Analytical and experimental study on a bent abrupt taper.

This work presents an analytical coupling model for perturbed abrupt fiber tapers in single-mode fibers. In addition to LP0m modes, the modeling predicts the presence of LP11 and LP12 modes for a bent taper. Our model also introduces a perturbation function that can match most cases of bending variations on a taper. We have shown that the tapering and bending effect can be treated separately within one abstract formulation. Agreement amongst the model predictions and experimental results support the viability of our method.

Practical interrogation scheme for the abrupt taper Mach-Zehnder interferometer refractive index sensor.

A practical interrogation scheme of a refractive index (RI) sensing system based on the abrupt fiber taper Mach-Zehnder interferometer sensor is designed, implemented, and demonstrated by experiment. The broadband light source and optical spectrum analyzer in the conventional design are replaced by two single-wavelength laser diodes modulated by a periodical square waveform and a simple photodetector (PD), which can significantly lower the cost and lead to easier integration. The photocurrent of the PD output signal is used as the indicator of the surrounding RI. Automatic data acquisition and processing is realized by LabVIEW programming. The experiment proves the feasibility of the new scheme and shows a high sensitivity (2371 mV/RIU) and high stability.

Reducing the complexity of perturbation based nonlinearity pre-compensation using symmetric EDC and pulse shaping.

Perturbation based nonlinearity pre-compensation has been performed for a 128 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal. Without any performance degradation, a complexity reduction factor of 6.8 has been demonstrated for a transmission distance of 3600 km by combining symmetric electronic dispersion compensation and root-raised-cosine pulse shaping with a roll-off factor of 0.1. Transmission over 4200 km of standard single-mode fiber with EDFA amplification was achieved for the 128 Gbit/s DP 16-QAM signals with a forward error correction (FEC) threshold of 2 × 10(-2).

Monitoring of vapor uptake by refractive index and thickness measurements in thin films.

We report a method for real-time monitoring of vapor uptake by simultaneous detection of the refractive index, n, and thickness, d, of thin transparent films with a precision of δn=10(-4) and δd<100 nm. The setup combines total internal reflection (Abbé) refractometry with an interferometric imaging method. A fast Fourier transform and phase fitting method is applied for accurate and independent determination of refractive indices and thicknesses. While the uptake of acetone vapor by polydimethylsiloxane is investigated, the system is also suited for characterization of other solid and liquid films.

Laser beam shaping using a single-mode fiber abrupt taper.

A new beam-shaping device was realized by an abrupt taper with a length of approximately 700 microm and a waist of approximately 40 microm. The insertion loss of the device is less than 3%. The diameter of the flat beam top can be up to approximately 900 microm with a small intensity variation (4%) and a small half-divergence angle (2.5 degrees). The conversion efficiency of the new device from a Gaussian-shaped to a flat-top profile is comparable with that of a long-period-gratings-based device, while keeping the fabrication cost low. The new device requires only a fusion splicer and standard SMF-28 fiber, eliminating the need for photolithographic procedures. The new device also has no obvious incident light polarization dependence.

Refractive index sensor based on an abrupt taper Michelson interferometer in a single-mode fiber.

A simple refractive index sensor based on a Michelson interferometer in a single-mode fiber is constructed and demonstrated. The sensor consists of a single symmetrically abrupt taper region in a short piece of single-mode fiber that is terminated by approximately 500 nm thick gold coating. The sensitivity of the new sensor is similar to that of a long-period-grating-type sensor, and its ease of fabrication offers a low-cost alternative to current sensing applications.

High-speed data transmission over a 1 km broad wavelength window multimode fiber.

For cost and design simplicity, various optical network architectures have been proposed in which downstream traffic from the optical line terminal to the optical networking unit is transmitted by carriers in the 1550 nm window, and upstream traffic by those in the 1300 nm window. A new generation of multimode fiber (MMF) has been designed to accommodate this requirement and to address technical challenges associated with fiber coupling. By restricting the number of modes at both fiber input and output, using off-the-shelf single-mode transceivers, single-wavelength 40 Gbit/s data transmission over a 1 km broad wavelength window multimode fiber has been demonstrated with only a 1.5 dB power penalty. The capacity in this new class of MMF is expected to increase with conventional technologies in single-mode fiber such as wavelength-division multiplexing and polarization multiplexing.

Gain-clamped S-band discrete Raman amplifier.

We demonstrate the advantages of an optically gain-clamped S-band discrete Raman amplifier: low gain variation over a large input dynamic range, effective suppression of Raman transients, and amplifier instability in the strong-pump-weak-signal configuration. We further investigate experimentally the operating conditions necessary for effective gain clamping and demonstrate gain flattening over 30 nm of bandwidth. Thus a gain-clamped discrete Raman amplifier shows promise for practical deployment.