Angle of incidence selective band pass filter for implantable chemical sensor

A method of detecting the concentration of an analyte using a sensor comprising a sensor housing, a graft on at least a portion of an exterior surface of the sensor housing, a light source contained within the sensor housing, indicator molecules distributed throughout the graft, an angle of incidence filter element contained within the sensor housing, a dichroic band pass filter contained within the sensor housing, and a photodetector contained within the sensor housing;

• the method comprising:
• irradiating, by the light source, excitation light to the indicator molecules;
• emitting, by the indicator molecules, emission light to the angle of incidence filter element;
• receiving, by a receiving surface of the angle of incidence filter element, light including the emission light;
• preventing, by the angle of incidence filter element, light of the received light having an angle of incidence greater than a threshold angle relative to an axis perpendicular to the receiving surface from reaching the dichroic band pass filter;
• propagating, by the angle of incidence filter element, light of the received light having an angle of incidence less than the threshold angle relative to the axis perpendicular to the receiving surface;
• preventing, by the dichroic band pass filter, light of the propagated light having a wavelength outside a band pass region of the dichroic band pass filter from reaching the photodetector;
• passing, by the dichroic band pass filter, light of the propagated light having a wavelength within the band pass region of the dichroic band pass filter to the photodetector;
• and
• receiving, by the photodetector, the passed light;
• wherein the angle of incidence filter element is a fiber optic bundle comprising a plurality of optical fibers.