Abstract: This research presents a novel, time-resolved fiber-optic "Optrode" system for accurate real-time in situ detection of fluorescent proteins produced by biosensor organisms. The Optrode fluorescence detection system was able to identify, characterize, differentiate, and quantify red and green fluorescently labeled organisms, individually and in mixed aqueous cultures. Detection was also possible in sand systems, where a consistent reduction in signal intensity indicates that signal collection volume was reduced by one-third. The optrode was shown to be sensitive enough to detect fluorescently labeled cell concentrations of 1.9 × 10(4) CFU/mL, indicating it is suitable for detecting typical concentrations of degrader organisms reported in bioremediation trials. The effect of fluorophore photobleaching was characterized for different fluorescent proteins and demonstrated a linear relationship to cell concentration, meaning the effect can be accounted for within methods of fluorescence collection and analysis. Proof of concept is provided for all aspects of this research, which represents an important step toward the goal of achieving a complete, nondestructive, in situ monitoring system to characterize all aspects of microbial activity and gene expression.
Abstract: We present a new way of improving the efficiency of optical coherence tomography by using the polarisation crosstalk of a polarising beam splitter to direct most of the available source optical power to the sample. The use of a quarter wave plate in both the reference and the sample arms allows most of the sample power to be directed to the detector while adjusting the reference arm to ensure noise optimised operation. As a result, the sensitivity of such a system can be improved by 6 dB, or alternatively the acquisition time can be improved by a factor of 4 for shot noise limited performance,compared to a traditional OCT configuration using a 50/50 beam splitter.
Abstract: We present an all-fiber tunable dispersion compensator based on a pair of fiber stretchers made with different fiber types in which the group delay and the second-order dispersion can be tuned independently. Its efficiency is demonstrated in a fiber-based optical coherence tomography (OCT) system operating in the 800 nm wavelength range. The average sample dispersion in OCT imaging or the dispersion of transmission lines could also be compensated by our system.
Abstract: We investigate the combined effect of Raman and parametric gain on single-pump parametric amplifiers. The phasematched parametric gain is shown to depend strongly on the real part of the complex Raman susceptibility. In fused silica fibers this results in a significant reduction in the available parametric gain for signal detunings beyond 10 THz. We are able to experimentally measure this effect for signal detunings ranging from 7 to 22 THz. Finally we discuss the implications of these results for the design of broadband optical parametric amplifiers.
Abstract: We experimentally demonstrate that continuous-wave supercontinuum generation in optical fibers can be significantly enhanced by using both multiwavelength pumping and dispersion management. We show by detailed spectral analysis that continuum enhancement is achieved mainly through a combination of Raman-assisted modulation instabilities, soliton compression, and dispersive wave generation. With this technique, an 800 nm wide (from 1.2 to 2.0 microm) 2 W supercontinuum source is reported that uses a three-wavelength pump and a dispersion-tailored four-optical fibers arrangement.
Abstract: We experimentally demonstrate the operation of a passively mode-locked Raman fiber ring laser with an ultrahigh repetition rate of 100 GHz and up to 430 mW of average output power. This laser constitutes a simple wavelength versatile pulsed optical source. Stable mode locking is based on dissipative four-wave mixing with a single fiber Bragg grating acting as the mode-locking element.
Abstract: We present a new kind of broadband continuous-wave source which outperforms any other broadband superluminescent or amplified spontaneous emission source both in terms of output spectral density and bandwidth. Our source covers the wavelength band of interest for fibre applications (from 1450 to 1625 nm) and has an output power of approximately 1.3 W. The source is obtained by pumping a conventional non-zero dispersion-shifted fibre with a continuous-wave Raman fibre laser tuned to the region of small anomalous dispersion of the fibre. The laser beam undergoes an extreme spectral broadening in the fibre. Our experimental results show clearly that the modulation instability (MI)-induced soliton fission is the key element leading to this spectral broadening. Modulation instability is seeded by fast intensity instabilities present in the laser output. We show that this source features good power stability and we believe that it might have very interesting applications in fibre sensing, for instance to avoid the need of amplification in the interrogation of remote Bragg gratings or to improve the resolution and dynamic range of optical coherence tomography setups.
Abstract: Supercontinuum generation can be achieved in the continuous-wave regime with a few watts of pump power launched into kilometer-long fibers. High power spectral density broadband light sources can be obtained in this way. Using a generalized nonlinear Schrödinger equation model and an ensemble averaging procedure that takes into account the partially-coherent nature of the pump laser, we fully explain for the first time the spectral broadening mechanisms underlying this process. Our simulations and experiments confirm that continuous-wave supercontinuum generation involve Raman soliton dynamics and dispersive waves in a way akin to pulsed supercontinua. The Raman solitons are however generated with a wide distribution of parameters because they originate from the random phase and intensity fluctuations associated with the pump incoherence. This soliton distribution is averaged out by experimental measurements, which explains the remarkable smoothness of experimental continuous-wave supercontinuum spectra.
Abstract: By taking into account the finite Raman bandwidth of silica fibers, we study the so-called Raman-induced spectral power tilt in arbitrarily large wavelength-division-multiplexed systems. Our numerical results reveal that the Raman tilt reaches a maximum for a total optical bandwidth slightly larger than the Raman frequency shift and decreases beyond that, in contrast to what is predicted by the usual triangular approximation. A new analytical formulation of the Raman tilt is derived that is valid for an arbitrary number of channels and unlimited optical bandwidth. An excellent agreement is found with numerical simulations (9 Refs.)
Abstract: We present a coupled mode theory that describes the combined action of stimulated Raman scattering and four-wave mixing in wavelength-division multiplexing systems. Our model takes into account the limited Raman bandwidth of silica fibers and is able to predict the nonlinear penalties that affect arbitrarily large WDM systems. With this model, we show numerically that the so-called Raman-induced power tilt reaches a maximum for a total optical bandwidth slightly larger than the Raman frequency shift and decreases beyond that, in contrast to what is predicted by the usual triangular approximation. A new analytical formulation of the Raman tilt is derived that is valid for an arbitrary number of channels and unlimited optical bandwidth. Our investigations also demonstrate that four-wave mixing leads to phase-sensitive periodic energy exchanges among channels that affect the Raman tilt (29 Refs.)
Abstract: We study experimentally the influence of chromatic dispersion and Rayleigh backscattering on cascaded Raman generation in silica optical fibers. Effects ranging from enhanced spectral broadening of the Stokes orders to generation of higher Stokes order at unexpected wavelengths are observed. Additionally, we show that four-wave-mixing processes can quench the noisy Rayleigh lasing lines generated in power Raman amplifiers. Our observations are confirmed by numerical simulations.
Abstract: We present a new numerical model of cascaded Raman fiber lasers that takes into account the chromatic dispersion of the fiber and includes the full spectrum of the intracavity field. This model explains and describes remarkably well a new operating regime found experimentally and reveals that chromatic dispersion is truly a new degree of freedom in the design of cascaded Raman lasers.
Abstract: A new laser regime for second-order pumping applications is described. Our laser is a dual-output-wavelength Raman fiber laser that generates a low-power first-order-pump line and a high-power second-order-pump line together. We demonstrate how using four-wave mixing combined to Raman gain in the laser cavity permits better stability of the first-order-pump laser line (5 Refs.)
Abstract: We present what is to our knowledge the first complete measurement of the dependence of Raman gain on chromatic dispersion, fully revealing the influence of parametric four-wave mixing on stimulated Raman scattering. In particular, a threefold increase of the Raman gain is observed under phase-matching conditions, in excellent agreement with theoretical predictions. Our experiments, which were performed in a photonic crystal fiber, demonstrate that these unique fibers can be exploited to boost the performances of fiber Raman amplifiers.
Abstract: We simulated the intra-acinar contribution to phase III slope (S_acin) for gases of differing diffusivities (He and SF_6) by solving equations of diffusive and convective gas transport in multi-branch-point models (MBPM) of the human acinus. We first conducted a sensitivity study of Sacin to asymmetry and its variability in successive generations. Sacin increases were greatest when asymmetry and variability of asymmetry were increased at the level of the respiratory bronchioles (generations 17-18) for He and at the level of the alveolar ducts (generations 20-21) for SF_6, corresponding to the location of their respective diffusion fronts. On the basis of this sensitivity study and in keeping with reported acinar morphometry, we built a MBPM that actually reproduced experimental Sacin values obtained in normal subjects for He, N_2, and SF_6. Ten variants of such a MBPM were constructed to estimate intrinsic Sacin variability owing to peripheral lung structure. The realistic simulation of S_acin in the normal lung and the understanding of how asymmetry affects Sacin for different diffusivity gases make Sacin a powerful tool to detect structural alterations at different depths in the lung periphery.
Abstract: Numerical study of continuous-wave (cw) supercontinuum generation using a generalized nonlinear Schrödinger equation model and an ensemble averaging procedure that takes into account the partially-coherent nature of the pump laser, we fully explain for the first time the spectral broadening mechanisms underlying this process. Our simulations and experiments confirm that cw supercontinuum generation involve Raman soliton dynamics and dispersive waves in a way akin to pulsed supercontinua. The Raman solitons are however generated with a wide distribution of parameters because they originate from the random phase and intensity fluctuations associated with the pump incoherence. This soliton distribution is averaged out by experimental measurements, which explains the remarkable smoothness of experimental cw supercontinuum spectra. The high incoherence, the remarkable smoothness and the powerfulness of those supercontinuum sources make them the ideal candidate as a source for an optical coherence tomography setup.
Abstract: Variable dispersion compensators are used to build time (TD-OCT) and spectral (SD-OCT) domain all-fiber optical coherence tomography systems. Their abilities are demonstrated in biological tissues with the TD-OCT system reaching a significant sensitivity of 86-dB (14 Refs.)
Abstract: We report on the design and experimental demonstration of an all-fiber optical coherence tomography system in which residual chromatic dispersion is compensated for by a pair of fiber stretchers made with different fiber types. Both the dispersion variations resulting from fiber inhomogeneities and from a fiber length mismatch can be compensated for. Additionally, we anticipate that our system could be used to compensate for sample dispersion. (10 Refs.)
Abstract: We describe a simple fiber optic fluorescence spectrometry system with a wide variety of biomedical applications. This low-cost, all-fiber system is portable, robust and has the capacity to acquire fluorescence spectra at rates up to 1 kHz. We demonstrate the capabilities of the system by presenting experimental measurements of action potentials in the di-4-ANEPPS stained heart and the concentration of GFP tagged bacteria. (9 Refs.)
Abstract: The Physics Education Technology (PhET) group at the University of Colorado, Boulder has created more than 60 open source, research based simulations that cover concepts in basic physics to state of the art research. We have added value to some of the PhET simulations by tinkering with the source code. The modified simulations are easily embedded into collaborative learning environments and online assessment systems. We believe this will lead to enhanced student interaction and learning outcomes. Examples of how we use these simulations in two open source environments will be presented. The first is a MediaWiki (the software that runs Wikipedia) wiki installation and the second is an online assessment and integrated study (OASIS) installation.
Notes: (Sydney (NSW), Australia, October 1-3, 2008)
Abstract: We demonstrate both theoretically and experimentally the influence of the Raman susceptibility on single-pump parametric amplifiers. We discuss the implications this result for the design of broadband optical parmetric amplfiers (5 Refs.)
Abstract: Three four-wave mixing processes are simultaneously observed in a fiber. Two are phase-matched, through higher-order dispersion and Kerr nonlinearity respectively, while the third one is Raman-assisted and involves an incoherent pump (2 Refs.)
Notes: paper ?? (June 17–22, 2007, Munich, Germany)
Abstract: We have developed a novel fluorescence imaging system using optical fibers that allows intramural functional imaging to be carried out in real time. Thanks to this probe, cellular-level electrical activities in cardiac muscles can be recorded in both in-vivo and in-vitro preparations. Currently, the system is under modifications to perform multi-functional imaging so as to make possible the identification of a particular group of cells and to record its electrical functionality at the same time. This can be helpful for studying, for instance, the recovering progress of in-vivo scared cells. Preliminary results will be presented at the workshop.
Abstract: We experimentally demonstrate passive mode-locking of a Raman fiber ring laser at a 100-GHz ultra-high repetition-rate through dissipative four-wave mixing by using a specifically designed fiber Bragg grating as a passive mode-locking element (4 Refs.)
Notes: paper CThC4 (May 21–26, 2006, Longbeach, California, USA)
Abstract: Continuous-wave supercontinuum generation is studied numerically. We show that the random fluctuations of the partially coherent pump beam play a dominant role in the spectral broadening process and explain the smoothness of experimental spectra (9 Refs.)
Notes: paper TuD6 (September 6–9, 2005, Dresden, Germany)
Abstract: We show experimentally that Raman fiber lasers exhibit fast intensity fluctuations on a time scale of a few tens of picoseconds. Observations are performed with a forward-pump Raman amplifier with zero walk-off (8 Refs.)
Notes: paper PD1 (September 6–9, 2005, Dresden, Germany), \textbfpostdeadline contribution
Abstract: Cancellation of Raman soliton self-frequency shift through cross-phase modulation with co-propagating pump pulses is demonstrated experimentally. Tunable fiber laser sources and optical switches can also be implemented with this technique (2 Refs.)
Notes: paper CD7-2-TUE (June 12–17, 2005, Munich, Germany)
Abstract: We present a new kind of broadband continuous-wave source which outperforms any other broadband superluminescent or amplified spontaneous emission source both in terms of output spectral density and bandwidth. Our source covers the wavelength band of interest for fiber applications (from 1450 to 1625 nm) and has an output power of approximately $1.3$ W. Additionally, it features a good power stability and we believe it might have very interesting applications in fiber sensing, for instance to avoid the need of amplification in the interrogation of remote Bragg gratings or to improve the resolution and dynamic range of optical coherence tomography setups (11 Refs.)
Notes: paper ?? (May 23–27, 2005, Bruges, Belgium)
Abstract: Continuous-wave supercontinuum generation is studied numerically. We show that the random fluctuations of the partially coherent pump beam play a dominant role in the spectral broadening process and explain the smoothness of experimental spectra (2 Refs.)
Notes: paper CD7-5-TUE (June 12–17, 2005, Munich, Germany)
Abstract: We study experimentally and numerically how chromatic dispersion and Rayleigh backscattering influence cascaded Raman generation in optical fibers. We report higher Stokes orders at unexpected wavelengths and quenching of Rayleigh lasing lines by four-wave mixing (8 Refs.)
Notes: paper MD3 (March 28–31, 2004, Toronto, Canada)
Abstract: We present a new numerical model of cascaded Raman fiber lasers that takes into account four-wave mixing processes. New operating conditions are found when the laser dispersion is properly tuned, in good agreement with experimental results (8 Refs.)
Notes: paper MD6 (March 28–31, 2004, Toronto, Canada)
Abstract: By enabling four-wave-mixing process within the cavity, a new type of Raman fiber laser for second-order pumping applications is demonstrated, exhibiting high stability down to a few milliwatts for the seed (1428 nm) (4 Refs.)
Notes: Paper ThB4 (March 23–28, 2003, Baltimore, Maryland, USA)
Abstract: We demonstrate experimentally that four-wave mixing leads to a three-fold increase in the gain of Raman amplifiers based on photonic crystal fibers. Our work illustrates the influence of dispersion on the Raman gain (2 Refs.)
Notes: paper CE4-4-Thu (June 23–27, 2003, Munich, Germany)
Abstract: Cascaded Raman generation in optical fibers, both in single pass and in laser configurations, is shown to be strongly affected by the chromatic dispersion profile of the fiber. Some applications of this phenomenon are discussed (7 Refs.)
Abstract: We demonstrate experimentally that four-wave mixing leads to a three-fold increase in the gain of Raman amplifiers based on photonic crystal fibers. Our work illustrates the influence of dispersion on the Raman gain (8 Refs.)
