Optical measuring device using a spectral modulation sensor having an optically resonant structure

An optical measuring device for measuring a range of values for a sensed physical parameter, wherein said optical measuring device comprises:

• light source means for emitting input measuring light of at least two wavelengths;
• optically resonant structure means;
• detection means;
• and
• light transmission means;
• wherein said optically resonant structure means has a reflectivity curve and a transmission curve, and has at least one operating segment on at least one of said reflectivity curve and said transmission curve;
• wherein said optically resonant structure means has an optically sensitive physical characteristic which changes as a function of said sensed physical parameter;
• wherein said changes of said optically sensitive physical characteristic microshift said at least one operating segment as a function of said sensed physical parameter;
• wherein said optically resonant structure means are for spectrally modulated said input measuring light as a function of said microshifts to produce spectrally modulated output light which is spectrally modulated as a function of said sensed physical parameter;
• wherein said at least one operating segment is selected to be less than about one resonance cycle in length for said range of values for said sensed physical parameter;
• wherein said at least one operating segment is microshifted less than about one resonance cycle over said range of values for said sensed physical parameter;
• wherein said wavelengths of said input measuring light are selected to fall at least substantially within said at least one operating segment over said range of values for said sensed physical parameter;
• wherein said at least one operating segment and said wavelengths of said input measuring light are selected such that over said range of values for said sensed physical parameter said spectrally modulated output light bears a unique one-to-one relationship to said sensed physical parameter;
• wherein said light transmission means are for conveying said input measuring light from said light source means to said optically resonant structure means and for conveying said spectrally modulated output light from said optically resonant structure means to said detection means;
• wherein said detection means are for deriving two electrical signals corresponding to any two different wavelength portions of said spectrally modulated output light;
• and are for taking the ratio of said two electrical signals to provide an output measuring electrical signal which is a function of said sensed physical parameter, to null errors in the measurement of the sensed physical parameter and to help to maximize both the useable length and the useable microshift of said at least one operating segment over said range of values for said sensed physical parameter;
• wherein said optically resonant structure means are for sensing the refractive index of a sensed fluid to measure and monitor at least one of said sensed fluid's density, composition, mixture composition and solute concentration;
• wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;
• wherein said body further defines opening means for permitting said sensed fluid to enter said cavity from outside of said optically resonant structure means;
• and
• wherein said optically sensitive physical characteristic is said index of refraction of said sensed fluid located within said cavity between said pair of opposed reflective surfaces.