Abstract: In an optical system a semitransparent mirror which is disposed at a predetermined angle with respect to an optical axis and which has a semitransparent surface (for instance, a front surface) and a transparent surface (for instance, a rear surface) is so designed as to split a diverging or converging light incident thereon into a first optical path of light flux reflected from the semitransparent surface and a second light path of light flux transmitted through both the semitransparent and transparent surfaces. Furthermore, in order that the position of an image focused by the light flux reflected from the transparent surface coincides with the position of an image focused by the light flux reflected from the semitransparent surface, the transparent surface is made non-parallel with the semitransparent surface of the semitransparent mirror. The thickness of the mirror decreases or increases toward image planes depending upon whether converging light flux or diverging light flux is incident on the mirror.

Abstract: An optical pH sensor and a gas sensor utilizing the pH sensor. The pH sensor includes an indicator whose absorbance is a function of the concentration of hydronium ions in a media surrounding the indicator. Light transmitted and reflected through the indicator of the sensor undergoes an absorption that is characteristic of the concentration of the hydrogen ion. The pH sensor can be used as to sense the concenration of a gas in a sample by surrounding the indicator with a liquid or liquid-containing media that changes pH as it is exposed to the gas, and separating the indicator and liquid or liquid-containing media from the gas with a membrane that is permeable to the gas to be measured. A measuring system used with the sensors transmits coherent radiation to the sensor through an optical fiber, separates the radiation returning from the sample into two wavelength bands, and digitally samples the photocurrents produced within the two wavelength bands.

Abstract: A self contained interior rearview mirror unit for a vehicle provides a head-up display image of vehicle information at a distance in front of the vehicle operator.