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A novel approach for producing sidelobe-free optical vortices is proposed, for the first time, utilizing object-oriented computer generated holograms (CGH). By conjugate-symmetrically extending the complex amplitude of any desired optical vortices prior to performing the discrete Fourier transform, the resulting real-valued number profile is encoded into an object-oriented CGH without having conventional forked-shaped fringes. On the basis of the CGH generated, use is first made of numerical simulations to reconstruct optical vortices with spiral phase profiles. Detailed experimental measurements employing a computer-controlled spatial light modulator and extensive numerical simulations are undertaken to verify the proposed technique. Excellent agreements between numerical simulations and experimental measurements are observed. Results show that optical vortices with a single primary intensity ring are generated without the occurrence of any sidelobes in the periphery for absolute values of topological charges as large as 20. [ABSTRACT FROM AUTHOR]