In one aspect, an apparatus for determining a property of a fluid is disclosed that in one embodiment may include a transparent member having an axis and a first end substantially perpendicular to the axis and a second end having an outer surface at a first angle to the axis, a light source directing light at the first end, a detector placed spaced from the second end, the space between the second end and the detector containing a fluid, wherein the detector detects light exiting from the outer surface at a second angle to the axis and passing through the fluid, and a controller for determining the second angle from the light detected by the detector. A processor determines the bulk fluid refractive index from the light detected by the detector and a property of the fluid therefrom.

This disclosure describes systems and methods for critical angle reflection (CAR) imaging to quantify molecular binding kinetics on a glass surface in some embodiments. CAR is a label-free method that measures the reflectivity change near a critical angle in response to molecular binding induced refractive index changes on the sensor surface. The sensitivity and dynamic range of CAR is tunable by varying the incident angle of light, which allows for optimizing the measurement for ligands with different sizes in both biomolecular and cell-based studies.

The present invention relates to the technological field of optical systems and refers to a device for identifying, at least one fluid, especially, fuel fluids in vehicle tanks. The device in question includes an optical guide having interaction surfaces and an emitter element emitting light beams and at least one receiving element of light beams. The information received from the receiving element includes the reflection emitted by interaction surfaces which are at the submersed region of the optical guide and indicates the type of fluid stored in the reservoirfor example: ethanol, gasoline or a mix of both. The interaction surfaces are inclined at different angles to provide total reflection for fluids with a different refractive index, including blends of fluids, to allow determination of the type of fluids according to the reflection by the interaction surfaces.

This disclosure provides calculation methods for the reflectivity of normal incident wave on the interface, the absolute reflection critical angle of the wave, the relative reflection critical angle of the wave, and the refraction-reflection symmetrical angle of the wave. These calculation methods can calculate the reflected wave energy on interface, the angle at which the incident wave would all be reflected on the interface and wave energy would be trapped, the angle at which the incident wave begins to be reflected, and the angle at which the reflected wave energy equals the refracted wave energy. The provided calculation methods could be widely used in various fields such as light, electromagnetic waves, sound waves and etc.

An optical sensor apparatus includes an optically transmissive structure (e.g., a prism) having two planar faces and a third planar face that connects the two planar faces, two or more light sources located outside the structure, and a photodetector array located outside the prism. The structure, light sources, and photodetector array are configured such that light from the light sources that is totally internally reflected at an optical interface between the prism and a sample outside the structure proximate one of the two planar faces is incident on a portion of the photodetector array that depends on a refractive index of the sample. The light sources are positioned with respect to the structure and photodetector array such that the totally internally reflected light from each light source corresponds to a different range of refractive index of the sample and maps to a corresponding portion of the photodetector array.