Optical position sensor for determining the interface between a clear and an opaque fluid

A method of measuring a length, x, along a one-dimensional curvilinear, coordinate system, X, comprising:

• a) emitting light from a primary fiber having a length=L, a first portion having a length=x, and a second portion having a length=L−x;
• b) collecting light emitted from the first portion of the primary fiber with a secondary fiber oriented substantially parallel to the primary fiber, and spaced apart from the primary fiber by a substantially constant distance, d, wherein d<<L;
• c) trapping and guiding some of the collected light inside of the secondary fiber;
• d) preventing light, emitted from the second portion of the primary fiber, from being collected by the secondary fiber;
• e) detecting, with a light detector that is optically coupled to an upper end of the secondary fiber, guided light that is emitted from the upper end of the secondary fiber;
• and
• f) calculating the desired length measurement, x, by analyzing an output signal, generated by the light detector, that increases monotonically as the length, x, of the first portion of the primary fiber increases;
• wherein the method does not comprise internally reflecting light, emitted from the first portion, off of a first side of a transparent liquid sensing surface, in a direction towards the light detector, when the transparent liquid sensing surface is wetted on its opposite side by a first liquid having a first refractive index;
• and
• wherein the method does not comprise refracting and transmitting light, emitted from the second portion, through the transparent liquid sensing surface, when a second fluid, having a second refractive index that is greater than the first refractive index, is present on the wetted side of the transparent liquid sensing surface.

An optical position sensor for measuring a length, x, along a one-dimensional curvilinear, coordinate system, X, comprising:

• light emission means, having a first portion with a length=x, and a second portion having a length=L−x, for emitting light along a length=L;
• wherein the axial distribution of light emitted by the light emission means is substantially constant along the X-axis;
• light collection means for collecting light emitted from the first portion of the light emission means;
• means for preventing light emitted from the second portion of the light emission means from being collected by the light collection means;
• and
• light detector means, optically coupled to an upper end of the light collection means, for detecting guided light emitted from the upper end of the light collection means, and for generating an output signal that is proportional to the intensity of detected light;
• and
• processor means operably connected to the light detector means, for calculating the desired length, x, by analyzing the output signal generated by the light detection means;
• wherein the output signal generated by the light detection means increases monotonically as the length, x, of the first portion of the light emission means increases;
• wherein the light emission means and the light collection means are combined into a single, dual-purpose, side-emitting fiber;
• further comprising a laser or LED source that passes pump light through a beamsplitter before being optically coupled to an upper end of the side-emitting fiber;
• and
• wherein light emitted from the upper end of the side-emitting fiber reflects off the beamsplitter in a direction towards the light detector means;
• wherein the side-emitting fiber is surrounded by, and is located at the central axis of, a hollow, structural tube having a reflective inner surface;
• wherein light emitted by the first portion of the side-emitting fiber reflects off of the reflective inner surface of the tube, and then travels back towards the first portion of the side-emitting fiber, whereupon some of the reflected light is collected by the side-emitting fiber, and then is guided inside of the side-emitting fiber back towards the beamsplitter, which directs the collected light to the light detection means;
• wherein the reflective inner surface of the structural tube extends along the entire length, L, of the side-emitting fiber;
• and wherein the open space inside of the structural tube comprises a clear fluid, an opaque fluid, or both;
• wherein the optical position sensor does not comprise means for internally reflecting light, emitted from the first portion of the light emission means, off of a transparent liquid sensing surface, in a direction towards the light collection means, when the transparent liquid sensing surface is wetted on its opposite side by a first liquid having a first refractive index;
• and
• wherein the optical position sensor does not comprise means for refracting and transmitting light, emitted from the second portion of the light emission means, through the transparent liquid sensing surface, when the transparent liquid sensing surface is wetted on its opposite side by a second liquid having a second refractive index that is greater than the first refractive index of the first liquid.