A tunable multi-channel optical parametric amplifier (OPA) using difference-frequency generation (DFG) in a periodically poled lithium niobate (PPLN) waveguide is proposed and simulated. The number of the channels can be selected. The working wavelength and gain of each channel can be tuned independently.
KEYWORDS: Polarization, Waveguides, Signal attenuation, Signal processing, Difference frequency generation, Sum frequency generation, Optical parametric amplifiers, Polarized light, Nonlinear optics, Lithium niobate
A type of high-polarization-isolation optical parametric amplifier (OPA) is reported based on the difference-frequency generation (DFG) process and the sum-frequency generation (SFG) process in a periodically polarized lithium niobate (PPLN) waveguide. Two OPA schemes using x-cut and z-cut PPLN waveguides are proposed and numerically demonstrated. The simulation results show that, the output polarization isolation up to 39.77 dB and 35.68 dB can be obtained with x-cut and z-cut PPLN waveguides, respectively.
A method is proposed to evaluate the interference of ultrawideband (UWB) signals to other systems outside its frequency band, by introducing two critical parameters Wob and Pob. These two parameters represent the total bandwidth and total power of the UWB signal to be evaluated exceeding the frequency mask, respectively. Wob is the bandwidth out of the frequency mask limit and Pob is the signal power exceeding the frequency mask. At last, the derivatives of the Gaussian pulse are evaluated up to third order, i.e. monocycle, doublet and triplet, when the original Gaussian pulse width varies from 60 to 350 ps. The results show that the interference introduced to outside band by the UWB signal decreases at first and then increases and finally decreases again, when the original Gaussian pulse width increases. To evaluate an optical UWB signal, this evaluation method should be applied after a simple photoelectric conversion.
Three metrics used in error measuring are introduced to measure the differences between the derivatives of typical signal pulses and the derivatives of Gaussian pulse, which is used as the standard ultrawideband (UWB) signals. Derivatives of two kinds of typical initial pulses compared to the standard UWB signal in the same order is evaluated under three reference metrics, when the initial pulses of them have the same pulse width. The results show that, the first metric δ1 changes linearly with the FWHM of the initial pulses TFWHM, while the second one δ2 presents a proportional relation to the square root of TFWHM, and the third one δmax does not change with TFWHM. In addition, the difference between the derivatives of hyperbolic secant pulse and the standard UWB signals are smaller compared to the derivatives of super-Gaussian pulse in the same condition.
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