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Accepted papers to appear in an upcoming issue

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Femtosecond Mode-locked Nd3+-doped Ba(Zr,Mg,Ta)O3 Ceramic Laser

Yuki Higashi, Hiroaki Nakao, Akira Shirakawa, Ken-ichi Ueda, Alexander Kaminskii, Satoshi Kuretake, Yuji Kintaka, Koji Murayama, and Nobuhiko Tanaka

Doc ID: 239827 Received 29 Apr 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We have demonstrated continuous wave (CW) laser operation and first sub-200 fs mode-locked laser operation of Nd3+-doped Ba(Zr,Mg,Ta)O3 ceramic. Its disordered crystalline nature exhibits a broad gain bandwidth of 30 nm with high emission cross section. It also has higher thermal and mechanical properties than Nd:glass. In CW operation, the maximum output power of 1.5 W under 6.2 W of absorbed pump power was obtained. In mode-locked operation, the pulse duration of 196 fs with the average power of 60 mW was successfully achieved. The laser spectrum straddled both fluorescence peaks of A-site and B-site Nd3+ ions.

Microfiber Bragg gratings with negative index modulation

Bai-Ou Guan, Yang Ran, Long Jin, Shuai Gao, Li-Peng Sun, Yunyun Huang, and Jie LI

Doc ID: 242264 Received 04 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: In this paper, Bragg gratings with negative index modulation are inscribed into microfibers. The larger germanium-doped core region of the multimode fiber provides the necessary photosensitivity to form type IIa grating when it is drawn down to the micro-scale. The formation of type IIa grating can be accelerated by reducing the diameter of the microfiber due to the lower saturate modulation and the amplified tension-strain transformation effect. This provides a highly efficient way for the fabrication of fiber gratings with 800 oC temperature resistance

Look-back-upon tree recurrence method for Geiger-mode avalanche photodiode performance prediction

Peng Zhao, Yan ZHANG, YuMing Hua, and WeiPing Qian

Doc ID: 242396 Received 12 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: Based on the Poisson signal distribution, this paper for the first time proposes the look-back-upon tree recurrence method under discrete time to predict the performance of Geiger-mode avalanche photodiodes with short dead time. The results of method proposed correspond to the results of previous methods for diverse input flux. The look-back-upon tree recurrence method possesses dramatically low time complexity and space complexity to realize real-time analysis of Geiger-mode avalanche photodiode performance among all the range of dead time and input diversity.

In situ fabrication of tunable microlens

Lei Zhang, Limin Tong, Wei Fang, zhiyuan Wang, Yichuan Wang, and Rui Qiu

Doc ID: 242547 Received 09 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We demonstrate an optofluidic variable-focus microlens formed by solid polydimethylsiloxane (PDMS) meniscus channel wall and tunable liquid lens body. A novel method for in situ fabrication of meniscus channel wall is developed by introducing liquid PDMS prepolymer into a microchannel followed by curing. Three light manipulation techniques including tunable optical focusing, collimating and diverging are realized by varying the refractive index (RI) of liquid lens body. Also, we present an absorption measurement of methylene blue (MB) with a collimated probing light, achieving a detection limit of 0.25 μM by using a 5 mm long detection cell.

High-power, widely tunable, room-temperature picosecond optical parametric oscillator based on cylindrical 5%MgO:PPLN

Suddapalli Chaitanya Kumar, Wei Junxiong, Jérôme Debray, Vicent Kemlin, Benoit Boulanger, Hideki Ishizuki, Takunori Taira, and Majid Ebrahim-Zadeh

Doc ID: 242954 Received 12 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We report a high-power picosecond optical parametric oscillator (OPO) based on cylindrical MgO:PPLN synchronously pumped by a Yb-fiber laser. The singly-resonant OPO is tunable in the near-infrared signal across 1413-1900 nm together with a mid-infrared idler coverage of 2418-4307 nm by angle tuning of the MgO:PPLN crystal at room temperature. With non-optimized output coupling of ~10%, the OPO simultaneously delivers 2.4 W of signal at 1664 nm and 1.7 W of idler at 2950 nm at an overall extraction efficiency of ~45% with high beam pointing stability <30 µrad and <14 µrad for the signal and idler, respectively. The generated signal and idler exhibit passive power stability better than 1% rms and 0.8% rms over 15 h, measured simultaneously at 1638 nm and 3036 nm, respectively, in high beam quality with TEM00 mode profile. The extracted signal pulses from the OPO have duration of 15.2 ps with a spectral bandwidth of 0.7 nm, corresponding to a time-bandwidth product of ΔυΔτ~1.2.

Polarization-sensitive optical coherence tomography system tolerant to fiber disturbances using a line camera

Manuel Marques, Sylvain Rivet, Adrian Bradu, and Adrian Podoleanu

Doc ID: 241308 Received 20 May 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: This Letter presents a spectral-domain, polarization-sensitive optical coherence tomography (PS-OCT) system where the light collection from the two arms of the interferometer is performed exclusively using single-mode fibers and couplers, and the two orthogonal polarization components are sequentially detected by a single line camera. Retardance measurements can be affected by polarimetric effects due to fiber birefringence and diattenuation in fiber couplers. This configuration bypasses such issues by performing polarization selection before the collection fiber, through the combination of a polarization rotator and a linear polarizer. Retardance calibration is achieved with a Berek compensator. Similar net retardance maps of a birefringent phantom are obtained for two different settings of induced fiber birefringence, effectively demonstrating the tolerance of the configuration to fiber-based disturbances.

Diode-end-pumped single-mode mid-infrared laser operation in a single Er:GGG microchip

you zhenyu, Jinglong Xu, Yan wang, Zhaojie Zhu, Jianfu Li, Hongyan Wang, and Chaoyang Tu

Doc ID: 241552 Received 28 May 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We reported on a diode-end-pumped single-mode microchip laser using a 600-μm-thick monolithic Er:GGG at ~2.7 μm, generating a maximum output power of 50.8 mW and the maximum pulsed energy of 0.306 mJ with repetition rates of pumping light of 200 Hz and 100 Hz, respectively. The maximum slope efficiency of the laser was 20.1%. The laser was operated in a single longitudinal mode centered at about 2704 nm with a FWHM of 0.42 nm. The laser had a fundamental beam profile that that the beam quality parameter M2 was measured as 1.46. These results indicate that the Er:GGG microchip laser is a potential compact mid-infrared laser source.

Optimal generation of high harmonics in the water-window region by synthesizing 800-nm and mid-infrared laser pulses

Cheng Jin, Kyung-Han Hong, and Chii Dong Lin

Doc ID: 242536 Received 11 Jun 2015; Accepted 22 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We propose a method to optimally synthesize a strong 800-nm Ti:sapphire laser pulse and a relatively weak mid-infrared laser pulse to enhance harmonic yields in the water-window region. The required wavelength of the mid-infrared laser is varied from about 2.0 to 3.2 μm. The optimized waveforms generate comparable harmonic yields as the waveforms proposed in [Sci. Rep. 4, 7067 (2014)], but with much weaker intensity for the mid-infrared laser. This method provides an alternative scheme, based on the available laser technology, to help realize tabletop light source in the water-window region by high-order harmonic generation.

Highly stable digital holographic microscope using Sagnac interferometer

Arun Anand, Vismay Trivedi, Bahram Javidi, Vani Chhaniwal, Priyanka Vora, and Swapnil mahajan

Doc ID: 236217 Received 17 Mar 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: Interferometric microscopy has grown into a very potent tool for quantitative phase imaging of biological samples. Among the interfermetric methods, microscopy by digital holography is one of the most effective techniques especially for studying dynamics of cells. Imaging of cell fluctuations requires digital holographic setups with high temporal stability. Common path setups in which the object and the reference beam encounters the same set of optical elements provides better temporal stability compared to two beam setups. Here we present a compact, easy to implement, common path digital holographic microscope based on Sagnac interferometer geometry. The microscope is implemented using a diode laser module employing a CCD array or a webcam sensor to record holograms. The system was tested for three dimensional imaging capability, numerical focusing ability and temporal stability. Sub nanometer temporal stability without external vibration isolation components were obtained in both cases. The higher temporal stability makes the microscope compatible to image cell fluctuations, which is demonstrated by imaging the oscillation of cell membrane of human red blood cells.

A new method to evaluate afterpulsing probability in single-photon avalanche diodes

Sheng-Di Lin, Jau-Yang Wu, Yi-Shan Lee, and Bo-Wei Tzou

Doc ID: 239665 Received 23 Apr 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We propose and demonstrate a new method for evaluating afterpulsing effect in single-photon avalanche photodiodes (SPADs). By analyzing the statistical property of dark count rate, we can quantitatively characterize afterpulsing probability of a SPAD. In experiment, the temperature-dependent DCR distribution becomes non-Poissonian at lower temperature and higher excess bias as the afterpulsing effect becomes significant. Our work provides a flexible way to examine afterpulsing probability in either single-device or circuit level.

High reflectance La/B based multilayer mirror for 6.x nm wavelength

Dmitry Kuznetsov, Andrey Yakshin, Marko Sturm, Robbert van de Kruijs, Eric Louis, and Fred Bijkerk

Doc ID: 240794 Received 21 May 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We report a hybrid thin film deposition procedure to significantly enhance the reflectivity of La/B based multilayer structures. This is of relevance for applications of multilayer optics at 6.7 nm wavelength and beyond. Such multilayers showed a reflectance of 64.1% @ 6.65 nm measured at 1.5 degrees off-normal incidence at PTB (BESSY-II). This was achieved by a special scheme of La passivation. The La layer was nitridated to avoid formation of the optically unfavorable LaBx compound at the B-on-La interface. To avoid the also undesired BN formation at the La-on-B interface, a time-dosed nitridation at the initial stage was applied. This research revealed a good potential for further increase in the reflectivity of multilayer structures at 6.7 nm.

Interferometric velocity measurements through a fluctuating phase boundary using a Fresnel guide star

Hannes Radner, Lars Buettner, and Juergen Czarske

Doc ID: 241500 Received 22 May 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: Laser optical techniques are widely used for flow measurements as they offer a high spatial and velocity resolution. However, an undisturbed optical access to the measurement volume is desired. In order to measure through a fluctuating phase boundary, we present the use of adaptive optics. In an experiment we prove, that the Fresnel reflex of a phase boundary can be used as a proper guide star for adaptive velocity measurements with a single optical access. Interferometric flow measurements through a fluctuating phase boundary have been accomplished by a Mach-Zehnder interferometer.

In-fiber whispering gallery mode resonator fabricated by femtosecond laser micromaching

Tao Zhu, leilei shi, Dongmei huang, Min Liu, Ming Deng, and Wei Huang

Doc ID: 240530 Received 07 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: An in-fiber whispering gallery mode resonator fabricated by femtosecond laser micromaching is demonstrated. The cylinder resonator cavity is fabricated by scanning the D-fiber cladding with infrared femtosecond pulses along a cylindrical trace with radius of 25 μm and height of 20 μm. Quality factor on the order of 103 is achieved by smoothing the cavity surface with ultrasonic cleaner, which is mainly limited by the surface roughness of hundreds nanometers. Resonant characteristics and polarization dependence of the proposed resonator is also studied in detail. Our method takes a step forward to the integration of whispering gallery mode resonators.

Giant Thermo-Optical Relaxation Oscillations in mm-size Whispering Gallery Mode Disk-Resonators

Yanne Chembo, Souleymane DIALLO, and Guoping Lin

Doc ID: 240828 Received 12 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: In this letter, we show that giant thermo-optical oscillations can be triggered in mm-size whispering-gallerymode disk-resonators when they are pumped by a resonant continuous-wave laser. Our resonator is a ultra-high Q barium fluoride cavity which features a positive thermo-optic coefficient and a negative thermoelastic coefficient. We demonstrate for the first time that the complex interplay between these two thermic coefficients and the intrinsic Kerr nonlinearity yields very sharp slow-fast relaxation oscillations with a slow timescale that can be exceptionally large, typically of the order of one second. We use a time-domain model in order to gain understanding into this instability, and we find that both the experimental and theoretical results are in excellent agreement. The understanding of these thermal effects is an essential requirement for every WGM-related applications and our study demonstrates that even in the case of mm-size resonators, such effects can still be accurately analyzed using nonlinear time-domain models.

High-beam quality, high-efficiency laser based on fiber with heavily Yb3+-doped phosphate core and silica cladding

Olga Egorova, Sergey Semjonov, Oleg Medvedkov, Maxim Astapovich, Andrey Okhrimchuk, Boris Galagan, Boris Denker, Sergei Sverchkov, and Evgeny Dianov

Doc ID: 241424 Received 22 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We have fabricated and tested a composite fiber with an Yb3+-doped phosphate glass core and silica cladding. Oscillation with a slope efficiency of 74% was achieved using core pumping at 976 nm with fiber lengths of 48-80 mm in a simple laser configuration, where the cavity was formed by a high-reflectivity Bragg grating and the cleaved fiber end. The measured M2 factors were as low as 1.05-1.22 even though the fiber was multimode at the lasing wavelength.

High Energy Non-collinear Optical Parametric Amplifier Producing 4-fs Pulses in the Visible Seeded by a Gas Phase Filament

Robert Levis and Johanan Odhner

Doc ID: 239705 Received 24 Apr 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We report on the design and characterization of a short-pulse-pumped, single-stage non-collinear optical parametric amplifier (NOPA) that achieves high pulse energies in the few-cycle pulse regime. Optimal pulse front-tilting and temporal compression of the short (35 fs) pump pulse are achieved using a 4-\textit{f} grating compressor, while spatial chirp at the NOPA crystal is eliminated with proper imaging using a pair of reflective telescopes. Gas-phase filamentation in an open-ended argon-filled cell provides a bright, stable seed source with little residual chirp that is suitable for temporal overlap with the short pump pulse without dispersion pre-compensation. Two seeding geometries are explored, and pulses as short as 3.5 fs are obtained by seeding with the entire filament bandwidth. Fourier transform-limited 4 fs pulses are obtained by filtering the IR portion of the spectrum

Second harmonic generation interferometry in magnetic dipole metamaterials

Irina Kolmychek, Anton Bykov, Evgeniy Mamonov, and Tatiana Murzina

Doc ID: 242893 Received 12 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We present the experimental studies on optical second harmonic generation from meta-surfaces exhibiting magnetic dipole resonances in the visible spectral range. The structure consists of a square lattice of 'nano-burgers' of the composition Au/MgF$_2$/Au with the average disk diameter of 140 nm and the period of the structure of 400 nm. We show that at normal incidence, the intensity of the second harmonic (SH) wave generated by the metasurface increases by an order of magnitude as the excitation wavelength approaches the magnetic dipole resonance, while the phase of the SH wave experiences a shift up to 330$^\circ$. Based on the phenomenological description of the SH process, the observed effects indicate the dominant role of the nonlinear magnetic dipole polarization driven by the $\hat{\chi}^{emm}$ susceptibility in second harmonic generation in 'nano-burgers'.

1.1 μm InAs/GaAs quantum-dot light-emitting transistors grown by molecular beam epitaxy

Chao-Hsin Wu, Cheng-Han Wu, Hsuan-An Chen, and Shih-Yen Lin

Doc ID: 243132 Received 17 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: In this letter, we report the enhanced radiative recombination output from an AlGaAs/GaAs heterojunction bipolar transistor with InAs quantum dots embedded in the base region to form a quantum-dot light-emitting transistor (QDLET) grown by molecular beam epitaxy systems. For the device with a 100×100 μm² emitter area, we demonstrate the dual output characteristics with an electrical output and an optical output when the device operating in the common-emitter configuration. The quantum-dot light-emitting transistor exhibits a base recombination radiation in the near-infrared spectral range with a dominant peak at λ of 1100 nm.

Optical injection and spectral filtering of high-power UV laser diodes

Vera Schäfer, Christopher Ballance, Calvin Tock, and David Lucas

Doc ID: 242223 Received 04 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We demonstrate injection-locking of 120mW laser diodes operating at 397nm. We achieve stable operation with injection powers of ~100 μW and a slave laser output power of up to 110mW. We investigate the spectral purity of the slave laser light via photon scattering experiments on a single trapped Ca40 ion. We show that it is possible to achieve a scattering rate indistinguishable from that of monochromatic light by filtering the laser light with a diffraction grating to remove amplified spontaneous emission.

Quasi-3D Plasmonic Coupling Scheme for Nearfield Optical Lithography and Imaging

Liang Pan, Yuan Wang, Zhidong Du, Chen Chen, Yongshik Park, and Xiang Zhang

Doc ID: 241707 Received 26 May 2015; Accepted 20 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: Near-field optical imaging and lithography rely on achieving both high resolution and efficient coupling. Particularly conventional Nearfield Scanning Optical Microscopy (NSOM) suffers from the tradeoff between resolution and efficiency. Planar plasmonic lens schemes can partially solve this issue utilizing plasmonic resonances but the performance is not robust over a large range of sample materials. In this work we show a novel quasi-3D plasmonic scheme to focus light into the extreme subwavelength region in the near field with an efficiency orders higher than NSOM. The superb performance comes from the strong coupling between the localized mode with an off-plane E field component and the sample being processed. Our scheme can efficiently focus light to a spot with a diameter down to 1/20 of its wavelength and the coupling efficiency can be as high as 10%. Theoretically, we demonstrate that the FWHM of the focus spot can be 7 nm with an enhancement of 800 at UV region. The focusing performance is constantly good over a large variety of materials and the illumination and collection imaging scheme has been demonstrated by simulation. An example design of this quasi-3D coupling scheme is fabricated and its imaging performance is characterized by the apertureless optical nearfield measurement. The high coupling efficiency at extreme subwavelength resolution of this quasi-3D coupling scheme opens the door to many applications such as optical lithography, nanoscale imaging, heat assisted magnetic recording, plasmon enhanced Raman spectroscopy, etc.

Arbitrary state of polarization with customized degree of polarization generator

Angel Lizana, Irene Estévez, F. A. Torres-Ruiz, Alba Peinado, Claudio Ramírez, and Juan Campos Coloma

Doc ID: 234146 Received 06 Feb 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: An optical set-up able to generate arbitrary states of polarization with customized degree of polarization is presented in this work. Compared with the few alternatives existing in literature, it presents an easy-to-built optical set-up and leads to a superior performance. In fact, experimental results are presented, providing an accurate control for the generation of states of polarization (maximum error of 1.7% and 3.3% for ellipticity and azimuth, respectively) as well as for the associated degree of polarization (full experimental variation from 1 up to 0.003, with a 1.7% maximum error). The system proposed may be useful for different applications, as for polarimeters testing, speckle metrology, and biological applications as example.

Whispering gallery modes in optical fibers based on reflectionless potentials

Sergey Suchkov, Misha Sumetsky, and Andrey Sukhorukov

Doc ID: 241332 Received 21 May 2015; Accepted 19 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We consider an optical fiber with nanoscale variation of the effective fiber radius supporting whispering gallery modes slowly propagating along the fiber, and reveal that the radius variation can be designed to support reflectionless propagation of these modes. We show that reflectionless modulations can realize control of transmission amplitude and temporal delay, while enabling close packing due to the absence of cross-talk, in contrast to conventional potentials.

Degree of polarization (uniformity) and depolarization index: Unambiguous depolarization contrast for optical coherence tomography

Martin Villiger, Brett Bouma, and Norman Lippok

Doc ID: 239767 Received 24 Apr 2015; Accepted 19 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: The degree of polarization (uniformity) has attracted increased interest as a functional contrast in optical coherence tomography (OCT). However, its computation from a single polarization state suggests an ambiguity that is strongly dependent on a sample's orientation. We here propose an improved metric to present depolarization with respect to the optical system rather than the propagating field. Using numerical simulations and optical frequency domain imaging, we evaluate the conventional DOP(U) for different polarization states and compare its performance with the unambiguous depolarization index.

Spin-dependent asymmetric diffraction of evanescent waves by subwavelength gratings

Guo Ping Wang and Kedi Wu

Doc ID: 242143 Received 02 Jun 2015; Accepted 18 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We present a robust way to observe spin-to-orbital conversion phenomenon. A spinning evanescent wave can be asymmetrically transformed into propagation waves through one certain diffraction order by a periodical subwavelength grating. By detecting diffraction field distribution behind the grating, we observed spin-dependent mirror symmetry breaking of diffraction light. Furthermore, we can also simultaneously observe multiple order diffraction of a spin evanescent wave by a Fibonacci grating. In this case, the diffraction lights can interfere to each other behind the quasi-periodical grating to from an asymmetric interference patterns. Our work provides another way towards the realization of spin-to-orbital conversion of light.

Enhanced internal quantum efficiency in non-polar ZnO/Zn0.81Mg0.19O multiple quantum wells by Pt surface plasmons coupling

Xinhua Pan, Shanshan Chen, Haiping He, Wei Chen, Jingyun Huang, Bin Lu, and Zhizhen Ye

Doc ID: 243077 Received 16 Jun 2015; Accepted 18 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: Non-polar oriented ZnO/Zn0.81Mg0.19O multiple quantum wells (MQWs) were grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The internal quantum efficiency (ηint) of the non-polar MQWs was only 1.8%. The degraded quality of non-polar MQWs is the main factor for the low ηint. Besides improving the quality of non-polar MQWs, an effective way has been used to enhance the UV emission of the non-polar MQWs by sputtering Pt nanoparticles. Employing the resonant coupling between UV emission from the MQWs and Pt nanoparticle surface plasmons (SPs), a 20-fold enhancement of the UV emission has been achieved under the optimized sputtering time. Moreover, the ηint value of the non-polar MQWs has been strongly improved with the help of Pt. 6.7-fold enhancement of ηint has been achieved due to SPs coupling. It paves a new way in designing highly efficient non-polar LEDs.

Optimization of acquisition systems for low light level robustness in space optical communications

Bai Shuai, Jia Qiang, Liang Zhang, and Jianyu Wang

Doc ID: 240509 Received 08 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: The channel establishment in space optical communications relies on the ATP (Acquisition, Tracking, and Pointing) systems to initially acquire and then stably track the beacon beam. However, insufficient optical power may lead to unstable acquisition or even acquisition failure. In this letter, we analyze the mechanisms causing the instability, and then propose an approach to constrain the acquisition velocity. The approach is based on velocity prediction obtained from the light spot centroids and angle measurement data. Theoretical and experimental results show that the acceptable minimum optical power for acquisition decreases by 5.5 dB after optimization, which effectively enhances the acquisition system’s robustness under low light level conditions. This approach improves the adaptability of satellite–ground optical communications and also has practical value for deep space optical communications.

3 µm mid-infrared pulse generation using topological insulator as the saturable absorber

Jianfeng Li, Hongyu Luo, Lele Wang, Han Zhang, Chunjun Zhao, HE-PING LI, and Yong Liu

Doc ID: 240558 Received 08 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We report an 1150 nm diode-pump passively Q-switched Ho3+-doped ZBLAN fiber laser using topological insulator (TI): Bi2Te3 as the saturable absorber (SA). The TI: Bi2Te3 prepared using the cost-effective hydrothermal intercalation/exfoliation method was dropped onto a CaF2 substrate to fabricate the free-space SA component. It has a low saturable peak intensity of 2.12 MW/cm2 and high modulation depth of 51.3% measured at 2 µm. Inserting this component into a linear cavity Ho3+-doped ZBLAN fiber laser, stable Q-switched pulses at 2979.9 nm were obtained with the repetition rate of 81.96 kHz and pulse duration of 1.37 µs. The achieved maximum output power and pulse energy were 327.4 mW at a slope efficiency of 11.6 % and 3.99 µJ, respectively only limited by the available pump power. Our work reveals that the TIs are absolutely a class of promising and reliable SAs for pulse generation at 3 µm mid-infrared waveband.

Theoretical treatment of the interaction between two-level atoms and periodic waveguides

Xiaorun Zang and Philippe Lalanne

Doc ID: 241270 Received 20 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: Light transport in periodic waveguides coupled to a two-level atom is investigated. By using optical Bloch equations and a photonic modal formalism, we derive semi-analytical expressions for the scattering matrix of one atom trapped in a periodic waveguide. The derivation is general, as the expressions hold for any periodic photonic or plasmonic waveguides. It provides a basic building block to study collective effects arising from photon-mediated multi-atom interactions in periodic waveguides.

UV-curable silicate phosphor planar films printed on glass substrate for white light-emitting diodes

Yong Soo Cho, Jin Woo Jang, Jun Sik Kim, Oh Hyeon Kwon, and Tae Hyeon Lee

Doc ID: 241629 Received 27 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We suggest a simple way of forming a nonconventional remote phosphor layer for white light-emitting diodes. A printing technology using a paste consisting of yellow (Ba,Sr,Ca)2SiO4:Eu2+ silicate phosphor and UV-curable polymer is applied to form solid planar films on a common soda lime silicate glass substrate through UV-radiation. Relative content of the phosphor was adjusted for best dispersion of the phosphor particles in the polymer matrix with better emission and luminescence performance. As a result, the 70 wt% phosphor-embedded film has a luminous efficacy of ~70.1 lm/W at 200 mA.

Self-starting ultrafast mode-locked fiber lasers using anhydrous alcohol

Li Zhan, Zhiqiang Wang, Jian Wu, Zou Zhixin, Liang Zhang, Kai Qian, Le He, and Xiao Fang

Doc ID: 241930 Received 28 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We report a novel saturable absorber (SA) based on anhydrous alcohol for mode-locked fiber lasers (MLFLs). The SA is an optical ferrule with one alcoholic end-facet sealed by a polyethylene (PE) film. Its modulation depth is measured to be 5.9 %. Also, a self-starting MLFL using such an alcohol-SA has been demonstrated to generate 972 fs pulses at 1594.6 nm. The single pulse energy is up to 1.8 nJ with the repetition rate of 20.97 MHz, and the signal-to-noise ratio (SNR) is higher than 50 dB. The MLFL exhibits the performance of self-starting, good stability, and high pulse energy. Such a cost-effective and easily-prepared SA with high damage threshold may lead to the significance on the applications for ultrafast lasers. It may arouse wide considerations on the mode-locking function of organic liquids for MLFLs.

Silica microwire based interferometric electric field sensor

Hui Ding, Han Chunyang, Fangxing Lv, and Chen Sun

Doc ID: 243240 Received 19 Jun 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: Silica microwire, as an optical waveguide whose diameter close to or smaller than the wavelength of the guided light, is of great interest because it exhibits a number of excellent properties such as tight confinement, large evanescent fields, and great configurability. Here, we report a silica microwire based compact photonic sensor for real-time detection of high electric field. This device contains a interferometer with propylene carbonate cladding. Based on the Kerr electro-optic effect of propylene carbonate, the applied intensive transient electric field can change the refractive index of propylene carbonate, which shifts the interferometric fringe. Therefore, the electric field could be demodulated by monitoring the fringe shift. The sensor was successfully used to detect alternating electric field with frequency of 50 Hz and impulse electric field with duration time of 200 μs. This work lays a foundation for future applications in electric field sensing.

Noise suppression in coherent population trapping atomic clock by differential magneto-optic rotation detection

Sihong Gu, Bozhong Tan, Yuan Tian, Chen Jiehua, and Huifang Lin

Doc ID: 243380 Received 19 Jun 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We propose and investigate a scheme for differential detection of the magneto-optic rotation (MOR) effect, where a linearly-polarized bichromatic laser field is coherent population trapping (CPT)-resonant with alkali atoms, and discuss the application of this effect to CPT-based atomic clocks. The results of our study indicate that laser noise in a vertical cavity surface-emitting laser-based CPT atomic clock can be effectively suppressed by the proposed scheme. The proposed scheme promises to realize a packaged MOR-CPT atomic clock that has significantly better frequency stability coupled with similar power consumption, volume and cost when compared with currently available packaged CPT atomic clocks.

Trapping light into fiber tapers

Dmitry Strekalov, Anatoliy Savchenkov, Ekaterina Savchenkova, and Andrey Matsko

Doc ID: 241213 Received 18 May 2015; Accepted 17 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: A tapered cylindrical dielectric optical waveguide acts as a high quality factor white-light cavity providing high field concentration as well as long optical group delay. It is possible to optimize shape of a lossless taper to suppress reflection of the input light and achieve infinitely high field concentration. These tapers can be used in sensing and opto-electronics applications instead of conventional microvacities.

Versatile, carrier-envelope phase-stable spatiotemporal light bullets

Audrius Dubietis, Ieva Gražulevičiūtė, Rosvaldas Suminas, Gintaras Tamosauskas, and Arnaud Couairon

Doc ID: 241561 Received 25 May 2015; Accepted 17 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: We present an extensive experimental investigation of self-focusing and filamentation of intense 90 fs, 1.8 µm, carrier-envelope phase-stable laser pulses in fused silica in the anomalous group velocity dispersion region. Spectral measurements in a wedge-shaped sample uncover dynamics of the spectral broadening, which captures the evolution of third harmonic, resonant radiation and supercontinuum spectra as a function of propagation distance with unprecedented detail. The relevant events of spectral broadening are linked to formation and propagation dynamics of spatiotemporal light bullets as measured by three dimensional imaging technique. We also show that at higher input power the light bullet splits into two bullets, which retain characteristic O-shaped spatiotemporal intensity distributions and propagate with different Group velocities. Finally, we demonstrate that the light bullets have stable carrier-envelope phase, which is preserved even after the bullet splitting event, as verified by f-2f interferometric measurements.

Anharmonic propagation of two-dimensional beams carrying orbital angular momentum in a harmonic potential

Yiqi Zhang, Milivoj Belic, Xing Liu, Wei-Ping Zhong, wen feng, and Yanpeng Zhang

Doc ID: 242661 Received 23 Jun 2015; Accepted 17 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We analytically and numerically investigate an anharmonic propagation of two-dimensional beams in a harmonic potential. We pick non-centrosymmetric beams of common interest that carry orbital angular momentum. The examples studied include superposed Bessel-Gauss (BG), Laguerre-Gauss (LG) and circular Airy (CA) beams. For the BG beams, periodic inversion, phase transition, and rotation with periodic angular velocity are demonstrated during propagation. For the LG and CA beams, periodic inversion and variable rotation are still there but not the phase transition. On the whole, the ``center of mass' and the orbital angular momentum of a beam exhibit periodic motion, but that motion is subject to external torques and forces and, depending on the intensity distribution, may not be harmonic. Our results are applicable to other superpositions of finite circularly asymmetric beams.

Phase derivative estimation from a single interferogram using Kalman smoothing algorithm

Pramod Rastogi and Rishikesh Kulkarni

Doc ID: 242277 Received 09 Jun 2015; Accepted 16 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We report a technique for the direct phase derivative estimation from a single recording of a complex interferogram. In this technique, the interference field is represented as an autoregressive model with spatially varying coefficients. The estimates of these coefficients are obtained using the Kalman filter implementation. The RTS smoothing algorithm further improves the accuracy of the coefficient estimation. These estimated coefficients are utilized to compute the spatially-varying phase derivative. The stochastic evolution of the coefficients is considered which allows to estimate the phase derivative with any type of spatial variation. The simulation and experimental results are provided to substantiate the noise robustness and applicability of the proposed method in phase derivative estimation.

Polarization by clusters of spherical particles at backscattering

Anne Virkki, Johannes Markkanen, Jani Tyynelä, Jouni Peltoniemi, and Karri Muinonen

Doc ID: 242421 Received 05 Jun 2015; Accepted 16 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: The linear and circular polarization ratios for clusters of spherical particles averaged over random orientations show a systematic pattern as a function of the refractive index and the size parameter. We show that, at backscattering, the depolarizing behaviour of orientation-averaged clusters of spheres can be approximated by second-order scattering of bispheres. The pattern is relatively invariable in terms of the number of particles. We also demonstrate the significance of the near-field effects for polarization at backscattering.

Optoelectronic cross-injection locking of a dual-wavelength photonic integrated circuit for low phase noise millimeter-wave generation

Gaël Kervella, Frederic Van Dijk, Mehdi Alouini, Grégoire Pillet, Marco Lamponi, Mourad Chtioui, and Loic Morvan

Doc ID: 240141 Received 19 May 2015; Accepted 16 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: We report on the stabilization of a 90 GHz millimeter-wave signal generated from a fully integrated photonic circuit. The chip consists of two DFB single mode lasers which optical signals are combined on a fast photodiode to generate a largely tunable heterodyne beat note. We generate an optical comb from each laser with a microwave synthesizer, and by self-injecting the resulting signal, we mutually correlate the phase noise of each DFB and we stabilize the beatnote on a multiple of the frequency delivered by the synthesizer. The performances achieved beat note linewidth below 30 Hz.

Highly Efficient Cascaded Amplification using Pr3+-doped Mid-Infrared Chalcogenide Fiber Amplifiers

Jonathan Hu, Curtis Menyuk, Chengli Wei, Brandon Shaw, Jasbinder Sanghera, and Ishwar Aggarwal

Doc ID: 236293 Received 17 Mar 2015; Accepted 16 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: We computationally investigate cascaded amplification in a three-level mid-infrared (IR) Pr3+-doped chalcogenide fiber amplifier. The overlap of the cross-sections in the transitions 3H6->3H5 and 3H5->3H4 enable both transitions to simultaneously amplify a single wavelength in the range between 4.25 µm and 4.55 µm. High gain and low noise are achieved simultaneously if the signal is at 4.5 µm. We show that 45% of pump power that is injected at 2 µm can be shifted to 4.5 µm. The efficiency of using a mid-IR fiber amplifier is higher than what can be achieved by using mid-IR supercontinuum generation, which has been estimated at 25%. This mid-IR fiber amplifier can be used in conjunction with quantum cascade lasers to obtain a tunable, high-power mid-IR source.

Transport of indirect excitons in ZnO quantum wells

Yuliya Kuznetsova, Peristera Andreakou, Leonid Butov, Maria Vladimirova, Eric Calman, Fedor FFedichkin, Thierry Guillet, Pierre Lefebvre, Thierry Bretagnon, J.M Chauveau, and Christian Morhain

Doc ID: 241087 Received 20 May 2015; Accepted 16 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: Indirect excitons in ZnO/MgZnO wide single quantum wells have been studied by spatially- and time-resolved emission spectroscopy. Transport of indirect excitons over the distances up to 4 μm has been observed.

High-speed continuous-variable quantum key distribution without sending a local oscillator

Guihua Zeng, Duan Huang, Peng Huang, Dakai Lin, and Chao Wang

Doc ID: 241439 Received 22 May 2015; Accepted 15 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: We report a 100 MHz continuous-variable quantum key distribution (CVQKD) experiment over a 25 km fibre channel without sending a local oscillator (LO). We use a ``locally' generated LO and implement with a 1 GHz shot-noise-limited homodyne detector to achieve high-speed quantum measurement, and we propose a secure phase compensation scheme to maintain a low level of excess noise. These make high-bit-rate CVQKD significantly simpler for larger transmission distances compared with previous scheme in which both LO and quantum signals are transmitted through the insecure quantum channel.

Fourier synthesis with single-mode pulses from a multimode laser

Andrei Fotiadi, Ivan Lobach, Sergey Kablukov, Evgeny Podivilov, and Sergey Babin

Doc ID: 245821 Received 23 May 2015; Accepted 15 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: Short pulses are generated by mode locking techniques: amplitude modulation in time domain [1] or frequency modulation in frequency domain [2]. Direct Fourier synthesis of radiation from several single-frequency sources [3] offers an opportunity to generate arbitrary waveforms. Here we report on a new technique of short pulse synthesis in the Fourier domain. Instead of independent laser sources, we use a single multimode laser with retrieval of its individual cavity modes into a time sequence coherently combined in an external cavity. Combining of 20 consequent single-mode pulses has been performed demonstrating a new way for arbitrary waveforms synthesis.

Tailoring of Spectral Response and Spatial Field Distribution with Corrugated Photonic Crystal Slab

raanan gad, Ofer Levi, Iliya Sigal, Costa Nicolaou, Wah Tung Lau, and Soroosh Ahmadi

Doc ID: 240098 Received 01 May 2015; Accepted 15 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: We report a new physical mechanism for simultaneous tuning of quality factors, spectral responses, and field distributions in photonic crystal slabs through removal of polarization mode degeneracy using a lattice of elliptical nano-holes. The quality factors in these structures can become higher than those obtained with much smaller circular nano-holes. Furthermore, the modes can be superimposed by either rotating or morphing the elliptical nano-holes into a corrugated grating. These findings will enable improved radiation-matter interaction in optical, microwave and THZ frequencies along with enhanced opto-acoustic coupling.

Phase-matched electric-field-induced second harmonic generation in Xe-filled hollow core PCF

Jean-Michel Menard and Philip Russell

Doc ID: 242141 Received 02 Jun 2015; Accepted 15 Jul 2015; Posted 15 Jul 2015  View: PDF

Abstract: A second-order nonlinearity is induced inside a Xe-filled hollow-core photonic crystal fiber (PCF) by applying an external dc field. The system uniquely allows the linear optical properties to be adjusted by changing the gas pressure, allowing precise phase-matching between the LP01 mode at 1064 nm and the LP02 mode at 532 nm. The dependence of the second harmonic conversion efficiency on gas pressure, launched pulse energy and applied field agrees well with theory. The ultrabroadband guidance offered by anti-resonant-reflecting hollow-core PCFs, for example kagomé-PCF, offers many possibilities for generating light in traditionally difficult-to-access regions of the electromagnetic spectrum, such as the ultraviolet or the terahertz windows. The system can also be used for non-invasive measurements of transmission loss in hollow-core PCF over a broad spectrum including the deep and vacuum UV.

Formation of in-volume nanogratings with sub-100 nm periods in glass by femtosecond laser irradiation

Ya Cheng, Yang Liao, Lingling Qiao, Yves Bellouard, Koji Sugioka, Wangjun Pan, and cui yun

Doc ID: 242249 Received 04 Jun 2015; Accepted 15 Jul 2015; Posted 15 Jul 2015  View: PDF

Abstract: we present direct experimental observation of the morphological evolution during the formation of nanogratings with sub-100-nm periods with the increasing number of pulses. Theoretical simulation shows that the constructive interference of the scattering light from original nanoplanes will create an intensity maximum located between the two adjacent nanoplanes, resulting in shortening of the nanograting period by half. The proposed mechanism enables explaining the formation of nanogratings with periods beyond that predicted by the nanoplasmonic model.

Exfoliated layers of black phosphorus as saturable absorber for ultrafast solid-state laser

Jingliang He, Baitao Zhang, Fei Lou, Ru-Wei Zhao, Jing Li, Xian-cui Su, Jian Ning, and Kejian Yang

Doc ID: 245771 Received 10 Jul 2015; Accepted 15 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: High-quality black phosphorus (BP) saturable absorber mirror (SAM) was successfully fabricated with few-layered black phosphorus (phosphorene). By employing the prepared phosphorene SAM, we have demonstrated ultrafast pulse generation from a BP mode-locked bulk laser for the first time to our best knowledge. Pulses as short as 6.1 ps with an average power of 460 mW were obtained at the central wavelength of 1064.1 nm. Considering the direct and flexible band gap for different layers of phosphorene, this work may provide a possible method for fabricating BP SAM to achieve ultrafast solid-state lasers in IR and mid-IR wavelength region.

Yb:fiber laser-based, spectrally coherent and efficient generation of femtosecond 1.3 μm pulses from a fiber with two zero dispersion wavelengths

Yuhong Yao, Wayne Knox, and Govind Agrawal

Doc ID: 242913 Received 12 Jun 2015; Accepted 13 Jul 2015; Posted 14 Jul 2015  View: PDF

Abstract: We report the first experimental characterization of spectral coherence properties of wavelength conversion inside photonic crystal fibers with two zero dispersion wavelengths (TZDW) and demonstrate a low noise femtosecond 1.3 μm source employing the TZDW fiber and a 1.3 W, 240 fs Yb:fiber amplifier as the seeding source. Theoretical investigation shows that pulse evolution in our TZDW fiber source is dominated by parametric amplification seeded by self-phase modulation broadening which efficiently converts the pump energy into two new wavelength bands in a deterministic manner, leading to low noise and coherent excitation of femtosecond pulses tunable in the 1.3 μm spectral region, with up to 3 nJ of pulse energy at 32% of conversion efficiency.

An electro-optical sun compass with a very high degree of accuracy

Daniele Murra, Paolo Di Lazzaro, Sarah Bollanti, Francesco Flora, Amalia Torre, Luca Mezi, Gian Piero Gallerano, Domenico De Meis, and Davide Vicca

Doc ID: 239968 Received 30 Apr 2015; Accepted 13 Jul 2015; Posted 14 Jul 2015  View: PDF

Abstract: We present a novel electro-optical solar compass which is able to determine the true North direction with an accuracy better than 1/100 of degree, superior to that of any other magnetic or electronic compass which do not resort to differential GPS. The compass has an electronic sensor to determine the line of sight of the Sun and a simple but effective algorithm to calculate the position of the Sun. The excellent results obtained during the experimental tests demonstrate the advantages of this compass, which is also compact and not expensive.

Optical two-tone signal generation without use of optical filter for photonics-assisted radio frequency quadrupling

Akito Chiba, Kazumasa Takada, and Yosuke Akamatsu

Doc ID: 239971 Received 01 May 2015; Accepted 13 Jul 2015; Posted 14 Jul 2015  View: PDF

Abstract: Optical two-tone (OTT) signal generation is demonstrated without optical wavelength filtering for wavelength-free operation in radio frequency (rf) upconversion assisted by photonics. This principle is based on selective polarization manipulation for the optical carrier; the optical carrier’s polarization is first tilted and the carrier is then suppressed using a polarizer. Owing to optimized conditions obtained from theoretical calculation and high polarization extinction ratio achieving a 25.7-dB carrier suppression, a 40-GHz separated OTT signal is successfully generated by an optical intensity modulator driven by a 10-GHz sinusoidal rf signal. Conversion into a frequency-quadrupled rf signal is also demonstrated experimentally.

A continuously tunable modulation scheme for precision control of optical cavities with variable detuning

William Yam, Matt Evans, Nergis Mavalvala, Sarah Ackley, and Emily Davis

Doc ID: 241390 Received 27 May 2015; Accepted 13 Jul 2015; Posted 14 Jul 2015  View: PDF

Abstract: We present a scheme for locking optical cavities with arbitrary detuning many line widths from resonance using an electro-optic modulator that can provide arbitrary ratios of amplitude to phase modulation. We demonstrate our scheme on a Fabry-Perot cavity, and show that a well-behaved linear error signal can be obtained by demodulating the reflected light from a cavity that is detuned by several line widths.

Laguerre-Gauss beams vs Bessel beams showdown: peer comparison

Job Mendoza Hernandez, Maximino Arroyo Carrasco, Marcelo Iturbe-Castillo, and Sabino Chavez-Cerda

Doc ID: 243706 Received 25 Jun 2015; Accepted 12 Jul 2015; Posted 13 Jul 2015  View: PDF

Abstract: We present for the first time a comparison in similitude of circumstances between Laguerre-Gauss beams and Bessel beams showing that the former can be a better option for many applications that have been attributed to Bessel beams. By solving the Laguerre-Gauss differential equation in the asymptotic limit of large radial index we find the parameters to perform a peer comparison showing that Laguerre-Gauss beams can propagate quasi-nondiffracting within the same region of space where the corresponding Bessel beams do. We also demonstrate that Laguerre-Gauss beams having the property of self-healing are more robust in the sense that can propagate further than Bessel beams under similar initial conditions.

Point-Spread Function Optimization in isoSTED Nanoscopy

Joerg Bewersdorf, Edward Allgeyer, Xiang Hao, and Martin Booth

Doc ID: 242676 Received 11 Jun 2015; Accepted 11 Jul 2015; Posted 14 Jul 2015  View: PDF

Abstract: IsoSTED nanoscopy, a variant of stimulated emission depletion (STED) microscopy, utilizes two opposing objective lenses and features the highest three-dimensional resolution of STED nanoscopes currently available. However, this technique is limited by axially repetitive side minima in the interference pattern of the depletion point-spread function (PSF) which can lead to ghost images. Here, we describe novel strategies to further improve the performance of isoSTED nanoscopy by reshaping the PSF. In particular, we propose employing moderate defocus on the depletion beam to reduce the side minima. Furthermore, we demonstrate a simplified alternative based on objective misalignment and quantitatively compare the expected performance between the two approaches.

Highly efficient plasmonic enhancement of graphene absorption at telecommunication wavelengths

Min Gu, Hua Lu, and Benjamin Cumming

Doc ID: 243986 Received 29 Jun 2015; Accepted 10 Jul 2015; Posted 13 Jul 2015  View: PDF

Abstract: A hybrid graphene system consisting of graphene and silica layers coated on a metal film with groove rings is proposed to strongly enhance light absorption in the graphene layer. Our results indicate that the excited localized plasmon resonance in groove rings can effectively improve the graphene absorption from 2.3% to 43.1%, even to a maximum value of 87.0% in five-layer graphene at telecommunication wavelengths. In addition, the absorption peak is strongly dependent on the groove depth and ring radius as well as the number of graphene layers, enabling the flexible selectivity of both the operating spectral position and bandwidth. This favorable enhancement and tunability of graphene absorption could provide a path toward high-performance graphene optoelectronic components, such as photodetectors.

Evolution of coherence singularities of Schell-model beams

Tatiana Alieva and Jose A. Rodrigo

Doc ID: 243139 Received 18 Jun 2015; Accepted 10 Jul 2015; Posted 13 Jul 2015  View: PDF

Abstract: We show that the propagation of the widely used Schell-model partially coherent light can be easily understood using the ambiguity function. This approach is especially beneficial for the analysis of the mutual intensity of Schell-model beams (SMBs), which are associated with stable coherent beams such as Laguerre-, Hermite-, and Ince-Gaussian. We study the evolution of the coherence singularities during the SMB propagation. It is demonstrated that the distance of singularity formation depends on the coherence degree of the input beam. Moreover it is proved that the shape, position and number of singularity curves in far field are defined by the associated coherent beam.

Towards a new radiative-transfer-based model for remote sensing of terrestrial surface albedo

Shengcheng Cui, Xiaobing Zheng, Zhen Wang, Shizhi Yang, Xuebin Li, Heli Wei, Honghua Huang, and wenyue zhu

Doc ID: 240111 Received 04 May 2015; Accepted 10 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: This letter formulates a simple yet accurate radiative-transfer-based theoretical model to characterize the fraction of radiation reflected by terrestrial surfaces. Emphasis is placed on the concept of inhomogeneous distribution of diffuse sky radiation function (DSRF) under real atmosphere conditions. Multiple surface-atmosphere interaction effects are considered when coupling surface anisotropic reflectance field with diffuse sky radiation field for the land surface albedo (LSA) model construction. The advantage of the presented model is that it can well elucidate the impact of DSRF on the surface volume scattering and geometry-optical scattering components respectively, especially for slant illuminations with zenith angle larger than 50 degrees. In addition, the consistency and convergence of our model is evaluated using the limit theory of radiative transfer equation. Intercomparisons between satellite and ground measurements indicate that our model is accurate and promising for land-atmosphere interactions study.

Experimental demonstration of laser damage caused by coupling effect of subsurface defects and coating layers

Yingjie Chai, Meiping Zhu, Kui Yi, Weili Zhang, Hu Wang, Zhou Fang, Zhengyuan Bai, cui yun, and Jianda Shao

Doc ID: 239785 Received 27 Apr 2015; Accepted 08 Jul 2015; Posted 09 Jul 2015  View: PDF

Abstract: The laser damage resistance of coatings for high power laser systems depends greatly on the surface quality of the substrate. In our work, experimental approaches were employed to understand the coupling effect of subsurface defects and coatings on the laser resistance of coatings. 1064 nm (1ω) anti-reflection coating was deposited by e-beam coater on fused silica with and without micro-scale pits (structural defects). The micro-scale pits were precisely fabricated by femtosecond laser processing to prevent the emergence of subsurface cracks. Different deposition temperatures and substrate cleaning methods were characterized in order to verify the intensity of the coupling effect of substrate and coating layers. Our experimental results indicate that impurities, introduced in the finishing process, shifted to the substrate surface, and aggregated during the heating process, play a much more crucial role than structural defects (Length: ~7μm; Width: ~3μm; Depth: ~0.8μm) in the laser-induced damage process. A comparative study on the deposition methods indicated that combination of relatively low coating temperature and HF substrate etching tend to decrease the coupling effect, resulting in higher laser-induced damage resistance .

Extended tunability of Nd-doped fiber lasers operating at 872-936nm

Mathieu Laroche, Baptiste Leconte, Hervé Gilles, Sylvain Girard, Benoit Cadier, and thierry Robin

Doc ID: 238408 Received 21 Apr 2015; Accepted 06 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: Efficient high-power operation of a Nd-doped fiber laser operating in a wavelength-tunable configuration using volume Bragg grating (VBG) is reported in this letter. High power operation on the 4F3/2-4I9/2 transition of Nd3+ at short wavelengths below 900 nm is demonstrated for the first time in silica fibers. A high efficiency (47 % laser conversion), output power up to 22 W and a narrow linewidth of 0.035 nm are achieved. This configuration is compared with a more conventional fiber laser setup using band-pass filter and dichroic high reflecting mirror.

How planar optical waves can be made to climb dielectric steps

Manfred Hammer, Jens Förstner, and Andre Hildebrandt

Doc ID: 240068 Received 23 Mar 2015; Accepted 02 Jul 2015; Posted 08 Jul 2015  View: PDF

Abstract: We show how to optically connect guiding layers at different elevations in a 3-D integrated photonic circuit. Transfer of optical power carried by planar, semi-guided waves is possible without reflections, without radiation losses, and over large vertical distances. This functionality is realized through simple step-like folds of high-contrast dielectric slab waveguides, in combination with oblique wave incidence, and fulfilling a resonance condition. Radiation losses vanish, and polarization conversion is being suppressed, for TE wave incidence beyond certain critical angles. This can be understood by fundamental arguments resting on a version of Snell's law. The two 90-degree corners of a step act as identical partial reflectors in a Fabry-Perot-like resonator setup. By selecting the step height, i.e. the distance between the reflectors, one realizes resonant states with full transmission. Rigorous quasi-analytical simulations for typical silicon/silica parameters demonstrate the functioning. Combinations of several step junctions can lead to other types of optical on-chip connects, e.g. u-turn- or bridge-like configurations.

Mid-IR femtosecond frequency conversion by soliton-probe collision in phase-mismatched quadratic nonlinear crystals

Morten Bache, Xing Liu, Binbin Zhou, and Hairun Guo

Doc ID: 241572 Received 25 May 2015; Accepted 29 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: We show numerically that ultrashort self-defocusing temporal solitons colliding with a weak pulsed probe in the near-IR can convert the probe to the mid-IR. A near-perfect conversion efficiency is possible for a high effective soliton order. The near-IR self-defocusing soliton can form in a quadratic nonlinear crystal (beta-barium borate) in the normal dispersion regime due to cascaded (phase-mismatched) second-harmonic generation, and the mid-IR converted wave is formed in the anomalous dispersion regime between λ=2.2-2.4 μm as a resonant dispersive wave. This process relies on non-degenerate four-wave mixing mediated by an effective negative cross-phase modulation term caused by cascaded soliton-probe sum-frequency generation.

>200W incoherently combined supercontinuum source using a 3×1 broadband fiber power combiner

Zilun Chen, Hang Zhou, Aijun Jin, Xuanfeng Zhou, Bin Zhang, Sheng-Ping Chen, Jing Hou, and Jinbao Chen

Doc ID: 237223 Received 31 Mar 2015; Accepted 23 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: We report an incoherently combined near-infrared SC source with >200 W output power using a 3×1 broadband fiber power combiner. A broadband fiber power combiner is designed and theoretically investigated. The power transmission efficiencies of light at different wavelengths of the combiner are calculated and the combiner is verified to be capable of combining broadband sources efficiently. Then a combiner is fabricated. Three ~70 W near infrared SC sources are constructed and then using the combiner a >200 W near infrared SC source is obtained. Conclusively, using incoherently combining method we can obtain a high power SC source and the thermo-management can be realized easily. We believe that this is a suitable method to obtain higher power SC source.

Spontaneous creation and annihilation of temporal cavity solitons in a coherently-driven passive fiber resonator

Miro Erkintalo, Stephane Coen, Kathy Luo, Jae Jang, and Stuart Murdoch

Doc ID: 240910 Received 13 May 2015; Accepted 19 Jun 2015; Posted 13 Jul 2015  View: PDF

Abstract: We report on the experimental observation of spontaneous creation and annihilation of temporal cavity solitons (CSs) in a coherently-driven, macroscopic optical fiber resonator. Specifically, we show that CSs are spontaneously created when the frequency of the cavity driving field is tuned across a resonance, and that they can individually disappear at different stages of the scan. In contrast to previous experiments in monolithic microresonators, we are able to identify these dynamics in real time, thanks to the macroscopic dimensions of our resonator. Our experimental observations are in excellent agreement with numerical simulations. We also discuss the mechanisms responsible for the one-by-one disappearance of CSs.

Evaluating Multi-Exposure Speckle Imaging estimates of absolute autocorrelation times

Syed Kazmi, Andrew Dunn, and Rebecca Wu

Doc ID: 241241 Received 20 May 2015; Accepted 10 Jun 2015; Posted 15 Jul 2015  View: PDF

Abstract: Multi Exposure Speckle Imaging (MESI) is a camera based flow imaging technique for quantitative blood flow monitoring by mapping the speckle contrast dependence on camera exposure duration. The ability of laser speckle contrast imaging to measure the temporal dynamics of backscattered and interfering coherent fields, in terms of the accuracy of autocorrelation measurements is a major unresolved issue in quantitative speckle flowmetry. MESI fits for a number of parameters including an estimate of the electric field autocorrelation decay time from the imaged speckles. We compare the MESI determined correlation times with accepted true values from direct temporal measurements with a photon counting photon multiplier tube and an autocorrelator board of flows both in vitro and in vivo. The correlation times estimated by MESI in vivo remain on average within 14 ± 11% of those obtained from direct temporal autocorrelation measurements, demonstrating that MESI yields highly comparable statistics of the time varying fields that can be useful for applications seeking not only quantitative blood flow dynamics but also absolute perfusion.

A simple method to enhance terahertz radiation from femtosecond laser filament array with a step phase plate

Jiayu Zhao, Lanjun Guo, Wei Chu, Bin Zeng, Hui Gao, Weiwei Liu, and Ya Cheng

Doc ID: 236756 Received 24 Mar 2015; Accepted 08 Jun 2015; Posted 24 Jul 2015  View: PDF

Abstract: In this work, we experimentally demonstrate a 200% enhancement of terahertz (THz) wave amplitude generated by femtosecond laser filamentation in air. The experimental setup simply uses a semicircular phase plate to generate two parallel filaments. Temporally overlapped THz pulses from two filaments coherently add up, giving rise to significant enhancement of the THz pulse amplitude. It has been foreseen that further enhancement would be achieved if the design of phase plates could be optimized to generate filament array. This simple method makes full use of the laser energy and might potentially open a new approach to remotely enhance the THz emission in air.

Comment on Asymmetric optical cryptosystem based on coherent superposition and equal modulus decomposition

Xiaopeng Deng

Doc ID: 240236 Received 12 May 2015; Accepted 08 Jun 2015; Posted 21 Jul 2015  View: PDF

Abstract: I comment on the recent Letter by Jianjun Cai et al. [Opt. Lett.40, 475(2015)], in which the authors claimed that the method can achieve high robustness against the special attack based on iterative Fourier transform. However, according to my analysis and simulation results, the asymmetric optical cryptosystem cannot resist the special attack based on iterative Fourier transform. So, I think their attack analysis and algorithm are ill-considered and worth discussing.

Room-temperature magnetic gradiometry with fiber-coupled nitrogen--vacancy centers in diamond

Aleksei Zheltikov, Ilya Fedotov, Sean Blakley, and Sergey Kilin

Doc ID: 237633 Received 07 Apr 2015; Accepted 12 May 2015; Posted 01 Jul 2015  View: PDF

Abstract: Differential optical detection of a magnetic resonance induced in nitrogen--vacancy (NV) centers in diamond is shown to enable a high-spatial-resolution room-temperature magnetic field gradiometry on a fiber platform. An ultracompact design of this fiber-based solid-state magnetic gradiometer is achieved by integrating an NV-diamond magnetic sensor with a two-fiber opto--microwave interface, which couples NV centers to microwave and optical fields, used to resonantly drive and interrogate the spin of NV centers.

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