Patent ID: 7840246

Claim:
An implantable system, comprising: an implantable housing comprising a window through which light can pass; at least one light source, within said housing, each of which transmits light of a corresponding wavelength, wherein an intensity of the light transmitted by each said light source is controlled by a corresponding drive signal that drives said light source, and wherein a portion of the light of each said wavelength exits said housing through said window; a measurement light detector, within said housing, to detect light of each said wavelength scattered back into said housing through said window, and to produce a measurement signal that is indicative of the intensity of the light of each said wavelength detected by said measurement light detector; an opaque wall that separates said at least one light source from said measurement light detector; a calibration light detector, within said housing on a same side of said opaque wall as said at least one light source, to detect a portion of the light of each said wavelength that has not exited said housing and has been reflected toward said calibration light detector without using a beam splitter, and to produce a calibration signal that is indicative of the intensity of the light of each said wavelength detected by said calibration light detector, which is indicative of the intensity of the light transmitted by each said light source; and circuitry operative to detect changes in the intensity of the light transmitted by each said light source based on the calibration signal; wherein said housing has an inner surface, a first portion of said inner surface coated with a reflective material to cause a portion of the light of each said wavelength that has not exited said housing to be reflected toward said calibration light detector, and a second portion of said inner surface not coated with the reflective material and corresponding to said window through which a portion of the light of each said wavelength exits said housing.