We have fabricated silica nanochannels with inner diameter as small as 20 nm using a scanned coaxial electrospinning and demonstrated their application for single molecule detection. A coaxial jet, with the use of motor oil as the core and silica sol-gel solution as the shell, is extruded through a coaxial source and deposited on the rotating collector as oriented nanofibers. They are then annealed to cross-link silica and eliminate motor oil, thereby forming nanochannels. Subsequently, a fluorescent dye was injected into the individual nanochannels via a capillary force and single molecule detection was performed by monitoring the photon signals from 5-Iodoacetamidofluorescein.

A fibre optic technique based on the Fresnel reflection from the fibre tip is used for measurements of the refractive indices of various liquids at wavelengths of 1310 and 1551 nm. Reflection signals from liquid-fibre interface are compared with reflection signals from air-fibre interface to obtain the refractive index. Values of refractive indices for distilled water measured by this technique compare very well with known values at both wavelengths only if the fibre effective waveguide index is used. Applying the double-pulse measurement technique, it is shown that a measurement resolution of about 2.5 x 10(-5) can be achieved.

A fiber optic reflectometer (FOR) technique featuring a single fiber probe is investigated for its feasibility of measuring the bubble velocity, diameter, and void fraction in a multiphase flow. The method is based on the interference of the scattered signal from the bubble surface with the Fresnel reflection signal from the tip of the optical fiber. Void fraction is obtained with a high accuracy if an appropriate correction is applied to compensate the underestimated measurement value. Velocity information is accurately obtained from the reflected signals before the fiber tip touches the bubble surface so that several factors affecting the traditional dual-tip probes such as blinding, crawling, and drifting effects due to the interaction between the probe and bubbles can be prevented. The coherent signals reflected from both the front and rear ends of a bubble can provide velocity information. Deceleration of rising bubbles and particles due to the presence of the fiber probe is observed when they are very close to the fiber tip. With the residence time obtained, the bubble chord length can be determined by analyzing the coherent signal for velocity determination before the deceleration starts. The bubble diameters are directly obtained from analyzing the signals of the bubbles that contain velocity information. The chord lengths of these bubbles measured by FOR represent the bubble diameters when the bubble shape is spherical or represent the minor axes when the bubble shape is ellipsoidal. The velocity and size of bubbles obtained from the FOR measurements are compared with those obtained simultaneously using a high speed camera.

A new and simple calibration technique that greatly enhances the measurement sensitivity of conventional fiber-optic reflectometry based on Fresnel reflection from the tip of a fiber is used for demonstrating the feasibility of measuring solute concentrations and index changes in fluids to very high precision. The amplitude of pulses originating from reflection from the fiber-fluid interface is compared in real-time with the amplitude of reference pulses from a fiber-air interface such that errors caused by pulse amplitude fluctuations and slightly varying detector responses are corrected. Using solutions of salt and water, it is demonstrated that the technique is capable of measuring index changes of about $1 {\times} 10^{-5}$ corresponding to a salt concentrations of 0.01 %.

A new and simple normalization technique that greatly enhances the measurement resolution of conventional fibre-optic reflectometry based on Fresnel reflection from the tip of a fibre is used for demonstrating the feasibility of measuring solute concentrations and index changes in fluids to very high precision. The amplitude of pulses originating from reflection from the fibre–fluid interface is compared in real time with the amplitude of reference pulses from a fibre–air interface such that errors caused by pulse amplitude fluctuations and slightly varying detector responses are corrected. Using solutions of sodium chloride and water, it is demonstrated that the technique is capable of measuring index changes of 2 × 10−5 corresponding to a NaCl concentration of 0.02%.

It is shown that the measurement of photocurrents induced by optical pumping at subband gap wavelengths may be a useful technique for studying deep-level traps in semiconductor lasers. In this experiment a 1.3 μm wavelength laser is used to probe a 0.78 μm wavelength GaAs laser device. The trap density of a predegraded and postdegraded device was measured. The measurement indicates a significant increase in the trap density for the degraded device over the nondegraded device. Rate equations describing this excitation process are given and are shown to describe the experiment very well.

A new technique that offers very high stability and repeatability in varying the optical path length by a few millimeters at a millisecond rate is demonstrated. The technique is simply based on a rotating optical cube with parallel facets. The optical path length is varied at a nonlinear rate, and the data can be presented in the frequency or the spatial domain.

An external cavity traveling-wave semiconductor ring laser with narrow linewidth is used as a light source for research in frequency domain reflectometry. The optical frequency of the laser is linearly chirped by an intra-cavity phase modulator. The time-delayed reflection signal is mixed with a reference signal to produce a microwave frequency that indicates the position of the reflection. For optical fiber measurement, a spatial resolution of 30 m and a one-way dynamic range of 28 dB for Rayleigh backscattered light have been achieved.<>

It is found that the presence of the asymmetric nonlinear gain causes the longitudinal modes of a Fabry-Perot laser as well as a nearly single-mode laser to couple such that the low-frequency relative intensity noise is greatly enhanced. For the first time we have included this asymmetric mode coupling to adequately model the translation of the enhanced low-frequency noise to the signal band of a subcarrier multiplexed transmission system in the presence of both modulation and fiber dispersion. This effect, which is crucial in determining the system's signal-to-noise ratio, is also verified experimentally. Theoretical and experimental investigations of system impairment caused by noise translation and fiber dispersion are also performed. Excellent agreement between the theoretical predictions and the experimental results is obtained.

A fiber resonator with a temperature drift rate of better than 5×10/sup /spl minus/4/spl deg// C/hour is used for controlling the frequency stability of a 1.3 μm wavelength external cavity semiconductor ring laser. A frequency stability of about 600 KHz/hour is achieved.

A mechanism that may reduce the effective differential gain due to the modulation of the confinement factor with carrier density in quantum-well lasers is described. This mechanism may limit modulation bandwidth for quantum-well lasers with high threshold carrier density and narrow confining layer.<>

The digital and analog lightwave transmission characteristics of p-doped active layer 1.3 mum InGaAsP Fabry-Perot (FP) lasers with semi-insulating current blocking layers were investigated experimentally. For a 1.2 Gbit/s digital lightwave transmission system, it was found that the pulse jitter and the resulting power penalty were strongly dependent on the carrier lifetime of the lasers. This indicates that p-doped active layer FP lasers with decreased carrier lifetimes may be usable in a wider range of gigabit lightwave applications than previously considered. For analog lightwave applications, p-doped active layer FP lasers showed a 3 dB modulation bandwidth of 22 GHz for CW operation. These results suggest that this p-doped active layer FP laser structure is suitable for use in both multigigabit digital and very-high-speed analog lightwave transmission systems. In order to design the facet reflectivities to maximize the modulation bandwidth, a detailed model based on experimental data for high-speed lasers is also presented.

Previous theories of intermodulation distortion (IMD) in semiconductor lasers are based on the single-mode rate equation and small-signal analysis and are limited to frequencies above 2 GHz. These models do not adequately describe N-channel IMD. Recent measurements show that because of longitudinal-mode competition, low-frequency (≤2 GHz) third-order IMD can be substantially increased in Fabry-Perot lasers.1 This effect, which seriously degrades system performance at low frequencies, is very important in subcarrier-multiplexed (SCM) transmission systems.2 In this paper, for the first time to our knowledge, we adequately model the laser’s IMD over the frequency range from 50 MHz to 10 GHz by performing a large-signal analysis of the general multimode rate equations.3 This analysis explains the low-frequency enhancement of IMD, including all third- order IMD’s for 60-channel signals. Additionally, we show that fiber dispersion further increases third-order IMD.

A new mechanism is described that is based on the modulation of the confinement factor with carrier density in quantum-well lasers. This new mechanism may limit modulation bandwidth for quantum-well laser with high threshold carrier density and narrow confining layer.

The carrier-induced index change of a semiconductor laser was measured for injected carrier density ranging from 3 * 10/sup 16/ cm/sup -3/ to 2 * 10/sup 18/ cm/sup -3/. A strong nonlinear behavior between index change and carrier density is observed. The derivative of the index change versus carrier density at low carrier density can be 15 times larger than the derivative of the index change at high carrier density.< >

A new mechanism is described that is based on the modulation of the confinement factor in quantum well lasers and that can reduce differential gain and thus hirdt bandwidth.