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A theoretical and experimental study of femtosecond supercontinuum generation in short tapered fibers with micrometer diameter waist has been carried out. In our numerical model, an extended nonlinear Schroedinger equation that involves the parameters of dispersion coefficient and effective core area varying along the length of tapered fiber is used to describe the evolution of intense femtosecond pulses centred at 850 nm. As a result, the supercontinuum is generated due to enhanced nonlinear effects in a narrow waist; the octave spanning spectra are found in an optimum structure with only short waist length of 8.0 mm and diameter of 2 μm for an input average power of 100mW. Experimental verification using a femtosecond pulse from a Ti: sapphire laser is then made and compared with the numerical simulations.

Mechanism of supercontinuum(SC) spectrum generation due to cross-phase modulation(XPM) in a dispersionflattened/decreasing fiber(DFDF) with low birefringence has been investigated theoretically and experimentally. By using a XPM, the measured SC spectum width becomes 33.6 % broader than that obtained by using only self-phase modulation (SPM). This fact implys that effectiveness and validity of the sc generation using XPM method. Furthermore, dependence of generated sc spectrum broadening on incident power, polarization angle of the input pulses, and modal birefringence are investigated. consequently, it was velifid that when a polarization angle of the input pulses is 45 degrees with regard to the principal axes of the fiber and incident average power is less than 0.147 mW, soliton trapping takes place due to a balance between soliton pulse powers and modal birefringence value. In addition, it was shown experimentally that for a polarization angle of the input pulses of 22.5 degrees, the sc spectrum is enlarged by the same amount as in the case of 45 degrees.

The measurement and evaluation of power spectrum of a semiconductor laser by delayed self-heterodyne interferometer is demonstrated with the use of a short delay fiber. The measured spectrum is analyzed numerically including the effect of a delay time much less than the laser coherence time. The theoretical formulation developed here is found to be found to be accurate since it exhibits a peak with finite width at the center frequency of the measured lineshape. The white and 1/f components of the laser FM noise are then separated successfully by fitting numerical analysis to the experimental results.

An optical heterodyne interferometer with a frequency-ramped laser diode (LD) has been constructed for amplitude measurements of a sinusoidally oscillating object. In order to eliminate the effect of intensity modulation without complexity in optical setup, an optical interferometry operating under a small index of intensity modulation has been proposed and its effect on the amplitude measurements of an oscillating object has been analyzed based on spectral analysis of interference beat signal. From the simplified analysis for some ratios of beat frequency to modulation (ramped) frequency and for some intensity modulation indices, it is confirmed that the theoretical analysis and the experimental results are in relatively good agreement.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The effect of fiber chromatic dispersion on the performance of a multichannel optical coherent CPFSK system is analyzed including also the effects of shot and thermal noises and crosstalk interference. The sensitivity penalty is found to increase due to waveform distortion caused by chromatic dispersion. The channel frequency separation is, therefore, required to increase to overcome the dispersion effect. The channel spacing requirements become worse with increase in intermedite frequency (IF) and IF bandwidth.

High-frequency response (about 50 MHz) is reported for a fiber-optic phase modulator that is coated with vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer, 80 about 90 microns thick, on a single-mode fiber of 80 microns diameter and made piezoactive by radial poling. A flat response of optical phase shifts is observed in the frequency range over 10 KHz to 3 MHz whereas at frequencies higher than 4 MHz it shows multiple peaks dominated by radial resonances of the fiber-jacket composite. An excellent agreement exists between the experimental data and theoretical calculations based on radial vibration analysis.