title: Comment on "Phase-shifting shearing interferometer".
abstract: The role of the liquid-crystal layer in the phase-shifting shearing interferometer that was proposed by Griffin [Opt. Lett. 26, 140 (2001)] is analyzed. An extra voltage-dependent phase difference is produced when the phase retarder is oriented at an angle from the optical axis of the laser beam such that the interferogram will not repeat itself after a 2pi phase change of the liquid-crystal retarder in either the common Mach-Zehnder interferometer or the phase-shifting shearing interferometer.
authors.forename: Kuo-Hui
authors.initials: KH
authors.lastname: Chang
authors.forename: A-Chuan
authors.initials: AC
authors.lastname: Hsu
authors.forename: Jyh-Long
authors.initials: JL
authors.lastname: Chern