Pigmentation Insensitive Pulse Oximeter
A photoplethysmographic sensor has a first light source, a second light source, an optical filter positioned within the path of the light emitted by the first light source and adapted to pass light within the spectral bandwidth of the first light source, an output aperture positioned to allow light passing through the optical filter and light emitted by the second light source to pass through, and a photodetector configured to detect light from the first and second light sources and to convert the detected light signal into an electronic signal. The first light source, the optical filter, and the output aperture configured to prevent light output by the first light source from passing through the output aperture without first passing through the optical filter.
1 . A photoplethysmographic sensor comprising:
a first light source adapted to emit light with a spectral bandwidth greater than 30 nm at 5% of peak intensity;
the first light source adapted to emit light with a peak intensity in the wavelength range of 620 nm to 770 nm;
a second light source adapted to emit light with a peak intensity in the wavelength range of 800 nm to 960 nm;
an optical filter positioned within the path of the light emitted by the first light source and adapted to pass light within the spectral bandwidth of the first light source;
the optical filter comprising a bandpass filter with a passband less than 30 nm at 5% of peak of the passband;
the optical filter adapted to attenuate light incident on the optical filter at wavelengths outside the passband by at least 85%;
an output aperture positioned to allow light passing through the optical filter and light emitted by the second light source to pass through;
the first light source, the optical filter, and the output aperture configured to prevent light output by the first light source from passing through the output aperture without first passing through the optical filter; and
a photodetector configured to detect light from the first and second light sources and to convert the detected light signal into an electronic signal.
2 . The sensor of claim 1 , wherein a housing contains the output aperture and the photodetector.
3 . The sensor of claim 1 , wherein the first light source is a light-emitting diode.
4 . The sensor of claim 1 , wherein the second light source is a light-emitting diode.
5 . The sensor of claim 1 , wherein the optical filter comprises two or more filters to provide a bandpass less than 20 nm.
6 . The sensor of claim 1 , further comprising opaque walls positioned between the first emitter and the optical filter to constrain the output aperture from passing light emitted by the first emitter that has not first passed through the optical filter.
7 . The sensor of claim 1 , further comprising a diffuser adapted to diffuse light from the first light source after said light passes through the optical filter and light from the second light source before either light is passed to the output aperture.
8 . A method of assembling a photoplethysmographic sensor, comprising the steps of:
positioning a first light source adapted to emit light with a spectral bandwidth greater than 30 nm at 5% of peak intensity and with a peak intensity in the wavelength range of 620 nm to 770 nm in the sensor;
positioning a second light source adapted to emit light with a peak intensity in the wavelength range of 800 nm to 960 nm in the sensor;
positioning an output aperture in the sensor, wherein the output aperture is positioned to pass light emitted from the first light source and the second light source;
positioning an optical filter between the first light source and the output aperture to prevent light output by the first light source from passing through the output aperture without passing through the optical filter;
wherein the optical filter is configured to pass light within the spectral bandwidth of the first light source and with a passband less than 30 nm, the optical filter further configured to attenuate light incident on the optical filter at wavelengths outside the passband by at least 85%; and
positioning a photodetector configured to detect light from the first and second light sources and to convert the detected light signal into an electronic signal.
9 . The method of claim 8 , wherein at least the output aperture and the photodetector are positioned within a housing.
10 . The method of claim 8 , wherein the first light source comprises a light-emitting diode.
11 . The method of claim 8 , wherein the second light source comprises a light-emitting diode.
12 . The method of claim 8 , wherein the optical filter comprises two or more filters to provide a bandpass less than 20 nm.
13 . The method of claim 8 , further comprising positioning opaque walls between the first emitter and the optical filter to constrain the output aperture from passing any light emitted by the first emitter that has not first passed through the optical filter.
14 . The method of claim 8 , further comprising positioning a diffuser in the sensor, wherein the diffuser is adapted to diffuse light from the first light source after said light passes through the optical filter and light from the second light source before the light from either light source is passed to the output aperture.