Optics Express (OPT EXPRESS)

Publications in this journal

• Article: Surface enhanced Raman scattering and plasmon enhanced fluorescence in zinc-tellurite glass

  Raja J Amjad, M.R. Sahar, M.R. Doust, S.K. Ghoshal, M.N.A. Jamaludin
  [show abstract] [hide abstract]
  ABSTRACT: In Press.
  Optics Express 07/2013;
• Article: High speed multispectral fluorescence lifetime imaging

  Farzad Fereidouni, Keimpe Reitsma, Hans C. Gerritsen
  [show abstract] [hide abstract]
  ABSTRACT: We report a spectrally resolved fluorescence lifetime imaging system based on time gated single photon detection with a fixed gate width of 200 ps and 7 spectral channels. Time gated systems can operate at high count rates but usually have large gate widths and sample only part of the fluorescence decay curve. In the system presented in this work, the fluorescence signal is sampled using a high speed transceiver. An error analysis is carried out to characterize the performance of both lifetime and spectral detection. The effect of gate width and spectral channel width on the accuracy of estimated lifetimes and spectral widths is described. The performance of the whole instrument is evaluated at count rates of up to 12 MHz. Accurate fluorescence lifetimes (error < 2%) are recorded at count rates as high as 5 MHz. This is limited by the PMT performance, not by the electronics. Analysis of the large spectral lifetime image sets is challenging and time-consuming. Here, we demonstrate the use of lifetime and spectral phasors for analyzing images of fibroblast cells with 2 different labeled components. The phasor approach provides a fast and intuitive way of analyzing the results of spectrally resolved fluorescence lifetime imaging experiments.
  Optics Express 05/2013; 21(10):11769-11782.
• Article: Analyzing the benefit of optical transmission systems based on Root Raised Cosine PS-QPSK and a flexible channel grid.

  A Seck, P Ramantanis, J Vuong, D F Bendimerad, C Lepers, B-E Benkelfat, Y Frignac
  [show abstract] [hide abstract]
  ABSTRACT: We numerically investigate the multi-channel transmission performance of Polarization Switched Quadrature Phase Shift Keying (PS-QPSK) and we compare it to the performance of Polarization-Division-Multiplexed QPSK (PDM-QPSK), using Root Raised Cosine (RRC) spectral shaping, in the context of a flexible channel grid. We point out the impact of the roll-off factor and the potential influence of different dispersion compensation scenarios. Finally, the advantage of PS-QPSK against PDM-QPSK is presented as a function of the system parameters, while we also discuss the benefit of a RRC spectral shaping against a tight filtering at the transmitter side with a 2nd order super-Gaussian-shaped filter.
  Optics Express 05/2013; 21(9):10496-501.
• Article: Wide-angle near infrared polarizer with extremely high extinction ratio.

  X L Liu, B Zhao, Z M Zhang
  [show abstract] [hide abstract]
  ABSTRACT: An infrared polarizer is designed with a predicted extremely high extinction ratio exceeding 3 × 10¹⁶ and transmittance higher than 89% for one polarization in the wavelength region from 1.6 to 2.3 µm. Moreover, the performance does not start to deteriorate until 60° tilting angle. The wide-angle high transmission is attributed to the excitation of magnetic polaritons and suitable LC circuit models, which could predict the resonance wavelengths quantitatively, are developed to better understand the underlying mechanisms. The proposed structure can be tuned by controlling the geometrical parameters for different potential applications such as polarizers, beamsplitters, filters, and transparent electrodes.
  Optics Express 05/2013; 21(9):10502-10.
• Article: Wigner function measurement using a lenslet array.

  Lei Tian, Zhengyun Zhang, Jonathan C Petruccelli, George Barbastathis
  [show abstract] [hide abstract]
  ABSTRACT: Geometrical-optical arguments have traditionally been used to explain how a lenslet array measures the distribution of light jointly over space and spatial frequency. Here, we rigorously derive the connection between the intensity measured by a lenslet array and wave-optical representations of such light distributions for partially coherent optical beams by using the Wigner distribution function (WDF). It is shown that the action of the lenslet array is to sample a smoothed version of the beam's WDF (SWDF). We consider the effect of lenslet geometry and coherence properties of the beam on this measurement, and we derive an expression for cross-talk between lenslets that corrupts the measurement. Conditions for a high fidelity measurement of the SWDF and the discrepancies between the measured SWDF and the WDF are investigated for a Schell-model beam.
  Optics Express 05/2013; 21(9):10511-25.
• Article: Coded aperture compressive temporal imaging.

  Patrick Llull, Xuejun Liao, Xin Yuan, Jianbo Yang, David Kittle, Lawrence Carin, Guillermo Sapiro, David J Brady
  [show abstract] [hide abstract]
  ABSTRACT: We use mechanical translation of a coded aperture for code division multiple access compression of video. We discuss the compressed video's temporal resolution and present experimental results for reconstructions of > 10 frames of temporal data per coded snapshot.
  Optics Express 05/2013; 21(9):10526-45.
• Article: High resolution irradiance tailoring using multiple freeform surfaces.

  Adrien Bruneton, Axel Bäuerle, Rolf Wester, Jochen Stollenwerk, Peter Loosen
  [show abstract] [hide abstract]
  ABSTRACT: More and more lighting applications require the design of dedicated optics to achieve a given radiant intensity or irradiance distribution. Freeform optics has the advantage of providing such a functionality with a compact design. It was previously demonstrated in [Bäuerle et al., Opt. Exp. 20, 14477-14485 (2012)] that the up-front computation of the light path through the optical system (ray mapping) provides a satisfactory approximation to the problem, and allows the design of multiple freeform surfaces in transmission or in reflection. This article presents one natural extension of this work by introducing an efficient optimization procedure based on the physics of the system. The procedure allows the design of multiple freeform surfaces and can render high resolution irradiance patterns, as demonstrated by several examples, in particular by a lens made of two freeform surfaces projecting a high resolution logo (530 × 160 pixels).
  Optics Express 05/2013; 21(9):10563-71.
• Article: Wavelet-based noise-model driven denoising algorithm for differential phase contrast mammography.

  Carolina Arboleda, Zhentian Wang, Marco Stampanoni
  [show abstract] [hide abstract]
  ABSTRACT: Traditional mammography can be positively complemented by phase contrast and scattering x-ray imaging, because they can detect subtle differences in the electron density of a material and measure the local small-angle scattering power generated by the microscopic density fluctuations in the specimen, respectively. The grating-based x-ray interferometry technique can produce absorption, differential phase contrast (DPC) and scattering signals of the sample, in parallel, and works well with conventional X-ray sources; thus, it constitutes a promising method for more reliable breast cancer screening and diagnosis. Recently, our team proved that this novel technology can provide images superior to conventional mammography. This new technology was used to image whole native breast samples directly after mastectomy. The images acquired show high potential, but the noise level associated to the DPC and scattering signals is significant, so it is necessary to remove it in order to improve image quality and visualization. The noise models of the three signals have been investigated and the noise variance can be computed. In this work, a wavelet-based denoising algorithm using these noise models is proposed. It was evaluated with both simulated and experimental mammography data. The outcomes demonstrated that our method offers a good denoising quality, while simultaneously preserving the edges and important structural features. Therefore, it can help improve diagnosis and implement further post-processing techniques such as fusion of the three signals acquired.
  Optics Express 05/2013; 21(9):10572-89.
• Article: Nanocavities at the surface of three-dimensional photonic crystals.

  Kenji Ishizaki, Kou Gondaira, Yuji Ota, Katsuyoshi Suzuki, Susumu Noda
  [show abstract] [hide abstract]
  ABSTRACT: We investigate nanocavities at the surface of three-dimensional (3D) photonic crystals, where the polarization-independent surface-mode gap can be utilized. We consider the formation of various nanocavities by introducing artificial defects utilizing the 3D structures around the surface and discuss the possibilities for increasing the Q-factors of the surface nanocavities with TE-like polarization based on the advanced designs of donor-type defects. We also introduce the design of acceptor-type defects and show that TM-like nanocavities are obtained. We then fabricate the designed nanocavities and examine their resonant characteristics; we successfully demonstrate TE-like nanocavities with Q-factors of ~40,000, which is four-times higher than previous surface cavities and as high as that of the cavities embedded inside 3D photonic crystals. TM-like nanocavities with Q-factors of ~22,000 are also demonstrated for the first time.
  Optics Express 05/2013; 21(9):10590-6.
• Article: Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes.

  Shaoqiang Chen, Masahiro Yoshita, Aya Sato, Takashi Ito, Hidefumi Akiyama, Hiroyuki Yokoyama
  [show abstract] [hide abstract]
  ABSTRACT: Picosecond-pulse-generation dynamics and pulse-width limiting factors via spectral filtering from intensely pulse-excited gain-switched 1.55-μm distributed-feedback laser diodes were studied. The spectral and temporal characteristics of the spectrally filtered pulses indicated that the short-wavelength component stems from the initial part of the gain-switched main pulse and has a nearly linear down-chirp of 5.2 ps/nm, whereas long-wavelength components include chirped pulse-lasing components and steady-state-lasing components. Rate-equation calculations with a model of linear change in refractive index with carrier density explained the major features of the experimental results. The analysis of the expected pulse widths with optimum spectral widths was also consistent with the experimental data.
  Optics Express 05/2013; 21(9):10597-605.
• Article: Widely tunable single photon source with high purity at telecom wavelength.

  Rui-Bo Jin, Ryosuke Shimizu, Kentaro Wakui, Hugo Benichi, Masahide Sasaki
  [show abstract] [hide abstract]
  ABSTRACT: We theoretically and experimentally investigate the spectral tunability and purity of photon pairs generated from spontaneous parametric down conversion in periodically poled KTiOPO₄ crystal with group-velocity matching condition. The numerical simulation predicts that the spectral purity can be kept higher than 0.81 when the wavelength is tuned from 1460 nm to 1675 nm, which covers the S-, C-, L-, and U-band in telecommunication wavelengths. We also experimentally measured the joint spectral intensity at 1565 nm, 1584 nm and 1565 nm, yielding Schmidt numbers of 1.01, 1.02 and 1.04, respectively. Such a photon source is useful for quantum information and communication systems.
  Optics Express 05/2013; 21(9):10659-66.
• Article: Self-stabilizing optical clock pulse-train generator using SOA and saturable absorber for asynchronous optical packet processing.

  Tatsushi Nakahara, Ryo Takahashi
  [show abstract] [hide abstract]
  ABSTRACT: We propose a novel, self-stabilizing optical clock pulse-train generator for processing preamble-free, asynchronous optical packets with variable lengths. The generator is based on an optical loop that includes a semiconductor optical amplifier (SOA) and a high-extinction spin-polarized saturable absorber (SA), with the loop being self-stabilized by balancing out the gain and absorption provided by the SOA and SA, respectively. The optical pulse train is generated by tapping out a small portion of a circulating seed pulse. The convergence of the generated pulse energy is enabled by the loop round-trip gain function that has a negative slope due to gain saturation in the SOA. The amplified spontaneous emission (ASE) of the SOA is effectively suppressed by the SA, and a backward optical pulse launched into the SOA enables overcoming the carrier-recovery speed mismatch between the SOA and SA. Without external control for the loop gain, a stable optical pulse train consisting of more than 50 pulses with low jitter is generated from a single 10-ps seed optical pulse even with a variation of 10 dB in the seed pulse intensity.
  Optics Express 05/2013; 21(9):10712-9.
• Article: Generation of infrared supercontinuum radiation: spatial mode dispersion and higher-order mode propagation in ZBLAN step-index fibers.

  Jacob Ramsay, Sune Dupont, Mikkel Johansen, Lars Rishøj, Karsten Rottwitt, Peter Morten Moselund, Søren Rud Keiding
  [show abstract] [hide abstract]
  ABSTRACT: Using femtosecond upconversion we investigate the time and wavelength structure of infrared supercontinuum generation. It is shown that radiation is scattered into higher order spatial modes (HOMs) when generating a supercontinuum using fibers that are not single-moded, such as a step-index ZBLAN fiber. As a consequence of intermodal scattering and the difference in group velocity for the modes, the supercontinuum splits up spatially and temporally. Experimental results indicate that a significant part of the radiation propagates in HOMs. Conventional simulations of super-continuum generation do not include scattering into HOMs, and including this provides an extra degree of freedom for tailoring supercontinuum sources.
  Optics Express 05/2013; 21(9):10764-71.
• Article: Linearity in the response of photopolymers as optical recording media.

  Sergi Gallego, Andrés Marquez, Francisco J Guardiola, Marina Riquelme, Roberto Fernández, Inmaculada Pascual, Augusto Beléndez
  [show abstract] [hide abstract]
  ABSTRACT: Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. To this goal the linearity in the material response is crucial to design the optimum irradiance for each element. In this paper we measured directly some parameters to know how linear is the material response, in terms of the refractive index modulation versus exposure, then we can predict the refractive index distributions during recording. We have analyzed at different recording intensities the evolution of monomer diffusion during recording for photopolymers based on PVA/Acrylamide. This model has been successfully applied to PVA/Acrylamide photopolymers to predict the transmitted diffracted orders and the agreement with experimental values has been increased.
  Optics Express 05/2013; 21(9):10995-1008.
• Article: Waferscale nanophotonic circuits made from diamond-on-insulator substrates.

  P Rath, N Gruhler, S Khasminskaya, C Nebel, C Wild, W H P Pernice
  [show abstract] [hide abstract]
  ABSTRACT: Wide bandgap dielectrics are attractive materials for the fabrication of photonic devices because they allow broadband optical operation and do not suffer from free-carrier absorption. Here we show that polycrystalline diamond thin films deposited by chemical vapor deposition provide a promising platform for the realization of large scale integrated photonic circuits. We present a full suite of photonic components required for the investigation of on-chip devices, including input grating couplers, millimeter long nanophotonic waveguides and microcavities. In microring resonators we measure loaded optical quality factors up to 11,000. Corresponding propagation loss of 5dB/mm is also confirmed by measuring transmission through long waveguides.
  Optics Express 05/2013; 21(9):11031-6.