US 4,303,855 A · System for separating an optical signal from ambient light

Abstract

An arrangement for separating disturbing ambient light from an optical data signal, comprising an interference filter (1), the passband of which matches the wavelength of the optical data signal, and further comprising two photodiodes which are so arranged that one photodiode receives the light (I.sub.S, I.sub.AT) transmitted through the interference filter, and that the other receives the reflected light (I.sub.AR). Adjusting means, e.g., in the form of a settable aperture (4) or an additional simple filter (5) are provided for adjusting the transmitted and reflected portions of the ambient light to each other. Output signal (S1, S2) of both photodiodes are subtracted from each other in compensation circuitry (6). This results in compensation of the ambient light components so that at the output a signal (SR) is available which depends only on the actual data signal (I.sub.S).

Claims8

Dependent claims

An arrangement for separating an optical signal of a given wavelength from ambient light, comprising an optical interference filter having a relatively narrow passband substantially centered at the said given wavelength of said optical signal, characterized by

first and second photodetector means (2,3) so arranged that the first (2) receives light waves in a substantially narrow band transmitted through said interference filter (1) and that the second receives light waves reflected by said interference filter, and
circuit means (6, FIG. 1;
FIG. 4;
FIG. 5) for generating a difference signal (SR) from the output signals (S1, S2) of said
first and second photodetector means, and means (4, 5, FIG. 1;
19, FIG. 5) for adjusting the relation between the output signals furnished by the said first and second photodetector means.

3 more elements

Dependencies are inferred from the claim text.

System for separating an optical signal from ambient light

Life of this patent

System for separating an optical signal from ambient light

Life of this patent

Abstract

Claims8