An optical microstructure is configured to work with an optical fiber or a different substrate and the optical microstructure includes a beam converter including a tapered optical guide configured to transform a gaussian optical beam into a first annular optical beam; an inverted cone having first and second reflection surfaces, each configured to reflect the first annular optical beam, having a radius R1, so that a resulting second annular optical beam has a radius R2 larger than the radius R1; and a prism having a reflection surface configured to reflect the second annular optical beam to form a third converging annular optical beam. The third converging annular optical beam includes plural single optical beams that intersect at a given crossing point, outside the optical microstructure. The plural single optical beams form an optical trap.