P.L. Chu

Highly tunable Bragg gratings in single-mode polymer optical fibers

A Bragg grating in a single-mode polymer optical fiber (POF) has been created. The novel grating has a length of 1 cm with a reflectivity of 80% and a linewidth of about 0.5 nm. The wavelength tunability of the POF grating by stretching was investigated and a wavelength tunable range of 20 nm has been achieved. Based on the properties of the polymer, we believe that this kind of grating has a wavelength tuning potential of more than 100 nm.

Nonlinear refractive index in erbium doped optical fiber: Theory and experiment

An intensity-dependent refractive index in erbium doped optical fiber has been observed for the first time. The effect has been observed by an interferometric technique using a two-core fiber. The effect is analyzed theoretically, and the important nonlinear parameters for thin material have been determined and are presented. >

Strain and temperature sensor using a combination of polymer and silica fibre Bragg gratings

We show that a sensor scheme consisting of a combination of a polymer fibre Bragg grating and a silica fibre Bragg grating gives large discrimination against temperature and strain. It provides large sensitivity and dynamic range for sensing temperature and strain changes simultaneously and independently.

Measurement of stresses in optical fiber and preform

A method of measuring the stresses, residual or applied, in an optical fiber or preform is presented. It is shown that the stress profiles can be obtained from the Abel transform of the derivative of the retardation. The axial stress profile is shown to bear the same shape as the refractive-index profile. Measurement results indicate that the applied tension during the fiber drawing process is frozen into the fiber, consequently affecting the intrinsic strength of the fiber. The method of estimating the fiber drawing tension from the fiber stress profile is also given.

Thermal tuning of polymer optical fiber Bragg gratings

Bragg gratings in polymethyl methacrylate (PMMA)-based polymer fibers were created and were tuned thermally. It is found that the tuning range is more than 18 nm over a temperature variation of 50/spl deg/C. More importantly, no hysteresis effect was observed as the gratings were heated up and cooled down.

Analytical method for calculation of stresses and material birefringence in polarization-maintaining optical fiber

An analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber. The method is based on the thermoelastic displacement c potential in which the principle of superposition applies. The method is applicable to any fiber structure. Its application to fibers with isolated stress-producing regions and a variety of core shapes is demonstrated. The optimum fiber parameters required to achieve maximum material birefringence for fibers with circular or bow-tie shaped stress regions are given. It is also shown that the thermal stresses tend to make the bow-tie fiber more crack-resistant than the fiber with circular stress lobes.

Optical switching in twin-core erbium-doped fibers

We report the theoretical and experimental investigation of switching in a nonlinear twin-core erbium-doped fiber coupler. It is shown that switching action takes place at a power of a fraction of 1 mW. Thus it provides a practical means of fabricating an all-optical fiber switch.

Effect of chirping on solution propagation in single-mode optical fibers

The evolution of a linearly chirped pulse into a soliton is studied. Even under severe chirping, a soliton can be generated if the initial amplitude is high enough. However, the resulting soliton will always be broader than in the unchirped case.

1-GHz optical communication system using chaos in erbium-doped fiber lasers

We experimentally demonstrated an optical communication system based on synchronized chaos between the transmitter and receiver with a sinusoidal signal of 1 GHz. In addition, we also experimented with the modulation of the system by a random bit stream at 140 Mb/s. Both experiments showed that the messages could be recovered at the receiver with a reasonable signal-to-noise ratio. These messages are directly embedded into the chaos through an electrooptic modulator in the transmitter. At the receiver the message is successfully recovered by both the subtracting method and the dividing method.

Optimum dispersion profile for compression of fundamental solitons in dispersion decreasing fibers

In this paper, we have investigated the effect of dispersion profile on the performance of pulse compression in a dispersion decreasing fiber (DDF). Four closely shaped profiles, namely linear, Gaussian, exponential, and hyperbolic, have been considered. We have shown that appropriate shaping of the dispersion profile, particularly when higher order effects are accounted for, is quite effective for adiabatic compression of fundamental solitons, producing high-quality compressed pulses in the sense that the soliton pulse is compressed as a single unit and pedestals do not form. It is concluded that the linear and Gaussian dispersion profiles are nearly optimum in regards to the quality of the compressed pulse and the amount of compression achievable, in particular in the case of subpicosecond soliton pulse compression.