Tapered Mach-Zehnder interferometer based on PbS quantum dots modified by polymers for copper ion sensing.

An optical fiber interferometer coated with PbS quantum dots (QDs) was developed for copper ion (${{\rm{Cu}}^{2 +}}$) detection. The QDs were modified by a multifunctional copolymer that enabled QD surface ligation, dispersion, and coordination with ${{\rm{Cu}}^{2 +}}$. ${{\rm{Cu}}^{2 +}}$ coordination with the polymer induced changes in the surrounding refractive index of the interferometer. The sensor was highly selective for ${{\rm{Cu}}^{2 +}}$ and showed a linear detection range of 0-1000 µM with a limit of detection of 2.20 µM in both aqueous and biological solutions.

Stable passively Q-switched erbium-doped fiber laser incorporating a PbS quantum dots polystyrene composite film based saturable absorber.

We demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) using PbS quantum dots in polystyrene films (QDPFs) as saturable absorbers (SAs). Compared to other SAs, PbS QDPFs have advantages of broad absorption range, high quantum yield, low cost, and facile preparation. We have successfully generated stable Q-switched pulses with an average output power of 40.19 mW, a single pulse energy of 586.1 nJ, a repetition rate of 68.04 kHz, a pulse width of 3.9 µs, and a signal-to-noise ratio of 50.5 dB under 660 mW pump power. The output of the EDFL has been monitored for 5 consecutive hours under laboratory conditions to show stable operation of the laser system.

Enhanced thermal stability of oleic-acid-capped PbS quantum dot optical fiber amplifier.

Poor thermal stability has remained a severe obstacle for practical applications of optical fiber amplifiers based on quantum dots (QDs). We demonstrate that thermal stability at elevated temperatures can be achieved by using oleic-acid-capped QDs. Optical fiber amplifiers using oleic-acid-capped QDs for the gain medium exhibited stable gain of more than 5 dB at 1550 nm between 25 °C and 50 °C that did not degrade upon cooling. In contrast, fiber amplifiers employing oleylamine-capped QDs exhibited reduced gain when heated and subsequently cooled.

Optical fiber amplifiers based on PbS/CdS QDs modified by polymers.

Optical fiber amplifiers based on PbS/CdS semiconductor quantum dots (QDs) modified by an amphiphilic polymer were demonstrated. Well-defined QDs and an amphiphilic copolymer were first prepared and the amphiphilic copolymer was then used to disperse the QDs into silica sol to allow uniform and reproducible incorporation of QDs into the silica coating of the optical fibers. QD-doped silica sol was deposited on the fusion tapered fiber coupler via dip-coating. A 1550 nm semiconductor light emitting diode as the signal source and a 980 nm laser diode as the pump source were injected into the fiber coupler simultaneously. Through evanescent wave excitation, a signal gain as high as 8 dB was obtained within the wavelength range between 1450 and 1650 nm. In addition, the optical fiber amplifiers based on PbS/CdS QDs showed enhanced thermal stability when compared to amplifiers based on PbS QDs.

Photophysical properties of C60 colloids suspended in water with Triton X-100 surfactant: excited-state properties with femtosecond resolution.

We examine the photophysics of a colloidal suspension of C(60) particles in a micellar solution of Triton X-100 and water, prepared via a new synthesis which allows high-concentration suspensions. The particle sizes are characterized by transmission electron microscopy and dynamic light scattering and found to be somewhat polydisperse in the range of 10-100 nm. The suspension is characterized optically by UV-vis spectroscopy, femtosecond transient absorption spectroscopy, laser flash photolysis, and z-scan. The ground-state absorbance spectrum shows a broad absorbance feature centered near 450 nm which is indicative of colloidal C(60). The transient absorption dynamics, presented for the first time with femtosecond resolution, are very similar to that of thin films of C(60) and indicate a strong quenching of the singlet excited state on short time scales and evidence of little intersystem crossing to a triplet excited state. Laser flash photolysis reveals that a triplet excited-state absorption spectrum, which is essentially identical in shape to that of molecular C(60) solutions, does indeed arise, but with much lower magnitude and somewhat shorter lifetime. Z-scan analysis confirms that the optical response of this material is dominated by nonlinear scattering.

Design and fabrication of a broadband polarization and temperature insensitive arrayed waveguide grating on InP.

An arrayed waveguide grating (AWG) with a novel S-shaped design for broadband operation is demonstrated for the first time with III-V semiconductors. This device design provided a polarization and temperature insensitive operation. It is also shown that, despite the wide operating range, chromatic dispersion does not degrade the performance of the AWG. The AWG is operational above the absorption edge of the semiconductor (1100nm) and can function for a wide range of wavelengths covering the coarse wavelength multiplexing range from 1270nm to 1610nm. A four channel AWG with this novel design was fabricated and characterized.

Modeling, design, fabrication, and testing of a fiber Bragg grating strain sensor array.

The modeling, design, simulation, fabrication, calibration, and testing of a three-element, 15.3 cm fiber Bragg grating strain sensor array with the coherent optical frequency domain reflectometry (C-OFDR) interrogation technique are demonstrated. The fiber Bragg grating array (FBGA) is initially simulated using in-house software that incorporates transfer matrices. Compared to the previous techniques used, the transfer matrix method allows a systemwide approach to modeling the FBGA-C-OFDR system. Once designed and simulated, the FBGA system design is then imprinted into the core of a boron-germanium codoped photosensitive fiber using the phase mask technique. A fiber optic Fabry-Perot interferometric (FPI) strain gauge calibrator is then used to determine the strain gauge factor of a single fiber Bragg grating (FBG), and the results are used on the FBGA. The FPI strain gauge calibrator offers nondestructive testing of the FBG. To test the system, the FBGA is then attached to a 75 cm cantilever beam and interrogated using an incremental tunable laser. Electric strain gauges (ESGs) are then used to independently verify the strain measurements with the FBGA at various displacements of the cantilever beam. The results show that the peak strain error is 18% with respect to ESG results. In addition, good agreement is shown between the simulation and the experimental results.

Origin of spectral modal noise in fiber-coupled spectrographs.

We describe the origin of spectral modal noise in a fiber-coupled spectrograph. Prior investigations of this phenomenon have considered optical fibers with large cores that support thousands of optical modes and used a statistical treatment to analyze spectral noise that arises from interference between the modes. We examine spectral modal noise for a fiber-coupled spectrograph with a smaller-diameter fiber core, optimized for adaptively corrected telescopes, that supports only a few propagating modes for visible and near-infrared light. Simulations to predict the minimum amount of fiber stretch required to shift spectral oscillations by a half-period are confirmed by experiment.