Fetal heart beat monitor using a fiber laser interferometric sensor: A preliminary study on the detection of the signals

摘要

We describe a fiber laser interferometer that has been designed with the purpose of non-invasive continuous fetal heart rate monitoring. The measuring principle is based on the measurement of the arterial wave of a fetus from the arterial pulse wave of a pregnant patient, so the application requires the measurement of arterial pulse waves with very high resolution. The main characteristics of the specific application interferometer are: First, it is based on a common path topology in order to simplify the design of the non-contact optical probe to place on the body of the patient. Second, it uses a low power semiconductor laser at a safe operating wavelength of 1,55 μm. Third, a phase modulation with digital demodulation scheme is used in order to increase range and resolution simultaneously. The resulting interferometer provides up to 1 nm resolution and one millimeter range. Results showing arterial pulse waves measured on the wrist and a finger nail of a patient are presented.