Abstract: Optical fibers having one or more polymeric coatings have been found to be sensitive to extraneous light arising either as incident light from outside the optical fiber or as light escaping the fiber at bends and being reflected back into the fiber by a coating acting as a secondary cladding. In either case the extraneous light intensity may be reduced by placing at least one light absorbing component in a coating. Where the light absorbing component is placed in a coating between the primary cladding of the optical fiber and the secondary cladding both sources of extraneous light may be reduced or eliminated. Particulate amorphous carbon is an effective light absorber because of the broad range of optical wavelengths absorbed and because of its efficiency of absorption (high extinction coefficient) over this range.

Abstract: A vacuum-operated, pressure-responsive valve is adapted for connection to the intake manifold of an internal combustion engine for monitoring supplemental airflow to the engine, the improvement of the present device providing precise adjustment of the supplemental airflow/intake manifold pressure relationship. An air cylinder, a pressure-responsive piston/valve mounted therein, a threadably mounted axially extending stem and valve-biasing spring, and a resiliently deflectable plate are assembled and cofunction to provide precision click stop adjustment of the supplemental airflow/engine vacuum relationship.