Optical system including multiplexed volume Bragg grating, methods, and applications

摘要

A method of reversible spatial mode selection and conversion between waveguides and free space is presented using a multiplexed volume Bragg grating (MVBG). The MVBG has an inherent angular selectivity, providing different losses for different transverse modes and converting a higher order mode in waveguide to a single fundamental mode in free space. Using the device in a resonator allows for a pure higher order mode to be guided and amplified in the gain medium, to increase the mode area, to extract accumulated excitation more efficiently, and, therefore, to increase gain of the amplifier. In the same resonator, the device is able to convert the higher order mode to a high brightness Gaussian beam in free space or to a fundamental mode in a waveguide.

主权项

1. A method for reversible conversion between fundamental and higher order spatial modes of a propagating optical beam, comprising:
providing an optical system including:
a multimode waveguide supporting propagation of a plurality of spatial modes including a fundamental mode and higher-order modes, which said higher-order modes are characterized by two, optical far-field, angularly separated side lobes and by a divergence of each lobe;an imaging system characterized by a magnification coefficient; anda multiplexed volume Bragg grating (MVBG) comprising two (a, b) volume Bragg gratings (VBGs) characterized by an angle, δθab, between input Bragg angles of the two VBGs, coincidence of output beams' Bragg angles, and an angular selectivity, δθa, δθb, of each VBG; propagating a higher order mode beam in the waveguide; imaging an exit facet of the waveguide to the MVBG such that the directions of propagation of converging lobes of the higher order mode coincide with the respective Bragg angles of the VBGs, while the angular divergence of the lobes remains less than the angular selectivity, δθa, δθb, of each respective VBG; diffracting the two lobes of the higher-order mode beam in the same direction by the MVBG; and outputting a beam consisting of a fundamental mode.