Patent ID: 8358888

Claim:
A method for generating an approximate Bessel beam, comprising the steps: (a) providing an input optical fiber that supports propagation in a fundamental LP 01 mode; (b) connecting the input fiber to a high-order mode fiber, wherein the high order-mode fiber includes an in-fiber mode converting device that provides phase matching, at a predetermined excitation wavelength, between the LP 01 mode input and a single selected azimuthally symmetric higher-order waveguide mode of the high-order mode fiber, wherein the azimuthally symmetric higher-order waveguide mode comprises N rings, N being an integer of at least 7; (c) feeding a coherent light beam through the input optical fiber to provide, as an input to the in-fiber mode converting device, an LP 01 mode input at the excitation wavelength, the in-fiber mode converting device resonantly exciting the selected azimuthally symmetric higher-order waveguide mode; and (d) providing the azimuthally symmetric higher-order waveguide mode as a beam output from an endface of the high-order mode fiber, wherein the beam output approximates a Bessel beam, such that the beam output has an aperture controlled by the waveguide mode size; and such that the beam output has a diffraction-resistant range that is controlled independently by the waveguide mode size and the high-order mode fiber index contrast.