Positioning errors and miscalibrations of the phase-stepping device in a phase-stepping interferometer lead to systematic errors proportional to twice the measured phase distribution. We discuss the historical development of various error-compensating phase-shift algorithms from a unified mathematical point of view. Furthermore, we demonstrate experimentally that systematic errors can also be removed a posteriori. A Twyman-Green-type microlens test interferometer was used for the experiments.

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The two wavelengths design of the majority of pulse oximeters assumes only two absorbing hemoglobin fractions, oxyhemoglobin (O2Hb), and reduced hemoglobin (HHb) irrespective ofthe presence of methemoglobin (MetHb) and carboxyhemoglobin (COHb). If MetHb or COHb is present, it contributes to the pulse-added absorbance signal and will be interpreted as either HHb or O2Hb or some combination of the two.In this paper we describe a noninvasive multi-wavelength pulse oximeter measuring O2Hb, HHb, MetHb, and COHb at a specified accuracy of 1 .0%. The system was designed with respect to the results of numerical simulations. It consists of 9 Laserdiodes (LDs) and 7 light emitting diodes (LEDs), a 16-Bit analog-digital converter (ADC) and has a sampling rate of 16 kHz. The laser diodes and LEDs were coupled into multi-mode fibers and led with a liquid lightguide to the finger clip and then the photodiode. It also presents the results of a clinical study, including a setup with a quartz tungsten halogen lamp (with fiber output) and a diode array spectrometer, a standard pulse oximeter and two in-vitro oximeters (Radiometer OSM3 and Radiometer ABL 520) as references.

A novel shearing interferometer is described that uses an optimized phase grating as the shearing element. The method has a number of advantages over a conventional Michelson interferometer shearing device, including light efficiency, simplicity, and low cost. Quantitative fringe analysis is easily carried out by in-plane translation of the grating and the use of standard phase-shifting algorithms. The influence of higher diffraction orders on the noise in the measured phase distributions is discussed. Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 05/15/2015 Terms of Use: http://spiedl.org/terms