Abstract: A method sequentially transmits signals of polarization states of light through an optical fiber. The optical fiber being a polarization preserving optical fiber. For each signal, a signal state is prepared as one out of a set of at least two non-orthogonal polarization states of light and sent through the optical fiber from a sender site to a receiver site. A method for quantum key distribution using polarization states of light is performed, wherein an alphabet of elementary information values is encoded in a set of non-orthogonal polarization states of light such that each elementary information value is represented by at least one of the polarization states. A classical message of elementary information values out of the alphabet is prepared, wherein the respective polarization states corresponding to the elementary information values of the classical message are prepared at a sender site as signal states.

Abstract: A method and apparatus is provided for implementing a parametric down-conversion (PDC)-based calibration comprising calibrating a measuring instrument; disposing a pinhole at a position of a light-emitting sample for which the measuring instrument needs to be calibrated; irradiating a nonlinear crystal with a light source; setting the nonlinear crystal by ensuring a phase-matching wavelength of the nonlinear crystal is set at one boundary of a desired bandwidth; acquiring one or more PDC spectrums by the measuring instrument; obtaining peak values and their corresponding wavelengths from each acquired spectrum; and obtaining a response function based on the peak values and corresponding wavelengths.

Abstract: A method and apparatus is provided for implementing a parametric down-conversion (PDC)-based calibration comprising calibrating a measuring instrument; disposing a pinhole at a position of a light-emitting sample for which the measuring instrument needs to be calibrated; irradiating a nonlinear crystal with a light source; setting the nonlinear crystal by ensuring a phase-matching wavelength of the nonlinear crystal is set at one boundary of a desired bandwidth; acquiring one or more PDC spectrums by the measuring instrument; obtaining peak values and their corresponding wavelengths from each acquired spectrum; and obtaining a response function based on the peak values and corresponding wavelengths.

Abstract: A mode conversion technique to convert higher-order-mode into a nearly fundamental Gaussian shape by using a beam expander is developed and is particularly useful in high-power lasers and amplifiers. By using a beam expander between a transmitted fiber and a conventional mode conversion system, the strict lateral tolerance requirement can be overcome with high conversion efficiency.

Abstract: A mode conversion technique to convert higher-order-mode into a nearly fundamental Gaussian shape by using a beam expander is developed and is particularly useful in high-power lasers and amplifiers. By using a beam expander between a transmitted fiber and a conventional mode conversion system, the strict lateral tolerance requirement can be overcome with high conversion efficiency.