Abstract: A pressure sensor comprises a chamber formed from two members micromachined in silicon or a similar substance. The members define a chamber with at least one pressure sensitive membrane and an optic fiber extending through the chamber parallel to the membrane. The membrane may have an optical grating formed thereon which may be coated with a surface plasmon supporting substance. Light is injected into the fiber with a wavelength that couples with the grating on the membrane, either in a Bragg relationship or in coupling to a surface plasmon. The coupling, and thus the light lost from the fiber, varies with separation between the membrane and fiber and thus with the pressure outside the chamber. The members also include a thicker wall which is not pressure sensitive but which couples with an identifiably distinct portion of the light in the optic fiber to provide a temperature compensated reference.

Abstract: Serveral improvements in fiber optic sensing systems are disclosed. One improvement incorporates a dielectric filter applied directly to the sensing end of an optical fiber detector which has the characteristic that it reflects back a reference light beam of one wavelength while passing a sensing signal of a different wavelength which is modulated in some predetermined fashion beyond the filter. Both light signals are reflected back through the fiber and are, accordingly, attenuated in the identical or nearly identical fashion in response to various noise sources. The ratio of the intensity of the two signals is proportional to the sensed parameter and renders the system essentially self-compensating. The dielectric filter is preferably directly coated onto the exit end of the fiber through vapor deposition techniques.

Abstract: A microbend fiber optic pressure sensor includes a short length of sensing fiber comprising a fiber of a transparent dielectric material surrounded by a layer of aluminum or similar metal for which the real part of the complex permittivity is negative over a range of electromagnetic radiation wavelengths. The layer of aluminum is hermetically sealed to the transparent material. The sensing fiber receives light in the range of wavelengths and is subjected to microbends on the dielectric/aluminum boundary by pressure responsive mechanical apparatus for a much greater microbend light loss and therefore greater sensitivity than is obtained with similar sensors using an all glass core/cladding boundary. The sensing fiber may be an aluminum coated single mode fiber with a very small core and a large cladding layer in which the cladding modes are used and the core modes ignored or it may comprise a single glass fiber coated with aluminum.

Abstract: A fiber optic detector head senses a light reflective or transmissive pattern on an encoder disk rotated by an engine shaft. The pattern results in three different light levels which are translated by a detector into an electrical pulse train having three different voltages. Patterns encoded into the single pulse train are decoded by a microprocessor to provide specific engine cylinder or cylinder pair position information even within the first spark firing period as well as engine speed information.

Abstract: A fiber optic detector head senses a light reflective or transmissive pattern on an encoder disk rotated by an engine shaft. The pattern results in four different light levels which are translated by a detector into an electrical pulse train having four different voltages including a reference or background voltage. One light level is reserved for an index mark, another level for cylinder position marks and still another level for finer measurement of position and speed between the cylinder marks. Patterns encoded into the single pulse train are decoded by a microprocessor to provide specific engine cylinder position information as well as engine speed information.

Abstract: A microbend fiber optic sensor uses a dual wavelength to determine the effect of microbending without interference from unwanted signal fluctuations arising from component changes, for example. Periodic microbending losses in single mode, step index fiber optics depend critically upon the wavelength whereby a modulation wavelength can be chosen close to a reference wavelength so that both are affected equally by the unwanted fluctuations but only the modulation wavelength is affected by the microbending. The ratio of the two signals or a log of the ratio yields a value which responds only to the microbend induced signal.

Abstract: A self aligning microbend sensor comprises a tubular housing having internal threads, an expandable insert with external threads loosely threaded into the housing with sufficient tolerance to allow expansion of the insert in response to a parameter being measured while maintaining registration of the threads, and a fiber optic element between the housing and the insert and extending transverse to the threads, such that upon expansion of the insert the fiber optic element experiences microbending due to deformation by the threads.