump wave in a so-called optical event horizon regime, may experience a blue-shift in frequency, which counteracts the SSFS induced by Raman scattering. The SSFS can easily be compensated by a suitably prepared pump wave, but usually the compensation is unstable and is destroyed after a certain propagation length. We study this kind of soliton-pump wave interaction by an adiabatic approach and quantify the parameter range in which the stable SSFS compensation is possible. The theory enjoys agreement with numerical simulations of soliton propagation.

Femtosecond pulse generation from a Ti3+:sapphire laser near 800 nm with voltage reconfigurable graphene saturable absorbers

Isinsu Baylam, Sarper Ozharar, Nurbek Kakenov, Coskun Kocabas, and Alphan Sennaroglu

Doc ID: 281433 Received 23 Nov 2016; Accepted 02 Mar 2017; Posted 13 Mar 2017  View: PDF

Abstract: We experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level, and hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2V). The fast saturable absorber action of the VCG-gold-SA and bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode-locker with adjustable loss.

Double-Layer Interlaced Nested Multi-Ring Array Metallic Mesh for High-Performance Transparent Electromagnetic Interference Shielding

He yan Wang, Lu Zhengang, Yeshu Liu, Jiubin Tan, Limin Ma, and Shen Lin

Doc ID: 282155 Received 05 Dec 2016; Accepted 02 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: We report a nested multi-ring array metallic mesh (NMA-MM) that shows a highly uniform diffraction pattern theoretically and experimentally. Then a high-performance transparent electromagnetic interference (EMI) shielding structure is consisted of double-layer interlaced NMA-MMs separated by transparent quartz-glass substrate. Experimental results show that double-layer interlaced NMA-MM structure exhibits a shielding effectiveness (SE) of over 27dB in the Ku-band, with a maximal SE of 37dB at 12GHz, normalized optical transmittance of 90%, and minimal image quality degradation due to the interlaced arrangement. It is thus indicated the great potential for practical applications in transparent EMI shielding devices

Ultrawideband microwave photonic filter with high Q-factor using a semiconductor optical amplifier

Han Chen

Doc ID: 286034 Received 03 Feb 2017; Accepted 27 Feb 2017; Posted 06 Mar 2017  View: PDF

Abstract: An ultrawideband microwave photonic filter (MPF) with high quality (Q) factor based on birefringence effects in a semiconductor optical amplifier (SOA) is presented and the theoretical fundamentals of the design are explained. The proposed MPF along orthogonal polarization in an active loop operates at up to Ku-band and provides a tunable free spectral range from 15.44 GHz to 19.44 GHz by controlling the SOA injection current. A prototype of the equivalent second-order infinite impulse response filter with a Q factor over 6300 and a rejection ration exceeding 41 dB is experimentally demonstrated.

Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures

Diego Pérez-Galacho, Carlos Alonso Ramos, florent mazeas, Xavier LE ROUX, Dorian Oser, Weiwei Zhang, Delphine Marris-Morini, laurent labonte, Sebastien Tanzilli, Eric Cassan, and Laurent Vivien

Doc ID: 286288 Received 07 Feb 2017; Accepted 27 Feb 2017; Posted 14 Mar 2017  View: PDF

Abstract: The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugations widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, on the realization of SOI Bragg filters based on subwavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a singleetch, 220 nm thick, Si Bragg filter featuring a corrugation width of 150 nm, a rejection bandwidth of 1.1 nm and an extinction ratio exceeding 40 dB. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch counterparts withsimilar bandwidths.

Four-wave mixing Bragg scattering in hydrogenated amorphous silicon waveguides

Kangmei Li, Hongcheng Sun, and Amy Foster

Doc ID: 286051 Received 03 Feb 2017; Accepted 23 Feb 2017; Posted 08 Mar 2017  View: PDF

Abstract: We demonstrate 15% conversion efficiency of four-wave mixing Bragg scattering in a hydrogenated amorphous silicon waveguide with only 55 mW and 194 mW peak pump powers in the waveguide. The lightwaves can be maintained in the telecommunications band and the operational bandwidth is measured to be larger than 4 nm.

Study of extra wide coherent optical combs generated by QW based integrated passively mode-locked ring laser

Valentina Moskalenko, Jeroen Koelemeij, Kevin Williams, and Erwin Bente

Doc ID: 284798 Received 01 Feb 2017; Accepted 20 Feb 2017; Posted 14 Mar 2017  View: PDF

Abstract: We present an investigation of an InP quantum-well based integrated extended cavity passively mode-locked laser which shows extra broad frequency comb generation. The ring laser was characterized in frequency and time domains for a range of the current levels injected in the SOA. The study showed an increase of the bandwidth to over 40 nm at the -20 dB level. The coherence between the longitudinal modes in the wide comb is demonstrated by characterization of a spectrally filtered signal in time and RF domains. The relative time delay across the optical comb was measured.

Step-scan Differential Fourier Transform Infrared Photoacoustic Spectroscopy (DFTIR-PAS): a spectral deconvolution method for weak absorber detection in the presence of strongly overlapping background absorptions

Lixian Liu, Andreas Mandelis, Huiting Huan, and Kirk Michaelian

Doc ID: 284787 Received 16 Jan 2017; Accepted 19 Feb 2017; Posted 13 Mar 2017  View: PDF

Abstract: The determination of small absorption coefficients of trace gases in the atmosphere constitutes a challenge for analytical air contaminant measurements especially in the presence of strongly absorbing backgrounds. A step-scan Differential Fourier Transform Infrared-Photoacoustic Spectroscopy (DFTIR-PAS) method was developed to suppress coherent external noise and spurious photoacoustic (PA) signals caused by strongly absorbing backgrounds. The infrared absorption spectra of acetylene (C2H2) and local air were used to verify the performance of the step-can DFTIR-PAS method. A linear amplitude response to C2H2 concentrations from 100 to 5,000 ppmv was observed, leading to a theoretical detection limit of 4.5 ppmv. The differential mode was capable of eliminating coherent noise and dominant background gas signals, thereby revealing the presence of the otherwise hidden C2H2 weak absorption. Thus, the step-scan DFTIR-PAS modality was demonstrated to be an effective approach for monitoring weakly absorbing gases with absorption bands overlapped by strongly absorbing background species

Rapid Localized Heating of Graphene Coating on Silicon Mold by Induction for Precision Molding of Polymer Optics

Lin Zhang, Wenchen Zhou, and Allen Yi

Doc ID: 283706 Received 09 Jan 2017; Accepted 17 Feb 2017; Posted 06 Mar 2017  View: PDF

Abstract: In compression molding of polymer optical components with micro/nanoscale surface features, rapid heating of the mold surface is critical for the implementation of this technology for large-scale applications. In this letter, a novel method of localized rapid heating process is proposed. This process is based on induction heating of a thin conductive coating deposited on a silicon mold. Since the graphene coating is very thin (~45 nm), a high heating rate of 10~20 C/s can be achieved by employing a 1,200 W 30kHz electrical power unit. Under this condition, the contact surface of the Si mold and the polymer substrate can be heated above the polymer’s glass transition temperature within 30s and subsequently cooled down to room temperature within several tens of seconds after molding, resulting in an overall thermal cycle of about 3 min or shorter. The feasibility of this process was validated by fabrication of optical gratings, micropillar matrices, and microlens arrays on polymethyl-methacrylate substrate with high precision. The uniformity and surface geometries of the replicated optical elements are evaluated using an optical profilometer, a diffraction test setup and a self-made Shack–Hartmann wavefront sensor. Compared with the conventional bulk heating molding process, this novel rapid localized induction heating process could improve replication efficiency with better geometrical fidelity.

Ultracompact X-ray dosimeter based on scintillators coupled to a nano-optical antenna.

Zhihua Xie, Hichem Maradj, Miguel Suarez, Lydie Viau, Virginie Moutarlier, Claudine Filiatre, Carole Fauquet, Didier Tonneau, and Thierry Grosjean

Doc ID: 284167 Received 05 Jan 2017; Accepted 15 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: We show that nano-optical antennas are capable of controlling the luminescence induced by the absorption of X-rays into matter. The X-ray excited luminescence from a tiny scintillation cluster coupled to a horn nano-optical antenna is highly directed and determined by the antenna geometrical parameters. Directionality is sufficiently high to efficiently outcouple the X-ray excited luminescence to a narrow single mode fiber, thus enabling ultracompact fiber-integrated X-ray sensors. Our nano-optically driven approach offers the possibility of X-ray profiling and dosimetry in ultra-confined environments, opening up new avenues in the fields of X-ray imaging, as well as medical and industrial endoscopy. With this study, nano-optical antennas make a first key contribution to the development of X-ray sensing protocols and architectures.

Dark-field Brillouin microscopy

Giuseppe Antonacci

Doc ID: 283328 Received 21 Dec 2016; Accepted 20 Jan 2017; Posted 23 Jan 2017  View: PDF

Abstract: Brillouin microscopy is a non-contact and label-free technique for mapping fundamental micro-mechanical properties in the volume of biological systems. Specular reflections and elastic scattering easily overwhelm the weak Brillouin spectra due to the limited extinction of virtually imaged phased array (VIPA) spectrometers, thereby affecting the image acquisition. In this Letter, we demonstrate a dark-field method to reject the elastic background light using an annular illumination and a confocal detection. To validate our method, images of polystyrene and liquid samples were obtained using both a confocal and the dark-field system. An extinction ratio of 30 dB was readily achieved.

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