Browsing by Author "Cao, Q"

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Approximate analytical description for fundamental-mode fields of graded-index fibers: Beyond the Gaussian approximation
(2001-01-01)
Cao, Q
;
Chi, S
;
光電工程學系
;
Department of Photonics
An approximate analytical description for fundamental-mode fields of graded-index fibers is explicitly presented by use of the power-series expansion method, the maximum-value condition at the fiber axis, the decay properties of fundamental-mode fields at large distance from the fiber axis, and the approximate modal parameters U obtained from the Gaussian approximation. This analytical description is much more accurate than the Gaussian approximation and at the same time keep the simplicity of the latter. As two special examples, we present the approximate analytical formulas for the fundamental-mode fields of a step profile fiber and a Gaussian profile fiber, and we find that they are both highly accurate in the single-mode range by comparing them with the corresponding exact solutions.
Axially symmetric on-axis flat-top beam
(2000-03-01)
Cao, Q
;
Chi, S
;
光電工程學系
;
Department of Photonics
A synthesis method for arbitrary on-axis intensity distributions from axially symmetric fields is developed in the paraxial approximation. As an important consequence, a new pseudo-nondiffracting beam, the axially symmetric on-axis flat-top beam (AFTB), is given by an integral transform form. This AFTB is completely determined by three simple parameters: the central spatial frequency S-c, the on-axis flat-top length L, and the on-axis central position z(c). When LSc much greater than 1, this AFTB can give a nearly flat-top intensity distribution on the propagation axis. In particular, this AFTB approaches the nondiffracting zero-order Bessel J(0) beam when L --> infinity. It is revealed that the superposition of multiple AFTB fields can give multiple on-axis flat-top intensity regions when some appropriate conditions are satisfied. (C) 2000 Optical Society of America [S0740-3232(00)01202-3].
Ultrashort pulsed sinc-Gaussian light beams
(2000-07-01)
Cao, Q
;
Chi, S
;
光電工程學系
;
Department of Photonics
A family of analytical solutions of the time-dependent wave equation, the ultrashort pulsed sinc-Gaussian light beams (UPSGLB's), are presented in the paraxial approximation. Each of them has the product form of the monochromatic Gaussian light beam with the central frequency v(c) times the sine function of the complex temporal-spatial beam parameter P-n. The complex temporal-spatial beam parameter P-n, which corresponds to the order n, is directly related to the temporal-spatial coupling properties of the n th-order UPSGLB. The UPSGLB's are used, for the first time to our knowledge, as an analytical expansion set for bandwidth-limited ultrashort light pulses emitted from mode-locked lasers with stable resonators (ULPEMLLSR's). Two special examples of bandwidth-limited ULPEMLLSR's, a single zeroth-order UPSGLB and a novel model of a nearly temporal-spatial Gaussian beam, are analytically investigated and compared with experimental results. (C) 2000 Optical Society of America [S0740-3224(00)02806-X].