Remote measurement of physical variables with fiber optic systems - methods, materials and devices

A device for the optical measurement of temperature by use of a probe and an interrogating light injected into said probe, comprising

• (a) a probe so characterized that, when illuminated with interrogating light of a wavelength or wavelengths within a spectral region specific for said probe, a fraction of the intensity of said interrogating light injected into said probe is absorbed by the probe and substantially converted into luminescence light at least part of the intensity of which is emitted at wavelengths .lambda..sub.1 different from the wavelength or wavelengths of the interrogating light, the value of said fraction and the intensity of said luminescence light increasing in a known manner with increasing temperature;
• (b) a source of said interrogating light;
• (c) fiber optic means for directing said interrogating light to said probe;
• (d) photodetection means adapted to measure the intensity of said emitted light of wavelengths including .lambda..sub.1,
• (e) fiber optic means adapted to direct a fraction of the intensity of said luminescence light to said photodetection means;

A fiber optic thermometer, comprising:

• (a) a fiber optic light guide for carrying illuminating light to an optical probe;
• (b) a source of illuminating light of wavelengths within a pre-selected wavelength region;
• (c) an optical probe at the end of said fiber optic light guide, said probe having a segment of optical fiber including a core and a cladding having an index of refraction lower than that of the core, the refractive index of said cladding varying as a known function of temperature within the temperature range being measured, thereby varying the intensity of the illuminating light transmitted by the probe;
• (d) a photoluminescent tip terminating said probe, said tip characterized by absorbing light of wavelengths within said pre-selected wavelength region and converting it into luminescence light having different wavelengths from those of the illuminating light;
• (e) a photodetector and associated electronic means for measuring the intensity of the luminescence light generated at said photoluminescent tip and collected by said optical probe, said intensity being an indicator of the index of refraction of said cladding and, hence, of the probe temperature;
• and
• (f) fiber optic means for directing a fraction of the intensity of said luminescence light from said photoluminescent tip to said photodetector.

A force sensing arrangement including

• (a) a relatively long force sensing optical fiber, said fiber including at least a core and a fluorescent cladding;
• (b) a light source proximate to the launch end of said fiber, said light source adapted to launch interrogating light pulses of submicrosecond duration into the core of said fiber, a force-dependent fraction of the intensity of said light pulses being deflected to said fluorescent cladding at each force sensing point along the fiber, thus generating fluorescence light pulses propagating in both the forward and the backward directions along said fiber, the times of arrival at the fiber launch end of the backward-propagating light pulses relative to the times of launching of the interrogating light pulses identifying the locations along the fiber of each sensing point;
• and
• (c) a photodetector and associated electronic means located near the launch end of said fiber for receiving the backward-propagating fluorescence light pulses generated at each sensing point along the fiber and for processing said fluorescence light pulses into force distributions along the fiber.

A fiber optic device adapted to sense variations in the magnitude of a physical parameter, including

• (a) a light-transmitting probe so characterized that, when exposed to the physical parameter and transmitting interrogating light of a wavelength or wavelengths suitable for said probe and an intensity P.sub.o injected into the probe, a fraction .alpha.P.sub.o of the intensity of said injected light is converted within said probe into a light separable from the interrogating light, at least part of the intensity of which is emitted from the probe at wavelengths .lambda..sub.1 different from the wavelength or wavelengths of the interrogating light, the value of .alpha. varying in a known manner with the magnitude of the physical parameter, said emitted light of wavelengths .lambda..sub.1 having an intensity which increases in a known manner with the value of .alpha.;
• (b) means for generating said interrogating light;
• (c) fiber optic means for directing said interrogating light to said probe;
• (d) fiber optic means for directing part of the intensity of said converted light of wavelengths including .lambda..sub.1 to photodetector means;
• and
• (e) photodetector and associated electronic means for processing said light